- Location: Lower Putney Shoulder, east of Red Mountain Pass
- State: Colorado
- Date: 2019/11/30
- Summary Description: 2 snowshoers caught, carried
- Primary Activity: Hiker
- Primary Travel Mode: Snowshoe
- Location Setting: Backcountry
- Caught: 2
- Partially Buried, Non-Critical: 0
- Partially Buried, Critical: 0
- Fully Buried: 0
- Injured: 0
- Killed: 0
- Type: SS
- Trigger: AI - Snowshoer
- Trigger (subcode): u - An unintentional release
- Size - Relative to Path: R3
- Size - Destructive Force: D2
- Sliding Surface: G - At Ground/Ice/Firm
- Slope Aspect: N
- Site Elevation: 12200 ft
- Slope Angle: 38 °
- Slope Characteristic: --
Snowshoers triggered and were caught in an avalanche on a north-facing slope above treeline. It was a soft slab avalanche, medium sized relative to the avalanche path and large enough to bury, injure, or kill a person. It broke on old snow near the ground (SS-AIu-R3D2-O). The avalanche broke about three feet deep, about 300 feet wide, and ran about 300 vertical feet. The avalanche started in areas of wind-drifted snow on a north-facing slope. The starting zone averaged 38 degrees in steepness. A second avalanche triggered sympathetically to the first. The sympathetic avalanche was to the east, closer to the weather station. It was a soft slab avalanche, small sized relative to the avalanche path and large enough to bury, injure, or kill a person. It broke on old snow near the ground (SS-AIy-R2D2-O).
Backcountry Avalanche Forecast
The Colorado Avalanche Information Center’s (CAIC) backcountry avalanche forecast for the North San Juan zone on November 30, 2019 rated the avalanche danger at Considerable (Level 3) at all elevations. An Avalanche Warning had expired at 6:00 AM on November 30. Two avalanche problem types were listed. First were Persistent Slab avalanches, highlighted on north, northeast, and east aspects near and above treeline. The likelihood of triggering was Likely and expected size was small to large. Storm Slab avalanches were the second problem type, highlighted on all aspects and elevations. Triggering was Likely, and expected size small to large. The summary from the backcountry avalanche forecast:
The howling Thanksgiving storm added a significant new load to our fragile early season snowpack, and it will be easy to trigger dangerous avalanches on steep slopes today. Avalanches will be larger on north and east-facing slopes at higher elevations that received the most wind-drifted snow from sustained southwesterly winds. These are the same slopes with the weakest snow near the ground. Avalanches breaking in the new storm snow can break into these deeper weak layers and produce avalanches big enough to bury you.
Shooting cracks or sounds of the snowpack collapsing are clear signs of unstable snow. You can trigger avalanches from a distance or from below, so pay attention to locally connected steeper slopes even if you're travelling in low-angled terrain. Slopes less than 30 degrees with steeper terrain overhead offer safer riding options.
A party of four snowshoers triggered an avalanche. The avalanche caught and carried two of the party members. One of the snowshoers described swimming while the avalanche was in motion. When the avalanche stopped, both snowshoers were minimally buried and uninjured. They dusted themselves off and hiked back to the trailhead.
The snowshoer’s involvement was reported second-hand. They spoke to another group in the area, and that group provided information to the CAIC. In field observations, CAIC forecasters initially recorded the avalanches as naturally-triggered.