In the past 3 days, the folks at the Colorado Avalanche Information Center have recorded 17 human-triggered avalanches, including this skier triggered R2/D1 slab on a southeast-facing slope near 12,100 feet, Upper Straight Creek (Summit County) on February 1st. The avalanche failed on a buried weak layer near the ground, releasing where the slope steepened and the snowpack was thinner.
Observation Summary
My partner and I had five excellent ski descents on the Straight Creek Headwall, and on one of the descents I triggered a R2D1 slab. The avalanche broke on a SE slope around 12,100′ at a point where the slope angle transitioned from the low 30º range into the mid 30s. The crown was about 2′ tall, 25′ wide, and the slide ran for approx. 150′. The slide appeared to fail on a buried weak layer near the ground, as it uncovered some rocks and vegetation when it slid. Admittedly, much of the snowpack is “near the ground” – the area we were skiing in had highly variable snow depths ranging from 0″ to over 60″ in favorable, drifted locations. This particular avalanche was on a face that gets cross-loaded or scoured depending on the day, and the snowpack was visibly thin at the margins of this face. Bystanders reported a tremendous whumph when the slide released about 15′ below me, and I also observed some shooting cracks / spider web cracks radiating horizontally and up the slope from the crown. I was able to traverse away from the avalanche and safely descend nearby.
Route Description
Straight Creek headwall / area known to some as Dr. Jay’s Bowl
Colorado Avalanche Information Center – CAIC
Drifted Snow Near Ridgelines
Avalanche danger is MODERATE (2 of 5) across much of the Northern Mountains. In the past 3 days, we’ve recorded 17 human-triggered avalanches, including a handful of remote triggers. The most significant activity has been around Vail and Summit County, where recent snow and wind have built stiffer slabs near ridgelines.
It is possible to trigger a large avalanche in these drifted areas, sometimes from a distance. The most dangerous slopes are those facing north through south, especially where the snowpack is thinner near rocks just below ridgelines. Shallow trigger points near rocks seem to be the main culprits in most human-triggered activity. Wind-sheltered, lower-elevation terrain (generally less than 30 degrees) offers safer, more enjoyable travel.
In other parts of the state, the slabs become more isolated. In the Central Mountains, the problem is mostly limited to terrain just below ridgelines. In the Southern Mountains, there are fewer slopes with a slab you can trigger, but it’s still worth avoiding firm, smooth-looking drifts on steep, rocky terrain.
If you’re traveling on sustained steep slopes, watch for Loose Dry avalanches. Even small sluffs can run farther than expected and become a problem in terrain traps.
