Avalanche anatomy: 1. Crown 2. Flank 3.Stauchwall 4. Deposition zone 5. Bed Surface 1. Crown Upper margin where the slide broke away from the rest of the snow pack 2. Flank The left and right borders of the slide. 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. 4. Deposit zone where the slide stops moving and ost debris is deposited 5. Bed surface the surface on which the snow slides. 2 Main Avalanche Types: 1. Loose Snow 2. Slab 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. 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. Relative to Path: R1: very small (0-20%) R2: small (20-40%) R3: medium (40-60%) R4: Large (60-80%) R5: Major (80-100%) 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 Slope Angles: 0-25° infrequent wet snow avalanche, green slopes Slope Angles: 25-30° Infrequent slabs in unstable conditions, blue slopes Slope Angles: 30-35° Slabs in unstable condition, Black diamond slopes Slope Angles: 35-45° frequent slabs of all sizes , double black diamond slopes Slope Angles: 45-55° many loose avalanches start, some small slabs, out of bounds Slope Angles: 55°+ Few avalanches, climbing terrain