THREE SNOWMOBILERS CAUGHT, ONE KILLED IN MONTANA AVALANCHE February 25th, 1996 Three snowmobilers were caught in a large avalanche they triggered while riding in the Lionhead area, located approximately 12 miles west of West Yellowstone, Montana. The avalanche released in a northeast facing bowl at an elevation of 9500 feet. The slide was 3 to 5 feet deep, 600 feet across, and ran approximately 800 vertical feet. The slope angles in the bowl ranged up to 45 degrees, with much of the area between 35 and 40 degrees. Branches were ripped off of trees up to 18 feet above the ground, some trees with trunk diameters larger than 12 inches were knocked over, and rescuers estimated that the depth of the debris in the deepest areas was over 20 feet. Montana has seen variable weather conditions this winter, ranging from subzero cold to mountain temperatures in the 40's with rarely much in between. A clear spell in late December resulted in the formation of a widespread weak layer. Subsequent burial of this layer in January led to a number of avalanche incidents. The end of January brought bitter cold, with nighttime temperatures down to 47 below in West Yellowstone. After a little more snow, the week of February 11th was warm and dry. On February 17th snow started falling again. Extrapolating data from a couple National Resource Conservation Service SNOTEL sites, it looks like about 3 inches of snow water equivalent fell at Lionhead during the week, with a new snow total of approximately 3 feet. By Thursday, February 23rd, southwesterly winds started picking up, and they really started blowing by Friday. Big Sky Ski Area (located approximately 40 miles north of Lionhead) had their upper mountain lifts shut down due to wind all day Friday and Saturday. Their datalogger at the top of Lone Peak (elevation 11,166 ft) recorded periods with average winds over 50 with gusts in excess of 70 mph. Field tests on Saturday indicated that there were several potential weaknesses within the snowpack, and on the avalanche advisory we were warning everyone that all slopes steeper than 35 degrees had a high snowpack instability. New snowfall stopped and winds began to diminish on Sunday. The advisory for strongly warned the public of the danger of avalanches on all steep slopes, especially those with recent wind loading from the southwest winds. On Sunday a group of three snowmobilers headed for a ride in the Lionhead area. The weather was mostly fair, with partly cloudy to mostly sunny skies. One of the three riders was a snowmobile guide in West Yellowstone riding on his day off. The other two riders were friends of his from Minnesota. Before they headed out the off-duty guide told the other two riders that avalanches were possible and that if they were caught in a slide that they should swim. That tip probably saved their lives. None of the riders was wearing an avalanche transceiver, or carrying a shovel or probe poles. The details of where exactly the people were on the slope is somewhat sketchy. It appears that one rider had made a low pass on a small steep slope at the edge of the bowl and was a couple hundred feet from the bottom of that slope with his back toward the slope. A second rider had his side to the main slope and was about 30 feet away from the first rider. Meanwhile, the off-duty guide made a higher pass on the small slope. He reportedly got stuck and pulled his machine around. Then he rode to the bottom of the slope and stopped with his back to the slope when the slide hit him. The avalanche that was released was large and fast moving. The two riders who were lower on the slope were hit so hard they were blown right off their machines, and they immediately started swimming. The slide carried them over and up a small hill and turned to the right, carrying them between two groups of trees before burying them with their feet touching each other. One person was buried to his neck and the other to his chest. One person said that he was under the snow almost completely until the snow stopped. Their snowmobiles were located right uphill from them, with one about 5 feet above them and the other one about 40 feet above them. The off-duty guide was carried to approximately the area that the other two people were hit by the slide and was buried under his snowmobile under about 4 feet of debris. Shortly after the avalanche hit, which was around noon, another group of snowmobilers happened by the site. Luckily, they were from the West Yellowstone Search and Rescue group and they were out for a ride, and they radioed for help. The initial group dug out the two partially buried victims, did a quick scuff search of the site, interviewed the other victims, and identified a last seen point. They then began some probing, focusing on a group of trees that was a likely burial area. The rescue group in West Yellowstone was on the trail with a search dog 15 minutes after the page went out, and arrived on the scene at approximately 1:50 pm. A well coordinated search was conducted with the dog and with an organized probe line, as well as a continuing scuff search with probing and digging in likely burial areas. Since the depth of the debris was well in excess of the length of the available probes, probing was difficult and frustrating, and often required digging into the debris to probe more deeply. Additional equipment and manpower arrived throughout the day. Around 8:00 pm a metal detector located the victim's snowmobile. Upon uncovering the upside down machine, the victim was found. The victim's location was somewhat to the side the fall line below the last seen point, and was right next to the edge of the debris. This area was not deemed to be a high probability area for burial, and was not extensively searched by the dog. Rescuers noted that there was a great deal of spilled gasoline from the snowmachine which may have further hindered the search dog. I visited the site the day after the avalanche, and I concur with the rescuers that, given the last seen point, this did not appear to be a high probability burial location. I dug a snow profile with Doug Chabot on the northern flank of the avalanche the day after the slide. It appeared that failure occured on a layer of faceted grains that were probably formed during West Yellowstone's late January cold spell. The depth of the fracture at the pit site was 100 cm, with 65 cm of settled new snow that fell during the past week over a thin ice crust formed during the previous week's warm weather, and 35 cm of older snow. The good news: the swimming motions of the two survivors (on the advise of their friend) quite possibly helped them to stay near the snow surface, and may have saved their lives. The initial rescue party took all the right steps, doing a scuff search, interviewing witnesses, identifying a last seen point, and searching likely burial areas. Finally, the West Yellowstone Search and Rescue group conducted a well organized, high quality search in a remote backcountry location. The bad news: the victims ignored the snowpack and weather conditions, and the warnings of the potentially dangerous conditions (a copy of the avalanche advisory for Sunday is attached). They carried no avalanche rescue equipment, and they were plaing on a slope with the most dangerous conditions given our recent southwest winds - a steep northeast facing bowl. Finally, they exposed everyone to the avalanche danger. With a little more bad luck, this avalanche could have killed all three people. If people have questions or comments, they can contact myself or Ron Johnson at (406) 587-6984. Karl Birkeland Avalanche Specialist February 27th, 1996 GALLATIN NATIONAL FOREST AVALANCHE ADVISORY SUNDAY, FEBRUARY 25TH, 1996 Good morning, this is Doug Chabot with your Gallatin National Forest Avalanche Advisory for Sunday, February 25th, issued at 7:30 am. The next advisory will be issued tomorrow morning. Today's advisory is sponsored by Friends of the Avalanche Center, an independent non-profit group supported by folks like you. This advisory does not apply to the local ski areas. The weather continues to produce snow. Yipee!!! There is a band of very moist air extending from the southwest that is colliding with an arctic air mass over our area. And the jet stream overhead is providing the needed dynamics to wring snow out of the clouds. Bridger Bowl is showing the most snowfall accumulation with another 16 inches in the last 24 hours. That brings their storm total to about 22 inches. To the south of us the storm has dropped anywhere from 6 inches to 2 feet of new snow. The ridge top winds in the Bridgers are averaging 30mph with gusts of 50 from the east and these should calm down a bit today. For all other areas the wind should be out of the southwest at 10 - 15 mph on the ridges. The temperatures are cooling off, with highs expected in the teens. This should make for a cold wind chill. The snow will continue today, with accumulations of 6-10 more inches in the mountains by tomorrow morning. That should be enough to satisfy the powder hounds in all of us! The mountains in our area continue to get loaded from the recent snowfall and widespread wind. This is creating various problems with the snowpack throughout our entire region. Karl and I went to Bacon Rind yesterday amidst the snowfall and swirling winds. This area is south of Big Sky, and the snow was deep. As we broke trail up to the ridge top we felt collapsing of the snow numerous times. With a closer look at the snowpack we found a buried surface hoar layer underneath all of the new snow that we received since Monday (about 2 1/2 feet). This layer was more prominent at the higher elevations and also on more northerly aspects. This layer is weak and is the main concern with the continued snow loading that we are currently getting. This buried hoar layer is consistent with the what has been observed in other areas in the southern mountains. In the northern areas this layer is absent, but other problems are developing there. And they relate to WIND. Southwest Montana has been quite a windy place these past few days. And if you step outside you'll see that today is no exception. In the Bridgers the wind has been blowing quite hard out of the east. The wind typically doesn't blow out of the east, so if you head into the Bridgers you'll have to pay particular attention to unusual loading conditions that these winds can cause. The Bridger Bowl Ski Patrol is reporting that the east winds are predominantly effecting snow from the ridge tops to about 300 feet down. Down in the southern areas the winds have been from the west-southwest. And they too have been blowing very hard. The Big Sky Ski Patrol is reporting widespread wind loading. It's also been reported to be quite windy in the mountains around Cooke City. Remember that wind is a wonderful transporter of snow. So with all the new snow that we've gotten, I recommend paying attention to the lee sides of ridge and gullies. This artificial loading could easily create avalanches, especially with a human trigger. It's also worth noting that there might be some wind slabs that are hidden from view because of all the fresh snow. So be extra careful as you travel around. We are very close to issuing an avalanche warning for the southern areas because of the recent loading and associated weak layers. Use extreme caution when traveling in the backcountry. Everyone should be familiar with identifying avalanche terrain and the quick use of an avalanche beacon. FOR TODAY I WOULD CALL THE SNOWPACK INSTABILITY HIGH ON ALL SLOPES STEEPER THAN 35 DEGREES IN THE BRIDGER, GALLATIN, AND MADISON RANGES. THIS INCLUDES THE LIONHEAD AREA OUTSIDE WEST YELLOWSTONE AND THE MOUNTAINS AROUND COOKE CITY. FOR SLOPES LESS THAN 35 DEGREES THE INSTABILITY IS MODERATE. But, please remember, that even with a moderate instability avalanches are possible, especially in light of all this snow and wind. If you're interested in increasing your avalanche skills, there is an advanced avalanche course being offered next week. The focus of the course will be to improve your backcountry decision making. Participants should have taken a basic avalanche course and feel good about using their avalanche beacon. The class is being offered through the ASMSU Outdoor Recreation Program, and will take place during the evenings of February 26th and 28th, with a field session on March 2nd. Pre-registration is required. Call 994-3621 for more information. Advisories are issued every day of the week except on Tuesdays. I will issue the next advisory tomorrow morning at 7:30 AM. If you have any recent snowpack or avalanche information to pass on, please give us a call at 587-6984. This advisory is also available on a recorded message at 587-6981 in Bozeman, 838-2341 in Cooke City, and 646-7912 in West Yellowstone. Advisories are available on the Internet at http://www.csac.org.