Chilkat Valley News - Serving Haines and Klukwan, Alaska since 1966

A difference of degrees: The innate risk in avalanche terrain

 

March 21, 2019

Left to right: Avalanche forecasters Jonny Cromwell and Erik Stevens dig a snow pit above the crown of the large avalanche that killed a backcountry snowboarder last week. Kyle Clayton photo.

Twenty feet below avalanche forecasters Erik Stevens and Jonny Cromwell, on a gray and frigid alpine slope behind Mount Ripinsky, passing clouds shroud then reveal a 3-meter deep fracture in the snowpack. The 400-meter long cleavage of snow is a crown line, one of at least seven where massive slabs of snow broke loose and cascaded down the mountain in an avalanche that, the day before, killed backcountry snowboarder David Dzenawagis.

Above the crown line, socked in by clouds and pounded by south winds that dangerously load snow onto the north-facing slope, Stevens and Cromwell finish digging a nine-foot pit in the snow. Like geologists studying rock strata, they analyze the slabs and layers that tell the history of this winter's snowpack.

They use an assortment of tools including probes, a crystal card and magnifying lens, digital inclinometers, shovels, thermometers and their fingers all in an effort to understand why the avalanche slid. Stevens documents various data points and maps a chart of the layers.

"Just looking at the chart, it's kind of a nightmare snowpack right here," Stevens said. "It's pretty much hard slabs that are really thick with super weak faceted layers underneath them."

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Faceted layers are snow surfaces that have been exposed to cold temperatures over time. February was mostly cold and clear. Cold air sucks moisture out of the warmer snow layer and change the rounded, well-bonded snow crystals into larger angular, sharp crystals. The longer the surface is exposed to cold temperatures, the deeper the faceted layer goes, the crystals become larger and weaker. Stevens likened faceted layers to a row of wine glasses with the fresher snow slabs, like cinderblocks, on top. With the right amount of pressure, the brittle faceted layers shatter, and the heavy snow slabs slide across them.

On Feb. 21, about a foot of snow fell on the mountains that flank Lutak Inlet. The following week, more clear and cold weather changed that powder into thick layers of weak faceted snow. On Sunday, March 10 a storm dumped another 16 inches of new snow on top of those weak layers.

"All that nice weather we had in most of January and February created those weak facet layers down low and then these storms came, and it's like parking a school bus on a bag of potato chips," Cromwell said.

For two days after the March 10 storm, moderate to strong south winds loaded even more snow onto the area Dzenawagis and his backcountry partners, Ted Cheney and Ted Hart, skied on Wednesday, March 13.

Stevens and Cromwell, along with Jeff Moskowitz who dug a pit further up the slope, are all paid staff of the Haines Avalanche Center. Their duties include submitting weather and snowpack observations, forecasting avalanche conditions and making avalanche reports. Such centers exist among a network across Alaska and down south.

Stevens and Moskowitz started the Haines center nine years ago, shortly after they moved to town from Colorado. They, as well as Cromwell, met in college and learned about snow science and backcountry skiing in the University of Colorado backcountry club. Their pursuit of backcountry skiing brought each of them to Haines. Before they started the local avalanche center, no online resources to check local avalanche forecasts existed. In the past nine years, they've taught dozens of avalanche and backcountry safety courses and have encouraged local skiers, snowboarders and snowmachiners to submit weather and snowpack observations, which is a common practice down south. In Haines, while participation has grown, it's not at the level seen in other regions where backcountry skiing is popular.

"There's no question about it down there," Stevens said. "People participate in the avalanche center. They check the forecast every day, religiously. Haines is an independent, strong-minded kind of community. Part of the joy of going into the mountains is doing that for yourself. So, there's kind of a tendency to take care of your own out there. It seems like a minor thing, but it's actually a very big difference that people here in Haines don't like to use their screens and devices as often."

Avid backcountry skiers, Cromwell, Stevens and Moskowitz provide as many observations as possible, but the sheer amount of terrain makes it impossible to provide good information across the board.

"It's a two-part thing," Moskowitz said. "There's this information that we provide, but there's also using it and participating with it, which has been a hurdle with the avalanche center for a long time. We're almost more appealing for people who are coming to visit. Locals tend to do their own assessment. Most don't use the website in the way that it's intended."

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In his house Saturday night where he finalizes his report that will be submitted to the national center in Colorado, Stevens is quick to dismiss any blame for last week's avalanche. Mellower slopes form the terrain most skiers ride in the Mumfords zone, with angles much less than 38 degrees, which is the angle where most avalanches occur. Dzenawagis, Cheney and Hart dropped into a bowl and chutes less commonly used by recreationists in the area. Knowing they were in riskier territory, they traveled through the trees that typically help anchor the snowpack, they dug hand pits to analyze the layers, tested various slopes, and skirted around the most dangerous areas, according to their interviews with Stevens.

"It is really serious terrain," Stevens said of the chutes, which have unavoidable avalanche terrain above them. "We certainly learned that you can do most of the things right, or maybe everything right like they did and be taking steps to minimize your risk like they were, but the avalanche that broke was really, really big for that area. I would have never expected to see an avalanche quite that big in that particular spot."

The skiers ascended through the forest to the top of the bowl where three chutes spill below it. Dzenawagis skied halfway down the middle chute, and waited in a safe area among a stand of trees for Cheney and Hart to meet him. Although no one can know for sure, the skiers above triggered the avalanche at a shallow point near buried trees, likely in the thick, faceted layers that formed last month. Although trees are often anchoring points in the snowpack, they can trigger avalanches if enough new snow falls on them.

"It's a balance between knowing if it's an anchor or if it's a trigger point," Moskowitz said. "If vegetation features such as alders get totally filled in and there's just a little bit of alder sticking up, then they might be anchoring the snow. But put a little more snow on top of that, and you have the nubbins of the alders, they're not anchoring anything. You're more likely to trigger a slide from that spot."

The thick-faceted layer broke and then stepped down to an ice crust much deeper in the snowpack in the middle chute. Because the terrain is so complex, the skiers couldn't see that the snowpack broke in different areas, in the bowl above, and across all three chutes. "When avalanches step down, they almost ripple out," Stevens said. "They come down out of sync with each other. Probably within a one-minute period I imagine all of those crowns had slid."

Based on the depth of the crowns and the amount of debris, Stevens, Cromwell and Moskowitz estimated the avalanche size at a D3. The size scale used by snow scientists ranges from D1 to D5. D3 means about 1,000 tons of snowpack breaks loose with enough power and mass to bury and destroy a car or a wood framed house.

Stevens and the others estimated the debris field to be 20 feet deep at the bottom of the chutes. Cheney and Hart found Dzenawagis buried under about three feet of snow in less than eight minutes, typically enough time to save a person from asphyxiating. The chances of surviving decrease rapidly beyond 10 minutes. The avalanche thrust him about 600 feet down the mountain and through trees. According to Haines volunteer medical crew, he sustained severe trauma.

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Stevens is adamant that based on everything he learned, what happened to Dzenawagis, Hart and Cheney last Wednesday afternoon could have happened to anybody. "I would say it really could have been any of us out there," Stevens said. "I don't think they did anything wrong necessarily. It could have been any of us and they did an incredible job and it's definitely not their fault."

Still, there are lessons that can be learned. One takeaway, Moskowitz said, is that many times you can know the snowpack underneath your skis, but you lose track of the macro terrain and variability that envelops you.

The mountain never gives a skier positive feedback. "You go down and you high five your buddies, but who knows if you just barely avoided that trigger point, if you barely got away with your life."

Ascending the mountain on the way to one of the crowns, Moskowitz compared the backcountry to the Stone Age. "It's a wild environment, unpredictable. Outside of investment banking, there's almost more uncertainty looking at a mountain and being able to understand everything when you can only see so much," Moskowitz said. "You're in an uncontrolled environment and it's up to you and your group to make decisions that can be life or death."

One assumes risk every time they venture into avalanche terrain. It's up to skiers to identify how much risk they're willing to take based on the knowledge they have. A difference of only a few degrees can trigger an avalanche. One small decision can mean the difference between life and death. The variables in the mountains are myriad, and the conditions where a skier is at any given point is not representative of the overall terrain. In essence, the bigger picture is too vast for a person to sufficiently process.

That's why Moskowitz and experienced backcountry skiers use checklists to synthesize terrain, weather and snowpack factors. These variables are continually considered as groups plan and execute their trips through the terrain. These skills are taught during avalanche training courses, two of which were offered this winter.

Others aren't as confident in their ability to provide reports online or use the technology that's now available. Matt Whitman has been skiing in the local mountains for more than a decade. He took his first Avalanche I course in January. He first started getting out into the backcountry 50 years ago down south when beacons and probes were just coming out.

"It's not something I've been involved with or ever done before. None of my peers that I've ridden with, it's not been a part of the discussion," Whitman said. "I realize I need to start. Being a product of the 70s, in backcountry culture, beacons were kind of just coming out. There weren't a lot of us out there doing it and riding. We got lucky in some ways."

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Driving away from the mountain after analyzing the snowpack, Stevens reflects on Dzenawagis, known locally as "Boston Dave." He attended local beacon and awareness courses during the past two years. Dzenawagis was an ideal backcountry participant, Stevens said, who moved to Haines for the mountains.

"He was always asking about the conditions. He was on the website a lot. He was checking the weather station. He was reading the forecasts and he would ask me about the forecasts in person," Stevens said. "I think he was really responsible about his approach to the backcountry. He tried to be as humble as possible. I think he had a lot of respect for the mountains."

It was eerie and frightening to be digging the pit so close to where the avalanche came down in what were still dangerous conditions. Cromwell and Stevens dug the pit on a 20-degree slope. Just twenty feet away, the crown's slope was 38 degrees.

This map shows the crown lines, the extent of the slide area and the positions of the skiers. Map courtesy of the Haines Avalanche Center.

The Haines avalanche center's accident report, one of 11 made since 2011, will be added to the national registry. "But it's also for the skiers here in Haines to read this report and try to understand what happened just so we know, but also so we can analyze our local snowpack a little better, the terrain better and maybe try to learn some lessons," Stevens said. "We can always learn lessons from any experience."

At the end of the day, every backcountry decision comes down to what one is prepared to risk. The human factor is the only factor that truly makes terrain dangerous. "Sometimes there are certain places where we ski, where the terrain is bigger than we are. It's bigger than we can manage," Stevens said. "We're making our own decisions out there and we all have our own level of risk acceptance."

You can view their report, submit observations and check avalanche forecasts at alaskasnow.org/haines-hac.

 
 

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