23-24

Another avalanche was triggered by the second party in the skin track. Triggered from below the slope. Photo: Anonymous 

Skiers in Middle Basin triggered an avalanche from below while breaking trail. Photo: Anonymous 

We observed three similar avalanches on Mt Abundance today (2/11). All were at about 9,900' and on NE-NW aspects. We were able to safely look at the crown of the first one, which was ~150' wide, 55cm deep, and with an HS of 145. It failed on 1-2 cm buried surface hoar. The other avalanches were on shallow unsupported rocky terrain. All were remote triggered from low angle terrain above, 20-50' away. One of the avalanches sympathetically released a gully and ran 800'.

On Mt. Blackmore we dug a pit on the east face near the ridgeline. We measured 10-12" of new snow that fell over the last week, equalling 0.7" of snow water equivalent. In the trees and less wind affected areas there were 14-16" recent snow, but we did not measure SWE there. In our snowpit on an east-facing slope at 9700' we found this new snow sitting on 2' of faceted snow, showing us that the structure is there to create avalanches. While stability tests were not remarkable with scores of ECTX and ECTP29, we did not feel like stepping into avalanche terrain was an appropriate decision for two reasons. First, we know the snowpack setup is capable of creating large avalanches and new snow will increase the likelihood of this. Second, recent wind has drifted the new snow into thicker denser slabs that will add additional weight to already unstable slopes. We saw clear signs of wind loading with fresh cornices forming at ridgelines and pillows of wind-drifted snow forming at the top of rollovers. While skiing out my partner and I both noted that the snow felt unsupportable with our skis breaking through to the facets below. We also discussed that as more snow and wind come this week dangerous avalanche conditions will continue to exist. 

Natural avalanches observed on east facing aspect of Miller Ridge on 2/11. Larger avalanche propagated widely on the north end of the ridge around 10,000 ft. Smaller avalanche further south on the ridge as well. 

A pit in the flank of an avalanche above Hebgen Lake. The stripe in the picture delineates the new snow over the unstable, old, faceted snow. This interface is where avalanches are occurirng. Karl Birkeland was using his 100 cm long Norwegian Battle Saw...a bit overkill. Photo: GNFAC

Crossing onto the debris of a large avalanche that likely released a couple days ago above Hebgen Lake. Photo: GNFAC