Turnagain Pass

A large avalanche was triggered yesterday by the third skier on slope on a north to northwest aspect on Big League in the Virgin Creek drainage in Girdwood. The depth of the avalanche ranged from 2-4′ deep and it propagated 200′ wide across several ridge and gully features on a complex piece of terrain. The avalanche released about 30′ above the skier who triggered it and the skier was swept 1000′ over multiple cliff bands, finally coming to rest partially buried at approximately 2800′. Due to the trauma of being carried through the steep terrain the skier suffered a fractured femur and required a helicopter rescue. Our best wishes go out to the injured skier and their party. Thanks to the local skier who saw the avalanche crown from Max’s and responded to assist with the rescue efforts. Thank you all for sharing your experience! (see ob here)

Avalanche crown along the N ridge of Big League with the party waiting for a helicopter rescue in the lookers right lobe of the debris. Photo Peter Ostroski 4.19.22

Based on the avalanche triggered in Girdwood yesterday we are elevating the deep persistent problem from an additional concern to problem 1. There is a lot of uncertainty about how widespread this avalanche problem is, but it seems most likely that a buried weak layer of facets from mid-March are the culprit in this very near miss. The depth of the avalanche, wide propagation, and fact that it was the third skier on slope all point towards a deeply buried persistent weak layer. It is possible that the warm air temperatures yesterday afternoon started to warm up the snow on the surface, even on this north facing aspect, and made this avalanche ripe for triggering. This avalanche was definitely unexpected from our perspective and could be an indication that the warming temperatures are starting to reactivate buried weak layers.

Very large human triggered avalanches 3-6′ deep will remain possible during the warm and stable weather over the next two days. Dry snow conditions are holding on at upper elevations on northerly aspects and therefore the snowpack is still behaving as if it is mid-Winter. Assessing snowpack stability using snowpits tends to be unreliable with deeply buried weak layers. Due to the potential consequences of being surprised by another avalanche like the one on Big League, we recommend conservative terrain selection if you are seeking out dry snow on high elevation north aspects.  

Another view of the large skier triggered avalanche on Big League in Virgin Creek in Girdwood. Photo 4.19.23 by Peter Ostroski

Temperatures are slowly creeping up and starting to reach into the high 30s or low 40s F even at upper elevations. These warming temperatures combined with strong solar warming could be enough to start causing widespread wet loose avalanches as the day heats up in the afternoon. Below 1500′ the snowpack is capped with a supportable melt freeze crust on the surface that is melting in the afternoon. Most of the wet loose avalanche activity we have observed recently is on steep southerly aspects, but as the temperatures increase these could become more widespread on east and west aspects as well.

The advantage of wet loose avalanches is that they are fairly predictable in terms of timing and aspect. East aspects exposed to the sun tend to heat up first, then southern aspects, and finally west aspects later in the day. You can monitor the conditions by looking for roller balls and wet loose avalanches releasing naturally from steep rocky terrain as an indication that the snowpack is weakening. It is also helpful to pay attention to how deep the wet snow is on the surface where you are travelling because that gives you a sense of how large the wet loose avalanches could become. If you are sinking in up to your ankles in wet snow then that is a sign to move to a shadier aspect because wet loose avalanches that release naturally could grow to become large enough to bury a person if they run down a large slope. So far the mountains have been mostly holding together and there has been less wet snow avalanche activity than normal for this time of year. With the warm temperatures and sunshine over the next two days this could change quickly to the beginning of a spring shed cycle.

Recent wet loose avalanches releasing naturally from steep south facing terrain. Photo 4.19.23