Avalanche Formation & Terrain Recognition Flashcards

Which avalanche type is characterized by a single point of origin that fans out in a triangular shape as it descends?

Answer: Loose-snow avalanche

Loose-snow avalanches start at a single point and widen as they gather more snow, forming a characteristic inverted-V or triangular shape.

What is the typical critical slope angle range where most slab avalanches release?

Answer: 30–45 degrees

Most slab avalanches release on slopes between 30 and 45 degrees, where gravitational stress exceeds the snowpack's strength most efficiently.

A persistent slab avalanche problem is particularly dangerous because:

Answer: Buried weak layers can remain reactive for weeks or months after burial

Persistent weak layers can be re-activated long after they are buried, remaining a hazard even when surface conditions seem stable.

What does a 'shooting crack' propagating away from your ski or board mean?

Answer: The slab is fracturing and conditions are highly unstable

Shooting cracks are a critical red flag indicating that slab layers are fracturing and propagating, signaling imminent avalanche danger.

What term describes an avalanche that occurs when the entire snowpack slides on the ground surface?

Answer: Glide avalanche

Glide avalanches occur when the full snowpack moves along the ground, often over smooth rock or grass, and can release with little warning.

Which observation most strongly indicates that a slope has recently avalanched?

Answer: A smooth, scoured bed surface with debris at the bottom

A scoured crown, smooth bed surface, and debris pile (runout zone) are classic evidence of a recent avalanche cycle.

How does rain affect avalanche hazard in winter snowpack?

Answer: Rain adds weight and lubricates layers, dramatically increasing wet avalanche danger

Rain rapidly weakens snow strength by adding weight and introducing free water that lubricates failure planes, causing an abrupt spike in avalanche hazard.