The Avalanche Review, VOL. 10, NO. 5, MARCH 1992
Copyright © All Rights Reserved; AAA

The Alpine Meadows Avalanche:

ONE EXPERT'S RECOLLECTIONS

By Chris Stethem

The Alpine Meadows avalanche of March 1982 was a tragedy that will not soon be forgotten by avalanche workers in North America. I was one of the outside experts who were brought in, long after the accident, to analyze the events in preparation for the 1985 trial in Auburn, California. The key issues were the foreseeability of the avalanche and the control measures taken prior to the accident.

An outside expert perspective is vastly different from that of the people who were there. Most of the experts had no experience at Alpine, but had the advantage of looking at the accident in hindsight and with lots of time to go over the accident with a fine-toothed comb. Those who were there making critical decisions during the height of the storm had to do so under pressure based on their experience and intuition.

Alpine had an approved snow safety plan in place. That plan, like most ski area plans from a similar era, relied on hazard evaluation and explosive avalanche control. Up to the time of the accident, that snow safety programme had worked for them. Should they then have recognized in March 1982 that something was about to go terribly wrong?

In operational avalanche forecasting and control we rely on our experience and local history when making decisions. The key issue, in my opinion, was therefore whether this storm was within the experience of the Alpine team and what actions were taken in comparison to past events.

The March 1982 storm was a big one, but was it unprecedented? Local knowledge suggested it was one of the biggest, but not unheard of. To answer this question, I compared the March 1982 storm trends to the records of other storms compiled at Alpine since the late 1960'x.

Nearly 8 inches of water equivalent was recorded in the snowfalls up to the morning of the 31 st of March. Winds were strong from the southwest, up to 90 mph at the ridge on the 30th. Base area temperatures started out above freezing, cooled to approximately 15 degrees F. and then warmed into the high 20's near the storm's end.

The long-term records indicated the prevailing storm wind was southwest and local knowledge suggested strong wind was common. Detailed wind records from the past were not available, as a heated anemometer had only recently been installed at the ridge. Base area temperatures in the range from above freezing down into the teens were also common during storms.

Accepting the fact that all storms and snowpacks are unique to some extent, I concentrated on the issue of precipitation, or load, in comparing major storms. In the Alpine Meadows records, there were fourteen storms with an excess of 5 inches of water equivalent over 72 hours (excluding storms with rain only).

Within these fourteen storms, the precipitation by water equivalent in March 1982 was ranked 14th in 24-hour precipitation amounts, 10th in 48 hours, 6th in 72 hours and 4th in 96 hours (see graphs). From these records, it seemed an experienced person on site would have seen the 1982 storm as a big one, but not something far greater than anything ever before experienced.

I then reviewed the past avalanche occurrence records for the Poma Rocks, Pond and Buttress slopes. Although several artificially triggered slabs and natural wet avalanches had been observed on the slopes, not one natural dry slab was recorded. Nor were there any records of deep slabs, propagations between these slopes or examples of long runouts similar to 1982.

Prior to the accident of March 1982, artillery control was carried out throughout the storm. Most of the firing was blind, with only glimpses of the terrain. Small volumes of debris were thought to have been seen in the Poma-Pond-Buttress area on the 29th and 31 st. At the same time, the team was considering the potential hazard from many paths, several of which were in their experience a greater problem than Poma-PondButtress.

*****
I concluded that the avalanche of March 31st was not foreseeable to the Alpine team and that in fact they were looking to other sites in anticipation of large avalanches. They took their pprogramme to its maximum based on their experience and lost out to Mother Nature.
*****

In light of the past records of similar or greater storms, I concluded that the avalanche of March 31st was not foreseeable to the Alpine team and that in fact they were looking to other sites in anticipation of large avalanches. They took their programme to its maximum based on their experience and lost out to Mother Nature.

It is interesting to note that in February 1986, a huge Sierra storm dumped 26 inches of precipitation at Alpine. The interval precipitation totals up to February 17 at Alpine were: 24 hours-7.67"; 48 hours-11.57"; 72 hours-15.98"; and 96 hours-17.64". These values were between 175% and 200% of past maximum water equivalents.

Although many avalanches ran in the ski area at Alpine during the 1986 storm, nothing ran to the 1982 extent. One size 5 to ground did run on the access road. Above 2500m in other parts of the Sierra, the massive amounts of heavy wet snow resulted in many huge avalanches which pushed their paths to new limits (Wilson 1986).

The avalanches resulting from the exceptional storm of February 1986 pushed the limits of theoretical predictions for the Sierras. The thorny question of acceptable level of risk and what criteria to therefore use for planning guidelines remains.

The question of acceptable protective measures also remains. Our knowledge tells us that if we use explosive control for protection of valley developments, sooner or later we'll shoot down the big one or it won't come until it's ready for the big natural. Planning guidelines therefore suggest other zoning and structural measures for protection. At many ski resorts, however, explosive control remains as the centre point of snow safety operations.

Chris Stethem is an avalanche consultant in Canmore, Alberta. In 1985 he was an expert witness for the defense in the Alpine Meadows trial.

The Avalanche Review, VOL. 10, NO. 5, MARCH 1992
Copyright © All Rights Reserved; AAA