CAIC: Colorado Avalanche Information Center

2010/02/13 - Alaska - Grandview, Placer River Drainage, Chugach NF

Published 2010/03/23 by Bill Romberg - Rescuer, Alaska Mountain Rescue Group


Avalanche Details

  • Location: Grandview, Placer River Drainage, Chugach NF
  • State: Alaska
  • Date: 2010/02/13
  • Time: 11:00 AM (Estimated)
  • Summary Description: 3 snowmobilers caught, 2 buried and killed
  • Primary Activity: Snowmobiler
  • Primary Travel Mode: --
  • Location Setting: Backcountry

Number

  • Caught: 3
  • Partially Buried, Non-Critical: 1
  • Partially Buried, Critical: 0
  • Fully Buried: 0
  • Injured: 0
  • Killed: 2

Avalanche

  • Type: SS
  • Trigger: AM - Snowmobile
  • Trigger (subcode): u - An unintentional release
  • Size - Relative to Path: R3
  • Size - Destructive Force: D3
  • Sliding Surface: I - New/Old Interface

Site

  • Slope Aspect: SE
  • Site Elevation: 1700 ft
  • Slope Angle: 39 °
  • Slope Characteristic: Concave Slope

Avalanche Comments

Witnesses interviewed post-accident reported that avalanche started near large rock mid-slope on north side of path and then continued to propagate north to south further up the slope and up the drainage. One witness described seeing multiple distinct releases as slope "zippered". No crown profile investigation was conducted on 2-13-10 due to hang fire and approaching darkness. A 7-day storm cycle started 2-14-10 preventing rescuers from entering the area until 2-20-10.

Weather Summary

The winter of 09/10 in coastal southcentral Alaska was heavily influenced by El Nino. Many warm storms brought rain to the lower elevations of the Turnagain Arm area in December, January, and February. In between storms, strong inversions set up with dense fog blocking the clear skies above. From Feb. 5 to Feb. 12, Turnagain Pass received approximately 4 feet of snow and 4 inches of snow water equivalent at 1800 feet. On February 9, temperatures warmed up considerably and the snow turned to rain below 1000-1500 feet elevation. Winds at 3800 feet in Turnagain Pass averaged 25-45mph out of the east with gusts to 86 mph from Feb. 9 to Feb. 12. February 13 was mostly sunny with light winds.

Snowpack Summary

A significant rain crust formed January 7 up to 3000 feet elevation. A layer of surface hoar formed on top of the crust Jan. 10 and 11 during a short spell of clear weather, and then two feet of snow fell from Jan 12 through Jan 19. Many class 1 and 2 skier triggered avalanches happened January 16-18 that failed on the surface hoar/crust layer. Long-running collapses on facets underneath the crust were also reported at the lower elevations below 2500 feet. Another layer of surface hoar formed when a strong inversion set up for 7 days from Jan 20 to Jan 26. Two days of rain/snow followed and produced a rain crust up to 1600 feet elevation and 6-8 inches of snow at the higher elevations. Two larger class 2 skier triggered avalanches happened on Jan 29 at 3000 feet elevation that ran on the most recent layer of buried surface hoar. Another strong inversion set up from Jan 30 to Feb. 4, and yet another layer of surface hoar formed during this time. 12 inches of snow fell on Feb. 5, and the next day skiers triggered two separate class 2 avalanches at 2500 and 3000 feet elevation. One skier was caught, carried, and partially buried. The avalanches failed on the most recent layer of buried surface hoar that formed on a paper-thin melt-freeze crust. Another foot of snow fell from Feb. 7-9, and then the storm ramped up in intensity. From Feb. 9 to Feb. 12, two feet of heavy wet snow fell at the higher elevations with pouring rain below 1500 feet. Five class 3 natural avalanches happened on February 12 in Turnagain Pass in addition to numerous large artillery-triggered avalanches along the Seward Highway.

Events Leading to the Avalanche

According to witness interviews, two groups of snowmachiners agreed to meet up for a day of riding in the Grandview area. There were a total of 10 riders in the group, some of whom ride in the area regularly, others who were less familiar with the area. The group accessed the ARR mile 45 area from the south (Trail Lakes/Moose Pass) and approached the area below the slope that avalanched from the north through openings in hemlocks. The area that the group was riding in is a classic terrain trap consisting of a 20' deep ravine/creek bed next to a stand of hemlocks at the base of slope 300-500' high with a slope angle that ranges from 33-42 degrees. Based upon the lack of hemlocks on this slope and the obvious flagging of trees as well as broken trees at the base of the slope, this path avalanches with some regularity. The weather was warm with blue skies and sun and witness statements indicate that some members of the party had traveled in the area before. However, the terrain at the accident site is very unforgiving, with high consequence deep burials inevitable in event of an avalanche. Subject #1 (J...)had gotten his machine stuck on a bench at the based of this slope at approximately 1550 ft just south of a large rock mid-slope. Subject #1 was standing next to his machine on the downhill side. Subject #2 (A...) was approx 200' ahead of Subject #1 at a similar elevation further along the bench below the slope riding to the south. Subject #3(C...) rode up to assist Subject #1 circling above him and coming to a stop facing downhill just below subject #1.

Accident Summary

It is uncertain which rider triggered the avalanche, but it is likely the combined weight of several riders caused the initial failure at the base of the slope which then propagated up-slope causing the avalanche. Subject #3 reported that he was three steps off his machine (facing downhill) when he saw the slope to his right start to slide. Subject #3 moved downhill toward his machine and had his hand on his handlebar when debris hit him, throwing him forward onto his handlebars which hammered his throttle and propelled him downslope and out of the debris. Subject #1 (standing by his machine) was overrun by debris and buried in place near his machine. Subject #3 and two other witnesses (who were 200' and 600' away to the north) reported seeing the debris hit subject #2. who was riding his machine south on a bench to the west of the creek bed at approx 10-15 mph. These witnesses reported that subject #2 did not see the avalanche coming and thus made no attempt to escape. At least one other rider following behind the three riders caught in the slide had to turn to downhill and north to avoid getting caught in the debris as well. Witnesses described seeing a series of avalanches ("like dominoes") that occurred over the course of several seconds moving right to left up drainage. Aerial photos show one large path and several adjacent paths at similar elevations but on slightly different aspects having released, two of which appear to be sympathetic releases (one at far left margin of crown, one at far right margin of crown above the large rock).

Rescue Summary

Members of the group immediately began companion rescue. Subject #1 (J...) was located near his machine via transceiver search and was buried approximately 6-7 feet. He was dug out within 30-40 minutes and CPR was performed for over an hour with no success. Another party of 4 riders arrived in the area and assisted with the search for subject #2. Subject #2's snowmachine was found mostly buried in debris on a knoll among sparse hemlocks because a ski was sticking out. The machine was dug out and the area around the machine was spot-probed. However, subject #2 was not wearing an avalanche transceiver and was not located on 2-13-10. Outside rescuers (2 from AST + Helo-1 and 1 USFS enforcement) arrived at ARR mile 47 around 1430 and coordinated transport of subject #1 who was confirmed deceased. A large, warm storm cycle began on 2-14-10 that dropped nearly 6 inches of water-equivalent precipitation at the accident site over the next 6 days--some of which fell as snow and most of which fell as rain at this elevation. The stormy weather finally broke on 2-20-10 allowing organized rescue teams to do avalanche control work around the avalanche site and to access the area to begin searching for subject #2. Approximately 2 feet of heavy wet snow had fallen at the elevation of the debris and both the new snow and old buried debris were very wet and dense due to the heavy rain that had occurred. A large, organized rescue effort involving over 150 people began on 2-20-10 and continued for 3 days. Between 40-60 searchers were transported to the accident site via helicopter (which was approx. 15-20 miles from nearest road access points). Searchers from the Alaska Mountain Rescue Group, AK Search and Rescue Dogs, Anchorage Nordic Ski Patrol and dozens of friends of the buried subject worked the deep, dense debris with search dogs, RECCO, magnetrometers, and organized probe lines using steel sectional probes. The debris zone was largely obscured by the new snow and rain that had fallen in the intervening week, but was pieced together from witness interviews and photos taken by witnesses and AST Helo-1 on the day of the accident. The debris area considered most likely to contain subject #2 was approximately 450' wide by approximately 500' long that extended through the ravine and into a stand of sparse hemlocks. The debris ranged in depth from 6-7' near the PLS to over 15' deep in the ravine and on the west side of the knoll (bottom of terrain trap). Over 30 visible trees were identified and searched within the debris zone. Additional buried and broken trees existing within the debris resulted in numerous false positive strikes with probes/probe lines. Fortunately, daytime temperatures remained at or above freezing for most of the three days of searching which kept the debris from freezing solid. Subject #2 was ultimately located around 1230 on 2-22-10 by an organized probe line working through a search segment in which a significant dog interest area was found. The location of Subject #2 was confirmed by probe strike buried under approximately 10-11 feet of snow--approximately 70 feet from the PLS and over 150 feet uphill and on 30-degree different trajectory than the subject's snowmachine.

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