Original subtitles

Male narrator:; Earth,

a 4.5 billion-year-old planet, still evolving.

As continents shift and clash,

volcanoes erupt,

and glaciers grow and recede,

the Earth's crust is carved in countless fascinating ways,

leaving a trail of geological mysteries behind.

And one of the greatest is right here

at Yellowstone National Park in Wyoming.

This is one of the world's most geologically active places,

shaken by up to 5,000 earthquakes every year,

and with more geysers and hot springs

than in the rest of the world combined.

Why is Yellowstone so active?

How did it form?

And why here in the heart of the Rockies?

Scientists studying Yellowstone are uncovering a violent past

carved by water, crushed by ancient glaciers,

and blasted by the biggest volcanic eruptions

ever known on the planet.

And even today,

Yellowstone is one of the most dangerous places on Earth.

Yellowstone National Park is one of the most amazing places

on Earth, and it's unique.

It contains some of America's most stunning scenery

and wildlife that attracts 3 million tourists a year.

To understand where Yellowstone came from

and why it is so active today,

we need to take a journey back into the distant past

of the North American continent

and deep into the Earth's interior.

Yellowstone sits 8,000 feet up on a remote mountain plateau,

primarily within Wyoming

but stretching into parts of lldaho and Montana.

The park covers 3,468 square miles,

63 miles north to south and 54 miles east to west.

And it's on top of one of the world's most unusual

and deadliest geological structures.

- What's unusual about the park?

Are the wildlife unusual?

No.

Is the wide open space unusual?

No. You've got it all over the western U.S.

What's unusual?

It's a very unusual geology that created the park.

Yellowstone was founded as the world's first

national park because of the geology.

Narrator: It's this strange geology

that attracts teams of scientists to the park.

Their task?

To piece together the story of the incredible processes

that built this unique, extraordinary landscape

by digging deep into Yellowstone's past.

- The geologic history of Yellowstone

goes back to the formation of the North American continent.

Some of the rocks in Yellowstone

are 2.8 to 3.2 billion-year-old rocks,

some of the oldest in North America.

- Only by traveling back into the past

can we figure out why in this particular location

there are 2,400 miles of rivers,

more than 300 waterfalls

and the world's greatest concentration

of 10,000 hot water springs,

bubbling mud-holes, gas vents and geysers.

What do these features reveal about this landscape

and how it was formed?

The investigation begins at Yellowstone's star attraction,

Old Faithful.

It's a key clue

to what's going on underneath the surface.

Located in the southwest of Yellowstone Park,

the geyser puts on an explosive display every 90 minutes or so,

blasting out thousands of gallons of scalding hot water.

Yellowstone is like no other place on Earth.

There is so much heat coming out here.

It's really a singular phenomenon.

Well, after about a 90-minute nap,

Old Faithful has roared back to life.

It wasn't actually napping, it was recharging,

and the temperature of the water was increasing.

The system was pressurizing.

Beneath Old Faithful

is a rather complex plumbing system

filled with caverns and conduits and constrictions.

Narrator. Rainwater saturating the ground around the geyser

slowly fills its underground reservoir.

Hot rocks belowground heat the water under pressure

for around 90 minutes.

Suddenly, some water spurts

through a tiny, five-inch-wide crack in the rocks.

This causes a drop in the pressure

within the water chamber.

In an instant, thousands of gallons of water

are turned to steam and blasted up into the air.

- When the pressure builds up enough,

steam bubbles start rising to the surface,

the system depressurizes, and a full eruption can occur.

Narrator: Old Faithful shows that rocks below the surface

are very hot.

Scientists find clues to a violent past

34 miles southeast of the hot springs

on the shores of a circular lake called Indian Ponds.

- As a field geologist,

my job is to basically be a rock detective.

And so I try to determine what their origin is

and what the history is of that particular rock.

There we go.

Okay, now, in this particular case-let's look at this.

This rock, when it started, it was just a loose sand.

You could just put your fingers through it.

Narrator: The solid boulder is formed

from millions of individual grains of sand.

Microscopic analysis reveals the grains

have been cemented together by chemicals and pressure

deep under the ground.

But how did the rock get to the surface?

Morgan has chemically dated the rocks

and discovered that 3,000 years ago,

the boulder was blasted out of the ground

by the hot water explosion of a gigantic geyser.

- You would see boiling water,

rock fragments and fine muddy material

being ejected up into the air as high as 3,000 to 5,000 feet.

And then, at some point,

material would start raining down from this explosion column.

Now, you wouldn't want to be standing next to one of those.

Narrator: Indian Ponds is the crater

that the geyser left behind.

But it is dwarfed by the crater Morgan has found

at Mary Bay in Yellowstone Lake.

Morgan has dated this geyser explosion to 13,000 years ago.

- So here we are in the middle of Yellowstone Lake,

and it's, as you can see, a beautiful day

and it's nice and placid,

but on the floor of Yellowstone Lake,

it's anything but quiet.

Narrator. Morgan's research proves that geysers

were exploding around the lake, and even under the water,

between 13,000 and 3,000 years ago.

And their size suggests

that whatever was powering them was huge.

But is it still active today?

A clue comes from underwater vents

at the bottom of the geyser crater.

They pump out vast quantities of hot water and gases.

To find out what's creating the gases,

Jake Lowenstern and his assistant

collect samples from the hot springs

in the center of the park.

The funnel they use is designed to collect up gas bubbles

before they reach the surface

so that they're not contaminated by ordinary air.

- So you let it sit for five minutes

and let the oxygen get out?

- Yeah.

It is a very complex mix of gases and-

but we have a-a lot of tools that we can use

to try to unravel this rather, uh, complicated information.

So we'll look at all of the gases that are coming out.

We can learn about the different kinds of rocks

beneath Yellowstone and try to understand

how things might be changing from-from week to week

or year to year or- or decade to decade.

Narrator: Analysis of the gases reveals

that they are a mix of carbon dioxide, sulphur dioxide

and hydrogen sulphide.

It is the same mix that is found coming out of volcanoes.

But the final clue to what's actually going on underground

is found on the edge of the same hot springs.

- So these are quartz crystals that we collected

on the side of the pool there.

This stuff is what remains.

It gets tossed up and forms a little berm

around the side of the cr-pool

and it's all beautiful little quartz crystals.

Some of them have a little bit of iron staining

and other things, um, but most-

most of them are-are nice, uh, shades of yellow and-and clear.

Narrator: Quartz crystals like these

can only have formed as a hot, molten rock lava flow

slowly cooled after being erupted onto the surface

from deep underground.

So the crystals are clear evidence

that under the springs is a volcano.

Yellowstone's hot water features all point to one conclusion.

Yellowstone must be powered by the heat of a volcano.

Geysers only erupt if the rocks are hot enough

to turn water into steam.

Gases from underwater have the same composition

as those from volcanoes.

Quartz in the hot springs

must have come from volcanic lava.

- There is an immense amount of energy coming out of the ground

that's expressed by the geysers,

the mud pots, the hot springs

and the steam vents.

Where's all that heat coming from?

It's coming from the molten rock

associated with the Yellowstone volcano.

Narrator: But that leaves a big question unanswered.

In this gentle rolling landscape,

where's the volcano?

Yellowstone's unique volcanic geology

is potentially deadly dangerous.

It makes it crucial to monitor what's happening

under the ground.

- The Yellowstone volcano

is a very, very active volcanic system,

and so it really requires observation.

Everything that we do here has a research component,

but it also has a volcano monitoring component

and, uh, you know, if-if- if activity picks up here,

we're going to want to know something

about the plumbing system beneath us here.

Narrator: To try and predict

when Yellowstone's hidden volcano

will erupt in the future,

scientists study its geological past.

- Part of our task is to look at the landscape

and read the geologic story,

and there are so many clues and so much evidence here

to look at that it's a fascinating place to work.

Narrator: Scientists began investigating Yellowstone

even before it became

the world's first national park in 1872.

But observations of this astonishing land

began long before that.

Dating ancient arrowheads

shows that Native Americans first lived here

11,000 years ago.

Their legends of Yellowstone's angry spirits

who made the ground tremble

were passed on to early explorers

such as Lewis and Clark.

Later reports from trappers, explorers and mountain men

like John Colter and Jim Bridger

told of geysers that fired 70 feet into the air

and springs so hot that meat was readily cooked in them.

But these were thought to be tall tales until the 1860s,

when geologists investigated and found that the lava flows

and hot vents were signs of volcanic activity.

But something clearly wasn't right.

Nobody could actually find the Yellowstone volcano.

- We say that Yellowstone

is one of the world's most active volcanoes.

People come out here- visitors, other scientists-

and they say, "What do you mean?

I don't see a smoking volcano.

I don't see a big steep volcanic, uh, crater,"

all the things that one normally thinks of

for an active volcano.

Narrator: So without obvious signs of a volcano,

scientists hunted for other clues.

They would find them in the sweeping forests

of lodgepole pines.

These are the only plants that thrive on the poor soil

that comes from a particular type of lava called rhyolite.

And Yellowstone's constant plagues of mosquitoes

also reveal the presence of that same rhyolite lava.

- The rhyolites are- are not very permeable,

and so in-it creates these little ponds of water

that never go away,

and those are wonderful breeding grounds for mosquitoes.

There are a lot of mosquitoes,

if you can't see them flying around my head.

Narrator. So the pine trees and the insects

both indicate that there's a lot of rhyolite

in Yellowstone.

And that's important,

because rhyolite lava creates incredibly violent

volcanic eruptions.

- It's much more like a bread dough.

It's about a thousand to a million times thicker

Oor more viscous.

If we put a bunch of gas in it,

we can have a very explosive eruption.

Narrator: But if rhyolite lava is that explosive,

how big a bang did it produce?

To find that out, scientists looked

not inside Yellowstone Park

but in a faraway river valley at Meadow Creek, Wyoming.

Cutting down through the land over millions of years,

the river has exposed an unusual thin layer

of black rock in the cliff face.

A nearby road cutting lets investigators

examine the mysterious dark rock.

- If you look at this sample, um, in detail up close,

you can see that here's a pumice fragment.

These-these red fragments here are-

are little rock fragments.

And, uh, if we were to make a thin section of this rock

and look at it under the microscope,

you would, in fact, see compressed, uh, glass shards.

Narrator: The black layer that geologists call obsidian

is actually a type of glass.

It's crucial evidence that the rocks and soil here

came out of a volcano...

because obsidian is forged

when boiling hot ash and gas rapidly cool

under great pressure.

And that's just what happens when hot volcanic clouds

roll out across the landscape.

The obsidian forms in the very bottom layers,

cooled from below

and crushed by the weight of hot debris on top.

The ash layer that crushed the obsidian at Meadow Creek

is still visible today.

- Its base is characterized

by this very thick, dense, obsidian as-

as the flow came to rest and was compacted

and then above this dense glass layer

as it grades upwards into a tan sort of region

and continues up for about an additional 30 feet.

And then up on top of that, as it's exposed today,

a modern soil has formed and we can see

growing up there various sorts of vegetation:

trees and grasses and things of that sort.

Narrator. Studying the mineral composition of the ash

proved that it came from an ancient volcanic blast

in Yellowstone Park.

And there's only one way that so much ash

could have been blasted so very far away

from its source.

The eruption must have been larger, far larger,

than anything ever seen by man,

so big that scientists now label it as a supereruption.

- We're looking at this deposit from a supereruption,

and yet we're over 50 miles from the source of the-

of the eruption.

Narrator. The geologists have re-created

what must have happened here

on the day that Yellowstone exploded.

Incandescent avalanches of ash

raced out of the park in all directions.

- So this is traveling at very high velocity,

easily over 100 miles per hour, across the land surface

and obliterating everything in its path.

- It was extremely hot when it arrived here,

and-perhaps as hot as- as 1,500 degrees Fahrenheit,

two-twice a pizza oven.

I mean, it's just very hot.

Narrator: So what would it have been like

to be standing on this spot

hundreds of thousands of years ago

on the day when the Yellowstone ash cloud

roared over the horizon?

- The-the impact of this would-

would be, uh, absolutely unimaginable.

It would be- - Yeah.

- 1 think you would be disarticulated, burned

and-and unrecognizable,

and it would be very difficult to find any of you.

Narrator: All of the evidence about the size

of the supereruption helped solve the mystery

of the missing volcano.

Scientists realized that the supereruption

was so enormous that it must have blown the volcano

to pieces.

[roaring and explosions]

Swarms of mosquitoes show that explosive rhyolite lava

underlies parts of the park.

Obsidian glass 60 miles away reveals that ash flows

spread for miles around Yellowstone.

And thick layers of debris confirm

how gigantic an explosion this must have been.

The problem now is the explosive legacy

that the supervolcano left behind,

because a deadly danger still lurks here

hidden deep under the ground.

For nearly a century after Yellowstone National Park

was established, nobody realized one astonishing fact...

that the park is located

inside one of the biggest volcano craters on Earth.

It wasn't until the late 1960s

that American geophysicist Robert Christiansen

realized that rock formations he had been studying

for several years all around the edges of the park

in fact formed a giant circular ridge.

He compared his findings on the ground

with a series of NASA pictures taken between 1966 and 1970,

confirming that the ring was the rim of a giant crater

45 miles across.

Parts of the crater rim are still clearly visible today,

but the other edge is almost out of sight.

Finding the crater

coincided with another scientific discovery

in a totally different part of the country.

In California,

scientists identified a strange, thin layer of ash

buried underneath the modern-day soil.

The ash matched material from the Yellowstone crater.

Dating the soil layers

proved that the ash arrived 640,000 years ago.

Scientists at last had a date

for the Yellowstone supereruption.

Ash was later found all over the western U.S.,

confirming the huge size of the eruption...

at least 80 times the size of the 1883 explosion

that destroyed the island of Krakatoa...

[rumbling]

And 2,500 times bigger

than the 1980 eruption of Mount St. Helens.

The almost unimaginable size of the Yellowstone blast

means that scientists now call it a supervolcano.

But that creates another mystery.

In this peaceful landscape,

where is the steaming hot crater

that the volcano must have left behind?

- Today, when you're looking out across the landscape,

you see rolling hills and-and trees,

so, obviously, there's not a big hole

left in the ground, um, from the eruption of the-

of the Yellowstone volcano.

So something else has happened.

One of the first processes was infilling

with all sorts of volcanic lava flows,

and if you look just down from the landscape

toward those trees,

you'll see one of the oldest lava flows that happened

after the 640,000 year eruption.

Narrator: Over hundreds of thousands of years,

this flow has weathered into soil

and been covered with trees.

But elsewhere in the park

are a different type of lava deposit,

still bare of vegetation

because this lava was still erupting

up until about 100,000 years ago.

The later lava was far less explosive and more runny

and cooled slowly.

It smoothed the harsh volcanic landscape

into Yellowstone's softer countryside.

That made Yellowstone, at first, more tranquil.

But there's evidence here

that the land was soon buried once again,

this time by freezing snow and ice.

The ice that polished the rocks has a story to tell.

It offers crucial evidence about volcanic forces

still shaping the park to this day.

Its tale unfolds through the tiniest of clues.

Scratches on the rocks reveal which way the ice was moving.

They show that glaciers always slid the same way,

outwards and downwards from an icecap

at the heart of the park.

The only conclusion

is that something pushed up Yellowstone Park

so much higher than the surrounding hills

that glaciers formed on the top.

But what force could possibly be powerful enough

to have raised Yellowstone's peaks

up into the air?

The first clue to help answer that question

comes from Yellowstone's numerous earthquakes.

- When the ground deforms,

it creaks and groans like a Stradivarius violin.

And the creaks and groans are essentially earthquakes.

Narrator: The quakes are recorded

by seismometers all over the park.

- The earthquake monitoring

is a critical part of the picture

because it's basically-

it's the stethoscope that we have

to really see and sense the- the heartbeat of the system.

Narrator. Smith is investigating a puzzling geological mystery.

Yellowstone has up to 5,000 earthquakes a year,

even though it's in the stable heart

of the North American continent.

Scientists needed to know what was happening underground

to shake the park so much.

To find out, they plotted the precise locations and depths

of earthquakes under the ground.

So why are there so many quakes?

The answer had to wait until the mid-1980s,

when ever-more powerful computers

first let scientists see into the Earth.

Seismic waves spreading out from earthquakes

travel rapidly through cold rock

but slow down when the rocks are hot.

The varying wave speeds can be translated by computers

into color 3D images,

revealing exactly where hot rock lies under the ground.

- Seismic waves propagate through the Earth

just like X-rays go through a body,

and so we use the same physics

to reconstruct the structure of the geol-

of the Earth beneath us.

Narrator: The seismic waves have outlined

the park's underground structures,

revealing a graphic history

of what's happened under Yellowstone.

They reveal this gigantic reservoir of molten rock

which created Yellowstone's crater

when lava erupted out

and the ground above collapsed into the space left behind.

And the seismic waves still slow down under Yellowstone today,

showing that the magma chamber still lurks under the park.

It's more than 30 miles long, 25 miles wide

and 10 miles in depth.

But its size alters from year to year

as it fills or empties with semi-liquid rock

at an incredible 1,500 degrees Fahrenheit.

This is the hidden beating heart of Yellowstone Park.

The way it moves deforms the ground above,

explaining the fault lines and the earthquakes

they produce.

And its heat ultimately powers

all of Yellowstone's hot water pools and geysers.

Subterranean Yellowstone is giving up its secrets.

Seismographs record thousands of earthquakes in the park,

and the evidence of earthquake waves

reveals a massive magma chamber

miles under Yellowstone's surface.

But the Yellowstone investigation

is far from finished because there's evidence

of another, even more monstrous sized structure

under the park.

By the beginning of the 21st century,

scientists investigating how Yellowstone was made

had images of what lay under the park.

But there was a problem.

Technology only allowed a view of a few miles

below the surface.

Then, as more and more data

was fed into more and more powerful computers,

there was a breakthrough.

In April 2006,

geologists published new diagrams

of hot structures, far deeper under the park,

and computers painted more detailed pictures.

The results were startling.

Investigators saw for the first time the sleeping monster

that lies below Yellowstone Park.

Snaking down hundreds of miles into the Earth,

far deeper than the relatively shallow magma chamber

is a colossal volcanic pipe.

Nobody's certain how deep it goes,

but they can picture it down to 400 miles or more,

twice the distance between Washington and New York.

Smith makes an educated guess

about what the underground plume is like.

- Our best estimates now as we start doing the physics

and the dynamics of these things,

it's like a conduit of melted rock,

like a chimney.

Narrator. That chimney, called a hotspot,

pumped up enough heat to melt the rocks of the crust

and fill the overlying magma chamber,

which then erupted to blast out Yellowstone's vast crater.

Understanding how the crater formed

was an important moment for the investigation,

because there was evidence that similar eruptions

had happened before, many times before.

Throughout the 1960s,

various teams of geologists studied the Snake River Plain

to the southwest of Yellowstone Park

and found traces of ancient volcanic craters.

The crater rims had long been eroded,

but their outlines were confirmed by aerial pictures

over the following decade.

They ran in a straight line along the plain,

heading for the heart of Yellowstone Park.

On average, each crater was a couple of million years older

than its neighbor.

Investigators realized that these are the remnants

of earlier supervolcano explosions,

an unbroken chain stretching far back into geological history.

It seemed clear that, time after time,

the hotspot had blasted out a supereruption

and then moved on.

The hotspot appeared to have traveled hundreds of miles.

But that posed yet another riddle.

How could a hotspot anchored to the core of the planet

be moving?

An important clue had been found in 1985

by American volcanologist William Scott.

He realized that plotting the location

of 30,000 earthquakes around Yellowstone

produced an amazing pattern.

The quakes traced out a giant V shape

on the surface of the Earth.

The V shape wrapped around the hotspot's location.

It seemed at first to confirm

that the hotspot was still moving,

rippling up the land around it with fault lines

and tens of thousands of earthquakes.

But the real answer lay with the theory of plate tectonics.

It showed that it's the American continent,

not the hotspot, that's moving.

And the chain of craters on Snake River Plain

is there because for millions of years,

the moving American continent has continually pushed new land

over the stationary hotspot.

- But as the North American Plate moved

across this source of heat,

it pops through the lid and creates the hotspot track.

That's the Snake River Plain.

Yellowstone is just the active component today.

Narrator. The repeated hotspot explosions on land

have made Yellowstone unique.

Other hotspots have been identified around the world,

like the one that has created the island chain of Hawaii,

but Yellowstone is the only place

where a hotspot has erupted in the middle of a continent.

Each of the earlier explosions

blew the original mountains to pieces.

Then the land smoothed over with later flows

of more runny lava that was released

from deep under the Earth's crust.

Multiple strands of evidence

combine to reveal Yellowstone's slumbering monster,

the gigantic hotspot plume lying under the park.

Earthquake maps show the hotspot's location.

Seismic waves reveal the depth of the plume.

And earlier craters prove regular supereruptions

over millions of years,

All of which leads to the most frightening question of all.

When will Yellowstone erupt again?

[rumbling and explosions]

Measuring the amount and geographical spread

of ashfall from Yellowstone's supereruptions

produced some terrifying figures.

[explosions]

640,000 years ago,

the eruption poured out around 240 cubic miles of material

enough to bury the whole of New York State

tens of feet deep in ash.

If it happens again, thousands will die

and vast areas of the United States

will be buried in volcanic debris.

But when will Yellowstone erupt again?

One clue to when that next eruption will happen

comes from investigating the eruptions of the past.

The hotspot punches out a supereruption, on average,

every 600,000 years.

And the last one was 640,000 years ago.

But geologists expect that there will be warning signs

before Yellowstone explodes again.

Volcanic eruptions are usually preceded

by an increasing number of earthquakes.

The quakes are a sign that underground volcanic chambers

are filling with molten rock and expanding

to stretch and deform the land up above.

Yellowstone Park usually experiences

an average of 12 tiny earthquake tremors every day.

Most are too weak to be felt by tourists

and register only on the most sensitive seismometers.

But in early 2009,

more than four times as many quakes

started striking every day.

Over one ten-day period, there were more than 500 quakes,

some of them up to magnitude 3.9,

powerful enough to frighten the visitors

and put the scientists on alert.

There's a second indicator of increasing volcanic activity.

If more molten rock does inflate the underground chamber,

the ground above will rise.

And that, too, seems to be happening right now.

Unusual evidence to prove it comes from an unlikely source:

the waters of Yellowstone Lake.

Around 100 years ago,

small steamships carried tourists

on sightseeing trips across the lake,

but one of the ships caught fire and sank forever

below the surface of the lake.

But now, Yellowstone's astonishing geological forces

have resurrected the ship's remains from their watery grave.

- Here we have a boat which burnt down to water level,

and so this tells us something about

the deformation of Yellowstone,

and basically, what's happened is that the floor of the lake

has risen, bringing the boat out of water.

Narrator: The reappearance of the wreck

shows that land under and around the lake is rising

because of the expansion of the magma chamber.

Even more alarmingly,

the rate at which it's rising seems to be increasing.

In geological terms, a huge area of Yellowstone Park

is positively soaring up into the air

faster than it's ever done before.

The biggest uplift of all has been recorded

just a few miles from the shore of the lake.

There's a GPS system here,

a much more sophisticated version of the one in your car.

It measures not only its surface position

but also its exact altitude to within fractions of an inch.

- There's a small radio antenna about the size of your thumb

that sits on top of this steel rod,

and it is anchored in two- about three or four feet,

so if the ground moves up and down,

the antenna moves up and down.

Narrator: The GPS and the land on which it's anchored

are moving upwards.

- We're above the magma chamber, and, beginning in late 2006,

this whole area of ground started to rise

at the order of two to three inches per year.

And as of today, this whole system right here

has risen about that much, and it's still moving today,

and so we're measuring and keeping close track

of the deformation, the-of the uplift

that we're seeing at this station.

Narrator: But does the uplift mean

that Yellowstone's supervolcano is threatening to erupt

once again?

- The question of what lies in Yellowstone's geologic future

is fascinating, and I and all of my colleagues

would love to know the answer to that question.

Narrator. The scientists keep a careful watch

on the volcano's activity.

- The idea of science is to understand the process,

and so we have a responsibility

to see how this system is deforming

and how it's working,

hence we have to be aware there is still a possibility

of-of volcanic eruptions or earthquakes.

After all, that's what made this system,

and there is no reason to think that volcanism has stopped.

Narrator: The Yellowstone investigation

has shown that the park's sleeping supervolcano

is still alive and dangerous.

Old Faithful's underground plumbing reveals volcanic heat.

Obsidian glass tells of a massive eruption.

Seismographs record thousands of earthquakes,

while the earthquake waves

reveal terrifying underground chambers.

And the reappearance of a sunken boat

shows that the land is rising.

And yet, the ultimate Yellowstone geological question

remains to be answered.

When will the supervolcano erupt once again?

- We know there's enough magma left.

We know there's enough heat.

We know that there will be future eruptions in Yellowstone.

But we don't know if there will ever be

another catastrophic eruption.

Narrator. So the investigation

is left with a deadly serious warning.

On the timescale that geologists work to,

a coming supereruption in Yellowstone

may well be right around the corner.

That corner could be 10,000 or 100,000 years

in the future.

Or it could be tomorrow...

a new and devastating chapter

in the ever-changing story of how the Earth was made.