- Location: Hermosa Peak on Barlow Creek side
- State: Colorado
- Date: 2018/12/16
- Summary Description: 2 snowmobilers caught, 1 partially buried - critical
- Primary Activity: Snowmobiler
- Primary Travel Mode: Snowmobile
- Location Setting: Backcountry
- Caught: 2
- Partially Buried, Non-Critical: 0
- Partially Buried, Critical: 1
- Fully Buried: 0
- Injured: 0
- Killed: 0
- Type: HS
- Trigger: AM - Snowmobile
- Trigger (subcode): u - An unintentional release
- Size - Relative to Path: R2
- Size - Destructive Force: D2
- Sliding Surface: I - New/Old Interface
- Slope Aspect: NE
- Site Elevation: 11700 ft
- Slope Angle: --
- Slope Characteristic: Planar Slope
This was a hard-slab avalanche that broke along a wind-loaded area of a ridgeline. It was small relative to the largest avalanche possible on this slope, but large enough to bury or kill a person. It was triggered by a snowmobiler and broke into the old snow (AM-HS-R2D2-O). This was a Persistent Slab avalanche.
December started off snowy in the Northern San Juan Zone with up to 20 inches of snow and 1.25 inches of snow water equivalent (SWE) reported from the December 1 to 3. Incremental snowfall continued through December 7. Strong west winds on December 11 to 12 drifted snow onto north to east-facing slopes near and above treeline. On the morning of December 13, CAIC forecasters measured 6 inches of snow and 0.4 inches SWE at the Lizard Head study plot (10,200 ft) north of the avalanche site. The Scotch Creek SNOTEL (9,100 ft), southwest of the avalanche site, reported 3 inches of snow and 0.1 inches SWE. The CAIC weather station in Rico (8,931 ft) reported 5 inches of snow and 0.3 inches of SWE.
The two days prior to the incident were mild and dry with daytime high temperatures in the upper forties. Nighttime low temperatures ranged between teens to low twenties. Winds were light to moderate.
On the day of the accident, high temperatures were 50F at the Scotch Creek SNOTEL and 47F on Lizard Head Pass. Winds at the Lift 8 weather station at Purgatory Ski Resort (10,795 ft), east of accident site, averaged 2 mph with a max speed of 4 mph out of the east. Wind speeds were similar at the Rico weather station, but southwest wind direction.
The snowpack in the San Juan Mountains began to build in early October. October snowfall persisted and began to facet on shady northwest through north to east-facing slopes near and above treeline. Small storms with generally light accumulations occurred in early November. A two-week dry spell in mid-November gave way to warm days and clear, cold nights. This weather pattern accelerated facet growth near the ground and multiple crust formed above. Many southerly and west-facing slopes melted down to bare ground during the November dry spell.
Thanksgiving marked a change in the weather pattern with a three-day storm that accumulated up to one foot of snow near and above treeline. Storm and wind-drifted snow built slabs over weak facets found mid-pack and near the ground. Despite a return to active weather, snow depth was thin with non-continuous snow cover across the North San Juan zone.
Another extended period of dry weather after December 4 contributed to further weakening of the snowpack and snow surface. Several strong wind events in early December easily transported weak surface snow, drifting additional stiff layers of snow above weaker snow. By mid-December, multiple buried weak layers were capped by multiple layers of thick, wind-drifted slabs. The CAIC received reports of 23 natural avalanches and four skier-triggered avalanches from December 9 to 14.
Events Leading to the Avalanche
A group of nine snowmobilers (on eight machines) left the Barlow Creek trailhead on the morning of December 16. Some of the group had ridden in the area on December 14. On that day there was a lot of new snow and they rode and played in the snow-filled meadows. They had a similar plan on this day, but hoped to cross over the ridgeline and spend some time on the south side of Hermosa Peak. They rode up the Barlow Creek road. One of the machines was running a little rough, and Rider 3 decided to turn around and head back to Colorado Highway 145. The rest of the group continue up the drainage and into the meadows at the base of Hermosa Peak. They rode and played in the deep snow under blue skies.
The group rode across a low-angle slope below a steeper slope on the lower part of Hermosa Peak. There was a wind drift at the top of the slope and evidence of old avalanche activity. The group did not stop or regroup. One of the riders climbed the slope and a few of the others stopped at the bottom to watch. Other members of the group climbed the slope while others watched from below.
Rider 6 came down off the slope and Rider 7 started his climb up. He was about halfway up the slope when Rider 2 started up from the bottom. Riders 2 and 7 climbed up towards the top of the ridge. Rider 7 maneuvered to extend his climb and the slope released.
The avalanche broke along the top of the ridgeline, at least 350 feet wide. Rider 2 was below the stauchwall of the slide. He was riding uphill, but turned to evade the moving debris. He was caught in the debris during his turn, eventually getting knocked off of his machine and buried with one arm out of the snow.
Rider 7 rode across the moving slab and off of the upper edge and out of the avalanche. He turned down to find Rider 2. Rider 1 was on the low-angle slope below the slide and waited and watched as the debris came to rest. He rode up to the debris and saw Rider 2's machine sticking out of the snow. He then saw Rider 2's arm sticking out of the snow. Riders 1 and 7 started digging with their hands. They were soon joined by Rider 5 and the three of them uncovered Rider 2's face. Rider 2's helmet had been torn off in the avalanche and he did not respond to verbal commands. Rider 1 cleared Rider 2's airway and the group encouraged him to breath and respond. Rider 2 opened his eyes and the rest of the group took out their shovels and dug him out of the debris.
Rider 2 was unhurt. He took Rider 1's machine and rode down to a sunny area below the avalanche to meet up with the rest of the group. The riders on the hill spent about an hour digging out Rider 2's machine. They joined the rest of the group below and eventually rode out to their vehicles on highway 145.
Everyone in the group rode away unharmed, but came very close to being part of a tragic accident. As is often the case, the group could have done a few things to avoid this situation. They also did some important things right and their actions lead to a good outcome.
Things to do better:
1- Only one person on the slope at a time. There were two people on the slope when the avalanche released. One rode out, but the other was caught and buried. If there was only one rider on the slope there would have been only one rider exposed to the avalanche. In this case no one would have been buried.
2- The group did not check the avalanche forecast before heading into the backcountry. The forecast that morning described a Moderate (Level 2 of 5) avalanche danger and warned of triggering an avalanche in a wind-drifted area. It also warned that avalanches could break into old layers of weak snow.
3- The group changed the type of terrain they were riding without checking in or discussing it. They were playing in low-angle terrain that was below treeline and protected from the wind. They changed to a steep, wind-loaded slope near treeline without talking about if this was a good idea. If they had stopped to talk this over they could have easily seen that the slope was wind-loaded. They could have also seen previous avalanche activity on this slope from the low-angle slopes below.
Things they did well:
1- The group was well prepared with avalanche rescue equipment. Everyone had avalanche rescue beacons, shovels, and probe poles. They were carrying their avalanche rescue equipment on their backs. When they needed to respond, they knew what to do.
2- The group performed a quick rescue and recovery. About 1 minute elapsed between Rider 2 being overrun by the debris and the group uncovering his face. The group responded quickly and worked together. They reached the buried rider's airway very quickly and continued to provide critical care by clearing his airway and encouraging him to breath while they continued to extricate him from the snow.
Another note: Rider 2 was wearing an airbag pack. The canister has been discharged by accident on a ride a week or two before this accident and was empty on this day.