Avalanche Formation & Terrain Recognition Flashcards

What is the most common trigger for avalanches?

Answer: Human activity

While natural factors like snowfall and wind can contribute to avalanche formation, human activity is the most common trigger for avalanches that involve people. Skiers, snowboarders, snowmobilers, and hikers often inadvertently trigger slides by adding weight to unstable snowpacks or disturbing weak layers. This highlights the importance of human decision-making in avalanche safety.

Which slope angle range is most prone to avalanches?

Answer: 30–45 degrees

Slopes between 30 and 45 degrees are considered the most dangerous for avalanches because they are steep enough for snow to slide but not so steep that snow cannot accumulate. Below 30 degrees, snow generally doesn't slide easily, and above 45-50 degrees, snow tends to sluff off frequently, preventing large, deep slabs from forming. This range represents the critical balance for slab avalanche formation.

What terrain feature can increase avalanche risk?

Answer: Convex slopes

Convex slopes are particularly dangerous because they often have a shallower snowpack near the top, which can act as a weak point, and the snowpack is under tension. As the slope steepens, the snowpack is stretched, making it more prone to fracturing and releasing an avalanche. The change in slope angle can also make it harder to assess snow stability.

What is a 'persistent weak layer' in avalanche terms?

Answer: An old snow layer prone to collapse

A persistent weak layer is a buried layer of snow, often formed early in the season, that remains weak and unstable over time. These layers, like faceted crystals or surface hoar, can persist for weeks or months, acting as a failure plane within the snowpack and making it prone to collapse under new snow loads.

Which sign indicates potential avalanche conditions?

Answer: Whumpfing sounds

Whumpfing sounds are a clear indicator of a weak layer collapsing within the snowpack, often accompanied by the ground settling underfoot. This audible sign signifies that the snowpack is unstable and that an avalanche could be triggered by additional stress.

How does wind affect avalanche formation?

Answer: Deposits snow on leeward slopes

Wind plays a crucial role in avalanche formation by picking up loose snow and redepositing it. It scours snow from windward slopes and deposits it onto leeward (downwind) slopes, forming dense, cohesive slabs that are prone to sliding, especially when built over weaker, underlying snow layers.

Which tool is essential for evaluating avalanche terrain?

Answer: Inclinometer

An inclinometer is an essential tool for evaluating avalanche terrain because it accurately measures the slope angle. Avalanche formation is highly dependent on slope angle, with most avalanches occurring on slopes between 30 and 45 degrees, making this measurement critical for risk assessment.

Why are north-facing slopes often riskier in winter?

Answer: They stay colder and preserve weak layers

North-facing slopes receive less direct solar radiation, especially in winter, causing them to remain colder. This cold environment can preserve weak layers within the snowpack, such as faceted crystals or surface hoar, for longer periods, making these slopes more susceptible to avalanche activity.

What is a 'terrain trap' in avalanche safety?

Answer: A gully or depression increasing burial depth

A terrain trap is a feature in the landscape that, while not necessarily triggering an avalanche, can significantly worsen the consequences if one occurs. Gullies, depressions, or cliffs can increase the depth of burial, make rescue more difficult, or lead to trauma, severely reducing survival chances.