-[suspenseful music] -[volcano thundering] (narrator) It was one of the most cataclysmic natural disasters in American history, destruction on an unimaginable scale.

But today, Mount St. Helens' volcano is experiencing a rebirth.

It's the site of earth's newest glacier, a glacier that is awe-inspiring from both above and below.

Why are these scientists here?

Because they hope the secrets within these frozen caves will help reveal the mysteries of far off planets, in our solar system and beyond.

[suspenseful music continues] It's spring 1980.

Mount St. Helens stands tall, the fifth highest peak in Washington state.

But on the morning of May 18th all of that changes in an instant.

[volcano exploding] The volcano explodes with 500 times the force of the Hiroshima bomb.

It's the most destructive eruption in U.S. history-- 57 people and thousands of animals die; 230 square miles of forest are leveled.

Devastation is widespread.

The blast creates a yawning crater about the size of downtown Seattle.

Not long ago, lava flowed through here, but now this massive caldera holds something wondrous, the world's youngest glacier.

It's known as Crater Glacier and has largely remained out of sight of the public.

Even more surprising than its location on an active volcano is the fact that the glacier continues to grow while most others around the world are in fast retreat.

What's driving its growth?

To understand it, you need to know how the crater formed.

The 1980 explosion caused the mountain's north side to collapse.

What remained was a crescent shaped husk.

The steep crater walls shade the glacier from sunlight most of the year.

These walls are so steep, in fact, that masses of snow, ice and rock slough off the rim and pile at the base.

Combine that with a large annual snowfall and it provides a steady diet of raw materials to feed a hungry little glacier.

Over the decades, this baby glacier grew into the hulk it is today, and it's growing in thickness by up to 15 meters per year.

This crater and its glacier have become a scientific curiosity.

This international team of scientists will spend a week up here researching it.

(Andreas) This is a very, very special place to be in the middle of a crater, which rose a mountain, and you're sitting in the middle of it, that's awesome.

(narrator) The glacier on which this camp sits is more than 200 meters thick in some places.

That's close to the length of two football fields.

(Kalind) It is definitely, definitely a dangerous place where you constantly have to be vigilant.

We woke up one day and a crevasse was forming, basically a break in the snow and we were worried our tent was just gonna go down with some of the glacier.

(narrator) Just getting to the research site is an adventure.

Boulders thunder down the steep walls of the crater with such frequency and speed that one area has been dubbed The Shooting Gallery.

(Carl) It's a little scary, right?

Like, especially the first few times while we were out on the glacier, having the rocks come down.

(Michael) It's a inherently dangerous place so we have to carry a lot of safety gear with us and then we have to haul all the gear up a mile hike.

(narrator) Although this glacier looks solid, it's actually riddled with cavities.

These caverns are a sign that the volcano remains active.

Vents in the crater known as fumaroles belch scalding hot steam and gases.

This hot steam and gas melts holes in the glacier.

(speaker) The fact that they're caused by volcanic gas and steam just makes them totally unique.

There's actually not many places like this in the world.

(Roberto) There's only that we know of for sure, maybe four or five sites around the world.

(narrator) Some of the caves can wind a mile or more through the glacier.

Inside, it's an alien landscape of dripping ice.

(Roberto) It's not a very welcoming environment.

You don't really know what's gonna happen because there are dangers everywhere.

(Andreas) Sometimes it's really foggy.

You don't know where you really are and where to go.

(Christian) Nothing is stable in these caves.

So anywhere you step could be a boulder that can roll down slope.

You could easily twist an ankle or hurt yourself and if you did, because of the difficulty of the terrain, it would be very hard to get you out.

(narrator) But to these scientists, the opportunity to study this unique environment is worth the risks.

Mount St. Helens is the most active volcano in the continental U.S., and this glacier could serve as an early warning system of sorts.

(Andreas) This is a great laboratory up there because everything what's going on under a glacier is in a time lapse, so driven by the fumes, these caves are really active.

If the melting is getting stronger and the glacier would retreat, this could be a sign for the next eruption.

[water splashing] (narrator) While St. Helens' big features like glaciers might hog the spotlight, some of these researchers are focused on smaller mysteries.

(speaker) I am an astrobiologist, and one of the things you try to do as an astrobiologist is you try to find an analog here on earth that is similar to an environment in space.

Mount St. Helens is a very extreme environment, especially in these glacier caves because it's dark and nothing has ever grown in these environments.

This is a very difficult environment for microorganisms to live in, and any kind of organism to live in.

(Roberto) Mount St. Helens is particularly unique because it's a fairly new system.

The eruption in 1980 basically sterilized the volcano.

So anything that we find here allows us to look at the ways that life can inhabit a new system.

(narrator) In this blank slate of life they're finding extreme bacteria recolonizing and growing beneath the ice, feeding off of the gases in these caves.

By learning about how the smallest forms of life develop in extreme environments on earth, the scientists are hoping to gain a deeper understanding of what to hunt for on places like Mars.

So by looking inward at this volcano, we're actually looking out into our solar system.

(Richard) The more we learn about these sort of systems the easier it will be for us to explore surfaces of other planets.

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

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