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Avalanches: The Bad, The Deadly, and The Oddities

All over the world, people are killed by avalanches either by skiing, driving in an avalanche-prone area, or ski mountaineering. Many places in Colorado and the States are at a high risk of avalanches in the winter. These areas in Colorado are any mountain with a grade higher than 30 percent. And areas where slides have happened in the past. There are many different types of avalanches but the killer avalanche is a slab avalanche. A “slab” is a cohesive plate of snow that slides as a unit on the snow underneath. If you are climbing up a mountain or skiing down one and you see a crack in the snow, that is the indicator that a slab avalanche is going to start. If you see a crack in the snow but the snow beneath the crack hasn't started to move yet. Don’t go near it, it’s waiting for something to trigger it. The bonds holding a slab in place typically fracture at 350 kilometers per hour (220 miles per hour) and it appears to shatter like a pane of glass. It’s typically about the size of half a football field, usually about 30-80 centimeters (1-3 feet) deep and it typically reaches speeds of 30 km/hr (20 mph) within the first 3 seconds and quickly accelerates to around 130 km/hr (80 mph) after the first, say, 6 seconds. Dry slab avalanches can lie patiently, teetering on the verge of catastrophe, sometimes for days to even months. The weak-layers beneath slabs are also extremely sensitive to the rate at which they are stressed. Many alpine touring skiers have triggered a slab and got caught in it. This avalanche doesn’t really allow you to escape because the crack often forms above the person or thing that triggered the slab to break loose. If you are caught in one and manage to survive, you are among the lucky few. The survival rate of a victim buried by an avalanche is roughly 91% if rescued in 18 minutes or less. When a rescue takes anywhere between 19 and 35 minutes after the avalanche. The survival rate drops down to 34%. Even if you do survive the initial flow of the avalanche, you are more likely to die from severe wounds, hypothermia, or suffocation. Loose Snow Avalanche. These avalanches are commonly called “sluff” avalanches. These happen when loose snow from a higher part of the mountain falls downhill or when a skier or snowboarder kicks up the powder causing it to fall down the mountain. These types of avalanches usually start from a point and fan outward as they descend, and because of this they are also called “point releases.” Sluffs kill very few people. The very few people who are killed by sluffs usually tend to fracture beneath you as you cross a slope instead of above you as slab avalanches often do. Many people call them “harmless-sluffs'' because they really don’t cause all that much damage to the body. However, if you do get caught in one, it can easily take you over a cliff, bury you in a crevasse, or put you in a terrain trap. Most of the people who get caught in these are climbers who are caught in naturally triggered sluffs. These are more prone to happen in wet or springtime conditions. This avalanche also has a good side to it. It can show a person in the snow is good enough to ski or walk across. When a sluff comes down a mountain and it doesn’t cause a slab avalanche in the process, that means that the snow that the sluff traveled over is strong enough to support a person.

Icefall avalanches. These happen when a glacier slides off the edge of a cliff like a waterfall but made of ice. Many high-altitude mountains, and mountains closer to the sea, have glaciers all across them. In the summer when the heat and the sun starts to melt the glacier. However, icefall avalanches are fairly random. They are more likely to happen in the summer and spring than the winter but they can happen at any time of the year. Despite this, icefall avalanches kill few people compared to the deadly slabs that people trigger themselves. Lots of the deaths from icefalls usually occur to climbers in big mountains who just happen to be in the wrong place at the wrong time. Deaths happen from campers camping underneath an icefall hazard. If you are camping, never camp under a potential icefall area. Given this, bad weather can prevent a person from seeing such a hazard. Most of the deaths happen this way.

Cornice avalanche. These types of avalanches are very similar to icefalls in the way that they don’t kill very many people. However, these are like slab avalanches in the way that they are often caused by people. One of the main dangers that cornice avalanches produce is breaking back further than you think. Most of the people who died from these types of avalanches are usually ski mountaineers and mountain climbers. You know, cornices aren’t all bad. You can use cornices to your advantage by intentionally triggering one to test the stability of the slope below or to intentionally create an avalanche to provide an escape route off of a ridge. That and they just look cool.

Wet avalanches. These avalanches are really hard to predict when they are going to happen. They are also strikingly similar to dry avalanches. Wet avalanches occur when warm air, the sun, or rain cause water to percolate through the snowpack and decrease the strength of the snow. In some cases, they can even change the mechanics and behavior of the snow itself. Once a wet avalanche happens they are really easy to escape because they move so slowly. These move at about ten to 20 miles per hour, unlike the dry avalanche that can move at speeds anywhere between 60 to 80 miles per hour. That’s a big difference. However, there is a twist. These avalanches can cause major damage to forests, they can inflict major property damage, and they can produce quite a hazard on a highway. Wet avalanches don’t have that many fatalities but that does not mean that they are insignificant. They still account for a reasonable percentage of avalanche fatalities in maritime climates, especially among climbers.

Glide avalanches. A glide avalanche is a type of avalanche that takes a reasonable amount of time to happen. They occur when the melted water from the snow lubricates the ground causing the snowpack to “glide” over the surface of the ground. Kinda like a glacier. These usually don’t release in a massive avalanche but when they do, they can have catastrophic results. Now if and when they come down is completely random. Which is why they are so similar to an icefall. The good this is that this type of avalanche does have a key indicator that there is a glide happening. There is usually a decent size crack in the snow. Now this avalanche is fairly difficult for a person to trigger because of the mass. However, is a good idea not to mess around on top of one or to camp underneath one. Glide avalanches usually happen in wet climates but they can be found in dry climates, usually in the spring. This avalanche is also a strange one. They don’t come down when you would expect them to. Most people think that they would come down during the heat of the day or when the snow melt reaches its maximum. But no, these usually come down with the arrival of cold air following the snowmelt down the mountain.

Slush avalanches. This type is a strange one in the avalanche world. These tend to happen in very northern latitudes like the Brooks Range, Alaska, or in northern Norway. These are weird because they usually happen on very gentle slopes. Slopes that range anywhere from five degrees to 20. Most avalanches happen on a slope steeper than 30. A typical slush avalanche happens when water starts to pool up in the permafrost soil and occurs during the rapid saturation of a thin, weak snowpack. When the water saturates the snowpack, it causes it to catastrophically lose its strength. These can run for a very long distance on very gentle terrain. Very few people are killed by these every year because of their common location. Very few people in the world live at high-altitude permafrost mountains. But they can create a reasonable amount of danger for structure in the wrong place or for a person.

All and all, avalanches can vary from downright deadly to you may get some bruises but that's all. Slab and sluff avalanches are like the polar opposite of each other. One will most likely kill you and the other will probably give you some bruises. Or in the case of a slush avalanche, they can just be downright strange. Even icefall, glide, and cornice avalanches have a chance of killing you. But with them, it’s more likely the wrong place at the wrong time.

Nate Meeter is a junior at Poudre High school. He mountain bikes, skis, and plays baseball and tennis for fun and for a living. But mainly for fun. This is his first year on the Poudre Press. He also runs a blog that you can check out here!

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