Avalanche Accident
Report
Preliminary
Monday, December 31, 2007
killed in avalanche
History: Because of its long arduous
approaches, snowmobilers are the predominate user group in the western
weekend
avalanche forecast program. Longer term funding was eventually established and
now advisories are issued on
the busiest
days of the week- weekends and holidays with an additional midweek update on
Wednesday. Since 2001,
there have
been seven avalanche fatalities involving six snowmobilers and one skier, but
each year there are many close
calls that we
never hear about.
Location:
Both Daniel’s
Accident and Rescue Summary: At
approx. 3:00, three experienced snowmobilers were riding in the area when one
rider,
Dale Christensen
started approaching the lower section of the slope and his sled quit running.
Two of his friends watched
from a
distance and discussed going to help their companion and started putting their
helmets on. They don’t know how
the
avalanche was triggered, but they heard something and noticed the avalanche
breaking well above Dale, quickly engulfing all
three riders.
One friend was partially buried, the other with just a hand and foot sticking
out of the snow, but he was located
quickly, dug
out and the two searched for their missing friend. Dale was buried about 3’
deep in a dished out terrain
feature
where debris
piled up very deeply. No one was wearing avalanche beacons, but several probes
and shovels were among the
group and
they found Dale about an hour later, just as Wasatch County Search and Rescue
arrived.
Avalanche Data: The avalanche averaged 4’-5’
deep, about 65” at its deepest
point, was 400’-500’ wide and ran
450’
vertically. Classified as a HS-AM-R4-D3-O, this avalanche failed on weak
facets near the ground. While slope angles
averaged 36
degrees, a steep
breakover about a third of the way upslope was
closer to 40 degrees. It was in this steep,
rocky section
where the snowpack was the weakest. The southern half of the range often
experiences weaker snow and
stronger winds.
Terrain: A 30 minute snowmobile ride gets
you into the steep slopes surrounding the Co-op trailhead. The access
involves
riding on a
low angle, groomed trail which may lead to a false sense of snowpack security.
However, plenty of snow stability
clues can be observed
along the trail. Ridges are usually scoured down to sage brush, large cornice
formation is easily seen in
distant bowls
and if you get off-trail it’s relatively easy to sense the inherent weakness in
the snowpack. There are literally
hundreds of
bowls where a rider could get into trouble.
Weather and Snowpack History: The
western Uinta snowpack is historically plagued by cold temperatures, shallow
snow
depths, very weak
snow and strong winds… this winter is no exception. An active weather
pattern in October, deposited early
season snows
above 9,000’ and it looked like a banner start to the season. The storm track
shifted north and the western
Uinta’s were left high and dry
throughout November. The first in a
series of storms began moving into the region on Dec. 1st,
depositing 12” of
snow, followed by a slightly stronger system on Dec. 7th. New snow
totals averaged 14” in the area the
accident
occurred and gusty southwest winds accompanied this storm. An avalanche watch
was issued on the 7th describing
an overall
danger of CONSIDERABLE in upper elevation wind loaded terrain. Clear, cold
weather following this storm allowed
near surface
facet development. A vigorous storm
system on the 21st stacked up an additional 16” of snow and
warranted
issuing an
avalanche warning as high winds and heavy snow created a HIGH avalanche danger
on steep northerly facing slopes.
A natural, albeit pockety, avalanche cycle occurred during the storm. The 22nd
dawned clear and cold and with new snow on a
weak
pre-existing snowpack, we knew all the ingredients for an avalanche accident
were aligning. Two snowmobile triggered
avalanches
occurred in the southern half of the range and probably many more that we
didn’t hear about, but no serious
incidents were
reported… we dodged a bullet. Another storm rolled in on Christmas Eve delivering
8” of very light density snow,
but west
and northwest winds gusting in the 50’s along the ridges accompanied the
system. The avalanche advisory posted
on Dec. 25th
called for an overall CONSIDERABLE avalanche danger on steep, upper elevation
slopes and specifically mentioned
there were
pockets of HIGH danger on these same slopes where wind drifts were present. In
addition, the advisory mentioned
“the
possibility of triggering a deep, scary avalanche that breaks into weak snow
near the ground still exists, especially in steep,
upper
elevation terrain facing the north half of the compass”. Unfortunately an
avalanche fatality on Christmas Day occurred near
1000 Peaks in
On the 27th and 29th,
two snowmobile triggered avalanches ran on facets near the ground in steep,
leeward upper elevation
terrain. 2007
went out with a bang as a series of storms continued to pound the region. The
Uinta’s were on the storm tracks
cusp and
what we lacked in storm snow we made up for with wind. West and northwest winds
began blowing on the evening
of Dec. 29th
with hourly averages in the 30’s, gusts in the mid 40’s. By the evening hours
of Dec. 30, nearly a foot of new
snow stacked
up and winds raged in the 70’s and 80’s. A Special Avalanche Advisory was
issued to warn the public of the HIGH
avalanche danger.
We continued the Special Advisory for Dec. 31st and most of our
local media contacts advertised the increased
danger for the
western Uinta’s in their newscasts. I warned of “large dangerous slides,
breaking into old snow near the ground,
especially on
steep, rocky, upper elevation slopes resulting in an unsurvivable avalanche.”
