Olympics

Lawinenprobleme

• 

  Persistent Slabs

  N

  NE

  E

  SE

  S

  SW

  W

  NW

  • Hochgebirge
  • Waldgrenze
  • Unterhalb der Waldgrenze

  Wahrscheinlichkeit

  Possible

  Größe

  1–2

  On Friday (12/16), an excellent observation confirmed the existence and reactivity of a slab overlying surface hoar buried 12/8. A column test near treeline in North Bowl failed on isolation on a thin gray line of surface hoar 15" below the surface. Test results on a SE aspect were more variable but still showed some reactivity. These results suggest the continued potential for human-triggered avalanches nearly a week after the last storm. Last weekend, the same layer was the culprit for a D1.5 natural avalanche (12/10) in Poma Bowl and a D2 remotely triggered an avalanche on a NW aspect at 5200 ft (12/11). These avalanches had all the hallmarks of failure on persistent grains. You don't want to get caught in one of these avalanches as the slab may be 1-2 ft deep in more deeply wind-loaded terrain. Buried surface hoar maintains notoriety for producing avalanches that can release on a low-angle slope, break above you, propagate widely, or trigger remotely as we have already seen.  Observations on this layer remain limited, leading to uncertainty of the problem's distribution. You should assume it exists throughout the terrain at this time. There's an old adage that when uncertainty increases, your terrain selection goes down. For this reason, we recommend more conservate terrain selection than you would normally choose on a Moderate day.  Stick to ridges, thick trees, and slopes less than 30 degrees to maintain a margin of safety. Give space to steeper, unsupported, or actively wind-loading slopes where the hazard will be most elevated. Whumps and rumbling collapses provide a warning that the risk of triggering an avalanche on a steeper slope nearby may be higher than forecast.

  For those that engage with avalanche terrain, recognize that you are accepting a lower likelihood, but higher consequence risk. You can use snow profiles and snowpack tests to confirm the presence of this layer, but they don’t prove its absence. Limit your risk as much as possible, by choosing smaller terrain features with friendly runouts (as opposed to terrain funnels or traps).