Avalanche: Big Cottonwood Canyon

Observer Name
B
Observation Date
Thursday, April 16, 2020
Avalanche Date
Thursday, April 16, 2020
Region
Salt Lake » Big Cottonwood Canyon
Location Name or Route
Upper Big Cottonwood
Elevation
9,900'
Aspect
Northeast
Slope Angle
Unknown
Trigger
Natural
Avalanche Type
Soft Slab
Avalanche Problem
New Snow
Weak Layer
Density Change
Depth
14"
Width
90'
Vertical
400'
Comments
Observed this Natural at 0900, and it appeared that it released in the early morning hours during the high PI rates combined with Moderate to Strong Westerly Winds. See photo 1. The Upper Crown is not visible in the photo but the vertically running right flank is, as well as a highly defined stress crack at the bottom of the chute. The stress crack is on the right flank as well, and it appeared that it did not release at the crack location due to the slope angle letting up. The debris was significantly covered up from Wind and New Snow, and it was likely that this occurred around 0300 on 20200416.
Second photo is a shot of just one of the debris piles created while intentionally triggering/slope cutting steep convex rollovers at 0830 on Steep (35 degrees and greater) N and NE aspects between 9200 and 9600 feet. Slabs were Four Finger Plus, Reactive, and easily located on these Specific type terrain features. See photo 2. Weak Layer was 1 cm layer of preserved Light Density Snow (Broken Stellars). See photo 3. This Light Density Layer fell as the initial inch in the latest rounds of snow that has been falling all week long. It was resting on the pre-storm m/f crust; and this crust may be found on all aspects up to at least 10,000 feet. Typical Crown: see photo 4. Cracking in the New Snow was Widespread and observed on all aspects with slope angles of 30 degrees and greater. (See photo 5)