Soldier & Wood River Valley Mtns

Problèmes avalancheux

• 

  Persistent Slabs

  N

  NE

  E

  SE

  S

  SW

  W

  NW

  • Alpin
  • Limite forestière
  • Sous la limite forestière

  Probabilité

  Likely

  Taille

  2–3

  Two prominent layers of weak snow are buried underneath thick, dense slabs here:

  1. Near the base of the snowpack, you'll find a layer of crusts, facets, and spotty surface hoar. This layer produced numerous avalanches before the major storm and continued to do so throughout the storm. In this area, this layer is now buried 2 to 3 feet below the snow surface.
  2. The weak layer that last week's storm fell on was thinner but similarly weak. In places, surface hoar is well developed here. Many of the avalanches that occurred during the storm failed on this layer, often stepping down to the deeper weak layer described above. This upper layer is now buried 1-1.5 feet down.

  The weak layers are widespread, and so are the slabs overlying them. This means you can trigger large, dangerous avalanches on just about any steep slope you encounter, even at lower elevations and in terrain sheltered from the wind. A professional avalanche course in the Lake Creek drainage yesterday reported unstable snowpack test scores on these weak layers and experienced a large collapse in terrain that had already been traveled through by other parties. I was in the Warm Springs drainage the day before and experienced an impressive collapse that rattled snow off of hundreds of small trees over a large area. Tilt these collapses up onto a steeper slope and you have yourself an avalanche.

  Persistent weak layers produce avalanches that behave in surprising ways. They can break wider than you'd expect and can be triggered remotely—from gentler terrain above, below, and to the sides of steep slopes. Plan your day expecting to be able to trigger these types of avalanches. Thanks to the widespread nature of the weak layer+slab combination, avoiding slopes steep enough to slide is the only way to ensure a safe return home. Playing on or below steep terrain continues to be a risky dice roll.

  ADDITIONAL DISCUSSION: Wind speeds increased for about 6 hours last night before calming back down. There is plenty of snow to move around and some slabs likely formed in exposed terrain. Though relatively thin, I expect these to be touchy. The wind will pick up again this afternoon and another round of slabs will be forming. Triggering one of these slabs can make for an effective trigger for avalanches failing on deeper weak layers.