Mont-Blanc
4 – HighSource: Météo-France
This is an AI-generated translation and summary. It may contain errors. Always read the full official Météo-France avalanche bulletin before any mountain activity.
Avalanche Report: High Risk (Level 4)
Title: Numerous instabilities at altitude.
Description:
Numerous instabilities at high elevations.
Triggered Avalanches:
- Above 2000 m: Numerous soft slabs in the fresh snow. These slabs are widespread, very sensitive, and thick: crown lines can easily exceed 1 to 1.5 m in accumulations, and they are wide. Size 2 (medium) to 3 (large), more rarely 4 (very large).
- Aggravating factors:
- On East/North/West aspects: A buried persistent weak layer may be triggered in a cascade, resulting in very large avalanches.
- On sunny slopes (adrets): In the sun, slabs may become temporarily more sensitive.
- Aggravating factors:
- In the high mountains: New slabs are forming on leeward slopes due to the north wind. Size 1 to 2.
- Between 1600/1800 m and 2000 m: Some slabs in the recent wet snow. Less sensitive and thick than at higher altitudes, these slabs will be temporarily more sensitive in the sun during the afternoon. Size 1 to 2 (small to medium).
Spontaneous (Natural) Releases:
- Below 2200 m: Glide slabs (full-depth). All aspects, but releases are more frequent on south-facing slopes. Releases occur on steep, smooth slopes (grassy slopes, rock slabs). Size 2 (medium) to 3 (large).
- Cornice collapses: Thick and voluminous, potentially triggering very wide soft slabs below.
- With daytime warming: Point-release (loose-wet) avalanches in the recent moistened snow. Size 1 to 2.
Avalanche Report: High Risk (Level 4)
Risk Level 4 (High) means the snowpack is very unstable. Natural avalanches are likely, and a single skier can very easily trigger a large slide. Travel in off-piste terrain is not recommended.
Title: Numerous instabilities at altitude.
Description:
Many dangerous conditions exist at higher elevations (typically above the treeline).
Triggered Avalanches (Slides caused by a skier or snowboarder):
- Above 2000 m: Many soft slabs (blocks of relatively soft snow that break away together) in the fresh snow. These are generalized (found almost everywhere), very sensitive (can be triggered by a single person), and thick: the break/crown line (the top edge where the snow snaps) can easily be over 1 to 1.5 meters deep in areas where snow has drifted, and the slides are wide.
- Size 2 (can bury or injure a person) to Size 3 (can bury and destroy a car). More rarely Size 4 (can destroy a forest or small buildings).
- Aggravating factors:
- On East/North/West slopes: A persistent weak layer (a hidden, fragile layer of sugary snow crystals buried deep down) could be triggered. This can cause a cascade effect (one slide triggering another), resulting in massive avalanches.
- On sunny slopes (adrets): Solar radiation can warm the snow, making these slabs even easier to trigger temporarily.
- High mountains (the highest peaks): New wind slabs (stiff blocks of snow moved by wind) are forming on leeward slopes (slopes protected from the north wind). Size 1 (small) to Size 2 (medium).
- Between 1600/1800 m and 2000 m: Some slabs made of recent, heavy wet snow. These are less sensitive than those higher up but will become easier to trigger in the afternoon sun. Size 1 to 2.
Spontaneous Releases (Natural avalanches occurring without human help):
- Below 2200 m: Glide slabs (also called "plaques de fond"). These occur when the entire snowpack slides off the ground like a rug. They happen on all sides of the mountain but are most common on south-facing slopes that are steep and smooth (like grass or rock slabs). Size 2 to 3.
- Cornice collapses: Large overhanging ridges of wind-blown snow at the top of ridges may break off. Their weight is enough to trigger huge slabs on the slopes below.
- Daytime warming: As the sun warms the snow, point-release avalanches (which start from a single point and fan out like a pear/triangle) will occur in the recent snow. Size 1 to 2.
| French | Translation & Notes |
|---|---|
| Risk level: 4 - High | Risk level: 4 - High The European avalanche risk scale goes from 1 (Low) to 5 (Very High). Level 4 indicates very dangerous conditions. |
| Nombreuses instabilités en altitude. | Numerous instabilities at altitude. 'Instabilités' refers to layers in the snowpack that are prone to sliding. 'Altitude' usually implies terrain above the tree line. |
| Déclenchements provoqués : | Triggered releases: This section refers to avalanches caused by 'external load,' usually a skier, snowboarder, or hiker. |
| Au-dessus de 2000 m : nombreuses plaques friables dans la neige fraîche. | Above 2000 m: numerous soft slabs in the fresh snow. 'Plaques friables' (soft slabs) are formed by recent snowfall without heavy wind; they are dangerous because they look like harmless powder but act as a cohesive block. |
| Plaques généralisées, très sensibles, épaisses : cassure pouvant facilement dépasser 1/1.5 m dans les accumulations, et larges. | Widespread slabs, very sensitive, thick: fracture line can easily exceed 1/1.5 m in accumulations, and wide. 'Sensibles' means they require very little weight to trigger. 'Cassure' refers to the crown or fracture line where the slab breaks. |
| Taille 2 (moyenne) à 3 (grandes), plus rarement 4 (très grandes). | Size 2 (medium) to 3 (large), more rarely 4 (very large). Reference to the international avalanche size scale (1-5). |
| Facteur aggravant : | Aggravating factor: Conditions that make the existing danger even worse. |
| en versants Est/Nord/Ouest : une couche fragile persistante enfouie peut être sollicitée en cascade et donner de très grandes avalanches. | on East/North/West slopes: a buried persistent weak layer can be triggered in a cascade and result in very large avalanches. A 'couche fragile persistante' is a dangerous, long-lasting layer (like faceted 'sugar' snow) that stays unstable for weeks. 'En cascade' means one small slide triggers a much larger, deeper one. |
| dans les adrets: au soleil les plaques pourront être temporairement plus sensibles. | on sunny slopes: in the sun, the slabs may be temporarily more sensitive. 'Adrets' is a French term for south-facing, sunny mountain slopes. Sun warms the snow, which can initially make it more unstable. |
| En haute-montagne : nouvelles plaques en formation sous le vent de nord. | In the high mountains: new slabs forming on leeward slopes from the north wind. 'Sous le vent' means leeward (the side protected from the wind where snow accumulates). 'Vent de nord' means the wind is coming from the north. |
| Taille 1 à 2. | Size 1 to 2. Relatively small avalanches (Size 1 usually cannot bury a person; Size 2 can). |
| Entre 1600/1800 m et 2000 m : quelques plaques dans la neige récente humide. | Between 1600/1800 m and 2000 m: a few slabs in the recent wet snow. At lower altitudes, the snow is 'humide' (wet/moist) due to warmer temperatures or rain. |
| Moins sensibles et épaisses qu'en altitude, ces plaques seront temporairement plus sensibles au soleil l'après-midi. | Less sensitive and thick than at altitude, these slabs will be temporarily more sensitive in the sun in the afternoon. The afternoon sun increases the water content in the snow, weakening the bonds between grains. |
| Taille 1 à 2 (petite à moyenne). | Size 1 to 2 (small to medium). Describes the potential volume and destructive power of the slides. |
| Départs spontanés : | Spontaneous releases: Natural avalanches that occur without any human or animal trigger, usually due to gravity, weather, or warming. |
| En dessous de 2200 m : plaques de fond. | Below 2200 m: glide slabs. 'Plaques de fond' are avalanches where the whole snowpack slides on the ground (often called glide avalanches). |
| Tous versants, mais départs plus nombreux dans les pentes sud. | All aspects, but more numerous releases on south slopes. 'Versant' is an aspect or mountain side. |
| Départs dans les pentes raides et lisses (pentes herbeuses, dalles rocheuses). | Releases in steep, smooth slopes (grassy slopes, rock slabs). Smooth surfaces like grass or slabs provide no friction, making it easier for the snowpack to slide off the ground. |
| Taille 2 (moyenne) à 3 (grande). | Size 2 (medium) to 3 (large). Slabs sliding off the ground are often large and carry heavy, wet snow. |
| Chutes de corniches, épaisses et volumineuses, pouvant solliciter de très larges plaques friables. | Cornice falls, thick and voluminous, potentially triggering very wide soft slabs. A 'corniche' is an overhanging edge of snow on a ridge. When they break, their massive weight can trigger a secondary slab avalanche below. |
| Au fil de l'ensoleillement, départ en poire dans la neige récente humidifié. | With increasing sunshine, point-release avalanches in the recent moistened snow. 'Départ en poire' literally means 'pear-shaped start,' the French term for a point-release (loose snow) avalanche. |
| Taille 1 à 2. | Size 1 to 2. Generally smaller releases, though Size 2 can still be dangerous. |
| French Term | English Term | Definition |
|---|---|---|
| Plaque friable | Soft slab | A cohesive layer of snow that is relatively low-density (often fresh snow) but still acts as a single block that can slide away. |
| Couche fragile persistante | Persistent weak layer | A buried layer of snow (often large, faceted crystals) that remains unstable and capable of collapsing for a long time. |
| Plaque de fond | Glide slab / Full-depth avalanche | An avalanche where the entire snowpack slides directly off the ground (soil, grass, or rock). |
| Départ en poire | Point-release / Loose-wet avalanche | An avalanche that starts at a single point and spreads out in a triangular or pear shape as it moves; usually occurs in unbonded snow. |
| Adret | Sunny aspect | A slope that faces the sun (usually South or South-West). |
| Sous le vent | Leeward | The side of a mountain or ridge protected from the wind, where snow tends to accumulate and form dangerous drifts or slabs. |
| Taille 1 | Size 1 | A small avalanche unlikely to bury a person, but enough to cause a loss of balance. |
| Taille 2 | Size 2 | A medium avalanche that can bury, injure, or kill a person. |
| Taille 3 | Size 3 | A large avalanche that can bury and destroy a car, damage a truck, or break trees. |
| Taille 4 | Size 4 | A very large avalanche that can destroy a forest or several buildings. |
| Instabilités | Instabilities | Structural weaknesses within the snowpack that make it prone to collapsing or sliding. |
| Cassure | Fracture line / Crown | The upper vertical wall of the remaining snow from which a slab avalanche has detached. |
| Déclenchement provoqué | Triggered release | An avalanche caused by a person, animal, or explosive. |
| Départ spontané | Natural release | An avalanche that happens without a direct human or animal trigger, caused by gravity or weather changes. |
Download the original Météo-France bulletin in French (PDF).
Download original PDF (French)