Everything You Wanted To Know About Avalanches

How can accidents happen? An expert explains the basics.

Last month an avalanche on Mount Everest killed 13 Sherpas and left three missing.

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But how do avalanches happen, and is there any way to survive? Eric Peitzsch, physical scientist for the U.S. Geological Survey, explains.

Ever see snow slide off of a car windshield?

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That's basically a tiny avalanche.

Avalanches need a few simple ingredients, and forecasters try to monitor them using any bit of data they can get.

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"We certainly can’t predict every single avalanche and where exactly it’s going to be," says Peitzsch. "If I could, I’d probably make a lot more money than I do."

The slab is the section of snow that's sliding, which breaks off at a weak layer.

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The windshield is the terrain, which has to be steep enough for snow to slide. The trigger can be anything from a skier to more snow (or in your car's case, a sunny day).

All snow is layered, and the weak layer is less cohesive than the others.

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Like this. Here Peitzsch is doing an extended column test to try to forecast potentially dangerous conditions. If a layer fractures across the isolated column of snow, the weak layer can crack across an entire slope.

Wind can also form cornices, or overhanging blocks of snow, usually on the tops of ridges. If they fall, they can also trigger an avalanche.

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This is a cornice. Pretty, but deceptive.

Most avalanches occur between 30 and 45 degrees.

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Here's a reminder of how steep that is.

So if you see one, you still have time to outrun it, right?

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Not really. Dry snow avalanches can travel at more than 100 mph. Wet snow avalanches, which have water running through them, are denser, making them slower but more powerful, like moving concrete.

There are also sluffs, or loose snow avalanches, that start at a small point near the top of a slope and fan out as they go.

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"[They’re] typically not as dangerous as slab avalanches, but they can be in what we call high-consequence terrain," says Peitzsch. Say you're close to a cliff. You can fill in the rest.

And the size of an avalanche doesn't necessarily matter, either.

Forest Service National Avalanche Center / Via fsavalanche.org

"Even on small slopes, avalanches can be dangerous," says Peitzsch. You'll have nowhere to go if there's a gully or creek at the bottom, especially if the snow piles on top of you.

But I go skiing all the time. Should I be worried?

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Mostly if you're in the backcountry. While we can't stop them from happening, a lot of ski areas do avalanche control where they trigger them on a regular basis using explosives and other artillery, says Peitzsch. That way the recreating public (you!) have a reduced chance of being caught in one.

When you're looking for someone who's buried, speed is crucial.

AP Photo/Gurinder Osan, File

One of the best pieces of gear you can have is an avalanche transceiver. After 10 minutes, a victim's odds of surviving drop significantly, says Peitzsch — especially with the impending threat of asphyxiation. The transceiver emits a signal to your party, who switch their receivers into search mode.

What happens if you get swept into one?

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Just keep swimming. Some advise to try and fight your way to the surface the best you can, but their sheer force makes that considerably easier said than done.

Even if you land on top, "it’s so powerful it can move you through some pretty gnarly terrain," says Peitzsch. You can be knocked into trees, rocks, or other debris, so trauma becomes an issue.

But if all goes well, you're found safe and sound.

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Knowledge is power, so stay informed!