Musical Bumps 190207

Final field day of AST2. Kept to TL and BTL for most of the day. Investigating effect of facetting on 190131 temperature crust, especially at its upper limit near treeline. We found that continued low temps, to -26C in the week since the storm had produced significant facetting of the crust, with facets to 3mm underneath and to 1.5mm above. The crust varies in thickness, with minimum being about 1cm at 1820-1900m. This varies with aspect as well, with the thicker crust on SW aspects. The crust is buried from 30-60cm deep, again depending on aspect and wind effect. In places there will be up to 40cm of fist density facetted snow on top. In compression tests, we got easy to moderate sudden collapses with some energy on the facets beneath the crust. Where the crust is still supportive, we had little concern, but where it has deteriorated to the point of failing under a rider, we are less confident. With continued Arctic influence, we expect facetting to continue. We rode this zone as we would with a danger rating of moderate. Lower BTL the crust is fully supportive and 6-8cm thick. We rode this as Low.

Sa reported elsewhere. Crown from 30-60cm on sudden convexity. Triggered from shallow slab depth and propagated widely. Sudden deposition on terrain trap with maximum depth of 1.5m. Clearly stopped while still in glide phase.