Sawatch

Avalanche

CMC AvalancheScience · Dec 15, 2018 · Sawatch

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Weather

New snow on 20181212 came with high winds. Clear weather followed over the last few days with warm temps 25-30. Mostly clear skies as well. Moderate winds midday that subsided in the afternoon. HS varied on different aspects, with East NTL and ATL HS near 100cm, North aspects NTL and ATL HS 100-125cm. South and West aspects NTL and ATL HS was 60cm, while in wind loaded areas HS was somewhat deeper.

Snowpack

Mostly faceted snowpack on all aspects and elevations. Harder slabs in the midpack are present on North, Northeast, East, Southeast and South aspects ATL and NTL. BTL, no slab was found. South and Southeast aspects ATL showing a reactive wind slab at the surface that was the cause of the avalanche on 20181214. 2-4mm basal facets at the base of the snowpack were observed on all aspects and elevations. A pencil hard layer was found at the base of the snowpack on West facing and some South facing aspects NTL and ATL.

Avalanche

Our group witnessed a skier triggered avalanche on 20181214 on the South aspect ATL path below Buckeye Peak that caught two skiers who were skinning up the gully. The fracture propagated quickly above the skiers and across some terrain features to deeper snow. Both skiers were caught in the slide and were able to extricate themselves. We coded the avalanche as HS-AS/u-R2-D1.5-I and estimated the crown width as 200m with a crown height ranging from 3cm to 150cm. We estimated the path length to be 100m. We returned to the site of the slide on Saturday 20181215 and verified the dimensions. We found a reactive wind slab above the crown that produced CTV results 9cm below the surface and CT20 at 50cm below the snow surface. The bed surface was pencil hard facets .5 to 1mm in size. Density measurements of the blocks in the debris showed 2 layers in the blocks, the upper part less dense at 296 kg/m3 and the bottom half of the block denser at 400 kg/m3. Evidence of a previous avalanche was noted skier's right of this slide, above the prominent cliff band.