CAIC: Colorado Avalanche Information Center

2017/11/18 - Colorado - Greg Mace Peak, Castle Creek

Published 2017/11/21 by blase reardon - Forecaster, CAIC


Avalanche Details

  • Location: Greg Mace Peak, Castle Creek
  • State: Colorado
  • Date: 2017/11/18
  • Time: 2:00 PM
  • Summary Description: 1 snowboarder caught and partially buried
  • Primary Activity: Hybrid Rider
  • Primary Travel Mode: Snowboard

Number

  • Caught: 1
  • Fully Buried: 0
  • Injured: 0
  • Killed: 0

Avalanche

  • Type: HS
  • Trigger: AR - Snowboarder
  • Trigger (subcode): r - A remote avalanche released by the indicated trigger
  • Size - Relative to Path: R2
  • Size - Destructive Force: D2
  • Sliding Surface: O - Within Old Snow

Site

  • Slope Aspect: NW
  • Site Elevation: 11320 ft
  • Slope Angle: 45 °
  • Slope Characteristic: Concave Slope,Sparse Trees,Gully/Couloir

Accident Summary

A party of two snowboarders (Rider 1 and Rider 2) had a close call when they triggered an avalanche from below that caught one rider, carried him down the gully they were riding, and left him partially buried but uninjured.

On the morning of the accident, Rider 1 read the Statewide Avalanche Avalanche summary from the previous day. He was aware that the storm the night before had changed conditions, so the pair planned to "get a workout and maybe a few turns without getting into serious terrain." They also hoped Rider 2 could get some practice transitioning on his splitboard.

They found 6 to 8 inches of fresh snow at the trailhead, more than they expected. They left the trailhead about 09:00 and reported breaking trail with their vehicle once they got above the Pine Creek Cookhouse above Ashcroft. On their approach, they saw intermittent blowing snow near ridgelines, as well as some scoured patches and some wind-loaded gullies. They observed no cornices or natural avalanches. 

Because of conditions, the pair decided to ride lower in the drainage than they originally planned. They skinned up lower-angled slopes at the base of Greg Mace Peak, sticking to slopes with scattered trees and avoiding open slopes. They found 2 to 16 inches of fresh snow, the variability due to extensive wind redistribution. They observed frequent cracks that broke up to 16 inches deep on a layer of facets between the slab and the ground. 

Their approach switchbacked up through terrain that gradually steepened. The pair stopped near treeline, in an area where the slope angle was approximately 35°. The terrain above was steeper and more open. They were below two wind-loaded snowfields but felt the snow they were on was disconnected from terrain above. They transitioned to downhill travel in an island of trees at about 11,150 feet. From there, they could access a half-pipe-like gully that drained the snowfields above.

After discussing safe stopping points, they entered the gully one at a time. Rider 1 descended and pulled up on rider's left in a rocky area with shallow snow. He tried to get completely out of the gully. When Rider 2 descended, Rider 1 felt a distinct collapse. Rider 2 passed him and went to their agreed-on safe spot on rider's right of the gully.

Rider 1 had his back to the slope above (regular riding stance). He felt what seemed like a blast of wind and then got clobbered by fast-moving debris from behind. He found himself in "a big, fast avalanche." He felt helpless. He reached for the trigger of his airbag but realized he wasn't wearing it. The debris pushed Rider 1's head downhill. He couldn't see, couldn't get above the snow, and thought he was going to hit a tree and die. He estimated he was moving at highway speeds.

Rider 1 stopped after about 400 vertical feet. He came to rest head downhill with his mouth and nostrils just above the snow. One outstretched arm was out of the snow, along with one leg. His snowboard was still attached. He could barely breathe, and snow fell into his mouth every time he moved. He said he was "iced in" by the debris. He was uninjured, though he felt beat up. 

The debris dusted Rider 2, but he was able to stay high enough on the gully wall to avoid getting caught in the debris. Rider 2 watched the avalanche go past, yelled several times, shuffled to get a better view, then started descending. He saw Rider 1's hand moving and thought it was a tree, then realized it was Rider 1. He rode down to Rider 1, reaching him about a minute after the slide hit. Rider 2 uncovered Rider 1 and the pair self evacuated. 

Rider 1 had over two decades of backcountry experience, extensive avalanche training (Level 1 and Level 2 courses), and some guide training. Rider 2 was also an experienced backcountry rider but did not have avalanche training, though he was scheduled to take a Level 1 course the next month at Rider 1's encouragement. They are regular riding partners. Rider 1 had traveled in the area several times in the weeks prior to the accident.

 Rider 1 reported the slide was 80-100 feet wide, with a crown depth of 2.5-5 feet deep and average depth of about 3 feet. It released at about 11,320 feet; Rider 1 was hit at about 11,000 feet and stopped at about 10,600 feet. The gully channelized and confined the moving debris, which left a narrow debris field that had some rectangular blocks.

In the 36 hours prior to the accident, the Upper Taylor SNOTEL (10,640 feet; 3.5 miles ESE) recorded 1.6 inches of snow water quivalent and temperatures dropping from the mid-30s to the single digits on the morning of the accident. Temperatures rose to the upper 20s by the time of the accident. Winds during the storm were strong to very strong, with gusts over 90 mph at Snowmass Ski Area (11,385 feet; 12 miles north-northeast).

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