Wind slabs larger than expected

CBAC CBAC Observations

Date of Observation: 02/12/2022
Name: Zach Guy

Zone: Southeast Mountains
Route Description: Snowmobiled on various aspects near and below treeline in Cement Creek drainage. I rode along the Double Top ridgeline for a while, and then to the headwaters of the Upper Cement to Tilton Pass.

Observed avalanche activity: Yes
Avalanches: Near Crystal Peak, I intentionally triggered a surprisingly large, hard wind slab from low on the slope on my second pass across the apron. The crown was 2 to 3 feet thick, composed of several iterations of wind drifted snow in the past week or two, and it failed on the January facets layer. The slide was on a SE aspect near treeline. The crown released on a typical slope angle for avalanches (~35 degrees), but it pulled into an unusually low angle terrain feature that was 26 to 27 degrees steep.
Another group of 3 that was skiing/boarding in the same area remotely triggered another large wind slab. They reported that this one was only 7″ thick, but it entrained enough snow to easily bury someone. This was on an east aspect near treeline. Both slides snapped a few small trees and had large debris piles: D2 in size.
I also spotted a handful of D1 to D1.5 natural hard slabs that ran in the past few days on a variety of aspects near and above treeline.
Weather: Mostly clear. Light northwest winds with moderate gusts with a few periods of light drifting.
Snowpack: 1″ of new snow. Along Double Top Ridge, wind slabs were small and isolated to just below ridgeline, about 4″ to 6″ thick. I got some localized cracking about 6 feet wide, but couldn’t produce any shooting cracks while riding across a number of drifts. As I got further up the drainage close to the headwaters, previous wind effects were far more pronounced, with huge sastrugi features and wind drifting in a specific distribution from northerly (down valley) winds. I got good views of a lot of alpine terrain in the Southeast Mountains. Ravaged by winds sums it up. Wind erosion is evident on all aspects, with some isolated areas where you could find drifted slabs, mostly at the bottom of the elevation band. Judging from textures, the most widespread wind slab formation is near treeline in this area.

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