warm hands for at least part of the day is something to be savoured. Several extra pairs may be worthwhile in certain conditions. Even the best climbers will not be able to complete their route if they do not learn what to wear, and how to wear it, in order to keep warm and comfortable.
Mobile phones
Coverage is mostly good, but users should be aware of the limitations of mobile phones, especially if tucked away inside any of the corries or deeper glens. When using a mobile phone to raise the alarm, dial 999 or the local police station and ask for Mountain Rescue, give your number to the police and remain switched on until the rescue team arrives or you are given the all clear to switch off. Remember that your phone will make 999 calls on any available network, so it is worth trying even if your phone shows no coverage on your network, and whether or not there is credit on your account. Texting is often a useful of way of preserving battery life.
Avalanches
Avalanches occur in the Cairngorms and on Creag Meagaidh every year, often with tragic results. Anyone intending to climb or walk in the Scottish mountains in winter is strongly advised to acquaint themselves with a basic understanding of avalanches. As well as various courses and lectures which are available during the winter months, there exist some excellent books on the subject, with A Chance in a Million by Barton and Wright being the classic text on avalanches in Scotland. The ability to judge the likelihood and consequences of an avalanche, and to know what to do in the event of an avalanche incident, could save lives.
Snow and avalanche
A basic knowledge of how and why avalanches occur is a prerequisite for learning how to avoid them. Storm cycles and changing weather conditions tend to build up a highly layered mountain snowpack. Avalanches usually occur when the bonds between adjacent layers, or that between the snowpack and the ground, fails. Changes that occur over time both within and between these layers can increase or decrease snow stability, depending on the circumstances.
Different types of avalanches exist and are generally classified according to their physical characteristics. An avalanche can release from a single point or a whole area (loose or slab); it may be the whole snow cover or only part of it that slides (full or partial depth); and it can be channelled or not (confined or unconfined). It may also be airborne or flow along the ground.
A full-depth avalanche on The Great Slab, Coire an Lochain
Avalanches are initiated because of either changing internal factors, such as bonds between layers being weakened by rising temperatures, or external factors, such as snowfall or a person walking or skiing on the slope. The details of the release process are complex and poorly understood. However, some basic principles are well known. Avalanches can release on slopes between about 20° and 60°, although slopes between 30° and 45° are the most likely to release, with about 38° being the optimum angle for slab avalanches. Above about 60° snow tends to slide off in small sluffs rather than building up to reach dangerous quantities. The greatest danger usually exists during and for approximately 24 hours after a period of heavy snowfall. This danger period is longer in cold temperatures, when the snow consolidates more slowly. Thaws, especially if accompanied by rain, produce a wet-snow hazard, as well as the danger of collapsing cornices. Even in the absence of snowfall or thaw, a significant avalanche hazard may be created by the wind redepositing the snowpack.
Avalanche types
There are various types of avalanche, and these tend to occur under different conditions and present different degrees of hazard.
Powder or loose snow avalanches typically occur during, or right after, a snowfall. Usually the failure begins at a point and spreads out down the slope in an inverted V shape. They are generally small in size, but in the confines of a gully they can be unpleasant and are sometimes large enough to knock a climber off.
A slab avalanche
Sgor an Lochain Uiane and An Garbh Choire from Ben Macdui (Cairntoul/Braeriach Amphitheatre)
A slab avalanche, on the other hand, occurs when a cohesive slab of snow slides on a weak layer. They are the most common, least predictable and, therefore, the most dangerous type of avalanche. This type of snow, called windslab, is formed when wind-transported, and therefore damaged, snow crystals accumulate in sheltered areas such as lee slopes. Windslab consistency can vary from soft to hard, depending mainly on the speed of the wind that transported the snow. Hard slab, in particular, is very deceptive, as it can be firm enough to walk on without sinking in and so feel safe to the unwary. However, it does tend to have a dull, chalky appearance and may squeak or creak when walked on or probed with an axe. Although most common on lee slopes, particularly below cornices, it can build up in unexpected places, even on windward slopes.
Wet-snow avalanches usually occur during a thaw, when the snow or its top layers become saturated. The extra weight and lubrication of this water can weaken the bonds between different snow layers, or between snow and the ground, and may cause a large area to slide. Although easier to predict, this type of avalanche can be particularly descructive due to the high density of wet snow. Wet-snow avalanches can harden rapidly on settling, and so it can be extremely difficult to escape from them unless this is done immediately.
Avalanche avoidance
Before starting out
Avalanche awareness should start long before the mountains are reached. Monitoring the weather in the days prior to a climbing trip is a basic precaution, with heavy snowfall accompanied by wind being the main danger sign. Long periods of cold temperatures tend to make any danger last longer, while a freezing level that rises and falls rapidly usually quickly consolidates the snow pack. Be aware of the recent and forecast wind direction, as the greatest danger is likely to be on lee slopes, the place where windslab accumulates. Consult the snow and avalanche forecast, and consider possible alternatives should conditions turn out to be worse than expected. Seek expert local advice – avalanches tend to have local characteristics. Have the appropriate equipment and know how to use it.
In the mountains
Ongoing observations on the hill should be used to confirm, and refine or adjust, your initial hazard evaluation. Avalanches occurring or signs of recent activity are the most significant indicators of an avalanche danger and should not be ignored. On the approach observe the nature of the snow on the ground and in the air. The behaviour of snow underfoot can be very informative. Cracking and breaking away of snow blocks from beneath your feet is an indication of slab and instability. Look for signs of recent windslab deposition. Spindrift is usually a danger sign, as even fairly light winds can redistribute huge amounts of snow, packing it in as windslab on lee slopes and in other sheltered locations. Even a light surface drift can produce localised danger, especially in the tops of gullies.
Signs of a rise in temperature – such as rain, wet snow, sun balls rolling down the slope, strong sunlight, and melting snow and ice – can all be danger signs, especially if large cornices exist. If the thaw is due to strong sunshine, then different slope aspects may make a large difference, with perhaps danger on south faces but safer northerly aspects. In these circumstances, slopes of a similar aspect and altitude should be considered extremely suspect.
Although general observation is important, a simple snow pit can give further information about the snowpack and its stability. A snow pit dug in a safe but relevant position for the suspect slope is useful. It is dug down to ground level or, more usually, to
