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Below is an account of a partial burial avalanche on the boundary of the Big Mtn Ski Resort in Northwestern Montana. This report was made by Kraig Lang, snow ranger and avalanche advisor for Glacier Country Avalanche Center. The victim was very lucky. Thanks much----Stan
1/29/98 Big Mountain Avalanche Report - Partial Burial
Weekly Weather Observations:
High for the Week - 38Fbr High for 24 / Hrs - 31Fbr Low for the Week - 14Fbr Low for 24 / Hrs - 18Fbr Current Temp - 29Fbr Total Snowpack - 67"br New Snow 24 / Hrs - 0"br Current Wind - 15 mph / SWbr
On Thursday 1/29/98 at about 1230 hrs we had a partial burial of an alpine skier in a hard slab slide on "FAA" peak just west of the Big Mtn Summit. The individual was part of a five person group that had gone just outside the ski area boundary to ski the steep chutes just below the snow fences to the north of the groomed snowmobile trail. The victim was the first to enter the top of one of the chutes and was the farthest to the west and slightly uphill from the others. He said he was cutting across the slope (to the north west) and slammed his edges into the snowpack "to see if it might slide" and IT DID! The 15" crown broke about shoulder level just up slope from him on a 40 degree slope angle. He yelled "slide!", stayed upright and tried to ski with it as things went down the elevator shaft. He felt he was at the leading edge of the slide when things came to an abrupt halt when he "pancaked" face down, onto the cat track of the Gray Wolf ski run about 25 yards below the starting zone. The rest of the debris piled up on top of him to a depth of about three to four feet. Only his right arm, beyond the elbow was exposed. He still had his skis on and a pole in one hand.
At this point his "pals" thought he had just skied down, so three of them dropped into other chutes along the slope to the east, this also triggered two other smaller slides. They were able to ski these out and kept going beyond and below the Gray Wolf run and headed down to the bottom terminal of chair seven on the back side where they reported starting an avalanche and dumping a bunch of snow on the cat track but nothing else.
In the mean time, the last guy in the group (who attended the Glacier Country Avalanche Center avalanche awareness class just prior) realized that one of the party was not visible after counting heads. Fortunately he had the common sense to search the debris on the cat track looking for the guy he could not locate. When he reached the northwestern edge of the debris he saw the arm of the victim sticking out from the snow and starting digging with his hands and a ski. It was about four to five minutes from the time of burial to when the victim's face was first exposed and another fifteen minutes until he was out of the snowpack. He was shaken but uninjured. None of the group had transceivers, shovels or probes.
I was in the patrol cabin at the summit gearing up for pit work and hazard evaluation when the lift attendant at the bottom of chair seven called the patrol dispatcher reporting the slide. I joined three patrollers and skied down to the site. We arrived just minutes after the victim was uncovered from the debris. The time was 1311. At the site two individuals were digging in the debris looking for a ski pole. One turned to me and explained that he had been buried in the slide and had "almost died". I immediately tried to figure out if anyone else could possibly be buried in the debris. The second individual was certain there was nobody else involved and he was very confident about that. A second witness had confirmed with him that no one else was buried. Both individuals felt they could ski down and did not want a snowmobile ride so we skied down to the base of Chair Seven and rode back up to the summit. At 1340 the Patrol Director and I interviewed the two individuals who were involved.
I then went back out to the slide location and recorded the following information:
1/29/98 WEATHER WAS CLEAR IN THE MID TWENTIES
FAA PEAK / NE ASPECT / 6700' ELEVATION / 40 DEGREES SLOPE ANGLE AT CROWN
SIZE CLASS 2 / HARD SLAB / HUMAN TRIGGERED - SKIER (29 year old male)
CROWN HEIGHT WAS 6-15 INCHES AND THE ENTIRE SLIDE WAS ABOUT SEVENTY FIVE YARDS WIDE WITH A VERTICAL DROP OF ABOUT 25 YARDS. THIS WAS ACTUALLY THREE SMALLER SLIDES THAT LINKED TOGETHER. THE CROWN OF THE PORTION OF THE SLIDE(S) THAT BURIED THE VICTIM WAS ABOUT 15 YARDS ACROSS.
THE SLAB WAS HARD AND BLOCKY - ONE FINGER TO PENCIL IN HARDNESS AND WAS ENTIRELY COMPOSED OF SNOW TRANSPORTED BY WIND ALONG THE GROUND FROM THE PAST 6-8 HOUR PERIOD.
THE WEAK LAYER WAS BURIED SURFACE HOAR ABOUT 1/8" - 1/4" THICK AND THIS LOCATION PRODUCED VERY EASY FAILURES IN SHEAR TESTING AND RUTSCHBLOCK TESTS. ISOLATED COLUMNS WERE FAILING WHILE ISOLATING AND THE RUTSCHBLOCK FAILED WITH A SLOPE ANGLE ADJUSTED SCORE OF A "1" (FAILED WHILE GENTLY STEPPING ON BLOCK - 28 DEGREE SLOPE). THESE WERE VERY "CRISP" SHEARS OF A VERY COHESIVE HARD SLAB.
THE BED SURFACE WAS COMPOSED OF AN OLDER WIND SLAB LAYER WITH ONE FINGER TO FOUR FINGER HARDNESS. BED SURFACE SLOPE ANGLES NEAR THE CROWN VARIED FROM 39 TO 44 DEGREES IN STEEPNESS.
WEATHER WAS A SIGNIFICANT AND UNIQUE FACTOR IN THE SLIDE. THE NIGHT BEFORE WAS CALM, CLEAR AND COLD. THESE CONDITIONS PRODUCED WIDESPREAD SURFACE HOAR IN THE BIG MOUNTAIN AREA. AT SOME POINT IN THE MORNING THE WIND PICKED UP OUT OF THE SOUTH EAST CAUSING SIGNIFICANT WIND TRANSPORT Of SURFACE SNOW ON TO THE LEEWARD NORTH EAST SLOPE PRODUCING THE WIND SLAB THAT SLID.
A PATROLLER LOOKED AT THE SLOPE IN THE MORNING ABOUT 0900 AND DETERMINED NO NEED FOR CONTROL WORK AT THAT TIME. IN THE HOUR OR SO I WAS AWAY FROM THE SLIDE INTERVIEWING THE VICTIM AND WITNESS MOST OF THE CROWN HAD FILLED IN WITH WIND DEPOSITION AGAIN. DURING THE 30 MINUTES I WAS WORKING AT THE SLIDE GATHERING DATA MY PACK WAS COVERED WITH 3" - 4" OF NEW WIND DEPOSITION.
I WOULD HAVE ESTIMATED THE WIND AT ABOUT 15 - 20 MPH. THE INTERESTING THING WAS THERE WAS LITTLE OR NO WIND AT THE SUMMIT JUST ABOVE FOR MOST OF THE DAY. THE WIND WAS ONLY PRESENT THROUGH THE LOWER SADDLE OUT OF THE SOUTH WEST. IT APPEARS THAT SOLAR WARMING OF THE AIR MASS IN THE BOWL JUST TO THE SOUTH WEST WAS CAUSING UP-SLOPE WINDS.
THE AVALANCHE ADVISORY ISSUED TWO DAYS PRIOR ON 1-27-98 BY GLACIER COUNTRY AVALANCHE CENTER RATED THE AVALANCHE HAZARD FOR THE BACKCOUNTRY AROUND BIG MOUNTAIN AS " " ABOVE 5500 FT.
KRAIG LANG - Snow Rangerbr Tally Lake Ranger Districtbr Flathead National Forestbr (406) 862-5400br