UDOT PLANNED AVALANCHE CLOSURES!!

Avalanche: Mary Lake Ridge

Observer Name
B
Observation Date
Wednesday, February 22, 2017
Avalanche Date
Wednesday, February 22, 2017
Region
Salt Lake » Big Cottonwood Canyon » Brighton Perimeter » Mary Lake Ridge
Location Name or Route
Mary Chutes/Theobald
Elevation
9,300'
Aspect
North
Slope Angle
45°
Trigger
Snowboarder
Trigger: additional info
Cornice Triggered
Avalanche Type
Hard Slab
Avalanche Problem
Persistent Weak Layer
Weak Layer
Facets
Depth
3'
Width
150'
Vertical
250'
Caught
1
Carried
1
Comments

At around noon a single snowboarder (holding his snowboard) he was walking out to the edge of the cornice to scope out the drop off of the Theobald Cliff/Cornice in the Mary Chutes. When he got close to the edge the Cornice collapsed and broke off sending the person over the cliffs and down the slope. The individual rode on top, and once the dust cloud had settled he was standing up brushing himself off, and he told the first responders he was ok and then rode off. The cornice was school bus size. The initial impact of the cornice triggered a 30 foot wide area of snow in the high cliff line under the cornice. This release was probably only 45 to 60 cm deep, and the likely weak layer at this location was Basal Facets/Advanced Facets. It was extremely rocky. Once this piece of the avalanche descended into the open bowl it stepped down to the Rain Crust / Melt Freeze Crust layer from three weekends ago. The structure of the slab was from top down was 45 cm of pencil, then an interface where the hardness changed to 40 cm of one finger. Then there was a 3 cm weak layer that was fist hard, and it was .5 mm facets showing signs of rounding. The bed surface was the slick crust that formed three weekends ago during the torrential rain event in early February. This weak layer was possibly formed by Melt Layer Recrystallization as previously reported in other observations.

The debris pile was at least 1.5 meters deep and it ran into the trees leaving snow deposits 20 feet up.

Coordinates