Northern San Juan
AvalancheAnonymous · Feb 27, 2024 · Northern San Juan
Weather
S2 or higher snowfall and high wind gusts, initially out of the SW and shifting to the NW. Skies ranged from obscured to broken.
Snowpack
Generally a shallow snowpack exists even on northerlies ATL, with the depth in the Alta Lakes zone ranging from scoured bare rock on ATL southerlies to 80-120 cms on NTL/ATL northerlies. 40-50 cm of widespread facets underlie the snowpack. I dug a hasty hand pit just before we skied the slope and found about 10 cms of wind slab beneath about ~8-12 cms new (or freshly wind transported) snow, that did not show planar failure on the new/old interface in that location. However, that wind slab was significantly deeper just above where we skied, where the avalanche released. Graupel fell in this area at the beginning of the storm, which may have contributed to particularly poor bonding in isolated areas. Heavy spindrift from the cliffs above also was likely contributed to accelerated stiffening of the slab.
Avalanche
Our group had transitioned and was preparing to descend one at a time. The first skier descended to a low angle area about 300' below the group. The second skier triggered a small (D1) soft wind slab avalanche, while setting an uphill boundary track with the steeper terrain. Skier 2 was in 28 to 30 degree terrain, and the avalanche propagated above her to an isolated pocket of steeper terrain (~35-37 degrees) above. The avalanche broke approximately 75-80' wide and ran for about 100-120' until it came to rest in planar, low angle terrain.