CAIC

Avalanche Details

Location: Mt Arkansas, Fremont Pass
State: Colorado
Date: 2018/03/07
Time: 12:00 PM (Estimated)
Summary Description: 1 backcountry tourer caught, partially buried, and injured
Primary Activity: Backcountry Tourer
Primary Travel Mode: Ski
Location Setting: Backcountry

Number

Caught: 1
Partially Buried, Non-Critical: 1
Partially Buried, Critical: 0
Fully Buried: 0
Injured: 1
Killed: 0

Avalanche

Type: HS
Trigger: AF - Foot penetration
Trigger (subcode): u - An unintentional release
Size - Relative to Path: R2
Size - Destructive Force: D1.5
Sliding Surface: I - New/Old Interface

Site

Slope Aspect: NE
Site Elevation: 13689 ft
Slope Angle: 45 °
Slope Characteristic: Ridgeline,Cornice

Avalanche Comments

The avalanche occurred in a northeast-facing couloir above treeline. Skier 2 triggered the avalanche by stepping onto a cornice and initiating a cornice fall that broke 1 to 8 feet deep. Both the cornice and the person fell onto slope below, triggering the avalanche. It was a hard slab avalanche, small relative to the path, and small enough to be relatively harmless to a person without a terrain trap. It broke to ground in the start zone, entraining surface snow as it moved through the track (HS-AF-R2-D1.5-G). The avalanche broke approximately 40 feet across the slope, was approximately half a foot deep, and ran 1000 vertical feet.

Weather Summary

On the day of the accident the temperature at the Fremont Pass SNOTEL site (approximately 4 miles northwest of the accident site at 11,400 feet) was 6 degrees Fahrenheit (F) when the party left their vehicle, and rose to 24F by 11am. There was no new snow in last 24 hrs, and 1 inch of snow and 0.1 of snow water equivalent (SWE) recorded in the previous week.

At the Copper Mountain METAR site (approximately 9 miles north of the accident site at 12073 feet) from March 1 through March 4, the wind was from the south averaging 10 to 20 miles per hour (mph) with gusts in 40s. On March 5, winds shifted to the west with gusts to 50 mph. By the morning of March 7, winds had become light and variable.

Snowpack Summary

The 2017/2018 winter season began with early season snowfall and prolonged periods of clear and dry weather. This led to the development of large-grained facets and depth hoar near the ground on shady slopes throughout the Sawatch zone. Mid-winter storms built thick slabs over this weak base. Southwesterly winds during the month of February formed wind-drifts on top of this weak snowpack structure. The seasonal snowpack was 100% of the long-term record at the Fremont Pass SNOTEL site in early March.

Events Leading to the Avalanche

Skiers 1 and 2 were very familiar with this area and had been touring on the north ridge of Mount Arkansas, also known as Sleeping Indian, on March 6. They left car at 6 am on the morning of March 7 and traveled east under Indian Basin. They ascended Sleeping Indian to Mount Arkansas, traversing east along ridge to top of Moonshine Couloir, their potential ski objective.

Accident Summary

Upon arriving at Moonshine Couloir, Skiers 1 and 2 decided not to ski due to the sizable cornice and drifted snow load. They read the avalanche forecast that morning and verified this was an area to avoid. After their discussion, Skier 2 stepped off rock onto the cornice to look into the couloir.

The cornice broke under Skier 2's foot and he fell onto the slope below with several cornice pieces. The combination of the cornice fall and skier on the slope triggered an avalanche. The avalanche carried Skier 2 through the couloir and partially buried him with his head and one arm exposed about 1000 vertical feet below the ridge.

Rescue Summary

Skier 1 could see Skier 2 in the debris on the slope below him and called 911 for assistance (9:48am). After some time Skier 1 hiked down the south slopes of Mt Arkansas to a Lake County SAR team. The SAR team and a local guiding outfit helped Skier 1 return to his vehicle via snowmobile.

Skier 2 was unable to free himself from the debris due to injuries sustained in the fall. Approximately 2 hours after the avalanche a team from the Colorado Rapid Avalanche Deployment program (C-RAD) arrived by Flight for Life helicopter. They dug Skier 2 from the debris, provided medical care, and transported him to the Flight for Life helicopter (approximately 700 feet/ 0.25 miles below).