Southern San Juan

Avalanche

Chris Bilbrey · Jan 7, 2019 · Southern San Juan

Weather

Light snowfall for most of the tour. Around 1430, skies began to break and overcast for another hour with no precipitation. By 1530, sun made a grand appearance. Temperatures remained below freezing throughout. West winds were light with moderate gusts on exposed portions of the ridge.

Snowpack

Measured 13" of new snow and 1.35" SWE at 10,650 feet. Recent storm slab was F to 4F (top to bottom) and overall good bonding with New Year storm interface and isolated sluffing on steeper slopes. ECTN results observed in storm slab. Weak facets and depth hoar found in pits on SE and N aspects below December snowfall. Multiple ECTs produced propagating results on same facet layer. Slab above weaker facets finally has enough depth and stiffness to help communicate failure in weak layers. Did not get great visuals of higher peaks, but this area only lacks a significant water load or continued incremental loading for widespread, large avalanches to occur. Snow depth ranged from 0.75-1.25 m throughout our tour. Began to observe widespread collapsing and surface cracking above 9,500 feet with multiple loud, audible collapses along ridges in wind-drifted pockets.

Avalanche

We remotely triggered an avalanche approx. 150 feet away from a lower-angled, treed rib. There was no overhead hazard where we triggered the slide from. Slope angle at trigger location was estimated less than 35 degrees. Crown line located at the top of a convex roll with an estimated slope angle greater than 35 degrees. Unknown how far downslope the slide ran, but path length estimated on topo map at 900 feet from crown line location.