Lecture 13: Snow avalanche Flashcards
1
Q
snow pack
A
- composed of several layers with different characteristics
- thickness, density, hardness, cohesion, strength
- formed under different weather conditions
- properties can change over time
1
Q
cohesion
A
- property of the particles of a material to stick together
- low-cohesion snow: fresh powder snow, 95% volume is void space
- cohesive snow: wet snow, liquid water between particles of ice
- compacted snow: snow particles densely packed and tightly bounded
2
Q
snow crystals
A
- new snow characterized by 6 sided crystals (diameter 0.5mm)
- aging crystals: more round; more densely packed; more cohesive
3
Q
weak layers
A
- within the snowpack, weak layers are sandwiched between stronger layers
- weak layers form: when wind is increasing during a storm; when hoar crystals develop
- denser layer of broken crystals on top of less dense layer of unbroken crystals, deposited under increasing wind conditions
4
Q
Hoar
A
- relatively large crystals formed by the deposition of water vapor - when hoar crystals grow, the density of the snowpack decreases
- depth hoar: vapor from underlying soil deposits on snow crystals at the base of the snowpack; density of the lower layer of the snowpack decreases
- surface hoar: surface hoar forms on cold clear nights; vapour from the atmosphere deposits on the surface of the snowpack
5
Q
three main parts of snow avalanches
A
- start zone: most volatile part of the slope where unstable snow begins to slide
- track: path followed by the avalanche moving downhill
- runout zone: zone where snow and debris stop and are deposited
6
Q
point release avalanche
A
- most often develop in low cohesion snow ***
- inverted v shape
7
Q
slab avalanche
A
- involves several layers of cohesive snow ***
- avalanche starts when fracture spreads to a weak layer at the base
- more dangerous
- larger and greater force
8
Q
slope angle of the start zone
A
- > 50 degrees - frequent point-release avalanches
- 25-50 degrees - infrequent, large dry slab avalanches
- 25 degrees - slab avalanches only
9
Q
cornice
A
snow structure formed by wind loading snow on the downwind side of an obstacle, often a mountain ridge line
10
Q
what triggers avalanches
A
- weather conditions: common after snow storms,
- human activities: recreational activities and purposful