2013/03/02 - Colorado - Nokhu Crags, Never Summer Mountains

Published 2013/04/23 by Ethan Greene & Brian Lazar - Forecaster, CAIC

A shallow snowpack in November and December of 2012 and cool temperatures formed a weak layer of depth hoar in the Never Summer Mountains. This layer was not continuous, but most prominent on north through east aspects and in the near-treeline elevation band. Steady snowfall and wind transport began in late January and extended into early March. This produced a series of wind slabs and small-grained layers of faceted snow in the mid and upper portions of the snowpack. This structure contributed to several notable human triggered avalanches in the Never Summer and Cameron Pass areas (see avalanche list in images section).

In early March, the snowpack near Cameron Pass was 100 to 150 cm deep, but some wind-loaded areas were over 2 meters deep. The upper meter of the snowpack had several buried persistent weak layers sandwiched between stiffer (1F to P) slabs 10 to 60 cm thick. There was a prominent melt-freeze crust/facet combination about 80cm deep. The bottom 40 cm of the snowpack consisted of well developed but rounding depth hoar.

A group of four skiers traveled west on Colorado SH 14 over Cameron Pass. They left the south side of the highway to travel into the Colorado State Park. This group divided into two groups, each with two skiers. One group had a dog (Group A) and traveled south, ascending the northern most ridgeline of the Nokhu Crags.

A second group (Group B) of two skiers, also left Colorado SH 14 and traveled south towards the Nokhu Crags. This group traveled along the same route as Group A. Both groups worked their way up the ridgeline to treeline. Group B stopped near the top of point marked 10880 ft, with the intention of skiing a north or northwest aspect. Group A was further ahead and continued ascending the ridgeline with the intention of skiing an east aspect, locally known as Paradise.

Group A moved up the ridgeline to a saddle in the ridgeline. They travelled along the ridge and then decided to ski a line that started at the base of the saddle and followed the trim line on the skier's left side of the slope. Skier 1 skied a line next to the sparse trees and stopped on the moraine at the bottom of the slope. Skier 2 descended a line approximately 10 yards to the skier's right of Skier 1's track. He made a few turns and then fell. The dog descended the slope and moved below Skier 2. Skier 2 stood up and began skiing a steep diagonal to the south (skier's right). The dog followed a similar trajectory to Skier 2, but was further down-slope. As Skier 2 moved downhill and to the south, the avalanche released. Both skiers and the dog were caught in the avalanche and swept downhill.

Group B witnessed Group A heading towards the saddle above Paradise. Upon gaining the ridge themselves, and slightly behind Group A, Group B noticed that a large avalanche had released on the east-facing side of the ridge.  They could see two ski tracks entering the fracture line. They did not see Skier 1, Skier 2, nor the dog they were traveling with on the slope or avalanche debris. They immediately called 911 (just after 1:00PM) with their cell phone. It took two calls from different positions to describe the situation to the 911 operator. Both skiers in Group B then descended an east-facing treed slope to the skier's left of the avalanche to initiate a companion rescue.

At the bottom of the slope they picked up a beacon signal and followed it to the burial location of Skier 2. They arrived at Skier 2 approximately 30 minutes after initiating their search at the ridgeline. After approximately 20 minutes of digging, they had partially extricated Skier 2 and cleared his head and shoulders of snow. They realized Skier 2 was deceased, and then turned their focus to locating Skier 1. They spent approximately an hour conducting a beacon and visual search for Skier 1 without success, and then left the scene and headed back towards to the trail-head to meet with emergency personnel.

The organized rescue was initiated by the Jackson County Sheriff's office minutes after receiving the 911 call. Jackson County Search and Rescue began their response at 1:15PM. Colorado State Parks staff was participating in a fund raising event for the local trail grooming program (Poker Run), which meant they had additional staff and sleds. The State Forest State Park office in Gould was notified at approximately 1:30PM, and immediately dispatched rescuers to the top of Cameron Pass with snowmobiles. Two State Parks officers departed from the pass on snowmobiles shortly before 2PM and ran into a group that had witnessed the accident from the Michigan Ditch and were exiting the field. This group confirmed that two people and a dog were caught in the avalanche.

The two State Parks officers continued along the Michigan Ditch road and after some tricky snowmobile riding, arrived at the scene of the accident at 2:35PM. They swept the area on snowmobiles and initiated a beacon search. They picked up two beacon signals, and after about 15 minutes followed a signal towards the buried skiers. They describe the beacon search as "tricky" (see Comments section). They saw Skier 2 partially excavated. The beacon signal lead them to Skier 1 and they saw the tips of his boots sticking out of the snow. They began to dig out Skier 1, believing he was also deceased given the time elapsed since the avalanche. They dug from the exposed boot tips towards the head, and when they got to Skier 1's waist they heard groaning from underneath the snowpack.  At this point they realized they had a live victim and required a full medical evacuation.

They radioed to the Incident Command asking for immediate medical response, and continued to dig out Skier 1. They extricated Skier 1 shortly before 4:00PM; he had been buried for almost 3 hours. Skier 1 was found on his back with an ice mask 3 to 4 inches above his face. Skier 1 was wearing an Avalung, which was deployed but was not in his mouth (most likely because he had completed his run and was at the bottom of the slope when the avalanche released). The second rescue group arrived at the scene shortly after Skier 1 had been extricated. Skier 1 was evacuated to the trail-head via snowmobile arriving around 6:00PM. From there he was flown by helicopter to emergency medical care.  Search teams reconvened the recovery of Skier 2 the following morning at 8am. Skier 2 was evacuated via snowmobile following the same exit route along the Michigan Ditch Road.

This was a large avalanche that broke into deep, hard, wind-deposited snow layers. As the southwest winds moved over the ridgeline and across the saddle, they cross-loaded the area and built a thick deposit of snow at the top of the snowpack. As a result the snow depth decreased from south to north and from top to bottom in the start zone. As the skiers descended the skier's left (north) side of the slope they traveled in a relatively shallow portion of the snow, which increased the chances of affecting the buried weak layer.

The debris in this avalanche ran well into the trees and caused significant vegetation damage. There were multiple spots where ski tourers might have collected to watch their group, which were overrun with large piles of debris. To avoid being caught, Skier 1 would have had to travel a significant distance from the bottom of the open slope, or found a high point in the terrain.

Both rescue groups reported difficulty in isolating the two different beacon signals. Although both victims were buried in the same portion of the debris, they were more than 10 meters apart (rough definition of close proximity for a multiple beacon search). The two victims were both wearing older, single-antenna beacons and the searchers were using newer, two and three antenna beacons. The difference in pulse rate of the two transmitting beacons may have contributed to the difficulty of the search.

The survival of Skier 1 after approximately a three hour burial is quite rare. A recent study examined the characteristics of avalanche accident survivals in Canada and Switzerland. The authors looked at 25 years of data from the two countries and found the chance of survival for complete burials over 36 minutes were 4% (101 cases with 4 survivals) in the Canadian accidents and 16% (461 cases with 75 survivals) in Swiss accidents. The longest burials, where the victim survived, in the Canada data set were 120 and 300 minutes. These were both in urban settings, which decreased the time from recovery to advanced medical care. The longest survival in a remote setting was 55 minutes. The rapid activation of organized rescue (call to 911 before leaving the ridgeline and beginning a companion rescue), a significant air pocket, treatment and transport by emergency personnel, and emergency room care all contributed to this amazing result.   

Reference: Haegeli et al., 2011: Comparison of avalanche survival patterns in Canada and Switzerland, Canadian Medical Association Journal, doi: 10.1503/cmaj.101435