Recent avalanches, concerning surface hoar layer

Recent avalanches, concerning surface hoar layer


Skied on Henderson mountain the afternoon of 1/16. Wind was calm, snowfall was light and steady through the day with 3-4" of new snow.

Dug a pit on the east side of Henderson at the ridgeline above Henderson Bench. ENE, 10,075' elev. ECTP19 x3 on a layer of surface hoar buried 60cm (2 feet) deep. HS 260cm. There was an avalanche a few hundred feet north on an east-northeast facing slope below the ridge. It appeared to be snowbike triggered and 1-2+ days old. 150' wide and 250' vertical. HS-AMu-R2-D2-O. It appeared to have broke about 2' deep on that layer of surface hoar. There was also a more recent natural avalanche (less than a day old) on Miller Ridge, slightly smaller. SS-N-R1-D1.5-O and probably broke on the surface hoar layer.

The location of these avalanches and poor stability test scores is concerning as they are in exposed areas, implying the surface hoar will remain an issue on large, steep open slopes that will likely be heavily wind-loaded at some point.

Additional photo of a cornice triggered avalanche on Miller Ridge that broke to the ground, appears to be many days or weeks old.

Cooke City
Location (from list)
Henderson Mountain
Observer Name
Alex Marienthal