Tiger Peak Avalanche Accident

Classification for this avalanche is HS-AMu-R3-D3-O

Avalanche Crown slope angle: 33 degrees

Avalanche Aspect: NW (290)

Avalanche width: 1000 feet

Avalanche length (max): 1350 feet

Alpha angle: 22 degrees

The area that the slide occurred on is a talus field, which can be seen by the aerial photo with the avalanche perimeter drawn on it (Photo 1).

Backcountry Avalanche Forecast

The day before the accident, the Idaho Panhandle Avalanche Center rated the avalanche danger as CONSIDERABLE for all three elevation bands in the Silver Valley Zone where this avalanche occurred. The avalanche center did not produce a forecast for the morning of the accident since they only produce forecasts two days a week, but the outlook from the previous day projected the avalanche danger to be CONSIDERABLE.

Friday’s forecast listed persistent weak layer as a problem with the trigger likelihood as possible and the size as Large to Very Large. Specific problem information from Friday’s forecast is as follows:

Well, our buried persistent weak layer didn't go away with the new storm, it just got buried deeper!  Many locations are still showing results of this in pit tests.  When you are digging pits to test your slope, make sure to go all the way down to the January rain crust.  The buried layer is resting a couple inches above that.  We also have graupel layers in there that are being reactive; this problem isn't as widespread, but something to note.  An avalanche in the upper layers has the potential to step down and trigger a slide in this layer.  Or that big trench that digs down 3 ft before you get momentum. 

No backcountry avalanche forecast is published for Saturday mornings, but the general avalanche information posted was as follows:

We received lots of light, cold snow across all the zones on Thursday and Friday creating storm slab and wind slab problems over our buried surface hoar persistent weak layer problem.  This persistent weak layer problem is becoming lower probability to trigger because it is buried so deep, but higher consequence if it does slide. Make sure to dig your pits deep enough to properly assess.  With only a few inches of snow predicted over the next couple of days, the storms slabs will have time to settle and stabilize.  Winds remain moderate, so if there is still snow available for transport, expect to find new wind slabs on the ridges and peaks.  Give them a wide berth, even a small wind slab has the potential to create an avalanche that could step down and trigger a much larger one on the buried persistent weak layer.

Look for the next forecast on Tuesday morning.  In the meantime, you can check the previous forecast by looking in the archives and current observations on that tab.

Snowpack and Avalanche Summary

The avalanche occurred at 6200’ elevation on a north west aspect (290 degrees) on Custer Peak north of Wallace, Idaho.  The avalanche location is approximately a half mile southeast of Tiger Peak.  The slope angle was 33 degrees on the lookers left side of the crown, estimated mid 30’s on the right side of the crown but was not visited due to visibility and hang fire. Reports from the riders were that the slide started lower on the slope where it then propagated to the top of the opening and larger slope above them. Best estimates of this location from the rider accounts is that it was 28 to 30 degrees, approximately 700ft below the crown (Photo 1). The crown of the avalanche was 120cm in height (Photo 2), and the maximum extent that the slide ran was 1350ft (measured on Google Earth).  The crown extended approximately 1000’ around the edge of the talus opening as seen on the photo from across the valley (Photo 3).  The runout angle (toe of debris to crown) was measured at 22 degrees.  The avalanche is classified as HS-AMu-R3-D3-O.

We did a fracture analysis at the crown of the avalanche as well as a snowpit in a safe, representative slope nearby and found a snowpack structure that has been seen widespread across the Silver Valley forecasting zone.  Prior to the accident, the most recent snowpit collected by the zone forecaster was from 2 days prior and approximately 4 miles as the crow flies due east and found similar results. The snowpit profile from the crown of the avalanche is attached (Photo 4).  At the crown, the avalanche broke on a “Fist” layer of buried surface hoar that was formed and grew between January 17th and Feb 3rd.  We were unable to find this layer intact in the surrounding snowpack, it presumably had collapsed when the rest of the slope slid. Remnants found on the bed surface were in the 5mm to 10 mm range. This layer has been found to be up to 20mm in snowpits from within the forecast zone in the weeks leading up to the Tiger Peak Avalanche. The bed surface was “4-Finger” hardness faceted snow that was sitting on top of the January 12th ice crust. The ice crust still required moderate force with kick steps to break through with ski boots and skis were not breaking it.  The slab at the crown was a mixture of hardnesses, from “pencil” to “fist”.  The slab at the crown of the avalanche had greater hardness than 500ft lower on the avalanche path due to wind affect. 

Accident Summary

On Saturday February 27th, 2021 a group of four snowmobilers had ridden from Dobson Pass and were riding and playing in the East Fork Nine Mile drainage (Photo 5). Three of the four riders were familiar with the terrain and rode this location often.  At approximately 15:45, the party reached the end of the road below the opening on the north slope of Custer Peak (Photo 6). Two of the party members started up through the trees, covering the 200ft vert and entering the opening. Rider 1 and 2 did one ride up the lookers left side of the opening, sticking close to the trees and avoiding the maid open bowl. The majority of this side of the opening is sub avalanche terrain but connected to avalanche terrain above it. The top out of their climbing area was in the low 30s.They climbed to the top of the left side of the opening and came down and traversed back along the trees.  As they were approaching the entrance to the area, they saw that Rider 3 had decided to come up.  Rider 1, going downhill, rode by Rider 3, and starting to make a turn to come back up with Rider 3. Rider 2 had remained above on a small bench area. Rider 2 could see snow sliding below him where Rider 1 and 3 were, closer to the right side of the opening. He saw Rider 1 turn and start riding out of the avalanche. He saw Rider 3 turn but then get caught. He then realized that the slope above him had started to slide and swept into him. Rider 2 stayed on top of his snowmobile and pinned the throttle, riding downhill on top of the slide. He deployed his airbag but stayed upright on his snowmobile. His snowmobile was slowed down and eventually stopped when it ran over a large tree that had been snapped by the slide.  Rider 1 was making a turn to go back to ride up with Rider 3 when he saw snow sliding behind him towards where Rider 3 was. He stayed on his snowmobile and was able to ride up and out of the right flank of the avalanche, getting his snowmobile into the trees.  Rider 3 was caught, carried, and fully buried. Rider 2 kept eyes on him for as long as possible, but had snow packed in his helmet while he was being carried by the avalanche.  (Photo 3)

As soon as the slide stopped, Rider 2 dismounted from his sled and had voice contact with Rider 1.  Rider 2 started downhill towards where he’d seen Rider 3 disappear.  After a few seconds he took off his airbag (deployed) because it was too difficult to walk with it on.  He grabbed his rescue gear and his extra rescue gear from his sled and left his airbag bag with his sled, which also contained his radio.  Rider 1 also started heading down the hill on foot with all his rescue equipment towards where Rider 3 had disappeared in the trees, calling 911 as he was headed down. He delivered coordinates, location, and basics of what happened. They started a transceiver search and had Rider 3’s signal immediately. They followed the transceiver signal until the numbers weren’t getting smaller. They were unable to locate Rider 3 with a probe strike, but quickly realized it was because he was too deep according to the transceiver numbers. They started excavating the area, removing 4 to 5 feet of snow and were able to get lower readings and able to probe Rider 3. They continued digging until they were able to uncover his face and body.  They estimated that he was buried under 12 to 14ft of debris and it took them roughly an hour of digging to reach his airway.  Rider 3 was pinned around a tree with visual signs of trauma. His airbag had been deployed but was deflated. Rider 1 performed CPR on Rider 3 for approximately an hour before he was no longer capable.  Rider 2 continued to dig to be able to extract Rider 3 from around the tree. (Photo 7)

When they had entered the trees where Rider 3 was buried, they had yelled down to Rider 4 who had remained on the road below when Rider 3 had come up through the trees.  Rider 2’s radio was up on his sled and Rider 1 didn’t have a radio, so they were unable to contact Rider 4. It is unknown what time Rider 4 left, but he did not help with the rescue.

During the rescue, Rider 1 had called a friend (Rescuer 1) very familiar with the riding area, who drove from Spokane to Dobson Pass and snowmobiled in. When he reached the area (approximately 1.5 hours after the slide), they started self-evacuating. Rider 2 went back up to get his snowmobile and dug it out, while Rescuer 1 and Rider 1 prepared deceased Rider 3 for transport. They then left the area to travel back to Dobson Pass.  Rescuer 1 transported the deceased Rider 3, and Rider 2 transported Rider 1.  They made it back to Dobson Pass at approximately 8PM where they transferred Rider 3 to medical personal. Medical personal transported Rider 3 down the Pass, where his wife was able to meet the ambulance.  Rescuer 1 then returned to the site of the avalanche and recovered Rider 1’s sled and towed it back to Dobson Pass.  Rider 3’s sled remained on site after the accident, located approximately 60ft downhill from Rider 3’s burial spot (Photo 8).  The toe of the debris was approximately 100ft downhill from the sled.  

Sherriff and Search and Rescue timeline:

911 call from Rider 1: ~16:00

SAR Standby for Call Out: 17:09

SAR Callout: 17:22

SAR Standdown: 20:10

Incident command including 6 Shoshone County Sheriffs Office Deputies, 10 Silver Valley Search and Rescue personnel was set up at Dobson Pass. Deputies and SAR were not deployed to the accident site.  Air support was requested but was called off by the avalanche party.

Avalanche forecasters from the Idaho Panhandle Avalanche Center (IPAC) visited the site on February 28th. On February 28th, the visibility was limited due to low lying cloud cover.  Winds were calm and there was no new precipitation. Overview photos were taken on February 27th by a witness who was riding across the drainage approximately 1.5miles away from the accident site (Photo 3). The rest of the photos were taken on February 28th during the site visit by IPAC. Visibility on the 28th and the knowledge that there was hang fire located on the right flank/crown limited the forecasters from visiting this side of the slide. The photos from the 27th were used to better delineate the avalanche. 

The avalanche was a hard slab avalanche in an open riding area that had a start zone area in the low to mid 30 degrees.  The open area is flanked by mature timber and funnels down to mature timber through a slight depression. Multiple 8” diameter trees were broken in the path of the avalanche and flagging occurred on larger timber that remained standing at the bottom of the slide path (photo 9 and photo 10).  The slide path ranged from 20 ft to 1350 ft at its longest length. Debris from the middle of the crown to the right flank ran the furthest of this extent.  Exposed bed surface ranged from 10ft to approximately 700ft.

Comments

All fatal avalanche accidents are tragic events. We do our best to describe each one to help people involved and the community as a whole better understand them. We offer these comments in the hope that it will help people avoid future avalanche accidents.

The accident involved a group of experienced riders with two members of the party having many years of experience in the general area and had ridden a lot in the specific area. They had read the avalanche forecast and they were aware of the avalanche conditions.  They had ruled out high-marking and riding on the steeper section (right side) of the open area.  They had been riding all day in similar areas and hadn’t experienced any red flags. When they came to this area, what was to be the last spot of the day, one rider asked about the exposure and the individual who knew the area said that it was an area that never slides.  

Rider 1 and Rider 2 entered the area and identified the steep slopes overhead on the right side as terrain to avoid. Unfortunately, they did not recognize the potential of triggering an avalanche from low-angle slope below steeper terrain.  They did not anticipate that an avalanche could break across multiple terrain features and run into an area they thought was safe. There were multiple reports of remote triggered slides breaking on this buried persistent weak layer over the month prior to this incident. This persistent layer problem is out of the usual in terms of magnitude and longevity for this forecasting area. It is very fortunate that Rider 1 and Rider 2 were not buried in this avalanche. It is always best practice to only expose one person at a time to avalanche terrain. 

The three riders were all wearing rescue equipment and knew how to use it.  The two riders that performed the search stated that they were extremely thankful that they had trained with their equipment and trusted it even when they weren’t able to probe Rider 3 due to the depth of burial. The practice allowed them to remain cool-headed and rationally think through what they needed to do to be able to recover Rider 3.

Photos:

Photo 1: Caltopo Aerial photo with slope angle shading. White outline is the extent to the avalanche. Approximate locations of Rider 1, 2, and 3 when the avalanche started and where they ended up.

Photo 2: Photo of the crown of the avalanche, which averaged 120cm in height. This was approximately 700ft upslope from the where the avalanche was triggered. Bed surface at the crown was 33 degrees.

Photo 3: View of the avalanche area and crown taken from approximately 1.5 miles away across the valley shortly after the slide on February 27th by D. Rising.  Shows rider locations and crown location.

Photo 4: Snowpilot profile from the crown analysis on February 28th.

Photo 5: Overview of the Dobson Pass and East Fork Nine Mile riding area.

Photo 6: Topo view of the approach to the avalanche area with the avalanche outline.

Photo 7: Excavated hole where Rider 3 was dug out. Orange is Rider 3’s deflated airbag.  300 cm avalanche probe for scale, Rider 1 and 2 estimate that 4 to 5 feet of snow had already been removed from this area before the photo was taken. Total burial depth was estimated between 12 to 14ft deep.

Photo 8: Rider 3’s buried snowmobile, located approximately 60 to 80 ft downslope. Arrow indicated Rider 3’s location in the trees upslope of the snowmobile.

Photo 9: Trees upwards of 8” in diameter littered the avalanche debris.

Photo 10: Flagging on mature timber in the avalanche path, skier for scale.