Detailed Accident Report
Submitted By: GNFAC; Doug Chabot
Place: MILLER MOUNTAIN-SHEEP CREEK
Summary: 3 snowmobilers caught, 2 partially buried, 1 buried and killed
MILLER MOUNTAIN-SHEEP CREEK AVALANCHE FATALITY: 3 Triggered, 3 Caught, 1 Buried and Killed
January 6, 2006
Written by: Doug Chabot, Director, Gallatin National Forest Avalanche Center
On Friday, January 6, 2006, three snowmobilers were riding up a steep ravine leading to the open bowls on the south face of Miller Mountain in the Beartooth Mountains of southwest Montana. This is accessed by difficult snowmobiling up Sheep Creek outside Cooke City. Near the top of the ravine they triggered an avalanche that came down from both sides of the bowl. Two of the riders jumped off their snowmobiles and ran up the side of the ravine and were only buried to their waist. The third rider was fatally buried under 7 feet of snow near the toe of the debris. The victim was located with an avalanche transceiver, but digging was slow since the other two did not have a shovel. After an estimated 30 minutes other snowmobilers arrived with shovels and helped dig him out. The total elapsed time between avalanche and body recovery is estimated to be 60-90 minutes.
The avalanche released on southeast to southwest aspects (140 to 220 degrees) at 10,300 feet. The avalanche was to 3-5 feet deep and ran 1,200 feet long, 750 feet vertical and 2,000 feet wide. The victim was found face down in the debris with his head proximately 2 feet from the snow surface. The slope angle at the crown averaged 37 degrees with the steepest pitch reaching 42 degrees. The avalanche was triggered on a 32 degree slope about 100 feet uphill from the toe of the debris. I was not able to measure the alpha angle since the slide path became confined into a deep gulley. The US Classification of the slide is HS-AM-D4-R4-O.
GPS Coordinates of the Western Crown Line:
GPS Coordinates of Avalanche Victim (toe of debris):
Cooke City experienced snowfall on 15 of the past 17 days prior to this accident, totaling 6.6 inches of SWE for over 6 feet of new snow. This was measured at the Fisher Creek Snotel site which is located at 9,100 feet in the Fisher Creek drainage, approximately 2 miles northwest of the avalanche. Winds were predominantly out of the west to southwest at 15-30 mph during this period, although that is extrapolated from sites tens of miles away. The mountains around Cooke City are alpine and notoriously windy.
Friday, January 6th was the second clear, sunny day since December 19th. Winds were light and temperatures that day had a maximum of 34F (1.1C) and a minimum of 22F (-5.5C).
The following details were relayed to me by the two riders, Barry (24) and Mike (24), who survived the avalanche. I investigated the scene on Saturday, January 7, 2006, with my volunteer field partner Felicia Ennis.
An experienced group of 10 snowmobilers from Minnesota arrived in Cooke City on Monday, January 2nd. While they were refueling in Livingstone, MT a police officer kindly informed them about the bad avalanche conditions in Cooke City and Avalanche Warning that was in place for the West Yellowstone area. Once in Cooke, they rented avalanche transceivers in a large part because of the conversation with the officer. Even though this was their 7th year coming to Cooke City, this was the first time they rented beacons. Asked if they read the avalanche advisory while they were in town, Mike said, ?No. But we knew that conditions were bad.? They were also aware of the fatality on Mt. Abundance from the day before. The avalanche danger was rated Considerable on all slopes steeper than 35 degrees this day.
On January 6th, the day of the avalanche, the group split up with Mike, Barry and Tracy (38) riding into the Sheep Creek drainage above the town of Cooke City. Sheep Creek is not as popular a riding area as the other drainages because it requires an expert ability in backcountry snowmobiling to get there. Once in the drainage all three began climbing up a narrow ravine/gulley that leads to the big bowls on the south face of Miller Mountain. The narrow ravine resembles the bottom leg of the letter ?Y?, with two distinct slopes forming the upper arms of the ?Y?. About 150? shy of the ?Y? intersection, Barry and Mike stopped side by side to talk. They were on a 32 degree slope and the ravine was only 40 feet wide. They were waiting for Tracy who was stuck 100 feet below them. Tracy was digging out his sled when he yelled ?Avalanche!? Barry and Mike jumped off their sleds and ran up the side of the ravine getting buried to their waist. Tracy?s warning likely saved their lives.
Using avalanche transceivers for the first time they located Tracy and started digging with their hands. None of the three had shovels. Furthermore, two of the three sleds were completely buried. The time was approximately 1pm.
Two other riders from their group had returned to town to fix a damaged sled when the three went up Sheep Creek. One of them said, ?I had a bad feeling, so I went looking for them.? These two arrived on the scene with beacons and shovels and helped extricate Tracy who was under 7 feet of debris. They estimated he was buried for 60-90 minutes.
Tracy was buried no more than 20 feet away from the toe of the debris, likely at the spot where he was stuck.
The slope failed on a thin (1cm) layer of 1.5mm facets of 1F- hardness. Where the slope was triggered, this layer was sitting on 55 cm of 1F+ hardness snow. Above it was 5 cm of mixed facets of 1F hardness. And topping this was 84 cm of 1F+ to 4F harness wind slab. These mixed facets covered the entire slope and propagated to both sides of the bowl. At the Western crown these facets were sitting on an ice crust with 150 cm of P hardness wind slab sitting on top of it.
Both of the slopes that avalanched were high elevation, wind loaded and exposed. The facets formed from sub zero weather in Nov and Dec.
If you have any questions you can contact me at 406-587-6984. I can also be reached via email at firstname.lastname@example.org
January 12, 2006