CAIC: Colorado Avalanche Information Center

2010/03/13 - Idaho - North of Schweitzer Ski Area, Idaho Panhandle

Published 2010/10/29 by Ken Davis - Idaho Panhandle Avalanche Center

Avalanche Details

  • Location: North of Schweitzer Ski Area, Idaho Panhandle
  • State: Idaho
  • Date: 2010/03/13
  • Time: Unknown
  • Summary Description: 1 snowmobiler caught, buried, and killed
  • Primary Activity: Snowmobiler
  • Primary Travel Mode: --
  • Location Setting: Backcountry

Number

  • Caught: 1
  • Partially Buried, Non-Critical: 0
  • Partially Buried, Critical: 0
  • Fully Buried: 1
  • Injured: 0
  • Killed: 1

Avalanche

  • Type: --
  • Trigger: AM - Snowmobile
  • Trigger (subcode): u - An unintentional release
  • Size - Relative to Path: R3
  • Size - Destructive Force: D3
  • Sliding Surface: O - Within Old Snow

Site

  • Slope Aspect: --
  • Site Elevation: --
  • Slope Angle: 35 °
  • Slope Characteristic: --

Avalanche Comments

One snowmobiler was caught and killed in an avalanche that occurred on Saturday, March 13th, 2010, in the Selkirk Mountains eleven miles north of the Schweitzer Ski area. The avalanche accident occurred on a north east facing slope below a ridge at about 6,200 feet elevation. The slope had been windloaded by two storm events that brought moderate snowfall and strong south/southwest winds the previous two days. The fatality occurred on the north flank of the avalanche where the victim was overrun by the avalanche and carried into a slight gully feature and the debris converged and deepened. It is apparent that the avalanche was triggered by the action of the snowmobiler.

Weather Summary

The weather during the week prior to the accident had been mild with nighttime mountain temperatures in the 20s and daytime temperatures slightly above the freezing level on north aspects but quite warm on southerly aspects. The mild conditions were due to a high-pressure system that prevailed influencing a strong melt-freeze cycle on southerly aspects. The persistent high pressure was also influencing the formation of surface hoar. The surface hoar was forming on top of the melt-freeze crust and lingering on northerly and easterly aspects. Direct sun was melting the surface hoar on south and west slopes. By mid-week, on March 11th, the weather had become unsettled with the first of two spring-like squalls predicted to move through the forecast area. The SNOTEL site at Hidden Lake reported 1.3 inches of snow water equivalent accumulation on the 24 hour period from 1500 on the 11th to 1500 on the 12th. Winds were strong out of the south/southwest depositing snow on a relatively undisturbed layer of surface hoar on north and east aspects. On the 24 hour period from 1500 on the 12th to the 13th the Hidden Lake SNOTEL site measured an additional .60 inches of snow water equivalent. Storm snow totals for the Selkirk Mountains were 10-12 inches of new snow with several feet of new snow possible in loading zones on lee aspects. By the 13th the second storm front had passed and only isolated squalls persisted for much of the day with patchy sun over the highest peaks in the Selkirk Mountains.

Snowpack Summary

The avalanche released on a layer of surface hoar above an ice crust. The surface hoar formed during the high pressure of the previous week and was buried by a March 8th storm system that dropping 1-2 inches of snow in the southern portions of the Selkirk Mountains. This was enough snow to bury surface hoar intact and preserve a very weak layering structure. Light snowfall continued on the 9th and the 10th high pressure returned to the region with clear skies, warm daytime temperatures and freezing conditions at night. This weather pattern influenced another layer of surface hoar above a breakable crust. This layering made up the upper 1 foot of the snowpack structure when the March 11th storm system affected the Selkirk Mountain weather. Storm snow layering that existed on March 13th was a denser layer of wind deposited new snow averaging 2.5 feet in depth on lee aspects below ridgetops.

Events Leading to the Avalanche

The 32 year old victim, from Newport, Washington, was snowmobiling with one other person and left from the Priest Lake side bound for the Selkirk Crest, a prominent north-south trending high elevation ridge. At about 1:00PM they reached the top of the crest at about 6,400 feet. The Newport man then decided to descend the slope. A witness, also at the top of the crest had decided not to descend the slope and watched as, seconds later, the Newport man headed down off the ridgetop. The resulting avalanche overtook the rider after he had descended about 10 percent of the slope. He was swept down the slope about 300 feet, was carried through a slight gully, and buried at the toe of the fan below the gully. The victim was buried about 4 feet deep in an upright position. Slope angles of the track and starting zones averaged 35 degrees with the steepest part of the slope being a slightly convex ridge with slope angles possibly exceeding 45 degrees. The width of the affected area was approximately 600 feet and the maximum runout distance was 500 vertical feet. The classification of this avalanche is SS-AM-R3-D3 (US classification system). The Canadian classification of this avalanche is a size class 3, meaning the slide could have buried a car or destroyed a small building.

Rescue Summary

Second party witnesses to the accident responded quickly. They used an alternate route to descend to the place where the victim was buried. The victim was wearing an avalanche transceiver and they were able to locate him in 20 minutes. Within minutes of digging they had the man’s head and shoulders cleared of snow and began CPR. They continued to excavate snow so they could perform chest compressions but the victim could not be revived. Weather and avalanche conditions were too severe to safely transport the victim so the recovery effort was suspended until the next day. Priest Lake Search & Rescue returned early on Sunday morning and the victim was transported via helicopter out of the basin.