Continental

Problemi valanghivi

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  Deep Persistent Slabs

  N

  NE

  E

  SE

  S

  SW

  W

  NW

  • Alta quota
  • Limite del bosco
  • Sotto il limite del bosco

  Probabilità

  Unlikely

  Dimensione

  3–4

  January was a month characterized by multiple extended periods of heavy snowfall above 2000' and heavy rain below.  In Valdez, 24.69" of water equivalent was recorded for the month, most of this being rain.  On Thompson Pass over 300" of snow was recorded at DOT camp.  This constant loading of the snowpack produced a major avalanche cycle on January 11-12 with dozens of D3 avalanches observed along Thompson Pass road corridor.  Deep slab avalanche activity stopped despite a continuation of heavy snowfall.  The exception to this was a few deep slabs that released in the Mt. Dimond area on the 19th.  

  The stormy month came to a climax with a storm on the 25-26th that produced 4-5 feet of snow on Thompson Pass and Valdez receiving 6.75" of water in 48 hours and 4"  in a single day.  After this storm there was very little natural avalanche activity.  A couple of days passed before the late January wind event started to redistribute the abundant amount of dry snow that was available for transport.  This loading of the snowpack tipped the scales in a few places and produced catastrophic full depth failure on North Ramp of Mt Francis, East face of Saphire, and the North Face of Three Pigs.

  These avalanches are very unlikely to be triggered by a human directly, but a larger load may be able to affect these layers,  Larger loads include a smaller human triggered avalanche that steps down and cornice fall.  These monster avalanches occurred on some of the tallest/most prominent peaks in the area on steep faces near the summit.  It would be wise to give extra caution to avoid climbing slopes with cornices.  With the weather pattern changing to one that is benign, the snowpack will slowly except the weight of the cumulative January snowfall.  The peak period of stress on the snowpack is now behind us, but with that said, it is not possible to quantify the stress vs strength relationship of the facets at the ground.  Large loading events have shown us that there is the potential for massive unsurvivable avalanches to occur.  

  

• 

  Wind Slabs

  N

  NE

  E

  SE

  S

  SW

  W

  NW

  • Alta quota
  • Limite del bosco
  • Sotto il limite del bosco

  Probabilità

  Possible

  Dimensione

  1.5–3

  Strong North winds began to affect our area on the 29th redepositing significant amounts of dry snow and building deep wind slabs.  Wind speed peaked on the night of the 30th with gusts in the mid 60's on Thompson Pass.  During this time numerous natural avalanches occurred mostly sized 2, but there were also a few full depth releases size 3-4.  Winds are on a slow decline but are expected to continue to be at least moderate through wind channeled terrain like Thompson Pass and high elevation ridges.

  Expect to find an array of wind-damaged snow out there today with wind slabs on lee aspects 1-3+ feet in depth.  These wind slabs are now a few days old and are becoming harder with age.  This increase in strength will make slabs stubborn- unreactive to triggers but if one were to fail it would have the potential for wide propagations, and could fail behind you once you have already traveled out onto the slab.  The likelihood of human-triggered avalanches is decreasing, but still should be considered as consequences would be high due to the knife hard snow that would be involved.  Although unlikely, wind slab avalanches could step down to deeper layers in the snowpack creating unsurvivable avalanches.

  The most likely areas to find reactive wind slab would be in isolated areas where they have freshly formed and are still soft enough that you could penetrate them on foot or skis.

  Wind slabs will have a hollow-drum-like feel and can have a smooth pillowed look or a rippled texture.  These will exist on the lee side of terrain features, cross loaded slopes and just below high elevation ridges.  Signs of instability are not likely to exist, but if they are encountered it is a a bullseye sign of instability.

  In areas where the snow is protected from the wind, good stability and snow structure have been observed in the top 1.5 meters of snow as recently as 1/31.