Avalanche Safety Study Notes

Avalanche Safety - Study Notes

• Avalanche Causation: Over 90% of fatal avalanches are caused by the victim or their group.

Avalanche Types

• Slab Avalanche: A dense layer of snow breaks off and slides on a weaker layer within the snowpack. This is highly dangerous, reaching speeds over 130 km/hr. Weak layers can stem from temp fluctuations or are created by storms. Slab avalanches are cohesive at first but break into chunks.

• Loose Snow Avalanche (or Sluff): A poorly bonded surface layer of snow slides downhill under its own weight. It has a less dangerous nature than slab avalanches, starting at one point and spreading like a tear shape.

• Cornices: Wind-deposited snow masses protruding from ridges/peaks. They can break off and trigger larger avalanches (or be a trigger for slab avalanches) due to stress from gravity, weather changes, or weight (human or machine).

Avalanche Formation

• Weather's Role: Weather is the primary driver of avalanche formation, creating different snowpack layers with varying strengths and weaknesses. Snow crystals bond differently depending on weather conditions over time, thus creating strong and weak layers.

• Weak Layers: Storm snow, surface hoar (frozen dew that creates feathery crystals), facets (different temp in snowpack, sharp sides of grains, no cohesion b/w snow crystals), depth hoar (persistent, large cup shaped layer), and crusts (melted then refrozen snow- often used as a sliding surface) are all problematic weak layers in snowpacks.

Avalanche Triggers

• Natural Triggers: New snow loading, windblown snow, rain, rapid temp increase, and strong solar radiation all initiate natural avalanches.

• Human Triggers: People and machines trigger many avalanches, and the triggering effect can be from many meters away!

• Artificial Triggers: Explosives are used (deliberately) to release avalanches in ski areas or highway passes, to keep the size manageable.

Avalanche Sizes

• Classification: Avalanches are rated from 1 (smallest) to 5 (largest) based on their destructive potential. Size 1 avalanches are relatively harmless to people but still pose risks. Sizes 2–5 can bury, injure, or kill people/destroy property.

Avalanche Terrain

• Terrain Characteristics: Avalanche paths (start zone, track, runout zone; sometimes delineated by trim lines) are critical areas. Slope angle is vital; 30-45 degrees is most common for slab avalanches. Steeper slopes (over 45 degrees) have fewer slab avalanches.

• Slope Shape: Convex slopes (steepest point near the top) are more prone to fractures.

• Terrain Traps: Terrain features like rocks, trees, and cliffs increase avalanche severity, as do sudden flat spots, which can lead to deeper burials.

• Slope Aspect and Wind: Slopes facing winds(windward), have wind slabs formed because they carry the snow to the leeward side of slopes. Solar radiation impacts sun-facing slopes with potential to form hard crusts and weakens the slope.

Avalanche Exposure Scale

• ATES: A system for rating backcountry terrain's avalanche exposure into Simple (green), Challenging (blue), and Complex (black) categories. Using 11 different weighted measures!

Avalanche Forecast

• Importance: The forecast is a key component of planning any backcountry trip, providing danger ratings (1-5), problems (types of avalanches and terrain), and details (local conditions, weather).

• Danger Ratings: Based on the North American public avalanche danger scale, which provides the likelihood of avalanches and their size.

• Avalanche Problems: Storm slab, wind slab (look for stiffness under feet, hollow noises), persistent slabs, wet slabs (rain, temp increase), cornices, loose wet, and loose dry (sluffs) are all discussed in detail to help assess danger.

Daily Process

• Group Formation: Create small and efficient groups (3–5 people).

• Trip Planning: Assess the forecast and create a plan, including plan B.

• Gear Check: Check and verify all necessary gear (batteries).

• Condition Verification: Check weather/snow conditions, assess safety, etc

• Communication and Travel Habits: Maintain communication, have a clear escape plan, and look for signs of instability like drifting/cracking/recent avalanches.

Companion Rescue

• Quick Action: Immediate actions are crucial.

• Leader Selection: Designate a leader.

• Scene Assessment: Assess safety, overhead hazards.

• Headcount and Search: Figure out where last seen.

• Transceiver Search: Signal, coarse, and fine search phases are explained. The transceiver shows distance and direction.

• Probing and Shoveling: Systematic techniques are given.

• When to Call for Help: Only if necessary, and don't take up too much rescue time.

Explore the critical aspects of avalanche safety with a focus on the types of avalanches, their causation, and formation factors. Understand the dangers associated with slab and loose snow avalanches, as well as the role of weather in their formation. This comprehensive overview is essential for anyone interested in outdoor safety in mountainous regions.