CAIC: Colorado Avalanche Information Center

2017/01/05 - Montana - Mt. Stanton, north of West Glacier

Published 2017/04/14 by Todd Hannan - Flathead Avalanche Center


Avalanche Details

  • Location: Mt. Stanton, north of West Glacier
  • State: Montana
  • Date: 2017/01/05
  • Time: 2:00 PM (Estimated)
  • Summary Description: 1 backcountry tourer caught, partially buried, and killed
  • Primary Activity: Backcountry Tourer
  • Primary Travel Mode: Ski
  • Location Setting: Backcountry

Number

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

Avalanche

  • Type: SS
  • Trigger: AS - Skier
  • Trigger (subcode): u - An unintentional release
  • Size - Relative to Path: R2
  • Size - Destructive Force: D2
  • Sliding Surface: O - Within Old Snow

Site

  • Slope Aspect: SW
  • Site Elevation: 7200 ft
  • Slope Angle: 35 °
  • Slope Characteristic: --

Avalanche Comments

The average slope angle of the starting zone was 35 degrees. The crown face depth ranged from 1 to almost 4 feet. The avalanche was approximately 270 feet wide and traveled downslope approximately 2300 vertical feet, and a total of 4100 feet in length. The crown was located at approximately 7360 feet in elevation and the toe of the debris was estimated at 5100 feet. The avalanche is classified as SS-ASu-R2-D2-O. This means that it was a soft slab avalanche (SS) unintentionally triggered by a skier (ASu). It was small, relative to the path, and large enough to bury, injure, or kill a person (D2). The avalanche released within the old snow (O) on weak, faceted snow above a firm, wind scoured layer.

Weather Summary

Temperature and wind data were collected from the Garden Wall weather station (maintained by the U.S. Geological Survey) at 7400 feet located approximately 15 km (9 miles) to the northeast of the accident site. Snow depth and snow water equivalent data were collected from the Flattop Mountain SNOTEL station (maintained by the NRCS) 6300 feet located approximately 20 km (13 miles) to the northwest of the accident site.

The winter season since December 1, 2016 was characterized by cool temperatures (all below freezing at 7400 feet, Garden Wall weather station) with three distinct intrusions of cold arctic air from the north. These arctic outbreaks occurred approximately December 5-9, December 13-19, and December 31 up to the day of the avalanche incident (Figure 1). Snow water equivalent (SWE) values hovered around average (88-108% of median) for most of December up to January 5, 2017. Flattop Mountain SNOTEL site (6300 feet) recorded approximately 21 inches of snow (settled snow measurements so snow accumulation could be higher) from December 25, 2016 to December 30, 2017. After this storm, cold air infiltrated the region once again accompanied by moderate to strong average wind speeds(17-37 mph) with extreme gusts (>38 mph) from the north-northeast. These winds diminished substantially on January 3, but cold temperatures prevailed across the region.

Snowpack Summary

These strong north-northeast winds created both soft and hard wind slab across the advisory area. Flathead Avalanche Center staff (and other observers) noted wind slabs in exposed terrain above 5000 feet. On Tuesday, January 3, 2017 FAC staff visited Noisy Basin in the Swan Range (approximately 35 miles to the south-southwest) where they noted variability in the snow surface that included debris from trees, sastrugi, hard wind drifts, and eroded cornices. They found hard wind slabs present well below the ridgelines, but these slabs showed variable results in stability tests. On a northwest aspect at 6400 feet, 5 extended column tests resulted in fractures that propagated across the column with easy force (ECTP4). The pencil hard slab proved more stubborn in stability tests on a northeastern slope (ECTN25). They also reported a weak structure in the mid and lower snow pack due to layers of weak, faceted snow about 2.5-3 feet from the surface, as well as, depth hoar developing near the ground. None of their tests produced results on these deeper layers.

The Flathead Avalanche Center avalanche advisory Bottom Line for January 5, 2017 read: “Wind slabs formed early in the week may no longer present obvious signs of instability and may prove stubborn in stability tests. However, it remains possible to trigger an avalanche in these ageing slabs particularly where they formed on weak, faceted snow. The avalanche danger is MODERATE above 5000 feet. Carefully evaluate wind loaded areas before committing to a slope and keep in mind that small wind slab avalanches could step down to deeper weak layers in the snowpack.” 

Accident Summary

A member of the party involved provided valuable information regarding the incident and all of the events of the day. We appreciate this individual taking the time to provide this information under such tragic circumstances. 

A party of three experienced back country skiers parked at the Lake McDonald Lodge parking lot in Glacier National Park at approximately 10:00 a.m. (Figure 8). They were all equipped with avalanche transceivers, avalanche shovels, and probes and they read the avalanche advisory that morning. They skied up the Going-to-the-Sun-Road (closed to vehicle traffic in winter) to the North Lake McDonald Road (1.5 miles). They put climbing skins on their skis in this vicinity and then continued skiing on this road to the Trout Lake trailhead (1.5 miles). They then followed the Trout Lake hiking trail for approximately 2.5 miles to a location just below where the trail crests Howe Ridge. From this location the skiers left the trail and started climbing up the west ridge of Mt. Stanton. Eventually this group reached the tree line where they encountered a short, steep rocky knob. At the top of this knob one member of the party mentioned that he was feeling ill and was going to eat some food and then descend their skin trail back to the hiking trail and retrace their path to the parking lot. It was decided that he would wait at the vehicle for the other two members of the group. 

Skier 1 and 2 continued to follow the west ridge of Mt. Stanton toward the summit. The party noted a weak snow pack on their ascent to the ridge, as well as, areas of weak snow and scoured surfaces along the ridge. Eventually they reached the summit, and, after a brief break, decided to descend the same ridge that they climbed. Skier 1 went first and carefully and slowly skied the ridge from the summit limiting his exposure. Both members of the group would either make 1 or 2 turns on the adjacent slope but then cut skiers right back to the ridge or just stay on the ridge. In this fashion they made their way down to the upper portion of the sub-ridge that separates the two large southwest facing avalanche chutes on Mt Stanton. 

At approximately 2:00 p.m. Skier 1 traversed across the relatively broad ridge and into the top skiers left of the western most of the two avalanche paths. He performed two ski pole tests in this area (to determine general snowpack structure), then made one left hand turn followed by an immediate right turn. Between these turns Skier 1 down weighted his skis once or twice in an attempt to test the snow stability. Shortly after completing his right hand turn he triggered the avalanche, possibly while down weighting. The avalanche broke uphill of Skier 1 and immediately knocked him off his feet. 

Skier 2 remained on the ridge during the time that Skier 1 traversed the sub-ridge and entered the avalanche path. When the avalanche occurred, Skier 2 was able to observe Skier 1 being swept downhill on top of the avalanche debris. Eventually Skier 1 was swept over a convex terrain feature (also known as a rollover on the slope) which effectively blocked the vision of the path for Skier 2. The avalanche had stepped down to the ground almost immediately, leaving a bed surface consisting of mostly rock. 

After losing sight of his partner, Skier 2 cut skier’s right of the slide hoping to descend faster via a snow surface than the bed surface. He quickly realized that there was a possibility of triggering another avalanche and determined it was best to descend the bed surface. He then switched his transceiver to receive and initiated a transceiver search while descending the bed surface. His descent was slow and difficult due to the rock bed surface and convex terrain features and small cliff bands. Eventually, Skier 2 exited the slide skiers right where the slope angled lessened and the risk of triggering a secondary slide decreased. He descended this snow until he reached the debris. Upon reaching the debris he was able to ski the debris to the toe. During this transceiver search, he was unable to obtain a signal. At this point, he removed his skis, stuck them in the snow, and proceeded to walk back up the debris. Upon reaching the top elevation of the debris he had still not yet picked up a signal. He called out for Skier 1 and was able to hear a faint reply. Skier 2 continued to call out, and eventually successfully located Skier 1 in this fashion. 

Skier 1 was above the debris field and not buried. He was on the snow surface against a tree with his head downhill and in a semi-conscious state. After evaluating the injured skier, Skier 2 determined that significant trauma had occurred, called 911, and requested a helicopter evacuation. While waiting for the helicopter, Skier 2 attempted to warm and comfort skier 1. Two Bear Air Rescue responded and extricated Skier 1 from the scene. 

The party was very experienced in both winter mountain travel and avalanche education. Skier 1 completed a Level 2 avalanche training within the past 3 years and Skier 2 completed a Level 1 avalanche training.

Rescue Summary

At approximately 3:15 p.m., Park Dispatch received a 911 call from Skier 2 and requested helicopter response from Two Bear Air Rescue, in conjunction with Flathead County Sheriff’s Office. Two Bear Air Rescue reached the scene at approximately 4:30 p.m., extracted Skier 1 using a long line hoist and then transferred him to an ALERT helicopter waiting along the Going-to-the-Sun Road. The Two Bear Air Rescue helicopter returned to the scene to hoist Skier 2. Skier 2 was transported from the incident scene to Apgar Visitor Center. 

We offer our sincere condolences and our thoughts are with family, friends, and all of those involved. We would like to thank Glacier National Park rangers for assistance in the field, Two Bear Air Rescue, and Flathead County Sheriff's Office.

Comments

With most human/avalanche involvements, there is a point where the day of recreation turned into a tragic event. The party of two intended to ski down the safe ascent ridge. The two discussed traversing to the safe ridge to descend. Skier 1 made two turns into increasingly steeper terrain before beginning his traverse to the ridge, and after his second turn he triggered the avalanche. He also completed 1-2 bounce tests (i.e. weighting of his skis) to assess stability. This is a test sometimes utilized by experienced individuals to test small slopes with low or no consequences should an avalanche occur. Unfortunately, the consequences of an avalanche on this slope were fatal. Snowpack depth and structure across the slope were variable with a wind slab present on one side of the cross-loaded slope and a shallow weak snowpack just meters away. If variability leads to challenging assessment of stability, then choosing low or no consequence terrain is favorable. 

We don’t know the exact reason Skier 2 was unable to obtain a signal from Skier 1 beacon. A few of the possible scenarios include: 

1) Skier 1 came to rest outside of the main avalanche path (east of path) and Skier 2 had to navigate terrain further west to safely descend a cliff area during the search. The crown width was 57 meters wide, thus making the bed surface at least that wide. A distance of at least 60 meters is typically the maximum limit or outside the range of most modern avalanche beacons. He may have been unable to obtain a signal due to the distance across the slide path to Skier 1’s location. 

2) Skier 2 also mentioned that due to the terrain he was traveling through he may not have turned his beacon to receive early enough as he was navigating the rocky bed surface and may have missed Skier 1’s position originally. However, when ascending the debris pile after not obtaining a signal, he still was unable to obtain a signal on the way up. Though, he mentioned he turned it back to transmit once on the hike back up while ascending a steep, rocky pitch in the gully. 

Flathead Avalanche Center report

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