Two snowmobilers were highmarking a southeast facing bowl. The upper snowmobiler triggered an avalanche from a low angle terrain feature. The avalanche propagated across the bowl. The lower rider had turned and was descending, and did not see the avalanche above him.
Snowfall in the East San Juans has been just above average for the winter to date. Snow fell early and often through the winter. Significant surface hoar layers have formed during brief clear periods, particularly in December. In the five days prior to the accident, 16.5 inches of snow fell at the CAIC/CDOT snow study plot at the Wolf Creek Pass (approx. 9 miles W of the accident site). Temperatures were very cold (minimum -12°F) and snow was low density.
The day before the accident strong northwest winds averaging in the teens and gusting in the 40-50 mph range caused considerable snow transport throughout the East San Juans. Clear blue skies and mild temperatures dominated the day of the accident. Air temperature at Wolf Creek Pass at the time of the accident was 23°F.
The morning of 2/4/07, three men headed up the Beaver Creek groomed snowmobile trail into the high country around North Peak. An ungroomed side trail took them into a large east through southeast facing bowl on the southeast shoulder of Pt. 12,494. They stopped on a large bench in the middle of an obvious large avalanche path. A recent avalanche (SS-N-R2D2-O/G) was visible on the climber's left side of the bowl. It had recently run in the period between 2/1 and 2/4.
The recent natural avalanche on the left side of the bowl (center) and debris from the fatal avalanche (right).
While one rider remained at the bottom of the bowl two riders began to high mark the extreme right hand side of the bowl. As one rider reached the ridge he triggered an avalanche that involved the entire right hand side of the bowl. Unfortunately, the other rider turned left into the bowl about halfway up unaware that an avalanche had been triggered. As he descended the rider at the bottom frantically waved to catch his attention, but the avalanche overran him before he could avoid or outrun it. The rider who triggered the avalanche was not caught and raced to the bottom of the bowl.
The approximate location where the avalanche was triggered. The slab only moved 10 feet.
The avalanche was triggered from a relatively low angle subtle convex role at the extreme right side of the bowl and propagated 900 feet to the west. The avalanche ran on a weak layer of old surface hoar that formed on or about 12/15. This season, several avalanches have run on this weak layer.
Slope angle at the trigger point was 23° (yes, 23°). The slab was also thickest here, 50 inches. Slope angles in the main part of the starting zone were typically 37°, and 40° at the steepest point measured. The aspect ranged from east-southeast to southeast. The crown height averaged 30 inches. The snow surface was very hard (knife hard).
A mid-slope cliff band stretched across the entire bowl. Considerable debris stopped on a bench above this cliff band, but as the debris flowed over the cliff band more avalanching occurred, with much of this area sliding to the ground. The slope angle below the cliff band was 37°. The slide descended 800 vertical feet and stopped where the slope angle eased to 5°. The avalanche debris exhibited both hard slab and soft slab characteristics and is classified HS/SS-AM-R3D2.5-O/G.
The fatal avalanche. Tracks on the right are from the snowmobiler who was not caught. Debris from the recent natural avalanche is visible past the trees on the left.
The victim's snowmobile came to rest at the toe of the debris partially buried and still running. Initial rescue efforts were focused near the snowmobile. The group did not have any avalanche rescue equipment, but began to search immediately. At 1116 hours the Rio Grande Country Sheriff's Office received a cell phone call from one of the party stating that a party member had been buried in an avalanche. Rio Grande County Search and Rescue respond. One of the party members met Search and Rescue at the trailhead and guided them back to the location. At 1410 hours, probing found the victim buried four feet deep, 8 to 10 feet south of his machine at the toe of the debris.
Mark Mueller, 2/6/07