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
Form of movement:
- airborne powder avalanche-through the air
- flowing avalanche-along the ground
The humidity of snow:
- dry snow avalanche
- wet snow avalanche
Snow gets its strength from…
the interlocking of snow crystals and cohesion caused by electrostatic bonding of snow crystals.
Snow remains on the slope if:
strength(interlocking, frisction, cohesion) > stress(a component of the wight down the slope)
What triggers an avalanche:
- changes in overlying pressure
- compaction of new snow
- temperature changes
- movement of meltwater through snow
Loose avalanche often happens soon after…
snowfall.
Slap avalanche often happens later when…
the snow has developed some cohesion(they are larger).
Afforestation is used to…
prevent avalanches as it reduces the amount of snow reaching the ground, reduces insolation.
Fences and walls can be built on…
accumulation zone to prevent the avalanche from reaching large momentum.
Deflections can be built under…
the slope to deflect the mass of snow sideways, away from the village
