Avalanche Awareness: Part 3: Recognising Avalanche Terrain: A Critical Skill for Backcountry Safety

In the first part of this 7-part course on avalanche safety, we explored the types of avalanches, their causes, and the risks they pose. In the second part, we covered essential avalanche equipment—your lifeline in the backcountry—and emphasised the importance of not only carrying the right gear but also knowing how to use it effectively.

Missed Part 2? Click here

With that foundation in place, this third section focuses on one of the most vital skills in avalanche safety: recognising avalanche-prone terrain. 

Avalanches don’t happen randomly—they are tied to specific terrain features and conditions. Learning to identify these areas is crucial for safe travel in the backcountry. Even small avalanches can be fatal if the terrain amplifies their impact, so understanding these hazards is critical for making smart route choices.

Let’s break this down into the factors that influence avalanche terrain: slope angle, slope aspect, terrain traps, and other features like cornices. By the end of this section, you’ll have the knowledge to evaluate terrain and make more informed decisions in avalanche-prone areas.

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Slope Angle: Where Avalanches Happen

The steepness of a slope is one of the most critical factors in determining avalanche risk.

• High-Risk Angles:
• Most avalanches occur on slopes between 30° and 45°.
• Slopes steeper than 45° often shed snow naturally before large accumulations can build, while slopes below 30° rarely produce avalanches except under unique conditions (e.g., wet snow avalanches or extreme loading).
• How to Measure Slope Angle:
• Use an inclinometer to measure the angle of the slope. Many backcountry ski poles have built-in inclinometers, or you can use smartphone apps like Theodolite (but ensure your phone is charged and functional in the cold).
• Estimate angles visually when possible, but rely on tools for precision—eyeballing can lead to dangerous misjudgments.

Slope Aspect: How Wind and Sun Affect Stability

The direction a slope faces (its aspect) plays a huge role in avalanche risk because of how wind and sun affect the snowpack.

• Leeward Slopes (Windward vs. Leeward):
• Leeward slopes, or those facing away from the wind, tend to accumulate wind-blown snow, creating wind slabs—dense, heavy layers that are often poorly bonded to the snow below. These slabs are highly prone to triggering.
• Windward slopes (those facing the wind) often have less snow and may be scoured down to harder layers, reducing avalanche risk but posing other hazards, like ice.
• Solar Radiation (Sunny vs. Shady Slopes):
• South-facing slopes (in the Northern Hemisphere) receive more sunlight, which can destabilise the snowpack during warm periods, especially in the spring. Wet avalanches are more likely on these slopes.
• North-facing slopes remain colder, preserving weak layers for longer and increasing the likelihood of dry slab avalanches.
• Actionable Tip: Be mindful of how the aspect of the slope aligns with recent weather conditions. For example, after a storm with strong winds, prioritise routes that avoid leeward slopes.

Terrain Traps: Amplifiers of Danger

A terrain trap is any feature of the landscape that can increase the consequences of even a small avalanche. These areas are particularly dangerous because they concentrate snow, debris, and victims, making rescue more difficult and survival less likely.

Common Terrain Traps:

1. Gullies and Creek Beds: These natural depressions act like funnels, concentrating snow and debris. Avalanches in these areas can bury victims deeply, making rescue efforts much harder.
2. Cliffs and Rock Bands: Being swept over a cliff or pinned against rocks is a common cause of trauma-related avalanche fatalities.
3. Tree Wells: These are hollows formed around the base of a tree, often hidden beneath fresh snow. Avalanches can push victims into these wells, where they become stuck and immobilised.
4. Flat Runouts: Flat terrain at the base of a slope can seem safe but often becomes a deposition zone where snow piles deeply during an avalanche. This creates a high risk of burial.

How to Avoid Terrain Traps:

• Plan your route to stay above or well clear of these features whenever possible.
• If you must cross potential traps, move quickly and expose only one person at a time.

Cornices: Hidden Hazards Above

Cornices are overhanging masses of snow that form on ridgelines due to wind. While they might look stable, they are often precariously balanced and can collapse under weight, vibration, or warming temperatures. Cornices are double hazards because they:

1. Can trigger avalanches on slopes below when they collapse.
2. Can cause injuries or fatalities themselves if you fall with one.

How to Safely Navigate Cornices:

• Stay Back: Keep a significant distance from the edge of ridgelines, as the true edge of a cornice is often farther back than it appears.
• Avoid Stopping Below: When traveling in valleys or across slopes, identify potential cornices above you and avoid stopping in areas where they could collapse.
• Beware of Shadowing: Cornices are often difficult to see from above, especially in low visibility. Use a probe or cautious approach to ensure you’re not walking on overhanging snow.

Other Terrain Considerations

Convex vs. Concave Slopes:

• Convex Slopes: These bulge outward and are more likely to trigger avalanches, as the snowpack is under tension at the transition point.
• Concave Slopes: These curve inward and can sometimes be safer as they distribute weight more evenly, but they often lead into terrain traps like gullies.

Anchors (Trees and Rocks):

• Trees, boulders, and shrubs can sometimes stabilise snow by acting as anchors, especially in dense forests. However, sparse trees can be deceptive, as they often do little to stop avalanches and may even increase trauma risk during a slide.

Practical Examples of Recognising Avalanche Terrain

1. Scenario 1: After a snowstorm with high winds, you’re skiing in a backcountry bowl. The slope is 38° and leeward, with visible signs of wind deposition. You notice a gully at the base.
• Risk Assessment: High avalanche risk due to slope angle, wind loading, and the terrain trap below. Avoid this slope.
2. Scenario 2: You’re traversing a ridge line on a sunny day in spring. The ridge has large cornices hanging over a north-facing slope.
• Risk Assessment: High risk of cornice collapse due to warming. Stay well back from the edge, and avoid traveling directly below the slope.
3. Scenario 3: You’re ascending a steep couloir with no visible cracks or recent slides. The slope angle is 50°, and the snow feels loose underfoot.
• Risk Assessment: Lower risk for large slab avalanches but higher risk for loose snow avalanches due to steepness and unconsolidated snow.

Key Takeaway

Recognising avalanche terrain is not just about identifying dangerous slopes but understanding how the terrain interacts with snow conditions and weather. Use tools like inclinometers, study the landscape carefully, and plan routes to avoid high-risk areas like leeward slopes, terrain traps, and cornices. Always be willing to adapt your plan based on the terrain you encounter and the conditions of the day.

Ready to follow onto the next lesson? Click here for chapter 4 - Field Observations and Snowpack Testing: Assessing Stability in Avalanche Terrain