- Cold temperatures
- Recent heavy snow fall (although slabs can remain dormant for some time)
- Wind loaded slopes
- A weak layer in the snow pack
- Rain can create a wet layer which re-freezes and forms a slip layer for subsequent snow falls (signficant in Australia)
- Recent heavy snow fall can result in a fresh/dry cornice
- Strong winds increase size of cornice and load snow on leeward slopes
- Rising temperatures can weaken cornice structures
- Skiing or walking too close to cornice edge (don’t go there to “have a look”)
- Steep slopes
- Warm temperature
- Hot sun
- Sodden wet snow pack
- Rain permeating snow can create a “slip layer” on grass (particularly in Australia)
- Cold temperatures
- Recent heavy snow fall
- Steep terrain
- Large scale mountains (e.g. New Zealand Alps, European Alps, Himalayas, Rocky Mountains)
- Reports of local avalanche conditions (not normally issued in Australia but are common overseas)
- Snow going “whump” and settling under your skis (slab avalanches)
- Cracks in the snow radiating from skis when in transit
- Slab fracture lines observed (slab avalanches)
- Avalanche debris observed down slopes and in gullies
- A “slip layer” and slab observed when a snow pit is dug.
- High temperatures (wet snow avalanches)
- Most avalanches occur on a slope angle of 30 degrees or steeper. They occur most frequently on slopes 35 to 50 degrees.
- Lee slopes (relative to the prevailing wind direction) are the most dangerous as they get heavily laden with wind deposited snow.
- Avalanches can travel considerable distances and onto terrain that would otherwise be considered safe – including forested snow slopes and gentle slopes in valleys. This is not commonly observed in Australia.
- Consider the terrain above your route and look for steeper slopes that may avalanche. Beware when travelling below or across gullies and obvious avalanche chutes and don’t loiter in high risk zones.
- Slopes that funnel into a gully (a “terrain trap”) are much more dangerous than those that fan out as an avalanche is concentrated and funneled into the gully (particularly in Australia).
- Convex rollovers on slopes create tension in the snowpack where the snow is more prone to fracture.
- Snow pit tests – dig a pit and examine snow layers
- Rutschblock test – dig out a pit and approach it from above on skis
- Shovel shear test – use a snow shovel to assess the strength of a snow column
- Ski pole test – probe the snow with your pole to assess weak layers
Note that these skills are best learnt by instruction on an avalanche or mountain safety course.
Route finding in alpine terrain to mimimise avalanche risk
- Stick to ridges, staying well away from cornices
- Ski windward slopes that have been stripped of loose snow
Safe practices for descents
- Everyone in the party should have an avalanche transceiver, avalanche probe and snow shovel
- Assess avalanche risks using snow stability tests before skiing the slope. If in doubt, don’t ski the slope.
- Don’t ski slopes of a similar aspect to those where avalanches have already occured.
- Ski low angle slopes first
- Ski a suspect slope one at a time with others in the party watching from safe locations
- Don’t stop below avalanche chutes or paths
- Don’t descend directly above a partner or other group
- Avalanche transceiver searches, Bush Search and Rescue Victoria