This was a hard slab avalanche unintentionally triggered by a backcountry skier. It was medium in size relative to the path and produced enough destructive force to bury, injure, or kill a person. It broke on faceted snow in the middle or bottom of the snowpack and ran to the ground in many places (HS-ASu-R3D2-G). It averaged two feet deep, was over 600 feet wide, and ran 800 vertical feet. The avalanche split in two partway down the path and the eastern section funneled through a narrow gully. The western portion of the avalanche swept Skier 1 downhill and ran through small, sparse trees in the lower half of the avalanche track. Both sections of the avalanche converged at the bottom and piled debris over six feet deep in the ravine.

The Colorado Avalanche Information Center’s (CAIC) forecast for the Berthoud Pass area for December 3, 2024, rated the avalanche danger at Considerable (Level 3 of 5) near and above treeline and Moderate (Level 2 of 5) below treeline. There were two avalanche problems listed. The first problem was Persistent Slab avalanches on northwest to northeast through southeast aspects. The likelihood was Likely, and the expected size was Small to Large (up to D2). The second problem listed was Wind Slab avalanches on east through southeast to south aspects near and above treeline with a likelihood of Possible and an expected size of Small to Large (up to D2). The summary statement read:

"You can trigger an avalanche on northerly, easterly, and south-facing slopes. You can trigger slides that only break in drifted snow, but the bigger hazard is slides that break in weak snow near the ground. On northerly and easterly aspects, weak snow is abundant close to the ground and slides can easily step down to this layer resulting in a large avalanche. You may not see any signs of instability before you trigger an avalanche. Low-angle and wind-sheltered slopes are safer options."

October storms left shallow, faceted snow on high-elevation slopes with a northerly aspect in the Front Range. Storms during the first half of November buried the October snow under stiff, wind-drifted layers.

A large storm from November 25 to 27 increased the height of snow by a foot (1.3 inches of snow water equivalent) at the Berthoud Summit SNOTEL site at 11,300 feet, 0.75 miles west of the avalanche site. Despite relatively low wind speeds during the storm, it produced a widespread cycle of natural avalanches. Wind speeds increased after the storm, and wind drifting caused another spike in avalanche activity. An avalanche released naturally in the Mines 1 avalanche path on December 1, 2024, during this wind-loading event. A CAIC forecaster visited the Mines 1 avalanche and published a field report on December 2, 2024 describing weak snow buried or sandwiched between layers of drifted snow. The avalanche in Mines 1 broke on faceted snow in the middle or bottom of the snowpack and ran to the ground in many places. CAIC staff found a similar snowpack structure when investigating the Mines 2 avalanche.

Skier 1 left his car at the top of Berthoud Pass around noon on Tuesday, December 3, 2024. He was traveling alone and planned to ascend and descend the low-angle, heavily trafficked west-facing slopes on Colorado Mines Peak, east of the pass. Skier 1 had skied on Berthoud Pass many times but only a few times on the east side. He made a plan to avoid avalanche terrain because he was alone. He did not read the current avalanche forecast on the day of the accident.

On his first run, Skier 1 ascended west-facing slopes and descended tight trees back to the road. He decided to go a little further north to a slightly different aspect for his second run, towards the north face of Colorado Mines Peak. He stopped about 600 vertical feet below the summit on the ridge dividing the westerly-facing from the north-facing slopes – close to the top of an avalanche path locally known as Mines 2 – to remove his skis and prepare to ski downhill. He did not see the large natural avalanche that ran two days before in Mines 1, a nearby avalanche path uphill and to the east of his transition point.

Skier 1 descended along the ridgeline above the Mines 2 avalanche path. He made “one or two” turns into the top of Mines 2. He did not intend to ski the slope and only wanted to check the snow conditions. He saw a large crack shoot out in front of him and an avalanche break above him. He took a hard left turn and skied off the moving snow. Another wave of moving snow hit him from above and carried him down the slope.

The avalanche dragged Skier 1 through small trees lower on the slope. He “swam” and kept his feet and skis oriented downhill. The avalanche eventually dragged him under, and he lost both skis. During the avalanche, Skier 1 knew that "when the debris slowed down, it was my chance to try and fight and get my head above the snow." When the debris stopped, Skier 1’s arms were out of the snow but his face and head were buried by about six inches of debris (partially buried - critical). Despite suffering a dislocated shoulder in the avalanche, Skier 1 was able to dig himself out of the debris and call 911 on his cell phone. The avalanche had swept him about 400 vertical feet through small trees, and he came to rest about three-quarters of the way down the avalanche path.

Skier 1 hiked down the avalanche debris into the drainage and downhill towards US 40. He met Grand Country Search and Rescue (GCSAR) one and a half to two hours after the avalanche. GCSAR transported him to the highway and transferred him to a waiting ambulance that transported him to emergency care.

Skier 1 was traveling alone and did not read the current avalanche forecast. As such, he planned to avoid avalanche terrain (although he was wearing a beacon and carrying a probe and shovel). He would have avoided the avalanche hazard if he stuck to his plan. Things went awry when he deviated from his plan and made several turns into the top of the Mines 2 avalanche path. In an interview with the CAIC, Skier 1 said he "didn't have a stop-and-think moment soon enough." If he had seen the natural avalanche in the Mines 1 path, it may have prompted him to stop and stay on his planned route. Fortunately, Skier 1 survived and shared his experience with the CAIC to hopefully allow other people to avoid similar situations in the future.