Avalanche Danger Flashcards
What are the characteristics of the two different avalanche types?
Loose Snow Avalanche: start in a small area and grow as they descend. They are associated with steep slopes, warm weather, and recent snow.
Slab Avalanche: Most happen 35-40 degrees and are large layers of cohesive snow breaking off and sliding. Speeds can be 65-150mph!
What is the difference between a maritime and a continental snow-climate and how does that affect avalanche danger?
Maritime: Mild climates, avalanches are usually following snow storms, and rapidly stabilized by radiation and warm weather. Sierra Nevada Mountains are in a maritime climate.
Continental: Cold temperature thin snowpack with high temperature gradients leading to weak faceted crystals.
How does wind affect avalanche danger?
Wind contributes to loading of a slope on the top (top-loading), or from the side (side-loading) which can lead to slab formation. These are unstable snows.
How does temperature and radiation affect avalanche danger?
Gradual warming of a snowpack causes strengthening of the bonds between grains. Shaded slopes don’t get this strengthening, and thus hold their weaker layers. Warm temperatures that cool are associated with more instability.
What terrain characteristics increase the likelihood of avalanches?
Prime slab avalanche terrain is 30-50degrees.
Leeward (opposite wind) deposits of snow increase snowpack and avalanche risk.
Intense direct sunlight can weaken the bonds between grains.
Full shade/shadow can cause weak layers to persist.
Anchoring can be provided by trees, boulders, ledges.
Convex slopes are more likely to fracture than concave.
How do rounding/faceting contribute to avalanche risk?
Rounding: uniform, rounded grains create strong bonds.
Faceting: when significant temperature changes exist within/between layers, angular grains create weak bonds and layers are weakly associated.
What are the red flag values for avalanche activity observations, snowpack, and weather associated with increased avalanche danger?
Recent avalanche activity on similar slopes
Visible cracks from underfoot.
Sloughing debris underfoot.
Sunballing (snowballs rolling down the slope)
Excessive snowfall (>1”/hr for 24hrs)
Heavy rain, wind loading.
