Turnagain Pass

Yesterday afternoon, during the tail end of a 1.5 day intense northwest wind event, we were able to get a look around as to the damage these winds caused. The majority of the natural wind slab avalanches seen were south of Turnagain Pass in Summit Lake and down toward Seward. There were a few natural wind slabs along Turnagain Arm and one larger slab on Raggedtop near Girdwood. We did not see any new avalanches from the road in Turnagain Pass itself despite a significant amount of wind effect.

Natural wind slab avalanche releasing sometime overnight on Thursday (4.8) or early Friday morning (4.9) in the Summit Lake are seen from the Seward Highway. This slope is the northern most avalanche path on Summit Peak. Slab looks to have stepped down into weak layers near the ground. 4.9.21.

Natural avalanche on Raggedtop in the upper Girdwood Valley/Crow Creek area. Released sometime during the NW winds on 4.8 or 4.9. This is the 4th time a portion of this face has slid over the past few weeks. Photo taken 4.9.21.

A bone-fide dust storm (a haboob if we were in the Sahara) tore down Turnagain Arm Thursday and Friday. 4.9.21.

 

A blanket of dust now covers the slopes on Kern and Blueberry mountains along Turnagain Arm.

With a quiet, but cold, weather day on tap before the next system moves in tomorrow, lingering wind slabs formed by the strong northwest winds will be the main concern. These slabs should be quite hard and on a variety of aspects due to the intense pummeling of the winds in a variety of directions. Although much of the snow surface saw scouring, exposing old sun crusts on southerly aspects and forming anti-tracks wherever old tracks existed, there are sure to be some newly wind loaded terrain features to watch out for. Additionally, wind slabs could be overlying old weak layers, especially to the south of Turnagain Pass around Summit Lake where a much thinner and weaker snowpack exists (more in Problem #2).

Keep an eye out for areas where the winds deposited snow in large drifts or slabs. These often appear as smooth rounded surfaces where stiffer snow sits over softer snow. Slabs could be found lower on the slopes and even in the trees. Watch for cracks that shoot out from you or collapsing (whumpfing) in the snowpack. These are clues you’ve found a slab.

Even though we may see some sunshine and warming daytime temperatures, surface crusts are not likely to warm or soft much with the cold temperatures and light breeze.

The north side of Tincan seen yesterday. Much of the soft surface snow appears to have been wind effected. Note the wind ripples and anti-tracks along the CRF ridge on the right side of the picture. 4.9.21.

The natural avalanches seen in both Raggedtop near Girdwood and Summit Lake mentioned above, both point to wind slabs overloading older weak layers. These are the facets and buried surface hoar in the top 3 feet of the pack that we haven’t stopped talking about. It’s clear the wind slab in Summit Lake broke into older weak layers creating a larger avalanche. The Summit Lake area has a thinner and weaker pack making this more concerning here. Also, judging by the photo from Raggedtop, old weak layers could have played a role here too. Although we have not seen this at Turnagain Pass recently, it’s good to keep on our radar anywhere we go. Slopes on the northern half of the compass are most concerning as they do not have sun crusts to help tie the pack together.

Knowing these layers are there, listening/feeling for whumpfing and watching for any other signs of instability are good things to keep in mind. As always, use good travel protocol, and consider the consequences if an avalanche does occur.