Avalanche Terminology Glossary

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Avalanche Terminology — Full Index

725 snow science and avalanche concepts with English definitions, sourced from EAWS, IACS, SLF, and national avalanche services.

Ablation (Snow Processes): Term: ablation; All processes that remove snow, ice, or water from a glacier, snowfield, etc.; in this sense, the opposite of accumulation. These processes include melting, evaporation, calving, wind erosion, and an avalanche. Air temperature is the dominant factor in controlling ablation, precipitation amounts exercising only secondary control. During the ablation season (usually summer), an ablation rate of about 2 mm h-1 is typical of glaciers in a temperate climate. The amount of snow or ice removed by the above-described processes; in this sense, the opposite of accumulation.
About EAWS (Avalanche Types): The primary purpose of European Avalanche Warning Services (EAWS) is to support its Members in preventing the loss of lives and damage due to avalanches by providing the society with efficient and effective avalanche forecasting and warning services.
Above Freezing Layer (Snowpack Properties): Also known as: AFL, Above Freezing Layers; A horizontal layer of air at some altitude in the atmosphere with a temperature above 0°C that lies between two sub-freezing air layers.
Accretion (Snow Grain Shapes & Crystals): Also known as: Accretions; Accretion is a term used when an ice crystal or snowflake in the atmosphere hits a supercooled liquid droplet, which then freeze wholly or partially together. A common example of this is graupel. It is also used to describe the accumulation of ice on objects such as power lines and lift lines by a similar process. This type of ice is usually described by the term rime.
Accumulation (Snow Processes): Term: accumulation; Also known as: accumulations, Accumulation Zone, Accumulations; See snow accumulation. In glaciology, the quantity of snow or other solid form of water added to a glacier or snowfield by alimentation; the opposite of ablation. Compare snowpack.
Accumulation de neige par vent latéral
Accumulation zone (Terrain): Also known as: Accumulation zones; Area of slope where snow, transported by wind, accumulates and builds.
Action du vent
Active Avalanche Control (Avalanche Types): Also known as: Active Avalanche Controls; To instigate avalanche occurrence or to stabilize slopes by ski cutting, explosives, or boot packing. In contrast with passive control.
Additional load (Avalanche Hazard & Assessment): Also known as: Additional loads; Low additional load individual skier/snowboarder, riding softly, not falling group with good spacing (minimum 10 m) keeping distance snowshoer
advection (Meteorology & Weather): The process of transport of an atmospheric property solely by the mass motion (velocity field) of the atmosphere; also, the rate of change of the value of the advected property at a given point. Advection may be expressed in vector notation by where u is the wind vector, φ the atmospheric property, and ∇φ the gradient of the property. In three-dimensional Cartesian coordinates, it is where u, v, and w are the wind components in the eastward, northward, and vertically upward directions, respectively. The first two terms compose the horizontal advection and the last term is the vertical advection. Also, it should be noted that the property φ may itself be a vector field. Often, particularly in synoptic meteorology, advection refers only to the horizontal or isobaric components of motion, that is, the wind field as shown on a synoptic chart. Regarding the general distinction (in meteorology) between advection and convection, the former describes the predominantly horizontal, large-scale motions of the atmosphere, while convection describes the predominantly vertical, locally induced motions. In oceanography, advection refers to the horizontal or vertical flow of seawater as a current.
Age Harden (Snowpack Properties): The hardening and strengthening of disturbed snow over time due to settlement and metamorphism..
Air Blast (Avalanche Types): Also known as: Air Blasts; (Also: Shock wave, Pressure blast, Pressure wave, Wind Blast) A strong rush of air which may precede some fast moving powder avalanches. Some slides, particularly large ones, appear to be preceded by an air blast or pressure wave. Destructive air blasts are not common. However, there are certain paths where the phenomena occurs regularly. When it does occur the air blast may extend about 100 meters beyond a major path. Sometimes reference is made to a shock wave. This is misleading since the air blast is not a true shock wave.
Air Mass (Snowpack Properties): Also known as: Air Masses; A large region of air with minimal horizontal temperature and moisture variation, classified by origin (continental/maritime) and temperature characteristics (tropical/polar/arctic).
Albedo (Meteorology & Weather): Term: albedo; Also known as: albedos, Albedos; The ratio of reflected flux density to incident flux density, referenced to some surface. Albedos commonly tend to be broadband ratios, usually referring either to the entire spectrum of solar radiation, or just to the visible portion. More precise work requires the use of spectral albedos, referenced to specific wavelengths. Visible albedos of natural surfaces range from low values of ∼0.04 for calm, deep water and overhead sun, to > 0.8 for fresh snow or thick clouds. Many surfaces show an increase in albedo with increasing solar zenith angle. See also plane albedo, planetary albedo, spherical albedo, directional-hemispherical reflectance, bihemispherical reflectance.
Alpha Angle (Terrain): Also known as: Alpha Angles, Beta Angle; The alpha angle is the angle between the horizontal and a line drawn from the highest point of the crown face to the toe of the debris. The alpha angle can be measured for an individual avalanche, but it is more commonly (and usefully) calculated for a specific return period. Extreme values for an alpha angle (such as that for a 100 year or 300 year avalanche) can be determined from historical records, tree ring data, or statistical methods. The alpha angle is also termed the angle of reach or the runout angle. For 100 year avalanches this angle typically ranges from about 18 to 22 degrees The beta angle is the angle measured to the top of the starting zone from the place where the slope first becomes 10 degrees (locally). This is a terrain feature of the particular path and is not different for different events, as the alpha angle is. An extreme event alpha angle (such as that of a 100-year avalanche) can be estimated from a beta angle using statistical methods, but the parameters vary from one mountain range to another (independent of prevailing climate). The graph below is an actual profile showing the alpha and beta angles and is from an avalanche engineering project by AlpenPro.
Alpine Elevation (Terrain): Also known as: Alpine Elevations; The highest elevation band of a mountain consisting of open, exposed terrain with few or no trees, most exposed to sun, wind, cold, and precipitation.
Altitudes (Terrain): Area within certain altitude ranges (accuracy ± 100 m)
Amount of new snow (Snow Types): Also known as: Amounts of new snow; Amount of new snow accumulated in a certain period of time, for example, three days.
Anchors (Snowpack Properties): Also known as: Anchoring; (Anchoring) Anything natural or built into a slope which stabilizes the snow on the slope, or inhibits snow glide. Anchors are usually considered to be a good thing. However, shallow snowpack anchors such as stumps, shrubs, and rock outcrops can become weak spots later when they are buried in some cases. Slopes with anchors may be more stable themselves but threatened from above also. For an example of artificial anchors see the webpage on the ones made by Geobrugge of Switzerland.
Anemometer (Meteorology & Weather): Also known as: Anemometers, Wind Speed; (Wind Speed) An instrument used to measure the velocity of wind. See the Campbell Scientific wind speed products for examples. [The actual descriptions and specs require Acrobat Reader.]
Angle of Repose (Snow Grain Shapes & Crystals): Also known as: Angles of Repose; The lowest slope angle at which a granular material will begin to slide, or the steepest incline at which it will not slide. One of the most basic examples is a pile of sand. If sand is poured slowly onto a pile it will form at a specific angle to the hozontal surface beneath the pile, which is the angle of repose. Any additional grains added to the pile will slide down its surface, perhaps causing some others to do the same. Another example is a sandy embankment along a stream. If this is at the angle of repose, which it often is, grains on the surface will slide down very easily and sometimes spontaneously. Snow can be a granular material, but as it sits on a slope it often is not. The grains are often bonded together into a slab.
anticyclone (Meteorology & Weather): Also known as: anticyclones; An atmospheric anticyclonic circulation, a closed circulation. The wind in an anticyclone is in the clockwise direction in the Northern Hemisphere and counterclockwise in the Southern Hemisphere. With respect to the relative direction of its rotation, it is the opposite of a cyclone. Because anticyclonic circulation and relative high atmospheric pressure usually coexist, the terms anticyclone and high are used interchangeably in common practice. Compare ridge.
Appareils de communication par satellite
Arbres espacés
Area adjacent to the ridgeline (Terrain): Also known as: Areas adjacent to the ridgeline, crest or summit; Terrain adjacent to ridgeline, crest or summit; highly influenced by wind.
Area distant from ridgelines (Terrain): Also known as: Areas distant from ridgelines, wide-open slope; Mountain terrain unconnected to a ridgeline.
Artifical avalanche release (Avalanche Hazard & Assessment): Also known as: Artifical avalanche releases; An avalanche triggered by artifically applied force (e.g. explosives, snow machines, people).
Artificial Avalanche (Avalanche Hazard & Assessment): Also known as: Artificial Avalanches, Human Triggered Avalanche; (Human Triggered Avalanche) An avalanches triggered by something in addition to the loading and behavior of the snowpack. A person or animal, equipment, active control methods such as explosives, etc. Also a field or laboratory simulation of an avalanche.
Artificial Control (Snowpack Properties): Also known as: Artificial Controls; A term used to distinguish avalanche control activities from naturally occurring avalanche or stabilization by natural causes, snow crystal metamorphism or snowpack deformation. The stabilization of slopes by explosives (hand charges, artillery), ski checking, or other non-natural means. The goal is an improvement in slope stability through avalanche release, sluffing, or settlement.
Arêtes
Ascendance
Ascendance convective
Ascendance frontale
Ascendance orographique
Aspect (Terrain): Term: aspect; Also known as: aspects, Aspects, Aspects, Exposure, Slope Orientation, Aspects, Aspects; The compass direction toward which a land slope faces. The direction is taken downslope and normal to the contours of elevation.
aspect of slope (Terrain): Also known as: aspects of slope
Atmospheric Convergence (Meteorology & Weather): Also known as: Atmospheric Convergences; Two or more streams of air flowing into one another, resulting in atmospheric lift and precipitation.
Atmospheric Lift (Meteorology & Weather): Also known as: Atmospheric Lifts; A general term referring to a group of processes that cause air masses to rise upwards in the atmosphere, driven by four mechanisms: convection, convergence, topographic interaction, and weather fronts.
Atmospheric Pressure: Also known as: Atmospheric Pressures; The weight of a column of air pressing down on a given area, commonly expressed in millibars.
Atmospheric River (Meteorology & Weather): Also known as: AR, Atmospheric Rivers; Long, narrow plumes of moisture originating from the tropics that deliver heavy amounts of precipitation and mild air.
Atmospheric Subsidence (Snowpack Properties): Also known as: Atmospheric Subsidences; The downward movement (sinking) of air parcels, compressing air and increasing temperature while reducing moisture capacity.
Au vent
Avalanche (Avalanche Types): Term: avalanche; Also known as: avalanches, landslide, snowslide, Avalanches, Avalanches; (Also called snowslide.) A mass of snow (perhaps containing ice and rocks) moving rapidly down a steep mountain slope. Avalanches may be characterized as loose and turbulent, or slab; either type may be dry or wet according to the nature of the snow forming it, although dry snow usually forms loose avalanches and wet snow forms slabs. A large avalanche sweeps a current of air along with and in front of it as an avalanche wind, which supplements its already tremendous destructive force. See wind slab; compare sluff. (Also called landslide.) A mass of earth material (soil, rock, etc.) moving rapidly down a steep slope.
Avalanche Airbag (Avalanche Types): Also known as: Avalanche Airbags; Protective equipment integrated into a backpack that inflates to increase wearer size, helping keep them on avalanche surface.
Avalanche Balloon (Avalanche Types): Also known as: ABS, ABS System, Avalanche Balloon System, Avalanche Balloons; (ABS, ABS System, Avalanche Balloon System) A relatively new, and expensive, device for preventing fatalities in avalanches. A self-inflating balloon in a small rucksack is carried and in the event of an avalanche a rip-cord is pulled to deploy the balloon. The balloon either keeps the person on top of the snow or at least shallowly buried under the balloon which stays on the surface. Use of this device is not widespread, but it is in use. Particularly in europe where it is gaining acceptance. It has been introduced in North America and is used by some guide services and some individuals but is still uncommon.
Avalanche bulletin (Avalanche Hazard & Assessment): Also known as: Avalanche bulletins; The avalanche bulletin provides detailed information on the snowpack and avalanche situation. Avalanche danger is ranked in accordance with the 5-level European avalanche hazard scale.
Avalanche Control (Avalanche Types): Also known as: Avalanche Controls, Control Work; (Control Work) Any measure taken to control the size and frequency of avalanches or to direct the path of an avalanche. This includes stabilization by explosives, ski-cutting, and other active means as well as passive methods such as diversion and anchoring structures. The act of carrying out active avalanche control is often called control work. Road, ski runs, or other areas may be closed during control work. Early in the year many advisories remind people that ski areas are not carrying out avalanche control work yet, meaning their terrain is the same as the backcountry.
Avalanche Cord (Terrain): Also known as: Avalanche Cords; A colored line which trails a traveler in avalanche terrain to aid in locating if caught and buried in an avalanche. While it may sound good in theory, and although one could argue that it is better than nothing, it has a poor track record and is rarely used anymore.
Avalanche Cycle (Avalanche Types): Also known as: Avalanche Cycles, Avalanche Cycles; A period of heightened avalanche activity, often associated with weather changes like snow, rain, wind, or warming.
Avalanche danger
Avalanche Danger Scale (Avalanche Types): Also known as: Avalanche Danger Scales; A system rating avalanche danger at five levels: low, moderate, considerable, high, and extreme, based on likelihood, size, and distribution.
Avalanche de neige mouillée sans cohésion
Avalanche de neige sans cohésion
Avalanche de neige sèche sans cohésion
Avalanche de plaque
Avalanche Debris (Avalanche Types): A mass of snow, soil, rock, trees, etc. brought down by an avalanche. Avalanche debris is very hard and difficult to dig in.
Avalanche Defense (Avalanche Types): Also known as: Avalanche Defenses; To protect against avalanche occurrences or damages. Anchor structures, reforestation, diversion structures, and snowsheds are a few examples of approaches to avalanche defense.
Avalanche dense / coulante
Avalanche deposit (Avalanche Types): Also known as: Avalanche deposits; Snow deposited by an avalanche. Such snow deposits frequently persist for longer periods on valley floors.
Avalanche Distribution (Terrain): Also known as: Avalanche Distributions; Where avalanche problems exist: widespread (most terrain), specific (certain aspects/elevations), or isolated (limited terrain).
Avalanche déclenchée par intervention humaine
Avalanche déclenchée à distance
Avalanche déclenchée à l'explosif
Avalanche en aérosol
Avalanche en marche d'escalier
Avalanche Essentials (Avalanche Types): Three key rescue items: transceiver, probe, and shovel, enabling companion rescue techniques.
Avalanche length (Avalanche Types): Also known as: Avalanche lengths; Total length of an avalanche measured from the highest point of the fracture line to the lowest point of the deposition.
Avalanche naturelle
Avalanche par sympathie
Avalanche Path (Terrain): Also known as: Avalanche Paths, Avalanche Paths, Channel path, channeled avalanche, toe, Avalanche Paths, Avalanche Paths; The area involved in an avalanche, subdivided into start zone, track, and runout zone.
Avalanche Probe (Avalanche Types): Also known as: Avalanche Probes; A long, thin, collapsible rod used by a rescuer to pinpoint the location of a burial subject beneath the snow surface.
Avalanche problems (Avalanche Hazard & Assessment): Term: Avalanche Problem; Also known as: Avalanche Problems; Eight types of snowpack instabilities: storm slab, wind slab, wet slab, persistent slab, deep persistent slab, dry loose, wet loose, and cornices.
Avalanche prone location (Avalanche Hazard & Assessment): Also known as: Avalanche prone locations, danger zone; Locations delineated by aspect or altitude where avalanches can trigger and people or objects are at risk.
Avalanche prone locations: Specific locations where avalanches are more likely to be triggered, typically identified by aspect, elevation, and terrain features.
Avalanche Runout zone (Terrain): Also known as: Avalanche Runout zones; An avalanche runout zone is the lower portion of an avalanche path where debris slows and stops, typically occurring on slopes of 15 degrees or less. It represents a high-consequence area even when the avalanche danger is low as avalanches may release from well above and reach low elevations.
Avalanche Shovel (Snowpack Properties): Also known as: Avalanche Shovels; A specialized shovel which has a handle that can be removed from the blade, used for companion rescue and snowpack testing.
Avalanche size (Avalanche Types): Term: Avalanche Size; Also known as: Avalanche Sizes, Avalanche Class, Avalanche Sizes, Avalanche sizes; Classification into five size classes based on destructive potential, from harmless to potentially destroying villages.
Avalanche Survival Techniques (Avalanche Types): Actions individuals can take to increase survival chances if caught in an avalanche.
Avalanche Terrain (Terrain): Any terrain on which avalanches occur (e.g., steep slopes and gullies.) This is a broader term than "avalanche path", which designates a specific area where an avalanche begins, runs, and ends. In some ways avalanche terrain appears to be easy to define, in theory and indoors. Identifying it outdoors is often not so simple or obvious. Not all avalanche paths are large and obvious.
Avalanche Terrain Exposure Scale (Avalanche Hazard & Assessment): Also known as: ATES, Avalanche Terrain Exposure Scales; Classification system for routes and terrain by avalanche hazard severity: simple, challenging, complex, and extreme.
Avalanche track (Terrain): Also known as: Avalanche tracks; Where the avalanche gains speed and travels downslope. It is the middle zone of an avalanche Path. Between avalanche initiation in the Starting zone and where the avalanche slows down and stops in the Runout Zone .
Avalanche Transceiver (Avalanche Types): Also known as: Avalanche Transceivers; An electronic device worn on the body to aid in finding buried avalanche victims; also called an avalanche beacon.
Avalanche types (Avalanche Types): Avalanches are categorized among different criteria. The most important distinctions are made regarding:
Avalanche Warning (Avalanche Hazard & Assessment): Also known as: Avalanche Warnings; A public broadcast to draw particular attention to a severe avalanche danger. Each forecast area has different criteria for issuing warnings (e.g., a warning may be issued if the avalanche hazard is rated high or extreme in all areas above 1500 meters.)
avalanche wind (Meteorology & Weather): Also known as: avalanche winds; The rush of air produced in front of an avalanche of dry snow or in front of a landslide. The most destructive form, the avalanche blast, occurs when an avalanche is stopped abruptly, as in the case of an almost vertical fall into a valley floor. Such blasts may have very erratic behavior, leveling one house without damaging its neighbor.
Avalanches de neige humide ou de fonte
Avalanches de neige récente
Avalanches liées à des structures de plaques
Avalauncher (Avalanche Types): Also known as: Avalaunchers; A two-chambered pneumatic (compressed gas) cannon used in avalanche control work. It is probably the most popular civilian weapn in use. The trajectory is varied by altering the firing angle and the nitrogen pressure. It's disadvantages include a short range and poor accuracy in strong winds.
Avaluator (Avalanche Types): Also known as: Avaluators; A portable decision-making aid designed by Avalanche Canada for backcountry decisions, including Trip Planner and Slope Evaluator cards.
Basal Facets (Snowpack Properties): Faceted snow found at the base of the snowpack, forming persistent weak layers in thin snowpack areas.
basal ice (Snowpack Properties)
Base of a rock wall (Terrain): Also known as: Bases of rock walls; Lowermost visible area of a rock wall, frequently scree at a highly divergent slope angle, the steepness tending to decrease as it descends.
Bed surface (Avalanche Types): Term: Bed Surface; Also known as: Bed Surfaces, Bed Layer, Bed Surfaces, Bed surfaces, Bed Surfaces; The surface on which an avalanche runs, lying immediately below the failure plane.
Below Treeline Elevation (Terrain): Also known as: Below Treeline Elevations; The forest-covered elevation band, usually covering the greatest area and snowpack variation on mountains.
Bergschrund (Terrain): Also known as: Bergschrunds; A bergschrund is a large crevasse at the head (top) of a glacier where the moving glacier ice separates from the static snow and ice above (typically on a headwall). Bergschrunds typically extend all the way down to the bedrock below the glacier and are very wide and deep. During winter they may fill in with snow, deposited both by storms and by avalanches off the headwall above. In summer and fall a bergschrund is typically open and presents a challange and a danger to alpinists. When skiing or climbing above an open or thinly bridged bergschrund it can present a terrain trap - even a small avalanche can have serious consequences here. Sometimes there is a large crevasse-like gap between a glacier or snowfield and the rock wall above it. This can form when the rock wall heats in the sunshine and melts the ice and/or snow adjacent to to. While this is often colloquially called a bergschund the proper term is a randkluft or rimaye.
Bise wind: Also known as: Bise winds; A cold, dry northeasterly wind common in Switzerland. The Bise can transport snow and form dangerous wind slabs, particularly on sheltered slopes.
black ice (Snow Grain Shapes & Crystals): Thin, new ice on freshwater or saltwater, appearing dark in color because of its transparency, which is a result of its columnar grain structure. On lakes, black ice is commonly overlain by white ice formed from refrozen snow or slush. A mariner’s term for a dreaded form of icing sometimes sufficiently heavy to capsize a small ship. A popular alternative for glaze. A thin sheet of ice, relatively dark in appearance, may form when light rain or drizzle falls on a road surface that is at a temperature below 0°C. It may also be formed when supercooled fog droplets are intercepted by buildings, fences, and vegetation.
blizzard (Meteorology & Weather): Also known as: blizzards; A severe weather condition characterized by high winds and reduced visibilities due to falling or blowing snow. The U.S. National Weather Service specifies sustained wind or frequent gusts of 16 m per second (30 kt or 35 mi per hour) or greater, accompanied by falling and/or blowing snow, frequently reducing visibility to less than 400 m (0.25 mi) for 3 hours or longer. Earlier definitions also included a condition of low temperatures, on the order of -7°C (20°F) or lower, or -12°C (10°F) or lower (severe blizzard). The name originated in the United States but it is also used in other countries. In the Antarctic the name is given to violent autumnal winds off the ice cap. In southeastern France, the cold north wind with snow is termed blizzard (see also boulbie). Similar storms in Russian Asia are the buran and purga. In popular usage in the United States and in England, the term is often used for any heavy snowstorm accompanied by strong winds.
Blowing snow (Snowpack Properties): Term: blowing snow; Snow lifted from the surface of the earth by the wind to a height of 2 m (6 ft) or more above the surface (higher than drifting snow), and blown about in such quantities that horizontal visibility is reduced to less than 11 km (about 7 statute miles). As an obstruction to vision, it is encoded BS in a surface aviation weather observation and as BLSN as an obstruction to vision in a METAR or SPECI observation. Blowing snow can be falling snow or snow that already accumulated but is picked up and blown about by strong winds. It is one of the classic requirements for a blizzard.
Bonded snow (Avalanche Types): Snow is “bonded” if the particles are interlinked (sintered) to such a degree that a carefully isolated block does not collapse upon itself. Bonded snow can be soft or hard.
Bonding (Snowpack Properties): Also known as: Bondings; (fetch failed)
Boot Packing (Snow Grain Shapes & Crystals): Also known as: Skier Compaction; (Skier Compaction) Mechanical reworking of snow to harden it and to prevent depth hoar formation, usually by a large number of people walking up and down the slopes or skiing on them. This increases snow density and strength. Boot packing affects deeper layers than skier compaction or ski-cutting. This method is generally limited to small areas due to the manpower required. Boot packing compresses any depth hoar which has formed and helps prevent its formation by decreasing pore space and is usually done early in the season. Skier compaction breaks up the continuity of new snow weaknesses and weak layers closer to the surface and is done throughout the season. Ski areas sometimes accomplish this by encouraging traffic on certain slopes. While these are methods used by organizations such as ski areas (and less commonly highways, etc) skier compaction does play a role in some off-piste and backcountry areas. Heavily used slopes are sometimes more stable in the upper layers because of this.
Bowl: Also known as: Bowls; Rounded or elongated concavity; typically tending to accumulate snowdrift.
Breakable crust (Meteorology & Weather): Term: Breakable Crust; Also known as: Breakable Crusts, Breakable crusts; A crust, usually thin, which will not support the weight of a person skiing, snowshoeing, or walking. This generally creates miserable travel conditions.
Bridging (Snowpack Properties): The use of this term has been debated among professional avalanche workers, but it is commonly used to refer to a situation where a strong layer of snow lies over a weak layer, thus "bridging" it. This is common mechanics problem in some ways, often called the "Simply Supported Beam with a point load". However, in the snowpack this bridge can be any length in any direction along the surface. The distance between supports is generally unknown. The material properties of the bridge material are poorly understood and often vary significantly throughout the bridge. And depending on how many people there are and how large the "bridge" is there may be multiple point loads. So when the term "bridging" is used it implies a weak layer underneath a stronger layer which is at least somewhat supportable. The question of whether the bridging is consistently strong enough to be safe to travel on is a difficult one.
Broad ridge (Terrain): Also known as: Broad ridges; A rounded, elongated shoulder of high terrain.
Burial (Avalanche Types): Also known as: Burials, Buried; (Buried) Referring to an avalanche victim who has less than one hand protruding from the snow after an avalanche stops.
Calorie (Snowpack Properties): Also known as: BTU, British Thermal Unit, Joule, Calories; (BTU, British Thermal Unit, Joule) A calorie is one of the units used in science and engineering to measure heat. The quantity of heat needed to raise the temperature of one gram of water one degree centigrade is defined as a calorie. Other units for heat are BTUs (British Thermal Units, l BTU = 252 calories) and Joules.
Canadian Hardness Gauge (Snowpack Properties): Also known as: Canadian Hardness Gauges; A spring frame mechanism that measures layer-parallel hardness by imparting different size discs into the layering.
Cantilever Beam Test (Snowpack Properties): Also known as: Cantilever Beam Tests; A cantilever beam is excavated in the snow. This can be used as a measure of tensile strength or changes in it. A standard mechanical cantilever beam loaded only with it's own weight is shown here. (In many engineering tests a single load is applied on the end and increased until the beam fails.) A cantilever beam test as performed in snow is shown below. No additional load is added, the only weight is from the beam itself. The tensile strength at the top of the beam where it is connected to the rest of the snowpack is a function of the thickness (T) and the length (L) of the beam. The bottom is generally undercut until failure and the length recorded. This must be done relatively quickly so that the snow behaves elastically and has a brittle failure. Slow loading on snow can result in ductile deformation without failure, or prior to failure. (See visco-elastic.)
Carte d'évaluation de la pente
Carte Planificateur d'excursion
Cascade triggering: Also known as: Cascade triggerings; When one avalanche triggers additional avalanches on adjacent slopes or below. The vibration or debris from the initial slide causes nearby weak layers to fail, leading to much larger overall destruction.
Cassure linéaire
Centrifugal Test (Measurement & Observation): Also known as: Centrifugal Tests; A method of measuring the tensile strength of a cylindrical snow sample by spinning in a centrifuge. From the rotational speed (in rpm) at which the sample breaks the centrifugal force and tensile strength of the sample can be calculated.
Challenging Terrain (Avalanche Types): Also known as: Challenging Terrains; ATES level involving exposure to well-defined avalanche paths with options to reduce exposure through careful route-finding.
Channeled Avalanche (Terrain): Also known as: Channel Path, Channeled Avalanches; (Channel Path) An avalanche and/or path which is constricted or confined for a portion of its flow by terrain features such as a gully.
Charge critique
chinook (Meteorology & Weather): Also known as: chinooks; The name given to the foehn in western North America, especially on the plains to the lee or eastern side of the Rocky Mountains in the United States and Canada. On the eastern slopes of the Rocky Mountains the chinook generally blows from the west or southwest, although the direction may be modified by topography. Often the chinook begins to blow at the surface as an arctic front retreats to the east, producing dramatic temperature rises. Jumps of 10°–20°C can occur in 15 minutes, and at Havre, Montana, a jump from -12° to +5°C in 3 minutes was recorded. Occasionally the arctic front is nearly stationary and oscillates back and forth over an observing station, causing the temperature to fluctuate wildly as the station comes alternately under the influence of warm and cold air. As in the case of any foehn, chinook winds are often strong and gusty. They can be accompanied by mountain waves, and they can occur in the form of damaging downslope windstorms. The air in the chinook originates in midtroposphere above the ridgetops, and its warmth and dryness result from subsidence. When moisture is present, a variety of mountain-wave clouds and lee-wave clouds can form, such as the chinook arch of the Canadian Rocky Mountains west of Calgary, Alberta. The chinook brings relief from the cold of winter, but its most important effect is to melt or sublimate snow: A foot of snow may disappear in a few hours. As with the foehn, researchers have attempted to classify chinooks as downslope winds with warming and boras as those accompanied by cooling. Again, these schemes have produced limited success because of the many ambiguous or erroneously classified cases.
Climax Avalanche (Snowpack Properties): Also known as: Climax Avalanches, Ground Avalanche; (Ground Avalanche) Usually defined formally as an avalanche involving multiple layers of snow. In practice it often refers to an avalanche for which the bed surface is the ground.
coarse (Snow Grain Shapes & Crystals)
Cohesion (Snowpack Properties): The attraction force by which snow grains are held together as a coherent unit. This may be from bonding, interlocking crystal branches, or capillary action within the snow liquid water content.
Cold Dome (Meteorology & Weather): Also known as: Cold Domes; A shallow lens of cold air that has formed by radiation cooling of a stationary air mass over a cold region.
cold front (Meteorology & Weather): Also known as: cold fronts, Cold Fronts; Any nonoccluded front, or portion thereof, that moves so that the colder air replaces the warmer air; that is, the leading edge of a relatively cold air mass. Compare cold type occlusion.
Collapse (Snowpack Properties): Also known as: Collapses; When fracture of a lower snow layer causes an upper layer to fall; also called a whumpf.
Companion Rescue (Avalanche Types): Also known as: Companion Rescues; Rescue efforts made by the members of a group involved in an avalanche incident, including observation, transceiver search, probing, and digging.
Complex Terrain (Avalanche Types): Also known as: Complex Terrains; ATES level with multiple overlapping avalanche paths, large steep areas, and minimal exposure reduction options.
Compression Failure (Avalanche Hazard & Assessment): Also known as: Compression Failures; 1. Stress relieved at the stauchwall where the slab-group fractures at 45 to maximum stress. 2. Where the weak-layer collapses under compressive load.
Compression Test (Avalanche Hazard & Assessment): Also known as: Compression Tests; Snowpack test applying incremental load to snow columns to assess weak layer strength and fracture character.
Compression Zone (Snowpack Properties): Also known as: Compression Zones; An area at the base of a slide path and/or slab where the terrain is concave and the snowpack stress is in compression.
Concave: The interior of a curved surface. Opposite of convex.
Concave Slopes (Terrain): A terrain feature rounded inward like a bowl's interior, going from steep to less steep.
Condensation (Snow Processes): Term: condensation; Also known as: Condensations, Deposition; In general, the physical process by which a vapor becomes a liquid or solid; the opposite of evaporation, although on the molecular scale, both processes are always occurring. In meteorological usage, this term is applied only to the transformation from vapor to liquid; any process in which a solid forms directly from its vapor is termed deposition, and the reverse process sublimation. In meteorology, condensation is considered almost exclusively with reference to water vapor that changes to dew, fog, or cloud. Condensation in the atmosphere occurs by either of two processes: cooling of air to its dewpoint, or addition of enough water vapor to bring the mixture to the point of saturation (that is, the relative humidity is raised to 100 percent). When either of these processes occurs, condensation ensues only if condensation nuclei or other surfaces are present. In the complete absence of such, condensation does not occur at nominal saturation. The spontaneous formation of liquid or solid droplets from water vapor (homogeneous nucleation) is opposed by the surface free-energy increase that attends the creation of new surfaces of the liquid or solid phase. Only for extreme supersaturation does this free-energy balance swing in favor of spontaneous nucleation.
Conduction: Also known as: Conductions; Transfer of heat from one touching object to another.
Considerable Avalanche Danger (Avalanche Hazard & Assessment): Also known as: Considerable Avalanche Dangers; The third danger level where natural avalanches are possible and human-triggered ones are likely; requires careful evaluation.
Considerable Danger (Avalanche Hazard & Assessment): Also known as: Considerable Dangers; Dangerous avalanche conditions where natural avalanches are possible and human-triggered avalanches are likely.
Consolidation (Snowpack Properties): The overall increase in snowpack strength due to the combined effects of settlement and sintering.
Consolidation de plaque
Convection (Meteorology & Weather): Term: convection; Also known as: convections, Convections, Forced Convection, Natural Convection; In general, mass motions within a fluid resulting in transport and mixing of the properties of that fluid. Convection, along with conduction and radiation, is a principal means of energy transfer. Distinction is made between free convection (gravitational or buoyant convection), motion caused only by density differences within the fluid; and forced convection, motion induced by mechanical forces such as deflection by a large-scale surface irregularity, turbulent flow caused by friction at the boundary of a fluid, or motion caused by any applied pressure gradient. Free and forced convection are not necessarily exclusive processes. On a windy day with overcast sky, the heat exchange between ground and air is an example of forced convection. On a sunny day with a little wind where the ground temperature rises, both kinds of convection take place. (Or gravitational or buoyant convection.) Motions that are predominantly vertical and driven by buoyancy forces arising from static instability, with locally significant deviations from hydrostatic equilibrium. Atmospheric convection is nearly always turbulent. Convection may be dry, that is, with relative humidities less than 100%, especially in the boundary layer, but is commonly moist, with visible cumuliform clouds. Most convective clouds are driven by positive buoyancy, with virtual temperature greater than the environment, but clouds with precipitation, evaporation, and/or melting can produce negatively buoyant convection. See slantwise convection. As specialized in atmospheric and ocean science, a class of relatively small-scale, thermally (can be driven by salt concentration in the ocean) direct circulations that result from the action of gravity upon an unstable vertical distribution of mass. (In the case of slantwise convection, though, the motions are larger scale, and are driven by a combination of gravitational and centrifugal forces acting at an angle to the vertical.) Almost all atmospheric and oceanic convection is fully turbulent and is generally composed of a collection of convection cells, usually having widths comparable to the depth of the convecting layer. In the atmosphere, convection is the dominant vertical transport process in convective boundary layers, which are common over tropical oceans and, during sunny days, over continents. In the ocean, convection is prominent in regions of high heat loss to the atmosphere and is the main mechanism of deep water formation. Moist convection in the atmosphere is characterized by deep, saturated updrafts and downdrafts, and unsaturated downdrafts driven largely by the evaporation and melting of precipitation. This form of convection is made visible by cumulus clouds and, in the case of precipitating convection, by cumulonimbus clouds. Moist convection and radiation are the dominant modes of vertical heat transport in the Tropics. In atmospheric electricity, a process of vertical charge transfer by transport of air containing a net space charge, or by motion of other media (e.g., rain) carrying net charge. Eddy diffusion of air containing a net charge gradient may also yield a convection current.
Convective Lift (Meteorology & Weather): Also known as: Convective Lifts; Vertical movement of air in which warm air rises and cool air sinks, creating tall clouds and showery precipitation.
Convergence atmosphérique
Convex: The exterior of a curved surface. Opposite of concave.
Convex Slopes (Terrain): Term: Convex Slope; Also known as: Convex Slopes; A slope that steepens as it descends, creating tension zones where avalanches often fracture.
Corn snow (Snow Processes): Term: Corn Snow; Also known as: Quasi-Corn, Spring Snow; Redirected to spring-snow.
Cornice (Terrain): Term: cornice; Also known as: cornices, Cornices, Cornices, Cornices; An overhanging structure of ice or snow formed at a topographic edge (such as a mountain ridge) by wind-driven deposition. Cornices can be extremely hazardous to mountain climbers. Cornice release can also initiate avalanches.
Corniches
Couche de faces planes et de croûtes
Couche fragile
Couche fragile persistante
Couloir (Terrain): Also known as: Couloirs, Couloirs, Couloirs; A couloir is a steep and narrow vertical gully on a mountainside, typically with rocky sides to it. These are often used as climbing and steep skiing routes. They may be subject to cross loading in addition to windloading at the top, new snow, and other more typical factors. The energy balance at the surface may also be different from open slopes near by. The safest season to climb or ski couloirs is spring. There is not a lot of opportunity to assess the snowpack conditions until the person or group is fully committed to the route. This is a common situation for climbers in spring and is the basis for our Climbers Avalanche Course. That course is specifically tailored to advance planning rather than assessing things enroute, which is often or usually not an option for climbers. Advance planning is also essential since escape routes or other options to mitigate consequences are almost always limited or non-existent. Couloirs are a type of terrain trap. Chute and couloir mean the same thing for all practical purposes. A gully is a somewhat more general term and some gullies are not steep enough to be called a couloir or chute.
Couloir d'avalanche
Coulée de neige
Coulées de neige
Coupe en skis
Couronne
Creep (Snowpack Properties): Term: creep; Also known as: Creep Tension; The movement of water under or around a structure built on permeable foundations that may lead to erosion. The slow, downslope movement of surface soil or rock debris, usually imperceptible except when observed for long durations.
Crevasse (Terrain): Also known as: Crevasses; A crevasse is a large crack in the ice on a glacier. These form from the motion of the ice. They range in size from narrow enough to step across to large, deep gaping holes. Crevasses present an additional avalanche danger in the form of a terrain trap. Even a small avalanche can have serious consequences if a person is swept into a crevasse. Especially if snow flows in on top of them, burying them deeply inside the crevasse. During winter crevasses are usually (but not always) bridged with new snow across the top. This can make them difficult or impossible to identify or spot. If these bridges are thin they can easily break under the weight of a person. Thin bridges are common in early winter, late spring and summer, and in places where the wind may allow them to form but not thicken. The large crevasse at the top of a glacier where it separates from the snow/ice above is called a bergschrund.
Critical depth of new fallen snow (Snowpack Properties): Also known as: Critical depths of new fallen snow; New fallen snow is a burden on the existing snow cover, can thus increase avalanche danger.In unfavourable conditions, e.g. poor layering, low temperatures, strong winds, even a few cm (10-20) can be critical. In favourable conditions, e.g. stable old snowpack, light winds, 20-30cm can be critical.
Critical Loading (Avalanche Types): Also known as: Critical Loadings; When new precipitation or windblown snow overloads a slab, potentially triggering natural or light-trigger avalanches.
Cross Loading (Avalanche Hazard & Assessment): Also known as: Cross Loadings; Wind blowing across a slope, depositing drifts on sides of gullies.
Cross-loading (Terrain): Also known as: Cross-loadings, Cross-loadings; Wind transporting snow from windward to leeward slopes, commonly creating wind slabs.
Crown (Avalanche Hazard & Assessment): Also known as: Crowns, Crowns; The uppermost part of the fracture of a slab avalanche, where the slab breaks away from the snowpack overhead.
Crown / Fracture line: Also known as: Crowns / Fracture lines; The line along which a slab avalanche fractures and separates from the stable snow above. The height of the crown wall indicates the slab thickness and avalanche severity.
Crown Face (Avalanche Types): Also known as: Crown Faces; The top fracture surface of a slab avalanche; usually smooth and clean-cut.
Croûte de pluie
Croûte de regel
Croûte de soleil
Croûtes
Crust (Snowpack Properties): Term: Crusts; Also known as: Crusts, Crusts; Hard snow layers created by liquid freezing on/near surface or from wind, including melt-freeze, rain, sun, and wind variants.
Crystal (Snow Grain Shapes & Crystals): Also known as: Crystals; (Ice Crystal, Snow Crystal, Crystal Habit, Column Crystal, Needle Crystal, Plate Crystal, Dendrite Crystal, Stellar) A crystal is any substance, usually a solid, whose atoms or molecules are arranged in an orderly array. Ice Crystal , Snow Crystal Any segment of ice in which the molecules are arranged in the same orderly array. Snow particle growth in the atmosphere begins in the form of small ice crystals. If the ice crystal continues to grow by sublimation a snow crystal is formed. This is a larger particle, often with an intricate shape, which is visible to the naked eye. Ice crystals have three symmetric axes in the basal plane (the a-axes) and one axis perpendicular to that basal plane (the c-axes). The three a-axes are separated by 120 degrees which leads to hexagonal symmetry in this plane. Crystal Habit "Habit" refers to the crystal shape which results from differing rates of growth in the different axis directions. Column Crystal , Needle Crystal An ice crystal, such as precipitated snow, in the shape of a needle or a hexagonal column with major growth along the c-axis. Some forms of surface hoar also have a needle shape. Plate Crystal An ice crystal, such as precipitated snow, shaped like a hexagonal plate with major growth along the a-axis. Dendrite Crystals, Stellar Crystals, Stellars Precipitated flat snow crystals with needle-like growth primarily along the a-axis. At high growth rates growth on the a-axes occurs more rapidly at edges and corners. The result is ore complicated forms such as dendrites. The dynamics of such growth is relatively poorly understood. All micrographs are by the USDA and as government products made with public funds are in the public domain.
Cup-shaped crystals
Cycle d'avalanches
cyclone (Meteorology & Weather): Also known as: cyclones; An atmospheric cyclonic circulation, a closed circulation. A cyclone’s direction of rotation (counterclockwise in the Northern Hemisphere) is opposite to that of an anticyclone. While modern meteorology restricts the use of the term cyclone to the so-called cyclonic-scale circulations, it is popularly still applied to the more or less violent, small- scale circulations such as tornadoes, waterspouts, dust devils, etc. (which may in fact exhibit anticyclonic rotation), and even, very loosely, to any strong wind. The first use of this term was in the very general sense as the generic term for all circular or highly curved wind systems. Because cyclonic circulation and relative low atmospheric pressure usually coexist, in common practice the terms cyclone and low are used interchangeably. Also, because cyclones are nearly always accompanied by inclement (often destructive) weather, they are frequently referred to simply as storms. See tropical cyclone, extratropical cyclone; compare trough.
Danger (Avalanche Hazard & Assessment): Also known as: Dangers; Conditions, circumstances or processes which can result in damage and/or injury.
Danger en surplomb
danger level 1 - low (Avalanche Hazard & Assessment): Term: low
danger level 2 - moderate (Avalanche Hazard & Assessment): Term: moderate
danger level 3 - considerable (Avalanche Hazard & Assessment): Term: considerable
danger level 4 - high (Avalanche Hazard & Assessment): Term: high
danger level 5 - very high (Avalanche Hazard & Assessment): Term: very high
Danger patterns (Avalanche Hazard & Assessment): Typical avalanche problems and danger patterns commonly indicate typical, repetitive and usually obvious danger situations that highlight an avalanche hazard situation.However it should be noted that while avalanche problems give an initial indication of possible danger factors (e.g. new snow), danger patterns provide deeper explanation into the processes within the snowpack and the causes of the problem (e.g. problem due to excessive new snow load on a weak layer). Therefore, danger patterns help to describe different scenarios or processes that signal the development of a particular avalanche problem. By recognising avalanche problems and danger patterns recreations can be forewarned about the development of dangerous situations and change their plans accordingly.
Danger Ratings (Avalanche Hazard & Assessment): In the U.S., a five-category estimation: Low, Moderate, Considerable, High, and Extreme.
Danger scale (Avalanche Types): Also known as: Danger scales; The avalanche danger is evaluated in the avalanche bulletin in each of the individual avalanche warning services and describes the avalanche danger using the five-level European avalanche danger scale.
Dangerator (Avalanche Types): Also known as: Dangerators; Tool estimating avalanche danger ratings using weather data and field observations for moderate to high danger levels.
Daytime changes (Meteorology & Weather): Also known as: during the course of the day; Evolving avalanche danger over the course of a day. Avalanche danger can vary greatly during the day. Springtime situations are typical: after a clear night, avalanche danger is low early in the morning, then increases over the course of the day due to daytime warming and solar radiation. Also common while heavy snowfall, prolonged wind activity and rain.
Decomposed snow (Snow Grain Shapes & Crystals): Irregular, forked particles resulting from snow crystal rounding and/or mechanical influences as e.g. wind drift. Fragments of original snow crystals are frequently still recognizable.
decomposing and fragmented precipitation particles (Snow Grain Shapes & Crystals)
Decomposition (Snow Grain Shapes & Crystals): Also known as: Decompositions; When the snow pack loses its integrity by reducing the size and/or number of bonds usually with kinetic growth or water infiltration.
Decreasing firmness (Snowpack Properties): Bonding between ice crystals deteriorates or is lost, diminishing overall capacity of crystals to absorb loading.
Deep Persistent Slab (Snowpack Properties): Also known as: Deep Persistent Slabs; Avalanche problem with weak layer near snowpack base resisting bonding for extended periods, often throughout season.
Deep Slab Avalanche (Avalanche Types): Also known as: Deep Slab Avalanches; Avalanches that break deeply into old weak layers of snow.
Delayed Action Release (Avalanche Types): Also known as: Delayed Action Releases, Post Control Release; (Post Control Release) Avalanche which occurs between storms as opposed to during or immediately after a storm, or well after active control procedures.
Dense flow avalanche (Avalanche Types): Also known as: Dense flow avalanches; Avalanche motion which primarily flows, slides, slips, in contrast to powder cloud avalanches.
Dense Trees (Snowpack Properties): Forested areas where tree canopies touch, sheltering snow and potentially anchoring snowpack.
Density (Snowpack Properties): Also known as: Dense, Heavy, Low Density, Light, Densities; (Dense, Heavy, Low Density, Light) Density refers to Mass per volume, usually specified in kilogram per cubic meter (kg/m^3). The density of water is 1000 kg/m^3 and snow density is usually measured as a ratio to this. So snow which is 100 kg/m^3 is specified as 100/1000, or 10 percent (of the density of water). The water content divided by the snow depth also gives the density of the snow. Example: 1.2" water equivalent divided by 15" of snow = .08 density (or 8 percent water content). New snowfall is typically between 7% and 12% but can be lower or higher than this sometimes. Wind exposure often increases the density to 20% to 30%. Higher density (heavier) snow typically results from warmer temperatures and/or winds while lower density (lighter snow) usually results from colder air with less wind. The density will increase over time due to snow settlement. Old snow may reach 40% to 50% density and firn can reach 60%. The highest density of ice known is fully mature glacier ice. When used qualitatively density is somewhat of a relative term. Dense snow usually refers to heavy snow that is not so much fun for skiing or snowboarding (but may be better for snowmobiling or snowshoeing). But Dense Powder means light powder snow which is just not as light (or low-density) as usual for the area. The density of a layer of snow in a snowpit can be measured with a density cutter.
Density Cutter (Measurement & Observation): Also known as: Density Cutters; A sampling tool used to make snow density measurements. This photo shows one kind being used in a snowpit to measure the density of one of the layers. It can be hung from any object inserted in the snowpit wall (such as a saw here) and the density is read directly off of a scale.
deposition (Meteorology & Weather): Also known as: depositions; Processes by which traces gases or particles are transferred from the atmosphere to the surface of the earth. Atmospheric deposition is usually divided into two categories, wet deposition and dry deposition, depending on the phase of the material during the deposition process. Thus, in wet deposition, the gas or particle is first incorporated into a droplet and is then transferred to the surface via precipitation. In dry deposition, the gas or particle is transported to ground level, where it is adsorbed onto a surface. The surface can be the ocean, soil, vegetation, buildings, etc. Note that the surface involved in the dry deposition may be wet or dry—the “dry” in dry deposition refers only to the phase of the material being deposited.
Depth hoar (Snow Grain Shapes & Crystals): Term: depth hoar; Also known as: cup-shaped crystals; Ice crystals (usually cup-shaped, faceted crystals) of low strength formed by sublimation within dry snow beneath the snow surface; a type of hoarfrost. Associated with very fast crystal growth under large temperature gradients. This is one way in which firn formation may begin. Depth hoar is similar in physical origin to crevasse hoar. Hoarfrost composed of crystals that have built up a three-dimensional complex of faceted, rather than rounded, crystals.
Depth of new: Also known as: Depths of new, fresh fallen snow; Amount of snow deposited in the previous 24 hours.
Dew Point (Snowpack Properties): Also known as: Dew Points, Dew Points; Temperature at which air becomes saturated with water vapor, determining surface hoar formation on snow.
Direct Action Avalanche (Avalanche Types): Also known as: Direct Action Avalanches; Avalanches that occur during or immediately after a storm or in immediate response to active control procedures.
Diurnal Cycle (Snowpack Properties): Also known as: Diurnal Cycles; Daily temperature variation reflecting warming during daylight and cooling at night, affecting melt-freeze crust cycles.
Dormant Layer (Avalanche Types): Also known as: Dormant Layers; A weak layer gaining strength to the point where slab avalanches become unlikely, though capable of reactivation.
Drifting snow (Meteorology & Weather): Term: drifting snow; Snow raised from the surface of the earth by the wind to a height of less than 6 ft above the surface. In aviation weather observations, drifting snow is not regarded as an obstruction to vision because it does not restrict horizontal visibility at 6 ft or more above the surface. When snow is raised 6 ft or more above the surface, it is classified as blowing snow.
dry (Snowpack Properties)
Dry Loose Avalanche (Snowpack Properties): Also known as: Dry Loose Avalanches; Loose snow avalanche composed of dry snow, most likely with deep, low-density surface layers.
dry snow (Snow Types): Snow from which a snowball cannot readily be made.
Dry Snow Avalanche (Snowpack Properties): Also known as: Dry Snow Avalanches; An avalanche occurring in snow below freezing temperatures.
Dust Cloud (Avalanche Types): Also known as: Dust Clouds; Mixture of air and snow particles accompanying an avalanche.
Détecteur de victimes d'avalanche
EAWS News: EAWS Conference Seggau/Styria, 06/2025
Elastic (Avalanche Hazard & Assessment): (elasticity, elastic deformation) Deformation without fracture. Capable of returning, to some limited extent, to its original shape after being deformed. Elasticity refers to how much deformation can occur before it becomes irreversible. Elastic deformation refers to any deformation which is elastic (within the limits of the materials elasticity). Snow is visco-elastic and has a certain amount of elasticity. It has been found that after an avalanche release the remaining crown line "rebounds" a small amount, like one half of a rubber band which has snapped. (However, the amount of elasticity in snow is much less than in a rubber band!)
Endangered traffic route (Avalanche Types): Also known as: Endangered traffic routes; Transportation route near a slope potentially endangered by avalanches.
Entrain (Avalanche Types): Where flowing avalanche snow incorporates adjacent snow along its descending path.
Equilibrium Growth (Snow Grain Shapes & Crystals): Also known as: Equilibrium Growths; (Equi-temperature metamorphism, ET, rounds, rounding, sintering, bonding, etc) Crystal growth or metamorphism which occurs at a slow (near-equilibrium) rate in the absence of a large temperature gradient or other strong non-equilibrium factors. Grains become rounded and bonding between grains (sintering) increases. In the advanced stages the crystals are well-rounded, bonded (sintered), and all very close in size. [Colloqially "Advanced ET"] This metamorphic process has always been believed to be driven by radius dependent vapor pressure gradients, but this is currently under investigation and is being re-thought by scientists.
Equilibrium metamorphism (Snowpack Properties): Also known as: isothermal metamorphism, snow crystal rounding; Transformation process of dry snow with a minimal temperature gradient in the snowpack.
Evaporation (Snow Processes): Also known as: Evaporations; Phase change (or conversion) of liquid into vapor, i.e. water into water vapor. Evaporation is the opposite of condensation.
Excavation
Explosives-triggered Avalanche (Avalanche Hazard & Assessment): Also known as: Explosives-triggered Avalanches; Avalanche intentionally triggered using explosives for safety programs, providing valuable hazard information.
Exposed (Avalanche Hazard & Assessment): Exposure to wind, sun, avalanches or other general danger.
Exposed transportation route (Avalanche Hazard & Assessment): Also known as: Exposed transportation routes; Sector of road, railway, or similar infrastructure facility at risk from avalanche danger; often the runout zone of an avalanche path.
Extended Column Test (Avalanche Hazard & Assessment): Also known as: Extended Column Tests; Snowpack test using wider snow columns than compression tests to better assess fracture propagation.
Extreme Avalanche Danger (Avalanche Hazard & Assessment): Also known as: Extreme Avalanche Dangers; Highest danger level where natural and human-triggered avalanches are certain; all avalanche terrain avoided.
Extreme Danger (Avalanche Hazard & Assessment): Also known as: Extreme Dangers; Avoid all avalanche terrain; natural and human-triggered avalanches are certain.
Facet/Crust Layer (Snow Grain Shapes & Crystals): Also known as: Facet/Crust Layers; Combination of facets and crust in close proximity, frequently creating instability conditions.
faceted crystals (Snow Grain Shapes & Crystals)
Faceted Snow (Snow Grain Shapes & Crystals): Snow grains within the snowpack that have transformed into larger, angular grains, often called sugar snow.
Faceted snow crystals (Snow Grain Shapes & Crystals): Also known as: grains; Snow grains, solid, with multiple flat glassy faces and sharp edges. Developed from faceting metamorphism, usually poorly bonded to one another (fewer contact points), a critical factor in avalanches if a faceted layer is covered with bonded snow.
Facteur déclencheur
Faible probabilité/conséquence grave
Failure Plane (Avalanche Types): Also known as: Failure Planes, Failure Planes; The weak snowpack layer on which the fracture releases during slab avalanches.
Fall Line (Terrain): Also known as: Fall Lines; A line perpendicular to the contour, which has the greatest pull of gravity. The line a round ball would roll down if the slope was free from obstructions.
Favourable situation (Avalanche Hazard & Assessment): Also known as: Favourable situations
fine (Snow Grain Shapes & Crystals)
Firmness (Snowpack Properties): Load-bearing capacity (resistance to disintegration). Depends on extent and quality of snow crystal bonding.
Firn (Snow Processes): Term: firn; Old snow that has become granular and compacted (dense) as the result of various surface metamorphoses, mainly melting and refreezing but also including sublimation. The resulting particles are generally spherical and rather uniform. Firnification, the process of firn formation, is the first step in the transformation of snow into land ice (usually glacier ice). Some authorities restrict the use of firn to snow that has lasted through one summer, thereby distinguishing it from spring snow. Originally, the French term, “névé,” was equivalent to the German term, “firn,” but there is a growing tendency, especially among British glaciologists, to use “névés” for an area of firn, that is, generally for the accumulation area above or at the head of a glacier
firn line (Snow Processes): Also known as: firn lines; The boundary of the area of snow on a glacier surviving one year’s ablation, thus becoming firn. In the absence of superimposed ice, this limit is equivalent to the equilibrium line. See climate snow line.
Firn mirror (Snowpack Properties): Also known as: Firn mirrors; A very thin layer of ice on the snowpack surface formed through interaction of solar radiation, melting, wind impact and outgoing radiation.
Firnspiegel (Snow Grain Shapes & Crystals): Also known as: Firn Spiegel, firn mirror, glacier fire, Firnspiegels; (Firn Spiegel, firn mirror, glacier fire) An ice crust formed on the snow surface on sunny, cold days. The sun's heat penetrates the surface snow layers and causes melt around the grains beneath the surface but meltwater at the surface is refrozen forming a thin layer of ice. This requires just the right heat balance. Firnspiegel is highly reflective and mirror-like, giving it the colloquial names of firn mirror and glacier fire..
Fissure de reptation
Fissures
Flanc
Flank (Avalanche Types): Also known as: Flanks, Flanks; The side of an avalanche, with two flanks connected by the crown.
Foehn (Meteorology & Weather): Term: foehn; Also known as: Or föhn., foehns, Foehns; (Or föhn.) A warm, dry, downslope wind descending the lee side of the Alps as a result of synoptic-scale, cross-barrier flow over the mountain range. The winds are often strong and gusty, sometimes forming downslope windstorms as a result of mountain wave activity. The air in the near-surface flow originates at or above the main crest height of the Alpine barrier, and achieves its warmth and dryness as a result of adiabatic descent. The foehn often replaces a retreating cold air mass from a polar or arctic front, producing dramatic temperature rises that reach 10°C and occasionally even 20°C or more, sometimes in a matter of minutes. This is especially true of the south foehn, which blows from northern Italy, where the air is warm, to the north of the Alps (Austria, Germany, Switzerland), where the air is cooler and could be cold arctic air as just described. The north foehn, blowing from a cooler to a warmer region, produces less dramatic temperature changes. The air in the foehn, originating from the mid troposphere, is characteristically clean. Its warm temperatures rapidly melt (or sublimate) snow, sometimes producing flooding, and the extreme dryness can lead to dangerous fire weather conditions. The Alpine foehn has been extensively studied by European scientists, and it is recognized as the type wind for similar downslope winds, resulting from cross-barrier flow, in other parts of the world. In other mountain ranges the foehn has a variety of local names, including chinook in the Rocky Mountains in North America; zonda for a westerly foehn from the Argentine Andes; ljuka in Carthinia (northwestern Croatia); halny wiatr in Poland; austru in Romania; and favogn in Switzerland. A northeasterly foehn descending the Massif Central in France and extending over the Garonne Plain is locally called aspre. A dry wind from the northwest descending the coastal hills in Majorca is named the sky sweeper. In New Zealand a foehn blowing from the New Zealand Alps onto the Canterbury Plains is the Canterbury northwester. A cross- barrier flow that produces strong winds and cooling is called a bora in many parts of the world. Many authors have attempted to classify strong wind events as foehn (or chinook) or bora, for example, for climatologies. These studies have had mixed success: Many wind events are easy to classify, but a number of events are difficult, depending on the data available (most studies attempt to use surface data) and the method used to differentiate between the two types of events. See foehn phase, high foehn. Defant, F. 1951. Compendium of Meteorology. 667–669.
Foehn Wall (Meteorology & Weather): Also known as: Crest Cloud, Foehn Walls; (Crest Cloud) In fohn wind conditions there is often a cloud bank formed over the crest where the dynamic change from lifting, cooling and precipitation on the windward side to to sinking and warming on the lee side. The edge of this cloud formation can be very abrupt, giving the appearance of a wall.
Forêt dense
Fracture (Avalanche Hazard & Assessment): Also known as: Fractures, Fractures; Stress relieved by catastrophic failure. On the microscale, this can be grain bonds breaking. On a larger scale fractures occur when layer adhesion is broken under shear stress along the bed surface, tensile stress along the crown, shear along the flanks, and/or compressive stress at the stauchwall.
Fracture depth (Avalanche Types): Also known as: Fracture depths; Slab thickness at the fracture line, measured vertically.
Fracture Line (Avalanche Types): Also known as: Fracture Lines; The line that forms the outer extent of the slab fracture of a slab avalanche.
Fracture Line Profile (Avalanche Types): Also known as: Fracture Line Profiles; A snow pit dug within the crown region of a recent slab avalanche, ideally within 24 hours after occurrence.
Free Water (Snowpack Properties): Liquid water present in the snowpack.
Freezing Level (Terrain): Also known as: Freezing Levels; The altitude at which air temperature reaches 0°C, determining precipitation type at different elevations.
Freezing rain (Meteorology & Weather): Rain that falls in liquid or supercooled liquid form that freezes upon impact and forms a coating of ice on the ground and or exposed objects. In aviation weather observations, this hydrometeor is encoded FZRA. Freezing rain occurs when the air temperature near the surface and skin temperature of objects are typically near or below freezing (0°C or 32°F). The droplet size diameter of freezing rain is ≥0.5mm. Freezing rain can sometimes occur on surfaces exposed to the air (such as tree limbs) with air temperatures slightly above freezing in strong winds. Local evaporative cooling may result in freezing. Freezing rain frequently occurs, therefore, as a transient condition between the occurrence of rain and ice pellets (sleet). When encountered by an aircraft in flight, freezing rain can cause a dangerous accretion of clear icing. NOAA, 2005: Federal Meteorological Handbook No. 1: Surface Weather Observations and Reports. Office of the Federal Coordinator for Meteorological Services and Supporting Research, FCM-H1-2019, 101 pp., https://www.icams-portal.gov/publications/fmh/FMH1/fmh1_2019.pdf. Federal Aviation Administration, 2021: Surface Weather Observing, Air Traffic Organization, JO 7900.5E CHG 1, 178 pp., https://www.faa.gov/documentLibrary/media/Order/JO_7900.5E_with_Change_1.pdf. Term edited 28 April 2025.
Fresh/new snow
Frittage
Front (Meteorology & Weather): Also known as: Cold Front, Warm Front, Fronts; (Cold Front, Warm Front) The boundary between two colliding air masses. Air masses in the atmosphere tend to remain distinct and rather than mixing they displace each other. The term "front" supposedly came about as an analogy to battle fronts in war. Warm Front An air mass discontinuity where warm air is pushing back a mass of cold air and riding over it. Cold Front An air mass discontinuity where a cold air mass is pushing under warm air. The slope of the interface or boundary between the air masses is steeper than that of a warm front, up to 1:25 Cold front precipitation is usually sharply defined and consists of bands perpendicular to the front. Duration of precipitation is typically on the order of 4-6 hours.
Front chaud
Front froid
Front occlus
Front quasi stationnaire
Frontal Lift (Meteorology & Weather): Also known as: Frontal Lifts; Atmospheric lift mechanism where cold, warm, and occluded fronts force air to rise, forming clouds and precipitation.
frontal lifting (Meteorology & Weather): Also known as: frontal liftings; The forced ascent of the warmer, less dense air at and near a front, occurring whenever the relative velocities of the two air masses are such that they converge at the front. See convection.
frost (Meteorology & Weather): The fuzzy layer of ice crystals on a cold object, such as a window or bridge, that forms by direct deposition of water vapor to solid ice. The condition that exists when the temperature of the earth’s surface and earthbound objects fall below freezing. Depending upon the actual values of ambient-air temperature, dewpoint, and the temperature attained by surface objects, frost may occur in a variety of forms. These include a general freeze, hoarfrost (or white frost), and dry freeze (or black frost). If a frost period is sufficiently severe to end the growing season (or delay its beginning), it is commonly referred to as a killing frost. See frost day, ground frost. See frozen ground. Same as hoarfrost. Compare rime.
Frost build-up/Riming (Meteorology & Weather): Firmly attached precipitation accumulating on wind-affected side of e.g. trees, electric lines and summit crosses during high humidity and wind. Also known as Rime Ice.
Frost Point (Meteorology & Weather): Also known as: Frost Points; Redirected to dewpoint.
Full depth slab avalanche (Avalanche Types): Also known as: Full depth slab avalanches; An avalanche which glides over the ground, across firn snow or atop a glacier in the fracture zone, sweeping the entire season’s snowpack with it.
Funicular Regime: Also known as: Funicular Regimes; Snow containing greater than 14 percent liquid water in its pore volume.
Givre
Givre de profondeur
Givre de surface
glacier (Snow Processes): Also known as: glaciers; A mass of land ice, formed by the further recrystallization of firn, flowing continuously from higher to lower elevations. This term covers all such ice accumulations from the extensive continental glacier to tiny snowdrift glaciers. Nearly all glaciers are classified according to the topographical features with which they are associated, for example, highland glacier, plateau glacier, piedmont glacier, valley glacier, cirque glacier. They are also classified according to their seasonal temperatures, or melting characteristics, as temperate glaciers or polar glaciers. If a glacier is flowing, it is active or living; but an active glacier may be advancing or retreating depending upon the rate of flow compared to the rate of ablation at the terminus. A glacier that has ceased to flow is termed stagnant or dead.
glaze (Snow Grain Shapes & Crystals): Also known as: glaze ice, glazed frost, verglas; (Also called glaze ice, glazed frost, verglas.) A coating of ice, generally clear and smooth, formed on exposed objects by the freezing of a film of supercooled water deposited by rain, drizzle, fog, or possibly condensed from supercooled water vapor. Glaze is denser, harder, and more transparent than either rime or hoarfrost. Its density may be as high as 0.8 or 0.9 g cm-3. Factors that favor glaze formation are large drop size, rapid accretion, slight supercooling, and slow dissipation of heat of fusion. The opposite effects favor rime formation. The accretion of glaze on terrestrial objects constitutes an ice storm; as a type of aircraft icing it is called clear ice. Glaze, as well as rime, may form on ice particles in the atmosphere. Ordinary hail is composed entirely (or nearly so) of glaze; the alternating clear and opaque layers of some hailstones represent glaze and rime, deposited under varying conditions around the growing hailstone. Compare rime, rime ice, hard rime, soft rime.
Glide (Snowpack Properties): Also known as: Glides, Gliding Surface, Glides; (Gliding Surface) The slow downhill movement of the entire snowpack along the ground surface, or similar relative slip between snow layers. Not to be confused with creep. The surface where the relative slip or glide occurs is referred to as the glide surface. This figure shows the effects of gravity on an inclined snowpack. The black arrows show glide, which is the motion that results if the entire snowpack slips at the base. There is no difference in motion through the snowpack with glide. The red arrows show creep. The difference in motion between the surface and the base introduces tension, particularly over convex features. The blue arrow shows settlement.
Glide crack (Snowpack Properties): Term: Glide Crack; Also known as: Glide Cracks, Glide cracks; Openings in snowpack created as glide slabs move slowly downslope.
Glide Slab (Avalanche Types): Also known as: Glide Slabs; A cohesive slab of snow, often consisting of the entire snowpack, that lacks significant support or friction from the bed surface.
Gliding sluff (Avalanche Types): Also known as: Gliding sluffs, gliding avalanche; When gliding movements become increasingly rapid, a gliding avalanche develops. Releases can occur anytime during day or night. Gliding avalanches are not induced by a crack in a weak layer.
Gliding snow (Snowpack Properties): Slow, gliding movement of the snowpack over smooth or wet ground, e.g. grassy slopes or smooth rock slabs, attaining velocities of a few millimeters to a few meters per day.
Gliding snow problem (Snowpack Properties): Also known as: Gliding snow problems; The gliding snow problem is characterized by gliding of the entire snowpack on the ground. These full depth avalanches release due to failure in the basal layer or failure at the snow soil interface. The presence of liquid water at the glide horizon is crucial for the release. Depending on the origin of the water, they can be classified into warm (melt water or rain is percolating the snowpack) and cold (the warm ground causes melt at the basal layer or groundwater outflow) events. They are difficult to predict, although glide cracks open usually before a release.
Gradient de température
Grain (Snow Grain Shapes & Crystals): Also known as: Grain Chain, Grain Size, Grain Type, Grains; (Grain Chain, Grain Size, Grain Type) A mechanically separate ice particle in the snow-cover, often without crystalline structure. Or it may contain several crystals. A Grain Chain is a group of grains linked by grain-to-grain bonds. The Grain Size is the mean diameter of a single snow grain's development. This is usually recorded as an average for a layer of similar grains within the snowpack. The Grain Type refers to snow with rounded grains (from equilibrium growth) as opposed to sharp-edged crystals (from kinetic growth). Other types include melt-freeze grain clusters and surface hoar.
Grain fin
grain shape (Snow Grain Shapes & Crystals): Also known as: grain shapes
grain size (Snow Grain Shapes & Crystals): Also known as: grain sizes
Grains à faces planes
Grains à faces planes situés à la base du manteau neigeux
Graupel (Snow Grain Shapes & Crystals): Term: graupel; Precipitation in the form of white, opaque ice particles that are easily crushed and typically have a diameter of 2 mm or more. They often fall in shower form, rebounding when they impact a hard surface and commonly breaking apart. Graupel forms from the accretion of supercooled droplets collected on what is initially a falling ice crystal, freezing on impact and leading to the formation of rime on the surface of the ice crystal. Its shape can vary and largely depends on how it forms and falls, e.g., lump or round graupel usually develops from frozen drops and/or tumbling during the growth process, while conical graupel typically forms from snow and the accretion of rime on the bottom of the falling particle. Also referred to as snow pellets in operations. Term edited 3 April 2024
Ground avalanche (Avalanche Types): Also known as: Ground avalanches; General term for an avalanche, frequently occurring during spring, that sweeps away the soil in its track, and is thus often mixed with soil and debris.
Groundwater outflow (Snowpack Properties): Also known as: Groundwater outflows; Water coming out of the soil, for example lifted through a hydraulic pressure gradient between the soil surface and the overlaying snowpack. The water either gets advected through channels in the soil or is stored as ice in the soil which gets melted. Also springs are called ground water outflows. Both is leading to liquid water at the snow-soil-interface, destabilizing the snowpack.
Gully (Terrain): Also known as: Gullies; Usually a steep, elongated, eroded trench; typically prone to snowdrift accumulation.
hail (Meteorology & Weather)
Hand Charge (Avalanche Types): Also known as: Hand Charges; An explosive charge used in avalanche control which is hand carried to the control site and either thrown or implanted into the snow before detonation.
Hand Lens: Also known as: Hand Lenses; A small microscope used to identify snow particle shapes, usually 10 to 20 power.
Hand Shear Test (Snowpack Properties): Also known as: Hand Shear Tests; Quick snowpack test isolating shallow snow columns and pulling with hand to assess bonding strength.
Hangfire (Avalanche Types): Also known as: Hangfires; Unstable snow left on slope above slab avalanche fracture line, posing rescue risks.
hard (Snowpack Properties)
Hard Slab (Avalanche Types): Also known as: Hard Slabs; Dense, wind-packed or long-settled snow more difficult to trigger but with greater destructive potential than soft slabs.
Hard Slab Avalanche (Snowpack Properties): Also known as: Hard Slab, Hard Slab Avalanches, Hard Slab Avalanches; (Hard Slab) An avalanche containing a hard slab identified by blocks of slab snow which retain their shape throughout much or all of the track. A cohesive group of snow layers of a single snow layer of high density, often formed by wind compaction, is called a Hard Slab.
Hardness (Snowpack Properties): Resistance to penetration. Commonly recorded in the field using the Hand Test: Fist hard: A gloved fist can penetrate at least 5cm with a 5-10 N force. Four-finger hard: Four gloved fingers can penetrate at least 5cm with a 5-10 N force. One-finger hard: One finger can penetrate at least 5cm with a 5-10 N force. Pencil hard: A hand held pencil can penetrate at least 5cm with a 5-10 N force. Knife hard: A hand held knife can penetrate at least Scm with a 5-10 cm N force.
Hazard (Avalanche Hazard & Assessment): Also known as: Hazards; (Avalanche Hazard, Avalanche Danger, Danger Scale, Hazard Scale) The hazard, or danger, is a measure of risk in a given area at a particular time. It is usually with respect to the threat to people, property, or other human interests. There is a universal scale established with five levels. Differences in the scale between countries are now very minor. For html and PDF versions see the CSAC danger scale section.
Heat of Fusion (Snowpack Properties): Also known as: Latent Heat, (Latent; (Latent Heat, (Latent) Heat of Melting, Heat of Solidification) The heat of fusion is the heat in calories required to convert 1 g of a material from the solid to the liquid state at its standard melting temperature. When the change is from the liquid state to the solid state this heat is released. When heat is added to a solid, the kinetic energy of the molecules in the solid increases and the increased motion of the molecules is reflected by a rise in the temperature of the solid. When the melting point of the substance is reached, however, the temperature remains constant as the change of phase occurs. The continued addition of heat at that temperature is used to cause changes in potential energy, which result in the loosening of bonds between the molecules. The heat required to change a solid to a liquid with no change in temperature is called the latent heat of fusion. For ice/water the heat of fusion is 80 calories per gram. See also "Heat of Vaporization"
Heat of Vaporization (Snowpack Properties): Also known as: Heat of Condensation; (Heat of Condensation) The heat of vaporization is defined as the heat required to vaporize one mole of a substance at its standard boiling point. The heat of vaporization is expressed in kJ/mol. The use of kJ/kg is also possible, but less customary. When the change is from the vapor state to the liquid state (i.e. condensation) this heat is released. When heat is added to a liquid, the kinetic energy of the molecules in the liquid increases and the increased motion of the molecules is reflected by a rise in the temperature of the liquid. When the boiling point of the substance is reached, however, the temperature remains constant as the change of phase occurs. The continued addition of heat at that temperature is used to break down the intermolecular attractive forces, and also must provide the energy necessary to expand the gas. The heat required to change a liquid to a solid with no change in temperature is called the latent heat of vaporization. The heat of vaporization of water is about 40.6 kJ/mol (2260 kJ/kg). This is quite a lot: five times the energy needed for heating the water from 0 to 100 degrees Celsius. See also "Heat of Fusion"
height of new snow (Measurement & Observation): Also known as: heights of new snow
height of snowpack (Measurement & Observation): Also known as: heights of snowpack
High additional load (Avalanche Hazard & Assessment): Also known as: High additional loads
High alpine regions (Terrain): Areas above approximately 3000 m (particularly glaciated areas).
High Avalanche Danger (Avalanche Types): Also known as: High Avalanche Dangers; Second-highest danger level where avalanche conditions are very dangerous and terrain travel is not recommended.
High Danger (Avalanche Types): Also known as: High Dangers; Very dangerous avalanche conditions; travel in avalanche terrain not recommended.
High Marking (Avalanche Types): Also known as: High Markings, High Markings; (Snowmobiling Term, Also: High Pointing, Hammer Heading) High Marking Snowmobiling Term, Also: High Pointing, Hammer Heading Riding up a steep slope to leave the highest mark. Usually done on a slope which cannot be climbed to the top. When the sled bogs down a turn is initiated and the rider comes back down. Many snowmobiling avalanche incidents involve high marking, particularly cases where the rider has become stuck and gotten off the machine to pull it around. Sometimes with the help of others who have riden up the slope to assist.
High Pressure (Terrain): Also known as: Anticyclonic, Divergence, High Pressures; (Anticyclonic, Divergence) Meteorological (weather) terms. An area of clockwise turning winds, high barometric pressure, and fair weather. (In the Northern Hemisphere.) The geostrophic (high altitude) winds are nearly circular on a large scale, but surface friction causes an outward component to the circular motion. This is called "divergence."
High Pressure System (Meteorology & Weather): Also known as: High Pressure Systems; Weather system resulting in clearer skies and reduced precipitation through atmospheric subsidence.
Hoar (Snow Grain Shapes & Crystals): Redirected to hoarfrost.
hoarfrost (Snow Grain Shapes & Crystals): A deposit of interlocking ice crystals (hoar crystals) formed by direct deposition on objects, usually those of small diameter freely exposed to the air, such as tree branches, plant stems and leaf edges, wires, poles, etc. Also, frost may form on the skin of an aircraft when a cold aircraft flies into air that is warm and moist or when it passes through air that is supersaturated with water vapor. The deposition of hoarfrost is similar to the process by which dew is formed, except that the temperature of the befrosted object must be below freezing. It forms when air with a dewpoint below freezing is brought to saturation by cooling. In addition to its formation on freely exposed objects (air hoar), hoarfrost also forms inside unheated buildings and vehicles, in caves, in crevasses (crevasse hoar), on snow surfaces (surface hoar), and in air spaces within snow, especially below a snow crust (depth hoar). Hoarfrost is more fluffy and feathery than rime, which in turn is lighter than glaze. Observationally, hoarfrost is designated light or heavy (frost) depending upon the amount and uniformity of deposition.
Homogeneous (Snowpack Properties): Similar throughout. Can refer to a snowpack.
Howitzer (Avalanche Types): Also known as: Howitzers; A portable military artillery piece for firing an explosive round into a distant target. Both 75mm pack howitzers and l05mm howitzers are used in avalanche control.
Human-triggered Avalanche (Avalanche Types): Also known as: Human-triggered Avalanches; Avalanche triggered by person or machine, accounting for 90% of fatal incidents.
Ice: The solid form of water.
Ice avalanche (Avalanche Types): Also known as: Ice avalanches; Glacier ice which breaks and plunges over a steep step, sometimes sweeping snow in the avalanche track with it. Often responsible for large-scale disasters.
ice column (Snowpack Properties): Also known as: ice columns
ice crystal (Snow Grain Shapes & Crystals): Also known as: ice crystals; Any one of a number of macroscopic, crystalline forms in which ice appears, including hexagonal columns, hexagonal platelets, dendritic crystals, ice needles, and combinations of these forms. The crystal lattice of ice is hexagonal in its symmetry under most atmospheric conditions. Varying conditions of temperature and vapor pressure can lead to growth of crystalline forms in which the simple hexagonal pattern is present in widely different habits (a thin hexagonal plate or a long thin hexagonal column). In many ice crystals, trigonal symmetry can be observed, suggesting an influence of a cubic symmetry. The principal axis (c axis) of a single crystal of ice is perpendicular to the axis of hexagonal symmetry. Planes perpendicular to this axis are called basal planes (a axes related to the prism facets) and present a hexagonal cross section. Ice is anisotropic in both its optical and electrical properties and has a high dielectric constant (even higher than water) resulting from its water dipole structure. The electrical relaxation time for water is much shorter than for ice (109 Hz compared with 104 Hz), resulting from a chain reaction requirement for molecules to relax through defects in the ice lattice. In the free air, ice crystals compose cirrus-type clouds, and near the ground they form the hydrometeor called, remarkably enough, “ice crystals” (or ice prisms). They are one constituent of ice fog, the other constituent being droxtals. On terrestrial objects the ice crystal is the elemental unit of hoarfrost in all of its various forms. Ice crystals that form in slightly supercooled water are termed frazil. Ice originating as frozen water (e.g., hail, graupel, and lake ice) still has hexagonal symmetry but lacks any external hexagonal form. Analysis of their sections (0.5 mm) in polarized light reveals different crystal shapes and orientations, depending on the freezing and any annealing and subsequent recrystallization process.
ice formations (Snow Grain Shapes & Crystals)
ice layer (Snowpack Properties): Also known as: ice layers
Ice Lens (Snowpack Properties): Also known as: Ice Layer, Ice Lenses; (Ice Layer) A very hard layer or lens shaped section in a snowpack of solid or near solid ice. This can be formed by the freezing of meltwater.
Ice lense (Snowpack Properties): Also known as: Ice lenses; Thin ice layer inside the snowpack resulting from rain or melt-water refreezing. No single grains are visible.
Ice pellets (Snow Grain Shapes & Crystals): ice pellets A type of precipitation consisting of transparent or translucent pellets of ice, less than 5 mm in diameter. They may be spherical, irregular, or (rarely) conical in shape. Ice pellets usually bounce when hitting hard ground and make a sound upon impact. Now internationally recognized, ice pellets includes two basically different types of precipitation, known in the United States as 1) sleet and 2) small hail. Thus a two-part definition is given: 1) sleet or grains of ice, generally transparent, globular, solid grains of ice that have formed from the freezing of raindrops or the refreezing of largely melted snowflakes when falling through a below-freezing layer of air near the earth’s surface; 2) small hail, generally translucent particles, consisting of snow pellets encased in a thin layer of ice. The ice layer may form either by the accretion of droplets upon the snow pellet or by the melting and refreezing of the surface of the snow pellet. Compare hail, graupel. Term edited 11 July 2016.
Important Links (Avalanche Hazard & Assessment): Glossary Downloads/Resources Imprint Privacy policy
In particular (Avalanche Hazard & Assessment): In general, avalanches can be triggered by high additional loading, in isolated cases by minimum additional loading.
Inclinaison de la pente
Inclinometer (Measurement & Observation): Also known as: Inclinometers, Inclinometers, Slope Meter; Tool measuring slope angle, valuable for assessing avalanche likelihood on 30-45 degree slopes.
Incoming radiation (Snowpack Properties): Also known as: Incoming radiations; External radiation which strikes the snowpack.
Increasing firmness (Snowpack Properties): Bonding between ice crystals improves, increasing overall capacity of crystals to absorb loading.
Indicator Slopes (Avalanche Hazard & Assessment): Snow slopes which characteristically release first during recognized loading conditions and may be used to estimate instability on similar slopes.
Inneralpine regions (Terrain): Areas enclosed by high alpine ridges, subject to weakened precipitation.
Instability (Avalanche Types): Also known as: Instabilities; Usually refers to unstable conditions within the snowpack structure, either loose snow avalanching, or a recognized weak basal zone combined with a cohesive slab group leading to a slab avalanching.
Inversion de température
Isothermal (Snowpack Properties): "Same temperature." A snowpack which is 0 degrees C (32 F) throughout. Any mixture of ice and water will generally be 0C so the amount of free water in an isothermal snowpack may vary widely. An isothermal snowpack may still retain much of the structure acquired as it developed, such as crusts and harder and softer layers.
Isothermal Snow (Snowpack Properties): Snow at same temperature throughout depth range, typically at 0°C melting point, losing cohesion.
Isothermal snow cover (Snowpack Properties): Also known as: Isothermal snow covers; Equal, constant temperature through entire depth of the snow cover.
Isothermal snowpack: Term: Isothermal conditions; State of the snowpack when its entire depth is at 0°C. Promotes liquid water production and snowpack destabilisation.
Jet Roof (Meteorology & Weather): Also known as: Jet Roofs; A wing-like structure, often built upon a ridge top, to inhibit cornice formation and wind drifting.
Kinetic Growth (Snow Grain Shapes & Crystals): Also known as: Kinetic Growths; (Temperature-Gradient metamorphism, TG, Facets, Angular Grains, Depth Hoar, etc) Crystal growth or metamorphism which occurs at a very fast (much greater than equilibrium) rate due to a large temperature gradient or other strong non-equilibrium factors. Grains become faceted and bond poorly. [Colloquially called "sugar snow" sometimes.] In the advanced stages the crystals are layered, scrolled, cupped and often hollow. [Colloquially "Advanced TG" or "Depth Hoar"] A layer of these facets often forms early in the season if a thin snowcover sits on the ground under steep temperature gradients for while. This layer often reaches the advanced stages and is subsequently buried. "Depth hoar" usually refers to this bottom layer.
Kinetic metamorphism (Snowpack Properties): Also known as: faceting; Transformation process of dry snow with a strong temperature gradient in the snowpack. Crystals develop into faceted, hollowed grains, growing in size with hollows receding. Bonding between grains decreases with a lessening of density in the affected layers. The greater the temperature gradient, the more intense is the rate of change.
Laminar Flow (Meteorology & Weather): Also known as: Laminar Flows; Laminar flow describes fluid flow which occurs in "sheets" parallel to each other. If there is a surface nearby the flowlines typically run parallel to it. Two particles put in the flow as markers would flow parallel to each other but possibly at different speeds. In nonscientific terms laminar flow is "smooth". When this nice, neat pattern breaks down the flow becomes turbulent. It no longer flows in parallel sheets, and two marker particles placed in the flow together would trace out paths that would be independent and largely random. Fluid flows often change from laminar to turbulent when they go over an abrupt feature. (Such as wind going over a mountain ridgeline.) This photograph of fluid flowing around a cylinder from left to right shows laminar flow except behind (downstream of) the cylnder. In that area is a section of turbulent flow. In snow and avalanche studies this topic is important in understanding wind and wind transported snow as well as descriptions or models of flowing snow (i.e. avalanche dynamics). It is the shearing force of the laminar windflow along the surface that picks up snow for transport. There is a three-page sequence on Wind Transport of Snow in our Education Center. (And three additional supplemental pages available to members.) That short tutorial explains these things in more detail.
lapse rate (Meteorology & Weather): Also known as: lapse rates; The decrease of an atmospheric variable with height, the variable being temperature, unless otherwise specified. The term applies ambiguously to the environmental lapse rate and the process lapse rate, and the meaning must often by ascertained from the context.
Layer (Snowpack Properties): Also known as: Layers, Snow; A snowpack stratum differentiated from others by weather, metamorphism, or other processes.
layer thickness (Snowpack Properties): Also known as: layer thicknesses
Layering (Snowpack Properties): Also known as: Layerings; The stratigraphy of snow layers.
Lee slope (Terrain): Term: Lee Slope; Also known as: Lee Slopes, Lee slopes; Slopes sheltered or protected from the wind. An eastern aspect would be on the lee side for a western wind.
Leeward (Terrain): leeward A descriptive term used to refer to location. Leeward refers to the downwind or sheltered side of a flow obstacle such as a mountain or ridge. Opposite of windward. Term edited 2 June 2020.
Lieu sûr
Ligne de crête
Likely (Avalanche Hazard & Assessment): Also known as: something is likely; Event with a probability of occurrence exceeding 50%.
Limite forestière
Limite pluie/neige
liquid water content (Snowpack Properties)
Loading (Meteorology & Weather): Also known as: Loadings; The addition of weight on top of a snowpack from precipitation, wind drifting, or a person.
Local (Terrain): Also known as: from place to place; Areas limited to slopes and basin areas.
longwave radiation (Meteorology & Weather): In meteorology, a term used loosely to distinguish radiation at wavelengths longer than about 4 μm, usually of terrestrial origin, from those at shorter wavelengths (shortwave radiation), usually of solar origin. See also terrestrial radiation.
Loose Snow (Snow Grain Shapes & Crystals): Snow grains can have low cohesion between them for a variety of reasons. In cold conditions new snow may initially have low cohesion between the crystals (until some settlement takes place) and dry loose snow avalanches (or sluffs) can occur. In warm conditions, or with rain, snow grains may have low cohesion due to an excess of water in the snow, which may percolate down through the snowpack. Metamorphism can also result in the faceting of crystals and the lose of cohesion between them.
Loose snow avalanche (Avalanche Types): Term: Loose Snow Avalanche; Also known as: Loose Snow Avalanches, Loose Snow Avalanches, Point Release, Sluff, Loose snow avalanches, point release avalanche, Loose Snow Avalanches; Avalanche starting from surface point, gathering mass fan-like without slab fracture, composed of unconsolidated snow.
Low additional load (Avalanche Hazard & Assessment): Also known as: Low additional loads
Low Avalanche Danger (Avalanche Types): Also known as: Low Avalanche Dangers; Lowest danger level where conditions are generally safe but avalanches possible on isolated features.
Low Avalanche Hazard (Avalanche Hazard & Assessment): Also known as: Low Avalanche Hazards; Generally safe conditions where natural and human-triggered avalanches are unlikely.
Low Pressure (Terrain): Also known as: Cyclonic, Convergence, Low Pressures; (Cyclonic, Convergence) Meteorological (weather) terms. An area of counter-clockwise turning winds, low barometric pressure, and stormy weather. (In the Northern Hemisphere.) The geostrophic (high altitude) winds are nearly circular on a large scale, but surface friction causes an inward component to the circular motion. This is called "convergence."
Low Pressure System (Meteorology & Weather): Also known as: Low Pressure Systems; Weather system generating cloudy skies and precipitation through atmospheric lift.
Low-probability/High-consequence (Avalanche Hazard & Assessment): Scenario where avalanche triggering is unlikely but would result in very large, destructive slides.
Lubricating Layer (Snowpack Properties): Also known as: Lubricating Layers; 1 - A layer within a snowpack which has been wetted by free water percolating through the snow. Sometimes any weak layer or cohesionless layer which has acted as the basal zone in a slab avalanche. 2 - A layer with weak internal strength and/or poor bonding to adjacent layers which facilitates mechanical failure within the snow pack. A recognizable lubricating layer may or may not be present in an avalanche.
machine made snow (Snow Grain Shapes & Crystals)
Manteau neigeux de couches inversées
Masse d'air
medium (Snow Grain Shapes & Crystals)
melt forms (Snow Grain Shapes & Crystals)
Melt Freeze (Snow Processes): Also known as: Melt Freezes; (definition not extracted)
Melt Freeze Snow (Snow Grain Shapes & Crystals): Snow grains that have partially melted and then frozen again.
Melt Water (Snowpack Properties): A term used to distinguish liquid water content in the snow due to melting as opposed to water introduced by rain.
Melt-freeze crust (Snowpack Properties): Also known as: Melt-freeze crusts, melt-freeze crusts; Layer of hard-compacted snow resulting from a melt-freeze process; increases firmness.
Melt-freeze metamorphism (Snow Processes): When snow is warmed to 0 °C, a mixture of ice crystals and water is created.
Metamorphism (Snow Processes): Also known as: Metamorphisms; (definition not extracted)
Metamorphism of Snow (Snow Processes): Change of snow crystals over time, driven by temperature gradients and sublimation/deposition processes.
Mixed avalanche
Moderate Avalanche Danger (Avalanche Types): Also known as: Moderate Avalanche Dangers; Second-lowest danger level with heightened conditions on specific terrain features.
Moderate Danger (Avalanche Hazard & Assessment): Also known as: Moderate Dangers; Heightened avalanche conditions on specific terrain features; human-triggered avalanches possible.
moist (Snowpack Properties)
Moisture Content: Also known as: Moisture Contents; (definition not extracted)
Multiple starting zones (Avalanche Types): Area in which a number of discrete avalanches originate. The term is often associated with avalanche sizes 4 to 5.
Métamorphisme de la neige
Natural Avalanche (Avalanche Types): Also known as: Natural Avalanches, Natural Avalanches; Avalanche triggered by factors other than people or animals, including loading, warming, and falling debris.
Naturally triggered avalanche (Snowpack Properties): Also known as: Naturally triggered avalanches, natural release; Avalanche not caused by external forces, e.g. snowfall or loss in firmness due to weather conditions.
Near-Surface Facets (Avalanche Types): Persistent weak layer forming at snow surface during cold, clear weather, responsible for many slab avalanches.
Necks (Snow Grain Shapes & Crystals): Narrow connections between grains which give strength to the snowpack.
needle (Snow Grain Shapes & Crystals): Also known as: needles
Neige de tempête
Neve (Snow Types): Redirected to n-v.
New fallen snow (Snowpack Properties): Freshly fallen snow.A neither transformed, nor densified nor settled snow layer, from current or recent precipitation.
New Snow (Snowpack Properties): Term: new snow; Recently fallen snow in which the original form of the snow crystals is recognizable. The amount of snow fallen within the previous 24 hours.
New snow problem (Snowpack Properties): Also known as: New snow problems; The new snow problem is related to current or recent snowfall. The additional loading on the existing snowpack or a lack of cohesion in the newly fallen snow can cause avalanche activity. The problem is widely present, often in all aspects and lasts usually until a few days after the snowfall event.
Niveau de congélation
No distinct avalanche problem (Avalanche Hazard & Assessment): Also known as: No distinct avalanche problems
North-facing slope (ubac): Term: North-facing slope; Also known as: North-facing slopes; The shady, north-facing side of a mountain. Snow persists longer and weak layers are better preserved on ubac slopes.
Nuclei (Snow Grain Shapes & Crystals): Very small particles that initiate the formation of water droplets or ice crystals in the atmosphere.
Occluded Front (Meteorology & Weather): Term: occluded front; Also known as: occluded fronts, Occluded Fronts, Occluded Fronts; (Commonly called occlusion; also called frontal occlusion.) A front that forms as a cyclone moves deeper into colder air. This front will separate air behind the cold front from air ahead of the warm front. This is a common process in the late stages of wave-cyclone development, but is not limited to occurrence within a wave cyclone. There are three basic types of occluded front, determined by the relative coldness of the air behind the original cold front to the air ahead of the warm (or stationary) front. 1) A cold occlusion results when the coldest air is behind the cold front. The cold front undercuts the warm front and, at the earth’s surface, coldest air replaces less cold air. 2) When the coldest air lies ahead of the warm front, a warm occlusion is formed, in which case the original cold front is forced aloft at the warm front surface. At the earth’s surface, coldest air is replaced by less cold air. 3) A third and frequent type, a neutral occlusion, results when there is no appreciable temperature difference between the cold air masses of the cold and warm fronts. In this case frontal characteristics at the earth’s surface consist mainly of a pressure trough, a wind-shift line, and a band of cloudiness and precipitation. See bent-back occlusion.
Old Snow (Snowpack Properties): Term: old snow; Deposited snow in which the original crystalline forms are no longer recognizable, such as firn, spring snow.
Old snow cover (Snowpack Properties): Also known as: Old snow covers, old snowpack; Snow layers deposited from earlier precipitation, prior to fresh fallen snow.Old snow layers consist of metamorphosed snow crystals.
Old snowpack: Also known as: Old snowpacks; The snow layers from previous snowfall events that have undergone metamorphism. Weak layers within the old snowpack can persist for weeks or months.
Open Trees (Snow Grain Shapes & Crystals): Forested areas with open canopy where wind and sun effects are greater and surface hoar grows readily.
Organized Rescue: Also known as: Organized Rescues; Professional rescue efforts by trained personnel using prepared plans and extensive resources.
Orientation de pente
Orographic Lift: Also known as: Orographic Lifts; Atmospheric lift occurring when air encounters mountain barriers and is forced upward.
Orographic Lifting (Terrain): Term: orographic lifting; Also known as: orographic liftings, Orographic Liftings; Ascending air flow caused by mountains. Mechanisms that produce the lifting fall into two broad categories: 1) the upward deflection of horizontal larger-scale flow by the orography acting as an obstacle or barrier; or 2) the daytime heating of mountain surfaces to produce anabatic flow along the slopes and updrafts in the vicinity of the peaks. The first category includes both direct effects, such as forced lifting and vertically propagating waves, and indirect effects, such as upstream blocking and lee waves. Even though this term strictly refers only to lifting by mountains, it is sometimes extended to include effects of hills or long sloping topography. When sufficient moisture is present in the rising air, orographic fog or clouds may form.
Outgoing longwave radiation (Snowpack Properties): Also known as: Outgoing longwave radiations; The snowpack surface emits longwave radiation (infrared) into the atmosphere.If skies are clear, the surface cools significantly (up to 20°C) below air temperature.
Overhead Hazard (Avalanche Types): Also known as: Overhead Hazards; Avalanche slopes or hazards like cornices threatening areas below them.
Overnight Freeze/Recovery (Snowpack Properties): Also known as: Overnight Freezes/Recoveries; Snowpack returning to frozen state after warming, improving stability for early morning travel.
Partially Buried (Avalanche Types): Referring to avalanche victims who are covered by snow anywhere from the ankles to the neck when the avalanche stops.
Pass area (Meteorology & Weather): Also known as: Pass areas; Lowest area on a ridgeWind velocity is heightened, snowdrift accumualtion enhanced.
Passive Control (Terrain): Also known as: Passive Controls; Avalanche control which includes defense structures within the track or runout regions (earth mounds, dams, wall, sheds, etc.), or structures to inhibit initiation within the starting zone (fences, posts, reforestation, etc.).
Pelle d'avalanche
Pendular Regime (Snow Grain Shapes & Crystals): Also known as: Pendular Regimes; Snow containing less than 14 percent liquid water in its pore volume. When the water content is this low the water is trapped in rings around the contact points of grains, called pendular rings. When the water content increases to the point where all of the water can no longer be held in these rings by capillary pressure the snow is said to be in the Funicular Regime. These terms are also used in subsurface hydrology and petroleum engineering to describe the water content of soil or the distribution of oil in soils.
Percent Water Equivalent (Snowpack Properties): Also known as: Percent Water Equivalents; A measure of snow density in terms of water (e.g., 100 kg/m3 snow density = 10 percent water equivalent).
Percolation (Snowpack Properties): Also known as: Percolations; The downward motion of liquid water through interstitial pore spaces in a snowpack due to gravity.
Perforated Crust: Also known as: Perforated Crusts; A crust that does not have a consistent ice fabric.
Persistent Slab (Snowpack Properties): Also known as: Persistent Slabs; Avalanche problem defined by slab formed over persistent weak layer resisting bonding.
persistent weak layer problem (Avalanche Hazard & Assessment): Term: Persistent weak layers
Persistent weak layers (Snow Grain Shapes & Crystals): Term: Persistent Weak Layer; Also known as: Persistent Weak Layers, Persistent Weak Layers; Weak snowpack layer resisting strong bonding with neighboring grains over extended time.
Pinpoint Search (Avalanche Types): Also known as: Pinpoint Searches, Probing; Using probe to locate buried avalanche victim following successful transceiver search.
Plan de rupture
Plaque
Plaque de glissement
Plaque de tempête
Plaque dure
Plaque friable
Plaque persistante
Plaque profonde et persistante
plate (Snow Grain Shapes & Crystals): Also known as: plates
Points de déclenchement
Poorly bonded layer (Snow Grain Shapes & Crystals): Also known as: Poorly bonded layers; A weak layer with poor bonding between individual crystals or grains. eg facets or buried surface hoar.
Pore Space (Snow Grain Shapes & Crystals): Also known as: Pore Spaces; The space between ice grains within the snow-cover occupied by air or water or both. For more detailed scientific information related to pore spaces in snow you can check out these two articles, both of which include diagrams and graphs: "Volumes and areas of pendular rings with non-zero contact angles" - Calculations of the volume and surface area of water in the pore space at low "unsaturated" amounts. "Pore-Space Characterization of Wet Snow in the Pendular Regime"
Possible (Avalanche Hazard & Assessment): Also known as: potential; Event with a probability of occurrence not exceeding 50%.
Powder avalanche (Avalanche Types): Term: Powder Avalanche; Also known as: Powder Avalanches, Powder avalanches, powder cloud avalanche; An aerosol of fine, diffused snow that behaves as a sharply bounded body of gas.
Powder Snow (Snowpack Properties): Term: powder snow; Also known as: Colloquial; A skiing term for a cover of dry snow that has not been compacted in any way.
Precipitation (Meteorology & Weather): Also known as: Precipitations, Precipitations; All hydrometeors formed in the atmosphere, including liquid, solid, or a combination of the two (e.g., resulting from incomplete melting or freezing or from accretion), that are large enough to fall as a result of gravity. The amount, usually expressed in millimeters or inches of liquid water depth, of the water substance that has fallen at a given point over a specified period of time. As this is usually measured in a fixed rain gauge, small amounts of dew, frost, rime, etc., may be included in the total. The more common term rainfall is also used in this total sense to include not only amounts of rain, but also the water equivalents of frozen precipitation. For obvious reasons, precipitation is the preferred general term. Term edited 9 March 2021
Precipitation Intensity (Measurement & Observation): Term: precipitation intensity; Also known as: precipitation intensities, P.I., Precipitation Intensities; The rate of precipitation, usually expressed in millimeters or inches per hour.
Precipitation Intensity Factor (Avalanche Types): Also known as: P.I. factor, Precipitation Intensity Factors; Index of possible hazard due to direct action soft slab avalanches. Use average P.I. (average P.I.) x (No. hrs wind above critical level) (average P.I. of 0.15 in/hr.; High winds for 10 hrs. = P.I. factor of 1.50. Normally a P.I. factor over 1.00 indicates high avalanche hazard.
precipitation particles (Snow Grain Shapes & Crystals)
Precipitation Types (Meteorology & Weather): Four types tracked: snow, rain, freezing rain, and ice pellets, each impacting snowpack differently.
Probe (Avalanche Types): Also known as: Probes; A metal rod used to probe through avalanche debris for buried victims.
Probe Line (Avalanche Types): Also known as: Probe Lines; A line of rescuers, formed along a contour and facing uphill, organized to probe the snow with poles to locate an avalanche victim. Due to the time needed to assemble an adequate number of probes and people this is typically a body recovery technique, especially in the backcountry.
Probe Pole (Snowpack Properties): Also known as: Probe Poles; A long, thin pole used to locate avalanche victims. Also used to measure depth to important horizons in the snow layering.
Problèmes d'avalanche
Prone to triggering (Avalanche Hazard & Assessment): A snowpack or snow layer that tends to release from additional loading.
Propagation (Avalanche Hazard & Assessment): Also known as: Propagations; The spreading of a fracture or crack within the snowpack.
Protective Skiing (Avalanche Types): Deliberate day-to-day skiing of avalanche slopes to stabilize the snowpack. The starting zone is cut several times in a criss-cross pattern to break up the slab. Not recommended for hard slab conditions.
Quasi-liquid Layer (Snow Grain Shapes & Crystals): Also known as: Quasi-liquid Layers; A thin layer on the surface of ice grains where the water molecules are not in rigid solid structure, yet not in the random order of liquid.
Radiation (Meteorology & Weather): Also known as: Radiations, Radiations; Heat that is emitted as electromagnetic radiation from any body not at absolute zero. The exchange of energy between bodies of electromagnetic radiation. (e.g., light, heat, radio waves, x-rays, etc.).
Radiation balance (Meteorology & Weather): Also known as: Radiation balances; (Negative Radiation Balance, Positive Radiation Balance, Radiational Cooling, Energy Balance) The sum of all the radiation heat inputs and losses at a surface (e.g., a snow surface) is called the Radiation Balance. For snow this includes incoming solar radiation, outgoing long-wave (infra-red) radiation from the snow into a clear sky, and sometimes other factors as well. When the snow surface loses heat by infra-red radiation faster than it gains heat the condition is sometimes called a negative radiation balance, and the result is called radiational cooling. When it gains more heat than it loses it is then called a positive radiation balance. In snow and avalanche work we often use the term energy balance to be synonymous with radiation balance, but the energy balance may actually need to include other non-radiation factors such as forced convection.
Radiation Recrystallization (Meteorology & Weather): Also known as: Radiation Recrystallizations; Metamorphism near the snow surface when radiational heat losses forms strong temperature gradients to enhance kinetic growth.
Rain Crust (Snowpack Properties): Also known as: Rain Crusts, rain crusts; A clear layer of ice formed when rain falls on snow surface then freezes.
Rammesonde (Snowpack Properties): Also known as: Rammesonden; (Ram Penetrometer, Ram Profile, Ram Resistance) A cone penetrometer driven vertically into the snowpack by a weighted hammer on a rule guide rod. A graphical profile that exhibits ram resistance with depth is called a Ram Profile. The ram resistance is an index of the relative hardness of snow as measured by a rammesonde. R=nHf/P, where n=number of blows, f=vertical fall height of the hammer, H=weight of the hammer and guide rod, and P=penetration depth.
Reactive snowpack: Also known as: Reactive snowpacks; A snowpack that responds easily to additional loads or triggers. Signs include whumpf sounds, shooting cracks, and recent avalanche activity — indicating widespread instability.
Recco (Avalanche Types): Also known as: Reccos; The Recco system is useful for searching for avalanche victims close to developed areas, such as out-of-bounds or off-piste skiers at ski areas. It consists of reflectors which are low-cost and can be inserted into pockets designed into many items of ski clothing for that purpose. The detector is large and expensive but owned by and/or available to many major ski areas and rescue teams.It detects reflected signals from the reflectors in the victims clothing.
Recoilless Rifle (Avalanche Types): Also known as: Recoilless Rifles; A military artillery piece with severe backblast which eliminates recoil. Mounted either on a permanent platform or on the bed of a vehicle. Both 75mm and lO5mm rifles are used for avalanche control.
Recrystallization (Snow Grain Shapes & Crystals): Also known as: Recrystallizations; Any process which changes the crystal structure of ice can be called recrystallization. Most commonly used to denote some form of kinetic growth or radiation recrystallization.
Refreezing: Also known as: Refreezings; Overnight freezing of the snow surface forming a hard crust. Refreezing temporarily stabilises the snowpack but strength decreases with daytime warming.
regelation (Snow Processes): A twofold process in which a localized region on the surface of a piece of ice melts when pressure is applied to that region (pressure melting) and then refreezes when pressure is reduced. Regelation was discovered by Faraday, who found that two pieces of ice at 0°C would freeze together if pressed against each other and then released. Regelation occurs only for substances, such as ice, that have the property of expanding upon freezing, for the melting points of those substances decrease with increasing external pressure. The melting point of pure ice decreases with pressure at the rate of 0.0072°C per atmosphere. Since this rate is very small, regelation only occurs at ice temperatures of 0°C or very slightly less. The fact that snowballs can be packed well at near 0°C but not at much colder temperatures is a consequence of regelation.
Region (Avalanche Types): Also known as: Regions, regional; Areas comprising several valleys.In avalanche bulletins, regions are generally subdivided climatically or geographically.
Relative Humidity (Snowpack Properties): Also known as: Relative Humidities; Ratio, in percent, of actual amount of water vapor in a body of air to the maximum amount that body can hold at a given temperature. Relative humidity varies with temperature for a given amount of water vapor.
Remote Trigger (Avalanche Hazard & Assessment): Also known as: Remote Triggers, Remote Triggers; Trigger mechanism in which person is on terrain but avalanche fractures and affects area below.
Remote triggering (Avalanche Hazard & Assessment): Term: Remote Triggering; Also known as: Remote Triggerings, Remote triggerings; The release of an avalanche far away from the place where stress is applied. One example of remote triggering is a sympathetic release.
Reverse Loading (Avalanche Types): Also known as: Reverse Loadings; Wind depositing snow and creating slabs opposite the primary wind direction.
Rib (Terrain): Also known as: Ribs; Elongated sub-ridge or ravine in a slope or mountain face.
Ridge (Terrain): Also known as: Ridges, Ridges, Ridges; An elongated area of relatively high atmospheric pressure, almost always associated with and most clearly identified as an area of maximum anticyclonic curvature of wind flow. Opposite of a trough. The locus of this maximum curvature is called the ridge line. Sometimes, particularly in discussions of atmospheric waves embedded in the westerlies, a ridge line is considered to be a line drawn through all points at which the anticyclonically curved isobars or contour lines are tangent to a latitude circle. The most common use of this term is to distinguish it from the closed circulation of a high (or anticyclone); but a ridge may include a high (and an upper-air ridge may be associated with a surface high) and a high may have one or more distinct ridges radiating from its center. Also used as reference to other meteorological quantities such as equivalent potential temperature, temperature, and mixing ratio. That is, an elongated area of relatively high values of any particular field emanating from a maximum. In oceanography, a linear accumulation of broken ice blocks projecting upward, formed by ice deformation, often at the edge of a floe. A ridge is distinguished from a hummock by being much longer than it is wide. The term ridge is often used to describe an entire ridged ice feature, in which case the portion above the water line is termed the sail and the portion below the water line is termed the keel. Term edited 25 November 2025.
Ridgeline (Terrain): Also known as: Ridgelines; Long mountain ridge silhouette
Rime (Snow Grain Shapes & Crystals): Term: rime; A white or milky and opaque granular deposit of ice formed by the rapid freezing of supercooled water drops as they impinge upon an exposed object. It is denser and harder than hoarfrost, but lighter, softer, and less transparent than glaze. Rime is composed essentially of discrete ice granules and has densities as low as 0.2–0.3 g cm-3. Glaze is generally continuous but with some air pockets and has much higher densities. Factors that favor rime formation are small drop size, slow accretion, a high degree of supercooling, and rapid dissipation of latent heat of fusion. The opposite effects favor glaze formation. Both rime and glaze occur when supercooled water drops strike an object at a temperature below freezing. Such formation on terrestrial objects constitutes an ice storm; on aircraft, it is called aircraft icing (where rime is known as rime ice). Either rime or glaze may form on snow crystals, droxtals, or other ice particles in the atmosphere. When such a deposit is wholly or chiefly of rime, snow pellets result; when most or all of the deposit is glaze, ordinary hail or ice pellets result. The alternating clear and opaque layers of some hailstones represent glaze and rime, deposited under varying conditions around the growing hailstone. See also hard rime, soft rime.
rime ice (Snow Grain Shapes & Crystals): Same as rime, but especially applied to rime formation on aircraft. Flight through an extremely supercooled cloud (-10°C or colder) is very conducive to rime icing. This type of ice weighs less than clear ice, but it may seriously distort airfoil shape and thereby diminish the lift. In aviation parlance, ice that has the ideal rime character may be called kernel ice, and that intermediate between rime and clear ice may be called milky ice.
Risk (Avalanche Hazard & Assessment): Also known as: Risks; Likelihood of occurrence combines mathematical probability, risk exposure and possible damages.
Risque d'avalanche considérable
Risque d'avalanche extrême
Risque d'avalanche faible
Risque d'avalanche modéré
Risque d'avalanche élevé
Rollerballs: Small cylinders or balls of wet snow that roll down a slope under gravity. They indicate the snow surface is warming and losing cohesion — an early warning sign of wet-snow avalanche activity.
Round snow grains (Snow Grain Shapes & Crystals): Small, spherical grains resulting from snow crystal rounding. Snow layers of round-grained snow are matt white, not glassy.
rounded grains (Snow Grain Shapes & Crystals)
Rounding faceted particles (Snow Grain Shapes & Crystals): Faceted crystals with rounding facets and corners. Trend to a transitional form reducing its specific surface area; corners and edges of the crystals are rounding off in response to a decreasing temperature gradient.
Route Finding (Avalanche Types): The process of safe travel around avalanche terrain.
Runnels: Also known as: slang; Erosion patterns on the snow surface from water runoff.
Runout Zone (Avalanche Types): Also known as: Deposition Zone, Runout Zones, Runout Zones; (Deposition Zone) The part of an avalanche path where deceleration is rapid, debris is deposited, and the avalanche stops.
Runout/deposition zone
Réchauffement solaire
Safety spacing (Avalanche Hazard & Assessment): Also known as: Safety spacings; Precautionary backcountry measure: maintaining a distance between persons to minimize exposure to avalanche hazards by reducing loading on a slope and minimising all person involvement in an avalanche release. i.e. reduce risk in dangerous terrain.
Sastrugi (Meteorology & Weather): An erosional feature on the snow surface from wind. Sastrugi point into the wind.
Saturation (Snowpack Properties): Also known as: Saturation Vapor Pressure, Saturations; (Saturation Vapor Pressure) A parcel of air at a given temperature is said to be saturated with water vapor at that temperature when the addition of any more water, or any decrease in temperature, will lead to condensation. The water vapor pressure in the atmosphere at which saturation is achieved for a given temperature is called the Saturation Vapor Pressure.
Sauvetage autonome
Sauvetage organisé
Secured areas (Avalanche Types): Areas protected from avalanches and other alpine hazards through technical or temporary measures.
Settlement (Snowpack Properties): Also known as: Settlement Rate, Settled Snow, Settlements, Settlements, Settlements; (Settlement Rate, Settled Snow) The slope-perpendicular decrease in thickness due to gravity and metamorphism. Often misused to refer to a rapid collapse or "whumpf" of the snowpack. Significant settlement (25%) of new snow is generally favorable for the stability of that layer. The rate at which snow settles, calculated from the ratio of new snow depth to change in total snow depth, is the settlement rate. Deposited snow which has increased in density after deposition is called settled snow.
Shady slope (Terrain): Also known as: Shady slopes; Slopes in shadow, untouched or little struck by sunlight, typically north-facing.
Shear (Snow Grain Shapes & Crystals): Also known as: Shears; (Shear Failure, Shear Stress, Shear Test, Shear Strength, Shear Frame) Shear Stress - The downward force, gravity, acting parallel to the under surface on a slab layer. Shear Strength - Breaking strength. Bond or anchorage of a snow layer to its adjacent surfaces, under surface, and sides. Shear Failure - Fracturing of snow in response to shear stress. In snow this can occur between ice grains within and between snow layers and at the flanks walls of a slab avalanche. Shear Test - Any test or experiment designed to measure the shear strength in snow or between snow layers. Shear Frame - A device to estimate shear strength of natural snow layers. A rectangular shape frame which is placed within the snow parallel to the snow layering, then pulled across the layering with a dynomometer.
Shooting crack (Snowpack Properties): Term: Shooting Cracks; Also known as: Shooting cracks; Surface cracks propagating across slope indicating instability.
Short Waves (Measurement & Observation): Also known as: Meteorology Term; (Meteorology Term) Smaller scale fluctuations that move through the long wave patterns.
Shovel Test (Measurement & Observation): Also known as: Shovel Tests; A field test of shear strength. A shovel is pushed behind an isolated column of snow until shear failure is observed.
Simple Terrain (Avalanche Types): Also known as: Simple Terrains; ATES level with minimal avalanche exposure, straightforward travel, and no specific route requirements.
Sintering (Snow Grain Shapes & Crystals): Also known as: Sinterings, Sinterings; sintering Sintering is the process whereby ice crystals adhere through the diffusion of water vapor from regions of positive curvature to regions of negative curvature, such as the boundary between the two crystals.
Size of the starting zone (Avalanche Types): Also known as: Sizes of the starting zones; Distance between fracture line and lower boundary (stauchwall) of the slab.
Ski Checking (Avalanche Hazard & Assessment): Also known as: Ski Checks, Test Skiing, Ski Cutting, Test Slopes; (Test Skiing, Ski Cutting, Test Slopes) An attempt to release avalanches on selected small test slopes by skiing across the normal fracture zones high on the slope. The skier keeps some momentum and moves from one safe spot to another one on the other side. A partner should be watching and test slopes should be chosen carefully with regard to potential consequences. Ski patrollers do this frequently and sometimes get caught and even buried. But they work on established routes and slopes, and they travel in pairs with each person being experienced, so injuries are rare.
Ski Cut (Avalanche Types): Also known as: Ski Cuts; A stability test where a skier/rider crosses a starting zone to check for avalanche initiation.
Skier-triggered release: Also known as: Skier-triggered releases; An avalanche caused by the weight of a person (skier, snowboarder, hiker) or by explosives. The additional load collapses a weak layer, causing the slab above to fracture and slide.
Slab (Snow Grain Shapes & Crystals): Also known as: Slabs, Slabs, Wind Slab; Slab Group, Slabs; Cohesive snow layer overlying weak layer, central to slab avalanche formation.
Slab avalanche (Avalanche Types): Term: Slab Avalanche; Also known as: Slab Avalanches, Slab avalanches; Avalanche where cohesive slab releases along failure plane, often large and destructive.
Slab thickness (Avalanche Types): Also known as: Slab thicknesses; Slab thickness at the fracture line, measured at a right angle to the slope.
Slab width (Avalanche Types): Also known as: Slab widths; Maximum distance between the two lateral boundaries of a slab avalanche.
sleet (Meteorology & Weather): See ice pellets. In British terminology, and colloquially in some parts of the United States, precipitation in the form of a mixture of rain and snow.
Slide (Avalanche Types): Also known as: Slides; A mass of snow sliding, tumbling, or flowing down an inclined surface; same as avalanche.
Slope
Slope Angle (Terrain): Also known as: Slope Angles, Incline, Slope Angles, slope angles; Angle of slope steepness; 30-45 degree slopes most prone to avalanches.
Slope discontinuity (Terrain): Also known as: Slope discontinuities; A slope area where the slope gradient suddenly becomes significantly steeper; highly prone to accumulate drifted snow masses
Slope Distance (Terrain): Also known as: Slope Distances; Down-slope distance measured along the snow surface.
Slope Evaluator Card (Terrain): Also known as: Slope Evaluator Cards; Part of Avaluator system providing structured slope suitability assessment based on conditions and terrain.
Slope face/aspect
Slope gradient (Terrain): Also known as: Slope gradients; moderately steep: less than 30° steep: 30° and more very steep: 35° and more extremely steep: 40° and more The slope gradient is measured in the fall line at the steepest part of a slope, in a map with scale 1:25000 or estimated on-site.
Slope Loading (Avalanche Hazard & Assessment): Also known as: Slope Loadings; Anything that adds stress to a snow slope (e.g., new snow, wind loading, skiers, etc.).
sluff (Avalanche Types): Also known as: sluffs, Sluffs; A small downhill movement of snow.
Sluff Management (Avalanche Types): Techniques managing loose avalanche exposure through timing, speed, and terrain choice.
Slush (Snowpack Properties): Separated rounded particles completely immersed in water (liquid water content > 15% (volume fraction)).
Slushflow (Snow Grain Shapes & Crystals): Also known as: Slushflows; A mudflow-like avalanche composed of slush—very saturated snow. Commonly occurring after rainfall and/or intense thawing have produced more water than can drain through the snow. Slush avalanches can occur on very gentle slope angles. They usually occur in Arctic climates on permafrost soil when dry depth hoar becomes rapidly saturated with water in spring.
Small scale (Terrain): Slope areas or margins ranging in size from a few meters to approximately 20 m.
Snow (Snow Grain Shapes & Crystals): snow Precipitation composed of white or translucent ice crystals, chiefly in complex branch hexagonal form and often agglomerated into snowflakes. For weather-observing purposes, the intensity of snow is characterized as 1) light when the visibility is 1 km (5/8 statute mile) or more; 2) moderate when the visibility is less than 1 km (5/8 statute mile) but not less than 1/2 km (5/16 statute mile); and 3) heavy when the visibility is less than 1/2 km (5/16 statute mile). See also thundersnow
Snow accumulation: Also known as: Snow accumulations; Wind-deposited snow, often in significant depth behind ridges and obstacles. Accumulations form dangerous wind slabs.
Snow Barrier (Avalanche Types): Also known as: Snow Barriers; An avalanche defense structure built on snow.
Snow base (Snowpack Properties): Also known as: Snow bases, fundament; Lowermost layers of the snowpack close to the ground.
Snow conditions / Snow depth: Term: Snow conditions; The depth and distribution of snow on the ground across a mountain range. Varies with elevation, aspect, and snowfall history.
Snow cover (Snowpack Properties): Term: snow cover; Also known as: snow covers, Snow Covers, Snowpack, Snow covers, snowpack; The areal extent of snow-covered ground, usually expressed as percent of total area in a given region. In general, a layer of snow on the ground surface. Compare snowfield, snowpack. The depth of snow on the ground, usually expressed in inches or centimeters.
snow crystal (Snow Grain Shapes & Crystals): Also known as: snow crystals; Any of several types of ice crystal found in snow. A snow crystal is a single crystal, in contrast to a snowflake, which is usually an aggregate of many single snow crystals.
Snow density (Snowpack Properties): Term: snow density; Also known as: snow densities, Snow densities, snow densities; The ratio of the volume of meltwater that can be derived from a sample of snow to the original volume of the sample; strictly speaking, this is the specific gravity of the snow sample. Freshly fallen snow usually has a snow density of 0.07 to 0.15; glacial ice formed from compacted snow (or firn) has a maximum density of about 0.91. Values as low as 0.004 have been measured. Compare water content, water equivalent.
Snow depth (Snowpack Properties): Term: Snow Depth; Also known as: Snow Depths, Snow depths; Redirected to snow-accumulation.
Snow depth increase (Snowpack Properties): Also known as: Snow depth increases; Increase in snow depth within a specific time frame.
Snow dunes (Meteorology & Weather): Also known as: ripples; Snow deposits formed by wind-transported snow. Ripples are small transversal depositional features. Dunes are typically larger in scale and often Barchanoid.
Snow Fence (Avalanche Types): Term: snow fence; Also known as: snow fences, Snow Fences; An open, slatted board fence usually 1–3 m high, placed upwind of a railroad track or highway. The fence serves to create eddies in the downstream airflow, resulting in a reduced wind speed such that snow is deposited close to the fence on its leeward side. The intent is to provide a comparatively clear zone along the railroad track or highway. A snow fence is also used to accumulate drifting snow in a flat windswept area to reduce the depth of ground frost and increase soil moisture as the snow melts. Same as Wild fence.
snow flurry: Also known as: snow flurries; Common term for a light snow shower, lasting for only a short period of time.
snow garland (Snowpack Properties): Also known as: snow garlands; A rare and beautiful phenomenon in which snow is festooned from trees, fences, etc., in the form of a rope of snow, several feet long and several inches in diameter, formed and sustained by surface tension acting in thin films of water bonding individual crystals. Such garlands form only when the surface temperature is close to the melting point, for only then will the requisite films of slightly supercooled water exist.
snow grains (Snow Grain Shapes & Crystals): Also known as: granular snow; (Also called granular snow.) Precipitation in the form of very small, white opaque particles of ice; the solid equivalent of drizzle. They resemble snow pellets in external appearance, but are more flattened and elongated, and generally have diameters of less than 1 mm; they neither shatter nor bounce when they hit a hard surface. Descriptions of the physical structure of snow grains vary widely and include very fine, simple ice crystals; tiny, complex snow crystals; small, compact bundles of rime; and particles with a rime core and a fine glaze coating. It is agreed that snow grains usually fall in very small quantities, mostly from stratus clouds or from fog, and never in the form of a shower.
snow hardness (Snowpack Properties)
snow ice: Ice formed by freezing of a mixture of snow and water.
Snow Layer (Meteorology & Weather): Also known as: Snow Layers; A distinct layer within the snow caused by wind shift, temperature change, or change in precipitation intensity during a storm; snow deposited during different storms; changes in the snow surface between storms, or metamorphism of existing snow layers.
Snow layering (Snowpack Properties): Also known as: Snow layerings; Stratification of the snowpack
Snow line (Terrain): Term: snow line; Also known as: snow lines, Snow lines; In general, the outer boundary of a snow-covered area. It has at least two specific applications: 1) the actual lower limit of the snow cap on high terrain at any given time; 2) the ever-changing equatorward limit of snow cover, particularly in the Northern Hemisphere winter. Same as firn line. See climatic snow line.
Snow Load (Snowpack Properties): Also known as: Snow Loads; The measured load of snow which depends on snow density (q), snow thickness (h), and gravity (g). Slope-parallel load, tg=hqg cos o, Slope-normal component of load, qg=hqg sin o.
Snow metamorphism (Snow Grain Shapes & Crystals): The process which changes the shape and size of snow grains in the snowpack. There are 2 main processes: isothermal and kinetic metamorphism.
Snow Pellets (Snow Grain Shapes & Crystals): Redirected to graupel.
Snow Pillow (Measurement & Observation): Term: snow pillow; Also known as: snow pillows, Snow Cushion, Snow Pillows; An instrument designed to provide a direct estimate of water equivalence of a snowpack by measuring the pressure due to the mass of overlying snow.
Snow Pit (Snowpack Properties): Also known as: Quick Pit, Hasty Pit, Data Pit, Snow Pits; (Quick Pit, Hasty Pit, Data Pit) A hole dug in the snow-cover to expose the vertical stratigraphy. Weak layers and slabs can be indentified, hardnesses tested and recorded, and stability tests performed. The amount of time invested in, and the details obtained from, a snowpit can vary greatly. In many cases "hasty pits" provide quick bottom-line information and can quickly be done at a variety of locations reflecting conditions at different elevations and on different aspects. These are often dug near the starting zone of an avalanche path, to quickly determine instability by locating any potential slab structures. At the other end of the spectrum, operations typically perform full "data pits" in a consistent study plot location in order to follow and record in detail the development of the snowpack over time.
Snow plume (Meteorology & Weather): Term: Snow Plume; Also known as: Snow Plumes, Snow plumes; Snow being carried by the wind away from a peak or ridge into the air.
Snow profile (Snowpack Properties): Term: Snow Profile; Also known as: Snow Profiles, Snow profiles; A cross-section view of snow stratigraphy and associated physical parameters, usually obtained from a snowpit.
snow roller (Terrain): Also known as: snow rollers; A rolled-up, cylindrical mass of snow, rather common in mountainous or hilly regions. It occurs when snow, moist enough to be cohesive, is picked up by wind blowing down a slope and rolled onward and downward until it either becomes too large or the ground levels off too much for the wind to propel it farther. Snow rollers vary in size from very small cylinders to some as large as 1.5 m long and more than 2 m in circumference.
snow sampler (Measurement & Observation): Also known as: snow samplers, snow tube; (Also called snow tube.) A hollow tube for collecting a sample of snow in situ. See Mount Rose snow sampler
Snow Saw (Measurement & Observation): Also known as: Snow Saws; Any saw designed to cut snow. Used for a variety of purposes - executing stability test in snowpits such as the rutschblock test or the compression test, cutting blocks to build walls for shelter or for a windblock, cutting cornices off, etc. Several types of snow saws are available, including some which fit inside the handle of shovel and some which can be extended by attaching them to the ends of ski poles. See the CSAC Avalanche Store for details on a variety of saws available.
Snow Scale (Measurement & Observation): Also known as: Snow Scales; Redirected to snow-stake.
Snow Shed (Avalanche Types): Also known as: Gallery, Snow Sheds; (Gallery) A shed built over a transportation corridor (i.e. a road or a rail line) to divert avalanches over the top.
snow shower (Snow Types): Also known as: snow showers; A brief period of snowfall in which intensity can be variable and may change rapidly. A snow shower in which only light snow falls for a few minutes is typically called a snow flurry.
Snow Stake (Snow Types): Term: snow stake; Also known as: snow scale, snow stakes, Snow Stakes; (Also called snow scale.) A wooden scale, calibrated in inches or centimeters, used in regions of deep snow to measure its depth. The scale is bolted to a wood post or angle iron set in the ground.
snow strength (Snowpack Properties)
snow survey (Snowpack Properties): Also known as: snow surveys; The process of determining depth and water content of snow at representative points, for example, along a snow course.
snow temperature (Snowpack Properties): Also known as: snow temperatures
Snow thickness (Snowpack Properties): Also known as: Snow thicknesses; Thickness of the snowpack measured at right angle to slope.
Snow water equivalent (Snowpack Properties): Also known as: Snow water equivalents, Snow Water Equivalents, snow water equivalents; The height of the water column if a snow sample is melted (measured in millimeters), with reference to the same area. The water equivalent of a 20 cm snow sample with a mean snow density of 100 kg/m³ is 20 mm. With a density of 500 kg/m³ the equivalent of a 20 cm snow sample is 100 mm of water.
Snowdrift (Meteorology & Weather): Also known as: Snowdrifts; 1. A smooth rounded deposit of transported snow. 2. The process of transporting snow by wind.
Snowdrift accumulations (Terrain): Also known as: snowdrift deposit; The result of snow transport. Drifting and blowing snow usually forms a dense layer deposited on lee slopes, often with brittle, fragile bonding. Areas prone to drifting are gullies, bowls, slope discontinuities and areas adjacent to ridgelines.
Snowfall (Meteorology & Weather): Term: snowfall; Also known as: snowfalls, Snowfalls; In surface weather observations, usually expressed as centimeters or inches of snow depth per six-hourly period. The accumulation of snow during a specified period of time.
Snowfall Intensity (Snow Types): Also known as: Snowfall Intensities; Rate at which snow is deposited during a storm. Expressed in inches (cm) of snow per hour.
Snowfall level (Terrain): Also known as: Snowfall levels; Altitude above sea level at which precipitation falls as snow which is deposited on the ground.
Snowflake (Snow Grain Shapes & Crystals): Term: snowflake; Also known as: snowflakes, Snowflakes; Colloquially an ice crystal, or more commonly an aggregation of many crystals that falls from a cloud. Simple snowflakes (single crystals) exhibit beautiful variety of form, but the symmetrical shapes reproduced so often in photomicrographs are not found frequently in snowfalls. Broken single crystals, fragments, or clusters of such elements are much more typical of actual snow. Snowflakes made up of clusters of crystals (many thousand or more) or crystal fragments may grow as large as three to four inches in diameter, often building themselves into hollow cones falling point downward. In extremely still air, flakes with diameters as large as 10 inches have been reported.
Snowmelt (Snow Processes): Also known as: Snowmelts; Rounded crystals formed by melt-freeze metamorphism, frequently in large clusters. Can be moist (= 0°C). When frozen, snowmelt is forming a melt-freeze-crust.
snowpack (Snow Processes): Also known as: snowpacks, Snowpacks; A laterally extensive accumulation of snow on the ground that persists through winter and melts in the spring and summer.
Snowpack capable of bearing loads (Snowpack Properties): Also known as: Snowpacks capable of bearing loads; Snow surface layer strong enough to support a person walking on it.
Snowpack Structure (Snowpack Properties): Also known as: Snowpack Structures; Ordered snow layering.
Snowpack Tests (Snowpack Properties): Field procedures assessing snowpack stability including compression, extended column, and hand shear tests.
Snowpit (Snowpack Properties): Also known as: Snowpits; A pit dug vertically into the snowpack where layering is observed and stability tests performed.
soaked (Snowpack Properties)
soft (Snowpack Properties)
Soft Slab (Avalanche Types): Also known as: Soft Slabs, Soft Slab Avalanche, Soft Slabs; Recent, less-consolidated snow easier to trigger than hard slabs but with less propagation potential.
Soft Slab Avalanche (Avalanche Types): Also known as: Soft Slab Avalanches; A slab avalanche of soft or low-density snow.
Solar Radiation (Meteorology & Weather): Term: solar radiation; The total electromagnetic radiation emitted by the sun. To a first approximation, the sun radiates as a blackbody at a temperature of about 5700 K; hence, about 99.9% of its energy output falls within the wavelength interval from 0.15 to 4.0 μm, with peak intensity near 0.5 μm. About one-half of the total energy in the solar beam is contained within the visible spectrum from 0.4 to 0.7 μm, and most of the other half lies in the near-infrared, a small additional portion lying in the ultraviolet. See insolation, direct solar radiation, diffuse sky radiation, global radiation, extraterrestrial radiation, solar constant, total solar irradiance. Fritz, S. 1951. Compendium of Meteorology. 17–19.
Solar Warming (Meteorology & Weather): Temperature increase from solar radiation, particularly on sun-exposed aspects.
Sonde d'avalanche
Sous le vent
South-facing slope (adret): Term: South-facing slope; Also known as: South-facing slopes; The sunny, south-facing side of a mountain. Snow becomes wet more quickly due to solar radiation.
Spacing distances (Snowpack Properties): Also known as: maintaining distances; Precautionary measure in outlying terrain: maintaining distances between persons to reduce snowpack loading.
Specific Avalanche Distribution (Terrain): Also known as: Specific Avalanche Distributions; Problem existing only on certain aspects, elevations, or terrain types.
Specific Gravity (Snowpack Properties): Also known as: Specific Gravities; See density.
Spindrift (Avalanche Types): Spindrift, as far as snow goes, is defined as fine grained snow being carried by wind or falling. In practice it is usually used to describe the frequent sluffs of snow that fall down steep slopes, gullies, and faces. This iccurs frequently during snowfall or warming, but may occur at other times and for other reasons as well. The reason very steep slopes have less of a slab avalanche danger is because the snow tends to fall off frequently enough to avoid an accumulation, in the form of spindrift avalanches. Climbers on steep routes during storms often encounter spindrift at regular intervals. They can even anticipate the next one by keeping an eye on their watch. The intervals will depend on rate of snowfall, winds up above, density of the snow, etc. These frequent spindrift avalanches are rarely dangerous or harmful and few deaths or accidents are atributed to them even though climbing reports of ascents with frequent spindrift are not hard to find. The photo shows spindrift coming down a rock wall adjacent to a famous ice climb in the Canadian Rockies called the "Weeping Wall". It was taken by Tuan of terragalleria.com on an ice climbing trip with CSAC director Jim Frankenfield in 1994. The term is also used for ocean spray blown by the wind, and it probably originated with this use.
Spot Probing: Also known as: Spot Probings; Probing specific suspected burial areas before full pinpoint search patterns.
Spring Avalanche (Avalanche Types): Also known as: Spring Avalanches; One of several types of avalanches which exhibit and/or result from particular characteristics most common in spring time. For more information on spring avalanches see this article.
Spring Conditions Icon (Avalanche Types): Also known as: Spring Conditions Icons; Forecast indicator showing melt-freeze cycle patterns affecting avalanche stability.
Spring Snow (Snowpack Properties): Term: spring snow; Also known as: corn snow, granular snow; (Also called corn snow, granular snow.) A coarse, granular, wet snow, resembling finely chopped melted ice, generally found in the spring.
Stability (Snowpack Properties): Also known as: snowpack stability; The strength of a snowpack to withstand internal and external disturbances.Stability is determined by firmness vs. stress inside a snow layer.
Stability Test (Snowpack Properties): Also known as: Stability Tests; A procedure estimating snowpack stability, including Rutschblock, compression tests, and slope cuts.
Stabilization (Snowpack Properties): A process which reduces or eliminates the avalanche hazard, including natural metamorphism processes which improve the bonding and strength within the snowpack, settlement, and active control procedures which relieve stresses through the release of small avalanches under controlled and manageable conditions.
Stabilized (Snowpack Properties): Also known as: consolidated; See: Increasing firmness (of a snow layer)
Stable (Avalanche Types): A snow slope which is well anchored and/or posses sufficient internal strength so as not to be susceptible to avalanching. Also used to refer to a generally widespread condition or period when slopes in general have a low chance of avalanche.
Start Zone (Terrain): Also known as: Start Zones; Area where avalanches typically start, characterized by slope incline, aspect, and ground features.
Starting zone (Terrain): Term: Starting Zone; Also known as: Starting Zones, Starting zones, Starting Zones; The area near or at the top of an avalanche path where unstable snow breaks loose from the snow-cover and starts to slide. The starting zone of a particular slab avalanche can be outlined by the flank, stauch, and crown walls. The starting zone of an avalanche path includes the collective outline of all potential avalanche fracture surfaces (slab and loose-snow avalanches).
Starting/release zone
Stationary Front (Meteorology & Weather): Also known as: Stationary Fronts; An air mass discontinuity that is not moving.
Stauchwall (Avalanche Types): Also known as: Stauchwalls; The bottom (downslope) boundary of a slab where it rides up over the snow below. Usually difficult to impossible to identify after an avalanche.
Steep slope: Also known as: Steep slopes; Slopes steeper than approximately 30°, where most slab avalanches occur. The steeper the slope, the lower the additional load needed to trigger a release.
Steep terrain (Terrain): Also known as: Steep terrains; Terrain with a slope angle exceeding 30°, regardless of form or type of terrain.
stellar (Snow Grain Shapes & Crystals): Also known as: stellars
Stepping Down (Snowpack Properties): Also known as: Stepping Downs; When a slab slides a short distance and breaks down into deeper weak layers.
Storm Load (Avalanche Hazard & Assessment): Also known as: Storm Loads; The amount of snow deposited during a distinct storm period.
Storm Plot: Also known as: Storm Plots; The graphical presentation of weather and snow data shown over the period duration of a storm
Storm Slab (Avalanche Types): Also known as: Storm Slabs; Avalanche problem formed by recent snow accumulating over existing weak layer.
Strain: Also known as: Strains; Mechanical deformation within a material as the result of stress.
Strain Harden (Snow Grain Shapes & Crystals): Under tensile and shear deformation snow often gains strength and the grains may bond or sinter.
Stratigraphy (Snowpack Properties): Also known as: Stratigraphies; The order and thickness of layers within the snowpack.
Stress (Snowpack Properties): Also known as: Stresses; Stresses in the bonding of grains inside a layer of the snow cover, caused by weight and downward creep of the layers of snow atop it.
Study Plot (Meteorology & Weather): Also known as: Study Plots; A flat, sheltered area which is protected from wind, snowdrift, and travelers and is designated to collecting snow and weather data .
Sublayer / Underlying layer: Term: Underlying layer; Also known as: Underlying layers; A buried snow layer beneath more recent layers. A weak underlying layer can fail under load and trigger slab avalanches.
Sublimation (Snow Processes): Term: sublimation; The process of phase transition from solid directly to vapor in the absence of melting. Thus an ice crystal or icicle sublimes under low relative humidity at temperatures below 0°C. The process is analogous to evaporation of a liquid. Colloquially the terms are used interchangeably for the solid–vapor transition (evaporation). For growth, the term sublimation has been replaced by deposition since the 1970s. There is evidence that deposition nucleation does occur, although there may be an adsorbed layer prior to nucleation. It appears that most nuclei in the atmosphere require near–water saturation before they initiate ice.
Subsidence atmosphérique
Sun Crust (Snowpack Properties): Also known as: Sun Crusts, sun crusts; A snow layer melted by sun radiation and subsequently refrozen.
Sunball (Terrain): Also known as: Sunballs; Balls of snow which roll down a steep slope after sun action. The trail they leave is sometimes called a "snow snake".
Sunny slope (Terrain): Also known as: Sunny slopes; Terrain heavily impacted by direct solar radiation.
Supercooled: Water or water vapor that is cooled below the normal freezing or condensing point but remains liquid or vapor. This happens to small droplets inside clouds.
Supersaturation: Amount of water vapor in excess of saturation.
Surface crust (Snowpack Properties): Also known as: Surface crusts; Encrusted layer of the snowpack surface.
Surface de glissement
Surface Energy: Also known as: Surface Energies; The energy required to form a certain amount of new surface, for example between ice and air.
Surface hoar (Snow Grain Shapes & Crystals): Term: surface hoar; Also known as: Hoarfrost, Hoar Crystals, hoar frost; Fernlike ice crystals formed directly on a snow surface by deposition; a type of hoarfrost. Hoarfrost that has grown primarily in two dimensions, as on a window or other smooth surface.
Surface Roughness (Avalanche Types): Also known as: Surface Roughnesses; A description of the snow surface which distinguishes surface of a strong and weak crust, wind slab, and powder.
Surface-layer slab avalanche (Avalanche Types): Also known as: Surface-layer slab avalanches; Slab avalanche which glides inside the snowcover.
Swiss Test (Measurement & Observation): Also known as: Swiss Tests; A shear test where a 3 x 3 x 3m triangle wedge is cut upslope from an excavation snow pit. Shear strength is noted if the wedge moves slowly from cutting out the tensile anchors. or if a skier needs to move onto the wedge, or if the skier needs to jump up and down on the wedge.
Sympathetic Release (Avalanche Hazard & Assessment): Also known as: Remote Triggering (related, Sympathetic Releases; (Remote Triggering (related)) An avalanche which releases in direct response to the release of a neighboring avalanche. The term is often used in control work when a slopes which is intentionally triggered causes another slope to slide as well. As sympathetic avalanche usually results from one form of remote triggering.
Sympathetic Trigger (Avalanche Types): Also known as: Sympathetic Triggers; When one avalanche triggers another avalanche some distance away.
Système de basse pression
Système de haute pression
Tassement
Temperature gradient (Snowpack Properties): Term: Temperature Gradient; Also known as: Temperature Gradients, Temperature Gradients, Temperature gradients, Temperature Gradients; Rate of temperature change with depth in snowpack, driving metamorphism processes.
Temperature Inversion (Meteorology & Weather): Term: temperature inversion; Also known as: temperature inversions, Temperature Inversions, Inversion, Temperature Inversions; A layer in which temperature increases with altitude. The principal characteristic of an inversion layer is its marked static stability, so that very little turbulent exchange can occur within it. Strong wind shears often occur across inversion layers, and abrupt changes in concentrations of atmospheric particulates and atmospheric water vapor may be encountered on ascending through the inversion. When an inversion is mentioned in meteorological literature and discussion, a temperature inversion is usually meant. See frontal inversion, subsidence inversion, trade-wind inversion.
Tensile Failure (Avalanche Types): Also known as: Tensile Failures; Fracture due to tensile stresses. In snow this occurs at the crown of a slab avalanche, although that may or may not be the first (initial) part of the slab to fail.
Tensile Strength (Avalanche Types): Also known as: Tensile Strengths; (yield tensile strength, ultimate tensile strength) In a slab the tensile strength is important at the crown. The tensile strength of a material is the maximum amount of tensile stress that it can be subjected to before it deforms or breaks. Once past its elastic limit, a material will not relax to its initial shape after the force is removed. The tensile strength where the material becomes plastic and suffers irreversible deformation (strain) is called yield tensile strength. The ultimate tensile strength (UTS) of a material is the stress at which the material actually breaks, with sudden release of the stored elastic energy. Tensile strength is measured in units of force per unit area. In the SI system, the unit is newton per square metre (N/m² or Pa - Pascal). The U.S customary unit is pounds per square inch (or PSI).
Tensile Stress (Avalanche Types): Also known as: Tensile Stresses; The stress within a material when it is stretched. In a slab the crown is under tensile stress.
Tension Zone (Avalanche Types): Also known as: Tension Zones; A region of snow which is under tension, such as: 1. The crown region of an avalanche. 2. A convex portion of an avalanche path.
term (Avalanche Types): Also known as: terms; Slab Avalanche An avalanche involving the failure of a distinct, cohesive layer (slab) of snow. Or perhaps more than one such layer.
Terrain complexe
Terrain exigeant
Terrain simple
Terrain Trap (Avalanche Types): Also known as: Terrain Traps, Terrain Traps, Terrain Traps; Terrain feature channeling avalanche debris, increasing burial depth and consequence severity.
Thoroughly moist snow (Snowpack Properties): A thoroughly moist snow layer has a temperature of 0 °C; water is not visible and cannot be pressed out; it is easy to form into a snowball.
Thoroughly wet snow (Snowpack Properties): A thoroughly wet snow layer has a temperature of 0 °C. Water is visible and can be pressed out.
Tilt Table: Also known as: Tilt Tables; A tilting table used to identify shear planes. Blocks of snow are places upon the table. The table is tilted and tapped until shear occurs.
Track (Terrain): Also known as: Tracks, Tracks, Tracks; Area covered by avalanche motion, connecting start zone to runout zone.
Transceiver (Snowpack Properties): Also known as: Transceivers, Avalanche Beacon, Transceivers; Avalanche rescue device switching between transmit and receive modes for locating buried victims.
Transceiver Search: Also known as: Transceiver Searches; First phase of companion rescue using transceivers to locate general burial area.
Transition of a Slope (Terrain): Also known as: Transitions of a Slope; Any point where the profile grade makes a sharp change.
Transport de neige par le vent
Transported snow (Avalanche Types): Re-deposition of snow occurring at a wind speed greater than about 4 m/sec for loose snow, and greater than 10 m/sec for denser snow.
Tree line: Also known as: Tree lines; The border of a forest, e.g. in the alps a maximum of 2.400m (Zermatt) the Pyrenees of Catalonia at 2400m, in SW Poland at 1600m.
Treeline Elevation (Terrain): Also known as: Treeline Elevations; Transition zone between alpine and below-treeline elevations with scattered trees and open terrain.
Trigger (Avalanche Hazard & Assessment): Also known as: Triggers, Explosive Triggering, Triggers, Triggers; Factor initiating avalanche such as additional load, steep slope, or weak layer weakness.
Trigger Point (Avalanche Types): Also known as: Trigger Points, Trigger Points; Specific location where slope steepens, stress concentrates, and avalanche likely initiates.
Trip Planner Card (Avalanche Hazard & Assessment): Also known as: Trip Planner Cards; Avaluator component matching terrain ATES ratings with daily danger ratings for route selection.
Troposphere (Snowpack Properties): Also known as: Tropospheres; The lowest layer of the atmosphere, about 40,000 feet thick, where our weather occurs.
Trough (Meteorology & Weather): Also known as: Troughs, Troughs; An elongated area of relatively low atmospheric pressure, almost always associated with and most clearly identified as an area of maximum cyclonic curvature of wind flow. Opposite of a ridge. The axis of a trough is the trough line. This term is commonly used to distinguish the previous condition from the closed circulation of a low (or cyclone), but a large-scale trough may include one or more lows, an upper-air trough may be associated with a lower-level low, and a low may have one or more distinct troughs radiating from it. See front, dynamic trough, easterly wave, equatorial wave Term edited on 25 November 2025.
TROWAL (Meteorology & Weather): Also known as: TROWALs; Trough of Warm Air Aloft; elevated front created when cold front lifts warm front off ground.
Unbonded snow (Snow Grain Shapes & Crystals): Snow lacking cohesion. The term “loose snow” is used for slack new fallen snow, depth hoar or very developed faceted crystals; however, the definition also applies to very wet snow. Loose snow can lead to loose snow avalanches.
Unconfined Avalanche (Avalanche Types): Also known as: Unconfined Avalanches; An avalanche path that has no terrain constraints throughout its motion.
Unstable (Snowpack Properties): See: Loss in firmness
Upside-Down Storm (Snowpack Properties): Also known as: Upside-Down Storms; A snowstorm depositing denser snow over less-dense snow, creating slab/weak layer combination.
Valley avalanche (Avalanche Types): Also known as: Valley avalanches; Very large or extremely large avalanche that runs all the way to the valley floor.
Valley flank (Terrain): Also known as: Valley flanks; The lateral sides of a valley from valley floor to ridge.
Vapor Pressure (Snowpack Properties): Also known as: Vapor Pressures; The pressure freely mobile water molecules exert. Two features of vapor pressure that influence snow metamorphism are: 1. Vapor pressure rises with temperature and, 2. Vapor pressure is higher over convex surfaces than over concave surfaces.
Vapor Transport: The process where water molecules move through the air from one location to another.
Verglas: Redirected to glaze.
Vertical Fall Distance (Terrain): Also known as: Vertical Fall Distances; The elevation differences between the starting zone and deposition zone of an avalanche.
very coarse (Snow Grain Shapes & Crystals)
very fine (Snow Grain Shapes & Crystals)
very hard (Snowpack Properties)
Very light new snow (Snowpack Properties): New fallen snow with very low density: typically 30 kg/m³ (champagne powder, diamond snow).
very soft (Snowpack Properties)
Very steep (Terrain): Also known as: extreme terrain; Quite unfavourable slope with regard to angle (steeper than 40 degrees), terrain profile, proximity to ridge, smoothness of underlying ground surface.
very wet (Snowpack Properties)
Viscosity: Also known as: Viscosities; The internal friction of a fluid. Snow is visco-elastic and therefore is, in part, a viscous substance.
warm front (Meteorology & Weather): Also known as: warm fronts, Warm Fronts; Any nonoccluded front, or portion thereof, that moves in such a way that warmer air replaces colder air. While some occluded fronts exhibit this characteristic, they are more properly termed warm occlusions.
Warming / Thaw: Also known as: Warmings / Thaws; A significant rise in temperature that can weaken the snowpack by melting snow grains and introducing liquid water. Increases the risk of wet-snow avalanches and slab failure.
Water Equivalent (Snowpack Properties): Also known as: Water Equivalents; A measure of snowfall or snow height in terms of the equivalent amount of liquid water.
Water Saturation: See funicular regime.
Water Vapor: The gas phase of water.
Weak Interface (Snowpack Properties): Also known as: Weak Interfaces; A poor bond between two adjacent layers of snow.
Weak layer (Snowpack Properties): Term: Weak Layer; Also known as: Weak Layers, Weak Layers, Weak layers, Weak Layers; Snowpack layer with poor bonding to surrounding grains, foundation for slab formation.
Weather Front (Meteorology & Weather): Also known as: Weather Fronts; Boundary between air masses with different temperature and moisture properties.
Wedge Test (Measurement & Observation): Also known as: Wedge Tests; (fetch failed)
wet (Snowpack Properties)
Wet Loose Avalanche (Avalanche Types): Also known as: Wet Loose Avalanches; Loose snow avalanche composed of wet/moist snow losing strength through melting.
Wet Slab Avalanche (Avalanche Types): Also known as: Wet Slab Avalanches, Wet Slab Avalanches; Slab avalanche occurring when surface layers lose strength through melting and water percolation.
Wet Snow (Snow Types): Term: wet snow; Deposited snow that contains a great deal of liquid water. If free water entirely fills the air space in the snow it is classified as “very wet” snow.
Wet snow avalanche (Avalanche Types): Also known as: Wet snow avalanches, Wet Snow Avalanches; Avalanche of wet snow masses.
Wet snow problem (Snowpack Properties): Also known as: Wet snow problems; The wet snow problem is related to the weakening of the snowpack due to the presence of liquid water. Water infiltrates the snowpack due to high radiation impact (sunshine) which leads to melt or rain (advecting energy into the snowpack leading to melt as well).
Wet-Loose Avalanche (Avalanche Types): Also known as: Wet-Loose Avalanches; A loose-snow avalanche involving wet snow.
whiteout (Snowpack Properties): Also known as: milky weather, whiteouts; (Also called milky weather.) An atmospheric optical phenomenon in which the observer appears to be engulfed in a uniformly white glow. Neither shadows, horizon, nor clouds are discernible; sense of depth and orientation is lost; only very dark, nearby objects can be seen. Whiteout occurs over an unbroken snow cover and beneath a uniformly overcast sky, when, with the aid of the snow blink effect, the light from the sky is about equal to that from the snow surface. Blowing snow may be an additional cause. This phenomenon is experienced in the air as well as on the ground.
Whoumf
Whumpf (Snowpack Properties): Also known as: Whumpfs; (Whumpfing, Collapsing, Cracking, Settling (misused)) When there is a weakness buried in the snowpack which has a lot of air space between grains and which is weak under compression a "whumpf" sound may be heard when this weak layer fails and air is compressed out of it. This may or may not be accompanied by the appearance of shooting cracks. This sound, with or without cracking, usually indicates a highly unstable situation. The types of failures which produce this "whumpf" sound are ones which can propagate great distances, including upslope from a runout zone.
Whumpfing collapsing sound (Snowpack Properties): Also known as: Whumpfing collapsing sounds; Distinctive noise (resembling a “whumpf” sound) occurring when a weak layer beneath a slab collapses. The air of the weak layer is forced outside the snowpack, with the resulting whumpf sound being heard.
wind chill (Meteorology & Weather): Also known as: wind chills; The portion of the cooling of a human body caused by air motion. Air motion accelerates the rate of heat transfer from a human body to the surrounding atmosphere, especially when temperatures are below about 7°C (45°F).
Wind crust (Snowpack Properties): Term: wind crust; Also known as: wind crusts, Wind crusts, wind crusts; A type of snow crust formed by the packing action of wind on previously deposited snow. Wind crust may break locally, but, unlike wind slab, does not constitute an avalanche hazard.
Wind Effect (Avalanche Types): Also known as: Wind Effects; Wind transporting, loading, and compacting snow, creating cross-loading and wind slabs.
Wind Loading (Avalanche Types): Also known as: Wind Transport; (Wind Transport) Wind transport is the process of moving snow by wind. This can cause snow deposition and the formation of wind slab in localized lee areas. The resulting loading of lee slopes is called wind loading. This can happen either in conjunction with or in the absence of new precipition. A cornice often indicates that wind loading occurs on the slopes below it. There was a three-page sequence on Wind Transport of Snow in our Education Center, with three additional supplemental pages available to members. It is now being moved to a short course within the Avalanche Institute.
Wind metamorphism (Snow Grain Shapes & Crystals): Also known as: mechanical transformation of crystals; Mechanical transformation of snow crystals by wind in which forkings and other distinct shapes are obliterated.
Wind Scour (Terrain): A process where wind transports snow away from windward slopes, leaving them scoured with a hard surface.
wind slab (Avalanche Types): Also known as: wind slabs, Wind Slabs, Wind Slabs; A type of snow crust; a patch of hard-packed snow that is packed as it is deposited in favored spots by the wind (in contrast to wind crust, which is packed after deposition). Wind slabs can be quite rigid, but they adhere poorly to the underlying snow and hence may be readily dislodged, causing an avalanche.
Wind slab problem (Terrain): Also known as: Wind slab problems, Wind slabs; The wind-drifted snow problem is related to wind-drifted snow. The transported snow is typically packed on leeward sides into gullies, bowls and behind ridgelines or other wind-sheltered locations. Also commonly known as “windslab”. The problem is less widespread distributed than the new snow problem.
Wind speed (Meteorology & Weather): Also known as: Wind speeds; low: 0 – 20 km/h moderate: 20 – 40 km/h strong: 40 – 60 km/h very strong: 60 – 100 km/h gale, hurricane: > 100 km/h
Wind Transport (Terrain): Wind moving snow from windward to leeward areas, redistributing snowpack.
Wind-blown snow
Windward (Terrain): windward A descriptive term used to refer to location. Windward refers to the upwind side of a flow obstacle such as a mountain or ridge. Opposite of leeward. Term edited 2 June 2020.
Windward slope (Terrain): Also known as: Windward slopes; Slope facing the wind.
Work Harden: Hardening of snow by mechanical mixing (e.g. boot packing).
Zero-degree level (Snowpack Properties): Also known as: Zero-degree levels; Altitude above sea level at which air temperature is 0 °C.
Zone alpine
Zone d'écoulement
Zone de départ
Zone de dépôt
Zone sous la limite forestière
Échelle d'exposition en terrain avalancheux
Échelle de risque d'avalanche
Équipement essentiel

Avalanche Terminology Glossary

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