- [Host Joe Hanson] The Rocky mountains are famed for their beauty, but behind that exquisite facade, a predator lurks.
Powerful and mysterious, they are one of the most deadly natural disasters in the US.
But to avoid the big one, you have to do something unexpected.
[blasting] You have to start them.
[exciting techno music] ♪ - [Woman] Attention all mitigation routes, radio check.
- [Man] We got fire in 100 seconds.
We got 4 1/2 round 23.
[wind blowing] - [Joe] This is Solitude Mountain Resort in Northern Utah.
[exciting music] 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.
- [Ian] 60 to 75% of our terrain at the resort is what's considered avalanche terrain.
- [Joe] For the past 27 years.
It's been Ian Reddelle'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, like, solid block.
- [Joe] 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.
[wind blowing] - [Joe] With several inches of fresh fallen snow and high winds, the avalanche danger today is high.
[exciting music] - [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 of you going home in an ambulance or not.
[exciting music] - [Joe] Sometimes the slopes need a good strong shove to start an avalanche.
[match striking] - [Man] Fire!
- [Joe] The best method they've found is to use explosives.
- [Ian] Explosives produce a tremendous shockwave [blasting] that is able to penetrate the snow pack and make a weak layer veil.
When that weak layer fails an avalanche happens.
[exciting music] Our goal is to create lots and lots of small avalanches, [blasting] so we don't have these big avalanches.
[blasting] If we just waited for the snow to build and build and build - [Man] Fire!
It sets us up for disaster [blasting] or having more catastrophic and destructive avalanches.
[wind blowing] - [Joe] But what makes some areas more avalanche prone?
- [Man] The angle of the slope is a major factor and the sweet spot's right around 38 degrees - [Joe] 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.
[snow crunching] Sometimes the slope just needs a little gentle encouragement to avalanche.
That's what ski cutting does.
- [Man] You're pushing down the slope, giving it more force than what you would if you were just a ski over it.
And then you get your skis straight again and keep going.
- [Joe] Don't try this on your own.
These are professionals equipped with special avalanche gear.
- [Man] 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 be caught in an avalanche.
[exciting music] - [Man] All right, all right.
[walkie talkie clicking] - [Man] Your heart does not stop beating for days.
I remember thinking I did everything right.
- [Joe] 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 why was the mistake.
You are in an avalanche.
You made a mistake, - [Joe] 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 back country, remote areas outside the boundaries of traditional ski resorts.
[exciting music] - [Chago] There is avalanche danger.
[exciting music] Everything might look stable but they're pockets of instability.
- [Joe] Idaho sees hundreds to thousands of avalanches each winter.
[snow crunching] 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.
- [Joe] The snow pack 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 snow pack, 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 snow pack exist helps prevent disaster.
[scratching] - [Chago] You can be on a safe area and you only move several meters and you entered it, then you're sunk.
How do you anticipate that?
[exciting music] - [Joe] To solve this the researchers are trying to develop new and more efficient ways to detect instability in the snow pack.
They're using technology, both on the ground [machine whirring] 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.
[exciting music] - [Joe] What they're learning could one day lead to advances that will help people like Ian Reddell.
[blasting] For now Ian and the team rely on more traditional methods.
- [Ian] The best part of the job is skiing your favorite ski line at the resort without having to worry about an avalanche coming down after you.
- [Woman] Whoo!
[exciting techno music] ♪