Soldier & Wood River Valley Mtns

Avalanche problems

• 

  Persistent Slabs

  N

  NE

  E

  SE

  S

  SW

  W

  NW

  • Alpine
  • Treeline
  • Below treeline

  Likelihood

  Likely

  Size

  2–3

  A very large natural avalanche failed on Galena Peak sometime between Friday night and Saturday morning. The crown spanned 2,000 feet of terrain and the slide ran over 1,000 vertical feet. Skiers remotely triggered a smaller (but still large enough to bury you) slide just south of Galena Peak yesterday. The photo at right/above shows a large slide that was triggered by the Sun Valley Ski Patrol earlier this week. These are the types of avalanches that you are likely to trigger today.

  Under the recent storm snow, you will find thick, very dense slabs sitting on layers of very weak snow. Watch this video to get a sense of just how dense these slabs are. If you dig down, you'll find thick piles of facets with or without surface hoar on shaded aspects, and crust+facet combinations on slopes that get more sun. You can trigger avalanches that fail on this weak snow from long distances away. Any avalanche that fails on this weak layer will be large and destructive. 

  Because the slabs on top of this weak layer are so dense, you aren't likely to encounter many or any signs of instability before triggering a large, potentially unsurvivable avalanche. As a local professional wrote in their observation on Friday, "stability felt good, until you dug into the snowpack..." Keep this weak snow at the front of your mind when you are moving through the mountains. The only guaranteed way to avoid this problem is to steer clear of avalanche terrain and slopes threatened by overhead hazards. 

  

• 

  Wind Slabs

  N

  NE

  E

  SE

  S

  SW

  W

  NW

  • Alpine
  • Treeline
  • Below treeline

  Likelihood

  Likely

  Size

  1–2

  Recent storms brought several feet of fresh snow to this zone. Expect to encounter a range of issues related to this new snow:

  Wind slabs: Our weather station on Peak 2 in the Soldiers reports northerly winds blowing at loading speeds since yesterday afternoon. Winds on top of Baldy have been lighter. There was plenty of loose snow to move around when the winds started blowing. Look for drifts, ripples, and dunes on the snow surface as indicators that the wind has been at work, and expect fresh wind slabs to be sensitive to your weight. These slabs are likely to be stiff and dense where winds have been stronger.   Cracking in fresh slabs is a sure sign of instability. These slabs can produce slides large enough to bury you. 

  Loose snow: Sluffs of new snow will be easy to trigger on steep slopes without crusts or wind slabs at the surface. Natural loose snow slides may occur on slopes that face the sun if the clouds allow more sun through than expected. If the snow you are traveling through is becoming moist and you are seeing balls of wet snow rolling downslope, these small slides may be releasing naturally. Slides that entrain moist/damp/wet snow can quickly become larger and more powerful than you might expect.

  Slabs at new/old interface: Snowpit observations and natural avalanches point to the potential for avalanches failing at the base of the new snow, even in terrain sheltered from the wind. Our observations are limited, and we can't yet say with confidence if this interface will be a longer-lived weak layer or just a flash-in-the-pan. Some of the observed avalanches that failed on this layer in neighboring zones broke many hundreds of feet wide. 

  Even small slides can knock you off your feet and send you for a ride in ugly terrain. Surficial slides will travel fast and far on the stiff surfaces underneath. Remember that all of these smaller avalanches take place on the stage set by the Persistent Slab problem above. Smaller slides can be effective triggers for much larger Persistent Slab avalanches as they rocket downslope.