There have been 3 primary instability cycles this season around Mores Creek Summit (MCS), that we are aware of. Mid-December, mid-March, and April 1st. Each of these cycles included natural and skier-triggered avalanches that were D3 (mid-December and April 1st) or D4 (mid-March) in destructive size.
These observations (made on March 19) were of avalanches that are estimated to have occurred on March 15. Approximately 150mm of new SWE was deposited between March 13-15 in the MCS zone. Our helicopter photos were taken on March 16. Six separate avalanches were observed on March 16 from the helicopter, and again on March 19 from the ground.
Other observations: debris piled on uphill side of trees is 1.2-3.5 m deep. In many locations at the crown, the uppermost ~1 m of the bed surface rolled over from 31 degrees to 29 degrees against the base of the crown—meaning, when the avalanche released, the slab was able to pull a small amount of additional slab from the lower angle fringe at the very top of the crown’s perimeter. Several large blocks were observed above the crown (up to 20m in size) that fractured but moved less than a half meter down slope.
1. Overview, looking southwest, taken March 16. General path, plus Sunset Peak Lookout in background for reference; note equally large avalanche in background/left, northeast of Sunset Peak.
2., 3. CalTopo mapping of crown, slope angles, and 2 crown profile locations (CP1 and CP2); outline of separate avalanches observed shown in orange polygon (including ones in the Steep Creek drainage).
4. through 9. Photos of crown, bed surface, debris piled on uphill side of trees, slab blocks, and fractures.
10., 11. Photos of rounded surface hoar crystals, 1-2mm @ 1.24 cm depth