Soldier & Wood River Valley Mtns

Avalanche problems

• 

  Persistent Slabs

  N

  NE

  E

  SE

  S

  SW

  W

  NW

  • Alpine
  • Treeline
  • Below treeline

  Likelihood

  Possible

  Size

  1.5–2

  Ten human-triggered avalanches occurred during the past week, including at least seven this past weekend (read more in the Forecast Discussion below). Most of these broke 1-2' thick on persistent weak layers buried during the first week of January. Surface hoar seems to be the most common culprit, but facets and/or crusts may also be present. Also, most of these avalanches occurred in middle elevation terrain on slopes where signs of wind loading were not obvious. While none of these were "huge" slides, around half of them were large enough to bury or injure people, and all were capable of carrying someone into a gully, through trees, or over cliffs.

  While these persistent weak layers are slowly gaining strength and triggering a slide is less likely than it was this weekend, they are still capable of producing avalanches. Surface hoar is a particularly sneaky weak layer—definitely not one to be underestimated! Wind-loaded areas will be slowest to stabilize, but you could also trigger persistent slab avalanches on very steep (>35 degree), wind-sheltered slopes. Avalanches can also be remotely triggered from gentler terrain above, below, and to the sides of steeper slopes. Reduce your risk by sticking to less steep terrain and avoiding slopes with terrain traps in the runout zones.

  ADDITIONAL DISCUSSION: In addition to the persistent weak layers in the top few feet of the snowpack, there are more deeply buried layers to keep on your radar. These facets (often above or below crusts) are buried beneath dense, 2-4+ thick slabs—making them difficult to trigger but capable of producing very dangerous avalanches. While triggering them is unlikely, it can't be ruled out in steep, rocky, wind-affected alpine terrain. Slopes like these have variable snow depths, with thinner areas of the snowpack that allow us to impact deeper weak layers. 

  

• 

  Wind Slabs

  N

  NE

  E

  SE

  S

  SW

  W

  NW

  • Alpine
  • Treeline
  • Below treeline

  Likelihood

  Possible

  Size

  1–2

  We're a few days out from recent wind events, and most wind slabs have likely stabilized. However, a few could remain sensitive to your weight—especially where they sit atop persistent weak layers (see Problem 1). Look for these slabs near ridgelines and in mid-slope terrain features like gullies. Pay attention to how deep and how dense the snow you are traveling in is. If the snow depth and density increase you are likely traveling through a wind-loaded area. Cracks shooting out from your skis or machine clearly indicate that you've found an unstable wind slab.