South Arapaho Peak, Colorado
December 18, 1999
2 hikers caught, 1 partly buried and 1 presumed buried and killed

Accident Summary
A 23-year-old CU student likely died in a small avalanche Saturday afternoon northwest of Eldora in the Front Range of Colorado. Eldora is a small mountain hamlet just west of Nederland. The victim and a friend were descending from South Arapaho Peak in worsening weather when they decided to take a short cut. Well above tree line the two men headed south planning to rejoin the trail just below tree line. This short cut would save at least several miles of effort, but sadly it cost one life.

The pair walked into a shallow depression that narrowed and steepend just above tree line. The snow-filled gully looked to provide a easy and quick descent to the trail below. The rocky and grassy slopes to the sides of the gully were much steeper. The pair were walking down just as a cold front swept into the area bringing an abrupt and nasty change to the weather.
At about 1500 hours the two were separated by about 15 feet when they triggered a small slab avalanche. The survivor was on the edge of the slide and was carried only about 30 feet. When he turned around his friend was gone. The survivor searched the avalanche for about 90 minutes without success before heading out to get help. The survivor was sure his friend had not been caught, but where could he have gone.
 

Rescue
In deteriorating weather members of the Rocky Mountain Rescue Group, Boulder Sheriff's Department, and Boulder Water Department started the search effort. By the time rescuers got into the field almost a half-a-foot of new snow had fallen. Moderate snow continued to fall during the evening, and one search team triggered a slab avalanche trying to find the original avalanche. Due to dangerous avalanche conditions, moderate snow and strong winds the search was halted for the night. By midnight 12 inches of snow had fallen in the search area.

The next morning (Sunday) rescuers found signs of the survivor's tracks near the trail The snow-filled tracks lead searchers to the avalanche. At the same time other searchers continued to search cabins, trails and the valley floor with hope the missing man might be some where other than in the avalanche.

At and just above tree line searchers found the avalanche debris spread out in a fan shape. Fortunately the strong winds kept the debris clear of new snows. Unfortunately the same winds reloaded the starting zone with several feet of snow.
Searchers found no other tracks leaving the avalanche and no sign the missing man traveled along either side of the slide. A hasty search of the debris with probing of likely burial areas and search dogs found no one. There is a reasonable chance the victim was buried in the gully, but high avalanche danger precluded any searching of the gully. Worsening weather and visibility chased searchers off the slide late Sunday afternoon.

During the week searchers continued the search both of the debris and surround areas with out success. But because of bad weather and high avalanche danger searchers were not able to search the gully. Sunny skies finally returned on Thursday, and members of the Breckenridge Ski Patrol used explosives to trigger the newly drifted snow in the gully. A large probe effort along with several avalanche dogs failed to find the man.

Additional searching after Christmas has failed to find the missing man. On Wednesday (12/29) searchers were able to track the victim's footprints into the avalanche. Additional searching is planned.
 

Avalanche Data
The avalanche that likely still hides the missing man was a combination soft and hard slab that ran 500 vertical feet. It released from a south-facing gully loaded by West and Northwest winds. On the second day of the search a quick fracture line profile was conducted on the far east edge of the fracture line. This was only visible part of the fracture line and the only part of the starting zone that could be accessed safely. The rest of the fracture line was drifted over. At the fracture line the slope angle was 36 degrees, but gully did steepen further down slope. The fracture line depth ranged from 6 inches to just over 1-foot deep and was about 70 feet across. The slab formed from light snows that fell during the previous week. The weak layer was a soft 2-3 inch layer of small faceted sugar-snow grains. This layer likely formed after the light snows that fell at Thanksgiving.
It may seem odd that this thin slab could produce enough snow to bury someone, but it did. The volume added up when the entire gully for 250 vertical feet released. The debris then spread out fan-shaped below the gully over rough and irregular terrain. Significant portions of the debris were less then 1-foot deep, but in many areas the debris piled up 4 and 5 feet deep over logs, willows and boulders. In the gully snow in spots was up to 10 feet deep.
 

Comments
Two points need to be addressed. First, why the victim has not been found, and second, an opinion about the men's "short cut." It is not uncommon for searchers to miss victims of early season avalanches. This lack of success is generally due to bad luck and not from a lack of effort. The Boulder County Sheriff's Department and the Rocky Mountain Rescue Group (assisted by numerous other groups and agencies) have done good job coordinating and managing the search. Unfortunately trying to find a buried person in an avalanche with probe poles is somewhat like using knitting needles to find a lost needle in a haystack. The probe pattern (70 cm X 75 cm) used by searchers worldwide on average only gives a 70% chance of detecting the victim, if the probe search is textbook perfect. If the victim is on his side the probability of detection can drop to 15%, or even less. Unlucky probing along with bad weather and tricky ground cover also worked against the searchers.

In the first few days of the search high winds, snow, blowing snow, and temperatures in the single digits limited any quality searching. It is in the early part of the search that dogs are most effective, and clues (e.g., equipment, clothing, and tracks) are usually found. The strong winds disperse the scent too quickly for the dogs to pinpoint while at the same time drift snow over any and all clues. Along with nature not cooperating with searchers early in the search, the ground cover also made the search even more difficult.

The avalanche swept the first layer of snow over very rough ground that is littered with rocks, willows, downed trees and krummholz (scrub-like tree islands). It is likely the victim was pushed beneath a rock, log or dense brush and remained hidden from the searchers' probes. Also, a bit discouraging has been the lack of scent for the search dogs.

Trained avalanche dogs are the searchers' best tool when the victim is not equipped with an avalanche transceiver or a RECCO tab. Dogs can usually find buried victims, but not always. At this avalanche dogs have shown some interest in a few spots, but follow-up probing and digging failed to locate the man.

For many people and probably even to these two men the general lack of snow means no avalanche dangers. Ironically, these dry winters may be the most dangerous in terms of avalanches to the unsuspecting mountain traveler. What little snow has fallen turns to weak, faceted sugar-snow. Above tree line this fragile snow layer is topped by wind slab. When weak layer and slab are combined onto a steep slope the missing ingredient for an avalanche is the trigger.

There was very little snow on the ground when the two men hiked up South Arapaho Peak. They did not have nor need snowshoes. Their decision to take a short cut was reasonable given the nasty change in the weather that was bearing down upon them. To untrained avalanche eyes the gully provided a quick and logical route to evade the charging storm. The adjacent rocky slopes were even steeper and far more challenging than a quick slide down the gully. This gully posed no challenge to the missing man. His family described him as a very good alpine skier, and any good skier would have been right at home in this gully.

Unfortunately, these men lacked avalanche awareness training, and such training might have made a difference. They might have chosen the rocky slopes adjacent to the gully had they known a few key clues to avalanche danger. The unsuspecting pair were the trigger: the final ingredient necessary for a slab avalanche. The other three ingredients were plainly there: steep slope, weak layer and slab. In general terms steep snow-filled gullies in dry winter conditions should not be trusted.

Dale Atkins
12/30/99
 
 
 

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