CAIC: Colorado Avalanche Information Center

2013/02/02 - Colorado - Clothesline Path, Cement Creek, near Silverton

Published 2013/02/15 by Mark Gober, Susan Hale, Matt Steen, Ann Mellick - Forecaster, CAIC


Avalanche Details

  • Location: Clothesline Path, Cement Creek, near Silverton
  • State: Colorado
  • Date: 2013/02/02
  • Time: 1:30 PM (Estimated)
  • Summary Description: 3 skiers caught, 1 buried and killed, 1 partially buried, 1 injured
  • Primary Activity: Backcountry Tourer
  • Primary Travel Mode: Ski
  • Location Setting: Backcountry

Number

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

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: 11690 ft
  • Slope Angle: 38 °
  • Slope Characteristic: Convex Slope

Avalanche Comments

This skier-triggered avalanche was a soft slab that was medium sized relative to the path, with the destructive force sufficient to bury, injure or kill a person, and ran on old snow and the ground (SS-AS-R3D2-O/G). The initial failure occurred within old snow layers, but the avalanche subsequently stepped down to the ground taking out the entire season's snowpack. The crown face was 24 to 36 inches deep and over 200 feet across. The avalanche removed only a portion of the snow in the start zone, leaving some lingering hazard above the fracture line. The slide ran through terrain that ranged from glades to dense forest. Several trees ranging from 6 to 8 inches in diameter were snapped off by the force of the avalanche.

Weather Summary

After a dry early winter, a potent storm arrived on Saturday, January 26th. The CAIC's closest snow study plot on Red Mountain Pass recorded 41.5 inches of snowfall with 3.45 inches of water content between January 26th and January 30th. Silverton Mountain, one mile from the accident site, recorded 38 inches of snow with roughly 3 inches of water in the same period. On February 1st, the day before the accident, the Putney weather station (closest alpine station) recorded a high temperature of 17°F and northwest winds averaging in the 20-30 mph range with gusts into the 40's. The high temperature on February 2nd, the day of the accident, was 27°F at the Putney weather station. This was the first time the air temperature rose above 20°F in several days.

Snowpack Summary

Before the snow storm on January 26th, the snowpack in the Silvertion area consisted of weak, faceted snow. A small storm on January 11th brought modest snow accumulations to the region. Warm and dry weather in mid January formed a melt-freeze crust on the surface of this Jan 11th layer.

There were two natural avalanche cycles in the Cement Creek drainage during the January 26th storm. The first took place on January 26th and 27th. The second on January 28th. The slope where the accident took place did not slide during either cycle.

The snow from the January 26th storm fell onto this melt-freeze crust. The combination of a large new snow load, on a firm crust, all resting above a weak foundation of faceted snow grains, created a conditionally unstable snowpack. Although many of the slopes in this area released naturally during the storm, the snow on this slopes hung in the balance waiting for more time to adjust to the new load or a trigger to produce an avalanche.

Snow pit tests the day after the accident showed a moderate load could produce propagating cracks (ECTP 14 Q1) directly below the mid January melt/freeze crust.

Events Leading to the Avalanche

A party of three backcountry skiers toured off of the Corkscrew Pass road (San Juan County Road 10). They made two runs before heading for the last run of the day in Clothesline. The first two runs were on a fairly low-angle (25-30°), northeast aspect. Clothesline is an east aspect, with an average slope angle of 38° in the start zone.

Accident Summary

Skier 1 entered 'Clothesline' skier's right of the main avalanche path and skied part way down the slope before stopping behind a large tree. Skier 2 entered and skied a similar area before stopping with Skier 1.

Skier 3 entered the slope and skied to the right of the previous tracks, triggering the avalanche. The avalanche propagated to the skiers right at the top of the path causing a lot of snow to run through fairly thick timber and into the main avalanche path, and sweeping Skiers 1 and 2 from their location behind the tree. Skier 3 was pushed up against a tree and partially buried. He was able to quickly extricate himself and could see Skier 1 from his location. Skier 1 was mostly on the surface of the snow, but pinned to a tree. Skier 3 helped Skier 1 out of the snow and assessed his injuries. Skier 1 was injured but able to travel downhill. Skier 2 was further downhill and fully buried.

Rescue Summary

Skier 3 initiated a beacon search that led him to Skier 2. Skier 2 was fully buried under approximately 5 feet of snow. Upon partial extrication, Skier 2 had no pulse and was not breathing. Skier 3 performed first-aid until Skier 1 arrived. Skiers 1 and 3 decided to go for help, and initiate a 911 call as soon as they could obtain cell phone coverage.

Skier 3 descended into the valley and met up with another group of backcountry skiers as he reached the Corkscrew Pass Road (San Juan County Road 10). A member from this group volunteered to ski out and make the 911 call. When that individual reached San Juan County Road 110, he flagged down the driver of the Silverton Mountain shuttle bus, and told the driver that there had been a backcountry avalanche and that 2 people were caught.

At 14:25, the driver radioed the ski area mountain manager with the accident information. The mountain manager drove a snowmobile up County Road 110 to the Corkscrew Pass turn-off.  At that time, a second member of the unaffiliated touring party arrived with information that there was one deceased and one member with a possible fractured femur. This information was radioed to the Silverton Mountain helicopter, which in turn picked up the owner of the ski area, a flight medic, the snow safety director and an additional patroller along with basic life support and rescue supplies. Meanwhile, the mountain manager called Durango-based Flight for Life at 14:45 to assist with the evacuation of the injured party. The Silverton Mountain helicopter landed above the avalanche path at 14:40, dropping off the 4 staff members, the basic life support pack and rescue sled. They immediately established the need for an additional patroller and another rescue sled. The patrollers and the medic continued downhill into the avalanche path, while the helicopter pilot flew back to the ski area for the additional personel and supplies.   

The first group of rescuers arrived on scene at 14:50. The final patroller and rescue sled arrived by 15:20.  The EMT-Paramedic on scene conducted a full assessment of the injured party and established that there was no femur fracture, but a lower leg injury and a dislocated shoulder. The rescuers loaded the injured skier (Skier 1) into a rescue toboggan and transported him to County Road 110 where they arrived at 15:50. The remaining 3 patrollers on scene completed the extrication of Skier 2 and prepared to transport him out of the field. They reached County Road 110 at 16:50.

The San Juan County Sheriff’s Office and Search and Rescue arrived on County Road 110 at Corkscrew Pass at approximately 15:00 to assist with ground support and coordination of the Flight for Life helicopter.  Skier 1 refused transport via helicopter and opted for ground transport with San Juan County Ambulance.

Comments

There are several factors that independently may not be responsible for this accident, but on this day combined for a very tragic outcome. Some issues that other backcountry travelers should consider are:

  1. The January 26th storm was the first big load on a very weak snowpack. It is common to see natural avalanches during a large storm followed by a period when natural avalanches are not likely, but triggered avalanches are. This period typically lasts from hours to days depending on the structure of the snowpack. Slopes in the 35 to 45 degree range typically remain dangerous for the longest period of time.  Snow pit tests the day after the accident indicated it was unlikely that the slope would avalanche naturally, but it would not take a large trigger to produce an avalanche.
  2. The group began the day skiing two runs in 25 to 30 degree, northeast facing terrain, which probably gave them some confidence in the snowpack. Their last run was on a 38 degree, east facing slope. The change to steeper, more committing terrain, on a different aspect put the group in avalanche conditions that were different than they had seen earlier in the day. On this particular day it was a more dangerous situation.
  3. The group chose to ski and regroup, probably to maintain communication. Maintaining communication between group members is generally a good practice when traveling in avalanche terrain. In this case the stand of old-growth trees did not give them enough protection as the avalanche swept through the trees and pushed the skiers downhill and into other large trees.

The coordination between reporting parties and Silverton Mountain staff was excellent. A very quick and efficient rescue took place with multiple parties involved in the coordination.

The unaffiliated touring party had an avalanche accident in close proximity (in both time and space) to this fatal avalanche accident. In both cases, the characteristics of the slope (aspect and elevation) and the snowpack (slab and weak layer) were very similar. The avalanches released within about 20 minutes of each other. Although in many ways these avalanches were quite similar, the outcome for the two parties was quite different.

Media

Images

Snowpits

Image Missing
Figure 16: Fracture line profile.