Original subtitles

[announcer speaking]

[narrator] A mummified Siberian body

is found encased in a mysterious burial shroud.

When you come across something this unique,

so many questions start racing through your mind.

[Dr. Cantor] A find like this is quite rare.

This place is very remote.

[narrator] Could a turn-of-the-century

Antarctic camp found floating on an iceberg

lead researchers to a lost one-of-a-kind polar vehicle?

How could it have gotten onto one of these giant icebergs in the first place?

[narrator] An ominous dark hole suddenly appears on a glacier

on Mount St. Helens.

Researchers think it looks like

what could be an entrance to a monster's lair.

This is a potentially lethal environment.

[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.

Northern Siberia,

its very name evokes some of the world's toughest people

battling winter's harshest wrath.

Northern Siberia, is legendary for its intense winters

and remote inaccessible areas.

At certain times of year,

villages can be completely disconnected

from one another.

[narrator] In 2015, researchers make a grim discovery

at a place known as Zeleny Yar.

They uncover an unusual-looking burial site

in the frozen ground.

Inside, they find a body wrapped in what appears to be tree bark.

When you come across something this unique,

so many questions start racing through your mind.

Who is this person?

Why are they wrapped in a shroud?

[Dr. Cantor] A find like this is quite rare.

We're talking about Siberia.

This place is very remote.

[Marina] Finding a body like this is pretty unusual.

Why would someone wrap a body in bark?

[narrator] To get some answers,

they transport the body to a lab for testing.

[Alison] When we find a body wrapped in something,

we recognize that there's a certain amount of care

that was given to the preparation of the body.

There was a certain amount of respect that was being paid to this individual.

[narrator] The size of the shroud

leads them to believe it could be a teenager.

When researchers delicately cut open the shroud,

they discover a hidden layer of reindeer fur.

Could this bark cloth and reindeer fur hint

at some special burial ritual?

[narrator] Below the fur, they make another strange discovery.

Carefully placed upon the body, covering the face, chest,

abdomen, and groin are four large flat pieces of copper.

This burial custom has never been found in graves in Siberia.

[narrator] Removing the copper pieces from the face,

they realize it's not a teenager,

but the eerie mummified body of a young boy.

[Alison] It's astonishing

to look into the perfectly preserved face

of one that was so young.

[narrator] The boy died when he was only seven years old,

around the year 1250,

during the medieval period.

But as researchers continue their excavation,

they make an astounding discovery.

They find 88 separate hidden graves in the frozen ground,

all buried between the 8th and 13th centuries.

[Alison] It's actually pretty amazing,

this boy's grave was part of a hole in Acropolis.

But without any distinctive artifacts,

we still don't know who these people were.

[narrator] As researchers uncover the bodies,

another strange anomaly comes to light.

Out of the 88 corpses,

they only find one adult female.

[Morgan] It's hard to understand just why

they didn't bury their women in the same grave site.

This discovery is really strange.

Maybe they had a completely different ritual for burying the women.

[Marina] In some cultures, soldiers are buried separately

from the rest of the population.

So, it's possible that there were no women

in this burial simply because they were separated from the soldiers.

[narrator] Some of the other bodies are also buried with copper plates

and some are partially mummified.

But out of the 88 bodies found,

the boy in the birch bark shroud

is in the most advanced state of mummification.

Beneath his body, still wrapped inside the bark shroud,

researchers discover an axe, a knife, and multiple rings.

Certainly, he could have worn the rings

and he could have used the knife and used the axe in his daily life.

Some have suggested that the copper plates found on his body

might have been some kind of rudimentary armor.

The copper pieces might also be symbolic of armor,

but as a metal, it's far too soft to offer much protection.

If he were a young warrior,

the copper plating would have been no match for an iron sword.

If he suffered a traumatic death,

you might expect to find evidence of injuries

like broken bones or lacerations on the skin.

But in fact, there are no puncture wounds,

there's no evidence of slashing anywhere on the body.

[narrator] Ancient mummification techniques

remove key organs from the body.

But CT scans of the boy reveal his brain

and internal organs are still intact.

In some cultures, only their leader mummified.

Like the famous mummies found in Egypt.

Even if he wasn't a young warrior,

he was clearly someone of high status.

[narrator] If he and many of the other bodies

weren't mummified on purpose,

how could it have occurred?

Copper has antimicrobial properties.

Which means that bacteria have a really tough time surviving on that surface.

The copper plates may have slowed the decay

in the areas they were placed.

[Dr. Cantor] Plus, the boy was buried in tundra conditions

where snow covers the ground ten months of the year.

The cold temperatures also slow down decay.

[Alison] In extreme environments,

like high altitudes and polar regions,

it's possible to find bodies that have been accidentally mummified.

This is why scientists call it accidental

or natural mummification.

But they still don't understand

why they buried their dead this way

and why in this location.

Whoever they were, they must at some point have lived close by,

if their dead are buried there.

[narrator] Could the nearest town of Salekhard, 20 miles away,

hold clues to the lost identity of the 88 Siberian graves?

[Marina] The town wasn't established until the 16th century.

So these bodies predate the town by hundreds of years.

[Alison] This is a huge necropolis that has attracted burials for centuries,

and yet archaeologists haven't found any evidence

of a contemporary settlement nearby.

[narrator] The Yamal peninsula has been home to the Nenets

and Khanty people for centuries.

They've migrated and herded reindeer

through this northern tundra for generations.

The Nenets are a nomadic people,

and so archaeologists wonder whether the boy

might still be a distant ancestor.

[narrator] When researchers compare the boy's DNA to the Nenets people,

they discover a genetic connection.

But strangely,

the Nenets don't have an oral history

of the massive Zeleny Yar burial site.

Could a rare burial practice of the local Nenets people

reveal a hidden connection to the ancient acropolis?

[narrator] In remote Siberia,

an Aryan acropolis is found containing 88 unmarked medieval graves.

Experts believe they are distant ancestors

of the indigenous Nenets people.

But the Nenets have no knowledge of the vast grave site.

Perhaps there are cultural similarities

that could shed light on why they were buried here.

The memory of who these people were has disappeared.

But maybe some of their traditions have endured.

In Nenet culture, when someone dies,

there is a tradition to punch a hole

through the bottom of a metal pot or bucket.

The idea is that the cauldron itself is broken,

it can no longer be used in this world.

But it will be intact and whole, ready for use in the afterlife.

So it is possible that the pieces of copper found on these bodies

are just another example of that tradition.

[narrator] But if the people buried here do have relations to the Nenets community,

researchers still wonder,

what is the significance of this place?

Zeleny Yar, the area where the necropolis was found,

is situated by a river on a floodplain island

and it's the highest point in the area from miles around.

This location is where two rivers meet

and the higher ground would have been less prone to flooding.

[Alison] It's really interesting that all of the bodies

are positioned facing the river.

Usually, when you find a group of bodies

arranged according to some geographical feature, like a river,

it indicates that there's some significance there.

Like, maybe this river is sacred.

In many cultures, rivers and bodies of water holds special significance.

And in fact, there are lots of myths and legends around

crossing rivers into the afterlife.

[narrator] But with no written records, the mummified boy,

his incredible grave goods, and the 88 other graves

are all that's left to bear silent witness to a mysterious people.

We don't know what happened to these people,

but the preservation of this boy is giving him a second life in our world.

[narrator] Antarctica,

one of the most brutally cold places in the world.

A frozen desert where no life exists except for at its melting edges.

On its southern side

sits a deep bay known as the Ross Sea.

It's here that America's McMurdo Station

has become a hub of international polar exploration.

It's a bleak and inhospitable place.

Blizzards and katabatic winds can blow in from nowhere and last for days.

[narrator] In 1963,

a looker on the American icebreaker USS Edisto

spots a stadium-sized iceberg in the Ross Sea

and signals for the ship to stop.

The Ross Sea, it's a graveyard

for these enormous icebergs that carve off the front of the Ross Ice Shelf.

It happens all the time there.

[narrator] The cliffs of the iceberg

are an incredible nine storeys high.

But about halfway up,

there's a strange dark smear visible in the pristine ice.

As the ship gets closer,

it looks like debris stuck in the iceberg.

But what is it?

[Amma] In Antarctica,

planes go missing at an alarming rate.

So maybe these are the remains

of a plane that crashed into the side of an iceberg.

[narrator] To see better, the captain creeps the Edisto

as close to the iceberg as he dares.

Suddenly,

a dark shadow snaps into focus.

Huge boards of wood and large pieces of canvas

are sticking out of the iceberg's face.

The crew of the Edisto marvel at this strange sight.

Could these materials be from a lost camp once used by Antarctic explorers?

In the early 1900s,

adventurers were obsessed with discovering the South Pole.

Famous Antarctic pioneers like Robert. F. Scott, Ernest Shackleton,

and Admiral Richard Byrd all built camps on the continent.

If it is one of these famous explorers camps,

how could it have gotten onto one of these giant icebergs in the first place?

[narrator] The helicopter is ready,

it flies over the iceberg for a better look.

The flopping sections of canvas appear to be large pieces of tarpaulin.

The wooden boards look like the interior walls of a hut.

What is the tarpaulin covering?

Could it be the roof of some kind of makeshift structure?

[narrator] When the helicopter lands on the surface of the iceberg,

the crew are stunned.

[Amma] Four thick poles are jutting out of the ice.

They look like telephone poles.

[narrator] The presence of these poles

clearly indicate that this was some kind of camp.

But do these poles provide enough of a clue

to figure out whose camp it is?

[narrator] In 1940, just three miles into the Ross Ice Shelf,

an American crew is building Rear Admiral Richard E. Byrd's

third Antarctic base,

Little America III.

By then, Byrd had completed two successful trips to Antarctica.

He was well on his way to being considered a legendary explorer.

He was the first person to fly across the South Pole.

[narrator] Little America III

was bigger than his first two camps.

With room for more equipment

and a powerful radio broadcasting station

that required several large telephone poles...

- [telephone ringing] - for transmission.

Are these large poles sticking out of the iceberg evidence of Byrd's old camp?

Well, they could be,

but they have to be completely sure.

There is one smoking gun piece of evidence that, if found,

would confirm that this was Byrd's camp.

[narrator] Byrd arrived in Antarctica

with what at the time was the most advanced piece

of equipment ever built for polar exploration.

He called it the Antarctic Snow Cruiser.

Part ice tank, part ice bus,

part invincible travel lodge.

[Mike] It was last seen partially buried on the Ross Ice Shelf.

If they can find that,

they'll have found a monumental relic of polar exploration.

[Amma] It was supposed to have a range of 5,000 miles.

Byrd wanted a five-person crew to be able to explore Antarctica for days

without ever having to leave the vehicle.

[narrator] The Snow Cruiser was 56 feet long,

19 feet wide, and 16 feet tall.

Smooth ten-foot-tall balloon tires were custom-built

to handle Antarctica's choppy ice and wide crevasses.

A pair of six-cylinder diesel engines

powered four diesel electric drive trains,

generating an intimidating four-wheel-drive machine.

They ran a combined 300 horsepower

and a maximum speed of 30 mph.

Fully loaded,

the Snow Cruiser weighed 37 tonnes.

And on the inside,

there were sleeping quarters,

a workshop,

a galley,

plenty of storage space,

and even a dark room.

But that's not all.

Byrd wanted room on top

to carry a small plane

that would fly ahead

and scout safe routes

for the Snow Cruiser.

[narrator] The Snow Cruiser cost $150,000

almost $3 million today.

The price and the innovation of the design

propelled the Snow Cruiser to instant fame.

[narrator] But as the Snow Cruiser arrives

with Byrd standing victorious on top,

the makeshift gangway breaks.

[narrator] The destroyed camp of famous Antarctic explorer Admiral Richard Byrd

may have been seen by the crew of the USS Edisto

on an iceberg floating in the Ross Sea.

But where is his innovative polar vehicle called the Snow Cruiser?

After narrowly escaping a crash upon arrival,

the Snow Cruiser struggles to live up to its reputation.

This thing weighed 37 tonnes. If it went down,

it's staying down.

[Amma] Things went from bad to worse.

Byrd learned the hard way that smooth wheels

provide near-zero traction on ice and snow.

[narrator] A research team managed to complete

a 92-mile journey soon after arrival.

But the smooth treadless tires frequently slipped

and sank the giant vehicle deep into the snow.

[Mike] The crew added chains to try and get better grip on the tires.

They found they got the best traction going backwards.

So, they did the whole thing in reverse.

[Dr. Cantor] The Snow Cruiser barely made it back to base camp

and it never drove more than 100 miles.

His massive Antarctic exploration machine was a bust.

It's thought that Byrd would have parked it near the main building

and it would have been used as extra storage or living quarters.

[narrator] If experts can establish where Byrd parked the Snow Cruiser,

it could help them determine if the debris in the iceberg

is in fact Byrd's camp.

The helicopter crew from the Edisto are not equipped to dig down

through 20-plus feet of ice to further investigate the camp.

[Dr. Cantor] So the helicopter crew, they just stood there on this iceberg.

They didn't really know what to do.

[Morgan] Have they found the entire camp,

did only part of the camp breakaway?

And where is the Snow Cruiser?

They have no idea.

And the iceberg is too unstable

to safely repel down to the building.

[narrator] The captain of the Edisto makes a tough decision,

he calls the helicopter back to the ship.

The helicopter pilot told them he thought it was Little America III,

but that doesn't solve the second part of our mystery.

Was the Snow Cruiser hidden in there too?

The crew watched the iceberg and the camp with it

float away toward the horizon.

[narrator] But in 2005, two American researchers

decide to take another look at the lingering mystery.

The researchers first analyze satellite imagery

of the Ross Ice Shelf from 1957 to 1962,

the years the iceberg was most likely to have calved into the ocean.

Ice shelves are like fingernails,

they grow from the back, but then break off on the front edge.

It could take years, sometimes even decades

for a section of ice shelf to become an iceberg.

[Dr. Cantor] What they discovered

is that Byrd's camp would have been pushed

to the edge of the ice shelf.

Perfect location to calve off into an iceberg.

[narrator] They calculate that an iceberg calved

without anyone noticing sometime between 1957 and 1962.

Then after working its way 300 miles across the Ross Sea,

it was on course to meet the Edisto.

Either the Snow Cruiser plunged into the water when the iceberg broke off

or it's still on the far side of the visible hut encased in ice.

It is a mystery to this day where that Snow Cruiser has gone.

[narrator] The researchers closely examine photographs and maps of Byrd's camp,

looking for any evidence of the Snow Cruiser.

Based on the position of the main huts,

the air hangar and the large telegraph poles,

they conclude the Snow Cruiser likely fell into the ocean sometime

before the rest of the camp was sighted on the iceberg.

This spot is where some researchers think

is the most probable location for the Snow Cruiser,

but it's covered by the Ross Ice Shelf.

The good news is that the water underneath the ice shelf

is anywhere from 1,000 to 3,000 feet deep.

So a search mission is technically possible.

Maybe one day someone will find it down there

and we'll finally get another look

at this legendary piece of polar technology.

[narrator] Until it's located on the ocean floor,

the Antarctic Snow Cruiser's final resting place

remains a secret buried in the icy depths.

[narrator] 50 miles northeast of Portland, Oregon,

on the western edge of the Cascade mountains

rises the icy peak of Mount St. Helens.

The highest peaks of the Cascades

are steeply-sloped active volcanoes.

The terrain here is rugged.

It's not for the faint of heart.

At 8,300 feet, Mount St. Helens

is covered with snow year around.

And around the lava cone is a young glacier rapidly growing.

How can a glacier that's rapidly growing

exist over the top of an active volcano?

[narrator] In 2012,

scientists conducting an aerial survey over Mount St. Helens

discover an odd-looking feature.

As they approach the glacier that sits on top of the mountain,

they see an ominous-looking black object in the ice.

[narrator] As the scientists get closer,

they realize that it's a massive hole

60 feet wide.

Researchers think it looks like

what could be an entrance to a monster's lair.

So they dub it The Godzilla Hole.

[Morgan] What is this thing?

How and why did this hole form?

[narrator] Mount St. Helens is the site of the deadliest volcanic eruption

in US history.

In 1980, after lying dormant for over 100 years,

the volcano suddenly erupts,

spewing 540 million tonnes of ash into the air.

The explosion triggers a massive landslide, killing 57 people

and decimating everything within an eight-mile radius.

Could the appearance of the Godzilla Hole

mean Mount St. Helens is about to awaken?

The crater of Mount St. Helens is so dangerous,

it's strictly off-limits to the public.

Only researchers monitoring for signs of future eruptions

are allowed anywhere near it.

[Meagan] The interior of Mount St. Helens' crater is a perilous environment.

It's prone to rock slides,

which sends huge boulders thundering down crater walls.

Scorching steam is blasting out of the ground

and this glacier is covered in deadly crevasses and unstable ice.

[narrator] To find out what's going on inside,

researchers must descend into the mysterious hole.

Despite the incredible danger of entering an active volcano,

they make their way from base camp

and prepare to descend into the dark icy cavity.

The hole could be a direct pathway into a thermal vent.

This is a potentially lethal environment.

Similar volcanoes emit poisonous gases

such as carbon dioxide, hydrogen sulfide,

and sulfur dioxide.

They have to be ready for anything and everything.

[Meagan] They have to bring climbing equipment, gas monitors,

self-contained breathing apparatus,

as well as the necessary scientific and medical equipment.

[narrator] As scientists ease over the edge of the hole,

they repel 40 feet into its dark passage.

Will its icy depths reveal an impending eruption?

[narrator] A mysterious hole has appeared

on Mount St. Helens' rapidly-growing glacier.

Could it be the ominous sign of another impending catastrophic eruption?

In order to investigate, a team of researchers

descends into its frozen depths for the first time.

[water drop]

Humans have never set foot here before.

It's completely uncharted territory.

[narrator] What they find at the bottom is an eerie, cavernous ice cave.

It has 100-foot ceilings and it's like nothing they've ever seen before.

Tall and narrow, the huge ice cavern looks strange and otherworldly.

The heat from volcanoes generating tremendous amounts of steam.

Light trickles in from the entrance

and illuminates thousands of these scallops on the cave walls,

these tiny indentations in the ice.

Beneath the ice is this vast group of towering caves

that are absolutely breathtaking.

What earthly forces or dynamics

could have created something this spectacular?

[narrator] Seismic readings determine Mount St. Helens is not about to erupt.

These glacial volcanic caves are extremely rare

and only exist in a few places in the world.

Unlike rock cave formations,

these caves are constantly shifting and changing as the glacier grows.

Many glaciers around the world are retreating,

but this one is actually growing and expanding up to two feet per day.

This glacier is only 25 years old,

but parts of it are over 600 feet thick

and over half a square mile in area.

[narrator] But is it the heat of the volcano rising through the ice

that carves out this giant space?

Maybe the size and shape of each cave

can give us some clue as to how these caves were formed.

[narrator] To probe the mystery of the caves' creation,

the researchers decide to construct a 3D map.

[Mike] The team uses a Disto laser to determine the volume of the cave

and map its entire 3D structure.

So much easier than measuring it all by hand.

[narrator] They discover a highly unique set of caves.

They're able to map out over 7,500 feet of passages

and discover ten distinct caves,

some several 100 yards long.

But what forces could be creating

such an unusual pattern of tunnels beneath the ice?

[Mike] Normally, meltwater carves out

these glacial caves horizontally.

But here we see a vertical cave with dry, rocky ground.

At any moment,

hot steam can blast from volcanic vents

underneath the rock that this glacier sits on.

[Mike] The steam in these events can get to 140 degrees Fahrenheit.

If the researchers so much as touch the wrong rock, they could be badly burned.

[narrator] But rising steam by itself

doesn't account for the eerie scalloped patterns.

[Alison] It's not quite that simple.

What could be propelling the steam?

If you stand in this cave,

you can feel a surprising amount of air blowing past you.

[narrator] As snowfall above causes the glacier to grow,

underneath, the caves are also expanding.

Hot air from the volcanic vents rises and melts the ice.

The melting cools the air in the ice cave,

which then interacts with the outside airflow,

causing it to drop back down,

creating winds within the caves

that sculpt the walls into strange, mesmerizing formations.

The caves essentially have their own weather systems.

[narrator] The unique hot and cold dynamics within Mount St. Helens' caves

are representative of how weather often behaves on Earth.

But as experts continue hunting the ice caves

for clues to their mysterious existence,

they're stunned to discover the uncanny birth of a brand-new world.

[narrator] Researchers investigate a giant hole

in a glacier on Mount St. Helens.

And after discovering a unique collection of ice caves,

could they pose otherworldly implications for the future?

They discover that when you have

all these things coming together,

the heat and the ice interacting,

something mysterious happens.

[narrator] Researchers find new signs of life

mushrooms,

moss,

and rare microbes are growing in the ice caves.

This cave is incredible.

It doesn't just have its own weather system, it has its own ecosystem.

[Meagan] The newly-formed caves are filled with volcanic gases.

So how is it possible for new life to begin forming

in such a hostile and unstable environment?

As harsh of an environment as this is,

given how many toxic aspects are in one place at once,

you wouldn't expect anything to thrive here.

But life, it finds a way.

So who knows what this place will evolve into?

It's so new that we're just beginning to probe its mysteries.

[narrator] If new life is growing here

inside one of the most paradoxical environments in the world,

researchers wonder how long this fragile mystery will last.

Poking out of the harsh Bering Sea, 300 miles west of Alaska

is a small island known as St. Paul.

It's part of a remote five-island chain called the Pribilofs

that are rocky tundra outcrops in the middle of nowhere.

This place is about the size of San Francisco

and it gets pounded by howling winter storms

and huge waves at the best of times.

[narrator] In 2003, on St. Paul Island,

a group of American scientists discover a strange vertical cave.

At the bottom of the cave, under a rock,

they find what looks like a long broken dinner roll.

But in reality, it's a well-preserved ancient mammoth's tooth.

What is a mammoth tooth doing in a cave, on an island

300 miles off of Alaska?

It's an extraordinary find.

Mammoths could swim,

but they couldn't swim 300 miles across the Bering Sea.

So how did they end up here?

[narrator] Mammoths went extinct from mainland North America

between 10,000 and 14,000 years ago,

at the end of the last ice age.

Did ancient mammoths roam this island?

If they did, then this tooth could change everything

we know about how they went extinct.

[narrator] The team sends the tooth for routine carbon dating,

but this is no ordinary tooth.

Scientists are stunned when it turns out to be only 6,500 years old.

That's an incredible 5,000 years after the mainland mammoth extinction.

How could this be?

[Dr. Cantor] How did the St. Paul mammoth survive so much longer

than the other North American mammoths?

And if they did, what happened to them, why aren't they still there?

[narrator] 21,000 years ago,

in the middle of the last ice age, St. Paul is not an island.

Walls of ice over a mile high cover Alaska and Canada.

And in between those walls are melted corridors created by hot springs,

volcanoes and micro climates.

St. Paul Island is in a volcano-ridden area

on the southern end of the Bering land bridge.

It's a giant stretch of land connecting Asia to North America.

People walked from the Asian continent across this land bridge

into North America and they hunted along the way.

They hunted the saber-toothed tiger, the short-faced bear,

the giant sloth,

and the woolly mammoth.

[narrator] During the end of the ice age,

as the human population grows,

the mammoth population mysteriously shrinks

and almost two thirds of the larger mammals become extinct.

The most obvious question is, did humans kill the St. Paul mammoth?

[Morgan] We've all seen those videos where a bunch of desperate ice age hunters

are throwing spears at a mammoth

and they all celebrate when they take it down.

But is that really how the mammoths died?

Overhunting does seem plausible,

but ancient hunters usually didn't kill more than they needed.

We know humans used mammoths for food, for clothing, for shelter,

and there is evidence of mammoth hunting across North America.

[narrator] The local indigenous tribe called the Aleuts

have had a wide presence in the Arctic region for thousands of years.

But scientists can find no evidence on St. Paul Island

that large groups of mammoths were slaughtered.

Once part of a connected landmass about 14,000 years ago,

the giant walls of ice began to melt, causing sea levels to rise.

The ocean swallowed the lowlands and stranded higher land like St. Paul

into an island about 6,000 years ago.

[Alison] Is it possible that mammoths and other animals

living in the area were trapped by rising sea levels?

It took thousands of years for sea levels to rise,

so maybe some animals didn't notice until it was too late.

[narrator] To understand how the mammoths may have survived,

the scientists focus on something key to all creatures' survival,

water.

They turn to a lake known as Lake Hill,

only a quarter-mile away from the cave where they found the tooth.

This would have been a place that many animals would have used.

[narrator] Is it possible that the lake holds a clue

to the secret of the mammoths' disappearance?

After finding a rare woolly mammoth tooth

dated to thousands of years after mainland mammoths went extinct,

researchers believe an Arctic lake on St. Paul Island

may hold the key to unlocking a centuries-old mystery.

Scientists return to St. Paul once the cold has set in

and the lake is frozen

in order to be able to drill

for samples of ancient mud at the bottom.

Did these mammoths visit Lake Hill regularly?

[narrator] On a small island surrounded by saltwater,

scientists believe many animals would have depended

on the lake for freshwater, including mammoths.

As they drink, they drop things like plants they're chewing,

dung, and with it all, their DNA.

All this falls to the bottom of the lake, and overtime,

layer upon layer builds up into a record of what happened.

After four days of drilling,

they gather 150 feet of tubing containing about 400 pounds of mud.

The lake samples may be their only hope of finding answers.

[Alison] The next step is to look for mammal DNA

and they find one that's unclassified,

one they've never seen before.

[narrator] But how do they figure out who the DNA belongs to?

[Alison] They compare the DNA to what would be the mammoths'

closest relative,

African elephants.

And bingo, it's a match!

[narrator] In all core samples dated between 11,000 to 5,600 years ago,

they find mammoth DNA.

So these mammoths died off about 5,600 years ago.

It's just incredible that we can pinpoint this ancient secret,

when the last mammoth roamed this island to within a century.

[narrator] They now know when they died,

but can they figure out how they died?

The island sits very close to the Ring of Fire,

a massive volcanically active area stretching from Alaska to South Asia.

Could the mammoths have died from the fumes of a nearby volcanic eruption?

[narrator] As a volcano erupts, it spews ash,

cinders and rocks into the air.

The bigger you are, the bigger your lungs,

and it don't get much bigger than a mammoth.

If the atmosphere was poisoned,

then the mammoths might have been the first to go.

[narrator] When they look at the lake samples,

they don't find any traces of volcanic ash

during the time of the mammoths' disappearance.

But they do find a telltale sign of impending disaster.

Around 7,800 years ago,

the lake starts to transform.

They discover a change in the population of algae and plugs,

which indicates the temperature is rising.

The rise in temperature causes the lake water to evaporate.

Plants can get trampled and die around the edges of the lake.

When plants and trees disappear,

that also causes the lake to shrink.

So the lake shrinks by quite a lot.

This changes the quality of the water, making it not only shallower,

but murkier and less pure.

[Morgan] The mammoths begin to lose their main water source,

and they need a lot of it.

They drink up to 50 gallons a day.

So for a shrinking lake, like this one,

it probably couldn't keep supporting that many creatures.

And for the mammoths, they may have just hit a breaking point.

[narrator] One day, Lake Hill shrinks

to below the level needed to support a mammoth population.

The island was a refuge

for one of the last remaining mammoth populations of North America.

But when their freshwater source became endangered,

they had nowhere to run.

They were trapped.

[narrator] The evidence indicates

that the St. Paul mammoths died of thirst.

Does this mean mammoths might still exist

if the freshwater lake on St. Paul Island hadn't dried up?

It's a tantalizing question.