As wintry conditions develop on the hills, we put questions from Walkhighlands users to Scottish Avalanche Information Service co-ordinator and senior forecaster for the Cairngorms, Mark Diggins.
1. How many avalanches are there in Scotland a year involving walkers and what are the most common causes?
During last winter 2019/20, 27 avalanches were human triggered – this basically means that they were set off by people who were traveling in avalanche start zones in avalanche terrain (see diagram below) walkers are equally susceptible in terms of entering this type of terrain when following paths that are covered by snow. For example, heads of glens, summit snowfields, and slopes to cols where the angle approaches the critical angle of 37 degrees.
The 27 avalanches last winter involving people included:
- 10 avalanches control triggered by Scottish Avalanche Information Service (SAIS) personnel/ski patrol/others during the avalanche hazard assessment process including one triggered using an explosive.
- 7 triggered avalanche involved people on skis or snowboards.
- 19 triggered avalanche involved people on foot either walking or climbing.
- 15 people in total were carried down by avalanches.
- Tragically, one fatality was recorded due to avalanche activity last year .
A number of avalanche occurrences with human involvement were minor, in that small releases occurred, but others were more significant and resulted in people being carried down by the avalanche, some with very lucky escapes.
2. How is the avalanche risk calculated and how up to date are the forecasts?
Avalanche hazard information is provided on a daily basis in the following 6 main mountain areas of Scotland: Torridon, Northern Cairngorms, Southern Cairngorms, Creag Meagaidh, Lochaber and Glencoe. Avalanche hazard assessment is achieved by traveling through the mountains on foot or ski, carrying out snow profiles and field observations, in combination with other factors. Having carried out snow observations and avalanche hazard evaluations in the field, the SAIS forecaster will begin to compile the avalanche forecast at the area base. A weather forecast provided by the Aberdeen Met Office team and discussion with the on duty weather forecaster (usually around mid afternoon) provides information which enables us to determine weather effects on snow distribution and snowpack stability. An avalanche hazard forecast is then produced and after discussion and verification between forecasters and the SAIS coordinator, an avalanche report is published, usually between 4 and 5pm each day.
3. What risk is too high to sensibly attempt a route?
Avalanches can potentially be triggered at any hazard level therefore it is important to read the text in avalanche reports as this will describe where instabilities may be located. At Low and Moderate levels the possibility of being avalanched will be limited to steep terrain in specific places. During Considerable and High avalanche hazards, avalanches will be larger and run further, therefore where you are in avalanche terrain will become very important. If you are in an avalanche path or a deposition zone you may still be exposed to danger and be affected.
4. Is there a slope gradient below which avalanches will not occur?
Usually below 20º is ok but looking at terrain and managing where you plan to go is important – wind swept places, ridge lines are safe options.
5. Is there a danger that many hill-goers rely on the avalanche forecast too much to assess whether a route will be safe, rather than learning to check and understand conditions on the ground as they do the walk?
Planning ahead by looking at weather forecasts, avalanche reports and condition reports is most important. Checking and reviewing conditions as we travel on foot is also a very important and is part of the process of decision making and safe travelling in the mountains. We would recommend that the Be Avalanche Aware app is downloaded and used in the planning process.
6. What should winter walkers be looking out for while out in the hills to provide extra warning of potential avalanche risk?
The BAA app is a useful tool as this describes, with diagrams and video clips, what you should look out for on your journey as well as containing tools that can be used to check slope angles and slope aspect avalanche hazard from SAIS reports.
7. I understand that conditions in Scotland can never justify a “Very High/5” avalanche risk rating on the European scale which the SAIS uses. Could this affect risk assessment by hillgoers – e.g. “Considerable” being a 3 on a scale of 1-4, not a scale of 1-5.
For this reason we do not use numbers as there is a risk of incorrectly using the number scale solely as a measure of hazard and risk. We are looking at displaying the hazard as four levels as Very High hazard is highly unlikely in our mountains due to scale and snow amounts.
8. Following an accident, the media will often report something like “the avalanche forecast was considerable” as a subtext that people shouldn’t have been out on the hill. Is misreporting undermining understanding of the importance of slope aspect, and of assessing conditions when out on the hill?
Difficult to answer this question as it depends on an understanding of the actual situation on the ground and the circumstance, activity and location of those affected in an incident.
We use the hazard rose in our reports to illustrate the range of hazard according to slope aspect, this helps with route choice and illustrates that the stated avalanche hazard isn’t everywhere in the landscape.
9. I know many people who never look at the avalanche forecast – do you have any numbers on how many people check the forecast and do you have any ways of trying to reach the many new folk who took up hillwalking after lockdown and will be heading for their first winter in the hills this year?
Yes there are many people that go into the mountains who may not know that the SAIS exists or may not think that referring to our service is relevant to their activity. It is always important to refer on a daily basis to weather, avalanche and conditions reports as this is critical information to consider, especially in our winter environment that can be both incredibly harsh and rapidly changing.
Over the course of the winter (we operate around 4 months) mid December to mid April, we can have up to 300,000 views of our avalanche reports and 700,000 views of our blogs that illustrate the mountains and describe conditions.
We expect and are conscious that potentially there will be many many new folk wishing to explore and enjoy the winter mountain following lockdown. The SAIS like all other agencies will be collaborating on campaigns and using opportunities to inform as best we can. Forums such as Walkhighlands also has a part to play in passing on information and articles like this will help.
Many thanks to Mark, and to everyone who sent in questions.
Full avalanche forecasts will start on 11 December for all 6 regions with a standby service for Northern Cairngorms and Lochaber regions in the meantime when significant winter conditions are present. Visit the Scottish Avalanche Information Service website for more information or download the Be Avalanche Aware app.