Avalanches Flashcards
Formation of avalanche starts with…
the first period of snowfall which covers the ground.
During day insolation…
melts the top layer in the snowpack. This creates a weak layer.
After a day there is a second…
period of snowfall and new “powder” snow falls on the old wet snow.
The weak layer is…
the slip plane.
A slab avalanche is when…
the whole layer of powder snow on slip plane moves.
On Concave slope…
a slab avalanche is more common as snow simply flows downhill.
On a rectilinear slope, the powder snow is…
blown by a wind from the convex slope. (Airborne powder)
In Airborne powder avalanche, the CO2…
is trapped between snowflakes and as the powder cloud accelerates down the slope, it reaches a high momentum.
Avalanches occur on slopes which are…
more than 22 degrees steep.
Avalanches occur on North-facing slopes where…
the sun inhibits the stabilisation(creates slip plane)
Avalanche is…
a mass movement of snow and ice.
The average speed of avalanche is…
40-60 km/h.
Type of breakaway:
- loose snow avalanche (single point)
- slab avalanche (from a large area leaving wall)
Position of sliding surface:
- full depth avalanche(whole snow cover included)
- surface avalanche (some top layer only involved)
Form of the track:
- unconfined avalanche-open slope
- channelled avalanche-in a gully
