2018/03/04 - Washington - Setting Sun Mountain, north of the Methow Valley

Published 2018/06/15 by Matt Primomo and Dennis D'Amico - Northwest Avalanche Center

Height of snow in the area the day after the incident ranged from 51” to 63” (130 cm to 160 cm). The upper snowpack was composed of decomposing fragmented and rounded grains likely from the two storm events that began late February and ended in early March. The mid-pack was a layer of rounding facets over a crust/facet sandwich. The crust likely formed from rain in early February while the faceting occurred during two periods of very cold temperatures. Beneath this pair of thin crusts, the lower snowpack was composed of basal facets and chains of depth hoar. Snowpack tests in a crown profile done the following day showed that cracks could propagate along the slab weak-layer interface down about 18” (45cm) from the surface, though no failures occurred on the thin crust that acted as the bed surface for the slide.

On Saturday 3/3, the party skied 30-33 degree terrain on the northeast shoulder of Goat Peak, (4 miles south of Setting Sun Mt). They dug 2 snow profiles on north and east aspects, looking for persistent weak layers and for recent wind slabs. They reported a Compression Test 12 on the 2/28 interface, which was small faceted grains. They did an Extended Column Test and it did not propagate. Rider A reported hearing a whumph, though Rider D stated he did not hear or feel any whumphing or collapsing this day. They had a great day out and made plans for the next day.

On Sunday 3/4, the party snowmobiled up with 4 machines toward Setting Sun Mountain. They were breaking trail by approximately 10:00 am and worked their way up the South Ridge of Point 7054. On the way up, they kicked small chunks of cornices on both sides of the ridge with minimal results. When they got to the top of the ridge, the group noticed wind drifting had occurred on both sides. They discussed their options and decided to further evaluate the Northwest facing slope below. Rider D descended approximately 20 ft into the upper part of the slope, found a location to dig a snow pit, utilized his probe to check depths, and began excavating. Skier C skied down to Rider D and they spoke about what they were finding. The snowpack where they dug their snow profile was approximately 47”  (120cm) deep. They discussed finding a crust/facet sandwich down 24” (60cm) and loose facets near the ground. They performed a Compression Test with no results. Meanwhile, A and B stayed on the ridge. They did a Shovel Shear Test, and an Extended Column Test but had no results on either. They decided to ski the slope.

Rider A did a ski cut to skier’s right of the open starting zone, then continued down crossing back over to skiers left. He stopped about 300 ft down on skiers left in thicker trees below the roll over. He then radioed up to send the next skier. Rider B was the second person on the slope and made approximately 4 turns before the slope fractured and slid. C and D yelled aggressively to alert Rider B of the avalanche. Rider A was waiting to the side, saw snow and trees flying above him but was able to slide out  of harm’s way. The avalanche occurred at approximately 1:15 pm.

Rider A radioed up to Rider D confirming he was “OK”, and began downhill with his beacon in search mode. C & D turned their beacons to search mode, and began searching the upper slope in parallel. Rider A got a signal, then stepped out of his board and continued following it. He found Rider B on top, partially buried headfirst after approximately 3 minutes. Rider A radioed up and alerted the rest to come down to help. Rider A dug out Rider B’s face without a shovel, opened his airway, and found that he had severe head trauma. He had no pulse.

When the others arrived, they moved Rider B onto his back and did CPR for 15 minutes. They made a call to 911 at 13:44 from the accident location and texted others. They attempted to improvise a litter but realized they needed to focus more on getting themselves out safely. Rider D relayed their GPS location to the Deputy and they began their way down.

On the way out, the group experienced a large whumph. They backtracked a bit, finding a thick stand of trees to travel through. Once safely back on the lower ridge, they skied down to their snowmobiles and rode out.

Early the next morning, Sid Patterson (NCMG/NCH) and Matt Primomo (NWAC) snowmobiled and skinned up to the area. They were met by Paul Butler (NCH) who got dropped off on the peak by helicopter after making an aerial survey of the scene with the Deputy who acted as Incident Commander for the search and rescue operation. The three of them safely navigated to the bottom of the debris and found B. From there they coordinated with the helicopter pilot who lined a litter into an open area nearby. They loaded the victim, Rider B, and performed a short haul rescue via helicopter. They then climbed up the slope to further investigate the path and the crown.

After the accident and investigation, a number of professional guides and forecasters commented how the snowpack on this slope was atypical or anomalous for the region at the time. The snowpack in this area was surprisingly thin and weak in comparison to more frequently traveled areas in the Washington Pass/Hwy 20 corridor.

The thin snowpack was likely due to its position in the range further east of the crest. The prevailing winds were from the Northwest for much of February, which tends to scour this slope near the starting zone. The arctic air that was responsible for the very cold temperatures in February likely exacerbated the faceting process on this locally shallow snowpack. The February 28th storm likely built a slab over the weaker old snow.

NWAC would like to thank all of the survivors of this tragic accident for their help on this report and to commend them on their willingness to be open with details and decision-making so that others may learn from it. We would also like to thank North Cascades Mountain Guides/North Cascade Heli, Deputy David Leeman, and the rest of the community in the Methow Valley for their continued help and support.