Avalanche Awareness: Part 4: Field Observations and Snowpack Testing: Assessing Stability in Avalanche Terrain

In the first part of this 7-part course on avalanche safety, we explored the fundamental types of avalanches, their causes, and the risks they pose. In the second part, we delved into essential avalanche equipment, emphasising the importance of carrying and practicing with the right tools. The third part focused on recognising avalanche terrain, teaching you how to identify features and conditions that elevate risk.

Missed Part 3? Click here

Building on that knowledge, this fourth section examines how to assess the snowpack in real time. Avalanches are not just about terrain—they are also about the snow itself, a dynamic system that evolves constantly with changes in weather, temperature, and wind.

In avalanche terrain, ongoing assessment of the snowpack is critical for staying safe. While no single test or observation guarantees safety, combining techniques like visual observations, listening for warning signs, and conducting snowpack tests can provide valuable insights into its stability.

This section will teach you how to read the snowpack, recognise signs of instability, and conduct effective tests in the field. By learning these skills, you’ll be better equipped to predict risks and make smarter, safer decisions. Let’s get started!

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Visual Red Flags: Clues You Can Spot Without Tools

Certain visual signs can indicate dangerous snow conditions. Always stay alert for these “red flags” during your journey:

1. Recent Avalanches Nearby
• What It Means: If avalanches have occurred naturally in the area, it’s a strong indicator of unstable snow conditions. Look for fresh avalanche debris, broken cornices, or crown fractures (the upper edge of a slab release).
• Actionable Tip: Treat slopes near recent slides with extreme caution—they may still be primed for another release.
2. “Whumpfing” Sounds
• What It Means: A “whumpf” is the sound of a weak layer collapsing under your weight, a clear sign of instability in the snowpack. This often occurs in areas with buried weak layers, like faceted snow or surface hoar.
• Actionable Tip: If you hear a whumpf, retreat to safer terrain immediately. This is one of the most reliable indicators of danger.
3. Cracks in the Snow Spreading Outward
• What It Means: Cracks that radiate from your skis, boots, or board indicate that stress is propagating through the snowpack—a precursor to slab avalanches.
• Actionable Tip: Avoid slopes where cracks spread easily. This is a strong sign of slab instability.
4. Snow That Feels Heavy, Wet, or “Slabby” Underfoot
• What It Means: Dense, wet, or slabby snow layers are more prone to sliding, especially if they are poorly bonded to the layers beneath. This is common after warm weather, rain, or wind-loading.
• Actionable Tip: Test the snow by isolating small blocks with your pole or shovel to check for weak bonds between layers.

Quick Checklist for Visual Red Flags:

• Fresh avalanche debris.
• “Whumpfing” sounds.
• Spreading cracks.
• Dense, wet, or slabby snow.

Snowpack Testing: Tools for Digging Deeper

While visual red flags are critical, snowpack tests provide more detailed information about stability. These tests help you identify weak layers and assess how likely they are to fail. However, they require practice to perform correctly.

1. Compression Test (CT)

• Purpose: To identify weak layers and assess how easily they fail under pressure.
• How to Perform It:
• Dig a pit on a representative slope (similar aspect, elevation, and angle to where you plan to travel).
• Isolate a column of snow approximately 30 cm wide and 30 cm deep.
• Tap the top of the column with increasing force:
• 10 light taps: Using just your wrist.
• 10 medium taps: Using your forearm.
• 10 hard taps: Using your whole arm.
• Observe where the column fractures and note the depth of the weak layer.
• What to Look For:
• Sudden collapses after light or medium taps indicate a weak and unstable layer.
• Progressive failure (breaking after many taps) suggests a more stable snowpack.

Limitations: The compression test only assesses local stability. Always combine it with other observations.

2. Extended Column Test (ECT)

• Purpose: To assess whether a weak layer will propagate a fracture, a critical factor in slab avalanche formation.
• How to Perform It:
• Dig a wider pit (30 cm x 90 cm) and isolate the column by cutting the sides and back.
• Apply taps as in the compression test.
• Watch for fractures spreading across the entire column.
• What to Look For:
• Fractures that propagate across the entire column indicate high avalanche risk.
• Fractures that don’t propagate suggest more localised instability.

Why It Matters: A snowpack with weak layers that propagate fractures is more likely to produce large, dangerous slab avalanches.

3. Hand Shear Test

• Purpose: A quick test to assess weak bonds between snow layers.
• How to Perform It:
1. Dig into the snow to expose a small block.
2. Apply pressure with your hand to see if the block slides away easily.
• What to Look For: Easy shearing indicates weak bonding and higher avalanche risk.

Limitations: The hand shear test is simple but less precise than the compression or extended column tests.

4. Deep Tap Test

• Purpose: To identify buried weak layers that are deeper than 100 cm.
• How to Perform It:
1. Isolate a column of snow that extends to the depth of interest.
2. Use firm, controlled taps with your shovel blade to see if deep layers fail.
• What to Look For: Weak layers deeper than 100 cm are harder to trigger but can produce massive avalanches if they fail.

When and Where to Perform Tests

Choosing a Representative Slope:

• Pick a slope that mirrors the conditions of the terrain you plan to travel:
• Same aspect (e.g., north-facing).
• Similar elevation.
• Comparable angle (e.g., 30°–40°).

Timing Matters:

• Conduct tests after recent weather events, such as heavy snowfall, wind, or warming. These events are often the tipping points for avalanche risk.

Limitations of Snowpack Testing

No test is foolproof. Snow conditions can vary dramatically across a single slope, so always combine test results with visual observations and weather knowledge. When in doubt, err on the side of caution and stick to safer terrain.

Practical Example: Combining Observations and Tests

You’re planning to ski a north-facing slope after a storm that brought 40 cm of new snow. During your approach, you notice:

1. Fresh avalanche debris on a nearby slope.
2. A “whumpf” sound underfoot.
3. Spreading cracks in the snow.

You conduct a compression test and observe a sudden collapse after light taps, confirming a weak layer buried 40 cm deep. An extended column test shows the fracture propagating across the column.

Decision: This slope is too dangerous to ski. You decide to stick to lower-angle terrain below 30°.

Key Takeaway

Field observations and snowpack tests are powerful tools for assessing avalanche risk, but they’re not guarantees. Use them in combination with visual red flags, weather knowledge, and terrain awareness. Most importantly, if you’re ever uncertain about the conditions, choose the safer route—there’s no substitute for good judgment in the backcountry.

Ready to follow onto the next lesson? Click here for chapter 5 - How Weather Affects Avalanche Risk