Avalanches occur every winter in the Highlands of Scotland, which surprises not only tourists but also some hikers and skiers.
Both summer and winter visitors to the Scottish Highlands have asked me if Scotland ever gets avalanches. Technically, these can occur wherever snow lies on terrain that is steep enough. In Scotland, we have plenty of steep-sided mountains and couloirs, together with significant snowfall during the winter so, yes, we experience avalanches. As in other countries, their unpredictability is an important factor when planning winter hill walking or ski touring journeys. So we’ll start by looking at their frequency and type, then get an intro to avalanche forecasting, rescue and education in Scotland.
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How common are avalanches in Scotland?
Skiers sometimes judge avalanche risk by looking at average snow depth at ski resorts. While this can offer insights in some places, here in Scotland it is a poor indicator of risk. This is because strong winds constantly redistribute our snow (to the extent that our ski resorts need snow fences to trap it!). Wind transport results in shallow cover on windward slopes and very deep snow on sheltered (‘lee’) slopes. Like in other mountain areas, these sheltered slopes can hold much greater avalanche risk. Every winter, mountaineers and ski tourers report avalanches and their debris to our excellent Scottish Avalanche Information Service (SAIS). However, many slides probably occur unseen due to bad weather or remoteness.
Are avalanches less common due to climate change?
It’s hard to say because our weather is changeable and winter seasons vary so much from year to year. Many climate models suggest Scotlands winter weather will involve higher temperatures, more precipitation and stronger storms. This could actually result in more avalanches!
Avalanche frequency
To get an idea of avalanche frequency, take for example the 2023/24 winter. The avalanche forecasting season lasted from the start of December to mid April during which snow cover was very varied across the Scottish Highlands. The SAIS recorded 171 avalanches in the period(1). In contrast, the winter only 3 years previously featured widespread unstable snow leading to 212 recorded avalanches*. So you can see that avalanches in Scotland are relatively common, but vary significantly from year to year.
*This unusually snowy season included surprisingly few human-triggered avalanches. Perhaps greater vigilance resulted from Covid travel restrictions.
Scotland doesn’t really have an ‘avalanche season’. Slides occur in response to daily and weekly changes in snow stability and weather conditions.
What type of avalanches do you get in Scotland?
By far the most common type of avalanche in Scotland involves windslab. This relatively dense and brittle type of snow results from wind action. It often develops on lee (wind-sheltered) slopes and can be much less stable than it appears. In fact, it can be so unstable that an impact in one location can cause a windslab avalanche to begin many hundreds of metres away (‘remote triggering’). Strong winds are the cause of another common winter hazard: cornices. These overhanging lips of snow can be enormous and trigger big avalanches when they fall onto slopes below.
Characteristics of windslab snow
- ‘Squeaks’ underfoot
- Clear footprints and sharp edges
- Cracks readily
- Breaks into blocks
- ‘Woompfing’ noises
- Relatively dry
- Bright, matt white colour
- Builds in lee areas
However, strong winds aren’t the only factor at play in Scottish winter. Because our mountains have a ‘subpolar oceanic’ climate type (based on the Köppen index), winters are also relatively mild and humid. Thus, very high temperatures and/or rain often result in a ‘purging’ of unstable snow from steeper areas as multiple wet snow avalanches – potentially even in mid-winter! These wet snow avalanches can be so powerful that sometimes the entire thickness of snowpack detaches from the ground (‘full depth’). Our relatively mild humid climate type means thaws are common and powder snow avalanches are unusual.
Next, let’s look in more detail at the events that trigger avalanches.
What are the main causes of avalanches in Scotland?
As mentioned before, windslab is a common type of snow in the Scottish mountains. It forms layers that can crack easily and, being cold and dense, it tends not to bond well to other types of snow. Unfortunately, this makes it prone to avalanche.
When an avalanche ‘triggers’, a weak layer within the snowpack detaches and slides downhill. As we saw previously, common avalanche triggers in Scotland include rapid temperature rise, cornice collapse, heavy snow and/or rain. ‘Natural’ triggers such as these account for the majority of our reported avalanches. However, human triggers are also possible. To illustrate, skiers, hikers and climbers triggered 17 reported avalanches during the 2023/24 Scottish winter season (total: 171 avalanches, source: SAIS).
⚠️ Statistically, most avalanches trigger on slopes of between 30° and 45°.
17 reported avalanches were caused by skiers, hikers or climbers during the 2023/24 Scottish winter season
Avalanches occur because of a significant difference in hardness, wetness or temperature between one or more subsurface snow layers. But sometimes a particularly weak, thin and deeply buried layer is the culprit. These weaknesses (called ‘Persistant Weak layers’) frequently occur in Scottish winters and consist of specific snow crystals such as ‘facets’, hoar frost , powder snow or graupel. Thin layers of ice can also form weaknesses.
Snow structure
As we know, snowflakes are actually crystals of frozen water (ie: ice). Although snowflakes are infinitely variable, they build up in layers of roughly similar crystals. Each layer also contains some liquid water and water vapour. However, no two layers are exactly the same and their structure changes with time. Because of this, some layers bond together better than others.
Compared to Europe or North America for example, avalanches almost never threaten roads or dwellings in Scotland. This is mainly because our mountains are smaller and infrastructure is usually well outside of avalanche zones. For similar reasons, Scottish forests almost never feature avalanche paths.
Scottish avalanche forecasting
Scotland is infamous among avalanche professionals for variable snow conditions and changeable hazards. Like other countries, we have our own government-funded avalanche reporting organisation. The Scottish Avalanche Information Service, as it is known, covers six areas: Lochaber, north Cairngorms, south Cairngorms, Glencoe, Creag Meagaidh and Torridon (see map). Each day throughout the season one or two expert forecasters travel within their assigned area and collect observations about the weather and snow distribution and stability.
📖 In the famous book
‘A Chance in a Million? ‘ Bob Barton and Blyth Wright describe their study of avalanches in Britain and the creation of the SAIS.
Scottish Avalanche Information Service forecasting areas
The six forecasting areas cover the most popular mountaineering and off-piste ski areas. Those travelling outside or between these areas must be extra cautious when interpreting forecasts and planning routes. A case in point was the exceptional winter of 2000/2001. During this season ski tourers and hikers witnessed avalanche activity much further south and at much lower elevations than normal (for example, on the sub-600m Pentland Hills near Edinburgh)(2).
International hazard scale
The internationally-agreed avalanche hazard scale features 5 precisely defined and colour-coded risk levels. They are:
- Low (green)
- Moderate (yellow)
- Considerable (orange)
- High (red)
- Very High (black)
Observers use a complex matrix to decide the risk level for the forecast period.
The SAIS works hard to deliver clear and accurate daily forecasts throughout the season, which are easily accessible online and in local outdoor shops. A great deal of international research and shared experience helps shape these reports, but avalanche accidents still happen which require rescue. This is what we will look at next.
Avalanche rescue in Scotland
Although burials are statistically rare, it remains true that victims almost always trigger their own avalanche. Survival time is approximately 15 minutes following burial, with only a very few victims surviving longer than this. ‘Companion Rescue’ offers by far the best chance of successful recovery because it can begin within seconds. It involves the victims companions following a strict search pattern using avalanche transceivers (see below).
Personal avalanche safety gear
Experts recommend companion rescue training for off-piste skiers and mountaineers in Scotland. This involves using avalanche transceivers, a probe and shovels to quickly find and dig out a buried victim. Outdoor shops in the main climbing and ski areas both sell and hire these items, making them relatively accessible. Interestingly, Avalungs and avalanche airbags are not a common part of people’s ski touring kit or winter mountaineering kit in Scotland. Why? Long, steep approaches, plus short descents probably make the weight and cost of these items hard to justify for most people.
victims almost always trigger their own avalanche
In contrast, mountain rescue team response times are 1-2 hours minimum, meaning they will almost never arrive within the critical 15 minute survival period. However, Scottish mountain rescue teams are well practised in avalanche techniques including the use of search dogs and line probing. Local ski patrollers and (weather permitting) coastguard helicopters can also provide valuable assistance.
Chalamain Gap avalanche
One of the Scotland’s largest scale avalanche rescues occured on the 14th February 2013 in the Chalamain Gap in the northern Cairngorms. Mountaineers triggered an avalanche which hit other mountaineers in a gully below. The estimated 75,000 tons of snow flowing into the gully resulted in a very deep accumulation of debris (7m), a situation known as a ‘terrain trap’. Rescuers reached one of the victims after nearly 2 hours of digging. 51 rescuers attended, along with search dogs and a helicopter. Tragically, 3 people died(3).
Survivors of heavy windslab avalanches often suffer traumatic injuries in addition to hypothermia. Although rescue teams possess the skills and equipment for dealing with this in the short term, casualties urgently need specialist hospital treatment. Acute care is available in only 4 hospitals in Highland region, namely Inverness, Wick, Oban and Fort William and ‘free at the point of need’ under the NHS. All mountain rescue, coastguard and helimed services in Britain are provided free of charge to the public (hence you do not need medevac insurance for winter activities). Notably, our mountain rescue teams are all charities with volunteer staff.
Do Scottish resorts use bombing for avalanche control?
Compared to many alpine countries, Scotland’s five small ski areas rarely if ever needed to use explosives for avalanche mitigation. Nowadays ‘piste bashers’ plough unstable slopes, sometimes tethered by a steel cable.
The famous saying ‘Avoidance is better than cure’ certainly applies to avalanche safety. Thus, our final topic is the role of avalanche education in Scotland.
Avalanche awareness and avoidance
As we have seen, avalanches are a signifiant risk in Scotland’s winter mountains, and human-triggered ones especially so. In fact, research strongly suggests that being avalanched is likely the result of your or someone elses actions, rather than a random natural event.
As you can see in the graph below, multiple human-triggered avalanches occur annually in Scotland, some of which sadly result in fatalities. The number of incidents has varied greatly over the years, likely due to many factors (which are beyond the scope of this article). In a bid to reduce accidents most providers of mountaineering and backcountry skills training in Scotland include avalanche education on their courses.
In addition experienced hikers, mountaineers and skiers may also attend a specialist ‘avalanche awareness course’. The course syllabus usually includes snow hazards, risk mitigation and companion rescue, together with up-to-date research on topics such as psychology and avalanche transceivers.
The ‘snow pit’ is a good example of how research informs best practise. Many years ago this was the key method for determining slope stability. However, studies suggested that using snow pits to determine avalanche hazard was too unreliable and time-consuming for most winter sports enthusiasts. Modern courses instead focus on studying forecasts, planning safer routes and continuously monitoring weather and snow conditions. Many courses also provide basic training on the psychology of decision-making, for example group organisation, situational awareness and ‘heuristic traps’ (see box).
Heuristic traps
Heuristic traps are well-known psychological ‘shortcuts’ which can cause individuals to unwittingly make poor decisions. The snowsports community know them by the following terms:
- Familiarity
- Acceptance
- Comittment
- Expert Halo
- Tracks (Social Proof)
- Scarcity
Beginners Ski Touring course (1 day)
Take the guesswork out of backcountry skiing by learning the basics on this popular one day intro course.
Based near Aviemore in the Cairngorms.
In addition to specific awareness courses, the standard of avalanche knowledge and skill amongst leaders and instructors is generally quite high, thanks to rigorous qualification processes and CPD (continuing professional development). Furthermore, the public can access excellent training materials and opportunities through various means including workshops, talks, ‘transceiver parks’, clubs, books, social media and the internet.
The avalanche doesn’t know you’re an expert
André Roche, Swiss avalanche researcher
Hopefully this post has given you a good overview of avalanches in Scotland’s winter mountains – what they look like, how they occur and how forecasting and mitigation works. Get good training, learn continually and adopt sensible safety margins and you should have many avalanche-free winter adventures.
Avalanches are a regular occurance in the Scottish Highlands during winter. Many are relatively small and go unreported, but a significant number are human-triggered and are capable of burying skiers.
Basically, avalanches start when one layer of snow slides upon another layer below it. Avalanche hazard depends on many factors, including slope angle, snow depth, temperature, moisture, slope shape and snow crystals.
These mental ‘rules of thumb’ which can actually result in poor avalanche safety decisions. Key ‘heuristic traps’ are Familiarity, Acceptance, Commitment, Expert Halo, Social Proof and Scarcity.
References
- 2023/24 Winter season report, SAIS
- 2000/01 Winter season report, SAIS
- Chalamain Gap Inquiry, SportScotland, 2013
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