[music playing] (narrator) The Rocky Mountains are famed for their beauty.

But behind that exquisite facade, a predator lurks: avalanches.

Powerful and mysterious, they are one of the most deadly natural disasters in the U.S.

But to avoid the big one, you have to do something unexpected.

You have to start them.

[music playing] (speaker) Attention all mitigation routes.

Radio check.

(speaker over radio) We got fire in 100 seconds.

It's about four and a half, route 23.

(narrator) This is Solitude Mountain Resort in Northern Utah.

Thousands of people are drawn here every year by peaks that reach 10,000 feet into the sky.

They are both breathtaking and avalanche-prone.

(speaker) Sixty to seventy-five percent of our terrain at the resort is what's considered avalanche terrain.

(narrator) For the past 27 years, it's been Ian Reddell's job to make sure ski holidays don't become tragedies.

(Ian) The most deadly avalanches are slab avalanche.

You get this crack that forms, and then the snow starts to move down the hill in one solid block.

(narrator) Avalanches like this can reach speeds upwards of 80 miles per hour.

(Ian) Those big massive powder clouds, those are slab avalanches that are causing that, and they're very destructive.

(narrator) With several inches of fresh fallen snow and high winds, the avalanche danger today is high.

(Ian) Every time it snows, we go up into our avalanche terrain.

We have to hike up there.

It's very narrow.

It's quite steep.

One false step might be the difference if you're going home in an ambulance or not.

(narrator) Sometimes the slopes need a good strong shove to start an avalanche.

(Ian) Fire!

(narrator) And the best method they've found is to use explosives.

(Ian) Explosives produce a tremendous shockwave... [explosion] that is able to penetrate the snow pack and make a weak layer fail.

When that weak layer fails, an avalanche happens.

Our goal is to create lots and lots of small avalanches so we don't have these big avalanches.

[explosions] If we just waited for the snow to build and build and build, sets us up for disaster for having more catastrophic and destructive avalanches.

(narrator) But what makes some areas more avalanche prone?

(Ian) The angle of the slope is a major factor, and the sweet spot's right around 38 degrees.

(narrator) Slopes between 30 and 45 degrees are at high risk of avalanche.

Slopes under 30 degrees aren't steep enough to overcome the friction between the snow layers.

And slopes over 50 degrees are usually too steep for the snow to accumulate.

Sometimes, the slope just needs a little gentle encouragement to avalanche.

That's what ski cutting does.

(Ian) You're pushing down the slope, giving up more force than what you would if you were just to ski over it, and then you get your skis straight again and keep going.

(narrator) Don't try this on your own.

These are professionals equipped with special avalanche gear.

(Ian) The risks that we face are very real.

If you can't make it to your safe area, then you shouldn't be doing the ski cutting, because that exposes yourself to being caught in an avalanche.

(skier) Oh, my God!

Oh, my God!

Your heart does not stop beating for days.

I remember thinking, I did everything right.

(narrator) Chago Rodriguez researches avalanche science and teaches avalanche safety, and his close encounter with death in the mountains of Argentina caused him to question everything he thought he knew.

(Chago) That avalanche took my confidence away.

I had to go back to the science and try to understand what was the mistake.

If you are in an avalanche, you made a mistake.

(narrator) Together with Hans-Peter Marshall and a team of researchers, he's trying to understand the root causes of avalanches.

To do this, they're researching in the backcountry: remote areas outside the boundaries of traditional ski resorts.

(Chago) There is avalanche danger.

Everything might look stable, but there are pockets of instability.

(narrator) Idaho sees hundreds to thousands of avalanches each winter.

To look for signs of unstable snow, these researchers dig snow pits.

(Chago) We dig a hole from the surface all the way to the ground.

We are looking at all of the structure of the snow pack.

(narrator) The snowpack is built like a layer cake.

Each time it snows, a new layer is added.

Some layers are thick, some thin.

Some strong, some brittle.

When new snow falls on top of feathery crystals, it doesn't bond well and a weak layer is created.

Slab avalanches occur when additional weight is added rapidly to the snowpack, overloading buried, weaker layers of snow.

These weak layers or facets are more brittle and easier to break and slide.

Understanding how and where these weak layers in the snowpack exist helps prevent disaster.

(Chago) You can be on a safe area and you only move several meters and you enter the danger zone, and how do you anticipate that?

(narrator) To solve this, the researchers are trying to develop new and more efficient ways to detect instability in the snowpack.

They're using technology, both on the ground... and up in space.

A new satellite being launched in 2022 could allow scientists to actually measure from space changes in the amount of snow on the ground.

(Hans-Peter) We are going to start getting these maps of snow information that we've never had before.

The new technology, what it's enabling us to do is make measurements much quicker, more objective, and at higher resolution, and that's teaching us something about how these properties vary over the landscape.

(narrator) What they're learning could one day lead to advances that will help people like Ian Reddell.

For now, Ian and the team rely on more traditional methods.

(Ian) The best part of the job is skiing your favorite ski line of the resort without having to worry about an avalanche coming down after you.

Whoo!

[music playing] Accessibility provided by the U.S. Department of Education.