- Location: First Creek, north of Berthoud Pass
- State: Colorado
- Date: 2020/12/26
- Summary Description: 1 backcountry skier caught, buried, and killed
- Primary Activity: Backcountry Tourer
- Primary Travel Mode: Ski
- Location Setting: Backcountry
- Caught: 1
- Partially Buried, Non-Critical: 0
- Partially Buried, Critical: 0
- Fully Buried: 1
- Injured: 0
- Killed: 1
- Type: SS
- Trigger: AS - Skier
- Trigger (subcode): --
- Size - Relative to Path: R2
- Size - Destructive Force: D1.5
- Sliding Surface: G - At Ground/Ice/Firm
- Slope Aspect: N
- Site Elevation: 11050 ft
- Slope Angle: 40 °
- Slope Characteristic: Dense Trees,Gully/Couloir
This was a soft slab avalanche, triggered by a skier, relatively small for the path, and not large enough to bury and kill a person without the terrain trap it ran through. The avalanche broke to the ground (SS-AS-R2D1.5-G). It was a Persistent Slab avalanche.
Backcountry Avalanche Forecast
The avalanche forecast for the Colorado Avalanche Information Center’s (CAIC) Front Range zone on December 26, 2020 rated the avalanche danger at Moderate at all elevations. It listed Persistent Slab avalanches as the only avalanche problem on northwest, north, northeast, east, and southeast aspects near and above treeline. The Likelihood was Possible and the size was Small to Large. The summary read:
You can trigger large and deadly avalanches on recently wind-loaded slopes. Avoid slopes over 30 degrees near ridgetop, especially those that face an easterly direction. These easterly ridgetop locations are where you are most likely to find thick wind-drifted slabs over deeply buried weak layers. A fresh large avalanche was reported from Berthoud Pass yesterday. Recent large avalanches were also triggered from below and from adjacent slopes. Whether you are skiing, snowboarding, snowshoeing, cross-country skiing or snowmobiling, avoid traveling on or underneath steep, wind-loaded slopes.
The CAIC measures snow and snow water equivalent (SWE) at a study site just below Berthoud Summit on the west side of the pass. The site sits at 11,280 feet in a below treeline area about a mile and a half to the south of the accident site.
At the beginning of November there was only 5 inches of snow on the ground on Berthoud Pass. CAIC forecasters measured 38 inches of snow with 3.65 inches of SWE during the month of November. This is only 88% of the 30 year mean November snowfall. The total snowpack depth was about 24 inches.
At the end of November and the beginning of December, Colorado sat under an entrenched ridge of high pressure which resulted in clear skies and calm winds. A weak storm made it over the ridge on December 2nd, and deposited 5 inches of new snow on Berthoud Pass. The next 8 days were clear and calm with light northwesterly winds. Daytime high temperatures at 11,000 feet were in the mid to high twenties Fahrenheit and even reached freezing on a few occasions. Nighttime low temperatures were mostly in the low to mid teens with temperatures dropping below 0 Fahrenheit on the coldest nights.
Between December 11 and December 13 CAIC forecasters measured 11 inches of new snow. A period of strong west to northwesterly winds on December 13 and 14 drifted snow onto lee-facing slopes above treeline. Between December 18 and 25 CAIC forecasters measured 15 inches of snow with 1.35 inches of SWE. On December 26, the morning of the accident, CAIC forecasters measured the snowpack depth at 36 inches.
The day of the accident was clear and warm with daytime high temperatures in the mid thirties. Clouds moved in during the late afternoon and light snowfall began around sunset. About 7 inches of snow fell between the time of the accident and when CAIC forecasters visited the accident site on December 27.
The snowpack in below treeline north-facing areas near the accident site was thin and weak. The total snow depth adjacent to the crown was 85cm (about 33 inches). Ski penetration in areas above and adjacent to the crown line was often to the ground. The bottom 40cm of the snowpack was an unconsolidated (F to 4F on the hand-hardness scale) layer of depth hoar that formed early in November. The crystals were well developed cups 2 to 4mm in extent and were chained together. The top of this basal weak layer was most likely the initial failure plane of the avalanche. Above the depth hoar there was a 15cm thick layer of faceted crystals 1 to 2mm in extent. This layer formed during the prolonged high-pressure period at the beginning of December. The upper layer of the snowpack was about 25 cm thick. It was soft (F to 4F on the hand-hardness scale) and composed of decomposing and fragmented precipitation particles. Investigators measured the slab density at 125 kg/m³. Snow pit tests in an area adjacent to the starting zone showed some ability for a crack to propagate, but the layers were almost too weak to confine a crack at a single interface. There was evidence of minor wind drifting on a ridge near the starting zone which may have helped a fracture propagate in that area.
Events Leading to the Avalanche
Skier 1 began his tour at the Second Creek trailhead, north of Berthoud Pass. His plan was to gain the ridge to the north, between Second and First Creek, and descend to the trailhead at First Creek. His companions dropped him off at Second Creek and then drove to the First Creek trailhead. He climbed to the ridgeline, spoke to his companions by cell phone, and then descended a narrow, rock walled gully locally known as Chimney Chute.
Skier 1 was alone and no one witnessed the avalanche. Skier 1 did not reach the First Creek trailhead. His companions called 911 at about 4:15 PM.
The Grand County Sheriff’s Office and Grand County Search and Rescue (GCSAR) responded to the 911 call. They arrived at the First Creek trailhead as it was getting dark and used a drone and moonlight to evaluate the accident scene. Skier 1’s companions told the search and rescue personnel that he was not wearing an avalanche rescue transceiver. GCASR did not pick up a transceiver signal during their initial search. They located Skier 1 using a probe pole.
The avalanche washed Skier1 into a dense stand of small trees. The avalanche buried Skier 1 under about 10 inches of avalanche debris and a tree about 5 inches in diameter. GSAR personnel recovered Skier 1’s body the night of December 26.
All of the fatal avalanche accidents we investigate are tragic events. We do our best to describe each one to help the people involved and the community as a whole better understand them. We offer these comments in the hope that it will help people avoid future avalanche accidents.
No one witnessed this accident. Most of the rescue occurred in the dark, which limited the rescuers’ ability to see the start zone and ski tracks in the upper part of the path. It began to snow during the rescue and there were seven inches of new snow the following morning when CAIC investigators visited the site. All of these factors limit our ability to describe the events leading up to the avalanche.
The snowpack in the area was exceptionally weak. Snow pit tests showed some ability for a crack to propagate through the pack, but the layers were almost too weak to confine a crack at a single interface. The snowpack was barely strong enough to keep the investigators off the ground as they descended a slope to the skier’s left of the chute. The skier’s left side of the chute showed some signs of recent wind drifting. That could have resulted in layers slightly stronger than the surrounding snowpack. The avalanche removed the majority of the snow in the bottom of the chute and from the apron below. Even after entraining this snow the debris was only a few feet deep in the deepest locations and often less than 1 foot deep. This was a small avalanche that produced tragic consequences by washing Skier 1 along a path full of obstacles.
Skier 1 was alone during his tour and not wearing an avalanche rescue transceiver. He sustained significant traumatic injuries in the avalanche. He might not have survived the avalanche even if he was touring with partners able to perform a quick rescue and recovery. An avalanche rescue transceiver would have certainly helped the organized rescue team that provided assistance. The avalanche created a fairly small debris pile and the team was able to locate Skier 1 without an extended search.
Figure 9: Snow profile observed adjacent to the avalanche crown.