Convict area - Old Mans Bowl, Fracture investigation
Signs of Unstable Snow
ESAC staff ventured into the Old Mans bowl today to conduct a fracture investigation of the Skier triggered avalanche reported on 3/26.
This Persistent slab avalanche occurred initiated at 10,500’ on a due east aspect and ran about 1500’. The crown was an average of about 45 cm (18”) deep with a max depth of about 60 cm (24”) and the crown was 120’ wide. It was a size D1.5 with a debris pile averaging about 50cm deep with a max depth measured of 80 cm.
Our fracture investigation showed a generally 4f-1f hard slab resting on a k hard melt freeze layer which formed during our last dry spell March 16-18. In between, we found a thin layer of near surface facets .5-1mm in size and this was the fracture plane.
Stability tests nearby pointed towards a relatively stable snowpack which was somewhat surprising but highlights the tricky nature of this current persistent slab problem. IE. Traditional warning signs may not proceed initiation of an avalanche.
We also discussed the isolated nature of the structure distribution and the relatively soft and unconsolidated nature of the overlying slab. This winter has been far from the “norm” and while it certainly felt like the end of March on the hill today our snowpack is not one to rest easy on for the near future. It will be interesting to see how this weak structure adapts to the new load that is promised with tomorrow’s storm.
Light , SW
The strong Sierra sun was out today making for a lovely spring-like adventure in the hills. Mostly clear skies prevailed with light winds out of the southwest and temperatures near freezing. All in all, it was a lovely day on the eastside.