Avalanche Accident Report         
Forest Service Utah Avalanche Center

Wednesday, December 24, 2008

Logan Peak – Two snowmobilers caught, carried, killed.

Preliminary Accident Report by Toby Weed (more to follow soon)

Location:

The avalanche occurred near the summit of the east face of Logan Peak at the head of Providence Canyon in an area known by local snowmobilers as the “Rodeo Grounds.” The land is managed by the U.S.D.A. Forest Service, specifically by the Logan Ranger District of the Uinta-Wasatch-Cache National Forest. The area is generally accessed in the winter with snowmobiles via a fairly steep assent of Providence Canyon above the town of Providence Utah. It took me a bit less than a half hour to reach the site of the avalanche on a snowmobile from the bottom of Providence Canyon.

Accident and Rescue Summary:

Four experienced local snowmobilers were riding in the “Rodeo Grounds” area on Christmas Eve morning, the first clear day after several consecutive days under stormy weather conditions. The party triggered a huge hard slab avalanche, which buried and killed two close friends, 22-year-old Erik Jorgensen of Paradise and 23-year-old Jesse Johnson of Hyrum.

The avalanche was reported to authorities at around 10:30 am via satellite phone by a member of a separate snowmobiling party. About twenty snowmobilers, who were riding in the area, helped the surviving members of the party with the rescue attempt. From what I could piece together at the scene, one of the victims was very deeply buried in the heavy debris (10-12’ deep). The other was recovered in the vicinity of a grove of large spruce and fir trees. Survival of such a deep burial in avalanche deposition is extremely rare, and trauma due to impacting trees while carried by an avalanche accounts for around 25% of avalanche deaths in North America.

The victims were recovered with the aid of avalanche transceivers, which each wore, and probes and shovels. After previous avalanche incidents in the area, extra probes and shovels are cached at a nearby warming hut by Cache Search and Rescue (Cache County Sheriff) and local snowmobilers…. Members of CSAR and the flight crew of the responding Life Flight medical rescue helicopter were unable to resuscitate the two young men.

(click HERE for an overview of the accident site with photos)

Terrain Summary:

The east face of Logan Peak, known by locals as the “South Rodeo Grounds,” is wide open alpine terrain. The steep, treeless face is divided by several prominent drainage gullies, all encompassed by this massive hard slab avalanche. The broad slope faces predominately east, with southeast through northeast exposures. The slope is certainly affected by its proximity to a wind-funneling saddle between Logan and Providence Peaks and is prone to extensive loading of wind deposited snow by south and west winds. Light density snow accumulates on lower angled southern and western slopes and is rapidly transported by common strong prevailing and pre-frontal winds into the easterly facing fetch areas of the massif.

At the far southern flank of the avalanche, I measured slope angles at the crown ranging from <30 degrees to ~41 degrees. Slope angles vary drastically across the wide slope, and the classic hard slab included fairly low angled terrain at its top (near the summit of the 9600’ Logan Peak). The slope rolls off into the 38-41 degree range in the upper mid-slope. The open run-out zone quickly flattens at the bottom of the steep face at around 9000’ in elevation, and previous avalanches have cleared a narrowing swath into the gently sloped spruce/fir forest below.

Avalanche Data: 

I am classifying the avalanche as a HS-AM-D3-R5-O/G. In plain English this means; a hard slab avalanche triggered by a snowmobiler with a destructive force rating of 3 (on a five-point scale) and a size relative to the path rating of 5. (The avalanche included 100% of the path’s width and ran full length, damaging mature trees in its descent.) The slab failure occurred in old faceted or sugary November snow, and the avalanche pulled most of the snow in the bowl down with it, leaving only small bushes and exposed rock still on the steep slope.

(Click HERE for a snowpit diagram)

Weather and Avalanche History: 

Snow began falling on upper elevation slopes in the region in early November, and significant rainfall with unseasonably warm temperatures built a widespread and very strong ice-crust on the snow surface on November 12^th and 13^th. This remained on the snow surface through the remainder of November. With a shallow snowpack, a sizable temperature gradient caused significant water vapor sublimation, and a very weak faceted or sugary layer developed below the crust. Small amounts of snow interspersed with graupel fell on Thanksgiving and in the first week of December, covering the solid and relatively warm crust with a thin airy layer of fresh snow. This was exposed to the temperature gradient/sublimation/faceting process while near the snow surface and would become a weak lubricating layer on top of the crust made up of small sugary crystals.

Regular and substantial snowfall began in mid-December and several feet of snow quickly built up above the crust…The regularly occurring storms were generally heralded in with strong southerly prefrontal winds, which drifted tons light density snow from the tail end of previous events into lee slope fetch areas like the east face of Logan Peak. With a potential bed surface and a couple weak layers already in place, a stout slab was building in these areas, with stiff, wind-deposited snow.

Large natural and human triggered avalanches were a common occurrence in the mountains of Northern Utah in the week prior to the avalanche on Logan Peak. Of particular interest was the occurrence of triggered deep slab avalanches in the Ogden Area Mountains, the first of these occurred and was reported the weekend before Christmas. At the time of the accident, no large avalanches had yet been reported or observed in the Logan Area, but I was certainly concerned about the building slab. I wrote in my avalanche advisory on the day before Christmas Eve (that),

It's only a matter of time (and weight) before we start seeing dangerous and large avalanches breaking into old snow in some areas.....Buried weak layers are present and a slab is building up on top of them.  It's difficult to tell exactly when a slope will reach the critical balance that will allow you to trigger it, but odds are, it'll be a storm like today's that does the trick.

(Seasonal Weather Charts)

 In addition, an avalanche watch was in effect, issued by our office through the National Weather Service.