Sawatch
SnowpackJason Konigsberg · Mar 29, 2018 · Sawatch
Weather
We only went up to ridgeline in the late afternoon and winds were light. Earlier in the day light wind loading was observed and ridgetop winds appeared to be moderate. Skies were clear in the morning with clouds increasing in the afternoon.
Snowpack
We went to investigate a Persistent Slab avalanche that was triggered by a snowmobiler on Tuesday (3/27/18). The snowpack in the area of the avalanche was 130cms or about 4 feet in depth except were wind loaded near ridgetop. The structure of the snowpack looks similar to many areas with the main layer of concern being a layer of facets on top of depth hoar. The location of this layer is anywhere from 40 to 60 cms from the ground. This is the layer that the avalanche broke on, though it did step down to the ground, and break on depth hoar, in a good portion of the start zone. We conducted snowpack tests and got no results in an extended column test but ~15/100 END results in a propagation saw test. It seems that it is extremely hard to affect this layer but this avalanche and tests show that the layer can still propagate a fracture if affected.--- The snowmobiler triggered the avalanche while almost to the top of this 40 degree slope. He said that he hesitated and had to accelerate to make it up the final pitch. When he accelerated, his track augured in and he felt the track breaking through the slab, impacting weak snow near the ground. The snowmobiler saw the slope fracture and he was able to make it over the fracture line and to the ridge. The area where this slope was triggered is the rockiest area on the slope.---A snowpit is attached with additional data. The snowpit was dug in a sheltered area. When we walked several feet uphill of the snowpit, the slab became much harder. In wind-affected areas the slab was up to knife hardness.