|
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
|
|
