The storm cycle that began on January 5th ended on the 13th. It was followed by a high pressure ridge and a strong cold front that passed over the region on the morning of the 15th. Large avalanches occurred naturally and were artificially triggered as this storm cycle ended, in its wake and in association with the frontal passage. Some of these events ran full path.

On Friday the 11th avalanche activity occurred at the lower elevations. In the Hoback canyon a spontaneous released slide was reported near granite Creek. A small hard slab occurred on a steep hillside near Nelson Drive in Jackson. This event may have been triggered by an animal. At midday the Wyoming Department of Transportation used explosives to trigger a three foot deep hard slab on the milepost 151 slide path south of Jackson. This slab ran to the east lane of the highway.

On Saturday the 12th a skier triggered a hard slab to the ground on a steep (38 degrees) northeast aspect of Angle Mountain. On Cache Peak, in the Gros Ventre Range east of Jackson, two skiers were caught in a slide while ascending a steep (38 degrees) southwest facing slope. One person was carried thought the trees and severely injured.

Figure 14.1 Photograph of a slab avalanche that severely injured a backcountry skier at an elevation of about 9,000 feet on a southwest aspect of Cache Peak. The party’s skin track is visible to the left of the slide.

Also on the 12th three snowmobilers were tragically killed in a large avalanche in the North Fork of the Cottonwood Creek Drainage in the Salt River Range. The three victims were locals who were experienced riders intimately familiar with the terrain. These riders routinely stopped in an open meadow on their way up canyon after a technical section of the trail exited thick woods. This opening lies beneath the avalanche path that caught and buried these men. These riders had historically witnessed numerous avalanche events on this path none of which approached the place where they routinely stopped to pause and regroup. These men were reported to have never ventured up into this path on their trips through this canyon. This event was not witnessed; however it is speculated that the victims were in the runout zone when a massive full path avalanche likely caught them without warning.

Figure 14.2 Photograph of the avalanche event that killed three experienced local riders in the Cottonwood Creek Drainage of the Salt River Range on January 12, 2007. The crown of the avalanche is visible along the ridgeline and extends along the trees on the left side of the path and into two adjacent slide paths to the left. Two of the victims were uncovered near the point where this picture was taken. The third was uncovered near the snowmobiles on the right side of the picture. The powder blast removed the snow from the trees along the side of the path.

Figure 14.3 Photograph of the western toe of the debris from the Cottonwood Creek Drainage avalanche. This picture was taken in the direction of flow near the middle of the debris field. This avalanche released on a west facing slope. Two of the victims were uncovered near the people in this picture. The debris from this avalanche ran to the edge of the forest growth in all directions. Three natural avalanches were observed on the east face of Red Top Mountain in the background.

Figure 14.4 Photograph of the debris field looking north up valley perpendicular to the direction of flow. Several natural avalanche events on similar aspects were visible further up this drainage. None of the natural avalanche activity observed would have been easily seen by the victims until they entered this avalanche runout zone.

Figure 14.5 One of the natural avalanches observed across the drainage on an east facing aspect of Red Top Mountain.

This avalanche event was likely at least a 30 year event for this path. Prior to this eight day storm cycle a shallow early season snowpack existed. This cycle included strong winds and likely deposited about six feet of new snow on a weak base of faceted snow. The depth of the crown this avalanche appeared to be 3 to 4 feet deep for most of its length; however it is estimated to have been six to eight feet deep in one area.

In the wake of the storm a high pressure ridge formed. On Monday the 14th there was a strong thermal inversion with morning valley fog below mostly clear skies. On that morning the ski patrol at the Jackson Hole Mountain Resort used a large explosive charge to trigger a 12 foot deep hard slab on the North Ridge.

Figure 14.6 Ski Patroller Elaina Macauley stands next to the crown of a huge hard slab avalanche triggered with explosives in an un-skied area of the Jackson Hole Mountain Resort.

Figure 14.7 Large dry snow avalanche descends into Tensleep Bowl from the North Ridge of Rendezvous Mountain.

Figure 14.8 North Ridge avalanche continues towards a glacial moraine in Tensleep Bowl on Rendezvous Mountain.

On the same day a large hard slab avalanche was skier triggered south of the boundary of the Jackson Hole Mountain Resort. This deep hard slab was triggered by the third skier to cross the starting zone that hangs above some impressive cliff bands at the head of the Green River Drainage. The skier who triggered this slab was not caught and ended up on the bed surface in the starting zone.

Figure 14.9 Crown of deep hard slab avalanche that was skier triggered south of the Jackson Hole Mountain Resort on January 14th. The tracks of two professional skiers are visible on the left. They skied across this slope and through the cliff area beneath it before this slab was triggered by an ensuing skier and cleaned what snow there was for them to cross from the cliffs below. The track of the skier who triggered this slab is visible to the right (Photograph courtesy of David Stubbs).

Figure 14.10 The cliff areas below the starting of a skier triggered hard slab (Photograph courtesy of David Stubbs).

After the high pressure ridge moved east strong fast moving cold front passed over the area on Tuesday morning, January 15th. This weather system deposited several inches of new snow and was accompanied by high winds. Gusts to 86 miles per hour caused whiteout conditions and rapidly loaded avalanche starting zones. A natural avalanche running down the Cow of the Woods avalanche path in Hoback Canyon impacted the highway on Tuesday.

When skies cleared on the morning of the 16th more large natural avalanches were observed to have occurred in the Southern Teton Range. A slab avalanche with a crown estimated to be 10 feet deep spontaneously released on a southeast aspect at an elevation of about 10,000 feet on a convex slope between Indian and Coyote Lake Cirques. A five foot slab also released spontaneously from Mt. Hunt. Several large avalanches were observed north of Ski Lake.

Figure 14.11 Hard slab avalanche triggered by a snowboarder on the “Taco Bell” slide path above the Town of Jackson on the night of January 15th. (Photograph courtesy of jhunderground.com).