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Find answers to the common questions we hear about the Bridger-Teton Avalanche Center. If you don’t find your answer here, please Contact Us and we’ll get back to you as soon as possible.
The most essential travel technique in avalanche terrain, whether on foot or a machine, is to travel one at a time. This can mean spacing out across steep areas, staying within communication reach when traveling (voice or radio), regrouping out of avalanche terrain, and communicating frequently, amongst other things.
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 the 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.
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 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.
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 rarer. 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.
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.
In 90 percent of avalanche incidents, the victim or someone in the victim’s party triggers the avalanche. This includes remotely-triggered avalanches, which are avalanches that can trigger some distance from a steep slope, from terrain above, below, or next to.
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
No, loud noises do not trigger avalanches, contrary to popular beliefs. Although it’s a convenient plot device in the movies, noise does NOT trigger avalanches. It’s just one of those myths that refuse to die. Noise is simply not enough force. Even sonic booms or low-flying helicopters trigger avalanches only in extremely unstable conditions where natural avalanches would likely occur independently. In 90 percent of avalanche fatalities, the avalanche is triggered by the weight of the victim or someone in the victim’s party.
Observations provide forecasters with important information regarding the snowpack to help us decide the avalanche danger. More observations mean more data points. And the more data points forecasters obtain, the better the understanding they have of the conditions. Forecast areas cover thousands of square miles, so it’s vital that the public help inform the avalanche center of the conditions they see out in the backcountry. Observations help us help you.
You can find our observation page here: https://bridgertetonavalanchecenter.org/observations/#/view/observations
You can find a map of all the weather stations here: https://bridgertetonavalanchecenter.org/weather-stations/#/
You can find a calendar of all courses and events here: https://bridgertetonavalanchecenter.org/events/