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Mt. Alyeska Avalanche
From "The Snowy Torrents"
April 14, 1973, 1 lift terminal destroyed. Weather Conditions:
From the first of April until midmonth, unsettled weather
prevailed over south-central Alaska. At Mt. Alyeska Ski Area,
it was mostly rain at the base area, mixed rain and snow with
high winds at 1,200 feet, and snow and high winds at higher
elevations. From April 6 to 10, 54 inches of new snow were
recorded. On April 11, skies were broken with intermittent snow
flurries. A new storm hit the next day with high winds and
continued into the 14th with gusts up to 50 and 60 mph. One
gust of 120 mph was recorded shortly before the power failed on
the 13th. On the morning of the 14th, an approximate
measurement showed 28 inches of new snow. Temperatures at the
1,200 foot elevation level remained fairly constant. From April
7 through 14, the temperature remained near 30-32 F. Saturday
morning, April 14, brought heavily overcast skies with snow,
light winds, and an air temperature of 33 F
Accident Summary: On the morning of April 7, after avalanche
control work, Snow Ranger Chuck O'Leary and Don Conrad, an
employee of Mt. Alyeska Ski Area, decided to close the area due
to bad weather and hazardous avalanche conditions. Seven rounds
from the 75-mm howitzer fired at Max's Mountain I resulted in
five large avalanches. One, the Slalom Avalanche, came down
quickly until it reached wet, heavy snow then rapidly slowed
down, almost coming to a stop. From there the snow moved more
like a lava flow than a snow avalanche and finally came to rest
about 300 feet above Rope Tow 3. Watching this avalanche,
Conrad became concerned; it was the same kind of avalanche that
had run from the upper area through the canyon and into the base
terminal of Chair 1 on April 12, 1969 (see "Mt. Alyeska
Avalanche", 4/12/69).
Conrad suggested delaying further control work in the upper area
until it stabilized. They fired seven rounds into the Shadows
area, releasing four large avalanches and then agreed to delay
shooting the upper part of the mountain. On April 8 and 9, the
area remained closed. Explosives and protective skiing measures
were used to release several small avalanches; the shooting of
the upper area was again postponed. On April 10, control work
began in the area from the Saddle to Alyeska Chute. They fired
13 rounds, but no large slabs and only small loose releases
resulted. The snowpack could not be dislodged. The ski area
was opened to the public on a limited basis, but a storm totally
shut down the area again on Friday the 13th, and the storm
continued into the early hours of the 14th.
At 03:40 hours on Saturday, April 14, the area known as Sunspots
released. A large, hard-slab avalanche accelerated down the
cirque wall into the ski area. Striking the wet snowpack, it
slowed rapidly, but this scarcely diminished its destructive
potential. Seconds later, it crashed into the lower portion of
Chair 2.
Later that morning, a patrolman climbed the Racing Trail to
assess the damage. He saw that the lower terminal of Lift 2 had
disappeared beneath the avalanche debris. Following control
work, O'Leary and others inspected the damage. They found the
cable broken and chairs scattered along the slope. Although
most of the avalanche debris was deposited in the upper part of
the canyon, they found one base tower some 1,200 feet down in
the canyon. The avalanche had also snapped the data cable
between the wind instruments higher on the mountain and the
recorder at the base area. The data trace stopped abruptly at
03:40, and thus the time of the avalanche was known.
Avalanche Data: This avalanche, classified as HS-N-S-G, started
at 2,700 feet in elevation and came to rest at the 800 foot
level, a vertical drop of 1,900 feet. The fracture, estimated
at about 8
feet in height and 900 feet in length, developed underneath the
steep rock walls of the west-facing slope. The avalanche
started as a hard slab on the 35-45 degree slope. It began
moving as a wet-snow avalanche near the lift terminal and
continued into the canyon.
Comments: A key factor here was the decision on April 7 not to
shoot the upper bowls. O'Leary and Conrad wanted to avoid a
repeat of the April 12, 1969, avalanche wherein the base
terminal of Chairlift 1 had been damaged. Avalanche and weather
conditions in 1969 had been almost identical to those facing
them in April of 1973. Their dilemma was whether to chance
creating a large avalanche or to wait until the lower slopes had
stabilized before shooting. They choose the latter course, and
when they did implement control measures on April 10, shooting
was ineffective. Then the area was hit by another large storm.
Following this accident, several changes were made at Alyeska
Ski Area. When Chair 2 was rebuilt, the lift was shortened and
the terminal moved uphill to the toe of the south-facing slope
thus moving it away from the mouth of the canyon and out of
range of the Sunspots avalanche. In addition, the canyon itself
was slightly modified. By deepening, rechanneling, and
constructing a diversion dam, ski area managers planned to slow
down any avalanche headed for the base area. They also began
more control work with a larger gun. The 75-mm howitzer was
replaced with a 105-mm recoilless rifle. The more powerful
weapon gave the area the capacity for continuous blind firing
during prolonged periods of poor visibility. By preventing large
accumulations of snow in the avalanche starting zones, the
potential for large, destructive avalanches has been decreased.
Since 1973, no avalanche has run the length of the canyon. |