CAIC: Colorado Avalanche Information Center

2019/02/16 - Colorado - Pearl Pass Road, Brush Creek Drainage

Published 2019/02/24 by Ben Pritchett - Forecaster, CAIC


Avalanche Details

  • Location: Pearl Pass Road, Brush Creek Drainage
  • State: Colorado
  • Date: 2019/02/16
  • Time: 8:49 AM (Estimated)
  • Summary Description: 2 backcountry tourers caught, buried, and killed
  • Primary Activity: Backcountry Tourer
  • Primary Travel Mode: Ski
  • Location Setting: Backcountry

Number

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

Avalanche

  • Type: SS
  • Trigger: AS - Skier
  • Trigger (subcode): u - An unintentional release
  • Size - Relative to Path: R3
  • Size - Destructive Force: D2
  • Sliding Surface: O - Within Old Snow

Site

  • Slope Aspect: SE
  • Site Elevation: 9350 ft
  • Slope Angle: 37 °
  • Slope Characteristic: Planar Slope

Avalanche Comments

This was a  soft slab avalanche unintentionally triggered by a pair of skiers. It was medium-sized relative to the path, and produced enough destructive force to bury, injure, or kill a person. It broke into old snow layers (SS-ASu-R3-D2-O). The avalanche failed on a layer of large, coarse-grained faceted crystals in the upper snowpack.The avalanche broke approximately 2 to 3 feet deep, 200 feet wide, and ran 120 vertical feet. 

The avalanche ran into Brush Creek, filling about half of the narrow creek gorge with debris. The abrupt transition from a steep slope to a flat, frozen creek bed caused the debris to pile up around 8 feet deep. There was a central channel of debris over 15 feet deep. The victims were buried on either side of this deepest debris.

This was a Persistent Slab avalanche.

Backcountry Avalanche Forecast

The Colorado Avalanche Information Center (CAIC) issued an Avalanche Warning on the morning of February 15, that expired on February 16 at 8:00 AM. The warning was replaced by a Special Avalanche Advisory on February 16. The text of the advisory read:

A strong storm on Thursday night brought 1 to 2 feet of dense snow with strong winds to many mountain locations. As snowfall continues through the holiday weekend, avalanche conditions will remain dangerous in many places throughout Colorado. You can trigger large avalanches that break in the new snow, large enough to bury a person, or even larger avalanches that entrain most of the season's snowpack. Backcountry travelers should consult their specific zone avalanche forecast before heading into the backcountry. All backcountry travelers should carry appropriate rescue gear and avoid dangerous avalanche terrain identified in the zone forecast.

The CAIC’s backcountry avalanche forecast for the Gunnison zone on February 16 rated the avalanche danger CONSIDERABLE (level 3 of 5) at all elevations and listed two avalanche problems. First were Persistent Slab avalanches, with a Likelihood of Likely, Size range Large to Very Large (up to D3), and all elevations and aspects except southwest. The second avalanche problem was Storm Slab avalanches, with a Likelihood of Likely, size range of Small to Large (up to D2), and at all elevations and all aspects. The Summary stated:

Avalanche conditions are dangerous. You can trigger destructive and broadly propagating avalanches on many slopes. Natural avalanches may run from large alpine slopes where newly drifted snow continues to accumulate. You're most likely to trigger a steep slope that's getting actively loaded from the westerly winds, but given the amount of recent storm snow the danger extends into sheltered terrain too. Especially in the shallower portions of the Gunnison zone, in areas with less than about 5 feet of total snowpack depth, consider that you can trigger deep and broadly propagating avalanches on any steep terrain feature.

Whether you're managing the newly fallen storm snow in the Ruby Range, or the chance of a deeper avalanche in Cement Creek, the bottom line remains the same. Choose terrain cautiously to reduce your chances and consequences of triggering an avalanche. Avoid the drifts. Stick to lower-angled slopes.

Weather Summary

The accident happened in the final hours of a multi-day storm that began February 13 and ended on February 16. This storm deposited one to two feet of very dense snow in the CAIC’s Gunnison forecast zone. The Butte SNOTEL (10,161 feet in elevation and approximately 4 miles west of the accident site) measured 1.7 inches of snow water equivalent (SWE) and 17 inches of snow during this storm event.

Southwest winds increased early in the morning of February 16 as the precipitation event wound down. The skies remained mostly cloudy, but the cloud ceiling rose and the winds became nearly calm in the hour before the accident.

Snowpack Summary

The shallow early-season snowpack in the inversion-prone canyon of Brush Creek repeatedly faceted during periods of clear weather between storms. Several thin crusts formed during mid-November, mid-December, early January, and late January. By mid-February these previously stiff structures had all changed into faceted grains. The weakest layer in the snowpack was a layer of 1mm near-surface facets immediately below the freshly drifted storm snow.

Winds drifted the storm snow throughout the February 13 to 16 storm. Two distinct periods with higher wind speeds loaded this particular slope, building a slab with approximately three times as much storm snow as compared to sheltered areas nearby. A widespread natural avalanche cycle occurred around the Gunnison forecast zone during the storm. 

On February 17, rescuers saw four natural avalanches between the Brush Creek trail head and the accident site that likely ran February 15th. Skiers 1 and 2 crossed the debris of two of these avalanches near West Brush Creek. Also on February 17, rescuers noted five large natural avalanches visible on nearby Whetstone Mountain

Events Leading to the Avalanche

Skier 1 and 2 departed the Brush Creek trail head around 6:30 AM, following Brush Creek Road along a route often used to access the Friends Hut. Their route also parallels a portion of the Elk Mountain Grand Traverse race corridor. The pair was registered for the race, scheduled for roughly five weeks after the accident.

Accident Summary

The accident was not witnessed and many details remain unknown. Rescue members found the pair with skis still attached to their boots, and climbing skins on. Presumably, they were breaking trail across the slope. Given their burial locations and the trajectory of the avalanche debris, it is likely the two skiers were fairly close together in the middle of the slope when the avalanche released.They were carried down an open 37 degree slope and their skis did not release. Skier 1 lost his poles, Skier 2 held onto his poles. Both skiers were buried approximately five feet (150cm) deep in the middle of the debris, on either side of a very deep channel of debris up to 15 feet deep.

Rescue Summary

Skier 2’s girlfriend reported the pair overdue to Mt. Crested Butte Police around 8:00 PM on February 16. Police dispatched Crested Butte Search and Rescue (CBSAR). Skier 2 carried a satellite tracking device and his family shared the track log with rescuers. The track log was still active, with forward progress ending between 8:39 and 8:49 AM. The location marks throughout the rest of the day were clustered over an area of several hundred feet in an area locally known as Death Pass. 

Rescuers considered the possibility of an avalanche, or that Skier 1 and 2 were injured and moving around a small area. Five rescuers departed around 10:00 PM on snowmobiles, with a planned route to avoid all avalanche terrain. Rescuers followed the skier’s track until it disappeared into avalanche debris in the Death Pass corridor. There was no track exiting the debris. Rescuers detected a faint signal from an avalanche transceiver, but it was too dangerous to conduct a further search of the avalanche debris at night.

On February 17, CBSAR, members of CBMR Ski Patrol, a CAIC forecaster, and Crested Butte Avalanche Center forecasters returned to the scene with helicopter support from Care Flight. At approximately 1:00 PM rescuers located Skier 1 and 2 using transceivers and probes.

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.

Unfortunately both Skier 1 and 2 were caught in the same avalanche. A common approach to reduce risk when crossing avalanche paths is to cross one at a time. If only one of the two skiers were caught and buried, the other may have been able to perform a successful companion rescue, turning a horrible tragedy into a near miss. Crossing the slope one at a time would have likely led to at least one of the skiers surviving this accident.

The avalanche occurred during a period when the snowpack was very unstable. There was an Avalanche Warning the day prior to the accident and a Special Avalanche Advisory on the day of the accident. The skiers skied past four avalanches and crossed over the debris of two slides before reaching the slope they triggered. They had to break trail through the large accumulation of dense snow and wind drifts left by the recent multi-day storm. 

Avalanche danger decreases slowly after large storm events like this one. Although the drop in danger from HIGH (Level 4 of 5) to CONSIDERABLE (Level 3 of 5) does reflect easing avalanche danger, that change is often gradual when dealing with persistent weak layers. In this case the CONSIDERABLE danger was much closer to HIGH, than it was to MODERATE (Level 2 of 5). It is important to consider the trend and yesterday’s danger rating to ascertain where today's conditions are on the avalanche danger continuum. 

Media

Video

Images

Snowpits

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Figure 12: A crown profile image. The slab is less-drifted, thinner, and weaker at the profile site. The slab that released was 2-3 feet thick and stiffer throughout.
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Figure 13: A close up of the slab and weak layer in the crown. The slab was thicker and more dense within the slab that released.