Tuesday, March 6, 2012

Invasive Species Avalanche

No, not an avalanche caused by non-native vegetation, but rather a Colorado avalanche killing a skier in Lake Tahoe.
Whereas Colorado is the poster child for the continental snowpack, Lake Tahoe is the same for maritime.  But not this season, given the highly unusual thin snowpack and extremely long dry spells.
Remember that although the three avalanche climates are useful for teaching purposes and for general awareness of typical avalanche "Problems" what matters most is what is happening right then and there on the slope you are contemplating travelling on, not broad generalizations.

The comprehensive incident report includes a video of a snowpit stability test that replicates the step-down nature of the fatal slide.  Also of note is that the party dropped a cornice that released a slab a few inches deep that propagated widely across the slope.  Unfortunately, this was not a sign that the slope could not slide any more, but rather that more was still to come.

The incident report is relatively silent on the party's decision making, but having skied extensively in Lake Tahoe with my brother over the years, I can understand how the skiers might have been lulled into a sense of complacency regarding the Red Flags noted in the incident report:
  • Recent avalanche activity
  • Whumphing noises, shooting cracks, or collapsing
  • Recent loading by new snow, wind, or rain
  • Terrain Trap

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