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 three 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 Idaho 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 US.
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.
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 travelling 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 pressurising.
Beneath Old Faithful is a rather complex plumbing system,
filled with caverns and conduits and constrictions.
Rainwater saturating the ground around the geyser
slowly fills its underground reservoir.
Hot rocks below ground 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 depressurises, and a full eruption can occur.
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.
OK, 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.
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 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.
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.
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 centre 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 we 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.
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 burr around the side of the 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.
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.
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.
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.
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... I don't see a smoking volcano, I don't see a big steep volcanic, uh, uh, crater,"
all the things that one normally thinks of for an active volcano.
So, without obvious signs of a volcano, scientists hunted for other clues.
They would find them in the sweeping forests of Lodge Pole 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.
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 or more viscous.
If we put a bunch of gas in it, we can have a very explosive eruption.
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.
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 characterised 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,
modern soil has formed and we can see growing up there
various sorts of vegetation, trees and grasses and things of that sort.
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.
The geologists have recreated what must have happened here
on the day that Yellowstone exploded.
Incandescent avalanches of ash raced out of the park in all directions.
CATHEY: So this is travelling at very high velocity, um,
easily over 100 miles per hour,
across the land surface and obliterating everything in its path.
NASH: 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.
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... CATHEY: Yeah.
I think you would be disarticulated, burned and... and unrecognisable,
and it would be very difficult to find any of you.
All of the evidence about the size of the supereruption
helped solve the mystery of the missing volcano.
Scientists realised 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 realised 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 realised
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 US,
confirming the huge size of the eruption.
At least 80 times the size of the 1883 explosion
that destroyed the island of Krakatoa.
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.
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.
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.
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 colour 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.
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 ten 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 21 st 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.
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 neighbour.
Investigators realised
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 travelled 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 realised 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.
SMITH: 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.
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.
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 to thr...
...about three or four feet, so if the ground moves up and down,
the antenna moves up and down.
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, uh,
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.
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.
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, uh, there is no reason to think that volcanism has stopped.
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?
HEASLER: 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.
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.