PBS Airdate: November 25, 1997
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ANNOUNCER: Tonight, on NOVA—

HELGA JONINA GUDMUNDSDOTTIR: It was shaking the house.

ERIKUR FINNUR GREIPSSON: The roof was just torn off.

ANNOUNCER:It strikes without warning and wipes out everything in its path. Now, scientists take you inside an avalanche to unlock its deadly secrets.

JIM DENT: Jay and I cannot move. We are buried inside the house.

ANNOUNCER: It's a battle to understand and control the "Avalanche."

Major funding for NOVA is provided by The Park Foundation, dedicated to education and quality television.

And by The Corporation for Public Broadcasting and viewers like you.

NARRATOR: Off the coast of Iceland, a rescue team races to a village in the grip of disaster. They arrive to find a sight of utter devastation. The town of Flateyri lies in frigid ruin under hundreds of tons of mountain snow. A score of residents are feared lost. Workers scramble to find the living and the dead, the victims of a sudden and massive avalanche.

HELGA JONINA GUDMUNDSDOTTIR: I woke up to these terrible loud noises.

ERIKUR FINNUR GREIPSSON: The earth was shaking.

HELGA JONINA GUDMUNDSDOTTIR: It was shaking the house.

ERIKUR FINNUR GREIPSSON: The roof was just torn off.


ERIKUR FINNUR GREIPSSON: Then the snow came.

HELGA JONINA GUDMUNDSDOTTIR: The bed had moved into the next room.

ERIKUR FINNUR GREIPSSON: I was crushed in between the walls and the roof completely stuck in the snow.

HELGA JONINA GUDMUNDSDOTTIR: When I came out everything seemed very strange and you could hear nothing else but the wind and you could hear people crying.

ERIKUR FINNUR GREIPSSON: Where houses had been before it was only snow and dark spots.

HELGA JONINA GUDMUNDSDOTTIR: The avalanche took a big part of Flateyri, just took it away in a few seconds, it was just gone.

NARRATOR: The avalanche, an event that is as extraordinary as it is horrifying. Over a million tumble down the mountains of the world each year. They range from harmless showers of snow to hurricane blasts that can strike with the force of two hundred pounds of TNT, and some do. In its wake, age-old questions arise: how can simple snow become so destructive? Can the avalanche be controlled? It is these questions that awaken avalanche specialists around the world each winter season and press scientists to extremes in pursuit of answers. All for what seems a fairly simple act of gravity. Nowhere has the search been pursued longer than in Switzerland. In the shadow of the soaring Alps, reinforced walls on homes, churches, slopes covered with protective barriers, and sheltered roadways tell of a people under siege. For centuries, a war has raged with the avalanche, one that has killed more people here than any other natural disaster. In that time, the Swiss have come to know their enemy, an elaborately complex phenomena, whose basic ingredients remain simple: that of snow and a slope.

OTHMAR BUSER: An avalanche is just snow sliding down a slope. The only force acting on the snow cover is gravity, so an avalanche will start because of its weight.

NARRATOR: Understanding these elements and how they are triggered to produce an avalanche is the job of Dr. Othmar Buser of the Institute for Snow and Avalanche Research in Davos, Switzerland.

OTHMAR BUSER: All around here are the mountains. They're all covered by snow. Some avalanches go, some slopes don't go. The question is why do they not go. The answer to this question is within the snow cover.

NARRATOR: Whether an avalanche begins or not depends on the snow's ability to stay together and resist the force of gravity pulling it down the hill. In a laboratory, scientists can measure the strength of the snow.

OTHMAR BUSER: I have here a sample of snow. I know how heavy it is. And what I wonder about is how strong it is.

NARRATOR: Here, Dr. Buser uses centrifugal force to imitate the effects of gravity.

OTHMAR BUSER: I'm going to turn now. Now. It's broken with, well a few hundred tons in a second and from that speed we can calculate the strength of the snow sample. We are interested in the strength of the snow sample because once it breaks we have an avalanche out in the field.

NARRATOR: But in the quest to predict when snow might break, scientists have to contend with one of nature's tiniest and most capricious wonders: ice crystals. Infinite in variety, ice crystals give snow its stability, yet they, themselves, are notoriously unstable. As frozen water vapor, ice crystals undergo continuous change with variations in temperature and humidity. How they become so individual is by way of an odyssey that begins when a water molecule freezes around a dust particle high above the earth. Then, out of the sky it falls, growing and shrinking as it drifts, picking up water molecules and ice crystals as it goes. A snowflake is a group of crystals, and the shape each crystal takes determines its crucial ability to bond within the snow cover. Small, rounded crystals pack tightly to create dense slabs of snow. Large and angular crystals tend to form loose, weak layers. How well these layers bond to each other is critical. If the bonds are weak, the seeds of an avalanche may be planted. Even an expert skiing the champagne powder of Montana cannot tell what dangers lie beneath the surface. Karl Birkeland is an avalanche forecaster for the Gallatin National Forest. He and his partner, Ron Johnson, go out daily to evaluate the latest snow conditions.

KARL BIRKELAND: Just like no two snowflakes are alike, no two snowstorms are exactly alike, either. We're going to have storms that are warmer where we'll put down denser snow, colder storms where the snow's all fluffy, and then we'll have some storms that are really windy and then the snow packs in tighter and then you get a denser layer. So, we're going to end up with these different layers in the snow pack.

NARRATOR: To get a look at the stability of these layers, forecasters dig a pit into the slope.

KARL BIRKELAND: I wonder if this was from that. You know the wind event we had, it was a week ago—

NARRATOR: By exposing a cross-section of the snow pack, they have a window on the history of the winter so far.

RON JOHNSON: Looks like this is that wind slab from yesterday's wind event.

KARL BIRKELAND: It's just that downhill wind, huh?

RON JOHNSON: Yeah, and all the softening. Snow's from the storm that came in last weekend—

NARRATOR: The story that unfolds reveals individual storms and even past changes in weather conditions.

RON JOHNSON: This is that big wind event from ten days, fourteen days ago.

NARRATOR: The strength of the layer is reflected in the light passing through a thin column. The darker layer is denser and more tightly bonded than the lighter snow on top.

RON JOHNSON: And see, this is the darker snow right here, and then this stuff up in here is a lot less dense so the light's coming through it.

NARRATOR: How these layers stack up determines the avalanche danger. An avalanche hazard begins to build when a weak layer forms on a slope. One classic type may consist of frozen dew. Known as surface hoar, these loose crystals are not, in themselves, dangerous. But if another layer is deposited on top with the help of the wind or a dense snow fall, a heavy slab can build up. When the force above becomes too much to bear, the result is an avalanche.

RON JOHNSON: This is the weak layer, a little slab on top when we load this thing up—

KARL BIRKELAND: Well, it's going to rock 'n roll then.

NARRATOR: For now, only a thin slab layer is on top, but the season is far from over. Karl and Ron will be closely watching the snows to come. But often, the discovery of avalanche prone slopes is by accident. All that's required is the addition of what, in effect, is the straw that breaks the camel's back.

CHRIS STONE: Yesterday, we were up skiing and right away we knew it was a dangerous day due to wind. It just makes for really weird snow.

NARRATOR: For fifteen years, Chris Stone has taken on the back country of Montana. Like hundreds of other skiers each year, he has found himself an unwitting participant in the creation of an avalanche.

CHRIS STONE: We're out there a lot. We have a feel for the conditions. We felt pretty safe. My partner went down first, cautiously, and watched me go by and I got out of sight from him and I got caught in an avalanche.

NARRATOR: In accidents like this one, even the most experienced skiers find they're no match for an avalanche.

CHRIS STONE: It was up to speeds so fast, there was no hope for any getting out of it. It took me and slammed me down.

NARRATOR: The role Chris played in the avalanche was that of a trigger. By applying the final increment of pressure, avalanche triggers cause buried weak layers to fail, releasing all the snow above. Most avalanches are triggered by rapid, heavy snowfall. But most avalanche accidents are caused by people. Whether trigger or victim, with ignorance or arrogance, they can transform a natural act into a natural disaster.

JILL FREDSTON: Avalanches don't happen by accident, they happen for particular reasons. It's the interaction of terrain and snow pack and weather that make it possible to have an avalanche. But there's no avalanche hazard until you introduce people. It's the human factor. And really, it does come down to attitude. We're going to accept a different level of risk if we want to just go out snow boarding for the day and come back and live for another day. We're going to have a different level of acceptable risk if we want to climb this mountain no matter what. And if you have a "ski to die," or "snowboard to die," or "I'm going to live here no matter what," probably sooner or later, you will die in an avalanche. I've dug out many, many bodies. I've been to lots of accident sites, they just didn't understand the risk they were taking.

NARRATOR: In mountains like these, the risk comes with the territory. Avalanches kill hundreds of people every year. Most avalanches occur on slopes between 30 and 45 degrees, about the range of the most challenging runs at ski resorts like Bridger Bowl in Montana. Over thirty storms drop more than twenty-five feet of snow per winter here. With just the right slope angle, and more than enough potential triggers, after a storm Bridger Bowl should be a scene of slaughter, but it's not. Here, the avalanche risk is vigorously controlled. Each morning, well before the skiers arrive, the ski patrol gets ready to open the slopes.

FAY JOHNSON: Things got skied heavily yesterday. We did get the ridge open and it got hammered.

NARRATOR: Led by Fay Johnson, these control specialists are preparing to trigger avalanches intentionally, before skiers can later by accident.

FAY JOHNSON: The north and south rope lines on Bridger need some attention, just the usual things. So we might as well head on up.

NARRATOR: At 9:00 a.m., the lifts will open, they have less than three hours to tame the mountain. They first use a technique called "ski cutting." They try to dislodge unstable snow by traversing the slope slowly, but at an angle to give them an escape route, should they trigger an avalanche.

RADIO VOICE: This is my last loop, when I come around, I'll be out of here.

RADIO VOICE: Ten-four. Go ahead.

RADIO VOICE: Thank you, Marvin.

NARRATOR: For other slopes, they turn to a different method.

M: Clear to the front, clear to the rear, ready to fire.

NARRATOR: A seventy-five millimeter recoilless rifle pounds the highest and most distant slopes of Bridger Bowl. Through the veil of a winter storm, each ten pound shell wallops a snowpack one mile away.

M: Ready to load. Loading. Locked and loaded. On target. Ready to fire. Clear to the front, clear to the rear. Ready to fire. Fire.

NARRATOR: In just minutes the gun can clear several slopes, a job that would take the ski patrol hours to accomplish on foot. Wind-packed cornices are attacked with poles and shovels. If resistant, they're hit with an explosive punch. More than 1,000 explosive charges are set off at Bridger Bowl every year.

M: It's not going to blow up yet. I've just put the fuse in there.

NARRATOR: The fuse gives them ninety seconds to place the bomb. For maximum effect, the charge is suspended above the snow pack where it's shock wave can do more damage. In just two hours, the ski patrol has made Bridger Bowl safe for another day. But that's only one square mile of the Bridger range. Outside the resort lays the vast back country, thousands of miles of untended, uncontrolled slopes. Skiers are coming here in ever greater numbers raising the stakes for forecaster Karl Birkeland.

KARL BIRKELAND: Over the past six years, we probably have about three times as many back country skiers as we ever did before. And if you get more people into the back country, you have more avalanche triggers and increasing death tolls. The most important things for me to do, as an avalanche specialist, is to get out in the field. I want to get out there. I want to walk on the snow pack, dig snow pits, do stability evaluations. I think that's all we're going to get for a break here, Ron.

NARRATOR: They combine field observations with the latest weather information.

KARL BIRKELAND: Yeah, it's going to be based on the models in this satellite route.

RON JOHNSON: Yeah. It might just give us a little bit of a shot of moisture tomorrow.

KARL BIRKELAND: You kind of see it dropping in, as this axis is off the West Coast in the northwest part of Montana.

NARRATOR: This forms the basis for their daily avalanche advisory.

KARL BIRKELAND: Good morning. This is Karl Birkeland with an avalanche advisory. I would call the avalanche danger mostly moderate to high on slopes steeper than forty degrees and moderate on gentler slopes in the Bridger, Gallatin, Madison and Washburn ranges, the Lionhead area, and the mountains around—

NARRATOR: But it's up to the individual to heed this warning.

KARL BIRKELAND: We hope to give people the tools to make better decisions in the back country which will hopefully save lives. I mean people are going out to the really radical lines as soon as they can. They're really pushing the boundaries.

NARRATOR: Typical are the snowmobilers. Thousands invade the national forests of Montana each year. With a one-hundred and thirty horse-powered engine, weighing a quarter of a ton and exceeding speeds of eighty-five miles per hour, the snowmobile makes an impressive toy.

M: Usually, there's about ten of us that go out riding. Our idea is just go out and have a good time and try not to break anything.

NARRATOR: Here, the thrill of open throttle in open country is so powerful, warnings often fall by the wayside. High marking is a favorite activity, but for two snowmobilers, it became a game of Russian Roulette.

JOHN LEIPHEIMER: We were climbing up the hill over here. Jim had went up it first and made a high mark on it. High marking's where you go up the hill, a pretty steep hill, as far as you can, and either, you either start to get stuck because it gets too steep and deep, or the snowmobile starts to lose power. Then you turn around right before you get stuck.

JIM GILMAN: We've had several avalanches come down on us before, but usually, you know, you're heading downhill when it's happened and you just kind of ride it out and it's been fine.

JOHN LEIPHEIMER: But you know, it didn't feel like, you know, we were ever doing anything really ridiculous. Jim went up the hill first and I waited till he got back down and then I went up.

JIM GILMAN: As soon as he made his corner up on top of the hill, it broke off up above him. I could see the suit tumbling in the snow, it carried his sled into the trees and then he disappeared.

JOHN LEIPHEIMER: I kind of remember swimming for a minute, and then I can remember just thinking to relax.

NARRATOR: The avalanche buried John under three feet of snow. A similar accident caught on video tape shows how survival depends on immediate rescue. John nearly suffocated. When he was found, he wasn't breathing and had no pulse.

JOHN LEIPHEIMER: If it wouldn't have been for the people that were with me, I'm sure I wouldn't be here. You read about it in the papers, but you figure it will never happen to me.

KARL BIRKELAND: A lot of people think that avalanches can't happen to them, but it's the same thing as someone who builds a home in a flood plain saying that they don't think that a flood will ever hit their house. If people go out and play on steep, snow-covered terrain, in other words, play in avalanche terrain, then there's always the potential for them to trigger an avalanche.

NARRATOR: The day after the snowmobile accident, Karl comes to investigate the site.

JONATHAN KLEIN: Karl, nice to see you again.

KARL BIRKELAND: Yeah, thanks for calling me.

JONATHAN KLEIN: You ready to take a ride?


NARRATOR: He joins forest ranger, Jonathan Klein.

KARL BIRKELAND: It sounds like a pretty interesting story.

NARRATOR: In making the journey here, Karl hopes to piece together how the snow pack failed.

KARL BIRKELAND: He ended up separated from his sled, didn't he?

JONATHAN KLEIN: Yeah, his sled was up slope of him, thirty, forty yards.


NARRATOR: Karl treats this frozen landscape like the scene of a crime.

KARL BIRKELAND: That must be where he was.

JONATHAN KLEIN: Where he was buried.

KARL BIRKELAND: If you imagine, you know, the snow coming right over the top here, imagine your head being—

NARRATOR: Avalanche debris is typically rock solid.

KARL BIRKELAND: Look at how hard that stuff is. That's just set up like concrete, you know? It's a rock.

NARRATOR: Warmed by the friction of the fall, the air forced out of it, the dense snow quickly refreezes after it comes to rest.

JONATHAN KLEIN: Makes for a good stairway, though, doesn't it?

KARL BIRKELAND: Yeah, it sure does. You can sure walk on this stuff easily.

NARRATOR: They head for the crown, the wall created when the avalanche broke away.

JONATHAN KLEIN: I'll shoot the slope when we get up here a bit.

KARL BIRKELAND: Great. This about looks like the steepest part. Take one more shot of the slope angle.


KARL BIRKELAND: This slide is classic, you know?

NARRATOR: They check the slope angle using an inclinometer.

KARL BIRKELAND: —that tends to get people in trouble.

NARRATOR: It falls within the most dangerous range at 36 degrees.

KARL BIRKELAND: It's just the perfect slope angle for just enough snow to build up on that surface.

JONATHAN KLEIN: Look at how much steeper the crown is over on our left.

NARRATOR: At the crown, Karl examines the snow pack. He finds a weak layer halfway down.

KARL BIRKELAND: Remember how we were looking at that double weakness, down at the—

NARRATOR: But there must be another weak layer below it.

KARL BIRKELAND: It's sitting on a pretty decent little ice crest. This is out more.

NARRATOR: To confirm it, Karl digs outside the avalanche where the weak layer should lie undisturbed.

KARL BIRKELAND: And then that other weak layer is just this thing.

NARRATOR: It doesn't take long to find it.

KARL BIRKELAND: Yeah this is a real thin weak layer right here. Look at this guy.

NARRATOR: The culprit is surface hoar, the large, loose crystals that form the weakest bonds.

KARL BIRKELAND: Yeah, look at that. You know, and right there, that's the layer that the avalanche released on. What you see is this first one—

NARRATOR: A shovel test shows how vulnerable this snow pack was.

KARL BIRKELAND: There's that first of those two breaks. So, I mean, it's possible that the guy triggered it in this upper layer and then it broke down low. And look—

NARRATOR: There is not one weak layer, but several.

KARL BIRKELAND: And there's that one. That's the one—

NARRATOR: Karl puts the results of this investigation together to form two possible scenarios. In one, the lower weak layer breaks first and brings down the whole snow pack. In the other, the top layer makes the initial break. Then, as the slab begins to move, its weight breaks the second weak layer below, resulting in the near fatal avalanche. But as Karl knows, understanding an avalanche after the fact is the easy part. It's heading them off that remains extremely difficult.

DENNY HOGAN: We've been shut down by a pretty big storm and we've had a total of forty-five inches of new snow. My job is an avalanche forecaster and I work closely with the highway crews to ensure the safety of the road crews and the traveling public.

NARRATOR: This is Colorado's Highway 550. With over 100 avalanche paths lining its route, this roadway is one of the most dangerous in America. Here, no one can afford to take any chances.

DENNY HOGAN: This stuff can build up and build up and then it'll run and we don't want it to run. So any time the avalanche danger is on the increase, we'll recommend that the highway is closed. Then when the storm's over, we can get our helicopters in with explosives to dislodge these pockets of unstable snow.

NARRATOR: With helicopters and hundreds of pounds of explosives, the operation entails a half dozen sorties in a day long pre-emptive strike. By closing the road and hitting every suspect hill, they give the avalanche room to run wild, to exhaust its deadly potential in an awesome display of power, speed and reach. But knowing ahead of time how far an avalanche can travel would help reduce the risk. A group of researchers at Montana State University are probing the hidden dynamics of the avalanche to help people protect themselves from its destructive power. They do what no other research team would dare attempt: trigger an avalanche onto themselves. Their risky experiment takes them to the cutting edge of avalanche science.

JIM DENT: What we would like to learn is what are the mechanics involved at the base of the avalanche, because if you can figure out what's going on at the base of the avalanche, then you can figure out what the overall avalanche is going to do.

SCOTT SCHMIDT: You're building a road through mountainous terrain and it'd be really nice to be able to locate that road so that it doesn't sit in a hundred year avalanche path and get wiped out. In order to do that, you need to know some of the mechanical properties, as it were.

NARRATOR: The actual experiment will take place later in the winter when the conditions are right. Today, they prepare a shack that will be a window on the avalanche, and the only protection from its force.

JIM DENT: The bomb goes off and about ten seconds later, after about ten seconds of quiet and anticipation, suddenly there's just a big whoosh as the avalanche goes by and over the top here. That's pretty exciting.

NARRATOR: From inside the shack, Jim will observe the avalanche first hand. He will monitor an array of instruments designed to capture the transformation of the snow pack from a settled mass to a raging torrent, and finally into ice-hard debris.

JIM DENT: There are going to be four velocity sensors in there, and as the avalanche goes by, what we're interested in is how does the velocity change from the surface up into the avalanche. And so we've got, we will have sensors in here at various depths to measure that velocity.

NARRATOR: What they're aiming for is a computer model of flow. From it, a more understandable picture of the avalanche should emerge, one that will foresee the worst a slope might produce.

SCOTT SCHMIDT: I think what we're shooting for is to build a model that will predict avalanche run outs.

JIM DENT: Whether it will cross a road, whether it will pick up a bridge and carry it down into the river bottom.

SCOTT SCHMIDT: In order to do that, you need to know some of the physical properties about the avalanche, how hard it's going to hit these structures and again, that relates to the mechanical properties of the flow.

JIM DENT: But, we're waiting for more snow now. We get another couple of feet of snow, and we're in business.

NARRATOR: Success here is no small matter. Misjudging the potential of avalanche terrain can lead to the most catastrophic disasters, as it did in Flateyri, Iceland. The steep walls of a rocky fjord dwarf this fishing village thirty miles from the Arctic circle. Avalanches were a fact of life here. The community felt it was prepared.

ERIKUR FINNUR GREIPSSON: We've had avalanches from the mountain. We've had avalanches even that have affected our houses. But in another part of Flateyri, not in this part of Flateyri.

NARRATOR: In choosing where to build their houses, the people of Flateyri took history as their guide. Over the years, many different avalanche paths emerged, but none reached beyond a certain zone, and that defined the avalanche danger. When an avalanche warning was declared, only homes in the danger zone were evacuated, as they were on October 25th, 1995, after a week of heavy snows.

HELGA JONINA GUDMUNDSDOTTIR: On Tuesday night, there was a warning and people closest to the mountain, they left their houses. And people thought, "OK, we are safe because we are down here. There's only a danger of avalanches up there."

NARRATOR: But townspeople learned that the mountain was about to declare a new danger zone. While the village slept, a disaster was building above them. At 4 o'clock in the morning, it descended. Scientists believe the avalanche began when a quarter-mile long, twelve foot high slab broke from the mountain. Within seconds, an enormous powder cloud formed on top moving at more than a 125 miles an hour. The avalanche soon took a path unknown in the history of Flateyri. Bypassing evacuated homes and roaring deep into town. In all, 250,000 tons of snow came to rest in the village of Flateyri, killing twenty people, destroying seventeen houses, and crippling its sense of security forever.

HELGA JONINA GUDMUNDSDOTTIR: In Flateyri, we always knew that there was a danger of avalanches, but we wouldn't have believed it if somebody would have told us that this could happen.

NARRATOR: In their complacency, the people of Flateyri are not alone. In Alaska, the city of Juno may be facing a similar fate. The people know well what looms above the city: a phalanx of seven avalanche paths. Every once in a while, one will remind Juno of its presence, as an avalanche did spectacularly in 1972 when its powder cloud rolled right through the center of the city. No one was hurt, but Juno hasn't always been so lucky. Ten years earlier, a massive avalanche swept through one neighborhood on the city's edge, damaging thirty-five homes. This disaster sent a clear message of what the mountains are capable of. But has the warning been heard? Many homes remain dangerously close to the mountain.

DOUG FESLER: This has been described over the years by a number of people as being the largest potential avalanche disaster in the makings.

NARRATOR: Avalanche educator, Doug Fesler, has been sounding the alarm for decades.

DOUG FESLER: It's an infrequent running path, but when it comes down big, look out.

NARRATOR: Flying over the most threatening path, the danger is obvious. But not to the residents below.

WOMAN: People that live here love it. It's so convenient and yet cozy. I don't know if I'm naive or in denial or what, but you know, the last time anything happened was thirty some years ago.

WOMAN: The house has been here since 1950 and it's still here.

MAN: It's something we're aware of and you know, it's not nice to have this sort of Damocles over your head, but I mean we were more than delighted to get this house.

DOUG FESLER: I doubt that any of these people, or very many of these people have ever been through a bad avalanche and they've never seen dead bodies or seen buildings ripped apart. The bottom line with this path is it is really not a question of if they're going to get nailed by a big one, it's like a ticking time bomb sitting there, waiting. And at some point, when the conditions are right, it'll come.

NARRATOR: To help end this perilous guessing game, fifteen hundred miles away, the research team from Montana State University heads back out into the Bridger Range. They plan to follow through on their experiment: to look at an avalanche from the inside and undermine forever its weapon of surprise. But first, they must find their shack of instruments, lost for now in the storm. They take care as they move, knowing that at any moment they could trigger a slide.

JIM DENT: I think that our concern today is wind loading off the cornices and since we don't have any wind coming through this general area, I feel like this is going to be good, but if you'll just keep an eye on me, I'll give it a quick speed cut.

NARRATOR: They risk only one person at a time across the most treacherous slopes.

SCOTT SCHMIDT: It didn't feel like it moved much, but you might want to make your run next to the tree.

JIM DENT: Yeah. Do you want to go Brett?

BRETT: I'll go for it.

NARRATOR: For a few brief seconds, each is on his own. Once they locate the shack, they have to remove the accumulated snow. They prepare their instruments and take measurements of depth and density. They will compare these numbers with those they find later in the avalanche and its aftermath. Their chance to observe the dynamics of the avalanche will last only a few brief seconds. Colored powder will help them measure velocity. To ensure the slide is triggered, they use four five-pound hand charges. Jim and Jay will be inside the shack. The rest of the team watches from a safe spot near the trees. All are tense. They have one shot.

M: Here she comes.

JAY: I cannot move. We need to be dug out.

M: Why don't you see if they're all right in there. Does someone got a radio?

M: I got them here. They're alive.

M: Are they happy?

JIM DENT: Well Scotty, Jay and I cannot move. We are buried inside the hut.

JAY: Tell them to get me out of here.

M: How are you doing? Are you guys all right?

JAY: Yeah, but you better dig fast, cause I'm like in a bad position.

NARRATOR: Being buried alive was not part of the plan. The size of the avalanche caught them off-guard. But in risking themselves, the researchers have obtained valuable information. They clock the avalanche at nearly 50 miles per hour.

JIM DENT: There's two distinct layers in the flow. And it's really homogenous.

NARRATOR: Despite its chaotic appearance, they find evidence of a multi-layered structure.

JIM DENT: And we saw something similar to that last week, remember?

M: A lot of times, we'll pick up some structure in the debris, like some finer chunks and stuff, but it all seems to be pretty smooth.

JIM DENT: It could very easily have come down, filled in all the irregularities that we'd left, deposited that, and then flowed over the top of that as the next, as a separate layer.

NARRATOR: These findings offer numerical clues to the rules that govern the power and extent of flow. It will soon be used with computers to predict avalanche run out, a tool of the future that could hold the key to protecting people, towns and roads. In Switzerland, nearly two-thirds of mountain roads wind their way through avalanche terrain. Until recently, sheltering them was one of the only options.

TOM RUSSI: There are a lot of avalanche defense structures there already, but to make the whole road absolutely safe would cost a fortune.

NARRATOR: A new approach is spearheaded by Dr. Tom Russi of the Swiss Institute. He is leading the development of the most advanced early detection system in the world. The plan is to capture a precise picture of what's happening where avalanches start, thousands of feet above the roadways. Here, on the shoulder of a ten thousand foot peak, Tom and his colleagues have come to where avalanches are born, an area known as the starting zone. They are looking for a spot to place a high tech station, one that will keep a watchful eye on the snow that accumulates here.

TOM RUSSI: It should be at an altitude where major avalanches actually start, but it's always a trade-off. The closer you get to the places where avalanches occur, the more problem you have to find a safe place.

NARRATOR: Already, these mountains are being watched by a nearly invisible web of over forty weather towers designed to safeguard the region's vital roads like Simplon Pass. A bloodline that links Switzerland with Italy, it has long been a victim to surprise avalanches. But maybe no longer, because high above the most vulnerable stretch of road, one experimental tower stands vigil. To be effective, it needs to be accurate. Tom takes the snow depth and temperature manually to compare to the readings taken by the tower. Along with snowpack data, the tower measures humidity and air temperature, all information vital to forecasters. For wind statistics, he relies on another tower perched fifteen hundred feet above. For the past few days, it has mysteriously gone silent. Wind direction and speed indicate whether snow is drifting from one side of the mountain to the other, overburdening the snowpack that threatens the road below. At this height, above any peaks or obstacles, true wind speed can be obtained. But it makes repair of the instruments a deadly challenge. Tom finds it encrusted with ice. With a few blows, Tom frees the wind meter. Now the station is ready to resume its work, giving local forecasters the vital statistics from the very locations where avalanches form. The next morning, Tom dials up the station he just visited. He confirms his repair of the wind station.

TOM RUSSI: A couple of days ago, we didn't get any data and now that the station works, wind speed is about twenty kilometers an hour.

NARRATOR: Then he checks the manual readings of temperature and humidity he gathered in the field. To his relief, they match the transmissions from the station. This constant stream of information is also being downloaded into computers at the Swiss Institute to help them better understand avalanches and forecasting.

OTHMAR BUSER: Exactly. What we want to know in the end is what the mechanical properties are. We are far away from that.

TOM RUSSI: In the past, weather forecasting was based on the forecaster's experience and intuition. And nowadays, weather forecasting is based on computer models. In avalanche forecasting, our understanding of the physics of snow and ice has improved a lot. And we now need to put this knowledge into computer models, and that will help to improve avalanche forecasting significantly.

NARRATOR: A rendering of the layers in the snow pack is at last emerging, fueled by vast amounts of data from the stations and a better understanding of snow dynamics. Half a world away, over another mountain range, Karl Birkeland is also conducting research to sharpen the tools of forecasting. Today's ambitious experiment is simple in design, but complex in execution. He's devised a way to measure how snow stability changes over the entire Bridger Range. Since dawn, the helicopter has been ferrying volunteers in teams of two to designated sites along the twenty mile ridge. They head down with the goal of digging as many snow pits as possible in one day.

KARL BIRKELAND: One of the first things we have to do is get out here, dig seventy to eighty pits and try and map what's going on on one given day throughout a mountain range. And no one's done that before.

NARRATOR: Stability tests find the weak layer, and a ram penetrometer measures how much force it takes to break through all the layers. These results, plus slope angle and direction, are carefully recorded.

KARL BIRKELAND: My hope is that we can take all this data and combine it in such a way that we can start to describe how snow pack changes with changes in terrain.

NARRATOR: Eventually, Karl is able to map snow strength across the entire range. The red marks areas most prone to avalanche, a deadly convergence of steep incline and weakly bonded snow. It is only a fleeting glimpse of conditions under constant change. But mapping is a first step in the eventual improvement of avalanche forecasting. But places like Iceland can't wait for better forecasting methods to be refined. Here, a town prepares for another winter.

MAGNUS MAR MAGNUSSON: It's been a little over a year ago since the disaster in Flateyri, which killed twenty people. And in this past year, we've been contemplating and designing defense structures for the town of Flateyri. We've come up with a design called a deflecting wall which is aimed at diverting avalanches away from the village.

NARRATOR: The mission is to anticipate the worst so the town will not be fooled again. At the base of the mountain, a wall is rising. Twenty million cubic feet of earth, reaching sixty feet high, it is designed to divert avalanches twice the size of the one that surprised Flateyri.

MAGNUS MAR MAGNUSSON: When the avalanche comes down, it comes shooting down this way, and hopefully it'll hit the wall right over here, and it'll be deflected down alongside the wall. And it's, it may not look like much right now, but we do have half of it built. We'll go another seven or eight meters up. And this way, we hope to give them a really good sense of security.

NARRATOR: More help may be on the way as scientists around the world work slowly, painstakingly, to unravel one of nature's most daunting puzzles. New technologies, new techniques and new understanding are transforming the tools of avalanche prediction and control. But while the future may hold promise, the snows will not wait. And with the coming of each winter season, those living among the mountains must brace once again for what might come their way: the Avalanche.

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Produced and Directed by
Beth Hoppe

Written by
Jack McDonald & Beth Hoppe

Stacy Keach

Co-Producer and Additional Directing
Jack McDonald

Edited by
Doug Quade

Director of Photography
Robert C. Poole

Associate Producers
Kate Churchill
Mary Canning Goldman

Rushmore DeNooyer

Pictures on the Wall

Sound Recording
Dave Ruddick

Assistant Camera
Kent Harvey
David Pickner

Avalanche Photography
Steve Kroschel

Additional Cinematography
Bill Snider
Scott Ransom
Ron Kanter

Additional Sound
Scott Simper
Deann Snider
James Brundige

Sound Mix
Richard Bock

Online Editor
Ed Ham

Brian Lovery

Production Assistance
Brad Puffer

Based on an idea for NOVA by
David Breashears

Production Support
Wilderness House

Additional Production Support
Black Diamond
Smith Optics
Northern Lights Trading Company

Archival Materials
Energy Film Library
Fusion Films
Icelandic National Broadcasting Service/Television
Real Action Pictures
Standard Films
Teton Gravity Research
The Icelandic Broadcasting Corporation

Still Photography
Electron Microscopy Unit, USDA-Agricultural Research Service
Skip Gray
Keith Hart

Special Thanks
Alaska Mountain Safety Center
Bridger Bowl Ski Area
Colorado Avalanche Information Center
Colorado Department of Transportation
Icelandic Meteorological Office
Gallatin National Forest
Southwest Montana Avalanche Center
Swiss Federal Institute for Snow and Avalanche Research
Utah Avalanche Center
Northwest Avalanche Center
Washington Department of Transportation
Randy Elliot
Kelly Elder
Ed LaChapelle
Mark Shaughnessy
Mike Garcia
Bill Boyle
Marc Peterson
Jeannette Weeks & Jerry Mills
Canadian Avalanche Association
Bruce Tremper
Silver Forest Inn
Karl Birkeland's research funded in part by the National Science Foundation

NOVA Series Graphics
National Ministry of Design

NOVA Theme
Mason Daring
Martin Brody

Closed Captioning
The Caption Center

Production Secretaries
Queene Coyne
Linda Callahan

Paul Marotta
Lisa Cerqueira

Nancy Marshall

Post Production Associate
Sandra Rizkallah

Post Production Editor
Rebecca Nieto

Post Production Online Editors
Mark Steele
Jim Deering

Post Production Director
Alison M. White

Unit Managers
Laurie Cahalane
Amy Trahant

Business Manager
Carolyn Birmingham

Science Editor
Lauren S. Aguirre

Senior Producer
Coproductions and Aquisitions
Melanie Wallace

Managing Director
Alan Ritsko

Executive Producer
Paula S. Apsell

A NOVA Production by the WGBH/Boston Science Unit in association with La Cinquieme and Sveriges Television.

© 1997 WGBH Educational Foundation. All rights reserved.


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