Investigated the fatal avalanche accident that occurred Jan. 5, 2019. Preliminary findings are narrated below. We will update this prelimary report with more images later today, and produce a full accident investigation in the future.
The avalanche occurred in South Waldron Creek, 0.75 miles north of Teton Peak, Teton County, at approximately 15:42 on January 5, 2019. This was a very large, hard slab avalanche (could bury/ destroy a car and break trees). The crown extended approximately 1750 feet across two east and east-southeast facing bowls at about 7800 to 7900 feet elevation. It varied from 1 to 5 feet deep, with an average depth of roughly 3 feet. The debris ran 700-800 vertical feet. The slide was a persistent slab avalanche that broke on weak, faceted snow above a crust roughly 11 inches above the ground. The slide paths were convex, with variable snow depths and numerous trigger points. When the slide released, 1 rider (Rider 1) was on the slope. A second rider (Rider 2) was off his snowmobile lower on the slope. Rider 1 was caught, carried, partially buried and injured. Rider 2 was caught, carried, fully buried and killed.
Snowmibiled to debris from Road 144; climbed to crown and descended. Returned via snowmobile.
Crown depth varied from roughly 1 to 5 feet. We climbed to the crown roughly above where the slide was triggered. A quick profile showed a slab 45 cm thick (at that point) composed of 4-finger and 1 finger snow. This sat above obviously older, weaker snow. The failure plane appeared to be a thin (~2 cm), fist-hard layer of depth hoar sandwiched between two decomposing crusts (1 finger hardness). The snow below the crusts was also soft, well-developed depth hoar. The combination of faceted snow above and below thin crusts provided a relatively uniform failure plane across the bowl, though the height above the ground likely varied from roughly 3-12 inches. The slope angles below the crown are generally 35-38 degrees; slope angles in the middle of the bowl are steeper - around 40 degrees - giving the bowl a convex shape. Trees and small outcrops in thise part of the bowl provide multiple trigger points. The variable crown depth indicates snow was scoured and drifted into the bowl in complex patterns. The slide broke across a rounded rib just north of the bowl where the riders triggered it, into a second bowl that faces east-southeast. Debris from this bowl produced a second lobe of debris that fell roughly the same distance.
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