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Karl Birkeland, Avalanche Specialist Gallatin National Forest Avalanche Center
The set up
Like much of the country, southwest Montana has had a slow start to the snow season. A couple snow storms in October began our season - the snow mostly melted away in the Bridgers, while in the area around Big Sky the October snow lingered into November. In November we had two main storms...the first was toward the middle of the month and the second was around Thanksgiving. This was followed by cool, clear weather which resulted in some surface hoar formation, widespread faceting of the near-surface layers, and continued depth hoar development. On Monday, December 8th and Tuesday December 9th approximately 12 inches of new snow fell at Bridger Bowl, which is still now open, and 6 inches fell at Big Sky, which is partially open. The new snow was accompanied by strong north, northwest, and west winds which continued after the snow stopped falling.
December 9th, 1997
On December 9th a group of three skiers and one dog headed up into the Challenger lift area of Big Sky Ski Area, which was still closed. Only minimal avalanche control work had been done so far this season in this area, which is now easily accessible by backcountry skiers due to a new development at the base of the lift. As the three were skinning up an area known as "Outer Limits" they triggered an avalanche on a small, steep rollover. The average slope angle of the bed surface was 36 degrees, with a maximum angle of 40 degrees and a minimum angle of 33 degrees. The slide failed on the near-surface faceted snow formed after Thanksgiving, and it broke out 50 cm deep (deepest part was 85 cm and it tapered to nothing on the sides), about 30 m wide and ran about 20 vertical meters downslope. The slab, which was primarily wind deposited, varied from soft (fist hardness) to hard (pencil hardness). All three skiers were caught, carried, and partially buried in this small terrain trap with only their heads out of the snow, while the dog managed to stay on the surface. One person also had his shoulders out, and he was able to get his shovel out of his back pack and dig himself out before working on extricating his partners in a process that took about an hour. The party was well equipped and aware of potential avalanche dangers but underestimated the instability as well as the ability of this small slope to produce a sizable avalanche. Subsequent conversations with Jon Ueland and Randy Spence (Big Sky Snow Safety) indicate that this slope frequently loads up and slides with north/northwest winds.
December 10th, 1997
Winds continued into the 10th at Bridger Bowl, where four people (three skiers and a snowboarder) were just one of several groups that headed up to make turns. Bridger has not been open yet this year, nor had there been any avalanche control work done by this date. The four headed to an area known as the Apron and worked their way up the slope between the Apron and Northwest Passage. They stopped above a small cliff in an area commonly loaded by north winds and were putting on their gear when they triggered an avalanche that was reportedly 3 to 4 ft deep and 40 ft across. It broke out 20 ft above them and caught three of them, slamming them all over the cliff. One person was deposited there, one person was carried about 200 ft and the other was carried about 400 ft. All of them were able to stay near the surface of the soft slab slide and were able to get themselves out once the slide stopped. None of them were injured, but all of them were a bit bruised up. All were carrying avalanche beacons and shovels, but they again underestimated the instability and put themselves on a slope with potentially dangerous consequences. These were not the only group up at Bridger Bowl the last several days. There have been numerous reports of triggered avalanches. My favorite is the person who reportedly went up by himself, walked up the hill and triggered a slide that carried him a couple hundred feet. He dug himself out, headed back up and triggered another slide which carried him down the hill again. At that time he decided to head home. Nothing like learning from experience!
What we are seeing in Montana is not unique. Like the
incident earlier this year at Taos, more and
more people around the west are heading to the
ski hills before they are open. We feel that these folks feel "safe" at
the areas since the terrain is so familiar. Some of the people are
completely unaware that avalanches exist in these areas, while others are
aware, but tend to be a little less vigilant in their backcountry routines
(like only exposing one person to avalanche danger at a time). The end
result is that we have seen an increasing number of avalanche incidents
within the boundaries of the ski areas both before they are opened and
after they are closed. Our response has been to try to educate people
(through our advisories and the media) that they are heading into the
backcountry when they go to the ski areas before or after the ski season.