Detailed Accident Report

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Date: 2006-12-16
Submitted By: BTNF AC
Place: Stewart Peak, Salt River Range
State: WY
Country: USA
Fatalities: 1
Summary: 2 snowmobilers caught and buried, one killed

Submitted By: Bridger-Teton National Forest Avalanche Center

Preliminary information provided by Star Valley Search & Rescue

Summary: Two snowmobilers caught and buried, one killed

At about 3:30 PM on Saturday December 16, 2006 two snowmobilers triggered an avalanche on the east side of Stewart Peak in the Salt River Range of Wyoming. The two riders were reported to be on the same slope when they triggered a large slab avalanche that pulled out an entire bowl. It was reported that a smaller avalanche was triggered in this bowl by these snowmobilers just before the entire bowl released. This avalanche failed on an east aspect at an elevation of approximately 9,500 feet and ran full track.

Both riders were caught, carried and completely buried. One rider was buried under six feet of avalanche debris. The victim was buried under approximately 8-10 feet of debris. Neither rider had an avalanche transceiver. Another party in the area that witnessed the event probed, found and uncovered the survivor within 20 minutes. This survivor was revived by CPR at the scene by a member of his party and was able to ride his machine home.

The victim was also found by probing and uncovered in about an hour. CPR was performed without success.

This event occurred in the aftermath of a large storm that initiated the first major avalanche cycle of the season. The storm began midweek and by Saturday morning had deposited 30 inches of new snow with 3.7 inches of water equivalent at the mid-mountain snow study plot at the Jackson Hole Mountain Resort, located approximately 36 miles north of the accident site. This storm was accompanied by strong winds gusting to 60 MPH and mild temperatures. Temperatures at 9,500 feet were in the upper teens to low 20?s during the storm. A cold front passed over the area Friday night. Temperatures on Saturday were in the single digits and skies were partly cloudy.

Prior to the arrival of this storm the shallow early season snowpack was subjected to an extended period with very cold temperatures that was followed by a high-pressure ridge with temperature inversions. During the inversions, daytime temperatures at 9,500 feet rose into the 40?s. The surface of the snowpack before the storm cycle began was comprised of slick crusts, windpack and well developed surface hoar and recrystalized powder (near surface faceted snow).

The rapid loading of these excellent sliding surfaces and well developed weak layers during the storm cycle created unstable conditions and initiated a cycle of widespread natural and human triggered avalanche activity. During the storm over 70 slab avalanches, 2 to 5 feet in depth were triggered by avalanche hazard reduction efforts in un-skied terrain at the Jackson Hole Mountain Resort. Although most of these avalanches were explosively triggered, many were triggered by ski cuts and several were triggered remotely and sympathetically. Many ran long distances.

Backcountry events during the storm on Thursday included a skier who was caught and carried and not injured in the Salt River Range at a similar elevation and aspect and some snowmobilers who were partially buried but not injured in the southern portion of the Salt River Range. When the storm ended and skies cleared on Saturday, numerous recent large natural avalanches were observed in the backcountry.

Due to the unstable conditions an avalanche watch was issued in the early portion of the storm cycle. This watch was upgraded to a warning as the storm progressed and down graded to a warning at the end of the storm when the potential for natural avalanche activity decreased. At the time of this incident an avalanche watch was in effect. The general avalanche hazard for the Greys River Area that includes the Salt River Range on Saturday was high.