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You’ve seen cartoons. You understand avalanches.
There’s fresh snow. Someone can’t keep their voice down.
Snow rumbles down the mountain and buries everything.
Then everybody digs themselves out, they learn their lesson, and then they get hot chocolate.
Except, that’s really not how it works at all.
Real avalanches are much more dangerous.
And even though a single skier can trigger one, the classic avalanche set off by a loud
yell probably never happens, because skiers create a lot more pressure than your voice,
no matter how loud you yell.
Just about the only thing cartoons get right is that avalanches happen on snowy mountains.
Snow builds up until it’s nearly heavy enough to overcome
the friction between it and what lies underneath
Then, with the slightest extra push, that snow starts sliding down the slope.
And once it gets going, you have yourself an avalanche.
The big ones can include up to millions of kilograms of snow, and can scream down a mountain
as fast as 150 kilometers per hour.
But there’s more than one type of avalanche, and each one unfolds in its own hardcore way.
Powder avalanches, also called “loose-snow avalanches”,
are kind of exactly what they sound like.
They can happen after relatively loose snow falls on snow that’s more densely packed.
If the denser snow has been there for at least a few days, it can be covered with a thin
layer of hard frost called surface hoar.
It keeps the new snow from mixing with the denser stuff underneath.
The result is two distinct layers, where the top is pretty loose and the
bottom is more dense and stable.
It only takes something small, like shifting snow or a skier,
to overcome the friction between the two layers.
And that sends some of the loose snow tumbling down.
The snow stays pretty loose, falling more like a big cloud than a snowball.
But don’t let the cloud simile fool you, there’s still a lot of snow.
Powder avalanches can tear roofs off houses and even obliterate thick cement walls.
That said, if you’re the skier who triggered one, you’ll probably be okay.
Powder avalanches tend to start relatively small, only picking up more snow and becoming
really dangerous as they move down the mountain.
Then there are slab avalanches, which account for about 90% of avalanche fatalities.
They also start with two unmixed snow layers, but this time, their positions are reversed:
the bottom layer is weaker, and the top is more dense.
Just like before, it only takes a small disturbance to get the top layer sliding along the bottom,
or even right against the ground, if it’s smooth enough.
But because the sliding layer is stronger this time, it doesn’t break up into a cloud.
It stays together in one or a few huge chunks, called slabs.
Each slab is like a densely packed snowball up to a meter deep and potentially hundreds
of meters wide, and it can crush anyone unlucky enough to get in the way.
The slabs can also break free far from whatever triggered them in the first place, thanks
to a sort of ripple effect where clumps of snow pull on one another.
And that’s another reason they’re so much deadlier than powder avalanches: Even if you’re
far from the trigger point, you could still be standing on the slab that’s about to fall.
Both kinds of avalanches can be started by a little extra pressure on the snowy surface,
anything from falling rocks to an avid snowmobiler going over the wrong spot at the wrong time.
So it seems to make sense that sound could trigger an avalanche.
After all, sound travels as pressure waves, where molecules push against each other.
So you’d think a loud enough sound could provide that extra pressure to start an avalanche.
And that is true, in principle.
Shockwaves from dynamite are used to set off intentional avalanches
so skiers can’t start them accidentally.
But the classic picture of a gunshot or a scream triggering an avalanche is generally impossible.
Even if loud sounds hurt your ears, they usually have less than one hundredth the pressure
they’d need to affect huge masses of snow.
After all, think of the loudest sound you’ve ever heard: concerts, airplanes, infants, whatever.
Now think about how much that sound physically squeezed your body.
Not how much your ears hurt, but how much your body was actually pushed and pulled by
the sound itself, like when you feel the beat of a drum in your chest during a concert.
Now, compare that feeling to a fully equipped skier jumping on your stomach.
The skier wins, and that’s why they can trigger avalanches but loud sounds normally can’t.
Even sonic booms, the shock waves that happen when something like a
plane breaks the sound barrier, tend to be too quiet.
Although over just the right combination of snow layers,
they can sometimes nudge things past the tipping point.
So if you’re ever on a slope and you’re worried about an avalanche, you can shout
at someone about it, just don’t go jumping around on the mountain.
But also, general tip: If you’re really worried about an avalanche,
maybe don’t go on that mountain.
Whether I’m hiking in the mountains here in Montana or just biking around town,
I’m always looking for new ways to film the world around me.
And that’s why I really like this Skillshare class by photographer Reuben Krabbe.
It’s called Adventure Sport Photography, and it teaches you the basics of how to shoot
and edit amazing action shots,
including some tips that could seriously help you out on your next ski trip.
If you’re headed to the mountains this winter, you’re in luck, too:
Right now, Skillshare is offering SciShow viewers 2 months of unlimited access for free.
That means you could take this class, or any other of Skillshare’s more than 20,000 classes,
all while supporting SciShow.
You can follow the link in the description to take advantage of this offer!
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