Detailed Accident Report
Submitted By: GNFAC; Scott Schmidt
Place: Lionhead area near West Yellowstone
Summary: 2 snowmobilers caught, 1 buried and killed
LIONHEAD AVALANCHE FATALITY
28 December 2006
One snowmobiler was caught and killed in an avalanche that occurred in the Lionhead area near West Yellowstone. The avalanche released on a wind-loaded slope, with an easterly aspect. The slope angle, which averaged 34 degrees, increased to 37 degrees at the crown. The crown was 3 feet at its deepest point, and 300 feet in width. The avalanche ran approximately 600 vertical feet, with a ??i - angle of 24 degrees. The avalanche was triggered remotely as the party traversed along a trail at the bottom of the slope. The distance from the trigger point to the avalanche crown was 975 feet slope distance. US classification of the avalanche is SS-AMr-R3-D2-O.
12 ?V 15 inches of new snow fall in the two days prior to the avalanche with the majority of the snow (7 ?V 10 inches) falling the evening of the 26th. An additional 4 ?V 6 inches of snow accumulated on the 27th. Strong northerly winds (25 ?V 45 mph), blew on the 28th starting around 4:00 a.m. These winds where cross-loading the east facing chute under which the party was traveling. Temperatures were seasonal with highs in the mid to upper teens.
19-year-old Joshua Scepaniac of Avon, Minnesota was riding with a group of 7 family and friends in the Henry Mountains near West Yellowstone, Montana. At approximately 12:30 in the afternoon the group crossed a basin near Lionhead Mt. The group broke trail well away from the large, open slopes that define the basin but as they neared the north end of the bowl, terrain and timber forced them to move in close to the bottom of several steep, wind-loaded chutes. The group spread out as they crossed a more obvious slide path on the north side of an island of timber. The first three rides crossed the path without incident and waited on the far side of the path. It appears that the avalanche released as the rest of the group moved through the trees. The three riders who had successfully crossed the slope stated that the avalanche was already running as Joshua (the fourth rider in the group) moved into the path. Joshua was struck by the oncoming avalanche and carried 40 feet before coming to rest ?V buried under 3 feet of snow ?V approximately 10 feet from his partially buried snowmobile. Andy Cramer was the 6th rider in the party and had not reached the island of trees when the avalanche released. He was caught and partially buried on the south side of the tree island but was able to self-extract. His snowmobile was completely buried. The fifth ride, Ben Thelen, was behind the tree island and was protected from the flow.
Joshua was not wearing an avalanche transceiver. One member of the party had an avalanche probe and, starting at the partially buried snowmobile, was able to locate Joshua in a short time. All members of the party had shovels and were able to extract Joshua within approximately five minutes from the time he was buried. This timeline is confirmed by two 911 calls the party made using a cell phone. The first call was made at 12:36 when the victim was first buried. The second call occurred at 12:41 when the party called back to report that they had recovered the victim and were starting CPR. The group preformed CPR for two hours until an organized SAR party arrived from West Yellowstone. There were no obvious signs of trauma and the deputy coroner ruled that the victim had died from traumatic asphyxiation.
The snowpack at the bottom of the path where the avalanche triggered was 94 cm deep. The bottom 30 cm was well-developed depth hoar approximately 2 mm in size. A layer of 10 mm surface hoar was located 53 cm from the ground. The avalanche appears to have initiated in the depth hoar layer, releasing the smaller slide on the south side of the tree island that caught and partially buried Andy Cramer. The fracture propagated over a small rib on the upper layer of surface hoar, into the wind-loaded chute to the north, releasing a large wind slab that caught and buried Joshua. Compression tests in the pit at the bottom of the slope produced clean, easy shears in the surface hoar and simultaneous failures in the depth hoar. Compression tests at, and above the crown, resulted in clean shears but moderate to hard force was required to cause failure.
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Gallatin National Forest Avalanche Center