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Problèmes avalancheux

• 

  Loose Wet

  N

  NE

  E

  SE

  S

  SW

  W

  NW

  • Alpin
  • Limite forestière
  • Sous la limite forestière

  Probabilité

  Possible

  Taille

  1–2

  Yesterday, I saw some fresh-looking wet loose avalanches in the Smoky Mtns. In the northern Sawtooths, an observer triggered a wet loose avalanche large enough to push or carry a skier or rider where they would not want to be. Professionals near Galena Summit noted the snow surface had become unsupportable on sunny, middle elevation terrain by early afternoon. I consistently fell through the snowpack to my waist when walking around and digging holes yesterday afternoon on sunny middle-elevation slopes in the same general area.

  Today's sunshine and warm temperatures will produce similar wet snow avalanche concerns. The threat of wet loose avalanches will follow the sun around the compass, beginning on E-SE aspects this morning, moving to SE-S facing slopes, and wrapping around to SW-W aspects in the afternoon. At lower elevations, shadier slopes may become an issue as well. As crusts and layers in the middle of the snowpack melt and break down, loose snow slides could gouge into the mush and be deceptively powerful. Where are wet avalanches most likely?

  • Very steep terrain (approaching 40 degrees)
  • Areas with a thin snowpack (less than about 3 feet deep)
  • Rocky terrain
  • Slopes below overhanging cornices that may naturally break and trigger slides beneath them

  Fortunately, managing wet snow avalanche hazard is fairly straightforward; it peaks in specific areas at specific times, and the more dangerous avalanche conditions are on slopes with miserable riding and skiing conditions. Some simple tips to help you stay out of trouble:

  •  If your boards or sled are punching deep into the snowpack, stick to gentle slopes or move to shadier terrain.
  • Expect many sunny slopes where the snowpack is thin (less than about 3 feet deep) to become wet and unsupportable.
  • Pay attention to what's above you. Wet avalanches release on their own much more frequently than dry avalanches. 
  • Things change rapidly. That slope you rode yesterday, or 30 minutes ago, may become an issue. Keep your head on a swivel. 

   

  ADDITIONAL DISCUSSION:The most prominent weak layers in this zone are depth hoar near the ground (buried 4-6' deep) and crusts associated with facets and surface hoar in the middle of the snowpack (buried 2-3' deep). Observations and a lack of recent slab avalanche activity indicate it's become very difficult for skiers and riders to trigger avalanches on these weak layers. But, the wet avalanches discussed above can act as triggers for larger avalanches failing on these deeper layers. The meltwater gradually seeping deeper into the snowpack also adds a layer of uncertainty to the slab avalanche equation. A large, destructive wet slab avalanche occurred in the Sawtooths during the warm-up at the beginning of March (photo here, details here). Steering clear of areas with gloppy, unsupportable snowpacks—including areas below large avalanche paths with mushy snow conditions—is a simple way to minimize the chances of triggering or tangling with large slab avalanches.