The avalanche was triggered by a backcountry skier near Mud Gulch above Yule Creek, south of the town of Marble. It was a soft slab avalanche, small relative to the path, and destructive enough to injure, bury, or kill a person. It released either on a layer of buried faceted crystals or depth hoar near the ground (SS-ASu-R2-D2-O/G). The crown face averaged about 1.5 feet deep and was about 300 feet wide. The avalanche ran about 500 vertical feet through sparse trees into a gully. Debris in the gully was over 13 feet deep in places.

Pertinent Weather & Snowpack

An atmospheric river event just before Thanksgiving brought 4 to 5 feet of snow in a few days. This was followed by a three-week dry spell, creating a pronounced layer of faceted snow grains. Several small storms in late December through mid-January added 3 to 5 feet of snow. Another weeks-long dry spell ensued, developing another prominent layer of faceted grains. Just before Valentine's Day, another atmospheric river event brought 3 to 4 feet of snow to the area in two days. Another storm from March 3 to March 8 brought an additional 2 feet of snow to the area.

The same slide path avalanched at least three times prior to the accident. During the Thanksgiving atmospheric river event, the slope avalanched naturally. Around January 10, a backcountry traveler remotely triggered an avalanche on the slope. During the Valentine's atmospheric river event, the slope had another natural avalanche. These repeated avalanches resulted in a shallow snowpack with more well-developed weak layers than adjacent slopes. The average height of snow was less than a meter adjacent to the avalanche, compared to 180 to 250 cm on nearby slopes at the same elevation.

Accident Summary Skiers 1 and 2 were familiar with the terrain in Yule Creek and current avalanche conditions. They left the trailhead and ascended a commonly used skin track up Marble Peak. They planned to “look around” and decide where they wanted to ski down. From Marble Peak, they decided to seek out north-facing, sheltered terrain further down the ridge to find better ski conditions.

After one short run in north-facing terrain, they skinned back to the ridge and started their descent from a point on the ridge with numerous other recent tracks. Skiers 1 and 2 descended the upper portion of the slope and regrouped. Skier 1 descended the next portion of the slope first, avoiding the steepest section above the gully, and waited for Skier 2.

Skier 2 skied into the steeper section and triggered the avalanche within his first few turns. The avalanche immediately knocked him over and carried him about 100 vertical feet before slamming him into a tree. He was seriously injured.

Rescue Summary

Skier 1 saw Skier 2 trigger the avalanche but lost sight of him in the moving avalanche debris. He was unable to make radio or verbal contact with Skier 2. Skier 1 immediately began to search with his avalanche transceiver. He did not have a signal and began to sidestep uphill across the avalanche debris. His skis were in downhill mode with no skins attached.

About halfway across the debris field, he picked up a signal at 52 meters and determined Skier 2 was uphill. He removed his skis and began crawling uphill. After ascending for several minutes, he heard Skier 2 moaning. He found Skier 2 on the uphill side of a tree, unconscious and partially buried, with only his head above the avalanche debris.

Skier 1 began to dig Skier 2 free. Skier 2 slowly regained consciousness but was unable to recall the events. Based on the extent of Skier 2’s injuries, Skier 1 triggered the SOS on his satellite communication device approximately 10 or 15 minutes after the avalanche.

Skier 1 freed Skier 2 and, with considerable effort, slowly moved him downhill–about 600 vertical feet–to lower-angled slopes in the sun to try and keep him warm. For several hours, Skier 1 provided care and comfort to Skier 2.

Four hours after Skier 1 triggered the SOS, a Search and Rescue (SAR) helicopter landed. SAR team members and flight medics loaded Skier 2 into the helicopter and flew him to a hospital for medical care.

Comments

We do our best to describe avalanche involvements to help the recreational community better understand factors that may have contributed to the outcome. We offer these comments in the hope that they will help people avoid future accidents. It is hard to admit mistakes and expose oneself to criticism. This group's willingness to do so is important in helping the community learn collectively.
The slope where they triggered the avalanche had avalanched at least three times earlier in the season. Thus, a thin and soft slab sat over a pronounced weak layer on the day of the accident. Avalanches were easier to trigger on this thin slope than on surrounding slopes with a much deeper snowpack. Skiers 1 and 2 were not aware of the seasonal history of this particular slope.

A common way to reduce avalanche exposure is to develop a trip plan that identifies terrain to avoid. Skiers 1 and 2 did not have a plan beyond ascending Marble Peak and choosing terrain to descend. While ascending, they met a friend. The friend said that ski conditions were not good in "Marble Bowl," the most common ski descent from Marble Peak. This steered Skiers 1 and 2 to consider other terrain. They followed other tracks along the ridge to a more north-facing slope.

A group made the tracks Skiers 1 and 2 followed the day before. One of the previous backcountry tourers triggered and was caught in a small avalanche just below the ridgeline. That group also remotely triggered an avalanche on a slope near the accident site. The slope with the remote avalanche, like the slope where the accident occurred, had avalanched several times during the season.

The two skiers mentioned that seeing tracks on the slope gave them some confidence that the slope was safe. Tracks on a slope do not mean the slope is safe, particularly when dealing with Persistent Slab avalanches. Previous tracks could have been made under different avalanche conditions, and sometimes, previous travelers were just fortunate enough to avoid triggering avalanches. The avalanche Skier 2 triggered ran over tracks made the day before.

Skier 2 was wearing a helmet. Despite the helmet, he sustained head injuries, including a concussion. Without a helmet, his head injury could have been more severe or even fatal. The forces in avalanches can easily exceed the protective capabilities of ski helmets, but helmets provide enough protection to be recommended for backcountry travel (Van Tilburg et al, 2017 )