Turnagain Pass and Girdwood

Lawinenprobleme

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  Wind Slabs

  N

  NE

  E

  SE

  S

  SW

  W

  NW

  • Hochgebirge
  • Waldgrenze
  • Unterhalb der Waldgrenze

  Wahrscheinlichkeit

  Likely

  Größe

  1–2.5

  Recent Avalanches: Yesterday we got reports of 2 large natural avalanches in the Girdwood area that likely occurred during the wind event on Saturday night. One of these occurred on Fish's Breath Mountain on a southeast facing slope at about 4,000'. The other occurred in Ragged Top Bowl on a northeast facing slope at 3,400'.  Both of these avalanches took snow to the ground in places and were large enough to bury a person. The snowpack on the north side of the Girdwood Valley (where these avalanches occurred) is different than the south (Alyeska) side. It has less snow making it more dangerous than the south side of the valley.

  Wind speeds yesterday in this zone were between 10 to 25 mph on the ridgelines from variable directions with a gust to 47 mph on Sunburst. Winds calmed briefly before picking back up again last night. These winds were strong enough to build wind slabs in the normal places like below ridgelines (see photo here of Fish's Breath natural avalanche) and in cross-loaded gullies. The photo below of the large natural avalanche in Ragged Bowl is a great example of cross-loading. One side of the avalanche is much deeper than the other. Both of these avalanches are larger than we would expect could be triggered by a person today in the heart of this zone in Turnagain Pass. Although, problem 2 below describes an unlikely event that is still in the realm of possibility.

  Variable wind direction occurred yesterday making wind slabs possible on any aspect in any area that has no vegetation for protection. Wind slabs sometimes look like "pillows" of snow. They may be smooth or have some texture, but they are always more stiff than the snow beneath. Shooting cracks are the "red flag" that tells us the snow needs some time to stabilize.

  Dry Loose Avalanches: In wind sheltered places there is plenty of cold snow that could be entrained on steep slopes in a dry loose avalanche or sluff. This type of avalanche isn't usually dangerous unless it takes you off your feet and into a tree or off of a cliff.

  

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  Deep Persistent Slabs

  N

  NE

  E

  SE

  S

  SW

  W

  NW

  • Hochgebirge
  • Waldgrenze
  • Unterhalb der Waldgrenze

  Wahrscheinlichkeit

  Unlikely

  Größe

  2–3

  The large natural avalanches in Girdwood yesterday likely occurred on weak snow close to the ground that was overloaded by wind deposited snow. As I described above, the snowpack is different on the north side of the Girdwood Valley and avalanches like this are not likely in the majority of this zone. However, this is the type of avalanche we think is unlikely, but not impossible above 2,500'. The weak layer we are concerned with is buried 2 to 6' deep and there is still a chance someone could find a thin spot and trigger an avalanche like the one pictured here. This problem exists in the same place as the wind slab problem so the safest thing is to look for softer snow below 2,500' for today.