Avalanche Formation & Terrain Recognition Flashcards
7 cards from real ASC practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.
Read the first 7 Avalanche Formation & Terrain Recognition flashcards as text
What is the primary role of the 'bed surface' in an avalanche?
Answer: The layer on which the avalanche slides after the weak layer fails
The bed surface is the interface exposed after the slab and weak layer are removed, and it's often a harder or denser layer that acts as a sliding surface.
Surface hoar is a high-risk weak layer because it:
Answer: Forms on the snow surface, becomes buried, and preserves its poor bonding for weeks
Surface hoar crystals form like frost on the snow surface and, once buried under new snow, create a persistent weak layer prone to avalanche triggering.
Which wind speed threshold is commonly associated with significant snow transport and slab formation?
Answer: 15 mph (25 km/h)
Winds around 15 mph are sufficient to begin transporting snow and forming wind slabs on lee slopes, a key avalanche formation mechanism.
An avalanche 'starting zone' is best identified by which combination of features?
Answer: Steep convex slopes, bowls, or gullies where snow accumulates and is prone to releasing
Starting zones are typically steep (30–45°), convex, or bowl-shaped terrain that collects snow and has sufficient angle to initiate avalanche release.
What phenomenon causes new snow to become denser and stronger over time through the pressure of overlying layers?
Answer: Sintering and settlement
Sintering bonds snow grains together through vapor diffusion and pressure, while settlement compacts snow under gravity, both increasing snowpack strength.
A 'trigger point' on an avalanche slope is most likely located:
Answer: On the shallower margins or convexities of a slope where the slab is thinner and more stressed
Shallow margins and convex rolls create stress concentrations where slab fractures nucleate, making them the most likely remote or direct trigger points.
What is 'whumpfing' (or 'whumpfing sound') an indicator of while traveling in avalanche terrain?
Answer: A collapsing weak layer beneath a slab, signaling serious instability
Whumpfing is the sound and feel of a buried weak layer suddenly collapsing under load, a critical warning sign of avalanche instability.