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Date: 2006-03-01
Submitted By: SNFAC; Lundy
Place: mountains near Antelope Creek
State: ID
Country: USA
Fatalities: 1
Summary: 1 snowmobiler caught, buried, and killed

Dry Fork of Antelope Creek Avalanche Summary

Location N 43? 34.628?

W 113? 39.686

Type HS-AMu-D2.5

Date 20060301

Aspect 305 Degrees

Elevation

Top of slide 8280?

Bottom of Debris 7530?

Slab max depth at crown 95cm

Slab depth at flanks 16cm

Slab width max 40m

Slope angle at crown 35degrees

Slope angle of bed surface

Max 37degrees

Average 35 degrees

Debris width ~18m

Victim buried ~85cm deep

Front of Sled ~155cm deep

Average debris depth ~100cm

The accident happened in Dry Fork of Antelope Creek. This area is just over the Fish Creek summit and is typically accessed via the Fish Creek Trailhead near Carey. The accident site was approximately 10 miles from the trailhead. March 1st was a clear sunny day with daytime temperatures likely in the high 30 to mid 40-degree range. Winds were light to moderate out of the south.

Avalanche Description

The slide was a class D 2.5 hard slab that was triggered by a single snowmobile. The top of the crown was at 8280 feet in elevation, and ran 750 vertical feet down slope. The aspect was 305 degrees. The maximum depth of the crown was approximately 3 feet deep while the average depth of the slab was around 1.5 feet deep. The depth of the slab at the point where the victim likely triggered the slide was about 6 inches. The maximum depth of snow at the crown beneath the bed surface to the ground was about 8.5 feet. The maximum width of the slab was approximately 40 yards.

Snow and Weather Conditions

A warm storm moved thru the area on February 27th and 28th depositing approximately 2 inches of water. The rain line in Dry Fork was approximately 7000 feet. The winds during the storm were strong out of the southwesterly and then shifted to the southeast just after the storm and remained moderate for approximately the next 12 hours. The slab was a large wind pillow formed from storm snow. The failure occurred on a small faceted layer below a 1 cm thick temperature crust. At the top of the crust there was a very thin (1/8 inch) ice lense. The distribution of snow from the last storm varied widely in the general area depending on aspect. The windward side of the ridge from where the slide occurred had a total of about 2 feet of snow with about 4 inches of new snow on top.

Events leading to the avalanche

At approximately 2pm the victim had just ridden up a gully and turned around. He was headed down the gully when he triggered the slide. His partner, who was about half way up the gully and to the side, witnessed the slide break loose and then tried to warn his partner. The victim apparently did not realize that he had triggered a slab. While moving down the gully he was over taken by the debris and was swept approximately 650 vertical feet down slope.

Rescue Summary

The victim was buried approximately 1.5 to 2 feet deep. He was not wearing an avalanche transceiver, although his partner was. The partner found the handle bars of the victims sled above the debris surface and proceeded to probe the general area with his shovel handle. He found his partner with a shovel handle/probe strike to the helmet about 6 feet directly uphill from the buried sled. The victim was buried between 30 and 40 minutes before his partner had his airway uncovered. The victim was found unresponsive. The rescuer provided CPR for approximately 1 hour before leaving the scene to return to the trailhead and call for help. The average depth of the debris was 3 to 4 feet deep with the maximum depth observed being about 5 feet deep. The coroner?s report indicates the cause of death was due to blunt trauma to the chest and torso.

Report written by

Matthew Lutz

Avalanche Forecaster

Sawtooth National Forest Avalanche Center