Accident: Hidden Canyon 12/13/2007

Observer Name:

Drew Hardesty

Observation Date:

12/14/2007

Occurrence Date:

12/13/2007

Occurrence Time:

Unknown

Region:

Hidden Canyon
Big Cottonwood Canyon
Salt Lake

Location

40° 35' 40.0848" N, 111° 33' 43.1964" W

Avalanche Characteristics

Elevation:

10200'

Aspect:

Northwest

Slope Angle:

Trigger:

Snowboarder

Trigger: additional info:

Unintentionally Triggered

Avalanche Type:

Hard Slab

Weak Layer:

Facets

Depth (avg):

18"

Depth Range:

12" to

Width:

100'

Vertical:

700'

People Involved

Caught:

Carried:

Partly Buried:

Injured:

Accident & Rescue Info

Accident & Rescue Summary:

Six snowboarders, all men in their mid-twenties, entered the Hidden Canyon side-country looking for fresh powder. After a quick scout, the first snowboarder center-punched a steep chute without incident, and, per good protocol, got out of the way at the bottom. The next snowboarder made two turns before triggering the hard slab that propagated 30’ above him, engulfing him and one of companions above. Both men rode the wave 700’ down the chute, with the second man sustaining an orbital fracture, a hairline jaw fracture and numerous facial lacerations and abrasions. Neither was deeply buried and the entire party was able to walk back out to the road.

Terrain Summary:

Hidden Canyon is a common destination for those seeking fresh tracks in an out of bounds environment. It is littered with steep chutes, cliffbands, and dense trees, but often holds good riding conditions with a relatively easy access back to the lifts at Brighton. It would be rated as Complex terrain that takes into account overall steepness, runout zones, number of terrain traps, forest density, and slope shape, among other factors.

Weather & Avalanche History:

Avalanche Data:

The avalanche measured 1-2’ deep and about 100’ wide, running 700’ vertically into the flats below. It would be classified as a HS-AR-R2D2-O, a hard slab avalanche artificially triggered by a snowboarder. It was large and dangerous enough to bury a person, with debris piling up 6’ deep in the runout zone. ‘0’ refers to the failure plane, as this avalanche in particular, similar to so many triggered within the recent couple of weeks, failed in an old snow layer – 2-3mm faceted grains. The slope angle was 39-41 degrees with a runout angle of 35 degrees.

Weather History:

Brighton, in the upper reaches of Big Cottonwood canyon, received 47’’ in a storm that lasted from December 7^th through the 8th. This snow came in on top of some very weak faceted snow from the early season storms in October. Winds had been generally light with a few hours of easterly winds earlier in the week producing some wind damage and loading along the higher elevations. Temperatures had remained cold since the storms with an overnight low of -2F the morning of the accident.

Snowpack and Avalanche History:

These two snowboarders were the sixth and seventh people caught and carried in backcountry avalanches this season, all of whom were surprised by slabs sitting on very weak faceted snow. In this case, it was the second person in the chute who found a thinner, more ‘tender’ spot to trigger the hard slab, and is a stern reminder that, with this structure, other tracks on the slope mean nothing for stability. Of interest was the timing of the incident, as another snowboarder found trouble in a similar style on the other side of Brighton off the Pioneer Ridge. He also sustained facial trauma, but did not require a hospital visit like our unlucky victim in Hidden Canyon.

The incident occurred only four days after the Utah Avalanche Center had issued a weekend-long ‘Avalanche Watch’, with a Considerable to High danger forecasted for steep mid and upper elevation northwest through northeast facing slopes. On the day of the incident, the danger was rated as Moderate, but the forecaster warned that dangerous avalanches could still be triggered in this type of terrain.

Snow Profile

General Comments

The Human Factor:

The group of six fit a certain profile: highly athletic, young, aggressive riders with boarding skills that far outweigh their avalanche skills. Only one had taken any sort of avalanche class, and none were wearing or carrying any rescue gear. Interviews with most of them led me to conclude that none of them had called the avalanche hotline or looked at the Utah Avalanche Center’s website that day. One had a brother who had suffered massive injuries and been life-flighted from the Snowbasin backcountry from an avalanche incident a couple years before.

Epilogue:

I went in to do the investigation with the help of some Brighton ski patrollers, who promptly had the access gate into the area closed to skier traffic until we were out ‘down and clear’. Not more than a couple hours after we were gone, two other large avalanches were triggered in the area that completely engulfed the terrain in which we’d been.

CLICK HERE FOR PHOTOS

Javascript is required to view this map.