SYNOPSIS WEATHER AND SNOWPACK

Transcription

1 Peak 6996 Avalanche Fatality Incident Report Glacier National Park, MT Date of Avalanche: 31 March 2010 Date of Investigation: 2 April 2010 Investigation Team: Erich Peitzsch (USGS), Ted Steiner (Chugach Adventure Guides), Jason Griswold (NPS), Brad Blickhan (NPS) PURPOSE Supplemental findings for Glacier National Park avalanche incident report (Glacier Case Incident #10-038) and contribution to a national database of avalanche accidents. SYNOPSIS On Wednesday, March 31, 2010, a lone snowboarder was riding on Peak 6996 (locally known as Palindrome Peak, Little Shields, or False Shields) near Marias Pass in Glacier National Park, MT, was caught in an avalanche and sustained fatal injuries. Rescuers were called to the scene at approximately 1400 on Thursday, April 1, The avalanche investigation took place on Friday, April 2, The avalanche occurred on a northeast facing slope just off the summit of Peak 6996 and funneled into a narrow gully. The average slope angle of the starting zone was approximately 33 degrees and the runout angle was 26 degrees. The crown face was an average of 1.7 feet deep and the slide was approximately 220 feet wide and ran approximately 1800 vertical feet. US classification of the avalanche is SS-ARu-D2.5-R2-O (Greene et al., 2004). GPS Coordinates: Crown: N, W Victim Location: N, W Toe of Debris: N, W Elevation of Crown: 6860 a.s.l. WEATHER AND SNOWPACK Weather data are from the USGS/BNSF/GNP Shed 7 weather station (48.3 N, W; 6363 ft.), Pike Creek SNOTEL site (48.3 N, W; 5930 ft.) and Flattop Mountain SNOTEL site (48.8 N, W; 6300 ft.). At the time of the accident, the winter of was characterized by below average precipitation and above average temperatures. Total Snow Water Equivalence (SWE) for the Flathead River Basin was hovering around 70% of average, but Pike Creek SNOTEL was around 33% of average. Beginning on March 28, 2010 a moist Pacific storm entered the region. From this day to March 31, snowfall amounts at Shed 7 totaled approximately 15 inches during the storm with wind gusts to 75 m.p.h on March 29. Pike Creek SNOTEL, located approximately 8 miles E of the accident site, recorded 1 inches of SWE. Flattop Mountain SNOTEL, located 40 miles NW of the site, recorded 3.2 inches of SWE and approximately 18 in. of snow.

2 The snowpack in the area was a below average, shallow snowpack for the region. Observations in mid-march adjacent to the Shed 7 avalanche path above the railway showed avalanche activity limited to the new/old snow interface after a small storm deposited approximately 6 inches of snow. Collapsing of the snowpack occurred on northerly aspects around 7000 ft. After that, relatively dry conditions persisted until the March 28 storm. The general nature of the surface snowpack varied by aspect with melt-freeze crusts on solar-exposed aspects, and soft surface snow on shaded aspects. Shaded aspects harbored small-grained facets near the surface, and even buried surface hoar in certain locations within the region. The avalanche site was investigated on Friday, April 2, We climbed a preexisting ski uptrack along the SSE ridge of Peak 6996 to the top. Upon summiting, we experienced collapsing ( whumpfing ) of the snowpack. A snow profile completed on the crown of the avalanche showed the storm-deposited snow sitting on a layer of mixed-form faceted crystals over a layer of larger, softer, mixed-form faceted crystals (Figure 6). The bed surface of the avalanche was the larger, softer layer of mixed-form faceted crystals. This layer was an average of 34 inches above the ground. As the avalanche progressed downhill it entrained wet, heavier snow. The bed surface was easily penetrable, and, in some cases, very soft and sugary. Stability tests and a full profile of the crown were completed (Figure 1). The Glacier Country Avalanche Center most recent avalanche advisory (issued March 26, 2010) previous to the avalanche accident read: During periods of thaw between the elevations of 5,000 and 7,500 ft. we rate the wet snow avalanche danger CONSIDERABLE. The dry snow avalanche danger between the elevations of 5,000 and 7,500 ft. is currently being rated MODERATE on all large, steep, open slopes lacking vegetative and terrain anchors. As well during dry snow periods, on anchored slopes below 7,500 ft. and all slopes, all aspects, below 5,000 ft., we're rating the avalanche danger as LOW. These danger ratings expire at midnight, Friday, March 26th. The outlook is for the avalanche danger to remain at current levels through the weekend. AVALANCHE Prior to the investigation, Glacier National Park released a press release that read, The fatality was reported to park rangers around 2 p.m. on Thursday, April 1. The reporting party told rangers they had last heard from [the victim] at 6 p.m. on Tuesday, March 30 when [the victim] texted friends that he was on Mt. Shields (elev ft.). When friends did not receive responses to subsequent text messages on Wednesday, they grew concerned. Thursday, a friend located [the victim s] vehicle at the Fielding Ranger Station trailhead and skied up to Mt. Shields where [the victim s] body was spotted high in a gully within the slide path of a recent avalanche. The backcountry party skied out and called park headquarters to report the avalanche and fatality. Details of the actual avalanche event are non-existent because the victim was alone. According to friends, the victim was very familiar with the area and snowboarded there quite often. Friends

3 believed that that the victim had an avalanche transceiver, but neither his transceiver nor backpack were found. Based on the investigation, evidence suggests that the victim completed two descents on the SSE ridge adjacent to the ski uptrack before beginning his descent down the NE slope (avalanche site) from the summit of Peak The victim s tracks intersect the avalanche debris from skier s right approximately 390 vertical feet from the summit (elev ft.) below a short, steep convexity. This entry point was approximately 250 ft. below the highest point of the crown. Another 533 ft. below that point (elev ft.), blood-stained snow was found among sapling sized trees. Just below this point and to the skier's left, snowboard tracks exited the debris and descended to where the victim s snowboard was found at 5868 feet. These tracks appear to be the tracks of the victim and the tracks the reporting party stated that he had seen when he found the victim. The victim s snowboard was located by the reporting party and placed vertical in the snow at the location where it was found. Investigators located the snowboard approximately 210 ft. below the exit track (elev ft). The victim was found an additional 441 ft. below the snowboard (elev ft.). The victim was located face-down on top of the avalanche debris with his head in the uphill direction. The toe of the debris was at an elevation of approximately 5080 ft. and measured approximately ft. in depth. Based on the above evidence and measurements, it appears the victim self arrested at around 6080 feet, traversed and descended on his snowboard skier s left across the slope to 5868 feet where he left his snowboard, and then descended the path on foot to his final point of rest at 5,427 feet. The map and images below illustrate the aforementioned observations (Figures 2-6). Again, because specific event details are unknown these observations are from evidence gathered during the investigation only. SEARCH AND RESCUE Glacier National Park rangers were notified of an avalanche fatality around 1400 on Thursday, April 1. National Park Service personnel were dispatched on the ground initially and skied into the site. Additional National Park Service rescuers were flown to the site via helicopter to recover the victim and arrived first on scene. This report was written to ensure accurate information is available and to assist others who may encounter themselves in similar situations in the future. This document will supplement an official report completed by Glacier National Park, and will become part of a database of avalanche accidents. Direct any questions regarding this report to either tedshred@centurytel.net or epeitzsch@usgs.gov or

4 PHOTOS AND MAPS Figure 1: Crown profile of the avalanche.

5 Figure 2: Looking down the avalanche path from just above the highest point of the crown.

6 Figure 3: Looking up from the track of the avalanche path.

7 Figure 4: Looking up from the victim s final point of rest.

8 Figure 5: Overview topographic map of the avalanche site.

9 Figure 6: Google Earth image of the avalanche site and points of interest. REFERENCES Greene, Ethan M., K. W. Birkeland, K. Elder, G. Johnson., C. Landry, I. McCammon, M. Moore, D. Sharaf, C. Sterbenz, B. Tremper, and K. Williams Snow, Weather, and Avalanches: Observational Guidelines for Avalanche Programs in the United States. Pagosa Springs, CO: American Avalanche Association. 140 pp.