- Location: Washington Gulch, north of Crested Butte
- State: Colorado
- Date: 2016/12/12
- Summary Description: 1 snowmobiler caught, buried
- 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: 0
- Type: SS
- Trigger: AM - Snowmobile
- Trigger (subcode): u - An unintentional release
- Size - Relative to Path: R2
- Size - Destructive Force: D2
- Sliding Surface: G - At Ground/Ice/Firm
- Slope Aspect: N
- Site Elevation: 11250 ft
- Slope Angle: 39 °
- Slope Characteristic: Convex Slope,Gully/Couloir
The avalanche was a soft slab, unintentionally triggered by a snowmobiler, small relative to the path, large enough to bury, injure, or kill a person, and broke into old snow layers just above the ground. (SS-AMu-R2-D2-O/G). The avalanche released in a steep gully feature on a north-facing slope near treeline, at an elevation of 11,250 ft. The avalanche broke approximately 3.5 feet deep, 175 feet wide, and ran 60 to 75 vertical feet. The slab had a Hand Hardness of 4 Finger to 1 Finger. It released on a layer of Fist Hard, faceted crystals. The debris was approximately 5 to 10 feet deep.
The Schofield Pass SNOTEL site (2.9 miles north of the avalanche site and approximately 10 miles north of Crested Butte) received 4.2 inches of snow water equivalent (SWE) from November 17 to November 28, and an additional 2.8” of SWE from December 2nd until December 11. The latter storm period culminated with a relatively warm storm system brought dense snowfall and strong winds through the Crested Butte area. From December 10 to the morning of December 11, the Elkton weather station (8 miles north of Crested Butte at an elevation of 11,100 ft) recorded 6 inches of new snow. The Schofield Pass SNOTEL site (elevation of 10,701 ft), recorded 8 inches of new snow in this same time frame, with 1.1 inch of snow water equivalent (SWE). Temperatures at both stations were in the 20s Fahrenheit during the December 10 storm, and winds at Elkton averaged 10 mph out of the WSW, with a max gust of 78 mph. Temperatures remained near 20F throughout, with a maximum temperature at Elkton of 21F and a minimum temperature of 17F. Winds increased on December 11, averaging 15 mph and gusting to 68 mph out of the WSW. They eased again on December 12, averaging 5 mph, gusting to 20 mph out of the WSW. The last measurable precipitation prior to the accident fell on December 11 at 7 a.m.
An unusually long and warm dry spell left all but high elevation, shaded aspects bare of snow until November 17. On these shady slopes, a thin layer of large grained facets developed. A series of storms from November 17 through November 28 developed a 23 inch deep snowpack at the Elkton Weather Station, which is approximately 2,000 feet southwest from the accident site. A dry, cold snap during the ensuing week led to some faceting throughout the snowpack and at the surface. Unsettled weather returned from December 2nd until the day before the accident, with a series of small storms increasing the snowpack depth by 10 inches. These two stormy periods developed a slab up to 3.5 feet thick at the location of the site, over a well developed faceted layer on the ground. There was also a mid-pack facet layer that formed in the lull between storms.
Events Leading to the Avalanche
A group of approximately eight snowmobile riders (Riders 1 through 8) made plans for a two-night hut trip to Elkton from Sunday, December 11 to Tuesday, December 13. The group rode up to the hut on Sunday afternoon and traveled across some nearby terrain that afternoon. Around 11:00 the next morning, December 12, the group left the hut to ride in some of the terrain on the southeast shoulder of Mt. Baldy above the hut. At least several of the members, if not all, checked the avalanche report from their smartphones that morning. Members of the group observed some collapses and cracking in the snow, but did not observe any avalanche activity as they were ascending along the base of Mt. Baldy. The riders communicated to each other the signs of instability and the need for a cautious approach in the terrain. Rider 1 got his snowmobile stuck in Rock Creek Basin, about 150 feet down slope from the avalanche accident location. Several members of the group descended to assist Rider 1. Some of them went around a prominent gully feature to reach Rider 1. Rider 2 and Rider 3 descended through the gully, spaced out about 30 seconds apart from each other. Rider 2 exited the gully towards where Rider 1 was stuck, alongside several other group members, including Riders 4, 5 and 6.
On December 12, 2016, at approximately 11:45 A.M., Rider 3 was descending down the middle of the gully when the avalanche released 60 vertical feet above him. The debris overtook Rider 3 and swept him and his snowmobile down slope about 50 feet. Rider 3 was fully buried and his snowmobile was partially buried, with only part of the ski and part of the front of the snowmobile visible at the surface. Rider 3 was buried on his side, head downhill, approximately 5 to 10 feet down slope of the snowmobile. He was buried an estimated 1 to 2 feet deep.
Riders 4 and 5 saw the avalanche occur and yelled to the rest of the group, “Avalanche! Avalanche!” Rider 2 made a U-turn and ascended the gully towards the point where he last saw Rider 3. He had a good visual on where Rider 3’s helmet was before burial, and was able to quickly dig him out without having to use his beacon or probe. Rider 3 was buried for approximately 1 minute or less, and his airway was blocked by snow during this time. Rider 2 quickly pulled the helmet off of Rider 3, who was attempting to gasp for air. Rider 2 encouraged Rider 3 to cough out the snow and he was able to clear his airway. Riders 4 and 5 also responded to the scene to aid in digging out Rider 3 and his equipment, while several other members of the group watched on from a safe location in case of any additional avalanches. After being excavated from the debris and clearing his airway, Rider 3 was alert and oriented, without any injuries. The group was able to extricate his snowmobile and return safely to the Elkton Hut.
Managing and communicating with a large group, especially on snowmobiles, is challenging in the backcountry. It is easy to lose visual contact of your partners which can amplify the consequences of an avalanche. This group did an good job of staying in contact, communicating, and responding to the avalanche quickly, while managing the potential threat of additional hang-fire in the gully. By staying within verbal and visual contact of each other, they prevented a fatality. They were all trained and prepared for avalanche rescue, which helped facilitate a speedy response.
The gully acted as a terrain trap, exacerbating the depth and consequences of the relatively small avalanche slope. Persistent Slab avalanche like this one can be triggered from the bottom of the slope, and there can be numerous tracks across or under an avalanche slope before someone initiates failure. Persistent Slab avalanches are the leading cause of avalanche fatalities in Colorado.
The avalanche danger was rated Considerable above treeline and Moderate near treeline the day of the incident. Moderate danger means that “heightened avalanche conditions exist on specific features.” This slope is a very steep, unsupported convexity, rolling over to as much as 44 degrees in steepness. That, along with its troublesome shaded aspect, which had been highlighted in the avalanche advisories, made it a problematic slope on that day.
Figure 5: Crown profile. The avalanche broke on the weak facets at the ground.