Skier caught and carried in a wind slab

CB Avalanche Center 2016-17 Observations, Accidents, Avi-map 16-17

Location: Crested Butte Area
Date of Observation: 02/21/2017
Name: Zach Guy and Ian Hoyer
Subject: Skier caught and carried in a wind slab
Aspect: North East, East, South East, South
Elevation: 9000-12000 ft

Avalanches: Observed an unintentional skier triggered wind slab on an E/NE aspect at 12,000 ft, above treeline. The slide broke a few feet above the skier and carried them about 700 vertical feet, resulting in a partial burial, several leg injuries, and a lost ski. The slab ranged from ~5 – 15″ thick, and broke on the 2/17 near surface facet layer. The slide was about 250 feet wide. HS-ASu-R1-D2-I
Weather: Broken skies in the a.m., decreased to thin scattered mid-day, increased to overcast in the p.m. Moderate WSW winds, no transport except some plumes on high peaks. Warm temps, green-housing. No precip.
Snowpack: On S/SE aspects N/BTL. The recent snow (1″-2″) is wetting and conforming to underlying crust layer. No signs of instability.
On a wind protected NE aspect NTL. A profile showed the 2/17 near surface facet layer (.5- 1mm) buried 8 cm deep. The 1/19 surface hoar layer was 85 cm deep, intertwined with rounded grains. Broken fracture on this layer with very hard additional loading steps. No signs of instability until we got to low elevation, northerly aspects, where we got some rollerballs in the moistening surface snow.
Near and above treeline, there were signs of wind drifting from both NW and SW loading patterns.

Crown ranged from 5-15″ in depth. The avalanche broke on recently buried near surface facets

The slope was a recently wind-loaded NE aspect above treeline in Coon Basin

The skier was partially buried in debris after being carried about 700 vertical feet.
Looking across the crown, which thinned down to ~5″. Slide broke around 250 ft wide.
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Profile in Climax Chutes showed unreactive surface hoar layer 3 feet deep, and a fragile layer of facets near the surface.

Avalanche Accident above Copper Creek

CB Avalanche Center 2016-17 Observations, Accidents, Avi-map 16-17

The complete accident report is available at this link.
Location: Crested Butte Area
Date of Observation: 02/02/2017
Name: Zach Guy
Subject: Avalanche Accident above Copper Creek
Aspect: West
Elevation: 12, 200 ft

Avalanches: We would like to sincerely thank the party involved for their prompt and thorough communications with CBAC. This helps turn an accident into a learning opportunity for everyone, helps us improve the accuracy of our forecasts, and we submit accident data to a national database for avalanche-related research.

The slide was unintentionally skier triggered on 2/1/17. We estimate the crown was a 12″-15″ thick hard slab, ~25 feet wide based on photos and descriptions from the reporting party, as well as our on-site observations. The slab likely failed on an old crust or faceted layer. The slab caught and carried the skier approximately 1,350 vertical feet, leaving the skier on top of about 3 feet of debris, a relatively small avalanche. I classified the avalanche as: HS-ASu-R2-D1.5-O.  The injured skier and the skier’s partner evacuated down the rest of the slide path and down part of Copper Creek Trail before CB Search and Rescue arrived and assisted in the evacuation. We will publish a full report summarizing the weather, snowpack, accident, and rescue in the future.
Weather:
Snowpack: No red flags in our tour to and from the avalanche location. No cracking, no collapsing, no recent avalanche activity (except small wet loose on steep southerlies from yesterday), no active wind or snow loading (despite strong to extreme winds today). The parties skin track from yesterday was still largely in tact, suggesting there was minimal snow transport in this area yesterday.
The slide was triggered on a west aspect above treeline at 12,200 feet, above Copper Creek. We traversed across portions of the same slope digging numerous hand pits. The snowpack is generally weak but lacking a slab because it is heavily wind-scoured. The structure consists of either a shallow (less than 50 cm) and fully faceted snowpack, or a faceted snowpack capped by a breakable melt-freeze crust. Behind a few isolated trees and in concavities on this slope, there were shallow hard slabs 3″-5″ thick over this structure. It appears that the slab that was triggered was an isolated drift over this weak structure, which likely failed on crust or facets. The crown was wind scoured or smoothed over by the time we visited the site, so we don’t have any direct crown observations from where the slide was triggered, except for a small pocket lower down on the slope that also pulled out.

Location of the avalanche, on a sub-ridge of White Mountain above Copper Creek.

Looking down the slide path from near the crown.

The crown of a shallow hard slab over weak facets that pulled out lower down the path.

The slide and skier were carried over a cliff band. Skier circled in red for scale.

Skier was recovered on top of about 3 feet of debris, a relatively small avalanche.

Location of skier triggered hard slab avalanche. Photo taken day of accident, 2/1/17

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Red Lady Skier Triggered Avalanche

CB Avalanche Center 2016-17 Observations, Accidents, Avi-map 16-17

Location: Crested Butte Area
Date of Observation: 12/18/2016
Name:
Subject: Red Lady Skier Triggered Avalanche
Aspect: South East
Elevation: Above treeline

Avalanches:

Watched 4 skiers ski the bowl from my house via a telescope around 12:30 PM. It appears they didn’t encounter any stability issues.

Then watched a lone skier top out at 3:20 PM. He traversed another 50 or so yards east along the summit ridge past the entry point of the 4 earlier skiers, and then dropped in. He had made 10 or so turns, and then it happened; a majority of the bowl ripped out above him, almost edge to edge. Luckily at this point he had skied skier’s right of his drop in point, and had re-joined the 4 tracks from earlier.

It appeared he was ‘slightly’ caught in some sluff before skiing down to a narrow island of the slope that didn’t slide (that spot is very visible). He stopped in the middle of all the chaos as the slide ran on both sides of him, far down the slope where it eventually reconnected as it continued down the bowl.

The slide was well past him and he was skiing down when I lost sight of him. I lost sight of him, but counted 5 tracks (4 plus his) after the slide. So I ‘think’ he was OK. Close call.

***CBAC Note*** We are all very grateful that the swath of snow in the middle of the bowl did not slide in this incident. We want to dispell any beliefs that this commonly skied portion of the bowl is a “safety island”.   Last December, a similar type of avalanche broke across the whole bowl.  See photos below.
Weather:
Snowpack:

red-lady-dec-18-2016

Red Lady Bowl. Photo courtesy of Ben Pritchett

12/18. Close call on Red Lady Bowl.

12/18. Close call on Red Lady Bowl. Photo courtesy of Chris Miller.

12/18 Skier triggered persistent slab in Red Lady Bowl

12/18 Skier triggered persistent slab in Red Lady Bowl.

12/18 Red Lady . Photo courtesy of Dustin Simoens

12/18 Red Lady. Photo courtesy of Dustin Simoens

Extent of 2015 natural avalanche in Red Lady Bowl.

Extent of December 2015 natural avalanche in Red Lady Bowl.

 

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Snowmobiler triggered, caught and buried by PS avalanche

CB Avalanche Center 2016-17 Observations, Accidents, Avi-map 16-17

 The complete accident report is now available here.
Location: Paradise Divide Area, Washington Gulch near Elkton.
Date of Observation: 12/12/2016
Name: Evan Ross
Subject: Snowmobiler triggered, caught and buried
Aspect: North
Elevation: 11,250

Avalanches: 2nd hand information. Snowmobiler triggered, was caught and buried by a persistent slab avalanche. They were rescued by the rest of their party, and did not sustain any injuries.

Average slope angle across the bed surface was 39 degrees. Crown was about 175ft wide and 3ft deep. Persistent slab failed at the ground on 2mm faceted grains, 4f- hard.
Weather:
Snowpack:

Crown Profile

 

Looking across the crown
Looking up at the crown
Burial Location
Looking upslope.  The burial location is in the foreground.
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