Updated Information of Avalanche Incident in Depuy Creek (formerly reported as McGinnis Creek) – 2/22/2014
Initially reported in McGinnis Creek, but avalanche technically occurred in nearby Depuy Creek and will be referred to as Depuy Creek avalanche hereafter.
Avalanche Incident Report
Depuy Creek, Whitefish Range, MT
Date of Avalanche: 22 February 2014
Date of Investigation: 23 February 2014
On Saturday, February 22, 2014, a snowmobiler triggered an avalanche on a northeast facing (aspect 65 degrees) slope in the Depuy Creek drainage in the southern Whitefish Range. We investigated the avalanche on February 23, 2014. The avalanche failed on a layer of weak, faceted snow sitting on top of a hard, melt-freeze crust about 95 cm (37 in.) from the surface. It was approximately 130 m (425 feet) wide, ran 166 m vertical (546 vertical feet) (from approximately 5556 feet to 5010 feet), and 362 m linear (1187 linear feet). Avalanche debris was approximately 2.75 m (9 feet) deep in a confined gully above an old logging road.
The alpha angle (toe of debris to the crown of the avalanche) was 31 degrees. The average slope angle at the crown was 37 degrees with a maximum slope angle of 41 degrees.
We received detailed information from the individual involved. One person was mostly buried with only his airbag visible to his companions, another individual remained on their sled and was only slightly buried.
The avalanche was classified: SS-AMu-D2.5-R4-I (This translates to a soft slab (SS) avalanche triggered unintentionally by a snowmobiler (AMu). The avalanche rates 2.5 out of 5 on the destructive scale (D2.5) which means it is on the high end of D2 on the scale and could bury, injure, or kill a person. It was large relative to the path (R4), and failed at the interface between the new and old snow (I).
WEATHER AND SNOWPACK
Weather data is from the Whitefish Mountain Resort Ski Patrol Weather Log at the summit of Big Mountain in the southern Whitefish Range which is located about 12.9 km (8 miles) southwest of the the incident site. The closest SNOTEL site is Flattop Mountain in Glacier National Park about 38 km (24 miles) to the northeast. This site showed the average snow water equivalent to be 112% of median, and the precipitation to be 101% of average.
Beginning February 1, 2014, an arctic air mass parked itself over the region until around February 10, 2014. Prior to this a melt-freeze crust formed on sunny aspects throughout the advisory area. Small accumulations of snow occurred periodically and fell on this crust. During the cold air outbreak, the surface and near surface snow became weak and faceted causing weak layers to form on top of the melt freeze crust. The next notable precipitation commenced the afternoon of February 10, 2014 and snow accumulated incrementally through February 22, 2014 (date of incident) (Figure 1). During that arctic outbreak mountain temperatures reached below -20 °F. When the cold air mass exited the region, temperatures rose with new snowfall throughout the advisory area (Figure 2) . This pattern created an upside down snowpack where heavier, dense snow fell on top of less dense, weaker snow. This new snow was accompanied by light to moderate winds according to Ski Patrol weather logs (Figure 3). On Sunday, February 16, 2014, an avalanche warning was issued for the Flathead Range and the warning remained in effect on February 17, 2014 and included the other ranges within the advisory area with a hazard rating of HIGH. Avalanche warnings for the entire advisory area were issued on each day thereafter until allowed to expire on Friday, February 21, 2014. A special avalanche bulletin was issued on Thursday, February 20, 2014 to advise backcountry travelers of elevated avalanche danger through the weekend.
Flathead Avalanche Center (FAC) staff were in nearby Kimmerly Basin and Canyon Creek on Thursday (2/20/2014) where they observed evidence of recent natural avalanche activity. They conducted a crown profile on a recent natural avalanche on a southeast aspect and found the failure to have occurred on a layer of weak faceted snow on top of the late January melt-freeze crust (profile). On Saturday (2/22/2014) FAC staff were in the Doris Creek drainage and found deep persistent slabs on multiple aspects and remnant storm slab instabilities.
Unstable conditions existed throughout the region and the avalanche hazard was rated as CONSIDERABLE in the Whitefish Range on the day of the incident. Other human triggered avalanches occurred on Saturday were reported that evening or Sunday. No natural activity was reported or observed in the Whitefish Range in the days leading up to this incident. The bottom line in the avalanche advisory for that day read:
“For today the avalanche hazard is rated as CONSIDERABLE. While natural avalanche activity has decreased human triggered avalanches are still likely, particularly on wind loaded slopes and slopes 35 degrees and steeper. Dangerous avalanche conditions still exist. The late January crust/facet layer still exists 2-4 feet deep and poses a potentially dangerous persistent slab problem. Careful snow pack evaluation, cautious route finding, and conservative decision making remain essential. Staying out of the runout zones, especially terrain traps, is important.
Note: We are in a period of tricky and potentially dangerous avalanche conditions. Many of us are powder starved and waiting to get into the backcountry. We need to ease back into the backcountry to see what is in store. Approach slopes today with caution and treat them as suspect until you can prove otherwise or not. Many areas adjacent to our advisory area are currently dealing with a deep, persistent slab problem. There is still a lot of uncertainty about this persistent slab problem in our area until we receive more information/data.”
FAC staff received a report of a snowmobile triggered avalanche on the evening of Saturday, February 22, 2014 in McGinnis Creek in the Whitefish Range (Figure 4 and 5). Staff spoke with one of the individuals involved in the avalanche and received another report via email from a witness of the avalanche. Initial reports stated no one was injured and everyone involved made it out without further incident. FAC staff visited the incident site on Sunday, February 23 (the day after the accident), and completed a fracture line profile on a northeast aspect (65 degrees) and found an approximately 100 cm (39 in.) slab sitting on a layer of faceted crystals over a 1 inch (3 cm) thick melt-freeze crust (Figure 6 and 7). The bed surface of the avalanche was the melt-freeze crust at 100 cm (39 in.) below the surface.
Stability tests on the crown of the avalanche did not initiate a fracture on the layer that the avalanche failed on.
The debris ran across a logging road in the Depuy Creek drainage. An individual that witnessed the avalanche initially reported the incident Saturday (2/22/2014) afternoon. We measured the debris in a confined gulley where the partial burial appeared to have occurred and found depths of up to 275 cm (108 inches). The total snow depth at the crown measured 261-274 cm (102-108 in.). The avalanche ran approximately 546 vertical feet, 1187 linear feet, and was about 425 feet wide at the widest extent of the crown (Figure 8 – 10).
On Saturday, February 22, 2013 six snowmobilers were traveling in the Depuy Creek drainage in the Whitefish Range. They departed from the parking lot at McGinnis Creek Road located off of the North Fork Road approximately 13 miles north of Columbia Falls, MT. The snowmobilers checked the advisory during the week prior to Saturday and knew the hazard was rated High throughout the week, but did not check the advisory that morning. They chose McGinnis Creek because, in their mind, it was a fairly safe place with less exposure and less high consequence terrain than other areas they considered. They thought they should stay away from steep, high consequence terrain that day.
Upon reaching an old logging road below the slope that was later triggered, one rider (Rider 1) decided to ascend the slope. Rider 1 had ascended the slope and was descending back down while two other riders (Rider 2 and 3) were off on the side of the slope when (Rider 1) triggered the avalanche. Rider 1 was knocked off of his machine, deployed his airbag (balloon), and was carried an estimated 150-200 yards downslope. Rider 1 came to a rest in a reclining position, almost fully buried with his helmet packed with snow. Only rider 1’s airbag was visible to his companions however he was able to wiggle himself free and extricate himself. Rider 2 stayed on his machine on the outer edge of the avalanche, was caught and carried downslope about 70 yards. Rider 2’s snowmobile was partially buried and he was only slightly buried while sitting on his sled. Rider 3 was able to get away from his machine and stay out of the avalanche. His machine was fully buried near the toe of the debris. The three other riders were sitting on the old logging road near the bottom of the slope. When they saw the slope begin to avalanche they all moved safely out of the path of the avalanche. All of those involved were uninjured. The party spent the next two and a half hours finding and extricating Rider 3’s snowmobile. They observed no natural avalanche activity that day, but did observe natural activity that had occurred the week prior. They observed no shooting cracks, collapsing or other signs of instability.
The group had advanced experience snowmobiling and were comfortable on most terrain. Rider 1 took an avalanche awareness course in the early 2000s, and another member of the party had taken a Level 1 course. Rider 1 thought the group handled the situation very well. Rider 1 feels like some of the lessons learned were that education is important and recognizing proper terrain for given conditions. He mentioned he had never seen a slide that large in this area, and was surprised by the potential.
The staff at the Flathead Avalanche Center wish to extend our gratitude to Rider 1 for his willingness to share this important, detailed, and personal information. This information helps all of us learn in the context of a real situation, and helps promote sound backcountry decision making.
SEARCH AND RESCUE
No search and rescue operations were initiated as the individuals involved were able to extricate themselves.
Direct any questions regarding this report to firstname.lastname@example.org or 406.261.9873.
Report prepared by Erich Peitzsch and Todd Hannan of the Flathead Avalanche Center. Special thanks to Snowmobile Ranger Lucas Stacy for assisting in the investigation.
All formal notation and recording guidelines can be found in:
Greene, Ethan M., D. Atkins, K. Birkeland, K. Elder, C. Landry, B. Lazar, I. McCammon, M. Moore, D. Sharaf, C. Sterbenz, B. Tremper, and K. Williams, 2010. Snow, Weather, and Avalanches: Observational Guidelines for Avalanche Programs in the United States. American Avalanche Association, Pagosa Springs, CO: Second Printing Fall 2010, 152 pp.