Avalanche on the Shuksan Arm

Summary: 1 snowboarder dead; 1 skier caught,buried-still missing and presumed dead

Location: Mt Baker Wilderness, just east of Mt Baker Ski area on Shuksan Arm
(just above the accident that occurred on 1/18/99) Elevation and aspect:
5400 ft (1646m), N-NE aspect; vertical fall ~1800 ft (549m)
Size: SS-N-5 ?? (previous skiers or snowboarders may have caused beginning
of shear failure to old crust, unclear whether there were other
skiers/boarders near the crown at the time of failure, but appears unlikely)
Weather: Partly cloudy
Preliminary Accident Narrative:
The day of the accident appears to have been the first time that the slope
on which the avalanche released had been skied or boarded for a week or
more. The slope which released was a convex roll that wrapped around a
cliff band and vertical rib about 100 yards beyond the developed area and
into the Mt Baker Wilderness. Slope angles near the fracture line were
estimated in the 30-45+ degree range, depending on the exact location of
measurement, with the size of the slab dimensions about 12-14 ft deep X 450
ft wide X 150-200 ft vertical, with this initial slab triggering multiple
secondary releases of 1-4 feet or more. Weight of the initial slab release
were estimated as containing 1-3000+ tons of snow, with significantly more
snow entrained by both the initial slide and the numerous secondary
releases. The class 5 avalanche (US classification, Size 4 in the Canadian
size scale) descended about 1800 ft (549m) vertical, overrunning several
lower benches, depositing large amounts of debris in both bench areas
(estimated at 10-20 feet + for over 100 yards), and destroying several trees
adjacent to the lower bench. Wind blast from the slide also was reported as
knocking over several skiers who witnessed the event from a knob just above
the lower bench/gully area. From piecing together eyewitness reports, it
appears that the snowboarder was in the process of traversing across the
path run-out just below the cliff band when the slab released. He
apparently tried to outrace the slide but was caught within the upper bench
area and his last seen area was marked and provided the information
necessary to begin and execute a probe line-which subsequently located the
victim in a vertical head-up position about 9 feet under the surface.
Meanwhile, the avalanche continued over a break-over below the upper bench,
triggering further releases and flowing on toward the lower bench and gully.
Two skiers who were on a knob to the skier's right of the lower bench
apparently saw the slide and attempted to ski out of the way. Unfortunately,
the skiers chose different directions for safety and only one was able to
escape the oncoming slide. The other skier was caught, and buried, with a
ski, hat and glasses blown high onto the flank of the gully and left as the
only visible clues once the avalanche came to rest lower in the gully
adjacent to the base of the Shuksan Arm Chair #8.
This slide probably released on a hard rain crust which was formed following
heavy rain in late December and subsequent cooling in early January. While
most recent avalanche activity had generally involved only the most recently
deposited snow, two other isolated but very large slides were reported
during the previous week or two at locations well removed from the Mt Baker
ski area (Crystal Mountain and Snoqualmie Pass). Also, despite the
insulating effect of very large amounts of recent snow (from 2-400+ inches
of snow during the previous month), there had been reports of poor
attachment of the very large amounts of new snow to the crust as well as
some faceting of the snow just above the crust-which generally was reported
as buried under 6-15 feet of new snow, depending on location.
Ancillary information-Prior to the accident NWAC forecasts indicated a
considerable avalanche danger above 5000 feet, and had singled out northeast
through northwest facing slopes on the northern volcanoes (including Mt
Baker) as having larger and more unstable wind slabs due to heavier recent
snowfall and strong winds.