Backcountry

Backcountry Safety Basics 1

This is not a substitute for a certified AIARE avalanche course.

Snow Layers

• Rounded snow is strong. Faceted snow is weak and has weak links.
• Faceting happens
• Temperature Gradient happens because the ground is insulated, so lower layers of snow are less cold. This is typically 0c. The outermost layer varies due to wind chill and air temp.
• Warm air holds more moisture than cold air. Since it's warmer near the ground, there's more moisture near the ground. This vapor pressure wants to move up.
• Crystalline structure needs moisture to keep it, but this moisture moves upward.

How does snow round?

The slower moisture leaves, the faster snow rounds! The deeper the snowpack, the lower the ratio of difference to depth. You want a smaller temperature gradient. This prevents the moisture from quickly exiting before it gives snow time to round.

Crusts

There are two types -- sun and rain. Sun always melts snow that has a strong southern aspect, which refreezes at night forming a hard crust. Rain crusts form when cold temperatures freeze moisture following a rain event. It's really smooth; a sheet of ice on top of snowpack.

Avalanche Problems

9 major problems.

Dry Loose

• Unconsolidated snow releasing
• Result of snow not consolidating in a cohesive layer
• Shape of a fan

Wet Loose

• Release of unconsolidated snow high in water content.
• Start from a point and move it in a fan shaped path downhill.
• Caused by intense sun and rain.

Cornice Fall (like a wave)

• Wind blows unconsolidated snow grains up and over a peak and creates a lip.
• This ridge can break and fall onto underlying terrain.

Trigger Layer Causes

• Weak Layers
• Stress on weak layer is large

Weak Layers (involve 6 types of avalanches)

Layers in the snow that serve as points of failure.

• Facets: Sugary, uncohesive snow. Pointy on the micro-level, low structural integrity.
• Surface Hoar (frozen equivalent of dew): layers are harder to trigger naturally but easy to trigger with external force. Can carry a lot of force if applied slowly (naturally).