Original subtitles

[narrator reading]

[narrator] A massive sunken vessel,

dredged from the depths of an Arctic bay.

How did one of the most remarkable sailing ships in the world

end up at the bottom of a bay in Nunavut?

A new expedition attempts to solve the infamous mystery

of nine dead university students.

[Anthony Morgan] Okay, missing tongues and eyeballs, slashed-up tents.

This is not a mystery, this is a horror film.

[narrator] An ice age-old mystery rises to the surface.

[Brooke Guzar] There's bones on top of bones

arranged in this particular way.

[Alison Leonard] This is a terrifying image.

What happened here?

[narrator] These are the strangest mysteries, trapped in the coldest places.

Lost relics.

Forgotten treasures.

Dark secrets.

Locked in their icy tombs for ages,

but now as ice melts around the world,

their stories will finally be exposed.

[narrator] Cambridge Bay, Nunavut.

This remote and isolated settlement is tucked high

into the Arctic Circle, just 1,100 miles from the North Pole.

[Michael Robinson] In the wintertime, six weeks go by without any sunlight at all,

and only for three months of the year is the bay ice-free.

[narrator] In 2016, below the bay's icy surface,

a salvage team inspects a mysterious wooden vessel.

[Meagan McGrath] This thing is heavy, and not just because it's massive,

its hull is encased in lead, but to the trained eye, this is a special boat.

Its construction is pretty unique.

[narrator] Whose ship is this? And how did it end up on the bottom of a frozen bay

high in the Arctic?

The ship is massive, 118 feet from bow to stern,

40 feet across the beam,

and the hull is wrapped with a layer of oak, more than two inches thick.

[Anthony Cantor] Oak is highly valued in shipbuilding because it's strong and durable,

but it's also flexible and it resists moisture.

But this ship had two extra inches of oak on the hull,

so that suggests that it was built for a very specific purpose.

[narrator] The protective layer of oak is similar to the kind of hull

built for war vessels.

Could this ship have been sunk in a forgotten battle?

On a wrecked warship, you'd be looking for cannons, guns

or other types of military equipment,

but they don't see anything like that.

[Robinson] Divers searching the site didn't find any evidence

that it was a warship.

So, then the question is, what else could it be?

[narrator] The traditional Inuinnaqtun name for the area

is Iqaluktuttiaq, which means "good fishing place."

Perhaps this wreck is the remains of a whaling ship.

And that makes sense. Before oil and gas,

whale blubber was used for lamp fuel, for soap, amongst so many other things.

[Cantor] Whalers could have tried expanding their hunting grounds

to meet the enormous demand for whale products.

There's just one problem with this theory.

If this were a whaling vessel, you'd expect to find

equipment like harpoons, nets and guns,

and none of that is present here.

[narrator] The layout of the ship is also unusual.

A whaling vessel would definitely be equipped with a compartment

large enough to store the meat after it was butchered.

This doesn't have anything like that.

So what was this ship and what was it doing here?

Determined to solve the mystery,

the salvage team raises the ship to the surface.

The ship's name has long since faded from its stern.

[McGrath] But a single word on one of the deck boards calls out from the past.

Amundsen.

[narrator] Who is Amundsen?

In 1917, in Oslo, Norway,

preparations are underway for the very first nautical expedition

to the North Pole, unthinkable at the time.

[Robinson] In the late 19th century, as people attempted

this expedition and failed, it gave the quest even greater and greater cachet.

[narrator] There was a very good reason past quests had failed.

It was solid ice all year round.

You couldn't just sail to the North Pole.

[narrator] But the Norwegian explorer leading this new expedition

believes it is possible.

His name is Roald Amundsen.

[McGrath] He was the Neil Armstrong of the early 20th century.

His life was the stuff of dreams.

He did things no one could imagine.

[narrator] In 1905, Amundsen accomplished a feat of navigation

that had tantalized Europe for centuries.

He sailed from the Atlantic to the Pacific through the Northwest Passage.

Six years later, in 1911, he outdid himself

by successfully reaching the South Pole.

[McGrath] His crew followed him,

because the man was adventurous and a visionary.

[narrator] Now, Amundsen wants to see if there's land beneath the ice

at the top of the world.

If so, he intends on claiming it in the name of his patron,

Queen Maud of Norway,

which he believed would establish his place in history forever.

His goal isn't to avoid the ice,

instead he'll sail directly into it.

[McGrath] He was following the latest, greatest science,

in that the Arctic ice is not some monolith.

It actually flows.

His idea was to sail to the Arctic,

let his ship get caught by the ice

so that it would drift to the North Pole.

It's not unlike a manned mission to Mars.

You load up your ship with provisions

and you sit there

until you arrive at your destination. Hopefully.

[narrator] But ice is not benign.

It crushes everything in its path.

[McGrath] For a project this big,

Amundsen needed a ship of the most sophisticated design.

He needed a ship that could withstand

the rigors of the Arctic ice pack.

[Cantor] Amundsen commissioned a vessel with a very specific shape,

and he oversaw every aspect of its construction,

even down to the choice of wood used.

Norway has huge forests, but Amundsen imported

what he considered to be higher quality wood from Holland.

[narrator] The three-masted schooner had a solid oak frame

for maximum structural strength,

and it was egg-shaped below the waterline.

So when pressed by ice from either side,

it would lift the ship up.

It had a four-cylinder, 240-horsepower engine

that drove a single-bladed screw.

The screw and the rudder were both retractable.

[McGrath] The ship was named Maud after the Norwegian queen,

and the ship was christened with a block of ice.

Rather than a bottle of champagne.

[narrator] Could this wreck that's been dredged

from the bottom of Cambridge Bay

be Amundsen's once-magnificent Maud?

[narrator] Experts wonder if a vessel salvaged

from the bottom of an icy bay in Nunavut

could be the long-lost ship of the Norwegian explorer Roald Amundsen.

At the time it was built,

it was one of the most sophisticated machines in the world,

and for it to have been forgotten about and really disappear,

it would be the equivalent of mucking around in your backyard and finding,

you know, a piece of a Saturn V rocket.

[McGrath] Right away, when you look at the salvaged ship,

you can see that the dimensions fit.

It's about 120 feet long and 40 feet wide.

But what really clinches it

is the ship's distinct egg shape.

He knew that that particular feature

would fortify his ship

against the crushing power of the Arctic ice pack.

[Robinson] How did one of the most

remarkable sailing ships in the world,

owned by the most famous polar explorer in the world,

end up at the bottom of a bay in Nunavut,

especially when it was launched 4,000 miles away

in Oslo, Norway?

[narrator] The Maud set sail from Oslo in June of 1918.

Amundsen's plan was to sail over the top of Russia,

across to Alaska,

and then enter the pack ice north of the Bering Strait.

[Cantor] But the pack ice was building up earlier

than Amundsen had anticipated.

So the ship's progress was halted while it was still north of Russia.

[Robinson] It took Amundsen two years to make it to Alaska.

You could get to Jupiter in less time.

[Cantor] For Amundsen, this North Pole expedition was a bust.

And by the time the ship got back to port in 1925,

it wasn't even his ship anymore.

[narrator] Amundsen was broke.

His creditors seized his assets, including his beloved Maud,

and she was sold to the Hudson's Bay Company.

[McGrath] The Hudson's Bay Company

had a radically different plan for the Maud.

She became a workhorse,

shuttling between Hudson's Bay outposts in the far north.

[Cantor] This was really a bit ridiculous.

It would be like using the Mars rover as a delivery van.

[narrator] In 1927,

the vessel once known as Maud arrived in Cambridge Bay

and never left.

[McGrath] Three years later, she sprung a leak

and sank near Cambridge Bay,

and that's where she lay for 86 years.

[narrator] In 2016,

the Norwegians decided it was time to bring Maud home.

[Cantor] This ship was an important part of Norway's history.

Seafaring is central to Norway's history,

and Amundsen was a national hero.

So the Norwegians spend a year digging out tons of mud

and preparing the ship for one final voyage.

[narrator] In 2017,

the ship made her way through the Northwest Passage for the first time.

She's now an exhibit at a museum dedicated to Amundsen's adventures.

But Norway's most famous son never made it home.

He disappeared years later, in 1928, on a search and rescue mission

somewhere over the Arctic.

His body has never been found.

[narrator] High in the wind-torn Russian Ural territory

lies a mountain called Kholat Syakhl,

which means "Dead Mountain."

The Urals are 800,000 square miles of cold, rugged mountain terrain.

No surprise it's not heavily populated.

[McGrath] The backcountry is so vast and remote

that if something goes wrong, you're on your own.

[narrator] On a cold, dark day in February,

500 feet from the top of the mountain,

an empty tent lies flapping in the wind.

Inside, a search and rescue team finds an oddly tidy scene.

Rucksacks, hiking gear and supplies all neatly arranged,

but it's the tent itself that sends shivers down their spines.

[McGrath] The main flap of the tent was closed,

but the tent was slashed open from the inside.

[narrator] Why would the tent be slashed from the inside? And not only that...

[McGrath] Equipment is your lifeline in the backcountry.

It's very strange that they left and never returned to their tent.

Where did they go?

[narrator] More than a month before the abandoned tent is discovered,

nine Russian university students, seven men and two women,

set out on a 200-mile long cross-country skiing trip.

All of the students were in excellent shape

and were experienced in backcountry skiing.

[Morgan] They knew this wasn't going to be easy,

but they were excited, this was going to be fun.

I mean, they brought musical instruments.

They were writing in their journals.

They were answering the call to adventure.

[narrator] The group sets off dropping caches of supplies to lighten the load.

Their plan was to return three weeks later on February 12th,

but they never showed up.

One day after the empty tent is found,

searchers make their first grisly discovery.

About a mile from the tent are two bodies partially covered in snow,

Yuri Doroshenko and Yuri Krivonischenko.

[Cantor] This discovery is really strange.

The two bodies are found huddled together under a cedar tree near a campfire,

and they're not wearing anything except their underwear and T-shirts.

[narrator] Shortly afterwards, they find two more bodies farther up the slope.

It's the expedition leader, Igor Dyatlov and Zinaida Kolmogorova.

Strangely, they too are both lightly dressed.

[Guzar] That February, the mountains were punishingly cold,

temperatures dropped to negative 25 degrees Fahrenheit.

[Cantor] What happened to them that made them move out

into the ice and snow so quickly

that they weren't dressed at all for these surroundings?

Whatever happened, happened fast.

[McGrath] Snow, mountains and a fast-moving danger,

that sounds like they were running from an avalanche.

[narrator] Searchers analyze the area where the hikers pitched their tent.

The tent is perched on a snowy slope.

It's evident that the hikers cut into the snow to create a flat surface to sleep on.

Could they have inadvertently triggered an avalanche while building their shelter?

[Cantor] If there's an avalanche,

you have to move quickly, so that could be a reason

that they had to get out of their tents because pausing for even a moment

could leave you crushed under a mountain of snow.

[McGrath] But there are two problems with the avalanche theory,

the incline of the hill and the timing.

[narrator] Searchers observed that the slope where the tent

was pitched was less than 30 degrees,

which isn't steep enough to cause an avalanche.

[McGrath] The timing doesn't match either.

It's when you disturb a slope that an avalanche is triggered.

So reasonably, it was when they were setting up their camp

that an avalanche would have been caused.

[narrator] And Dyatlov's camp was fully set up.

It was well-organized,

and the group appears to have had time to fall asleep.

A sudden avalanche doesn't seem likely.

And whatever happened to the rest of the group is still a mystery.

[narrator] On March 5th, investigators found the body

of one more hiker, Rustem Slobodin, near the others on the slope,

but there's still four hikers unaccounted for.

Rumors and conspiracies begin to swirl.

Why did this group of experienced hikers

flee their tent and how did they get separated?

Was the group attacked by someone?

[narrator] High in the Russian Ural Mountains,

a search-and-rescue team find five of nine hikers mysteriously frozen in ice.

Many of them were found without proper winter clothing.

The condition that the bodies were found in is probably the most intriguing

and the most confusing and the most vexing aspect of this mystery.

[narrator] Three months pass when searchers working farther

down the mountain discover a fragment of human flesh.

After hours of digging,

the final four bodies are found at the bottom of a ravine.

[Cantor] These people were dressed more appropriately for the weather

than the first five bodies that were discovered.

[narrator] But when medical examiners take a closer look at the remains,

they make a startling discovery.

Three of the four bodies had bizarre injuries.

They didn't die from exposure.

They died from severe trauma.

[narrator] Twenty-three-year-old Nikolay Thibeaux-Brignolle

died from a massive skull fracture.

What's really weird about the head injury is that it seems like

it came from a high-speed impact, the kind of thing you'd see in a car accident.

[narrator] Semyon Zolotaryov has multiple broken ribs,

but no sign of bruising on the outside of his body.

That kind of trauma, you know, broken bones without bruising,

that's the kind of thing you would expect to see from an explosion.

[narrator] Lyudmila Dubinina is found to have severe chest trauma

and many broken ribs.

[Morgan] With all three of these bodies, their injuries were too severe

for it to be the consequence of falling into a ravine.

It had to be something more violent.

[narrator] Strangely, they also find traces of radiation on their clothing.

Could this have anything to do with their deaths?

The Soviets had been known to use

the Ural Mountains to conduct military tests.

[Cantor] During this part of the Cold War,

the Soviets were conducting a lot of secret weapons tests.

We don't always know what they were testing, we still don't know.

On the night of the incident, locals observed flashes in the sky,

so that could suggest that they were testing some kind of explosives.

[narrator] Were the skiers accidentally killed by their own government?

[Morgan] Aerial explosions could explain why they would have left their tents

in the middle of the night, and the concussive force is consistent

with the kinds of bizarre injuries that we saw.

The shockwave of a bomb can cause the kind of massive internal damage

and relatively little external damage

that we saw on Semyon and Lyudmila's bodies.

[narrator] But if military weapons tests

had been carried out in this region, they would have left a trace.

You'd be able to find burns and damage.

[narrator] The area shows no signs of explosions,

no shrapnel, bomb wreckage or damage to the trees.

Adding to the mystery,

medical examinations show both Semyon Zolotaryov

and Lyudmila Dubinina's eyes are missing.

Dubinina is also missing her tongue.

Okay. Missing tongues and eyeballs, slashed-up tents.

This is not a mystery, this is a horror film.

[Cantor] All kinds of crazy theories arose from this incident. Of course they did.

People love to speculate.

And when there's not a clear explanation,

people can get really obsessed with it.

[narrator] In February 2019,

a group of Swedish archeologists hope to solve the mystery once and for all.

They set out to retrace the exact route

the doomed expedition took in 1959.

[narrator] Determined to solve the mystery

of what killed nine university students on a backcountry skiing trip,

two Swedish archeologists retrace the exact route the expedition took in 1959.

They set up camp on Dead Mountain and settle in for the night,

and the extreme weather they experience at their camp

leads them to explore a new theory.

[Guzar] Katabatic winds are intense winds caused by high-density air.

They can occur in Greenland as well as Antarctica,

and they are known to occur in the Ural Mountains as well.

[narrator] As air rises above the mountains,

it cools and becomes denser.

This high-density air is pulled down slopes

under enormous gravitational pressure,

causing winds to reach hurricane speeds.

[Guzar] Katabatic winds can reach speeds of 190 miles per hour.

That's strong enough to toss around debris,

and that could possibly account for the head injury on Nikolay.

[narrator] But some of the injuries contradict the theory.

The internal damage to Lyudmila and Semyon's bodies

aren't consistent with high-speed projectiles.

[man] Here we have a slope angle which is close to

the one above the tent, 28-29 degrees.

[narrator] But in 2020,

the katabatic wind theory inspires two Swiss professors

to consider a radical idea.

Radical only because it had already been dismissed long ago.

Avalanche, but not just any avalanche

[Guzar] In a photo taken just before sunset,

you can see the snow above their tent.

The slope isn't steep enough to potentially start an avalanche.

It seems like the adventurers knew what they were doing.

[narrator] But the professors suggest

that the snow just above the campsite

was not what it appeared to be to the hikers.

[Guzar] Instead of being one hard-packed layer of snow,

there's actually two distinct layers

that results in a less stable system.

[narrator] This is known as a weak layer, which is 80% air.

But then more snow comes down, forming a denser slab on top.

This allows avalanches to occur on slopes less than 30 degrees.

[narrator] The scientists theorize that the katabatic winds

then transported much more snow down to the campsite.

Eventually, it became too heavy for the slope to support.

This combination of events could have triggered

what's now known as a delayed avalanche.

[Cantor] If the group hadn't cut into the snow, they would have been fine.

But at a certain point, a crack could have formed,

causing the snow slab above the tent to release

and come barreling right into the tent,

where all nine were asleep.

[McGrath] Despite the terror they must have felt,

six members of the group reacted quickly.

They cut the side of the tent,

removing their injured companions and escaped to the tree line below.

The panic would have disoriented them,

and it would have been next to impossible

to find the tent again in the cold and the dark.

At that point, it's possible, maybe even likely, that the group split up,

one going to try to find their cache of food

and the other trying to go back to the camp,

both unfortunately succumbing to the cold.

As for the missing eyes and tongue,

it's possible that animals would have just scavenged their bodies.

[Cantor] This theory relies on cutting-edge science,

and a wind-induced avalanche really could explain

what happened at the Dyatlov Pass,

but only the nine people there that night know the full story

and they took that story to their graves.

[narrator] The Russian Plains,

known for endless frozen steppes and long, punishing winters.

For thousands of years, this area was a wasteland of ice and snow.

[Leonard] During the last ice age,

these plains would have been cold, stormy,

horrible weather most of the year-round.

For us, they would have been an undesirable place to live.

[narrator] And on their western edge, 300 miles south of Moscow,

an age-old mystery lies buried in the permafrost.

In 2014, not far from the city of Voronezh,

a team of Russian archeologists uncovered something unusual.

An enormous mammoth bone, but it's not just one.

A few feet below the surface, they uncovered another bone

and then another and then another.

[narrator] Eventually, they uncover a giant circle,

41 feet in diameter, constructed entirely from mammoth bones.

[Guzar] It's a really ominous setting.

There's bones on top of bones arranged in this particular way.

It's eerie.

This is a terrifying image. It makes you wonder what happened here.

[narrator] Two other mammoth bone circles have been unearthed in this area.

One in 1951 and another in 1970.

[Leonard] There have been lots of mammoth bones found in the area.

So in fact, the place name Kostenki

comes from the term kost, which means bone.

[narrator] The first two Kostenki circles

have been dated back to around 23,000 years ago,

at the tail end of the ice age.

[Elliott] The question is, though, why are they building with mammoth bones?

But in a treeless, harsh environment, you use whatever you can find.

So maybe these were being used like lumber.

[narrator] The first two circles

were thought to have been built as shelters

for humans to protect themselves

from the extremely harsh environment.

The bones are thought to have been used as the foundation of the shelter,

over which hides would be stretched.

[Morgan] But this structure is unusual.

It's completely different from all the others.

[narrator] Firstly, it's much bigger.

Archeologists estimate the site was built using the remains

of at least 64 different mammoths.

The walls would have been piled 20 inches high

and the circle is almost 10 feet wider

than any other circles at Kostenki.

[Morgan] Consider how many mammoths that is.

They had to hunt each one of these, drag their bones

all across the land. It's a lot of work.

[narrator] The average mammoth was over ten feet tall

and weighed around six tons,

closer in size to modern-day African elephants.

[Leonard] The sheer number of bones

that were brought to this location is truly staggering.

It honestly is difficult to believe.

[Morgan] It's possible that this new circle was also a domestic structure,

but that's a pretty big area to cover without extra support.

I mean, you'd expect to find holes dug for something to support a roof.

[Elliott] At other sites in the Ukraine,

we have evidence of skulls being used more like mooring holes

that perhaps poles were shoved into the eye sockets

in order to make supports.

[narrator] But at the site in Kostenki,

researchers don't see anything like that.

During an ice age, this area is regularly minus 4 degrees Fahrenheit.

Try living in a house like that without a roof.

So if it wasn't a dwelling, what was it?

[narrator] A massive circle composed of mammoth bones

is discovered on the central Russian Plains,

raising questions about what type of ice age structure

they might have been used for.

Determined to find answers, archeologists go looking for evidence of a fire.

For an archeologist, finding a fire or a hearth is great.

We can learn so much from plant remains, charred animal remains,

even just the charcoal.

Not only does this give us evidence as to what was taking place,

but it can also provide evidence for dating.

[narrator] Archeologists use a technique called archeology flotation,

which separates particles by submerging a sample of soil in water.

[Elliott] The heavier particles will sink

and the lighter particles will float and be recovered.

[Leonard] The use of flotation here was really successful.

It yielded a number of charcoal remains.

In fact, this is the first time

that any large pieces of charcoal have been found inside one of these circles.

Finding a small lump of wood doesn't sound exciting,

but it's important because it tells us

that there were trees in the area.

That means that they could have

used those trees to burn instead.

[narrator] Radiocarbon analysis on the charcoal remains places the fire

and the construction of the mammoth circle at around 24,000 BC.

For the archeologists, it's an astounding development.

That means that this 40-foot structure is at least 1,000 years older

than the other two Kostenki bone circles.

[narrator] The coldest and most severe stage of the last ice age

was passing through this area around 24,000 years ago,

just as this region was being settled.

The climate at the time would have been arid and cold,

not ideal for vegetation.

So the discovery that they were burning wood suggests

that they were thriving in this harsh environment.

Most historians will tell you that people at similar latitudes

would have just given up by this point,

but these were some tenacious people,

they weren't ready to give up that easily.

[narrator] But the 40-foot bone circle still harbors a significant question.

If early modern humans weren't living in it,

what else could it have been used for?

[Leonard] When we see something of this size,

we ask questions about power, about status,

perhaps thinking about ritual sites.

So it is possible that this represented some kind of special place.

[Elliott] From Stonehenge to Machu Picchu,

humans all over the world build incredible monuments.

Is it possible that this was a ceremonial site?

Usually if something has ritualistic

kind of importance for groups, then you'd find carvings,

artwork, something that lets you know that it's that important.

[narrator] At the more recently inhabited sites at Kostenki,

archeologists have discovered carvings made of mammoth tusk,

but they found no evidence of art or carvings here in the 40-foot circle.

But then they noticed something strange.

Inside the circle are more than 300 tiny flakes.

The offcuts and stone debris created by ancient tool-making.

[Elliott] All those tiny flakes suggest that tools were being made in this area.

So is it possible that they were butchering animals here, too?

A lot of the bones they added to these rings were still pretty fresh,

I mean, they had chunks of flesh and cartilage on them.

[narrator] Is the large bone circle an abattoir?

[Morgan] Even if they were hunting only a few of these mammoths,

each kill is still a lot of meat.

These things weighed, like, six tons.

That's a tractor-trailer full of meat.

These bones and their flesh would have given off a horrible stench.

They would have attracted predators.

This requires drying or preserving the meat in some way.

Humans have long known that frozen ground

is a great way to preserve food.

[narrator] Is it possible this was an ice age freezer?

They conclude that the 40-foot bone circle was likely a place

for preparing the meat to sustain the community

through yet another frozen year.

I do think it's a story about resilience and survival

and thriving in an environment

that a lot of people wouldn't expect

a group of people to thrive in.

[Leonard] Archeologists are still investigating

the potential uses of the site,

but at heart, the bones tell a story of survival

in the face of adversity.

[narrator] On the western edge of Antarctica lies the menacing Thwaites Glacier,

a vast expanse of ice that is larger than Florida.

The Thwaites Glacier is such a remote and inaccessible place to get to

that we know more about the surface of the Moon

than we do about the environment around this glacier.

[narrator] The glacier may be beyond the reach of most of human civilization,

but what's happening beneath it

could impact some of the biggest cities on Earth.

In the early 2000s,

alarm bells at a snow and ice research lab started ringing.

On the map, large areas of western Antarctica were turning red,

indicating Thwaites was rapidly losing ice and heating up.

[MacFerrin] Well, what the satellites were picking up at Thwaites

was something totally different.

This glacier is waking up in ways we hadn't seen before.

[narrator] Thwaites appears to be melting faster than any other glacier in the world.

What's going on in Antarctica?

[Guzar] The ice here is thousands of feet deep.

It's a huge glacier.

If this were to melt, it would be chaos.

[Morgan] If Thwaites collapses, we're looking at a global sea rise of two feet.

But if all of the unstable ice in western Antarctica melts,

we're looking at 11 feet.

[narrator] In this case, entire coastal cities could be wiped out.

Why is Thwaites melting so much faster than any other glacier?

A group of scientists decide to see for themselves.

[narrator] A group of scientists are making the trek to Antarctica

to see for themselves why Thwaites Glacier is melting faster

than any other glacier on Earth.

Working out on the Thwaites Glacier is risky.

It gets down to negative 40 or below

and it's covered with deadly crevasses.

[narrator] From the satellite imagery, researchers believe the main source of the heat

must be coming from below.

So the only way to find out what is going on is to look beneath the ice.

[Morgan] The ice is 4,000 feet thick,

so you can't just see what's going on,

unless you've got X-ray vision, which we kind of do.

[narrator] Scientists detonate multiple half-pound explosives throughout the glacier.

[MacFerrin] They drill a borehole 100 feet down,

place a small charge in there, blow it up.

[narrator] The seismic energy from the explosion

travels down to the bed of the glacier.

The time it takes to travel back to the surface

tells them how thick the glacier is above the rock.

Changes in these seismic waves tell us about the depth and makeup of this glacier.

More importantly, they tell us where it's vulnerable.

[narrator] This massive glacier

is only being held in place by a small rocky ridge

known as a grounding line, 1,000 feet below sea level.

Wait, is the only thing keeping Thwaites

from collapsing into the sea this thin piece of rock?

[narrator] Researchers need to know the temperature

of the water in front of the peak to understand how fast it's melting

and determine just how long it can hold on.

But how do they do that in one of the most punishing landscapes on the planet?

Scientists recruit the locals to help them out.

Large Weddell and southern elephant seals

live year-round on the ice around Antarctica.

[MacFerrin] The seals were tagged with sensors

to track water temperature and salinity.

Each antenna lasts for one season only and falls off naturally.

[Morgan] This is legit pretty cool.

I mean, we're using seals to investigate the guts of a glacier.

How awesome is that?

[narrator] The seals can dive up to 3,000 feet

into deep water and reach the trenches on the seafloor.

[MacFerrin] The data confirmed an unusual phenomenon.

The deeper the seals went, the warmer the water got.

[Guzar] Even the tiniest change in water temperature

can drastically affect how quickly the glacier may melt.

[narrator] But how is the warm water getting under the glacier?

Researchers deploy a specialized vehicle

that will allow them to go directly beneath the Doomsday Glacier.

It's an underwater robot called Ran,

a 25-foot long, two-ton autonomous submarine,

able to record high-resolution sonar and photographic images.

The results are staggering. No one's ever seen data like this before.

[narrator] Images from the Ran reveal

there are deep channels in the seabed that extend like fingers through the glacier.

[Morgan] These channels are deep.

You could put the Empire State Building in there

and still have plenty of room to spare.

And they act like the veins of this glacier, warming it up from underneath.

[MacFerrin] Because these channels are so deep and so wide,

they allow more and more deep water to get

underneath the Thwaites Glacier and melt it from below.

[narrator] All the water making contact

with the glacier is more than three degrees Fahrenheit warmer

than the glacier itself.

[MacFerrin] It's almost like this glacier was geometrically designed to collapse.

Once you start this process of collapse, there's very little to stop it.

[narrator] Researchers had thought collapse of the West Antarctic Ice Sheet

might happen within 250 years,

but this new data may change that.

[Morgan] Let's put this in perspective. Miami and Boston are gone.

Manhattan is underwater, and access to electricity for 470 million people

across the world is seriously threatened.

[Guzar] Life on Earth, as we know it,

would be significantly different.

[MacFerrin] This is an enormous problem,

and whether we address it or not,

we're going to see the effects from it one way or the other.