CAIC: Colorado Avalanche Information Center

2014/02/10 - Colorado - North Fork Swan River, south of Keystone Ski Area

Published 2014/07/14 by Becs Hodgetts - Forecaster, CAIC


Avalanche Details

  • Location: North Fork Swan River, south of Keystone Ski Area
  • State: Colorado
  • Date: 2014/02/10
  • Time: 11:45 AM (Estimated)
  • Summary Description: 2 skiers caught, 1 partially buried, 1 buried and killed
  • Primary Activity: Sidecountry Rider
  • Primary Travel Mode: Ski
  • Location Setting: Accessed BC from Ski Area

Number

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

Avalanche

  • Type: HS
  • Trigger: AS - Skier
  • Trigger (subcode): u - An unintentional release
  • Size - Relative to Path: R3
  • Size - Destructive Force: D3
  • Sliding Surface: O - Within Old Snow

Site

  • Slope Aspect: SE
  • Site Elevation: 11942 ft
  • Slope Angle: 35 °
  • Slope Characteristic: Planar Slope,Below Cornice

Avalanche Comments

This accident involved two avalanches. The first, was a hard slab, triggered by skiers falling through a cornice. It was small size, relative to the path, large enough to bury, injure or kill a person, and broke into old snow layers (HS-ASu-R2D2-O). The second, which buried and killed a skier, released sympathetically to the first skier triggered slide. It was medium size relative to the path, large enough to destroy a car or break a few trees, and broke into old snow layers (HS-ASy-R2D3-O).

Weather Summary

The Keystone Ski Area weather station, located approximately half a mile to the north of the accident site, received 23" of snow and 0.6 inches (15.5mm) of snow water equivalent (SWE) in the 5 days prior to the avalanche. West northwest winds throughout the period averaged 15-25 mph, drifting snow onto east and southeast facing slopes. Temperatures early in the period started at -10F at midday February 5th, climbing to 19F at midday on February 10th. Weather on February 10th was overcast skies, with light to moderate NW winds blowing snow, and a high temp of 20F.

Snowpack Summary

Below average snowfall at the beginning of the 2013-14 season developed a thin and variable snowpack throughout the Vail and Summit County forecast zone. Mild temperatures between early season storms developed several melt freeze crusts on south and east aspects, one of which was the bed surface for the February 10th avalanche. Very cold temperatures in early December accelerated the decomposition of these crusts and aided the formation of large faceted crystals directly above and below the crusts. Snowfall began in late December with three notable storms bringing the zone snowpack to 130% of average by the date of the accident. The first storm began December 24th, brought 7" of snow to the Keystone area and was followed by strong NW winds. Six days of clear calm weather gave way to the next storm which delivered 25.5" to the area with very light winds. The midpack strengthened during this time and persistent weak layers became stubborn to trigger. West winds picked up ahead of the next storm and triggered a widespread natural cycle on east facing slopes near and above treeline. The third storm began February 8th and delivered 23" of new snow with moderate west winds. These storms built 100 to 200 cm thick, cohesive slabs over the persistent weak layers, including basal depth hoar, on northeast through southeast facing slopes near and above treeline. Anecdotal evidence suggests the Vega Bowl avalanche path had run three times in the six weeks prior to the accident.

Events Leading to the Avalanche

This accident involved four skiers, identified as Group 1 and 2 (the two groups did not know each other).Groups 1 and 2  had been skiing Keystone Ski Resort on the morning of February 10th. Around 11:30 am, they rode a snowcat from Keystone's Outback Chair to the top of Wapiti Peak. Skiers A and B (Group 1) exited the snowcat ahead of Skiers C and D (Group 2), and began hiking toward Wapiti Peak. They left the ski area boundary, and hiked almost to the top of a feature locally known as Vega Bowl. As Skier A approached the cornice a piece broke free dropping into Vega bowl, but did not trigger an avalanche. They decided to avoid this area and instead head down the ridge to ski a lower angled, sparsely treed slope to the skiers right of Vega Bowl. By this time, Skier C had caught them, and they briefly discussed their decision before Group 1 skied away. 

Accident Summary

Group 1 descended into Vega Bowl via the sparsely treed area to the skiers right of the main avalanche path. They stopped on a prominent knoll in the lower third of the avalanche track at approximately 11,150 feet. Skier B stopped approximately 75 feet above Skier A.

Meanwhile, in Group 2, Skier C stepped to the edge of the cornice at approximately 12,075 feet, and fell through. That triggered a slide (HS-AS-R2D2-O) that swept down the skier's left side of Vega Bowl. Skier D then stepped toward the cornice and fell through, sliding down the slope and arresting 50 feet below skier C.

The first slide caused a second avalanche to release sympathetically (HS-ASy-R3D3-O). The first avalanche caught Skier A and swept him 200 ft down slope, partially burying him. The second avalanche swept Skier B from the knoll, and buried him 100 feet down slope in a small stand of trees.

Rescue Summary

Skier A dug himself out. He search the debris for approximately 15 minutes, and saw no sign of Skier B or his equipment. Neither skier was wearing an avalanche beacon. Skier A began hiking out the North Fork of the Swan snowmobile trail. Approximately 10-15 minutes later, Skiers C and D caught up to Skier A. He explained what had happened, and Group 2 skied out to Good Times Tours, where they called 911 and Keystone Ski Patrol.

Summit County Sheriffs Deputies, Summit County Search and Rescue, and local ski patrols responded to the accident site at 1:00 pm. Rescue crews were unable to locate Skier B that afternoon. They returned the next morning (February 11th), finally locating Skier B using RECCO detectors. Skier B was buried 143 cm deep in a small stand of trees.

Comments

This accident took place during a period of HIGH (Level 4) avalanche danger and an Avalanche Warning was in place for the Vail and Summit County forecast zone.

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