Avalanche Activity

Hatcher Pass received about 16″ of new snow this week on 2/2- 2/3 and 2/5.  New snow and wind contributed to tipping the balance in the snowpack, resulting in numerous slab and dry loose avalanches. The majority of the naturals occured on 2/4 and 2/5, with one remotely triggered slab avalanche reported on 2/6.  These avalanches failed in three locations in the snowpack:  1) storm snow 4-6″ deep on buried surface hoar and/or a crust on all aspects (most observed on SE through SW aspects) on slopes above 35º, and 2) 1-2 feet deep slabs failing on old weak mid pack facets, mostly on west through north aspects, on slopes above 35º, and 3) 2-3 foot deep slabs, in some cases remotely or sympathetically triggered, failing on weak facets close to the ground, generally West to North aspects, previously windloaded, on slope angles estimated at 35-38º. Loose dry naturals were observed on all aspects, on slopes above 35º.

Also noteworthy…a slab avalanche (SS-ASu-D2-O) was unintentionally human triggered on 2/4 on the W/SW aspect of Marmot. This person was caught, carried, pulled their airbag, and buried up to the chest. While being carried, another avalanche was sympathetically triggered, increasing the size, amount of debris, and consequence of this avalanche. The victim was reported uninjured. 

See Observations Here from Mid-week Summary

See Observations Here

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Above: 2/4 – Human triggered avalanche on Marmot Mountain, SW, 4000′

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Above: Crown cross section from avalanche labeled “B” in previous picture, showing an old wind deposited hard slab sitting over a relatively thin layer of weak snow.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Above: 2/4-5, Natural avalanche on Marmot Death Gully, WNW, 3900′, HS-N-D2-O

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Above: Debris from Death Gully avalanche, and additional subsequent, shallower avalanche on the SW nose feature of the Death Gully.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Above: 2/5 – Near Punk Spines, NW, 3200′, natural slab avalanches, one with wide propagation.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Above: 2/5 – Marmot, SW, 3000-4000′, Many thin, shallow, widely propagating, 4″ soft slabs, failed on BSH that formed between the 2/2-3 storm and the 2/4-5 storm. Since the avalanche activity on 2/4-5, just after the storm, this layer has stabilized relatively quickly. This is likely due to layer penetration of the surface hoar into adjacent soft snow layers. Currently this is not a primary avalanche concern.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Above: A thin line is visible in snow pits marking the 2/4-5 BSH. Notice it is very close to the surface of the snowpack.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Above: 2/6 – Idaho Peak, North aspect, 4000′. Estimated to have been a remotely triggered avalanche which sympathetically triggered a second avalanche adjacent to the first. The reporting group indicated that this slide covered the their tracks from earlier in the day. They believe they were the only group in the area, and remotely triggered it from the an area near the base of the slope. They did not see it happen. The avalanche failed on weak layers near the base of the snowpack, and was large enough to bury, injure or kill. No one reported to have been caught, carried, injured, or buried. Thanks to mtf_alaska on Instagram for sharing their photo.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Above: 2/7 – Subsequent to the last two snow storms, and in defiance to the cold temperatures the weather stations reported, widespread “drizzle” crusts formed up to at least 5000´ on the snow’s surface. These layers are currently not an avalanche concern, but once buried could become breeding grounds for thin, weak, faceted layers in the snowpack in the future. This crust has gained strength over the last few days, and in this picture, made a shooting crack. This shooting crack is only in the crust layer and does not represent a deeper shooting crack in the snowpack that would otherwise be a huge red flag for avalanches. It’s more like a stale candy bar with a brittle outer coat.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Above: 2/8 – On the surface of the snow, sitting on a drizzle crust, a new crop of widespread surface hoar has formed. Not a problem now, this layer could be problematic in the future. (Crystal card has 2.0mm grid)