Avalanche Accident Report          



Forest Service Utah Avalanche Center

December 26, 2008

Little Water Peak – Four foot burial and miraculous recovery.

Accident Report by Bruce Tremper

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Location:

Northwest side of Little Water Peak along the Big Cottonwood – Mill Creek ridgeline.  The area is locally known as Shangri-La.

Accident and Rescue Summary:

A group of four backcountry skiers were out for a tour in very conservative terrain because the Forest Service Utah Avalanche Center had issued an avalanche warning for the day and rated the danger as High on most slopes.  Three people (Matt Clevenger, Dan Steenblik and Paul Sharpentier ran into their acquaintance, Tom Diegel, who was skiing alone. The three suggested that Tom join them and they would go to an area known as “Shangra-La”. They went to terrain with gladed trees that is almost entirely less than 30 degrees in steepness, which is generally considered to be very safe terrain. On their climbing track back up, Tom Diegel was breaking trail and he got a little farther to climber’s left than usual and they came to a small opening in the trees that was 29 degrees in steepness at least a the bottom of the slope, which is not generally steep enough to slide in most conditions. But the upper section of the small opening had a short section that was 32-33 degrees in steepness.

Tom noticed that the slope above them was slightly steeper. So, to be safe, they decided to cross it one at a time.  Tom and Paul crossed the slope and waited on the other side.  When the third person, Matt Clevenger, began to cross, the entire slope collapsed and it slid, very slowly, down into some trees, catching both Matt and Dan, who were carried only about 10-15 feet down the slope where Matt was pushed up against a large fir tree and buried with his head between 4 and 6 feet deep (6 feet on the uphill side and 4 feet on the downhill side) and buried upright but hunched over. Paul was buried to his knees just a few feet away.  The rest of the avalanche went only about 100 feet down slope before coming to a stop on the gentle terrain.

Luckily, Tom Diegel regularly practices with his beacon and often practices deep burials.  He located the victim in about two minutes in deep debris piled up against trees.  He probed, hit him and organized the others and they began to dig.  He knew it was a deep burial so two of them dug while the third helped move snow away from the hole.  Since the victim was pushed up against a large, fir tree, they could not dig in from the downhill side so they dug straight down from above and they also had trouble digging through all the branches.  They uncovered Matt’s face in about six minutes but it could have been as long as 10 minutes from the time of burial.  Matt groaned when they uncovered his face, but he was blue-faced and unresponsive.  Tom could not tell if he was breathing on his own or not so he gave him some rescue breaths and Matt began to respond. They extricated him from the snow and Matt completely recovered but was very cold and shivering.  He was able to ski out on his own and even climb to the top of the ridge to descend the other side to the car.  It was a miraculous recovery considering the depth of the burial. See a video of my interview of three of the four party members two days after the rescue. (posted on the Utah Avalanche Center channel at You Tube).

Terrain Summary:

The area locally known as Shangri-La is just on the north side of the Big Cottonwood Canyon – Mill Creek divide and just north of Little Water Peak.  It is an area of gladed aspens and fir with gentle slopes.  It’s often a place where backcountry skiers go during high danger conditions.  I investigated the site two days later and Tom Kimbrough, a retired forecaster for the Utah Avalanche Center investigated the slope the day after. We both measured the slope to be northwest facing, about 9200 feet, 29 degrees where their climbing track crossed the slope but it steepened to an average of 32 degrees at the crown with a small section of 33 degrees. The snow on the steeper upper section moved about 100 feet down the slope and pushed the snow on the lower, gentler section and it was buckled up like pushing a blanket. Since the slope was so gentle, the snow did not move very far.

If looking from the bottom, the party crossed the slope from left to right. Matt and Dan stood on the left flank at the time of the fracture while Tom and Paul stood on the right flank. The crown was about 80 feet above them and the victims were carried about 15 feet into a tree.

Avalanche Data: 

The avalanche averaged 4 feet (120 cm) deep and was 100 feet wide. It slid about 400 feet down the slope loosing about 150 vertical feet. 

The slab was composed of snow that fell over the past two weeks.  The weak layer is an extremely fragile layer of faceted snow growing both on top of and below a prominent rain crust about 30 cm (a foot) above the ground.  See snow profile. Widespread avalanche activity had been occurring on that layer for the past week.  An avalanche warning was in effect and the avalanche danger was rated as High. On my snow profiles along the crown, flanks and adjacent slopes, it was difficult to isolate a column of snow on the fragile layer.

Weather and Avalanche History:  (Seasonal Weather Charts)

Snow started to pile up in early November but a month of dry weather followed, which metamorphosed all of the snowpack to very weak, depth hoar.  Around Thanksgiving, rain formed a clear and prominent crust on the snow surface throughout most of the mountains of northern Utah.  As more light density snow fell, finer-grained, faceted snow formed on top of the rain crust as well. A series of storms since December 13^th began to overload these layers, reaching a crescendo the day previous to the accident when over a foot of dense snow fell accompanied by very strong, southwesterly winds and warm temperatures.  An additional foot of light powder fell overnight, which covered up all the older, denser snow.  This Christmas storm initiated a widespread avalanche cycle on these buried weak layers.

Comments

Although, they should have found an alternative route around this particular terrain feature, this story has a happy ending, first because the party was knowledgeable and experienced enough to choose conservative terrain and carry proper rescue gear, and second, because Tom had been regularly practicing with his beacon using realistic scenarios, such as deep burials with a beacon in a buried pack.  He is an accomplished outdoorsman with extensive experience, so he is used to dealing with high-risk situations and training for them.  He indicated that his regular practice doing realistic drills with deep burials probably made the critical difference. He did not have to think, and he could quickly spring into action with little wasted effort. In addition, he is one of the most aerobically fit outdoor athletes in Utah and regularly places very high in competitions such as randonee rally, running and bicycle races. Paul and Dan are also very fit outdoorsmen and contributed significantly to the rescue efforts. Finally, Matt, the victim, is a very fit athlete, which probably contributed to his survival, both during the burial and his ability to ski out on his own afterwards. In short, because of their training and team effort, one person is alive in a story that could easily have an unhappy ending.

Despite this, obviously mistakes were made. Tom Diegel was breaking trail and was the default decision maker at the time. As he noted on the video I took of their party a couple days later when we visited the site, he looked up the slope and noticed that it became slightly steeper above, but it just did not register as being overly dangerous. The slope where he crossed was only 28-29 degrees, so he was lulled into the belief that it would be safe enough to cross. He was concerned enough to tell the others that they should cross it one at a time. In retrospect, he noted that he should have gone back downhill and crossed through the trees much lower on the slope. The other skiers did not object to his choice of the route, or if they did, no one spoke up. One person had skied there a couple days earlier and was more familiar with the terrain. As Tom noted later, he was cold and wanted to warm up, plus he enjoys breaking trail as exercise, so he was in front. Also, the two people in the rear were still in the thick trees, so they may not have even seen the slope before Tom broke a trail across it.

In our avalanche classes, we usually teach the students to use the ALPTRUTh and FACETS checklist, invented and popularized by Ian McCammon, as a way to assess avalanche danger and the human factors that may affect decisions. So I will go through those checklists here as well as an after-the-fact exercise.

ALPTRUTh Checklist

score: 5.5 out of 7

Avalanches in the past 48 hours?	X
Loading of new or windblown snow in the past 48 hours?	X
Path – is it an obvious avalanche path?	½ X
Terrain Trap – does the avalanche take you into trees, a gully or over a cliff?	X
Rating – is the avalanche rating Considerable or higher?	X
Unstable snow signs – collapsing, cracking?	X
Thaw instability?

In the ALPTRUTh system, you should avoid a slope if you get more than 3 checks and they had 5.5 checks here. I gave the avalanche path a half-check because it was neither very steep nor large, so an inexperienced person may not have recognized it as avalanche terrain, but it should have been an obvious path to someone with lots of avalanche experience. The increasing steepness above them did not quite register. If this was more obvious avalanche terrain, they probably would not have crossed the slope. Everyone in the party recognized the avalanche hazard that day. That is why they decided to ski in conservative terrain. They just did not recognize the problem with that particular terrain feature, or if anyone had concerns, they did not speak up.

Second, research clearly shows that human factors cause many, if not most, avalanche accidents, so I will use Ian McCammon’s FACETS checklist. These are “heuristics” or mental shortcuts that tend to make people take more risks in the presence of these clues.

FACETS Checklist:

Score: 4 out of 5

Familiar terrain - when you are in familiar terrain, you tend to take more risks. All of them had skied there before and knew the area. One person had been there two days earlier.	X
Acceptance – We all want acceptance from our peers, and especially from potential mates, so we tend to “perform” in ways that gain acceptance . Since they were the only group in the area that day and their group was composed of all males, seems less important. But acceptance is a factor in any group. For instance, I doubt that anyone was consciously trying to impress the others, but unconsciously, this occurs in most all groups. Tom knew the others only as casual acquaintances, so it is possible that he was unconsciously trying to be accepted by breaking trail for them and the others may have wanted acceptance by not speaking up if they felt it was a dangerous route.	½ X
Commitment – when we are committed to a goal, belief or identity, it simplifies our decisions because we choose based on what supports our commitment. In this case, there was no goal for the day except to ski in an area they believed was safe terrain, so there appears to be no commitment heuristic present.
Expert halo – people tend to take more risks when they are following an “expert”. Sometimes the expert is just the person who knows the route or they may have the strongest personality. In this case, they may have seen Tom as an expert because he had more backcountry experience than the rest of them, plus, he has a strong, confident personality and the others are softer spoken.	X
Tracks – or scarcity--when there are other parties in the area competing for the limited resource of powder, we tend to take more risks. No other parties were in the area that day and there was plenty of powder, so this was not a factor.
Social Proof – which I call the “herding instinct”—when we look to others for proof that what we are doing is correct. Most of us simply follow the crowd instead of go against the flow. This was probably present in this accident as they were all following the trailbreaker and no one questioned his route, or if they did, no one spoke up. In their defense, the last two people, who were also the ones caught, were in thick trees, so they may not have even seen the complete slope until Matt stepped out onto it and the avalanche occurred. Our brains are hard wired for safety-in-numbers and this often gives us a false sense of security. This is called “risky shift” in the business community, when larger committees tend to take more risks. Would anyone in that party have crossed that slope if he were skiing alone? Probably not.	X

Other human factors include what is known as “loss aversion”. In other words, once you gain something, you will do almost anything to avoid loosing it. In this case, after they gained some elevation, they did not want to drop back down to a safer crossing because they would have lost some of their hard-gained elevation. Tom is very fit and he enjoys breaking trail, so it was probably not much of a factor, but it is a powerful heuristic that affects us all. Going back the way they came—even for a short distance—is a choice that few people ever consider.

The weather may have contributed to the accident as well, because it was cold. Tom started out breaking the trail because he wanted to warm up. Other party members were more familiar with the more standard route up the nearby sub-ridge, which avoids the particular terrain feature that avalanched.

Finally, the U.S. Supreme Court was designed many years ago, so that one justice always wrote a dissenting opinion on important, close decisions. Early courts recognized the risks with social proof and acceptance heuristics. They found that if someone always took the “devil’s advocate” position, it forced the majority to reexamine their beliefs and address the problems in their logic illuminated by the contrary position. Similarly, in backcountry decisions, I feel that it is important not only for members to speak up when they see a problem, but for a leader to always ferret out other opinions from others in the group.

We have found these checklists useful, not only for judging danger before an accident, but as a post-accident debriefing. My report probably misjudged some of these factors, especially the human factors, which are subjective and uncertain. Regardless, we see a lot of checks in the boxes above.

We write these comments not to lay blame or judge, because we all make these same mistakes, but we use it as a way for others to learn. Telling stories is our most ancient learning method and it works well for avalanche accidents.