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Avalance Safety


This page could stop an Avalanche

Avalanches can happen wherever there is snow lying on ground at a sufficient angle. Accidents in recent years in most Scottish mountain areas as well as the English lakes, the Cheviots, the Pennines and Wales, demonstrate the truth of this in the UK context The vastly increased popularity of winter climbing and hill-walking, along with the growth of interest in ski touring and off-piste skiing, means that greater numbers are at hazard. Sadly, each year adds to the list of injuries or fatalities. Many of these accidents would have been avoidable, given greater care or knowledge, or if the victims had even paused to consider that avalanche hazard might be present.

In making practical assessments of avalanche hazard, there is no substitute for the instinctive feeling for snow conditions which can be gained only by years of experience. However; no-one is born with such experience and the novice or the less frequent winter mountain user; may still enjoy a safe day out if some basic principles are learned and acted upon.

Avalanches can happen to You

Having accepted this, you have greatly reduced your chance of ever being involved in an avalanche. Remember that experience in itself is no antidote to avalanches and that "the avalanche does not know you are an expert!"

What is an Avalanche?

Snow is deposited in successive layers as the winter progresses. These layers may have dissimilar physical properties and an avalanche occurs when one layer slides on another (Surface Avalanche), or the whole snow cover slides on the ground (Full-Depth). An avalanche may be Dry or Wet, according to whether free water is present in the snow. It may be of Loose Snow, when the avalanche starts at a single point, or a Slab Avalanche which occurs when an area of more cohesive snow separates from the surrounding snow and slides out. In practice, any snow slide big enough to carry a person down, is important. Avalanche configurations are illustrated in the SAIS "Avalanche Recording Form".

Weather

This is the most important factor in determining whether avalanches are likely and the evolution of the snowpack is entirely dependent on this. However, as the mountaineer can study both of these, it is useful to do so.

Many weather variables affect avalanche release and information can often be gained before setting out. The information provided on temperature, wind speed and direction often enables useful predictions to be made before leaving home. For instance, if a SW wind of 25 mph is indicated with freezing temperatures and snow known to be lying, then it may be assumed that some avalanche hazard will be building on NE - facing slopes.

Local advice can often be obtained regarding recent weather, while forecast information is available from the telephone numbers listed below. Remember that mountain weather is particularly difficult to predict and the likely influence of unexpected changes in weather; both on your own expectation as to snow stability, and on the SAIS published avalanche hazard outlook, should be considered.

Snowpack

When visibility is adequate, snowpack observation can begin from the roadside. Evidence of recent avalanche activity, main snow accumulation zones, fresh loading by new snow and drifting, can often be noted from below. Observations can continue on the approach, noting such details as depth of foot penetration, cornice build-up, ease of release of small slabs and the effect which localised wind patterns may have had on slab formation. Any suspect slopes which must be negotiated (bearing in mind that the safest course it to avoid them) may be tested by digging a snowpit. Pits should not initially be dug on the main suspect slope, but on small, safe slopes of similar orientation.

There is no need to dig to ground level, but only down to the first reasonably thick layer of nevé (old refrozen snow). The snow layers may then be identified by smoothing the back wall of the pit and probing with a finger all the way down it. This will help assess the hardnesses of the layers. The following features should be looked for:

Any of the above may be the source of a dangerous weakness in the snowpack.

These observations may be supplemented by a shovel test (see Fig 1). For this, a shovel is not necessary. Your ice axe and gloved hands will suffice.

Having made the snowpit observations, isolate a wedge-shaped block, cutting down to the top of the next identified layer. If the top layer then slides spontaneously, clearly a very poor bond exists between the layers. If it does not, then try to rate the ease with which you can pull the block off by inserting your shovel/axes/hands behind the block and pulling. Do this for each suspect layer in your pit. Performing this test many times will help you to build up a "feeling" for the stability of the layers. As you climb, digging stances, cutting steps or placing deadmen, all give you an opportunity to make a quick check on surface layers.

These techniques should enable you to make an educated hazard assessment. Remember that your snowpit observations will hold good only for slopes of similar orientation and altitude to your test pit. You will need to extrapolate for situations higher up, for instance below cornices, where surface windslab layers may be much thicker.

An attempt should be made to rate the slope Safe, Marginal or Unsafe. Even if a slope is Marginal or Unsafe, it may be possible to choose a safe route by careful selection.

Cornices

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

When walking above cornices, take care to give them a wide berth. Fig. 2 shows the possible fracture line.

Terrain

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

Travel in Hazard 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:

If Caught

In most avalanche situations, any defensive action is very difficult. Movement relative to the debris is often impossible. However, some of the following may be useful:

If Buried

Avalanche Rescue

If you witness an avalanche burial:

Avalance Checklist - Top 6 Factors

Avalanche Recording

SAIS keeps records of avalanche occurrences in Scotland and elsewhere in Britain and would appreciate hearing from you if you are involved in an incident or if you witness any avalanches. To report an avalanche click here.

Snow and Avalanche Reports

These are issued every day mid-December to mid-April for the Glencoe, Lochaber; Creag Meagaidh, Northern Cairngorms and Southern Cairngorms; Torridon is also covered during a reduced period. 

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scotland Avalanche Information Service (SAIS) Website: www.sais.gov.uk

Note: Reports are for areas OUTSIDE developed ski areas.  

Safety and skills information is provided courtesy of the Mountaineering Council of Scotland