February 17, 2018

Front Range – Bear Valley:

Near miss report: persistent slab instability

Remotely triggered from a NW, 30 degree, well-anchored slope at approx 2500′. I felt the collapse at my feet and heard the rumble as the energy propagated upslope. Crown fractured approx 500 ft vertical above us (approx 3000′) with a width of approx 500+ ft and ran close to 1000 ft.

We had previously observed recent avalanches on similar slopes. One earlier slide on a convex-roll stepped down to a deep layer. There are multiple buried persistent weak layers that may be responsible.

Persistent slabs can be remote triggered, especially when support of the slopes above are compromised by disturbing compressive support. The collapse I caused was close to a few
Hemlocks and those acted as a trigger point, propagating up the sub-ridge. Slab debris is cohesive with some blocks the size of chest-freezers. I know better… didn’t listen to the signs.