Twin Lakes Avalanche Incident 1/31/2016 Location: Place State Published by: Dave Bingaman (PAC), George Halcom (PAC), and Kent May (PAC) Twin Lakes, Salmon River Mountains Idaho Date 01/31/2016 Time Summary 1:00 PM (approx.) 1 snowmobiler buried and killed Number: Caught 1 Fully Buried 1 Injured 0 Killed 1 Avalanche Details: Type Hard Slab Trigger Subcode Size Weak Layer Aspect Elevation Slope Angle Character AM u D3 Surface Hoar NE 7700 FT 38 Degrees Convex, rocky, sparsely-treed slope funneling into a gully Crown Width 250 Feet Crown Height 2-3 Feet
Figure 1. Overview of accident location Accident Summary: Four snowmobilers rode into the Twin Lakes Basin from the Gordon Titus Trailhead, which is located approximately 8 miles north of McCall, Idaho. Twin Lakes is an additional 11 miles north of the trailhead with the final ½ mile being off trail. Two of the riders (Rider 1 and Rider 2) were experienced at riding snowmobiles in mountainous terrain and were very familiar with the area. Both riders regularly read the Payette Avalanche Center (PAC) Avalanche Advisory, and at least one of the riders had received basic avalanche training. After spending the morning sightseeing and looking at steeper terrain to the west of the accident site, Rider 1 decided to climb an untracked gully to a steep headwall. Rider 1 climbed
almost to the top and parked his sled perpendicular to the slope so he could look back down at what he had just climbed. Rider 2 then began climbing the lower portion of the slope but was not visible to the uphill rider. Rider 1 could hear Rider 2 s snowmobile engine as it climbed and then described hearing what he thought was the sled out of the snow for an instant. Rider 1 described what sounded like white noise and then the sound of the Rider 2 s engine being muffled. He yelled several times to Rider 2 and did not hear a response. He then rode downhill into fresh avalanche debris. Several other riders, including the other two members of the group (Rider 3 and Rider 4), were on the frozen lake below Twin Lakes. Upon arriving at the avalanche debris, Rider 1 scanned the debris and did not see Rider 2. The only visible clue Rider 1 could see was Rider 2 s partially buried snowmobile in the toe of the debris. Avalanche and Terrain Summary: The hard slab released mid-slope on a NE-facing aspect and ran approximately 500 vertical feet. The slide was triggered on a mostly treeless, 33-38 degree convexity and debris was funneled down a narrow gully. Several rock outcrops in the open slope created varying crown depths of 2-3 feet. The crown width was estimated at 250 feet. All of the debris was channeled into the gully and the lower angled slope below it. The bed surface was an old snow surface from the late December/early January period of generally clear and fair weather. Decomposing surface hoar was present on the bed surface. The debris was 8-12 feet deep in the deposition zone below the gully. Rescue Summary: Both of the riders were equipped with beacons, shovels, and probes. Each was wearing an avalanche airbag backpack. Both were familiar with the use of their beacons and the other avalanche rescue equipment they were carrying. After recognizing that there had been an avalanche, Rider 1 descended the slope, parked his sled in the debris, and began a beacon signal search. While searching, Rider 1 began yelling for help and calling other nearby riders on a radio. Several others started moving up the debris pile from the bottom and became an active part of the search. Unfortunately, some of these new rescuers still had their beacons in transmit mode; Rider 1 lost the beacon signal of the buried victim due to the additional signals. Rider 1 said that it took him a total of about 20 minutes to find the victim. Rider 2 was found buried approximately 4 feet deep, sitting upright, airbag deployed, and within a few feet of his partially buried sled. When the rescuers found him he was not breathing and did not appear to have sustained serious trauma. Efforts to revive him were unsuccessful. Valley County Dispatch was notified and an air ambulance was launched out of Ontario, OR. The air crew reached the accident location and evacuated the victim before local SAR personnel arrived.
Figure 2. Overview of accident site Snowpack and weather Summary: From December 25 th - January 12 th, a ridge of high pressure dominated the weather in the West Central Idaho Mountains. With little wind, overnight low temperatures hovering around zero F, and high temperatures in the mid-20 s F each afternoon, it was the perfect recipe for surface hoar formation. The high pressure was pushed out of the region on January 12 th by a series of Pacific storms. By the end of January, several cold storms with generally light winds deposited feet of low density snowfall, burying the surface hoar with six inches of snow water equivalent (SWE). The buried surface hoar was responsible for a widespread natural avalanche cycle that began on the Martin Luther King Holiday weekend and continued for several days. PAC forecasters were able to trigger sizable avalanches down to the buried surface hoar layer by releasing relatively small cornices on January 18 th (MLK). During the following week, several skier and snowmobile triggered avalanches were reported to PAC as the slab above the weak layer continued to thicken.
Figure 2. Brundage SNOTEL site SWE from 12-25 to 02-01 Recent Observation: On January 14 th (approximately 2 weeks before the accident), PAC forecasters visited Twin Lakes to gather data and track the layer of buried surface hoar. Figure 3. Magnification of buried surface hoar from January 14 th
Figure 4. Pit profile from January 14 th on an adjacent slope to accident site
Figure 5. Buried surface hoar from adjacent slope January 14 th Avalanche Advisory for 1/31/2016 On the day of the fatality, the Payette Avalanche Center rated the avalanche danger as MODERATE, with areas of CONSIDERABLE danger identified as wind loaded slopes over 30 degrees and protected slopes where the surface hoar layer was preserved below the new snow. The day s Avalanche Problems were wind slabs (primary problem) and a persistent weak layer (New Year s buried surface hoar, secondary problem). The advisory identified areas that the PAC Avalanche Specialists were most concerned about (wind slabs and buried surface hoar) with orange dots representing CONSIDERABLE danger: W, NW, N, NE, E, and SE aspects at elevations above 7,000 feet. Figure 6. Crown profile from fatal January 31 st avalanche
Figure 7. PAC Avalanche Specialist George Halcom performing crown profile. Snowmobile tracks from Rider 1 ascending the slope before avalanche was triggered
Figure 8. View of NE facing slope from Twin Lakes day after fatality
Analysis: The initial rescue was initiated quickly and advanced life support personnel were on scene rapidly considering the remote location. Twin Lakes is a known Life Flight winter landing zone due to its proximity to a cat skiing operation. Tragically, a life was lost. Some notable points and contributing factors: Persistent weak layer: The group had read the avalanche advisory, knew the avalanche danger was rated MODERATE, but did not read the whole advisory to see that there were areas of CONSIDERABLE danger to due wind slab and persistent slab avalanche problems. Initially, the group did not intend to climb any hills that day. After beginning their day sight-seeing and avoiding avalanche terrain, they decided to climb the slope that resulted in the fatality. No slope assessment was made to check for the presence of a persistent weak layer (buried surface hoar) before committing to the steeper slope. Terrain trap: The relatively wide slab avalanche was funneled into a tight gully that concentrated all of the moving snow. The slope angle decreased rapidly below the gully, causing the debris to pile up deeply in a small area. Companion Rescue: While some individuals possessed basic companion rescue skills, some critical accident scene management details were missed. Having additional rescuers turn beacons off and spot probing near clues (the snowmobile) could have saved valuable time. Burial time: The victim was buried for approximately 22 minutes. According to a 2011 paper by Pascal Haegeli (Comparison of avalanche survival patterns in Canada and Switzerland), individuals unharmed by trauma that are completely buried 21 minutes or more only had a 24.1% survival rate in Canada and a 43.9% survival rate in Switzerland. In complete burials where the individual was extricated between 11-20 minutes, 36.2% survived in Canada and 71.1% survived in Switzerland. Burials less than 10 minutes resulted in an 89.5% survival rate in Canada and a 93.6% survival rate in Switzerland. These statistics show that rapid extrication is paramount in surviving a complete avalanche burial (assuming trauma is not the cause of death).