Avalanche Awareness

A large slide in the Val d’Arpette on the second day of the Haute Route

In this upcoming series of blogs we are going to look at some factors that go into helping us make better decisions when we are travelling in snowy mountains. This applies to climbers, skiers, riders and extreme sledgers. 
Over the coming weeks we are going to explore some parts of the avalanche phenomenon and how to plan better for travel in avalanche terrain. However these blogs are in no way a replacement for proper avalanche training with a professional.

Avalanche Terrain
Choosing the correct terrain is the one tool we really have control over when we go out into the mountains in winter. Therefore, let us dig into some factors that go into helping us look at terrain as it relates to the avalanche issues. 
There are 5 main factors we need to consider when thinking about avalanche terrain. They are: Slope Angle, Aspect, Elevation, Trigger Points and Terrain Traps.

Slope Angle
The first step of terrain assessment is to identify whether we are in avalanche terrain or not. If we are travelling below treeline we can look for vegetation clues. Is there a large swath of trees that have been cut out of the terrain? Do any of the trees have obvious snapped (flagged) branches that all occur at the same height? All these are clues that you are in terrain that has avalanched in the past. Now in Scotland and the Alps the treeline doesn’t go very high so here we need to think primarily about slope angle. 91% of avalanches are triggered on slope angles between 30* and 45* with avalanche activity peaking around 38*(1). To give people a perspective of what that means a European Red Ski run will be 36* maximum slope angle. Basically right where most people want to ski is where the slopes are most dangerous. For climbers, think of the approach to any classic gully. The gully itself is maybe too steep to develop a slab avalanche but most gullies gradually ramp up in steepness so at some point you will cross through the “danger zone”. Be sure to think not just of the slope you are travelling on, but also what is above you. In certain conditions being connected to or below a steep slope can also be dangerous. So get out a map, measure your slope angles using the contour lines, then verify on the ground using an inclinometer (a tool that is always in my pocket when I ski).

Safe fun skiing below on the last day of the Haute Route

Aspect refers to the direction the slope we are travelling on faces. Often avalanches are confined to certain aspects. An example of this might be when the wind has been blowing from the south, it will deposit snow on the north side of the mountain, therefore increasing the hazard on the northern slopes. At the start of the day we might choose to totally avoid that aspect. Being aware of which side of the mountain we are on is very important. So, when wandering around on the Monroes in the clagg be sure to have your map and compass ready to check the direction the slopes face. Pay attention to subtle changes in a slope. Although the North Face of Ben Nevis faces north, ridges and terrain features create E, NE, NW and W facing aspects also.

This bowl in Rocky Mountain National Park has a variety of aspects in close proximity

As our Elevation on the mountain changes so do the avalanche conditions. When you get higher in the mountains, the weather is more extreme: colder, snowier and windier. Therefore, the avalanche danger is normally greater the higher your elevation. The main exception to this is when we are dealing with wet and warm snow. In this situation, there will be more danger on lower, warmer elevations. Avalanche forecasts predict the danger at different elevations so be sure to pay attention to this when planning and travelling in the mountains.

Trigger points are areas in the snow where you are more likely to trigger a slide. Trees, rocks and convex rolls are all areas where the snow is either weaker, or under strain, and therefore more likely to be a location where an avalanche can be triggered from. These areas should be avoided. 

This small avalanche in Colorado was enough to kill someone Photo: CAIC

Terrain traps are features in the terrain that increase the consequences of an avalanche. This might be areas where avalanche debris will pile up deeper (like a gully or a stand of trees). They might be an area of cliffs where you could get swept off; or maybe a body of water that could drown you. When you are climbing Point 5 Gully on Ben Nevis after the main ice pitches, the slope angle gets less and the climbing easier. However, you still have large cliffs (terrain trap) below you and even a small avalanche in this terrain could be devastating to an unroped party. Many climbers have died through letting their guard down in terrain like this.

As I mentioned before, our terrain choice (where we choose to go)  is the one parameter we have control over in the mountains. We don’t get to choose what the weather does or what the snow under our feet is like, but we can choose where we travel. So, if you have uncertainty choose safer terrain that is lower angled or a safer aspect/elevation. One of the keys to this is good planning so you always give yourself options (more on planning later). There are days when the best terrain choice is going to the Ice Factor! Want to know more?

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