Northern San Juan

Avalanche

Bill Nalli · Nov 30, 2019 · Northern San Juan

Weather

Light snow S-1 in AM ending around noon. Skies slowly clearing afternoon. Moderate gusty wind. First visibility post storm.

Snowpack

Snow depths range from 50 to 100 cm. A 40 cm thick slab of new wind blown snow sits on top of another 40 cm from early November. 2 cm of graupel from the beginning of the storm sits on top of the old snow surface and made for an upside down feel and difficult trail breaking. The old snow surface consists of 1mm near surface facets and hardness increases slightly with depth. All of this sits on to of F hard depth hoar on NW-N-E aspects wherever there is old snow from October. This weak structure is resposible for a widespread natural avalanche cycle that likely took place during the day Friday Nov. 29. Pictures are from a N facing wind loaded test slope near treeline. The entire slope waited to fail until I removed one ski to dig a pit and one foot penetrated the entire snowpack into the depth hoar. The failure propagated onto a 20 degree slope back onto the ridgeline. Very poor stability test results were recorded even after the slope had collapsed highlighting the instability found on similar slopes.

Avalanche

After pit confirmed poor structure and instability I continued higher up the slope and encountered a SS-N-R2,D2-O on a similar but larger slope. N aspect, 11,500' 35 degrees. 2' deep, 100' wide.