CAIC

Avalanche Details

Location: North of Yellow Mountain
State: Colorado
Date: 2020/03/20
Time: 1:30 PM
Summary Description: 2 backcountry riders caught, partially buried, and injured
Primary Activity: Backcountry Tourer
Primary Travel Mode: Snowboard
Location Setting: Backcountry

Number

Caught: 2
Partially Buried, Non-Critical: 1
Partially Buried, Critical: 1
Fully Buried: 0
Injured: 2
Killed: 0

Avalanche

Type: SS
Trigger: AR - Snowboarder
Trigger (subcode): u - An unintentional release
Size - Relative to Path: R2
Size - Destructive Force: D2
Sliding Surface: O - Within Old Snow

Site

Slope Aspect: N
Site Elevation: 11000 ft
Slope Angle: 37 °
Slope Characteristic: Sparse Trees,Dense Trees

Avalanche Comments

This was a soft-slab avalanche unintentionally triggered by a backcountry snowboarder. The avalanche was small relative to the avalanche path and large enough to bury a person. It broke two to three feet deep failing on a layer of small faceted grains that formed on the surface during the dry spell at the end of February (SS-ARc-R2D2-O). The avalanche started on a north aspect near treeline. It was up to 150 feet wide and ran approximately 500 vertical feet through an opening in the trees. Debris was three to four feet deep and soft enough to allow each person to self extricate.

Backcountry Avalanche Forecast

The Backcountry Avalanche Forecast for the North San Juan zone rated the avalanche danger as Considerable (Level 3) near and above treeline, and Moderate (Level 2) below treeline. The forecast listed Storm Slab avalanches as the primary problem on all aspects and elevations all elevations. The likelihood of triggering was Likely and the potential size Small to Large. Persistent Slab avalanches were listed as the second problem, on northwest, north, northeast, east, and southeast aspects near and above treeline. The likelihood of triggering was Possible and the potential size Large. The summary read:

Dangerous avalanche conditions continue. 15 to 20 inches of new snow over the last 48 hours is a quick shock load to the snowpack and it got pushed near its breaking point. Natural avalanches are still possible today but are becoming less likely now that the main loading period is over. Human-triggered slides remain likely and even where confined to the recent storm snow will most likely be large enough to bury or injure you. South-southwest winds built stiffer slabs at higher elevations and some drifts may exceed several feet thick – expect wind-drifted slabs to be touchier than fresh slabs in wind-sheltered terrain.

The new load also added a lot of weight and stress to weak, faceted snow now buried 2 to 4 feet deep. Slides failing in the storm snow have potential to break deeper creating a larger, more deadly slide. Stick to slopes less than about 35 degrees and give big, open, and steeper terrain an extra wide buffer if you have to travel below. Heed the warning signs of surface cracking and deep, rumbling collapses indicating unstable snow below your feet. Make conservative terrain choices and avoid avalanche start zones to help reduce your avalanche risk.

Weather Summary

February was dry, with lower than normal snowfall in the Ophir area. Telluride Mountain Resort (four miles northeast) measured 30 inches of snowfall. That was 68% of the 30-year average. Much of the snowfall came at the beginning of February and the last two weeks were dry with clear skies and mild temperatures. March started with a small storm with little wind on March 2, and two more small storms on March 9 and 14. On March 19 and 20 a bigger storm deposited 15 to 20 inches of snow containing 1.5 to 1.7 inches of snow water equivalent (SWE). There were moderate south winds during the storm.

Snowpack Summary

Very little snow fell in the San Juan Mountains before Thanksgiving. The majority of the early season snowpack developed during the last six weeks of 2019 and there was a generally strong and deeper than average snowpack to start 2020. Strong winds in January drifted dense, thick layers in some areas. In others, winds eroded snow, leaving a total snowpack depth less than four feet. February was dry and cool, which promoted the growth of faceted snow crystals and depth hoar in the areas of shallow snow.

By the end of February, many shady slopes below 11,500 feet developed a weak, cohesionless snowpack top to bottom. At the surface, small faceted grains also formed from diurnal recrystallization. Multiple small storms throughout the month of March buried the weak surface snow and increased slab depth, but did not overload the weak layer. Observers reported few avalanches.

In the days prior to the accident the March slab had increased to two to three feet thick. Northerly aspects had the deepest wind-drifted snow. There were 10 natural and triggered avalanches reported in the North San Juan zone March 19 and 20. These avalanches failed on either the near-surface faceted layer or depth hoar.

Events Leading to the Avalanche

A party of two, one male splitboarder and one female skier, planned a backcountry tour north of Yellow Mountain near Ophir. Their plan was to “ski something mellow where others had not been” on low angle, east-facing terrain in an area known as Jane’s. They parked at the lower Ophir trailhead and ascended the well-used route on the west side of drainage. They reached the ridge separating Waterfall Canyon from the steeper northwest facing slopes known as Eldorado. There were many tracks into the northwest aspects of Eldorado. They continued up the ridge and decided to descend a gentle ramp into Eldorado alongside other ski tracks. They descended the upper bowl and trended skier’s left toward a tree-covered slope. They reached an opening in the trees around 11,200 feet in elevation, and decided to ride the steeper slope below one at a time.

Rider 1 descended and stopped mid-slope at a perceived area of safety, so she could watch Rider 2 descend the whole slope. Rider 2 put his Avalung into his mouth and began his descent to the skier’s right

Accident Summary

The avalanche released on Rider 2’s second turn. It caught Rider 2 and tumbled him head over heels several times. The Avalung was ripped from his mouth. He attempted to aim for and hit a small tree to slow his descent. The impact broke one binding from his board, freeing one leg. The avalanche carried him over two small rock bands. He came to rest partly buried with his arms free 600 feet below the crown face. He had dislocated one shoulder in the avalanche.

Rider 2 cleared the snow from his mouth. He reached in his pack for his shovel, dug his other foot clear, and released his binding. He turned his transceiver to receive and immediately picked up a signal at 60 meters. He began walking uphill to find his partner, but the soft avalanche debris made ascending difficult. He heard no response when calling his partner's name. After climbing uphill about 200 feet, he heard Rider 1's muffled voice and saw her digging herself out of the debris.

Rider 2 triggered the avalanche uphill of Rider 1, and she watched the avalanche catch him. The avalanche propagated skier’s left, overran her location and engulfed her. The avalanche carried Rider 1, 400 vertical feet through trees. She was buried except for one arm, with her head under about one foot of avalanche debris (partially buried-critical) when the avalanche stopped. She used her free arm to uncover her face, and then began freeing herself. Rider 1 had mostly excavated herself by the time Rider 2 reached her. She injured a knee and lost one ski in the avalanche.

The pair were about 800 vertical feet above the trailhead. Though injured, Rider 1 could bear weight on her knee and descended on one ski. Rider 2 was able to reattach his binding. Bruised, sore, and tired they made it back to their car on their own.

Comments

Rider 2 had four years of backcountry riding experience. Both riders had been reading the avalanche forecasts all season. They read the current forecast on the day of the avalanche, and understood the hazard of recent storm snow on top of persistent weak layers. They did not intend to ride steep, wind loaded slopes.

By the time they reached the lower, steep slope, they had successfully descended through the more wind-exposed bowl just below the ridge. Reflecting afterwards, the pair believes that this, along with the many other tracks nearby were factors that lulled them into thinking they would be OK.

Both were surprised at how little control they had once the avalanche started. They were completely at the mercy of the slide.