Wind Loading:
Wind erodes snow from the windward (upwind) side of obstacles,
such as a ridge, and deposits the same snow on the leeward (downwind)
terrain. Wind loading is a common denominator in most avalanche
accidents. And no wonder because wind can deposit snow 10 times
more rapidly than snow falling from the sky. Moreover, wind-drifted
snow is ground up by bouncing along the snow surface and when
it comes to a rest it is often much denser than non-wind loaded
snow. In other words, it not only adds significant weight on
top of buried weak layers but it forms a slab that can propagate
a fracture very easily. Wind can turn very safe snow into very
dangerous snow in a matter of minutes. Wind is usually the most
important weather factor in avalanche accidents.
Luckily, we can easily recognize wind loaded slopes:
| |
Wind deposited snow |
Wind eroded snow |
| What does it look like? |
Smooth and rounded, sometimes called
“pillows” chalky, dull appearance |
Sandblasted, etched look |
| Where does it form? |
Lee terrain (downwind of an obstacle
such as a ridge). Often, a cornice overhangs the slopes |
Windward terrain (upwind side of an
obstacle, such as a ridge). Often a cornice faces away
from the slope |
| What does it feel like? |
“Slabby” or “punchy,”
meaning that denser and stiffer snow overlie softer snow |
Rough, difficult to travel on |
| What does it sound like? |
Sometimes sounds hollow like a drum |
Noisy from the rough texture |
It’s very important to memorize the look, feel and sound
of wind loaded slopes.
Always avoid steep slopes with recent deposits of wind drifted
snow unless you are experienced, and have checked it out very
carefully.
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