Hatcher Pass

Yesterday a human triggered avalanche occurred in the Martin Mine area. This avalanche is indicative of the current persistent slab problem. The skier who triggered the avalanche was approaching a steep slope when the avalanche failed at his feet. He was not caught. This avalanche failed near the ground, which exposed rocks, an additional hazard if you happen to be caught and carried. The group then retreated via their uptack and descended the green line.

11/27 – Martin Mine, SE, 4100′. Human triggered, full depth, large persistent slab avalanche

Yesterday we intentionally triggered a number of cornices which then triggered small wind slabs along the Marmot ridgelines, on both the SW face and the North face along the Rae Wallace chutes. Wind slabs were failing within the new storm snow and at the new/old snow interface of near surface faceted snow.

11/27 – Marmot Mt, NW, 4500′. SS-ACS-D1-I, Wind slab failed approximately  12+” deep x 10′ wide

Natural avalanches released during and just after the recent snow storm on 11/25.  Avalanches released within the new snow, at the new/old snow interface, and some released at the ground. A disproportionate amount of persistent slab avalanches occurred on the Punk spines compared to the core area, which saw much fewer natural avalanches in the 11/25 cycle. We hypothesize this is because of stronger winds in the Arkose Ridge area.

11/25 – Punk Spines, cropped photo of entire mountainside showing 5 of 7 natural avalanches. Winds during the storm cross-loaded terrain features, overloaded weaker, old snow, resulting in large slab avalanches failing near the ground. Notice the old avalanches in next photo from 11/9. There are some repeat offenders. This is a great puzzle to study closely.

11/26 – NW, 2700′. Just above “what used to be” the Motherload, ridge approach to Delia Creek. Small human triggered avalanche on facets near the ground. Tracks on left were from 11/26, which were partially covered with wind blown snow . Tracks on right are from 11/27. See observation HERE.

Persistent slab avalanches, 1-2 feet deep, will be possible to human trigger and natural avalanches will be unlikely on all aspects and at all elevations. It will be possible to remotely trigger persistent slabs in isolated locations, see recent observation HERE.

Winds and new snow amounts have been greater at the mid to upper elevations, so expect the persistent slab problem to be more prevalent there than at the low elevations. However, be cautious at the lower elevations where persistent slab problems may linger in isolated locations, on all aspects, on steep (35°+) terrain features.

Expect these slabs to fail near the ground, and therefore have enough volume to burry, injure or kill a person. Red flags include whumphing collapses and shooting cracks.

Persistent slabs will be difficult to predict. Hand pits, pole tests, test slopes, and instability tests will be useful in identifying the problem of stiffer snow overlying weaker snow. Collapses, whumphing and shooting cracks are red flags for this avalanche problem.

Yesterday’s human triggered avalanche in Martin Mine is the perfect example of what will continue to be a problem this weekend.

Below is a study pit from yesterday showing this season’s storm layers and weak layer problems. Stability has increased since the last loading cycle, with instability tests showing strong force needed to propagate an avalanche. While it is becoming more difficult and less likely to trigger a persistent slab, it is still possible and carries a significant consequence.

Moderate to strong winds over the last 48 hours have continued to build wind slabs at the upper elevations at and near ridgelines, on West to North aspects.

Wind slabs will be 5-12″ thick in pockets, possible to trigger, but small in overall dimensions and size.  Any wind slab triggered will have the possibility of entraining loose, weaker snow near the ground, which may increase the volume of the avalanche. With shallow coverage in the upper elevations, if caught and carried, expect to encounter rock hazards which will compound the hazard. Overall, the upper elevations steeps are just not quite ripe. As a good friend likes to say, “why sour your mouth with green bananas?”

Expect to find a combination of weak layers, including failures in the new, 11/25 snow, and failures on older, mixed forms, which are technically considered persistent grains. These soft, fresh wind slabs have been formed by recent winds over the last 48 hours, are located on leeward aspects, and are small in overall size.

Along with recent winds, note that small, extremely weak, cornice features are failing easily. This cornice failure triggered a small wind slab, difficult to see in the video:

Wind loading yesterday on Marmot Mountain:

11/27 – Wind loading on marmot ridge features, West, 3700′