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Observation: Turnagain

Location: Corn Biscuit

Date:
Observer:
Route & General Observations

Ascended/descended West face of Corn Biscuit to 3200′. Experienced localized collapsing below 1600′ off of the established skin track. We noted a handful of old (within the last two days) skier triggered small slabs on South aspect of Magnum, West face of Magnum and North aspect of Corn Biscuit. We could also see evidence of a few storm slabs and sluffs from mid to late storm from Sun/Mon. We did not see an new skier triggered avalanches from today.

Red Flags
Red flags are simple visual clues that are a sign of potential avalanche danger. Please record any sign of red flags below.
Obvious signs of instability
Recent Avalanches?Yes
Collapsing (Whumphing)?Yes
Cracking (Shooting cracks)?No
Observer Comments

-Recent skier triggered slabs from the last few days, with the exception of some sluffing nothing new observed today.
-Storm slabs from Sun/Mon - old naturals
-Localized collapsing experienced off of the skin track below 1600'. Dug down to facets sitting on old deteriorating melt/freeze crust

Weather & Snow Characteristics
Please provide details to help us determine the weather and snowpack during the time this observation took place.
Weather

Sunny clear skies
-1F at 11am at 1000' in shade
12F at 3200' at 2pm
Calm winds

Snow surface

Sun crust between 1cm - 3cm on Southerly aspects, in many places this curst had 1cm of near surface facets on top.
Surface hoar (3-6mm) was found below 2000'

Snowpack

New snow depths ranged from 8" to 14" (Slab was slightly wind affected in the alpine, and had a 4 finger density)

Pit at 2450' - WNW aspect, HS=220cm, 33 degree slope angle, pit height was 90cm - Dug specifically in a place that had a thicker slab (14".) This slab (4F hard) failed on Fist hard near surface facets and propagated, ECTP12. We also found the Feb.9 buried surface hoar 30" below the surface and it failed with strong force, but did not propagate, ECTN30.

3 pits at 3200' - all with slightly different Southerly aspects, SSE to SSW. Height of snow varied from 75cm to 255cm in this area. All three pits had similar surface conditions, 1cm of near surface facets sitting on a light sun crust (likely formed by radiation recrystallization.) The slab (new snow) was about 8-9" thick in all three pits and was sitting on various configurations of well developed near surface facets and an old sun crust. The most reactive pit (SSW aspect) had an 8" slab sitting directly on the sun crust with near surface facets (2-3mm in size, cupped shaped) below the crust. Extended Column Tests in this location failed with only 1 tap from the wrist (ECTP1 x3) See video. The other two pits had near surface facets above and below the sun crust. One pit failed with moderate strength below the sun crust, no propagation. In the other pit the slab fell apart (ECTX.) Below the new snow/old snow interface there were no other reactive weak layers, including a pit with a total height of 75cm that had old depth hoar in the bottom 1/2 of the pit. These old grains were forming bonds and varied in strength from pencil to 1F.

Photos & Video
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