Disaster Management in Fisheries

2.1.8 Avalanches

Avalanches can happen wherever there is snow lying on ground of sufficient angle. Accidents in recent years in most mountain areas, demonstrate the truth of this statement. The vastly increased popularity of winter climbing and hill walking, along with the growth of interest in ski touring 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.

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

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. Readouts from summit weather stations can be beneficial. 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 25mph 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 forecasts are always available. 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 should be considered.