CAIC: Colorado Avalanche Information Center

2020/02/15 - Colorado - South Fork of Dickson Creek, east of Red and White Mountain

Published 2020/02/25 by Kreston Rohrig and Ethan Greene - Forecaster, CAIC


Avalanche Details

  • Location: South Fork of Dickson Creek, east of Red and White Mountain
  • State: Colorado
  • Date: 2020/02/15
  • Time: 2:45 PM (Estimated)
  • Summary Description: 3 snowbike riders caught, 1 partially buried, 2 buried and killed
  • Primary Activity: Snowmobiler
  • Primary Travel Mode: Snowmobile
  • Location Setting: Backcountry

Number

  • Caught: 3
  • Partially Buried, Non-Critical: 1
  • Partially Buried, Critical: 0
  • Fully Buried: 2
  • Injured: 0
  • Killed: 2

Avalanche

  • Type: HS
  • Trigger: AV - Vehicle (specify vehicle type in comments)
  • Trigger (subcode): u - An unintentional release
  • Size - Relative to Path: R3
  • Size - Destructive Force: D2
  • Sliding Surface: O - Within Old Snow

Site

  • Slope Aspect: NE
  • Site Elevation: 9800 ft
  • Slope Angle: 37 °
  • Slope Characteristic: Sparse Trees

Avalanche Comments

This was a hard slab avalanche unintentionally triggered by 3 motorized snowbikers. It was medium-sized relative to the avalanche path and produced enough force to injure, bury, or kill a person. It broke into old snow layers and was likely triggered from the bottom of the slope (HS-AVu-R3-D2-O). The avalanche likely failed on an old layer of faceted snow about three feet below the surface. The crown face of the avalanche was 3 to 4 feet deep, 600 feet wide, and the debris ran about 300 vertical feet. 

The Persistent Slab avalanche broke on a steep slope with a mix of small cliffs and sparse trees. The slide ran down the slope and into the narrow bottom of the drainage. It turned, flowing down the drainage and filling the bottom of the gully with a deep pile of debris. The avalanche debris broke small trees and collected in deeper piles around larger trees along the bottom of the path. 

Backcountry Avalanche Forecast

The Backcountry Avalanche Forecast for the Vail-Summit County zone rated the avalanche danger as Moderate (Level 2) at all elevations. The forecast listed Persistent Slab avalanches as the primary problem on all aspects and elevations. The likelihood of triggering was Possible and the potential size Large to Very Large. The Vail-Summit County Summary on February 15 read:

Conditions are a little tricky right now. Avalanches are becoming harder to trigger but may go way bigger than you might expect. Add in the fact that this scenario exists on a wide range of aspects and elevations, and you will have to do your homework before committing to any steeper slopes. This is an excellent time to get your probe and shovel out to investigate the snowpack. Deeper areas seem to be more stable, but you will want to make sure there are no reactive weak layers in the upper portion of the snowpack or unsupportable layers further down. With higher amounts of uncertainty, it's always best to manage your terrain decisions and stick to lower angle slopes.

Just yesterday, I spied a handful of avalanches from Vail Pass through the 10-mile range on multiple different aspects, elevations, and terrain configurations, and other reports confirm the same: Gore Range, Vail Pass. The naturals likely failed a couple of days ago, but the ongoing activity is worrisome.

The bottom line is there are plenty of hazards out there right now that might not show themselves until it's too late. Wind-loaded terrain features and thinner snowpack areas are the most suspect, but any steep slope deserves your attention. Expect the danger to rise through tomorrow as more snow starts to fall.

Weather Summary

The Vail ski area, approximately 7 miles southeast of the accident site, reported 52 inches of  snowfall during the two weeks before the accident. The Vail Mountain SNOTEL site, located within the Vail ski area at an elevation of 10,300 feet, recorded 3.9 inches of snow water equivalent (SWE) in the same period. A majority of this snowfall came in a five-day period between February 6 and February 11, where the Vail ski area reported 36 inches of snowfall and the Vail Mountain SNOTEL recorded 3.2 of SWE. There were very strong westerly winds throughout this five-day storm period. The Vail’s Blue Sky station (elevation 11,109 feet) recorded sustained winds of 20 to 30 mph with gusts in the 40s. 

In the three days prior to the accident the Vail ski area reported an additional 8 inches of snowfall, and the Vail Mountain SNOTEL recorded an additional 0.4 inches of SWE. The Blue Sky station showed moderate westerly winds, generally in the teens and 20s with gusts in the 30s (mph).

The weather was mild on the day of the accident. The day started with partly cloudy skies, temperatures in the upper teens (Fahrenheit), and moderate ridgetop winds. Cloud cover and westerly winds increased later that  afternoon ahead of an approaching storm. 

Snowpack Summary

The total depth of the snowpack measured at the crown was around 5 feet (155 cm). The shallow snowpack in October and November turned to faceted snow grains during periods of clear and cold weather between fall storms. This created a weak foundation in the lowest three feet (100 cm) of the snowpack. A brief spell of warm weather during the first few days of February formed a distinct melt/freeze crust around ¼ in (1 cm) thick. The February 6 to 11 snowfall event covered this crust with a thick slab of consolidated snow. 

The February 6 to 11 storm produced a widespread avalanche cycle, with 35 avalanches reported in the Vail & Summit County forecast zone. The cycle included small to very large avalanches (D-Size 1 to 3), triggered naturally or by humans and explosives on all aspects. The highest concentrations were near and above-treeline, with eleven reported below treeline.

Events Leading to the Avalanche

A group of three snowbike riders (Riders 1 through 3) left the Red Sandstone Road winter access point at about 10:30 AM on Saturday February 15, 2020. Their plan was to ride in the Red and White Mountain area. They rode up the groomed road (US Forest Service road 700) making their way to Red and White Mountain, playing on low-angle slopes and in meadows as they went. At one point they saw a group of snowmobilers high marking near a recent avalanche. They did not know when the avalanche released, but decided to continue avoiding steeper slopes. 

At a hairpin turn in the groomed road (USFS Road 700 which goes over Muddy Pass), they spent some time playing in the meadows and open areas between the groomed tracks. Around 2:30 PM they crossed the groomed road and headed south up a narrow unnamed drainage with forested sides, near the headwaters of South Fork of Dickerson Creek. Rider 3 was in the lead, but started to bog down and made a sharp turn in a small open area to keep his momentum. Riders 1 and 2 continued up the drainage and Rider 3 looped around and followed their track (placing him at the back of the group). Riders 1 and 2 followed the creek bottom until it widened slightly and they reached an opening in the trees. There were dense trees ahead and on the slope to their left, but the northeast-facing slope to their right was broad, open, and steep with only sparse trees. Riders 1 and 2 made small looping turns in the bottom of the drainage and along the lower portion of the slope, so their bikes were facing down the drainage, back the way they had come.

Accident Summary

Rider 3 came into the open area and saw Riders 1 and 2 above him on the slope. He looked up and saw the avalanche breaking in the far upper left (southern) portion of the slope. He waved to Rider 1 as he turned uphill to head back down the drainage, passing between Rider 1 and Rider 2. All three riders were heading down the drainage, with Rider 3 furthest back the way they had come (to the north), when the avalanche overtook them. Rider 3 rode out the side of the avalanche into a group of dense trees. Only the track of his snowbike was buried in avalanche debris (partially buried-not critical).

Rescue Summary

Rider 3 got off of his bike and turned his avalanche transceiver to receive. The distance reading on the unit was 30 meters (98 feet) and the numbers decreased as he walked back up the drainage yelling for Riders 1 and 2. He reached an area where the distance reading dropped to 5 meters (16 feet), but could not find an area with a lower reading. He began to probe for his friends, but did not get a strike. He moved "3 or 4 feet" of snow off of the area and probed again. He got a strike and began to dig. After about an hour of digging Rider 3 had a narrow hole “about 10 feet deep”. He found Rider 1, but just a portion of his coat. Rider 3 knew he was going to need help. He got back on his snowbike and rode towards a yurt operated by Vail Backcountry Tours (VBT) that he passed that morning. 

When Rider 3 reached the yurt, staff from VBT alerted Vail Mountain Rescue (VMR) and eventually the 911 dispatch center for Eagle County. Two people from VBT and Rider 3 returned to the accident site to continue searching. On their way back they encountered a group of six people on four snowmobiles and one snowbike. The six riders joined the rescuers and the group of nine all returned to the site and began digging out Rider 1 and looking for Rider 2.

The group had some difficulty locating Rider 2. The lowest reading they could get on an avalanche transceiver was 5.5 meters (18 feet). Eventually they got a positive probe strike under a tree about 20 feet (6 meters) across and slightly down the drainage from Rider 1. They worked to free Rider 2 until about 9:00 PM when Vail Mountain Rescue reached the site. Given the time elapsed, darkness, increasing snowfall, and no easy way to evaluate the avalanche hazard above the site, the group left and returned to the Red Sandstone trailhead. VMR returned the following morning to recover the bodies of Riders 1 and 2.    

Comments

All of the fatal avalanche accidents we investigate are tragic events. We do our best to describe each one to help the people involved and the community as a whole better understand them. We offer these comments in the hope that it will help people avoid future avalanche accidents.

This group was prepared, but not planning, to travel in avalanche terrain. All three carried avalanche transceivers, probe poles, and shovels. Riders 2 and 3 had avalanche airbag packs, although the triggers were zipped up in their shoulder straps at the time of the accident. The group spent the entire day playing in dense trees or on low-angle slopes, specifically avoiding avalanche slopes. At the end of the day they decided to enter an unfamiliar drainage, and attempted to turn around and retreat when they saw the steeper slope. Maybe the only thing they could have done to avoid this situation is to use maps or a mobile phone app to look at the area before they left the road. Both the open nature of the slope and the slope angle over 30 degrees are apparent in satellite imagery and contour maps.

The avalanche forecast for the day described “tricky” conditions. The snowpack on this slope had one distinct and one subtle weak layer. Both were buried under a thick layer of snow about a week old. They were unreactive in Extended Column Tests and required fairly long cuts to get cracks to extend in Propagation Saw Tests. We don’t know what the snowpack looked like where the group triggered the avalanche or on the slope; all of that information was destroyed in the slide. However, data from snow profiles observed in the crown and flank of the avalanche are quite reflective of a spooky Moderate avalanche hazard: strong snow, avalanches are difficult to trigger, and avalanches large to very large maybe even bigger. A Moderate avalanche danger (2 of 5) can still describe dangerous avalanche conditions. In the last seven years, 32 people were killed in avalanches in Colorado. Eleven have died during periods of Moderate avalanche danger, including all four killed during the 2019-2020 season. 

The slide caught the group in a terrain trap, a gully that produced a deep burial. Both riders were buried between 8 and 10 feet (2.5 to 3 meters) deep. This contributed to a difficult rescue scenario. We did not interview every member of the rescue party, but the discussions we had indicate the probes they used were less than 250 centimeters long. The group had to move snow off of both riders to pinpoint their locations.    

Media

Video

Images

Snowpits

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Figure 10: A snow profile in the crown face of the avalanche in South Dickson Creek. Observed on February 16, 2020.
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Figure 11: A snow profile just north of the avalanche in South Dickson Creek and near the bottom of the avalanche. Observed on February 20, 2020.