Avalanche problems

New snow

What: related to current or most recent snowfall. The amount of additional load by new snow on the existing snowpack is the crucial factor; how critical it is depends on air temperature, wind and the old snow surface. Dry-snow slab and dry loose snow avalanches, natural and human triggered.

Where: in general widespread, often on all aspects.

When: during snowfall and up to a few days after.

Advice: wait until the snowpack has stabilised. With loose snow avalanches, being carried away matters more than burial — consider the consequences in extreme terrain.

Wind slab

What: wind slabs form when wind transports and deposits loose snow (new or old). Dry-snow slab avalanches, natural and human triggered.

Where: highly variable, but typically on leeward slopes, in gullies and bowls, near changes in slope angle, behind ridgelines and in other wind-sheltered places. More common above treeline.

When: can build very quickly during drifting snow; tends to stabilise within a few days after the storm.

Advice: avoid drifted snow in steep terrain. Clues: drifted deposits, recent avalanches, sometimes shooting cracks or whumpfs.

Persistent weak layers

What: one or more persistent weak layers in the old snowpack — faceted crystals, depth hoar or surface hoar. Dry-snow slab avalanches, mostly human triggered; remote triggering is possible.

Where: can be widespread or isolated; all aspects, more often on shady, wind-sheltered slopes.

When: weak layers can persist for weeks to months.

Advice: travel conservatively and avoid terrain where the consequences are large (large steep slopes). Be extra careful where the snowpack is thin and where it changes from thin to deep. A significant cause of avalanche fatalities.

Wet snow

What: the snowpack weakens because of liquid water from melt or rain. Wet-snow slab and wet loose snow avalanches, mainly natural.

Where: with melting — certain aspects (sun) and elevations (temperature); with rain on snow — all aspects below the rain line.

When: hours to days; stability can drop quickly, often as the day goes on.

Advice: after a clear, cold night the morning is usually safer; after a warm, overcast night the problem is already there in the morning. Plan your timing and watch avalanche runout zones.

Gliding snow

What: the entire snowpack glides on the ground, typically on smooth ground such as grassy slopes or smooth rock. Almost exclusively natural avalanches; human triggering is very unlikely. Release is hard to predict.

Where: on smooth ground, all aspects, more often sun-exposed slopes.

When: days to months; release can happen at any time of day, in spring more often in the afternoon.

Advice: avoid areas close to glide cracks.

Cornices

Wave-like, often overhanging formations of drifted snow on the leeward side of ridgelines. A cornice collapse can trigger an avalanche on the slope below. Cornices often break further back than expected. Advice: avoid travel on and below large cornices, especially during drifting snow or warming.

No distinct avalanche problem

A situation without a clear pattern, in which any avalanche type is possible. The absence of a typical avalanche problem does not mean safe conditions — normal caution is still advised.