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
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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
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2
Q

snow crystals

A
  • new snow characterized by 6 sided crystals (diameter 0.5mm)
  • aging crystals: more round; more densely packed; more cohesive
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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
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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
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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
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6
Q

point release avalanche

A
  • most often develop in low cohesion snow ***
  • inverted v shape
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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
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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
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9
Q

cornice

A

snow structure formed by wind loading snow on the downwind side of an obstacle, often a mountain ridge line

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10
Q

what triggers avalanches

A
  • weather conditions: common after snow storms,
  • human activities: recreational activities and purposful
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