CAIC

Details

Date: 2020/03/04

Observer: Ben Pritchett and Eric Murrow
Organization: Forecaster, CAIC

Location

BC Zone: Gunnison
Area Description: Long Lake

Weather

Ridgeline Wind Speed: 10-20 mph
Ridgeline Wind Direction: NW
Wind Loading: None
Temperature: 38 F
Sky Cover: Few
Weather Description: Hot day after a bitter cold start. Perfect melt freeze cycle. 50 degree F change from negative 10 to 40 between 7am and noon.

Snowpack

Snowpack Description: Persistent Slab avalanche structure exists on this slope below treeline with a 125cm total snowpack depth. The avalanche failed on a layer of facets below a thin crust 50-60 cm down from the snow surface. The slab is quite weak (4-finger to Fist hard) and includes the snow from the last two storms. Boot penetration to ground where HS <130cm. Nearby slopes with a bit more HS were supportive to boots.

Avalanches

Avalanche Description: This avalanche was triggered by a skier on a steep (37-40 degree) slope on 3/3/2020. The avalanche broke 50-60 cm deep on a layer of faceted snow below a thin crust. The avalanche measured about 250 feet wide, running around 200 vertical feet. The debris hit the lake with enough force to break the ice, creating a wet one to two foot deep sunken area in the ice and snowpack surrounding the debris. Cracks extended across the lake to the opposite shore of the lake. The debris ranged from three to ten feet deep. It appeared the skier was partially buried. Unfrozen lake water filled the hole where the person came to rest and skied out from the debris. A single ski track exited the debris pile and continued back to the nearby trailhead.

Date

Location/Path

Elev

Asp

Type

Trig

SizeR

SizeD

2020/03/04 ^†

Anthracite Mesa

<TL

AS / u

Media

Images

$<b>Figure 1:</b> A skier triggered avalanche on 3/3/2020. A track leaves from the apparent high point on the ridge and crosses the fracture line just looker's left of the largest conifer tree in the crown. (<a href=javascript:void(0); onClick=win=window.open('https://caic-production.imgix.net/iwm7wk75uf69geitqvbn90kvmdv1?ixlib=php-3.1.0&s=699b64340cce3e618cf2998261d0ac17','caic_media','resizable=1,height=820,width=840,scrollbars=yes');win.focus();return false;>see full sized image</a>)$ <b>Figure 2:</b> Debris was over 10 feet deep in places. (<a href=javascript:void(0); onClick=win=window.open('https://caic-production.imgix.net/lm148l5d9v8v1yq7dax1ubvzo6aw?ixlib=php-3.1.0&s=6201c74fafd05ed0e6dfe630413ddfe2','caic_media','resizable=1,height=820,width=840,scrollbars=yes');win.focus();return false;>see full sized image</a>)

<b>Figure 2:</b> Debris was over 10 feet deep in places. (<a href=javascript:void(0); onClick=win=window.open('https://caic-production.imgix.net/lm148l5d9v8v1yq7dax1ubvzo6aw?ixlib=php-3.1.0&s=6201c74fafd05ed0e6dfe630413ddfe2','caic_media','resizable=1,height=820,width=840,scrollbars=yes');win.focus();return false;>see full sized image</a>)

<b>Figure 3:</b> The avalanche broke in facets below a thin crust generally 50-60cm below the surface. (<a href=javascript:void(0); onClick=win=window.open('https://caic-production.imgix.net/th9010uf6f3o0g99m2l744qp0w02?ixlib=php-3.1.0&s=0fbf3d84ca8694c14b4997ae542b94e1','caic_media','resizable=1,height=820,width=840,scrollbars=yes');win.focus();return false;>see full sized image</a>)

<b>Figure 5:</b> The steepest part of the slope near the crown measured 40 degrees, with an average slope of 37 degrees. (<a href=javascript:void(0); onClick=win=window.open('https://caic-production.imgix.net/60283l74czf15qyh59rc22gc1qxy?ixlib=php-3.1.0&s=28012b0ae6c4bab4e1dff8a9a1b6a307','caic_media','resizable=1,height=820,width=840,scrollbars=yes');win.focus();return false;>see full sized image</a>)