Turnagain Pass

Turnagain Pass:

During our field day on Pete’s N yesterday we observed several large avalanches on surrounding peaks. The exact age of these is hard to tell from a distance, but our best guess is that they include the storm snow from the New Years storm and possibly older layers from the Christmas storm or deeper. The largest avalanche we observed was at 3000′ on the E aspect of Twin peaks. Another similar looking avalanche up Lynx creek at 3000′ on a N aspect. Finally, on the SW aspect of Lipps at 2800′. These all had relatively wide propagation and released mid slope, which we think is an indication that a persistent weak layer exists at these mid elevations.

Large avalanche on E face of Twin Peaks mid way down the slope. You might have to zoom in to see it, but it is lookers left of Twin Peaks at treeline on the forested ridge in the foreground. Photo 1.4.23

Smaller avalanche on the SW face of Lipps at 2800′. This crown is partially filled in with the strong winds yesterday morning, but looks like it is within the storm snow from Christmas and New Years. Photo 1.4.23

After several large storms this week, including 2-3′ of snow from the New Years storm and 0.5-1.5′ of snow falling on Wednesday, the snowpack needs some time to adjust to the new load. We have seen some large avalanches in the aftermath of these storms and are uncertain what weak layers are the culprit. The weather pattern is expected to calm down today which will decrease the likelihood of natural avalanches and give the snowpack time to gain strength.

Wind slabs up to 2’+ deep which formed at upper elevations over the past 24 hours are the primary avalanche problem today. These are likely for human triggering and typically found along ridgelines and gully features above treeline. To identify wind slabs look for deposits of deeper snow that have a firmer and possibly hollow feeling snow surface. Using small test slopes is a great way to see if wind loaded slopes are still reactive to the weight of a skier or rider. Due to uncertainty around the presence and distribution of persistent weak layers above 2000′ we are still recommending a conservative approach to terrain selection and decision-making today (see problem 2 for more details).

Strong E winds yesterday morning were rapidly building fresh wind slabs at upper elevations. Photo 1.4.23

We are still trying to piece together how the recent storms have impacted our existing persistent weak layers and possibly created new ones. The message is pretty simple though, very large avalanches 2-4′ deep above 2000′ are still possible. The best way to mitigate the risk from persistent slab avalanches is to stick to smaller terrain features and lower angle slopes.

The combination of a remote triggered avalanche in the Notch Peak area in Girdwood and several large avalanches on the southern end of Turnagain Pass near the Johnson Pass trail head have us scratching our heads a bit about what weak layer(s) is responsible. Most of this recent activity has been at mid elevations and releasing mid slope, which indicates that there is a weak layer that is most prominent around 2500-3000′. Our best estimate is that this is related to a weak interface between the mid-December facets and all the storm snow that fell during the Christmas and New Years storms, but there is a lot of uncertainty since we have not been able to investigate any of these avalanches in detail yet.