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Avalanche Warning Signs

Tristan Gooley
Avalanche Warning Signs

In some areas niche expertise is vital, literally.

The signs that warn of avalanches can be life-saving.

Nik Huggins spoke to Alan Halewood (pictured) for an inside track.

Alan Halewood has been winter walking and climbing for over 30 years. As well as holding the Winter Climbing and Mountaineering Instructor qualification he helps to train and assess new Award holders. He has worked and played in the mountains in locations as far apart as Antarctica and Afghanistan and still enjoys exploring unclimbed peaks and climbs more than anything else. Based in Fort William, Scotland, he teaches climbing and mountaineering year-round.

Alan Halewood

We spent some time with Alan to talk avalanches, winter navigation, near misses on Ben Nevis and how the clues and signs all around us in the winter environment can help us stay safe in the mountains…

Can you describe what’s taking place when an avalanche occurs?

An avalanche occurs when a mass of snow slides down a hill or mountain when something happens to release it from whatever surface it’s sliding on. The layers often break up as they slide down and on the way down they can collect debris like rocks, earth, trees or even people. The sliding surface could be a different layer of snow, or it could be something like a grassy hillside or a massive sheet of rock that’s buried beneath the surface.

What causes them?

An avalanche is usually caused by the layers of different consistency which are in turn are caused by varying weather factors, such as wind speed and humidity. The layers may not be well bonded to each other and something like a person walking on a layer or a cornice dropping onto it can overcome the bonds between the layers and that causes the slide to begin.

So, to create an avalanche we usually need a weakness in the snowpack and a trigger. One of the most common triggers is us adding a load to the surface of the snow. The instabilities can be caused by things going on inside the snowpack like moisture adhering to particular snow crystals, or, and this is very common Scotland, windslab of different consistency.

What’s windslab?

Windslab is caused when snow is affected by even moderate windspeeds, creating a cohesive layer of snow that’s all been subjected to similar weather conditions. That layer may not be very well bonded to a lower layer of older snow that’s been through a different weather experience.

What else can cause different layers to form?

Graupel, which is rounded balls that were snowflakes that got iced up by moisture and buried in the snowpack. A sudden squall changes the density of snow, creating instabilities. You can also get new triggers such as melting snow dropping from rocks or these collapsing cornices. As the weather changes it builds up a different history of the snow within these layers.

So would you say that the more disruptive the weather, the greater chance of avalanches?

Yes and this is the British problem, we have this incredibly dynamic weather system and because our weather changes so rapidly we have a really complex avalanche situation. Far more so than say a North American climate, where in general layers form and sit there for long periods, sometimes even a whole season. Whereas in our climate things change regularly, so that the snow you were happy walking on in the morning may not be safe to walk on in the afternoon.

What continues to interest you about them?


 As well as them being awe-inspiring and complex natural events I have to understand something about them to avoid them. I have been involved in avalanche situations four times and my behaviours have been forced to change accordingly. Because I’m out in a winter environment, they’re an important part of what I’m teaching people.

They’re also part of this incredible dynamic natural environment that we see in winter. Snow’s fascinating, fun and beautiful but if you don’t treat it with respect it can also be harmful.

The wind has scoured the plateau and deposited windslab around the rim of the coire

Is the avalanche activity we see in the UK unique?

Yeah, because our weather patterns are incredibly dynamic. There’s a handful of other places in the world that have this similar situation where they have a massive body of water just off the coast. Ours is driven by the Atlantic, which means we see these hugely variable temperatures, windspeeds, precipitation levels and types and that means our snowpack changes, even over short periods of time. Traditionally alpine snowpack are slower changing – weaknesses might persist for a month or even a season which makes them more predictable. But we’re seeing that with climate change alpine forecasters are already seeing faster moving changes in the snow.

The Scottish Avalanche Information Service (SAIS) have a really complex task interpreting the snowpack of any given day and then using weather forecasts to extrapolate a forecast for the next day’s avalanche hazard. Their experience of our dynamic environment is going to start feeding back into how forecasters operate in other parts of the world.

So as climate changes intensifies that will have a knock on effect?

Definitely. Dynamic weather equals dynamic snow equals dynamic risk assessment and decision making on the hill.

In your lectures, you talk about the precautions we can take to avoid avalanches – tell us more…

So you start with the SAIS website. Every day in winter a team of highly-trained forecasters go out in six different areas of Scotland, making observations of what they see on the hills. They combine this with a detailed forecast from the MET office to create a predictive forecast of what the hazard will be, where it’ll be and how bad it’ll be tomorrow. The SAIS website gives you all this information in a written form and a pictorial diagram. The scale, colours and definition of hazard used is common throughout the world

This is the pancake visual?

That’s right. The fortune cookie or ‘pizza of death’. The picture is easy to remember but it’s part of a process that asks you to consider three things: The weather and the snow, the terrain you’re travelling through and the people who are going with you. You do this in great detail in the planning phase – when you’re sitting at home making nice informed decisions with less of the conflicting problems you’ll encounter on the hill. Then, on your journey you look at the same three factors again, to confirm whether all the forecasted information you based your plan on is correct, because if things aren’t as they were forecasted to be in any of those variables your plan won’t be as effective. The third part of it is to pick a few key places before you go out, places where there are decision points where you can choose which way to proceed.

It’s important we verbalise the same three factors again and again, making the decision-making process conscious and out loud instead of subconscious and assumed in the back of the mind.

Can you explain a bit more about the relationship between Avalanches and Natural Navigation?

If you don’t know where you are and you don’t know where the problem is there’s no way you can avoid it. The avalanche forecast is very good at showing you which slopes, which aspect, which altitude there’ll be a problem on and if you can’t move around the mountains effectively determining how high up you are, or which angle is this slope, for instance, then you can’t avoid the hazard.

I’ve been lucky enough to climb on every continent and the weather conditions we face in Scottish winter are as fierce as anywhere in the world, so your navigation skills have to be good enough to cope with that environment. I’ve had a worse kicking up here than just about anywhere!

Are there any natural clues and signs we can use to spot avalanche activity?

When I’m on the hills I’m constantly clue gathering. Nothing is there by accident. And there are many signs to look out for…

Do I see windblown snow travelling on the ridge crests? Is that snow depositing in little hollows or filling the footsteps of the person in front of me? Where’s it coming from and being deposited?

On a poor visibility day even a single rock in front of me will offer lots of information. Snow deposited on the lee of that rock could show where it’s being deposited to on a larger scale. I can extrapolate that model to show how snow is being deposited on larger features like ridges.

On the other side of the rock I could see hard feathers of rime ice growing into the wind as moisture adheres to a cold surface. I need to know how old they are – were they formed recently or do I know enough about the history to say that’s old news I don’t need to worry about.

Sparkly, delicate snow crystals like tiny fish scales on the surface of the snow pack while beautiful are a potential weak layer.

Is water running below the ice telling me I haven’t reached the freezing level yet?

How reactive is the snow overall is it well-bonded and stubborn or is it touchy? Sometimes as you’re walking along a footprint can cause a fracture between the layers. A sign of this can be a shooting crack away from your foot. Or you may hear woomphing noises indicating how much energy might be stored in the layers.

Another clue to spot on the ground are inverted footprints that signal strong winds. These are footprint shapes that stick up, a few inches above the snowpack. This is caused when somebody has been walking through soft snow, and their weight has compressed the snow under their feet. Then, the wind comes along, stripping away all the softer snow around the footprint, whilst leaving the compressed snow behind. I’ve even seen examples of this with Mountain Hare tracks.

You get beautiful features like Sastrugi, an Eastern European word, which refers to planed wood-shavings. Winter winds can create similar patterns in the snow and you see these beautiful curling features or sculpted edges where the wind has come over a slope and begun to strip back the edge of a layer and re-distribute it to other places.

All of these are clues that tell me where has the wind been coming from, how strong is it and where’s it sending the snow.

These blocks show the thickness of the layer of windslab in this small purposely released windslab avalanche

Can you use signs like these to predict avalanche activity?

Possible yes. To do it really well you need to be very experienced with the different kinds of avalanches we get. You’ll need to be out in it a great deal to build a picture and history of how the snow pack has developed. You also need to be able to forecast the weather with a high degree of accuracy. The be avalanche aware process encourages us to use the clues and signs we see on the hill as a key part of our decision making process, to confirm or deny what was forecast and to tell you whether your plan is a good one for that day.

How much of our awareness of avalanches is determined by our own psychology?

This is the big area of change in education over the past decade or so.

Novices have an advantage in that they soon understand how much they don’t know and act accordingly. Really experienced hill-goers are often more at risk of making errors. The winter environment gives them what we call ‘ugly feedback’. People out on the hill make decisions and because they didn’t get avalanched they believe that they made really good choices. In fact, all to often they may have just been lucky – an hour later or 5 metres to the left the same slope they crossed might have avalanched. Getting away with it creates an illusion of expertise. I’ve been into number 5 gully on ben Nevis countless times and because I’ve never been avalanched there’s a bit of my brain that thinks: ‘I’ll probably get away with it today too’ and thus you fall into the trap of familiarity. It’s far safer to adopt a beginner’s mindset, taking each day on its individual merits. We need to stand the pyramid on its head.

What advice would you give to Natural Navigators who want to explore the mountains in winter?

Be curious. Be observant. What kind of snow can you see? Snow’s not homogenous, so ask yourself why it formed, why is it here? Embrace your inner snow geek.

Do rely on using the Scottish Avalanche Information Service forecasts. You can learn so much about snow by digging around on that website. Do read the words don’t just look at the pictures. Make conservative decisions on where to go. The mountain’s not going anywhere, the trick is to make sure you’re there to enjoy it as well. Go and learn about snow, go play in it and find out about it. It’s amazing stuff!

What are your top three clues and signs for avalanche warnings?

Wind. If I’m seeing snow on the move I want to know how much, where, when – watch the wind and how it’s interacting with the snow.

Temperature – if we get sudden rises that’s a de-stabilising influence and conversely if it’s been warm, cooling will stabilise the situation. The freezing process is our friend.

The third one is probably types of weak snow that raises a red flag – the evidence of graupel, sometimes called soft hail, for example can create an unstable layer. If this stuff is covered by fresh snow it’s like having a load of ball-bearings hidden beneath our feet.

Can you describe any personal near misses you’ve had?

I had a blue-sky day, so me and another experienced mountaineering instructor headed out to some rarely formed ice climbs near Ben Nevis. The avalanche forecast that day was moderate, which means they’re out there if you go looking for them.

We strolled in in the sunshine, quite happy, aware in the background that there was snow on the move but we had a fixed idea of doing an ice climb called ‘Italian Right Hand’ as a warm up for a harder route called ‘Panther Rose’. My friend led the first pitch, he put a couple of screws in as I paid out the rope and suddenly it went dark as a wave of snow washed down the crag. I heard a grunt and bang and when I opened my eyes the snow had finished falling and he was sitting there in the snow in front of me with a broken leg. He’d been swept off by a windslab layer.

Within an hour a mountain rescue helicopter had arrived and I was helping a winchman scoop him up, but like any other parsimonious mountaineering instructor he made us get his harness and trousers off him because he knew when he got to hospital they’d be cutting those off with shears. Meanwhile, I made my own way down the mountain carrying both rucksacks and all our gear. The photos of that day make for a great lecture on how two experts can fall into all the traps and get themselves avalanched.

For more on Alan Halewood

For more on the Scottish Avalanche Information Service

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