Maritime

Avalanche problems

• 

  Loose Wet

  N

  NE

  E

  SE

  S

  SW

  W

  NW

  • Alpine
  • Treeline
  • Below treeline

  Likelihood

  Possible

  Size

  1–2

  The #1 avalanche problem a user encounters today will depend upon the area they choose to travel.  The most active problem, though, will be wet loose in the low elevations of the Maritime snow climate zone.  This includes Keystone Canyon, where active natural wet loose activity was reported yesterday.  A short term peak in temperatures occurred yesterday, which should coincide with a peak in natural avalanche activity for the Port of Valdez area as temperatures have dipped below freezing in town.  It should be noted,  that temperatures remain well above freezing at 12 mile wx station as of 6 am, which is the closest working station to Keystone Canyon.

  In wind exposed areas, the snow that is available for wet loose activity is confined to the new snow that fell last week that has settled to ~ 6 inches.  This new snow sits above old, hard wind affected surfaces that will act as an effective bed surface but will limit the amount of snow available to slide and be resistant to breaking down with above freezing temperatures.

  In areas that are more wind protected, like Kestone Canyon and other steep canyons, the new snow is sitting on weak faceted snow created by the early February drought.  These facets will allow additional entrainment of wet loose material and could produce slides with more volume.  When assessing wet loose hazard it is extremely important to take the hazard in relation to the terrain you are exposing yourself to.  Are there terrain traps? Are there consequences if I were to be swept off my feet by even a small avalanche? 

  The size and shape of the terrain above you along with the amount of loose snow available to slide, directly correlates to the size of the wet loose activity that can occur. Terrain traps and exposure below you compound consequences.

• 

  Storm Slabs

  N

  NE

  E

  SE

  S

  SW

  W

  NW

  • Alpine
  • Treeline
  • Below treeline

  Likelihood

  Possible

  Size

  1–2

  New snow from the last week has been very gradually accumulating and will be the main concern for those traveling on the North side of Thompson Pass and at elevations above 1500' on the south side of the Pass.  The majority of this snow fell between 2/14-16, although trace amounts continue to accumulate.  With time and an increase in temperature, this snow has become more cohesive but remains shallow ~ 6 inches settled in most locations, making any avalanche activity shallow as failure beneath the new/old interface is currently unlikely.

  This new snow sits on a variety of surfaces.  Starting down low (below 2000') new snow sits on well developed buried surface hoar.  In these areas the new snow has shown signs of instability such as small shooting cracks.  The shallow depth of the new snow limits the hazard; however could be an issue in steep terrain that ends in terrain traps or in consequential terrain where being swept off your feet would result in falling over cliffs.  This layer is not yet listed as a separate avalanche problem as a persistent weak layer due to its shallow depth, but it will likely become one later as snow incrementally builds a deeper slab of consequence.

  Between 2-3k buried surface hoar becomes less developed in structure and size with signs of instability dissapearing.  The new/old interface is mixed and consists of old wind affected surfaces that have shown good bonding and more protected pockets of old facted snow where bonding is not as strong.

  Above 3k the bed surface beneath the new snow is mostly hard wind affected snow with good bonding.  The concern in these areas would be pockets of wind loaded snow where slabs are deeper and stiffer, creating the possibility for human triggered avalanches likely in small pockets.

  Pay attention to how much new snow there is, what the snow is sitting on and how this all relates to the terrain that you are travelling on. Expect this relationship to change as you move through the terrain.  Watch for signs of instability such as shooting cracks, collapsing, and natural avalanche activity.  The presence of any one of the indicates that the is unstable smow that is capable of producing an avalanche.