We saw this naturally-triggered avalanche on the SW side of Tenderfoot Ridge on
Saturday, 3/24 (see photo 1). This slide occurred sometime on Saturday morning
or Friday night. We believe the trigger was a small cornice break, which then
fell on the fresh and unstable wind slab sitting below the ridge crest.
This new wind slab was 5-10 inches thick and failed on top of an almost 2 inch
thick sun crust (see photo 2) which made for a slick bed surface. While the
touchy wind loaded portion of the SW face only extended about 20-30 feet
downslope, this slide entrained all the new snow on top of the sun
crust. The avalanche ran about 700 vertical feet and the debris was 2-4 feet
deep at the toe.
Pit tests next to the crown had this new wind slab failing on isolation on top
of the sun crust. However, a ski-cutting attempt further up the ridge on the
same face yielded no results.
This sun crust is prevalent on S, SE, and SW aspects throughout the region.