Detailed Observation

ObserverGareth Brown

General Observations

Gully One up to 2400′-  Headed up towards Gully One with the goal to dig a pit in the flats at the entrance to the Gully.  Wanted to get an idea of how reactive the November facets were in an area more protected from the brunt of the Thompson Pass wind.  What I found was TOUCHY!!  On the approach I found the surface snow to have no wind affect with ~2 feet of unconsolidated storm snow and settled snow on top of developed facets.  Several large collapses were experienced on the way up, with shooting cracks radiating circles around my skis at times.  About 400 feet above the valley floor,  I experienced a fairly large collapse on a slope with a 15° angle.  This collapse remotely triggered a ~32° slope about 300 feet away creating a D1 soft slab avalanche that was 2 feet deep on a slope with ~100 feet of vertical relief.  After a few seconds I saw that a slope far above and a bit down valley had been triggered as well.  This was a D2 soft slab that travelled about 600 vertical feet sending up a good sized powder cloud.  When I mapped this D2 on Google earth, it was half a mile away from the location where I caused the collapse.  This D2 then triggered a string of large sympathetic avalanches extending through three separate drainages (Gully 1 to Nicks).  The largest of these sympathetics was a D3 that spanned the entire width of the buttress between Gully 2 and Nicks with an estimated crown length of half a mile.   This slide sent a significant powder blast across the valley floor.   Crown heights appeared to be in the 2-3 foot range although it is very likely that it was deeper in spots.  I counted 8 separate avalanches when it was all said and done once I drove down the road to see the full extent.  All of the avalanches were soft slabs, no hard slab debris was noted.  The furthest sympathetic avalanche was over a mile away from the point of collapse.

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Observed Avalanche Activity