Accident: Mt Aire 2/5/2011

Observer Name:

Hardesty and Hosford

Observation Date:

02/07/2011

Occurrence Date:

02/05/2011

Occurrence Time:

Unknown

Region:

Mt Aire
Parleys Canyon
Salt Lake

Location Name:

Mt. Aire

Location

40° 43' 27.1272" N, 111° 41' 38.4252" W

Avalanche Characteristics

Elevation:

8400'

Aspect:

North

Northeast

Trigger:

Skier

Trigger: additional info:

Unintentionally Triggered

Avalanche Type:

Hard Slab

Weak Layer:

Facets Above Crust

Depth (avg):

10"

Depth Range:

8" to

12"

Width:

90'

Vertical:

800'

People Involved

Caught:

Carried:

Partly Buried:

Injured:

Accident & Rescue Info

Accident & Rescue Summary:

A party of two very familiar with the terrain were skinning up through the trees in the bowl. They were spread out following safe travel protocol. Climber's left had only weak snow, no slab. As the first skinner moved up and right to gain the ridge, he collapsed the newly formed wind slab (in the lee of the north/northwest ridge) above the faceted grains and it pulled out 10' above him.

Never caught how far he was carried, but he relayed that he was wrapped around a tree, lost a ski and suffered two broken ribs and a fractured tibial plateau. The two were able to self-evac with significant self-reliance and suffering.

By the individual caught, carried and injured -

"A bit of a rough ride after triggering a slide on the up track nearing the top of Mt Aire. Thankfully aside from some injuries all is well. The failure occurred on the new snow/old snow interface with wind loading being the culprit of the new snow. Even though the majority of the loading was happening on the south facing slopes enough had loaded to from a 6" slab that broke free about 10 feet above me. The fracture followed the ridge down for an undetermined distance. Just goes to show to that even some loading with no new snow can get things moving especially on solid crust. Thanks UAC for keeping us all informed."

Terrain Summary:

Mt. Aire has numerous slide paths on nearly every aspect. Many of them funnel into gullies and into aspens, willows, or alders. The starting zone slope angle was not measured, but was not unusual or necessarily significant. The north/northwest ridge clearly had allowed a hard slab to form just in it's lee. See photo below. One can make out part of the wind - lip and perhaps part of the crown up near the summit.

Terrain Photos:

Weather & Avalanche History:

Mt. Aire has the weakest, faceted snow I've seen from Ogden to Provo. It's mostly faceted grains with a few thin decomposing crusts thrown in. Weak snow, no load. The wind-loading provided the load. Of note, debris from other natural wind-instigated avalanches was seen in many of the tracks and runouts of other slidepaths. Alta's Mt. Baldy winds averaged 50 with gusts to 70 from the northwest for much of the morning and day.

General Comments

Photo below is what we found high along the ridgeline on a test slope while accessing the accident site. New wind slab over the gray facets. Video below also describes the snowpack structure on Mt. Aire.

Video 1:

General Comments 2

Hard slabs were forecasted due to the strong winds. They destroy the arms of the snowflakes and pack them tight into a hard slab. Soft slabs you ski or ridge through, hard slabs you stay above, as with the pic below.

General Comments 3

The crown was 8-12" in depth, but continued propagating 400' down the ridgeline. I found the ski with the skin still attached perhaps 500' down the slope. Hard slabs have the propensity to pull out above you when you've perhaps collapsed a thinner part of the slab onto the failure plane below. This seems to have been the case as the two were skinning up the slope and moving into the thinner part of the 'lens' of hard slab. Heading up and into the slab, having it break above you, and skinning doesn't give you much of a chance to escape. Fortunately, the two were spread out enough so that only one was caught.

General Comments 4

Looking down the slide path.

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