- Location: Mount Leidy, southwest of Togwotee Pass
- State: Wyoming
- Date: 2019/01/09
- Summary Description: 1 snowmobiler caught, buried, and killed
- Primary Activity: Snowmobiler
- Primary Travel Mode: Snowmobile
- Location Setting: Backcountry
- Caught: 1
- Partially Buried, Non-Critical: 0
- Partially Buried, Critical: 0
- Fully Buried: 1
- Injured: 0
- Killed: 1
- Type: SS
- Trigger: AM - Snowmobile
- Trigger (subcode): u - An unintentional release
- Size - Relative to Path: R2
- Size - Destructive Force: D2
- Sliding Surface: O - Within Old Snow
- Slope Aspect: E
- Site Elevation: 9500 ft
- Slope Angle: 36 °
- Slope Characteristic: --
The avalanche occurred on a steep east-northeast facing slope at an elevation of 9,500 feet. It was a soft slab avalanche that failed on a layer of coarse grained, faceted snow. A crown face profile was conducted above the location of the buried rider on January 10. At that location the total snow depth was 40 inches. The crown depth was 24 inches. The crown fracture propagated into adjacent terrain features. Although the slab was generally two feet deep there were portions of the crown fracture that were up to three feet deep. The slope angle at the location of the crown face profile was measured to be 36 degrees.
There was an abrupt transition in steepness at the base of the slope where the rider was buried. It is believed that the rider was at or near this change in slope when the avalanche was triggered. The avalanche debris was deepest at this slope transition and did not flow very far past that slope change. This avalanche was classified as relative size 2 and a destructive size 2 event.
This group remotely triggered a slab avalanche in the same drainage on a similar aspect earlier in the day. That slab released on a steep, east facing slope at an elevation of 9,170 feet. It was two feet deep and smaller.
This accident occurred in an area where the Bridger-Teton National Forest Avalanche Center provides daily avalanche hazard forecasts. Daily forecasts for this winter season began on November 2. Specialized weather stations operated by the Bridger-Teton National Forest are located in this forecast zone. The Togwotee Lodge precipitation station (9,150 feet) is situated approximately 13 miles northwest of the site. The Grouse Mountain (10,380 feet) wind station is located approximately 7 miles east of the accident site. Data from these weather stations and field excursions conducted by the avalanche center’s avalanche specialists were used to determine the weather and snowpack history that preceded this event.
At the end of December this region had a shallow early season snowpack that had been exposed to multiple clear cold periods and exhibited poor snow structure. At this time, snow depths in this area were generally 2 to 3 feet deep. The entire snowpack except for a crust at the base was comprised of faceted snow.
Two storm systems impacted this area between December 30 and the day of the accident. The first occurred on December 30. It brought nine inches of new snow to this area and was accompanied by strong winds with gusts to 80 miles per hour on the highest peaks. The second storm occurred on January 6 & 7 and brought another 7 inches of snow to this area. This storm was also accompanied by strong westerly winds with gusts from 50 to 80 miles per hour. The slope where the accident occurred is ideally orientated to be loaded by westerly wind events. Skies were partly cloudy on the day of the accident. Temperatures were inverted that morning and rose into the 30s at the elevation of the accident. Winds were light and from the west-southwest.
A crown profile was conducted at the accident site on January 10 (Figure 6). At the crown, a soft wind slab was situated above multiple layers of faceted snow. The slab failed on a weak layer of faceted snow at a height of 16 inches above the ground surface. Although no surface hoar crystals were observed in the crown at the location where the profile was conducted, avalanche specialist speculated that the failure surface was likely a surface hoar layer that formed during a cold dry period in early December.
On January 9 the general avalanche hazard rating for this area was moderate. That day’s avalanche hazard advisory stated that wind slab avalanches and persistent slab avalanches could be triggered by the weight of a single person on weak layers of faceted snow.
On January 9, a large group of snowmobilers were riding in the upper portion of the Leidy Lake drainage southwest of Togwotee Pass when a 29 year old male was caught and buried in an avalanche. Two riders were on the east side of a ridge on the south side of Mt. Leidy at 3 PM when the slope failed. The person, who was caught, triggered the avalanche from the bottom of a steep slope and was fully buried. His partner was looking the other way and when he turned to look at the slope the movement of the avalanche was ending. He did not see his partner or his sled. The witness then used a radio to call the other members of his group, who were in the vicinity, to come help.
The buried man was not wearing an avalanche beacon. Five members of the party began to search the avalanche debris for visual clues. As more members of the group arrived to help they spotted the handle bars of the buried rider’s sled in the avalanche debris. The group had two avalanche probes and plenty of shovels. They began to probe uphill and downhill of the sled. A probe struck the helmet of the buried rider about ten feet uphill of the sled. The buried man was then excavated by the group from beneath six feet of avalanche debris. He was found head downhill, face down and was still wearing his helmet and goggles. There was no mask of frozen snow around the man’s face and no snow was found to be in his mouth or nose. CPR was performed but he did not survive.
At 3:16 the Teton County Sheriff’s Office received a call from a member of the party and was informed that a person had been caught and buried in an avalanche. Teton County Search & Rescue volunteers were mobilized and a helicopter was dispatched to the accident site. The helicopter arrived at 4:08 and departed the site with the patient at 4:43 PM. The cause of dead was determined to be asphyxia by the Teton County Coroner.
This accident occurred on the south side of Mt. Leidy at a location that is approximately 13 miles southwest of Togwotee Mountain Lodge. This group of riders accessed this area from the lodge. A vicinity map (Figure 1) shows the location of the lodge, the accident site and groomed snowmobile trails that lead from the lodge towards the site. An accident site map (Figure 2) depicts the terrain features at the accident location, an outline of the area of the slide, and the burial location.
Figure 6: Drawing of a crown face profile that was conducted on January 10