2019/01/05 … Fatality at Upper Senator Beck Basin ~ Final accident report … CAIC

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Eric Ming photo

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CAIC photo

Avalanche Comments

This accident involved two avalanches. The first was a hard slab avalanche unintentionally triggered by the group of skiers, medium sized relative to the path, and had the destructive force to bury, injure, or kill a person (HS-ASu-R2-D2-O). The group triggered the avalanche near a shallow, rocky outcrop. It likely broke on a buried layer of near-surface facets that developed between storms during the first few days of the year. The avalanche stepped down to deeper weak layers near the ground, entraining the entire season’s snowpack. The face of the crown ranged from 12 inches to 54 inches deep. The avalanche released on a south-southeast facing slope around 32 degrees in steepness.

A crack from the first avalanche ran through the snow, releasing a second avalanche (remote trigger) on a connected east-facing slope. The second avalanche was a hard slab, medium sized relative to path, and had the destructive force to bury, injure, or kill a person (HS-ASr-R2-D2-O). Investigators estimated that the average depth of the crown face was 36 inches. The avalanche released on a slope around 35 degrees in steepness.

The debris from both slides overlapped at the bottom of the slope.

Events Leading to the Avalanche

The group met the morning of Friday, January 4, at the beginning of an American Institute for Avalanche Research and Education  (AIARE) 2 avalanche class at the Silverton Avalanche School (SAS). This is the second course in the recreational curriculum created by the AIARE. The class spent most of the day in Silverton. In the afternoon, ten students and two instructors went to the St. Paul Lodge near the top of Red Mountain Pass. Their plan was to spend the night at the lodge and Saturday in the backcountry. They planned to return to the lodge on Saturday night, and spend Sunday in the backcountry before the course ended on Sunday afternoon.

Friday evening in the lodge, they divided into two groups. The instructors assigned each group a large section of terrain on Red Mountain Pass and asked them to plan a tour for the next day. Group 1 planned to travel to the west side of US 550 and into the area around Senator Beck Mine. Group 2 would stay on the east side of the highway in the Prospect Gulch area. Group 1 spent about 2 hours planning their tour with their instructor (Skier 1). Eventually Skier 1 went to bed, but the rest of the group spent an additional hour on their plan for the next day.

Saturday morning the two groups left the lodge for their day in the field. They met with a staff member of the Silverton Avalanche School, who relayed current weather information, the avalanche danger rating, and the avalanche problem list from the January 5 backcountry avalanche forecast issued by the CAIC. Group 1 descended to the highway, crossed, and headed toward Senator Beck Mine.

Group 1 had a detailed trip plan that included a time schedule, a series of waypoints, and locations where they needed to make decisions. Their ultimate goal was to climb a peak locally known as South Telluride Peak (marked 13510 on USGS maps). They followed their planned route with a minor variation just below treeline. They stopped as planned at their first decision point, below a steep slope just above treeline. They decided that rather than ascend a snow-covered portion of the slope, they would ascended a slightly steeper section of the slope where grass was sticking out of the snow. They used the shallow snow on the southeast aspect to reduce their exposure to avalanches. They continued up the drainage, making observations, and discussing the avalanche conditions. They observed a whumpf in a grassy area of shallow snow, but no other signs of instability. At about 12,700 feet they dug a snow profile on a southeast-facing slope and conducted a series of column tests. None of the tests highlighted instability on a specific layer or showed propensity for crack propagation (STN, CTN, ECTN. Both the ECT and CT broke 57 cm off the ground with continued blows from the shoulder) (AAA 2016). Their route continued uphill towards point 13106 to the west of the Senator Beck Mine. It was almost 2:00 PM and they decided it was time to look for a descent route and return to the highway.

Their trip plan identified two descent options. The first was to descend the same way they had come up. The second was to descend the east side of a small cirque, travel to the northeast to their ascent route, and then descend the way they had come up. They decided on the second route.

After climbing to the top of point 13106, they moved west to the low point of the saddle between point 13106 and the rest of the cirque. Their plan was to descend a south aspect with shallow snow to reduce the risk of avalanches. They discussed moving the group from the saddle to a mid-slope bench where grass was sticking out of the snow. From there they would descend the rest of the slope, before returning to their skin track for the rest of the descent.

The group decided to travel down the first section to the bench in short succession. Skier 1 would start and when he was part way down, Skier 2 would follow. This would continue until the group was all on the bench. Skier 1 explained the plan and also where he wanted the group to travel on the slope, providing a boundary on the skier’s right (west) for them not to cross. He began his descent. Skier 2 followed, traveling a little to the skier’s right (west) of Skier 1. Skiers 3, 4, 5, and 6 all began sidestepping down the slope so they could see Skiers 1 and 2 as they descended. The snow surface was hard wind-packed snow. Skiers 3, 4, and 6 stopped to adjust equipment and get ready for their descent. Skier 5 continued to sidestep downhill. He saw a crack shoot across the slope and yelled “Avalanche!”

Accident Summary

The avalanche caught all six skiers. When the avalanche caught Skier 1, his ski bindings released and he fell forward, traveling head downhill on his belly. He was under the snow at times, but rose to the surface as the debris stopped. He lost both skis and one ski pole. He was carried to the bottom of the slope.

When the first avalanche stopped, Skier 1 was partially buried–not critical (his head was not under avalanche debris). He stood up and saw a second avalanche coming at him from an adjacent slope. The debris from the second avalanche ran over the debris of the first avalanche, but stopped short of Skier 1.

The first avalanche caught Skier 2 and carried him to the bottom of the slope. The rest of the group was preoccupied with their own involvement in the slide, so we do not know Skier 2’s condition at the end of the first avalanche. The second avalanche overran Skier 2’s position in the debris of the first avalanche.

The avalanche carried Skiers 3, 4, 5, and 6 between 15 and 20 feet downhill. The debris around them remained in large blocks, several feet thick and up to 12 feet wide. Skiers 3, 4, 5, and 6 stood up in the blocks of debris and looked around. They saw the second avalanche overrunning the debris of the first avalanche, but could not see Skiers 1 and 2.

~~~  CONTINUE  ~~~

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