Elkhorns

Avalanche problems

• 

  Persistent Slabs

  N

  NE

  E

  SE

  S

  SW

  W

  NW

  • Alpine
  • Treeline
  • Below treeline

  Likelihood

  Likely

  Size

  1–2.5

  The What: Last week's cold snap produced two persistent weak layers, that are now buried 1-2' below the snow surface.  Weak facets and surface hoar were observed yesterday in two snowpits, one at 8,000' (West Aspect) and the second a 6,000' (West Aspect).   In locations where a more cohesive slab has formed above these weak snow grains, we've seen numerous human-triggered avalanches this week.  They have been on a variety of aspects above 7,000'.  All of these slides have been remote triggered from low-angle terrain!

  The Where: You can find weak snow on nearly all elevations and aspects buried below the storm that rolled through last Sunday, which produced 1-2' of snow.  Last weeks frigid temperatures created weak snow at the surface which we call near-surface facets, and surface hoar.  This weak snow has been reactive in areas where a slab has formed above it.  

  What to do: Surface hoar and facets don't disappear overnight, that's why we call them a persistent weak layer.  You may feel whumping or collapsing or observe shooting cracks, but not always.  If you truly want to know what's beneath you, get out your shovel and do some digging.  If you find strong snow, over weak snow you have a slab.  Stick to lower-angle terrain, increase your margins, and ski and ride one at a time in steep terrain.  

  So What: Yesterday while out riding in the East Fork of the Pine, I observed snowmobile tracks on steep slopes, with numerous trigger points.  So how come these folks didn't trigger an avalanche, and why should I take your advice you might ask?  The reality is, the snowpack is incredibly forgiving, most of the time, even when the snowpack structure is poor.  But, when the structure is poor, I reduce my personal risk threshold, because all I have to do is find the sweet spot, and that might make the difference in whether I get to come home safe at the end of the day.  

  

• 

  Wind Slabs

  N

  NE

  E

  SE

  S

  SW

  W

  NW

  • Alpine
  • Treeline
  • Below treeline

  Likelihood

  Possible

  Size

  1–2

  The winds have backed off in the last 24 hours, but there still remains the possibility of triggering a more stubborn wind slab near and above the treeline.  Look for clues such as cracking, strong over weak snow, and surface texture for clues of windslab formation.  Triggering a windslab 1-2' deep is not out of the question on steep slopes >35 degrees today.  

  

• 

  Deep Persistent Slabs

  N

  NE

  E

  SE

  S

  SW

  W

  NW

  • Alpine
  • Treeline
  • Below treeline

  Likelihood

  Unlikely

  Size

  1–3

  We are still observing poor structure in our snowpack in the form of basal facets and crust facet combinations near the ground in the Elkhorn mountains and in the Northern Wallowas. These deeply buried persistent grain types are failing in snowpit stability tests, so the deep persistent problem is still on the table for the Elkhorn Mountains and Northern Wallowas. These deep persistent weak layers that reside at the bottom of our snowpack will get tested this weekend, especially at lower elevations by warm temperatures. The likelihood of triggering one of these very dangerous avalanches is low, but today, the added weight of a human might be all it will take for one of these deeply buried weak layers to fail. The consequences of triggering a low likelihood high consequence deep persistent slab avalanche would be severe and most likely unsurvivable. A deep persistent slab avalanche can be triggered on steep terrain where the snowpack is thin. Examples of where thin and weak areas are located would be shady lower elevations, the windward side of wind-swept ridges, and rocky cliff band areas. The best way to avoid triggering a persistent slab avalanche is to stay off of and out from under slopes steeper than 30 degrees while this problem persists, especially near shallow rocky areas and low-elevation locations where the snowpack is relatively thin.