7th Annual Utah Snow and Avalanche Workshop
|"Loud noises trigger avalanches"|
|Although it's a convenient plot device in the movies (and most recently on Jeep commercials) noise does NOT trigger avalanches. It's just one of those myths that refuses to die. Noise is simply not enough force unless it's EXTREMELY loud noise such as an explosive going off at close range. Even sonic booms or low flying helicopter trigger avalanches only in extremely unstable conditions in which natural avalanches would likely occur on their own anyway. In 90 percent of avalanche fatalities, the avalanche is triggered by the weight of the victim, or someone in the victim's party.|
|"An Avalanche is a bunch of loose snow sliding down the mountain"|
|Avalanche professionals call these "sluffs." Loose snow avalanches account for only a very small percentage of deaths and property damage. What we normally call avalanches are "slabs" or cohesive plates of snow that shatter like a pane of glass and slide as a unit off the mountainside. Picture a magazine sliding off the table, with the victim standing on the middle of the magazine. This is why avalanches are so deadly.|
|Avalanches "strike without warning"|
|We often hear the word "strike" used in the popular media. Stock market crashes, meteor impacts and lost love may strike without warning, but avalanches almost always have obvious signs. Second, avalanches don't "strike". They happen at particular times and in particular places for particular reasons. To repeat again because it's so important: In 90 percent of all avalanche accidents, the avalanche is triggered by the victim, or someone in the victim's party. Natural avalanches occur because new or windblown snow overloads weak-layers or because of rapid warming, but there's almost always obvious signs of instability by the time avalanches come down on their own.|
|"If you see an avalanche coming, get out of the way"|
|Well, at least you can try. An average-sized dry avalanche travels around 80 mph and it's nearly impossible for someone to outrun an avalanche or even have time to get out of the way. A fast snowmobile has some chance but everyone else has a slim chance at best. Also, avalanches that descend from above kill very few people. Do I sound like a broken record here; the vast majority of avalanche incidents are triggered by the victim or someone in the victim's party.|
|"All the avalanche experts are dead"|
|We're happy to report just the opposite. Skilled avalanche professionals enjoy a very low avalanche fatality rate compared to other groups. Less than one percent of all avalanche fatalities involve avalanche professionals.|
|"Spit to see which way is up"|
|It doesn't matter which way is up. You can't dig yourself out of avalanche debris. It's like you are buried in concrete. Your friends must dig you out.|
|How fast do avalanches go?|
|Dry slab avalanches typically travel 60-80 miles per hour. They reach these speeds within about 5 seconds after they fracture. Wet avalanches usually travel much slower, around 20 miles per hour.|
|What kind of avalanche is most dangerous?|
|Dry slab avalanches account for almost all avalanche fatalities. A slab avalanche is like a dinner plate sliding off the table. A cohesive plate of snow slides as a unit on top of weaker snow. The slab shatters like a pane of glass with the victim in the middle of the slab and usually there's no escape.|
|What causes slab avalanches to fracture?|
|Snow is a lot like people. It doesn't like rapid change. (Raise taxes slowly enough and no one notices.) Dry slab avalanches occur when the weak layer beneath the slab fractures, usually because too much additional weight has been added too quickly, which overloads the buried weak layer. Snow is very sensitive to the rate at which it is loaded or stressed. Two feet of snow added over two weeks is not a problem. Two feet of snow in two days is a much bigger problem. Two feet of snow in two hours is a huge problem. (Wind can easily deposit two feet of snow in two hours.) Then, finally the weight of a person can add a tremendous stress to a buried weak layer, not in two hours, but in two tenths of a second-a very rapid change. That is why in 90 percent of avalanche accidents, the avalanche is triggered by the victim (or someone in the victim's party). Wet slab avalanches occur for the opposite reason. Percolating water dissolves the bonds between the snow grains, which decrease the strength of the buried weak layer.|
|What kind of weather produces avalanches?|
|Wind is the most common cause of avalanches. Wind can deposit snow 10 times faster than snow falling from storms. Wind erodes snow from the upwind side of obstacles and deposits snow on the downwind (lee sides). We call this "wind loading". The added weight from snowstorms also causes avalanches. If the weight of new snow is added faster than the buried weak-layer can adjust to its load, then it fractures and forms an avalanche. Rapid warming can also cause dry avalanches but this is much more rare. Rain or melting of snow surface can also cause avalanches. For instance, rain on new snow almost instantly causes avalanches. Strong sun or warm temperatures can also cause melting of the snow and creates wet avalanches. Wet avalanches occur because of a decrease in strength of the buried weak layer because water dissolves the bonds between the snow grains. But wind, snow or rapid warming do not always produce avalanches. It depends on the condition of the pre-existing snow and the conditions during the storm. With very stable snow pre-existing snow, even heavy, new snow with wind can bond well and be perfectly safe in the right conditions. Stability analysis is a complicated process and it requires much study and experience to develop good stability analysis skills.|
|Who gets caught in avalanches?|
Avalanche victims are almost exclusively backcountry recreationists--snowmobilers, climbers, snowboarders, snowshoers, skiers and hikers. Snowmobilers lead the list with twice the number of fatalities as any other activity.
|How do people get caught in avalanches?|
|In 90 percent of avalanche incidents, the VICTIM or someone in the victim's party triggers the avalanche.|
|How do people die when buried in avalanche debris?|
The good news is that even dense avalanche debris is about 60-70 percent air, but that's not the problem. People die because their carbon dioxide builds up in the snow around their mouth and they quickly die from carbon dioxide poisoning. Statistics show that 93 percent of avalanche victims can be recovered alive if they are dug out within the first 15 minutes, but then the numbers drop catastrophically. After 45 minutes, only 20-30 percent are still alive and after two hours almost no one is alive. In other words, you don't have much time.
|What it's like to get caught in an avalanche?|
A personal story by Bruce Tremper
Utah Avalanche Center Director, Bruce Tremper, knows firsthand and here is his story:
It happened to me for the first time, I believe, in November of 1978. I was a cocky ex-national circuit ski racer, 24 years old, fresh out of college, and because I needed the money I was building chairlifts at Bridger Bowl Ski Area in Montana. I already thought of myself as a bit of an avalanche expert since I had grown up in the mountains of western Montana, my father had taught me the basics of avalanches when I was 10 years old and I had spent many days skiing backcountry avalanche terrain without. In other words I was a typical avalanche victim.
I was skiing alone (first mistake) and not even wearing a beacon (second mistake). After all, I wasn't skiing, I was working, tightening the bolts at the base of each chairlift tower with a torque wrench. Even in my ignorance, I could see that it was hardly a subtle situation. Over a foot of new snow had fallen the night before and it was blowing hard, loading up the steep slopes beneath the upper section of the chairlift with thick slabs of wind-drifted snow.
When I was finished with the tower at the top of the avalanche paths, I started to walk up the slope so I could gain the ridge and circle around to the tower on the other side of the avalanche paths. But since I didn't bring my backcountry skis or climbing skins (third mistake), what was an easy ski down was an exhausting pig wallow back up and the cliffs were too scary to climb in my slippery plastic boots. So I couldn't help but notice that there was only a 15-foot wide couloir that separated me from the safe slopes on the other side. And naturally enough, I thought that a good skier like myself should be able to get my speed up and zip across it before anything too bad happened (fourth mistake).
I did my ski cut according to the book. I build my speed up and I crossed the slope at about a 45 degree angle, so that in theory, my momentum would carry me off the moving slab in case it did break on me. Since I had never been caught in an avalanche before, I had no idea how quickly the slab can pick up speed after it shatters like a pane of glass. I heard a deep, muffled thunk as it fractured. Then it was like someone pulled the rug out from under me and I instantly flopped down onto the snow loosing all the speed I had built up.
So like a startled cow, I sat there on my butt and watched soft slab instantly shatter into little blocks and the blanket of snow rocketed down the slope as if sucked downward by extra heavy gravity.
I jumped to my feet and tried to build up my speed again so I could jet off to the side. But the blocks were moving all around me, like tumbling cardboard boxes blowing in the wind, and nothing seemed to work. It was only two or three seconds after it broke and the avalanche, with its unintended passenger, was already moving a good 20 miles per hour. Looking downhill, I saw a line of small trees coming toward me at a frightening speed, looking like a line of periscopes slicing through the water toward me, like an old war movie. I tried to maneuver to grab one of them. But the avalanche, as I discovered, pretty much has its way with you, and choice is one of those things you think you might have before you're caught in an avalanche, but never afterward. Luckily it took me directly into the smallest tree and I slammed it hard and grabbed on with all my strength. The snow pounded me, like standing under a huge waterfall and it felt like my neck would snap as each block of wind slab smashed into my head. Luckily, grabbing that tree probably saved my life because it let most of the debris pass by me (debris that is below you can't bury you) but unfortunately, the tree eventually snapped off, and I quickly rocketed down the slope again.
Then the tumbling started, over and over like being stuck in a giant washing machine filled with snow. My hat and mittens were quickly ripped off along with both my skis. Snow went everywhere, down my neck, up my sleeves, down my underwear, even under my eyelids, something I would have never imagined. Every time I opened my mouth to breathe, the avalanche kind of injection-molded my mouth and throat full of snow. I spat out the plug of ice and with the next breath just rammed my throat full of snow again. Just when I needed to breathe the most, I couldn't. Drowning to death, high in the mountains, in the middle of winter and miles from the nearest water.
But after a long while, after I was about to pass out from lack of air, the avalanche began to slow down and the tumbling finally stopped. I was on the surface and I could breathe again. But as I bobbed along on the soft, moving blanket of snow, which had slowed from about 50 miles per hour to around 30, I discovered that my body was quite a bit denser than avalanche debris and it tended to sink if it wasn't swimming hard.
I swam hard to stay on the surface, but something was pulling one of my legs down. This was in the days before ski brakes and I had safety straps attaching my skis to my boots. One had already torn free somehow but the other one felt like a boat anchor tied to my leg. The ski was beneath me in the slower moving debris and as the surface debris moved faster, it tipped me forward, shoving my face in the snow again and I struggled hard to pull that ski up through the debris with my furious swimming. Eventually, the swimming worked, and when the avalanche finally came to a stop I found myself buried only to my waist, breathing hard, very wet and very cold.
I remembered from the avalanche books that debris instantly sets up like concrete as soon as it comes to a stop but its one of those facts that you don't entirely believe. But sure enough, everything below the snow surface was like a body cast. Barehanded, (the first thing an avalanche does is rip off your hat and mittens) I chipped away at the rock-hard snow with my shovel for a good 5 minutes before I could finally work my legs free. On one foot, the heelpiece of the binding hung from the safety strap with a six-inch section of the top-skin of the ski still attached to the screws. It had pulled completely off the ski. On my other foot, the ski was still intact but both the tip and the tail were broken. It has always been a mystery to me how it could have broken both skis, yet none of my bones.
I decided that day that, no, I wasn't an avalanche expert, not even close, and that was the real beginning of my avalanche education. Within a month I luckily landed a job on the ski patrol doing avalanche control, and I've been studying controlling, and forecasting avalanches ever since. One of these days, I may even become an expert. I don't think it's possible to watch all the snow on a mountainside shatter like a pane of glass and roar to the bottom at 60 mph, ripping out trees, without it changing your life, especially if you triggered the avalanche, and more especially if you rode it down and survived. Avalanches bit me in the butt and they haven't let me go.
|What do I do if I get caught in an avalanche?|
You're first job is to GET OFF THE SLAB, which as you might imagine, is not very easy.
Skiers and boarders technique:
If you're descending on skis or snowboard, try heading straight down hill to build up some speed, then angle off to the side off the moving slab. If you're close enough to the crown, you can try running uphill to get off the slab, or running off to the side. If you're ascending when the avalanche breaks, there's really not much you can do.
If you're on a snowmobile you have the advantage of power. Grab some throttle and use your power and momentum to your advantage. If you're headed uphill, continue uphill. If you're headed across the slope, continue to the side to safe snow. If you're headed downhill, you're only hope is to try and outrun the avalanche. Remember that large avalanches travel 60-80 mph and they are difficult to outrun. Also remember that a disproportionate number of avalanche fatalities occur when one snowmobiler gets stuck on a slope and another person rides up to help them. Never go up to help a stuck buddy unless there are several other people in a safe place who can dig you out. This, of course, requires that everyone is wearing beacons and shovels and has practiced regularly with them.
|How do I judge the danger of avalanche terrain?|
|How do I judge snow stability?|
Look for obvious clues:
|If you see your friend get caught in an avalanche....?|
What is avalanche knowledge worth to you?
Do you use the Utah Avalanche Center to help you make decisions in the backcountry? Most of the cost of producing daily advisories and providing other avalanche information in Utah is paid for by donations and grants. We depend on users like you to help support the Utah Avalanche Center.
Please consider donating to the Utah Avalanche Center this season and have a great winter!