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Avalanche anatomy:
- 1. Crown
- 2. Flank
- 3.Stauchwall
- 4. Deposition zone
- 5. Bed Surface
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1. Crown
Upper margin where the slide broke away from the rest of the snow pack
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2. Flank
The left and right borders of the slide.
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3. Stauchwall
The bottom (downslope) boundary of a slab where it rides up over the snow below. Usually difficult to impossible to identify after an avalanche.
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4. Deposit zone
where the slide stops moving and ost debris is deposited
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5. Bed surface
the surface on which the snow slides.
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1. Loose Snow
- Dry: usually caused by fresh snow >12''. often referred as sluffs, can run fast and far depending on terrain.
- Wet: Similar to dry loose avalanche, however conditions are caused by rain or rapidly warming temperatures.
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2. Slab Most dangerous and devastating
Wet: usually caused by rain or prolongd warming on dry snow.
Storm Slab: usually caused by >12'' of new snow in 24hrs or less
- Wind Slab: usually caused from moderate winds (10-20mph) transporting snow which loads the leeward aspects.
- Persistant Slab: aused by persistent layers of strong hard slabs surrounded top and bottom by weak snow.
- Deep Slab: caused by weak layer buried deep (3') in the snow pack. usually triggered by a large load such as a cornice fall or explosive.
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Relative to Path:
- R1: very small (0-20%)
- R2: small (20-40%)
- R3: medium (40-60%)
- R4: Large (60-80%)
- R5: Major (80-100%)
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Destruction Potential:
- D1: Too small to injure of bury a person
- D2: Could bury, injure or kill a person
- D3: Could bury, destroy a car, damage a truck, destroy a small bldg., or break a few trees.
- D4: Could destroy a truck railway car, several bldgs., or up to 10 acres of forest.
- D5: could destroy a village or 100 acres or more of forest
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Slope Angles: 0-25°
infrequent wet snow avalanche, green slopes
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Slope Angles: 25-30°
Infrequent slabs in unstable conditions, blue slopes
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Slope Angles: 30-35°
Slabs in unstable condition, Black diamond slopes
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Slope Angles: 35-45°
frequent slabs of all sizes , double black diamond slopes
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Slope Angles: 45-55°
many loose avalanches start, some small slabs, out of bounds
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Slope Angles: 55°+
Few avalanches, climbing terrain
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