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Observation: Summit

Location: Tenderfoot Avalanche

Date:
Observer:
Route & General Observations

Standard route up Western Ridge of Tenderfoot to investigate a skier triggered avalanche that occurred yesterday (2/27/18) on the North side of Tenderfoot. Avalanche was triggered while skinning and two people were on the slab, but the debris stopped due to lower angle terrain that was supported. No one was injured or buried. The party experienced a large ‘whumpf’ as the slab released.

The slab averaged about 20″ thick, it was very hard and failed on facets below a thin crust. The crown was around 300′ wide and the debris ran over 500′ vertical feet into the trees below. The trigger spot was only 10″ deep where the slope rolled over onto a 31 degree slope. The slope angle was steeper further out onto the Northern slope.

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)?No
Cracking (Shooting cracks)?Yes
Observer Comments

Numerous large (D2) natural avalanches observed East aspects of Fresno, Colorado, Summit Peak. There was also a natural D2 avalanche on a North ridge near Silvertip creek.

Active wind loading on South aspect of Tenderfoot and evidence of recent loading on Northern aspects as well. On our way to Summit Lake we noticed confusing wind directions with loading on some South aspects, East aspects and North aspects.

Small localized cracking in fresh wind loaded areas.

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

Clear skies
NW wind 20-30mph
single digits F
No new snow

Snow surface

Variable surfaces due to strong winds - hard supportable to breakable wind slabs, sastrugi. At lower elevations protected in the trees soft snow was present.

Snowpack

Dug at pit at 2000' on a West aspect, 38* slope, HS=120cm. Found 20" wind affected slab (1F to 4F hard) sitting on deteriorating crusts with facets sandwiched between. Stability tests were inconsistent, but we did have one propagate on this layer. ECTXx2, ECTP11

Dug into the crown at 2700' on North aspect, HS=110cm. The slab failed on well developed 2mm facets sitting under a thin (1cm) rain crust. Extended column tests propagated with easy to moderate force. ECTP11, ECTP13
The slab was very hard (Knife hard to pencil hard) and the snow below the facets was also pencil hard and transition to 1F near the ground.

Photos & Video
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