Rivers of loose snow avalanches in Flanders Drainage

From Doug Chabot:

I went ice climbing in Flanders and got hit with a graupel storm (0830) which avalanched off the climbs on east-facing slopes for over an hour. It was pretty spectacular and we found knee deep graupel (small, ball-bearing like grains) 200 vertical feet from the bottom of the cliffs. The climbs that we saw this on were Big Sleep, Bobo Like and Killer Pillar. The snow appears to be sliding on a razor thin ice crust under the 3" of new snow that fell last night, which was dense (estimated 15%).

I dug a hand pit to the ground and found 2' of mostly solid snow (no obvious facets) with a couple ice crusts in the upper third. A CT cut with a ski pole yielded no fractures. Elevation 8,000', east aspect .