Starting late on Thursday, January 11th, southwest flow brought a prolonged period of rain to the region. This rain saturated the thick snowpack that has developed from the 144” of total summit snowfall to date this winter. By Friday night, over 2” of rain had fallen on the summit with temperatures in the 40’s F and nearing 50 F lower on the mountain at Hermit Lake. Sometime Friday the 12th a large wet slab avalanche occurred in the Headwall area of Tuckerman Ravine on a ski run and forecast area known as the Lip. The avalanche forecast for the day warned that, “wet slab avalanches may slide naturally without a human trigger today”, as well as, “the floor of Tuckerman Ravine is particularly threatened by a natural avalanche from the Headwall area.” After inspecting the site, it seems likely that the firm snowpack, weakened by rain, burst like a dam as water pressure built up in the stream channel beneath. The avalanche measured 160’ across the 12-20’ crown and ran 2,000’ with a vertical fall of 500’. By the avalanche size and destructive potential scales, this avalanche is classified as R3D3.5 or medium relative to path and capable of easily destroying wood frame houses or a railroad car.
This isn’t the first time for this type of avalanche in the Lip. The waterfall here creates this type of avalanche regularly in spring months as snow on the upper mountain melts, flows downhill, and saturates the snowpack. The one pictured below occurred on a busy spring ski day with two people narrowly escaping capture.
VIDEO: 2018-01-14 Aerial of Lip avalanche in the Headwall of Tuckerman Ravine