Turnagain Pass

A lot of people triggered avalanches yesterday and so far we have not heard of anyone caught or hurt. Most of these were remotely triggered and all reported to be around 1.5 to 2′ deep. The weak layer is confirmed to be buried surface hoar (BSH) in a couple avalanches that were investigated and suspected in the others. Avalanches were releasing in the trees and on open slopes. Here is a list of known avalanches:
– Eddies (westerly facing roll):  One skier triggered slab, several recent naturals seen.
– Tincan Trees:  Several slabs triggered in the trees, debris covering portion of an up-track
– Seattle Ridge (Widowmaker and SE side):  Four or more slabs triggered, many recent naturals
– Cornbiscuit/Magnum (Superbowl):  Recent natural slab avalanches observed

There was also a large avalanche that released overnight on Monday (two nights ago) that deposited debris onto the railroad tracks just a few miles SE of Girdwood. A northbound train ran into the debris and derailed. Two crew on board, no one hurt. Photos HERE and media report HERE.

Westerly roll on Eddies Ridge. Skier triggered with a ski cut. No one caught. Brady Deal, 1.17.23.

Example of many soft slabs that released in the Tincan Trees. Anonymous, 1.17.23.

Debris filling a terrain depression that an up-track often follows. Anonymous, 1.17.23.

Remotely triggered avalanches on Widowmaker from the ridge. Travis Smith, 1.17.23.

Debris from large natural avalanche near Kern Creek, covered railroad tracks, subsequent train derailment. Travis Smith, 1.17.23.

Triggering avalanches around 1.5 to 2 feet deep, similar to yesterday, will be likely again today. These are generally soft slabs that are releasing on a layer of surface hoar that was buried around a week ago (1/10 BSH). This is now becoming a ‘persistent slab‘ issue. As new snow piles up, the avalanches breaking on the layer will get bigger, as seen yesterday. Monday night’s snowfall exceeded expectations with 14-20″ at Turnagain Pass, hence slabs breaking around 2′ deep that were also composed of snow that trickled in over the last week. The storm headed in tonight could add another foot by tomorrow afternoon, creating larger slides if the storm verifies.

Adding to the issues in the top of snowpack, will be the possibility for wind slabs to develop today as ridgetop winds increase from the east. Winds are slated to start blowing hard enough to drift snow by noon. Wind slabs could overload the buried surface hoar, creating larger avalanches. Debris from a small wind slab could also trigger these 2′ deep slabs.

All in all, there are very touchy avalanche conditions currently and we haven’t even gotten to the issues at the base of the snowpack. More on that in Problem #2. Traveling in the mountains will require very careful terrain management. Even in treed areas we need to be on our guard. Small slopes can create enough debris to fill in depressions (as seen in the portion of the Tincan connector trail that was covered yesterday, photo above). Knowing we could trigger avalanches from a distance, from below a slope, or potentially threaten another group below, are all reasons to stick to mellow terrain.

A series of slabs triggered by a rider yesterday above the Widowmaker slide path on the backside of Seattle Ridge. Rider did not know these were triggered at the time of release. Photo by Travis Smith, 1.17.23.

At elevations above around 2,500′ triggering a really big avalanche that breaks near the ground is still a concern. The weak layer with this problem is that Thanksgiving crust/facet combo we have been talking about for a while, buried between 3 and 6′ deep. The last avalanches it produced were two large slabs on Cornbiscuit, 11 days ago. With more storms comes more loading and all this adds stress to the snowpack. However, it is uncertain whether the loads are big enough to make the deep weak layer more reactive.

In short, deep slab avalanches are notoriously tricky. They can go quiet for days, or weeks, then a small storm or person hitting just the wrong thin spot triggers one. When the uncertainty is high and the consequences are even higher, the only option to manage the problem is by staying conservative with terrain choices. In this case, similar to the travel advice stated above regarding the issues in the top couple feet of the snowpack.