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Avalanche: Lewis Peak Area

Observer Name
Doug Wewer
Observation Date
Wednesday, January 9, 2019
Avalanche Date
Monday, January 7, 2019
Region
Lewis Peak Area
Location Name or Route
Lewis Peak Area
Aspect
Northeast
Trigger
Natural
Avalanche Type
Hard Slab
Avalanche Problem
Wind Drifted Snow
Depth
4'
Width
300'
Vertical
150'
Comments
Found a few hard slab avalanches today along the ridge lines between 7500’and 8000’ on East through NNE aspects in the Lewis Peak Area. These likely failed during Monday’s wind event, but possibly earlier in the storm. The slope angles were what surprised me - I measured 27 and 31 degrees on one starting zone. I had to recheck it with my phone’s inclinometer because I didn’t quite believe it. Even lower-angled adjacent slopes slid that were connected to it. Large blocks of debris, many taller than my 130 cm poles. 
 
I tried to identify the weak layer layer that it failed on, but it was difficult to find unaffected snow on the flank that I felt comfortable being on. I found two thin (3-4” thick) wind slab layers that produced CTE’s with Q1-2 shears in the top 12” of snow. Weak layers were density inversions. I found a crust and facet layer identical to Mark’s recent video on the divide, but it was completely unreactive in my tests, and cohesive enough to hold the entire column together when I picked it up. I also got 2x CTM on facets near the ground. The slides appear to have slid mid-pack, and I suspect it slid near the crust/facet layer despite my test results. I didn’t have time to investigate other areas. 
 
The debris blocks had an interesting, artistically sculpted look from wind erosion. 
Video

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