Investigation of Skier Accidental LLSA backcountry Tylenols/ Purple Bowl connector slope

Snowpack

Profile immediately adjacent to the crown found an 80cm, highly faceted. snowpack with the recent storm load comprising the upper 20cm, 20cm deeper the January facets were well developed and of fist resistance. The November crust was gone with large chains of depth hoar in its place. Compression test found: CT11 RP down 20cm (Feb19 storm interface) CT12 Sudden Collapse down 40cm (Jan 27 Facets). The failure plane of the avalanche was clearly the January facets. The thin - to - thick aspect of this slope / feature allowed triggering of the adjacent snow drift at the top of the cross-loaded feature moving hard slabs up to 80cm thick and giving this relatively small slide some real destructive potential. The faceted nature of the weak, thin snowpack found on this slope allowed this slide to run a significant distance and entrain much more snow along its path. A baseline test profile was completed nearby on the flats at the base of Purple Bowl - attached for reference.

Avalanche

Avalanche Size

2

Number Of Avalanches

1

Avalanche Observation

24to48hrsAgo

Avalanche Occurrence Datetime

2021-02-24T23:00:00.000Z

HS at crown was 80cm fattening quickly into a crossloaded feature 5m away. It appears two skiers were on the slope at the same time and the slab was triggered directly by the first skier. Both ski tracks retreated skier's left after about 3-5 turns as failure was noticed. First skier's tracks were wiped out. The crown was about 40 cm deep at initiation but within 5m grew to a depth of 80cm or more as the crossloaded feature beside the ski line failed. Areas of the track were gouged to just above the ground and large chunks of slab bulldozed into the deposit. It appears the avalanche nearly stopped at a bench about 50m below the crown however it plowed into the slope below and ran a further 60-80m creating a significant deposit at least 2m deep (despite the fact that the avalanche was only 5m wide at the crown and 10m wide at the deposit). Time is estimated above.