CAIC: Colorado Avalanche Information Center

2016/01/21 - Colorado - Ruby Peak, Ruby Range west of Crested Butte

Published 2016/02/01 by Brian Lazar, Zach Guy - Forecast Staff, Colorado Avalanche Information Center and Crested Butte Avalanche Center


Avalanche Details

  • Location: Ruby Peak, Ruby Range west of Crested Butte
  • State: Colorado
  • Date: 2016/01/21
  • Time: 2:00 PM
  • Summary Description: 2 snowmobilers caught, 1 partially buried uninjured, 1 fully buried and killed
  • Primary Activity: Snowmobiler
  • Primary Travel Mode: Snowmobile
  • Location Setting: Backcountry

Number

  • Caught: 2
  • Partially Buried, Non-Critical: 1
  • Partially Buried, Critical: 0
  • Fully Buried: 1
  • Injured: 0
  • Killed: 1

Avalanche

  • Type: SS
  • Trigger: AM - Snowmobile
  • Trigger (subcode): u - An unintentional release
  • Size - Relative to Path: R3
  • Size - Destructive Force: D2
  • Sliding Surface: --

Site

  • Slope Aspect: SE
  • Site Elevation: 11000 ft
  • Slope Angle: 35 °
  • Slope Characteristic: Convex Slope

Avalanche Comments

The avalanche was a soft slab, unintentionally triggered by a snowmobiler, medium size relative to the path, large enough to bury and kill a person, and broke into old snow layers (SS-AMu-R3-D2-O). The avalanche released on a slope ranging from 32 to 42 degrees in steepness, near treeline (around 11,000 ft), and facing east-southeast. The avalanche was approximately 3 feet deep, 500 feet wide, and ran 140 vertical feet. It released on a layer of small facets with a Hand Hardness of 4 Fingers that sat atop a thin melt-freeze crust. The alpha angle for this avalanche event was 26 degrees.

 

Weather Summary

A late November and early December dry spell ended mid-December, when a significant storm cycle deposited 94 inches of snow (6.45 inches of snow-water equivalent (SWE)) in the last two weeks of December at the Irwin Guides study plot, located 0.5 miles to the southeast of the avalanche site at 10,200 ft. The first six days of January brought clear skies, light winds, and large diurnal temperature swings. From January 6th to January 9th, 15 inches of snow (0.7 inches SWE) fell under light southwest to northwest winds, with gusts reaching 30 to 40 mph at Scarp Ridge wind station, located 1.3 miles to the northwest of the site at 12,000 ft. January 10th to January 14th was dry, mostly sunny with little wind, and daytime high temperatures in 20’s and 30’s (F).  

A series of storms brought 7 consecutive days of snowfall from January 14th to January 20th. Storm totals during this week-long period were 65 inches of snow and 3.25 inches of SWE. Winds on Scarp Ridge were out of the south-southwest during the first 5 days of the storm, averaging 13-18 mph, and gusting into the 40’s. Scarp Ridge station malfunctioned during the last three days leading up to the accident, but observers in the area reported moderate to strong winds that veered to the northwest on January 19th. Northwest winds continued up until the day of the accident (January 21st). Skies cleared on the morning of January 21st. Winds were moderate to strong out of the north-northwest with large plumes off of the peaks in the morning.  

Snowpack Summary

The snowpack in the Ruby Range began to build in late October. The snowpack was thin, shallow, and weak through November. A dry period in early December further weakened the existing snowpack before an extended storm cycle from mid to late December built an early-season slab over depth hoar and basal crust layers. The late December storms produced a widespread natural avalanche cycle during the Christmas week.  

By the start of the New Year, the height of the snowpack was 46 inches at the Irwin Snow Study Plot. An extended dry spell in early January promoted faceting through the entire snowpack, and left a thin melt-freeze crust at the surface on southerly aspects. This crust was buried on January 6th with 10 inches of new low-density snow, and facets subsequently formed above and below the crust. The crust/facet combination was further buried by a series of storms beginning on January 14th. Between January 14th and 20th, the height of the snowpack at the Irwin Snow Study Plot increased by 21 inches.  Southwest winds veered to northwest through this stormy period, and drifted the low-density storm snow into deeper and more cohesive slabs on leeward slopes.  

Clear skies on January 21st revealed numerous natural slab avalanches in the Lake Irwin area, including a D2.5 on the southeast face of Purple Peak (Figure 1) and a D2 on the southeast face of Ruby Peak (Figure 2). Both of these avalanches appeared to fail near the January 14th interface the previous night.

At the accident site, new and wind-drifted snow from the previous week formed a soft slab approximately 1 to 4 feet thick (averaging 3 feet thick) over the January 14th crust/facet layers. The slab increased in hardness with depth, from a Hand Hardness Index value of Fist at the surface down to 1 Finger near the weak layer. 

Events Leading to the Avalanche

On the morning of January 21st, a group of 6 riders (Riders 1 through 6) discussed going on a backcountry tour. Given the dangerous avalanche conditions described in the forecast, they opted to forego the backcountry tour in favor of a seemingly safer alternative of snowmobiling out to a small slope in the Ruby Range and building a jump they could ride off on their snowboards. The group departed the Kebler Pass trailhead on snowmobiles around 9 AM. They road to the bottom of the slope and left a couple snowmobiles at this location. They proceeded uphill on 4 snowmobiles to the area where they built the jump.

Their plan was to use the snowmobiles to shuttle riders to the top of the slope so they could descend to the jump on their skis and snowboards. The top of the snowmobile track ended and turned downhill at the bottom of the slope that eventually avalanched. Rider 1 put in ascent and descent tracks using his snowmobile, and completed approximately 8 laps prior to the accident. Two riders also hiked up the slope to ride the jump prior to the avalanche. 

Accident Summary

At approximately 1:45 PM, Rider 1 picked up Rider 2 and they climbed the ascent track riding two abreast on a snowmobile. They reached the top of the ascent track and were turning the snowmobile to descend back downhill when they triggered the avalanche from the bottom of the slope. Rider 1 was on the throttle side of the snowmobile, and Rider 2 was on the brake side. As soon as the avalanche broke, Rider 1 told Rider 2 to hang on, and then hit the throttle to try and drive out of the moving debris. They avalanche overtook them, and both riders were thrown from the snowmobile.  Rider 1 was partially buried up to his shins and was able to dig himself out of the debris. Rider 2 was caught and washed downhill about 30 feet into a small stand of trees. He was completely buried along with the snowmobile. 

Rescue Summary

Riders 1, and 3 through 6 immediately responded. Some members of the group did a beacon search while others grabbed 3 big metal shovels that they used to build the jump. They were close to Rider 2 within a couple minutes and began pinpointing with probes in the small tree stand. They were unable to get a probe strike, so they began digging in the probe area. They dug a hole approximately 6 feet deep on one side of a tree, but did not locate Rider 2. They dug a second hole, also about 6 feet deep, on the other side of the tree, and still did not locate Rider 2. At that point they began probing in the second the hole, and hit something with their probes. The began digging yet again, and realized their probes struck the buried snowmobile. 

They started probing near the buried snowmobile and pinpointed Rider 2 approximately 7 feet deep, or 1 foot deeper than the bottom of their second hole. He was buried very close to the snowmobile. The group dug until they could access Rider 2's airway, and immediately began CPR. They had Rider 2 fully extricated in a couple more minutes, and continued CPR throughout. They estimate that Rider 2 was buried for approximately 15 minutes before they exposed his airway, 

Once Rider 2 was located, one member of the group (Rider 3) jumped on his snowmobile and raced to the nearby Irwin Guides buildings were they could get additional help. Rider 3 contacted Irwin Guides at 1:57 PM. Two Irwin Guides (Guides 1 and 2) prepared to respond as soon as they made contact with Rider 3. Guides 1 and 2 departed from the Irwin Guides facility with a medical kit including an automated external defibrillator (AED). Difficult snowmobiling delayed their arrival on site, but they nevertheless arrived on scene around 2:05 PM. 

Guides 1 and 2 reported that Rider 2 was fully extricated when they arrived, but CPR was not ongoing at that time. They called for emergency helicopter response immediately, and once again began CPR. After some communication with the emergency response personnel, Guides 1 and 2 called off the helicopter response and instead asked for an ambulance to meet them at the Kebler Pass trailhead. They would bring Rider 2 to the trailhead with snowmobiles and a rescue toboggan. 

Guides 1 and 2 ,with help from other group members transported Rider 2 back to a well established cat road where they transferred him to a more robust rescue toboggan.  They continued CPR all the way to the trailhead. They arrived to the trailhead around 2:50 PM and transferred care of Rider 2 to emergency medical services. Emergency medical services transported the rider to medical facility where he later succumbed to his injuries.

Comments

The group was aware of and discussed the avalanche hazard. They thought they chose a safer alternative to a backcountry tour that day by electing to build a jump in lower-angle terrain. The snowmobile tracks they made avoided going onto obvious steep wind-loaded slopes. Unfortunately, the very top of the snowmobile track went underneath a steeper slope. They triggered the avalanche from the bottom of the slope in area a little more than 20 degrees in steepness. With Persistent Slab avalanches it is possible to initiate a crack from low-angle terrain that then runs onto a steeper slope and releases the avalanche. So while the group tried to avoid suspect terrain, they did not recognize the potential to trigger a steeper overhead slope from a gentler area. There were also natural avalanches in the same area that ran on similar aspects and elevations. The group did not notice these avalanches. These signs of instability may have impacted their slope choice this day had they seen them.

The slope that avalanched was relatively small compared to surrounding terrain, but the trees and tree wells in the runout created debris piles up to several meters deep.The depth of the burial, and the location in the dense stand of trees made pinpointing and digging difficult. This, combined with the time consumed digging multiple holes around 6 feet deep, cost the group critical time and delayed access to the victim's airway. 

Media

Images

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Figure 1: Natural avalanche on south to southeast face of Purple Peak visible morning of January 21.
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Figure 2: Natural avalanche on the southeast face of Ruby Peak visible morning of January 21.
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Figure 3: Blocks of the slab below the bottom edge of the crown.
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Figure 4: Cracks extending beyond the southern flank of the slide, where the slope angle mellowed out to 30 degrees.
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Figure 5: Debris on the southern flank of the slide.
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Figure 6: Estimated uphill path of Riders 1 and 2 (red line) and trigger point (red star). The yellow and red ovals indicate the approximate location of the victim and the snowmobile.
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Figure 7: Google Earth image of the accident site. The avalanche is outlined in red.
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Figure 8: Looking downhill at the extent of debris. Debris piles were several meters deep near the trees.
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Figure 9: Looking down slope at the tree well where the victim was buried.
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Figure 10: Looking down slope from the crown towards the approximate trigger point (in red) and approximate burial location (in yellow).
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Figure 11: Looking north along the crown face.
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Figure 12: Looking north along the crown face.
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Figure 13: Looking north towards the crown (Image courtesy of Irwin Guides).
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Figure 14: Looking northwest across the bed surface of the avalanche.
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Figure 15: Looking northwest towards the crown. The first profile was conducted at the red oval. The second profile was conducted at the green oval.
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Figure 16: Looking southwest at the slide from Scarp Ridge. The avalanche is bottom center of the image. The south ridge of Ruby and Beckwith Range in the background (Image courtesy of Irwin Guides).
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Figure 17: Looking southwest towards the avalanche from Scarp Ridge (Image courtesy of Irwin Guides).
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Figure 18: Looking towards the southern flank of the avalanche.
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Figure 19: Looking uphill from the burial location towards the estimated trigger location (in red).
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Figure 20: Southern Ruby Range. The avalanche site is indicated by the red arrow. Older slides visible on Ruby Peak (foreground) and Purple Peak (background).
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Figure 21: The jump that the group had built that day. They were snowmobiling up to the run-in of the jump when they triggered the slide

Snowpits

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Figure 22: Crown profile of avalanche on Ruby Peak. ESE aspect 11000 ft. 1.21.16
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Figure 23: Crown profile of avalanche on Ruby Peak. ESE aspect 11000 ft. 1.21.16