Avalanche terrain is any area steep enough for unstable snow to slide, or any area in the avalanche path. Most skiing and climbing take place in potential avalanche terrain.
Commercial ski area operations control the slopes in their area. If you travel in the wilderness and in off- piste sking areas it is not controlled – you are on your own.
When going to an area for the first time, you need to gather relevant information in order to make a judgement of snow stability and avalanche hazard.
Good steps for Hazard Evaluation
Prior to you trip
Identify where you’re going to ride, ski, travel.
What direction does your climb or slope face?
Is it the right trip for your level of experience in the expected conditions ?
Obtain weather forecasts so that you know what the weather has been doing.
Obtain avalanche bulletins via television, telephone, radio, internet, newspaper or any other source.
Ask valued locals or colleagues who have been in the area recently about present snow conditions.
Get the right equipment and know how to use it properly – more importantly make sure your friends know how to use it properly.
On the day
Check avalanche bulletins and weather.
Identify your route, view it and scope it out.
Carry out field observations on a small slope of the same aspect to check for signs of weakness.
Gut reaction – what do you feel about it!
On the mountian
Be cautious. – move like something may happen – its good practice.
Ski, board it one at a time if you are suspicious about a slope.
Stop in safe places. Beware of terrain trapseg, gullies, cliff edges and crevasse areas.
Look out for one another.
Considerations for Terrain Travel
Ridge tops / Gently sloping windward side of ridges / Level ground far away from steep slopes / Dense forest.
Ribs of higher ground or promontories on a slope / The higher parts of steep slopes / Clumps of trees / Rocks and rock buttresses.
Steep slopes / Lee side of ridges / Slopes exposed to the sun for several hours / Gullies / Terrain traps.
The following should be used as a guideline for carrying out field observations when you are in the mountains and should be continually evaluated throughout the day.
- Observe the snow depth – if it is deep and soft, it may slide on a weakly bonded hard layer below.
- Look for recent and current avalanche activity – if small slides are happening naturally then this is a bad sign.
- By various probings with ice axe and ski sticks on relevant snow slopes feel and test the snow – are their any differences in the layers: hard on soft or loose Crystal layers?
- Look for signs of wind action – cornices, snowdrifts around objects, sastrugi and rime ice etc. – they tell you where the wind blowing snow has loaded slopes.
- Take notice of the temperature and the sun’s action – avalanches can start once the sun starts heating a slope.
- Use penetration of the snow to gauge snow strength. Use heel of skis, reversed ski sticks, probes etc. If the snow breaks into blocks then this is a bad sign.
- Test short slopes in a safe location. By jumping on or releasing small cornices you can tell if it triggers a release on small slopes – if so it’s bad.
- Continually evaluate your judgment as you travel throughout the day.
- Monitor changing conditions of precipitation, temperature and wind.
Snow profiles can be dug with your snow shovel and the layers can be looked at in more detail – obvious differences in layer hardness are the main things that you are looking for or, if one layer slides easily on another. Remember though that this information provides a very small amount of information as is only a part of your overall hazard evaluation.
You need to have more snow knowledge to get the most from this type of observation.
Testing weak layers
Terrain traps are features and obstacles that can: trap the snow or persons in the event of an avalanche occurring and either assist burial, cause injury or both.
Travelling in narrow valleys and gorges limits escape and increases the risk of burial if an avalanche descends on to you from above, but even travelling on slopes amongst cliffs, rocks, trees and crevasses can inhibit escape.
What would normally be insufficient snow to bury a person would be enough to carry you over or into terrain traps where you would be injured or buried.