Original subtitles

NARRATOR: Ocean waves hide a mysterious monument.

- This is huge. Who or what could have created it?

NARRATOR: Satellite images uncover a shocking find

on an isolated Arctic island.

- This is absolutely astonishing.

NARRATOR: Drone footage shows a pair of huge craters.

- What happened here?

NARRATOR: And state-of-the-art technology reveals

an unsettling subterranean mystery.

- Is this a ticking time bomb?

NARRATOR: Everywhere we look on our planet,

there's evidence of the past.

In nature...

in buildings...

..in relics. Each holds a mystery

that technology now allows us to see from above.

What new secrets are revealed?

- (monitor bleeping)

- (light music)

NARRATOR: The world is full of strange

and seemingly inexplicable places and phenomena...

..puzzling humans for centuries

and giving rise to epic myths and legends.

But looking down from above,

the secrets behind these ancient stories are revealed.

At the far southwestern tip of Japan,

around 2,000 kilometres south of Tokyo...

..lies a chain of islands that make up

the most remote part of the country.

And the waters around the westernmost island, Yonaguni,

hide a massive secret.

- The ocean here is full of coral reefs

hosting amazing marine wildlife, like dolphins,

sea turtles, and sharks.

NARRATOR: But a view from above hints that

there's more than just sea life below the waves.

- I can see there's a large shape just under the surface,

but it's impossible to tell what it is.

NARRATOR: To discover the secret hidden in these dark waters,

we have to investigate the mystery from above...

..from below.

- It looks like these steps descending into the ocean.

- With all of these sharp edges and right angles,

I mean, it looks almost structural.

- It looks like an underwater city. What is this place?

- It really reminds me of legends and myths such as Atlantis.

NARRATOR: Atlantis has captured the imagination for centuries,

a story about an ancient civilization

cast into the sea by angry gods.

BELLINGER: Atlantis is like many other legends of lost utopias:

El Dorado, Camelot, Shangri-La.

I think these stories live on because we want to believe

that there's more to discover out there in the world.

- This raises some really big questions.

- What on earth is this thing? How did it get here?

- What is it made of?

AGRAWAL: I think the most crucial question is,

is this manmade, or is it a natural phenomenon?

WALTERS: It looks like it's been made by modern machinery,

but if it's quite modern, then why has it been flooded?

NARRATOR: What human-made object could be this vast

and submerged below the ocean surface?

Can a catastrophe over 2,000 kilometres away,

on the northeast coast of Japan, offer a clue?

WALTERS: Back in March 2011, this part of the world

faced a once-in-a-lifetime disaster.

It was known as the Great East Japan earthquake.

RISKIN: This was the most powerful quake ever recorded in Japan,

but what made it infamous was the tsunami it created.

GUY: Massive waves, some recorded at a whopping

39 metres high, smashed the coastline.

NARRATOR: This disaster sparks an immense building project

to face the increasingly destructive powers of the ocean.

- Before the 2011 disaster, Japan already had

a considerable network of seawalls.

Now, seawalls are massive concrete structures

which are designed to protect inhabited coastal areas

from large waves that can come in from typhoons and tsunamis.

- But even the world's biggest seawall at the time, in Kamaishi,

which was two kilometres long, was overwhelmed by the 2011 tsunami.

- After the disaster, the Japanese government was

absolutely determined to build back better.

AGRAWAL: This project is gargantuan, covering hundreds of kilometres,

and it reaches 15.5 metres at its highest points.

It's estimated to have cost over $12 billion US.

NARRATOR: Could the strange formation on Yonaguni

be a part of this major seawall construction project,

or an older seawall overcome by a tsunami?

RISKIN: The island does have seawalls,

but they're all near inhabited areas or infrastructure

like coastal roads or the airstrip.

The view from above shows that this part of the coastline

doesn't really have anything to protect.

NARRATOR: if it's not part of a modern engineering project,

could it be something more ancient?

AGRAWAL: When you look closer underneath the water,

that's when you really begin to sense the scale

and the shape of this massive object,

and start noticing these details that look architectural.

BELLINGER: To me, it kind of resembles ruins

of huge ancient structures called ziggurats.

NARRATOR: Over 7,500 kilometres away,

in a region known as Mesopotamia...

..could Bronze Age ruins hint at the cause?

BELLINGER: Ziggurats are distinctive stepped structures

developed in Mesopotamia thousands of years ago.

They're believed to be primarily religious

and may even have inspired the Tower of Babel story in the Bible.

AGRAWAL: We're not exactly sure how tall they were,

but what we can see today are the remains of

much taller structures that have eroded.

But one of them, the Chogha Zanbil in Iran,

is still 24 metres high.

RISKIN: And they're still incredibly imposing.

It's amazing to think these structures

have survived for so long.

NARRATOR: Could the strange underwater formation

on the shores of Yonaguni be a similar ancient edifice?

BELLINGER: There certainly are marked similarities

between the structures.

The underwater site has step-like features

leading up from the base, just like a ziggurat,

and it's 25 metres high, around the same

as the ruins of the Chogha Zanbil.

- Now, the base is much bigger than any Mesopotamian ziggurat.

So, if that's just the foundation of a building,

you can start to imagine how tall it would be.

- Could it be a similar type of religious structure?

NARRATOR: Or could this be the remains

of something more substantial?

An ancient city swallowed by the ocean?

BELLINGER: We're used to thinking about cities lost under the sea

in terms of myth, like the city of Atlantis,

but it has actually happened more than once

and sometimes, catastrophically fast.

NARRATOR: Almost 15,000 kilometres away, in Port Royal, Jamaica,

a sudden disaster claimed a thriving city.

- Port Royal was known as the wickedest city on Earth.

And that was for good reason because it was a haven for piracy

and a major slave-trading hub.

Now, what on earth is gonna take out such a wealthy and thriving city?

RISKIN: The secret is actually hiding under the city.

Instead of being built on bedrock, it was just sand,

which turned out to be the city's Achilles heel.

WALTERS: When a massive earthquake began shaking the island in 1692,

it all started to fall apart.

NARRATOR: But how could the disaster sink the city?

RISKIN: The tremors likely caused something called liquefaction.

That's a process that turns the seemingly solid ground

into something more like quicksand.

That, combined with a huge tidal wave from the quake,

caused an unbelievable two-thirds of the city to sink.

NARRATOR: So, could the massive feature

under the coastal waters of Yonaguni...

..be part of a lost city hidden by natural forces?

RISKIN: It's an interesting theory. One Japanese marine geologist,

Masaaki Kimura, who has studied the site for years is

convinced that there are signs that this is part of a long lost legend.

- He has found what he believes are clear signs that this is manmade.

GUY: There are shapes that he thinks look like tool marks,

and even writing in some of the rocks.

- There are areas that look like stairs, gutters, and even doorways.

BELLINGER: And there are two features he believes are art:

a carving of a turtle, and a face.

NARRATOR: Are these marks and shapes

evidence of human hands at work thousands of years ago?

BELLINGER: Kimura connects this site to an ancient civilization

on the legendary Lost Continent of Mu.

NARRATOR: Do these clues reveal the secrets

of a forgotten eighth continent hidden beneath the Pacific Ocean?

- The concept of Mu first came about in the late 19th century,

and it was a reiteration of sorts of the Atlantis myth.

NARRATOR: In the 1920s, an occultist expanded the story,

describing a 50,000-year-old civilization of 64 million people,

thriving on a continent bigger than South America

in the middle of the Pacific.

- Now, he claimed that Mu was this kind of Ur civilization,

the origin of all those great historic civilizations that we know

in places like Egypt, Greece, Central America.

-The legend says that the continent disappeared in a single day

due to a combination of volcanoes

and granite bedrock riddled with caves and full of explosive gases.

- Could anything possibly have made a massive continent vanish?

The short answer to that is no.

GUY: The problem is it's just not scientifically plausible.

A continent that big can't just disappear in a moment, even if

it's full of caves and holes, as some of the myths highlight.

- Frankly, it's complete BLEEP.

And that's not the only flaw with Mu.

BELLINGER: As the story goes, the Mu civilization

was dominated by a self-styled superior white race,

and its modern Pacific descendants denigrated as uncivilized cannibals.

Unfortunately, typifying the racist pseudoscience

popular in the 19th and early 20th century.

WALTERS: Scientific racism has always been historically used

as a kind of way of justifying social inequality.

What it does is it makes it seem like all those status differences

are a product of "nature".

Now, that is complete nonsense.

It's seriously nasty, actually,

and it's really very harmful as well.

NARRATOR: So, what else could explain

the massive formation at Yonaguni?

Is it possible that humans weren't involved at all?

- Could this be an entirely natural geological formation?

NARRATOR: All over the world, we find incredibly perfect

rock formations made entirely by nature.

- The rock here on Yonaguni is mudstone and sandstone,

which can create dramatic geometric formations too,

like the ones in Utah or Arizona.

- If you look around the island, there are some notable

natural landmarks that look quite similar to some of the shapes

that we see on the monument.

- In these formations, you can see the same kind of

angular shapes that we see underwater.

There's even a rock that looks like a face.

- But does that necessarily mean that this awe-inspiring

natural monument has never been shaped by human hands?

NARRATOR: Might ancient humans have built upon

this natural formation when it was above the water?

- You have to go back something like 10,000 years to find a time

when this would've been above the surface of the ocean.

So, were there humans on the island back then?

BELLINGER: It's impossible to say for sure.

There are signs of human habitation on nearby Taiwan

around 20,000 to 30,000 years ago,

so perhaps part of this rock might have been accessible too.

RISKIN: And evidence shows that this has been underwater

for thousands of years.

That is plenty of time for ocean currents

to smooth away the fine details.

GUY: And if there's one thing we know about humans,

we love to leave our mark.

NARRATOR: From ancient legends, to dramatic geological wonders,

to prehistoric humans, theories abound.

There is no way to know for certain the true cause

of this underwater monument.

And, for now, the ruins remain a mystery.

AGRAWAL: I'm quite confused actually.

I can't really tell if it's a natural or human-made structure.

WALTER: To me it looks manmade. It's got lots of straight lines,

it looks kind of geometric, it looks deliberate.

RISKIN: I think the most plausible explanation is that

this is a natural formation.

GUY: For me, what's most interesting is

everything that we are learning in search of that answer.

- Either way, it's a fascinating and impressive sight,

and one that is really uncovered by looking down from above.

NARRATOR: From tropical waters to the freezing Arctic Ocean,

the view from above reveals strange sights that inspire

timeless legends and hide shocking histories.

Over 6,000 kilometres north of Yonaguni,

just off the coast of Siberia,

lies the craggy, deserted island of Kolyuchin.

- This is a very rocky island with high cliffs,

and it's in the Arctic, so we know right away

that it must be pretty inhospitable for most humans.

NARRATOR: There shouldn't be anything out here,

but high-resolution satellite images reveal something unexpected

on the northern tip of the island.

WALTERS: What I can see are these kind of greyish,

boxy shapes that stand out from the green of the surrounding land.

NARRATOR: Drone footage reveals a closer look at the stunning site.

- They are some kind of houses, but they look run down and damaged.

- Clearly, this is some kind of abandoned site.

NARRATOR: And among the ruins, an even more shocking scene.

- Polar bears!

It looks like an abandoned town, but polar bears are all over.

GUY: There's around 30 of them, which is pretty astonishing.

They're standing in these dilapidated buildings,

poking their heads out of windows, doing things that I wouldn't

really expect polar bears to be doing.

- You know, it just looks wrong.

BELLINGER: The mythology of many Arctic peoples is rich

with stories of polar bears as powerful, human-like creatures

who could act as friend or foe.

- But could legends actually explain what they're doing here?

NARRATOR: Two mysteries are entwined on Kolyuchin:

why are the polar bears here,

and what are these strange abandoned buildings?

- Why would anyone build these structures

on this really isolated island?

I mean, what on earth are they for?

- Could any events from the island's past shed light

on why these buildings are here?

NARRATOR: Archival footage from the early 1930s reveals

a harrowing event in the seas nearby that may hold a clue.

RISKIN: You can clearly see that this massive ship

is stuck in the ice, but why was it even here in the first place?

Why would anyone sail in these dangerous waters?

WALTERS: This is the S.S. Chelyuskin,

a Soviet ship, which was on an expedition to see if a ship

that wasn't an icebreaker could make it through something

called the Northern Sea Route.

RISKIN: The Northern Sea Route is of major interest today

because of how it could significantly reduce the time

and the cost of some shipping routes.

And that possibility was just as attractive back in the 1930s.

NARRATOR: The voyage starts August 2nd of 1933,

with a film crew aboard to document their bold mission.

And after weeks at sea, it seemed destined for success.

- The S.S. Chelyuskin was just a few miles

from open water when disaster strikes.

- They get caught in the ice.

BELLINGER: For months they drift farther and farther north

as winter approaches and the days get shorter and darker.

GUY: They're regularly radioing the mainland to ask for help,

but it gets even worse.

WALTERS: It's February the 13th, 1934,

and that ice pressure finally overpowers the ship's hull.

And as a result, the ship begins to sink

and one crew member is killed.

- Luckily, they'd planned for the worst

and managed to abandon the ship.

But then how do they survive?

RISKIN: This is the Arctic in the middle of winter.

So, it's incredibly cold, it's dark,

and the weather can change in a moment.

You can get blizzards, you can get fog, you can get storms

that spring up out of nowhere.

That all makes any rescue attempt difficult and dangerous.

So, how is it even possible?

NARRATOR: A daring air mission begins

to attempt to rescue the survivors.

- The stranded survivors built a makeshift airstrip on the ice

so that the planes can land.

RISKIN: But these planes are so small, it takes several

of these dangerous trips to rescue everyone.

- What's astonishing is that they actually make it.

I mean, these people had survived out on the ice for months,

and they make it home safely.

NARRATOR: But what can this incredible rescue

reveal about the strange buildings on Kolyuchin Island?

RISKIN: Could the buildings on the island somehow be connected to

the original mission of the Chelyuskin

sailing the Northern Sea Route?

WALTERS: The secret lies in

the 20th-century ambitions of the Soviet Union.

The potential for the Northern Sea Route is phenomenal.

But as the S.S. Chelyuskin discovered,

to succeed you need up-to-date information

about all the local conditions.

That is absolutely crucial for success.

RISKIN: The ocean and the weather along the Northern Sea Route

are really intense and dangerous, and they can change really fast.

YATES-ORR: The Soviets had to figure out how to manage the danger

of this unpredictable region. So, what did they do?

WALTERS: The Soviet Union started to build this whole network

of polar stations all the way along their northern coastline.

And in 1943, one was built on Kolyuchin.

RISKIN: But with climate change making the Northern Sea Route

more accessible than ever, Russia still needs these stations,

so why was this one abandoned?

WALTERS: The late 1980s and the early 1990s were a time of huge,

vast upheaval for the Soviet Union,

and ultimately led to its collapse at the end of 1991.

RISKIN: The new Russian government just didn't have the cash to keep

funding this scientific outpost, so it closed in 1992.

YATES-ORR: So, the people move out because the money is gone,

but when do the polar bears move in?

And why?

NARRATOR: Could the myths and legends of the arctic peoples

reveal the secrets of this uncanny polar bear behaviour?

WALTERS: The Chukchi people have been living in Siberia

for hundreds, actually, perhaps thousands of years,

and they've mastered how to survive in this fantastically harsh climate.

Even today, many are still relying on the traditional ways

of herding reindeer and hunting sea mammals to survive.

NARRATOR: With their long history in the Arctic, polar bears have

long been a familiar sight to the Chukchi people.

- And the Chukchi legends are full of stories about polar bears

who think, talk, and act much like humans.

They say polar bears are so human-like that

they live in villages, and even have their own country

far out on ice floes in the open seas.

NARRATOR: And just 420 kilometres away,

a nearby island offers a clue to the source of these legends.

BELLINGER: This real-world island may have inspired

the legend of the polar bear country.

- This is Wrangel Island, a UNESCO World Heritage site,

and the most biodiverse region in the High Arctic.

- Wrangel Island is an absolute haven for polar bears.

More polar bears give birth here than anywhere else.

GUY: It really makes you wonder, I mean, what's so special

about this island, and why are there so many polar bears here?

- Location, location, location.

As the weather begins to warm in the spring,

sea ice retreats northward.

Polar bears need somewhere to stay until the thick ice cover returns.

NARRATOR: But this idyllic haven may be turning into a trap.

RISKIN: Climate change has been messing with

the polar bear's schedule. The ice melts earlier in the year

and it freezes later, meaning the polar bears

are stuck on land for longer periods.

GUY: So, this is a big problem because polar bears

mainly hunt on the ice.

- On land, they're basically fasting.

NARRATOR: Could climate change be connected to the appearance

of the polar bears on Kolyuchin Island?

GUY: It's rare that polar bears appear on Kolyuchin

in such large numbers, and a few elements

have to combine to make this happen.

RISKIN: No one knows exactly why, but every few years,

the floating ice on the sea remains near the shore in the summer months.

And that means the bears don't travel

as far north to follow the ice.

GUY: When this footage was taken, there were fewer bears than normal

on Wrangel Island, indicating that the ice was keeping

these bears further south, like in Kolyuchin.

- But why are they poking around these old buildings?

RISKIN: Polar bears are extremely curious animals.

It's actually not that unusual for them to poke around

and try to get into doors and windows.

NARRATOR: With global warming continuing to drastically affect

the Arctic, we can only wonder what other changes are in store.

GUY: I can't be sure what will happen next for the polar bears,

but climate change is likely to continue to present them

and the rest of this ecosystem with a lot of challenges moving forward.

But whatever happens, I'm sure that these amazing

and intelligent animals will continue to surprise us.

NARRATOR: From the hidden secrets of the Arctic

to ancient, jagged mountains, myths seek to explain

the astonishing and unexpected,

but a search from above could uncover the truth.

Over 8,000 kilometres to the southwest,

in the warm waters of the mediterranean,

lies the home of one of the most famous pantheons in history:

Greece.

BELLINGER: When you look at the dramatic landscape

of the country, it's no wonder the ancient Greeks

told so many stories about gods in connection with

strange features in the landscape.

NARRATOR: Legends like Mount Olympus, home of the gods,

the sacred Psychro Cave where Zeus was born,

and the Pholoe Forest where centaurs and dryads roamed.

And in the quiet, arid mountain brush of the Argolis region

does the bird's-eye view reveal one more?

YATES-ORR: There are two massive craters

smashed into the side of this mountain!

GUY: It looks like a giant almost took their fists

and slammed them into the earth.

RISKIN: These are really big.

Both of them are over 200 metres across.

- The land around looks quite arid with some green brush,

but inside, you see this much richer, brighter plant life.

- What are these things? BELLINGER: What made them?

Was it some sort of natural geological process,

or is it a sign of some kind of human activity?

- Did these just suddenly appear, or have they been around a long time?

- And there are already two of them, are more going to appear?

NARRATOR: What clues can be found looking down from above?

- What could create round holes like this, and in pairs?

- Is there anywhere else we can see this sort of formation?

NARRATOR: About 190 kilometres to the north,

another pair of round features in the landscape raise questions.

- These holes are a similar size to the ones on the mountain.

RISKIN: But these holes are full of water.

It's pretty unusual to see an almost perfectly round lake,

but to see two of them side by side is really weird.

NARRATOR: What could have created these strange features?

GUY: For a long time it was thought that these might be

volcanic in origin, but a study in 2010

found something unexpected in the lake bed.

RISKIN: There was molten zirconium at the bottom of the lake,

and that's wild because the melting temperature of zirconium

is over 1,800 degrees Celsius.

It's insanely hot.

GUY: So, you think something that hot must be from a volcano,

but lava only gets up to a temperature of about

1,200 degrees Celsius.

So, where did all that extra heat come from?

NARRATOR: To make something that hot and cause a hole that big,

you're looking at powers from out of this world.

GUY: The researchers believe that the lakes were caused

by a meteorite that smashed into this area at least 7,000 years ago.

NARRATOR: Could these two rocky holes in Argolis

be the result of a space rock crashing into the mountainside?

GUY: So, it's one possible explanation,

but confirmed impact craters are quite rare.

In fact, there's only around 40 in Europe.

- And we just don't know if there are telltale geological signs

of meteorite impact at this site in Argolis.

- So, ultimately, a meteorite impact is pretty unlikely.

So, are there any other possible explanations?

What else could be going on here?

NARRATOR: Perhaps a more modern disaster could hold a clue.

Around 11,000 kilometres away,

Guatemala city residents hear something alarming.

- It was 2010, locals reported that they could hear the crash

or the thud of materials underground.

NARRATOR: And on May 30th, 2010,

a massive hole suddenly opens in the ground.

RISKIN: The satellite view and aerial footage from helicopters

show paved roads plummeting into this huge pit in the ground.

YATES-ORR: What could've caused this kind of damage

in the middle of a modern city?

GUY: A lot was happening around Guatemala City in May of 2010.

First, we've got the eruption of the Pacaya volcano on the 27th,

and many of the tremors destabilized the ground.

YATES-ORR: Then Tropical Storm Agatha dumped rain on the city,

causing landslides and flooding the streets.

The water and ash filled the city's drain pipes with water and debris.

BELLINGER: And this overwhelmed the poorly maintained system.

It's a recipe for disaster.

RISKIN: Some pipes burst, and suddenly you've got

a tsunami's worth of water surging into the ground.

NARRATOR: But how did some leaky pipes

cause a cavernous hole in the middle of the street?

- Guatemala City is built on top of layers and layers of volcanic ash.

BECHTEL: The volcanic ash contains some very, very fine particles

that makes it unstable when you introduce water.

GUY: So, during a big storm or with a burst pipe,

that process of erosion suddenly gets a lot more intense.

BECHTEL: That movement of water down through the volcanic ash carries

the very fine particles with it, and that creates a void.

This gets closer and closer to the surface.

Eventually, the roof is thin enough that it can't support

the weight of whatever's up there, so it falls in,

and it leaves this terrifying-looking wormhole.

NARRATOR: So could these two holes in this Greek mountainside

be the result of the same dramatic process?

RISKIN: There are really important elements missing.

First of all, this area is really arid.

Argolis is actually one of the driest places in Greece.

GUY: You can see by looking down from above,

this is nothing like a major city, right?

There definitely aren't any leaky pipes seeping water into the ground.

BECHTEL: And the terrain in Greece is not at all

geologically like the terrain in Guatemala City.

This is not volcanic ash. This is true karst.

RISKIN: Karst is a type of land made up of rocks like limestone

that can dissolve in water,

and because of that, they tend to be full of networks of caves.

BECHTEL: I was immediately reminded of the cenotes

in the Yucatan Peninsula in Central America.

NARRATOR: The Yucatan is around 10,600 kilometres away, in Mexico.

BELLINGER: The ancient Maya believed the cenotes

were a gateway to the underworld,

and made offerings to the gods they believed to dwell there.

GUY: The Yucatan cenotes were likely formed about 150,000 years ago

during the last interglacial period.

They continued to be shaped as the glaciers grew

and sea levels dropped heading into the last ice age.

BECHTEL: Over thousands to millions of years,

rainwater that falls infiltrates into the rock, and as it flows,

it dissolves the rock and creates openings.

RISKIN: And in some places, the roof collapses,

creating these cenotes or sinkholes.

GUY: When the last ice age ended and sea levels rose,

the caves once again filled with water.

NARRATOR: Are the craters in Argolis

cenotes on the other side of the world?

RISKIN: Cenotes can form anywhere if the terrain is right,

but these craters are missing fresh water.

GUY: So, does this mean that there was never enough water here

to make a sinkhole in the limestone terrain?

NARRATOR: There may be a clue in ancient Greek myths.

BELLINGER: Just like the ancient Maya, Greek mythology is rich

with stories of underground rivers tied to the land of the dead:

the underworld.

- There are so many stories that are consistent with karst features.

Like the River Styx in karst, there really are underground rivers.

YATE-ORR: Now, this hints at a real-world historic knowledge

of flowing water under the surface,

which would've made caves in the limestone here.

BECHTEL: Because of the arid conditions in Greece,

there's not enough water for significant dissolution

to be happening, so these features happened in the distant past

when it was a much wetter climate.

GUY: These craters may have looked just like the cenotes

in the Yucatan, but when? And where did all the water go?

NARRATOR: When in history was this arid region

wet enough to create these caves and sinkholes?

BECHTEL: Earth's climate has changed dramatically in the past,

thousands to millions of years.

The network of solution cavities that allowed these craters to form

were mostly dissolved at a period when climate was a lot wetter.

YATES-ORR: If we look deep into the geologic past,

about 7 to 11 million years ago,

this part of the world was humid and experienced heavy rains.

RISKIN: So, it makes sense to think that these two craters

are cave-collapse sinkholes that were formed millions of years ago.

NARRATOR: And there's one more mystery.

- How these craters may have formed is one part of the story,

but I'm really interested in what's happening

inside these craters, right?

That vegetation seems to be so much more lush than the surrounding area.

BECHTEL: Crater walls tend to produce ecological isolation

so that ecosystems develop inside these.

The crater itself has produced a little microclimate.

NARRATOR: And that provides the conditions for these trees

and grasses to flourish in this otherwise arid land.

- We can't be 100% sure what caused these craters

without further investigation on the ground,

but the view from above has uncovered strong theories

about the ancient past of this site.

GUY: These craters are relics of a time when our world

looked vastly different than it does today.

- And it reminds us of the powerful geologic forces

that are enshrined in ancient myth.

NARRATOR: From mountain peaks to fiery powers

lurking beneath the earth's surface...

..when these legendary forces break free, they shape the world,

and inspire foundational myths.

Almost 10,000 kilometres away,

amid the mountains of the American West,

lies a world-famous site.

GUY: Yellowstone National Park is one of America's treasures,

known for the wildlife that live there,

but also the amazing landscape.

YATES-ORR: There are thousands of unique and beautiful sites

around the park that look very different

from the usual forest and fields of the Midwest.

BELLINGER: These unique and enduring features made the area

a holy site for many Native American peoples.

The Apsaalooke people, through their traditions,

consider this area a very important spiritual place

which sustains them throughout their lives.

And Kiowa legend says their creator gave them this area as homeland,

earned when an ancient hero bravely dove into a boiling lake.

NARRATOR: But what is behind this legendary landscape?

And what can it tell us about the future of this wilderness?

In late 2022, new technology examined the site from above

and revealed hidden secrets plunging deep into the earth.

- We have the technology these days to basically take

an x-ray of the Earth.

GUY: So, a supercomputer analysed the latest seismic data

around Yellowstone, and created this 3D picture

of exactly what is hiding underneath the surface.

YATES-ORR: And what researchers discovered was almost unbelievable.

As we're looking at the land, there's something that lies beneath;

kind of a core.

KOUROUNIS: Think of this as a cross-sectional

side view of Yellowstone.

At the top, we've got the surface where all of the trees

and parking lots, and Old Faithful is,

but then as you go deeper down, we can see these vast chambers.

- It appears that there's this massive hole filled with something.

RISKIN: It's in different chambers at different depths,

and all of it is very dynamic and moving.

NARRATOR: And this subterranean phenomenon is unbelievably vast,

stretching 72 kilometres across and over 150 kilometres down.

- I wanna know what we're looking at and if it's potentially dangerous.

KOUROUNIS: How long has this been here?

And is it changing?

NARRATOR: What is going on beneath Yellowstone Park?

There may be a clue best seen from several kilometres straight up.

- It can only truly be seen when you look down from a satellite.

GUY: There's this massive depression in the earth.

It almost looks like the ground between the mountains

is sinking back down.

NARRATOR: What could create this vast imprint,

covering an area of 70 by 45 kilometres?

- It's an absolutely enormous volcanic caldera.

- But what kind of volcano could make a caldera that huge?

And where is it? I mean, this area is flat.

- Yellowstone is actually something called a supervolcano.

And the only thing scarier than a volcano is a supervolcano.

NARRATOR: These are far larger than regular volcanoes.

Mount St Helens, source of the deadliest eruption

in US history, is dwarfed by Yellowstone.

The caldera is over 20 times as big.

- In a regular volcano, magma spews out from a vent

in the Earth's crust, and then it solidifies,

and it builds up volcanic shape like a cone or a dome on the surface.

But in a supervolcano, the magma can't push up through the crust,

so the pressure just builds and builds,

and it forms this huge bulge in the surface.

Then, cracks form and gas and ash leak out

until finally, the whole thing just bursts with one massive blow.

Once the magma has escaped, the chamber collapses inwards,

and it leaves this massive caldera.

- That means that the huge area of molten rock under Yellowstone

must be volcanic magma.

KOUROUNIS: This partially liquid, half-melted rock is sitting there

just building pressure slowly over thousands and thousands of years

- It's rather unsettling to picture a massive lake

of boiling rock under your feet.

- And its base extends even farther down.

The Yellowstone plume is thought to be

something called a 'mantle plume'.

That means the root of this plume is something like

3,000 kilometres down in the earth.

- And those weird features on the surface,

steam seeping out of the earth, boiling lakes, geysers,

they're all signs of the heat and pressure hiding below.

NARRATOR: And the 3D image reveals something even more shocking.

- We're actually closer to the conditions

of an eruption than we ever thought.

GUY: The new images reveal that the magma is only about

three miles deep, higher than the experts previously thought.

RISKIN: And the melt, that's the fluidity of the magma,

is higher than we knew.

GUY: Magma is a mixture, right?

You've got this liquid rock, but also dissolved gases,

crystallized minerals, and larger chunks of rock.

So, the melt percentage is just how much of that mixture is molten rock.

- And here, it's around 16-20%.

GUY: That's unnerving, because as far as we know,

the melt percentage only needs to be around 35 to 50% to explode.

- Is this supervolcano a ticking time bomb?

NARRATOR: With every supervolcano, it's not a question of if but when.

- It makes you wonder when and how it'll finally reach the surface.

NARRATOR: A clue might lie around 5,000 kilometres away,

in the middle of the Pacific Ocean: the island of Hawaii.

This is Mauna Loa, one of the most active volcanoes in the world.

BELLINGER: Hawaiian myth says Pele, goddess of volcanoes and fire,

created the whole chain of islands

and is behind the eruptions even today.

NARRATOR: But what forces power this mythic goddess?

- Mauna Loa is over a hotspot, just like Yellowstone is,

and the ongoing eruptions there over millions of years

have formed the Hawaiian Islands.

- But what can these eruptions tell us about Yellowstone?

NARRATOR: The clue lies in the lava itself.

GUY: Hawaiian eruptions like the one from Mauna Loa

aren't these massive explosions but rather these slower,

ongoing flows known as effusive eruptions.

- This really fluid lava is made largely of basalt,

and when it cools, it can leave very specific types of land formations.

YATES-ORR: So, the question is are there any signs

at Yellowstone like this?

RISKIN: There is one famous and ancient site

in Yellowstone National Park that connects

to this Hawaiian-style basalt lava flow.

NARRATOR: Obsidian cliff.

GUY: The appearance and composition of the Obsidian Cliff tells us

that it was created by this thick lava flow that cooled very quickly,

similar to what we see at Mauna Loa.

YATES-ORR: So, that means we could see another flow like this,

but Yellowstone is capable of something much, much bigger.

NARRATOR: What explosive superpower could burst

from below Yellowstone National Park?

And what devastation will it unleash?

- How can we figure out what will happen next?

NARRATOR: A clue may lie around 14,000 kilometres away in Indonesia.

The idyllic waters of Lake Toba hide the caldera of another supervolcano.

GUY: It's a massive lake, 100 by 30 kilometres,

and just over 500 metres deep.

- Toba is another supervolcano that erupted around 74,000 years ago.

KOUROUNIS: And the reason it left such a big mark on the landscape?

The Toba event was gigantic.

It's the biggest known eruption of the past 2.5 million years.

- So, what was the impact of this massive explosion,

and what clues can it give to what might happen at Yellowstone?

RISKIN: When Toba erupted, it unleashed a tonne

of destructive power. First, there was the lava flow,

at least 2,500 cubic kilometres of dense pyroclastic material.

That volume is so big, it's hard to imagine.

It's almost twice as big as all the water in Lake Ontario.

- It also had a massive ash cloud that spread westward

across the Indian Ocean and reached Africa.

- And the blast probably caused tsunamis reaching India,

Africa, and even Australia.

NARRATOR: Could an eruption of this magnitude happen at Yellowstone?

- To find the answer, we need to look down from above.

RISKIN: Yellowstone caldera is a remnant

of one of these major eruptions.

But astonishingly, there are two more gigantic calderas.

GUY: That means there have been three major

supervolcano-level eruptions here.

But when? And how big were they?

YATES-ORR: The oldest and biggest caldera is the result of the largest

of Yellowstone's big three eruptions.

RISKIN: This one happened a little more than two million years ago,

and it released a whopping 2,500 cubic kilometres of material.

That had ash fall at least as far as California,

probably all over the world.

BELLINGER: But this was a time when no humans were at risk.

Now, there are over 300 million people in the US.

NARRATOR: So, what would it mean if something like that happened today?

GUY: The potential magnitude of an eruption from

the Yellowstone supervolcano is mind-blowing.

KOUROUNIS: Because of the massive pyroclastic flows,

about a 100-kilometre radius around the volcano would be a kill zone.

RISKIN: And some computer models predict that depending on

the duration of the eruption, you would be looking at ash fall

across the whole of the United States.

- With that much ash, an impact on the global climate is also possible.

- This would really be a world-altering event.

NARRATOR: With so much at stake, can modern science help us predict

when Yellowstone will blow?

RISKIN: There's actually some really cutting-edge technology

that's improving our ability to predict volcanic eruptions.

NARRATOR: Around 3,800 kilometres away, in Guatemala,

one project takes place above the active Volcan de Fuego.

GUY: The best place to measure data from a volcano

is near an active vent... but that also happens to be

the most dangerous place you can be.

KOUROUNIS: With a place as active as Volcan De Fuego,

you'd be risking your life to get near the top.

- The solution? Specially designed drones.

These amazing machines can climb over three kilometres up

and then fly right into the ash clouds above the volcano

to collect measurements and samples.

GUY: It's amazing. These drones are going places

that humans never could,

and they're collecting data from above to solve

the mysteries of volcanic eruptions.

NARRATOR: Ancient civilizations created fascinating myths

and legends to explain the potent volcanic powers of the earth,

powers we're still seeking to fully understand even today.

KOUROUNIS: What I find fascinating is how little

we really know about it, despite the fact that it's

one of the most closely monitored volcanoes on planet Earth.

GUY: For now, we'll just have to keep our eye on

these "Mysteries From Above".

BELLINGER: Given the grandeur of so many natural features

in our world, it's no wonder people resort to tales of gods

or sorcery to explain what they see.

NARRATOR: With cutting-edge technology and a view from above,

we can pursue the answers to these mysteries.

Subtitles by Sky Access Services