Accident: West Bowl 12/3/2006

Observer Name:

Brett Kobernik

Observation Date:

12/04/2006

Occurrence Date:

12/03/2006

Occurrence Time:

Unknown

Region:

Salt Lake
Big Cottonwood Canyon
Silver Fork
West Bowl

Location

40° 35' 56.508" N, 111° 37' 45.2928" W

Avalanche Characteristics

Elevation:

9900'

Aspect:

North

Northeast

Slope Angle:

Trigger:

Skier

Trigger: additional info:

Intentionally Triggered

Avalanche Type:

Soft Slab

Weak Layer:

Facets

Depth (avg):

Depth Range:

14" to

Width:

1/4 mile

Vertical:

600'

People Involved

Caught:

Carried:

Partly Buried:

Fully Buried:

Accident & Rescue Info

Accident & Rescue Summary:

Accident Summary:

Three skiers left the town of Alta Tuesday for a ski tour into Big Cottonwood Canyon. They ascended the south facing slope above the town of Alta. They decided to ski down into the West Bowl of Silver Fork. This was an east northeast facing slope. When they regrouped, it was decided to ascend the more northerly facing slope to regain the ridge. As they were ascending, the slope fractured and avalanched. All three were caught. One grabbed a tree and was not carried far but did lose a ski. Another was carried around 30 feet and was buried enough so that he was not able to move without digging himself out. The third was missing.

Rescue Summary:

After determining that one person was missing from the party, the other two initiated a search with avalanche transceivers. They were aided by another nearby solo skier. The location of the missing person was quickly located between 100 and 200 feet downhill from where he was caught and they struck him with the first attempt with an avalanche probe. He was reportedly buried around 4’ deep. When they uncovered him, he was face down. They checked his airway for snow but it was already clear. They noticed that he was breathing but it was labored. They started to treat for hypothermia by placing the victim on top of backpacks and putting on spare layers of clothing. Rescuers were contacted via a cell phone and a life flight helicopter was dispatched. The victims labored breathing improved and he became coherent. He was able to ski himself down around 200 feet to where the helicopter was able to land. He was then evacuated.

Weather & Avalanche History:

Avalanche Data:

The avalanche is classified SS-AS-R4-D3-G. Rough measurements on a topographic map indicate this avalanche was around 2000 feet wide. It ran 600 vertical feet. The fracture line depth ranged from 14 to 36 inches and averaged around 28 inches. The slope angle ranged from 35 to 40 degrees in steepness. The aspect ranged from northwest to northeast. It released at about 10,000 feet in elevation. A second avalanche released sympathetic to the original. It was around 100 feet wide, 30 inches deep, and ran around 500 feet vertical distance. It was on a northwest facing slope. Faceted snow near the ground was the weak layer for both these avalanches. Depth of the debris averaged 3 to 4 feet but areas up to 6 feet deep were measured.

Weather History:

The Wasatch range received some snow storms in September and October that were subject to weather conditions that promoted faceting of the crystals. This sugary type of snow was then covered up by a series of snow storms in early November that were accompanied by a number of windy days that produced a stiff wind slab on top of the faceted snow. Avalanching from this snow structure was observed during the weekend previous to this accident. The day of the accident, many professional snow workers as well as recreational users produced avalanches in this same snow structure.

Snow Profile

General Comments

All of the skiers involved had some formal avalanche training but two of them had more training then the buried victim. They chose the West Bowl of Silver Fork because of its low angle options which would be appropriate for the conditions that day. They performed some snow stability tests on the way up from Alta. They noted some weakness within the new snow. They were also aware of faceted snow near the ground on northerly facing slopes. They did not experience any cracking or collapsing and successfully skied one run. This is when things started to go wrong. They decided to walk up a northerly facing slope to regain the ridge and then walk east on the ridge. It appears this deviated from the original plan of sticking to low angle terrain. Perhaps since they successfully skied the run and did not see any cracking, collapsing, or other avalanches, this influenced their decision. Excitement about the new ski season could have also played a role. At least one member of the party had reservations about some of the decisions but did not speak up. Later when the group discussed the accident, the other two had reservations as well but there was not complete communication. This fits into the “no leader” category where no one is in charge of making sure complete communication is occurring. Many accidents occur due to communication problems and no one is immune to making similar mistakes. It should be noted that this was a text book example of a perfect rescue which was accomplished only because the touring party had the proper rescue gear and was trained in using it.

General Comments 2

This is the north facing slope where the accident occurred on Nov 14. The red arrow indicates the skiers location when the slope avalanched. The yellow arrows are each flank of the avalanche. The purple arrow is the avalanche that released sympathetically to the first one.

General Comments 3

This is above where the skiers were caught. This is less then 1/4 of the size of the avalanche.

General Comments 4

This is looking back down what is left of the skin track from about where the person breaking the trail was located. The stars indicate approximate locations of the other two skiers.

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