Accident: Claytons 12/16/2008

Observer Name:

Brett Kobernik

Observation Date:

12/17/2008

Occurrence Date:

12/16/2008

Occurrence Time:

Unknown

Region:

Salt Lake
Big Cottonwood Canyon
Claytons

Location

40° 35' 35.9808" N, 111° 33' 37.6344" W

Avalanche Characteristics

Elevation:

10400'

Aspect:

Northeast

Slope Angle:

Trigger:

Snowmobiler

Trigger: additional info:

Unintentionally Triggered

Avalanche Type:

Hard Slab

Weak Layer:

Facets

Depth (avg):

18"

Width:

1000'

Vertical:

500'

People Involved

Caught:

Carried:

Partly Buried:

Accident & Rescue Info

Accident & Rescue Summary:

A group of three snowmobilers left from Big Cottonwood Canyon and traveled over Guardsmen’s Pass for a day of recreation. Once over the pass they headed south toward Claytons Peak. While playing around at the bottom of an avalanche path one of the snowmobilers triggered a large avalanche that released 400 to 500 feet above them. He was able to escape it but his friend was caught. The large avalanche carried the victim and his sled a short distance. The sled ended up completely buried and the victim was buried to his waist, uninjured. Rescue involved digging out the victim and the sled which was not damaged. The very lucky group was then able to ride back out to Big Cottonwood Canyon.

Terrain Summary:

There is lots of avalanche prone terrain near Guardsmen’s Pass. Claytons Peak has numerous avalanche paths that run off of it in various directions. The slope off Claytons Peak where the avalanche was triggered faces northeast and is 35 to 40 degrees in steepness. This slope is popular with both snowmobilers as well as skiers and snowboarders leaving the Brighton Ski Resort. It is a well know avalanche path that slides frequently.

Weather & Avalanche History:

Avalanche Data:

The avalanche was up to 1000’ wide and ran about 500 feet vertical. It was most likely in the 1 to 2 foot deep range. The exact details about this avalanche are not known but it had a very similar snowpack structure to numerous other locations around the upper Cottonwood Canyons. More likely then not, the snow failed either in faceted snow just above the late November crust or in facets just below the crust. This avalanche was originally reported as a natural avalanche to the Utah Avalanche Center.

Weather and Avalanche History:

Snow started to pile up in early November. During one of the periods of snow a rain/rime event occurred and produced some crusts. These were buried by more snow. This snow sat around and faceted for a number of weeks until another storm occurred around Thanksgiving. This storm also produced another rain/rime event that was even more pronounced then the first. A bit more snow fell on top of the resulting crust then faceted in early December. The set up was a crust sandwiched between faceted snow above and below it. Another storm occurred on the 8^th of December which was not enough to build a dangerous slab. However the next series of storms starting on the 13^th would be enough to produce avalanches. By December 16^th numerous natural and human triggered avalanches had occurred and were reported daily by the Utah Avalanche Center.

General Comments

This slope is the exact location described in the daily avalanche advisory (Advisory 12-16-08) of places where you were most likely to trigger an avalanche. The weak crust/facet combination with a slab on top of it is just the set up needed to be able to trigger avalanches from a distance which is what this group did. They ignored a cardinal rule of thumb in that only one person should be on any given avalanche path at a time. Luckily, this story had a happy ending. This could have just as easily been a tragic accident ending with a fatality.

Here is a photo of the avalanche that one of the UAC observers took from near Peak 10420. He thought the avalanche had occurred naturally.

CLICK HERE FOR PHOTOS

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