Detailed Accident Report

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Date: 2010-03-27
Submitted By: West Central Montana Avalanche Center
Place: Missoula Lake 10 miles SW of Superior, MT
State: MT
Country: USA
Fatalities: 1
Summary: 1 snowmobiler caught, buried, and killed



View full report online with photos:


On Saturday March 27, 29 year old Timothy James Grieser (TJ) from St Maries, Idaho died in an avalanche accident near Missoula Lake on the Superior Ranger District of the Lolo National Forest. This area is on the MT/ID border 10 air miles SW from Superior, MT. TJ was descending a steep NW facing slope at the end of a day of riding when the slab released. TJ was caught and carried an estimated 800-900 feet, was strained through trees and completely buried (about 4 feet deep) in a terrain trap. His partners were in a safe location, witnessed the avalanche and quickly located their friend with transceivers and dug him up. He was breathing when dug up but died from his injuries shortly thereafter. First responders and the acting coroner arrived on scene at 2134.


A group of six spent the day riding in the Missoula Lake/Oregon Peak area near the MT/ID border in the Northern Bitterroot Mountains. They are very familiar with the area having made several trips to the site earlier this winter. Late in the afternoon, TJ's father and uncle decided to return to the vehicles (about 10 miles down the Cedar Creek road) while the remaining members of the group decided to get another ride to the summit. Some of the group, including TJ, had made 3 to 5 runs to the ridge that overlooks and separates Oregon Lake from the Missoula Lake and Oregon Lake basins. One of the 4 group members who remained on site parked to the side in a safe area to watch the others climb and descend one at a time. This was to be the last climb and descent of the day. The 3 who made the ridge proceeded down the slope one at a time to the safe area. TJ was the last of the group to descend. The slab released when he was approximately 200 feet below the ridge line. TJ tried to power out of or outrun the slide as his friends reported hearing the sled “power up” and heard him yelling.


Having witnessed the slab release, the remaining 3 quickly moved to the debris field, located TJ with their transceivers and dug him out within approximately 5 minutes. He was breathing but seriously injured. One of the witnesses tried to contact 911 via cell phone, was unable to attain service but noted the time at 17:50 hrs. One of the group departed the area immediately to initiate EMS response which occurred at approximately 19:50 hrs when TJ's uncle reached the closest residence to the site in Cedar Creek. The accident site is approximately 22 road miles up the Cedar Creek drainage from Superior, MT. Mineral County Sheriff's Office responded with an ambulance and units from the Mineral County Search and Rescue organization. The staging area for the ambulance is approximately 10 miles from the accident site. First responders as well as the acting coroner reached the accident site at 2134 hrs at which time Mineral County S&R units advised Mineral County Hospital Emergency Department staff that this was no longer a rescue mission. All rescue units and remaining group members were off the mountain at 0009 hrs on 03/28/2010.


A Forest Service LEO and a Superior Ranger District avalanche specialist visited the site the next day (3/28/10) to document the accident. Time and weather constraints prevented a more comprehensive site review to take measurements and a crown profile however a pit was dug on one of the flanks close to the burial site and is representative of conditions seen in the general area for the past several weeks.

The coordinates for the accident: 47 03' 19.95"N, 115 06' 36.43"W

This was a wet slab avalanche that released on a bed surface of surface hoar and small grained facets that formed during cold clear weather at the end of January. The avalanche was on a 6200' NW aspect and was triggered late in the day. Average slope steepness is 35 degrees. The slope had direct sun on it for a few hours and temperatures were above freezing for several hours prior to the incident.

The crown was estimated to be about 2 - 2.5 feet deep and 300-400 feet across. Distance from the crown to the toe of the debris field is approximately 1300 feet and drop of approximately 500 vertical feet.

The classification for this avalanche is: WS-AM-R3-D3-O.

The avalanche advisory posted by the West Central Montana Avalanche Center (WCMAC) on 3/26 gave a moderate rating for all slopes above 6000 feet with the danger rising to considerable during periods of warming or rain. The advisory also continued mentioning the buried surface hoar layer that has been troublesome since Presidents Day weekend.


The snowpack for the area is less than 50% of normal for the end of March.

The closest SNOTEL site is Hoodoo Basin SNOTEL at 6050 feet, Latitude 46.98; Longitude -115.03, approximately 6.8 air miles southeast of the accident site.

Hoodoo SNOTEL temperatures for the week prior to the avalanche were above seasonal norms and the area had been through several melt-freeze cycles. Daytime highs were in the high 30's and mid 40's for the 10 consecutive days prior to the 27th. The temperature reached 41 degrees on 3/27/10.

During the last week of January, cold clear nights allowed large surface hoar crystals to form over a widespread area of western Montana which was later buried 4-6 inches deep in a minor storm that passed through the area the first few days of February. This surface hoar formed during a period when we were also seeing steep temperature gradients that allowed near surface facet growth in the top few centimeters of the snowpack. This combination layer of facets persisted for a much longer period than we typically see during the more moderate temperatures of February and March. Slopes on the north half of the compass stayed cold while warmer sunny days strengthened this layer on the more sun exposed aspects.

WCMAC started receiving reports of human triggered avalanches during the Presidents day weekend February 13-15. These reports (all of which involved the faceted layer 12-18 inches deep) continued intermittently up to the end of March when a large Pacific storm dropped 3.7 inches of snow water equivalent or about 30 inches of heavy wet snow on the Hoodoo Pass area and lessor amounts in other Bitterroot mountain locations. On March 31, we received a report of a large human triggered avalanche near Hoodoo Pass on a northeast aspect at 6500 feet. This slab also failed on the deeply buried facets.


Assessing stability of a buried surface hoar layer(s) can be one of the more difficult decisions backcountry users, as well as professional avalanche forecasters, face when making a snow stability evaluation. They can be difficult to see in a snow pit and can persist for weeks and months after they are buried. Sometimes stability tests can give a false sense of security if other factors are not taken into consideration such as ability of a slab to propagate over distance, the quality of the failure plane, terrain features, etc.

That has certainly been the case this year in western Montana. Under normal late season conditions we can safely assume that in the warmer afternoons when the southern aspects warm up, we can find safer snowpack conditions on the more shaded and cooler north facing aspects. Not so this year. The cooler temperatures found on the northerly aspects help preserve and in some cases may even further weaken an already persistent weak layer.

We have endured a winter of thin snow that started out with very weak basal layers that gradually strengthened to where we re-focused our attention to a layer of buried near surface facets and surface hoar that formed the last week of January. This layer became problematic over the entire forecast area by mid-February. It is early April and we are still hearing about avalanches involving this layer.

Additional snow information from earlier this winter can be viewed at the following sites:

January 31 snowpack video:

March 4 snowpack video near Missoula Lake area:

Photo of surface hoar taken January 28:

Steve Karkanen

Avalanche Specialist / Director

West Central Montana Avalanche Center