ThinkWINTER: Avalanche | Mountaineering Scotland

ThinkWINTER

ThinkWINTER: Avalanche

Photo by Duncan Gray

If you're climbing Scotland's hills and mountains in winter you need to know about avalanches. Every year people are injured or die as a result of avalanche, but many of these accidents would have been avoidable given greater awareness of the hazards and approrprate action to avoid them.

The first step is to realise that avalanches don't happen at random and that, by learning the factors that cause them - type and depth of snow, nature and angle of slope, temperature, presence of humans (!) etc - you can better avoid situations where an avalanche is likely.

Download the Be Avalanche Aware leaflet

Check the forecasts

There are experts in the science of avalanches whose advice you can draw on throughout the winter. The sportscotland Scottish Avalanche Information Service, publishes a daily forecast of avalanche, snow and climbing conditions for six areas of Scotland each winter. You can now get easy access to these reports, receive important alerts and measure slope angles on your phone with their new app.

Download the app for free on iOS and Android devices

Read the danger signs

Visible avalanche activity. If you see avalanche activity on a slope where you intend to go, then go somewhere else.
New snow build-up. More than two centimetres per hour may produce unstable conditions. More than 30 cm. of continuous build-up is regarded as very hazardous.
Slab lying on ice or nev�, with or without aggravating factors such as thaw.
Discontinuity between layers, usually caused by loose graupel pellets or airspace.
Sudden temperature rise. The nearer this brings the snow temperature to zero degrees Centigrade, the higher the hazard, even if thaw does not occur.
Feels unsafe. The �seat of the pants� feeling of the experienced observer deserves respect.

This BMC/Association of Mountaineering Instructors video looks at how you can confirm and build on avalanche forecast information while you approach your route.

A free training resource is available to help hillwalkers, climbers, mountaineers and skiers understand and avoid avalanche dangers in the hills.

Aimed at individuals making critical decisions in the winter mountains, the free digital version of the �Be Avalanche Aware� planning tool is clear and easy to follow, equipping people travelling in mountain terrain with practical information and advice to make them more aware of the avalanche risks and the factors that influence their own planning and journey decision making.

The online avalanche awareness training initiative has been created by The Snow and Avalanche Foundation of Scotland (SAFOS), with development support from member organisations Mountain Training Scotland and Glenmore Lodge.

Access the SAFOS avalanche awareness e-learning

Travel in hazardous areas

It is rarely essential to negotiate an avalanche-prone slope. It is usually possible to find another way, or retreat. 90% of avalanches involving human subjects are triggered by their victims.

If it is essential to proceed, the following should be borne in mind:

Solo travellers in avalanche terrain run particularly grave hazards
Skiers are in greater danger than walkers - the lateral cutting action of skis readily releases unstable snow. All off-piste skiers should use avalanche transceivers and have them switched on before leaving base. They should carry collapsible probes and shovels. Climbers and walkers should consider the use of these items
Direct descent or ascent is safer than traversing
Go one at a time � the others should closely observe the progress of the person on the suspect slope
Belay if possible, although this is rarely feasible on wide, open slopes

Many avalanches are cornice-triggered. In general, climbing below cornices should be avoided:

During snowstorms or heavy drifting
Immediately (24-48 hrs) after snowstorms or heavy drifting
During heavy thaw or sudden temperature rise

When walking above cornices, take care to give them a wide berth. This photo of a cornice on Aonach Mor shows the possible fracture line.

Depending on conditions, the cornice could break off even further back than the line indicated

On most hills in Britain, avalanche hazard can be avoided completely by sensible choice of route.

Slope Angle - Most large slab avalanches run on slopes between 25 and 45 degrees. This range includes the average angle of coire back walls and approach slopes to crags.
Ground Surface - Smooth ground such as rock slabs will predispose to full-depth avalanches. Rough ground has large boulders which will tend to anchor base layers in position, making avalanches less likely. Once these boulders are covered, however, surface avalanche activity is unhindered.
Slope profile - Convex slopes are generally more hazardous than uniform or concave slopes. The point of maximum convexity is a frequent site of tension fracture, with release of slab avalanches.
Ridges or Buttresses � �Ridges are bridges� Ridges are better choices than open slopes and gullies when avalanche conditions prevail. The crests of main mountain ridges are usually protected from avalanche while, in climbing situations, rock belays on ribs and buttresses can often provide security.
Lee Slopes � Lee slopes should be avoided after storm or heavy drifting. Their location will obviously vary according to wind direction, but will include the sheltered side of ridges and plateau rims.

A terrain trap is a topographical feature on the mountainside. Classically it can be a depression, concavity or flattening, such as a gully, corrie basin or abrupt change of slope angle which would allow avalanche debris to accumulate rather than flow away downhill.

Examples in the Scottish mountains would be Coire na Ciste on Ben Nevis, Coire na Tulaich on Buachaille Etive Mor, the Chalamain Gap and the moraines in Coire an't Sneachda in the Cairngorms and G&T Gully on Aonach Mor. Four of these locations have been the sites of multiple avalanche burial fatalities as a direct result of their being terrain traps.

Since shovelling takes such a long time, deep burials have a very low chance of survival. Even a small avalanche off the side of a small gully can have significant consequences if the debris has nowhere to run to. Avalanche danger will rise and fall throughout the season as the snow pack and weather conditions varies, but the topographical structure of the mountainous terrain that you choose to travel through remains constant.

The key to avoiding terrain traps is to make good route choices:

Plan ahead before you leave the comfort of your living room and study the terrain for your intended route on the map.
Always be flexible and have alternative plans.
Stay high: choose ridge lines and broad shoulders.
Avoid gullies, abrupt slope transitions and corrie basins in times of high avalanche risk.
Remember: it might not be you that triggers the avalanche. You could just be in the firing line.

Scottish Avalanche Information Service - avalanche forecasts

SAIS Avalanche Aware leaflet

SAIS 'Be Avalanche Aware' app

Avalanche rescue