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Earth, a 4.5- Billion-year-old planet,
still evolving.

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As continents shift and clash, volcanoes
erupt, and glaciers grow and recede,

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

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leaving a trail
of geological mysteries behind.

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And one of the greatest is right here, at
Yellowstone National Park in Wyoming.

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

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shaken by up to 5,000 earthquakes
every year,

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and with more geysers and hot springs
than in the rest of the world combined.

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Why is Yellowstone so active?
How did it form?

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And why here in the heart
of the Rockies?

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Scientists studying Yellowstone
are uncovering a violent past.

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Carved by water, crushed by
ancient glaciers and blasted

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by the biggest volcanic eruptions
ever known on the planet.

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And even today, Yellowstone is one of
the most dangerous places on Earth.

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Yellowstone National Park is one
of the most amazing places on Earth,

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and it's unique.

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It contains some of America's
most stunning scenery

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and wildlife that attracts
three million tourists a year.

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To understand where Yellowstone
came from, and why it is so active today,

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we need to take a journey back
into the distant past

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of the North American continent
and deep into the Earth's interior.

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

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primarily within Wyoming, but stretching
into parts of Idaho and Montana.

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The park covers 3,468 square miles,
63 miles north to south

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and 54 miles east to west.

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

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and deadliest geological structures.

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What's unusual about the park?
Are the wildlife unusual? No.

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Is the wide open space unusual? No.

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You've got it all over the western US.

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What's unusual?

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

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Yellowstone was founded
as the world's first National Park

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because of the geology.

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It's this strange geology that attracts
teams of scientists to the park.

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Their task, to piece together
the story of the incredible processes

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that built this unique,
extraordinary landscape

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by digging deep into Yellowstone's past.

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The geologic history of Yellowstone
goes back to the formation

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of the North American continent.

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Some of the rocks in Yellowstone
are 2.8 to 3.2 billion year old rocks,

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some of the oldest in North America.

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Only by travelling back into the past

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can we figure out why
in this particular location

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there are 2,400 miles of rivers,
more than 300 waterfalls...

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...and the world's greatest concentration
of 10,000 hot water springs,

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bubbling mud-holes, gas vents
and geysers.

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What do these features reveal about
this landscape, and how it was formed?

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The investigation begins at
Yellowstone's star attraction,

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Old Faithful.

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It's a key clue to what's going on
underneath the surface.

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Located in the southwest
of Yellowstone Park,

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

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blasting out thousands
of gallons of scalding hot water.

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Yellowstone is like no other place
on Earth,

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there is so much heat coming out here.

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It's really a singular phenomenon.

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Well, after about a 90-minute nap,
Old Faithful has roared back to life.

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It wasn't actually napping,
it was recharging,

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and the temperature of the water was
increasing, the system was pressurising.

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Beneath Old Faithful is a rather
complex plumbing system,

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filled with caverns and conduits
and constrictions.

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Rainwater saturating the ground
around the geyser

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slowly fills its underground reservoir.

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Hot rocks below ground heat the water
under pressure for around 90 minutes.

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Suddenly, some water spurts through
a tiny, five-inch wide crack in the rocks.

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This causes a drop in the pressure
within the water chamber.

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In an instant, thousands of gallons
of water are turned to steam

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and blasted up into the air.

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When the pressure builds up enough,
steam bubbles start rising to the surface,

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the system depressurises,
and a full eruption can occur.

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Old Faithful shows that rocks
below the surface are very hot.

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Scientists find clues to a violent past
34 miles southeast of the hot springs,

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on the shores of a circular lake
called Indian Ponds.

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As a field geologist,

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my job is to basically be a rock detective.

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And so I try to determine
what their origin is

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and what the history is
of that particular rock.

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There we go.

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OK, now, in this particular case...
Let's look at this.

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

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you could just put your fingers through it.

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The solid boulder is formed from millions
of individual grains of sand.

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Microscopic analysis reveals the grains
have been cemented together

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by chemicals and pressure
deep under the ground.

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But how did the rock get to the surface?

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Morgan has chemically dated the rocks
and discovered that 3,000 years ago,

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the boulder was blasted out of the
ground by the hot water explosion

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of a gigantic geyser.

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You would see boiling water,
rock fragments and fine muddy material

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

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And then, at some point,

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material would start raining down
from this explosion column.

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

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Indian Ponds is the crater
that the geyser left behind.

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But it is dwarfed by the crater
Morgan has found

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at Mary Bay in Yellowstone Lake.

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

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So here we are in the middle
of Yellowstone Lake,

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

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but on the floor of Yellowstone Lake,
it's anything but quiet.

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Morgan's research proves that geysers
were exploding around the lake,

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and even under the water,
between 13,000 and 3,000 years ago.

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And their size suggests that whatever
was powering them was huge.

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But is it still active today?

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A clue comes from underwater vents
at the bottom of the geyser crater.

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They pump out vast quantities
of hot water and gases.

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To find out what's creating the gases,

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Jake Lowenstern and his assistant
collect samples from the hot springs

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in the centre of the park.

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The funnel they use is designed
to collect up gas bubbles

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before they reach the surface,

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so that they're not contaminated
by ordinary air.

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So we let it sit for five minutes
and let the oxygen get out?

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Yeah.

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It is a very complex mix of gases
and... but we have a... a lot of tools

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that we can use to try to unravel this
rather, uh, complicated information.

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

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we can learn about the different
kinds of rocks beneath Yellowstone

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and try to understand how things might
be changing from... from week to week,

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or year to year or... or decade to decade.

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Analysis of the gases reveals

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that they are a mix of carbon dioxide,
sulphur dioxide and hydrogen sulphide.

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

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

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is found on the edge
of the same hot springs.

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So these are quartz crystals that we
collected on the side of the pool there.

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This stuff is what remains.

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It gets tossed up, and forms a little burr
around the side of the pool

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and it's all beautiful
little quartz crystals.

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Some of them have a little bit of
iron staining and other things, um,

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

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Quartz crystals like these
can only have formed as a hot,

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molten rock lava flow slowly cooled
after being erupted onto the surface

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from deep underground.

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So the crystals are clear evidence
that under the springs is a volcano.

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

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Yellowstone must be powered
by the heat of a volcano.

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Geysers only erupt if the rocks
are hot enough to turn water into steam.

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Gases from underwater have the same
composition as those from volcanoes.

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Quartz in the hot springs must
have come from volcanic lava.

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

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that's expressed by the geysers,

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the mud pots, the hot springs
and the steam vents.

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Where's all that heat coming from?

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It's coming from the molten rock
associated with the Yellowstone volcano.

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But that leaves a big
question unanswered.

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In this gentle rolling landscape,
where's the volcano?

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Yellowstone's unique volcanic geology
is potentially deadly dangerous.

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It makes it crucial to monitor
what's happening under the ground.

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The Yellowstone volcano
is a very, very active volcanic system,

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and so it really requires observation.

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Everything that we do here
has a research component,

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but it also has a volcano
monitoring component

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

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we're going to want to know something
about the plumbing system

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beneath us here.

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To try and predict when Yellowstone's
hidden volcano will erupt in the future,

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scientists study its geological past.

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Part of our task is to look at the
landscape and read the geologic story,

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and there are so many clues
and so much evidence here to look at

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that it's a fascinating place to work.

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Scientists began
investigating Yellowstone

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even before it became the world's
first national park in 1872.

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But observations of this astonishing land
began long before that.

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Dating ancient arrowheads shows

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that Native Americans first
lived here 11,000 years ago.

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Their legends of Yellowstone's angry
spirits who made the ground tremble

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were passed on to early explorers
such as Lewis and Clark.

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Later reports from trappers,

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explorers and mountain men
like John Colter and Jim Bridger

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told of geysers
that fired 70 feet into the air

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

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

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when geologists investigated and
found that the lava flows and hot vents

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were signs of volcanic activity.

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But something clearly wasn't right.

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Nobody could actually find
the Yellowstone volcano.

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We say that Yellowstone is one of
the world's most active volcanoes.

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People come out here,
visitors, other scientists,

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and they say, "What do you mean?

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

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all the things that one normally
thinks of for an active volcano.

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So, without obvious signs of a volcano,
scientists hunted for other clues.

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They would find them in the
sweeping forests of Lodge Pole pines.

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These are the only plants
that thrive on the poor soil

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that comes from a particular
type of lava called rhyolite.

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And Yellowstone's constant plagues
of mosquitoes also reveal

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the presence of that
same rhyolite lava.

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The rhyolites are... are not
very permeable, and so in... it creates

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these little ponds of water
that never go away,

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and those are wonderful
breeding grounds for mosquitoes.

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There are a lot of mosquitoes, if you
can't see them, flying around my head.

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So the pine trees and the insects
both indicate

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that there's a lot of rhyolite
in Yellowstone.

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And that's important,

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because rhyolite lava creates
incredibly violent volcanic eruptions.

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It's much more like a bread dough.

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It's about a thousand to a million times
thicker or more viscous.

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If we put a bunch of gas in it,
we can have a very explosive eruption.

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But if rhyolite lava is that explosive,
how big a bang did it produce?

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To find that out, scientists looked,
not inside Yellowstone Park,

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

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Cutting down through the land
over millions of years,

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the river has exposed an unusual,
thin layer of black rock in the cliff face.

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A nearby road cutting lets investigators
examine the mysterious, dark rock.

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

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you can see that
here's a pumice fragment,

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these... these red fragments here
are... are little rock fragments,

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and, uh, if we were to make

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a thin section of this rock
and look at it under the microscope,

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you would in fact see

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compressed, uh, glass shards.

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The black layer that geologists call
obsidian is actually a type of glass.

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It's crucial evidence that the rocks
and soil here came out of a volcano.

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Because obsidian is forged
when boiling hot ash and gas

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rapidly cool under great pressure.

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And that's just what happens

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when hot volcanic clouds roll out
across the landscape.

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The obsidian forms in the very
bottom layers, cooled from below

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and crushed by the weight
of hot debris on top.

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The ash layer that crushed the obsidian
at Meadow Creek is still visible today.

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Its base is characterised by
this very thick, dense, obsidian

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as... as the flow came to rest
and was compacted.

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And then, above this dense glass layer
as it grades upwards

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into a tan sort of region and continues
up for about an additional 30 feet.

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

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modern soil has formed
and we can see growing up there

229
00:18:27,647 --> 00:18:31,481
various sorts of vegetation, trees
and grasses and things of that sort.

230
00:18:32,967 --> 00:18:35,247
Studying the mineral composition
of the ash

231
00:18:35,247 --> 00:18:40,401
proved that it came from an ancient
volcanic blast in Yellowstone Park.

232
00:18:42,087 --> 00:18:45,567
And there's only one way that so
much ash could have been blasted

233
00:18:45,567 --> 00:18:48,400
so very far away from its source.

234
00:18:49,407 --> 00:18:52,967
The eruption must
have been larger, far larger,

235
00:18:52,967 --> 00:18:56,327
than anything ever seen by man.

236
00:18:56,327 --> 00:19:01,765
So big that scientists now label it
as a supereruption.

237
00:19:02,767 --> 00:19:05,327
We're looking at this deposit
from a supereruption,

238
00:19:05,327 --> 00:19:09,286
and yet we're over 50 miles from
the source of the... of the eruption.

239
00:19:12,727 --> 00:19:15,527
The geologists have recreated
what must have happened here

240
00:19:15,527 --> 00:19:18,767
on the day that Yellowstone exploded.

241
00:19:18,767 --> 00:19:24,205
Incandescent avalanches of ash
raced out of the park in all directions.

242
00:19:25,567 --> 00:19:28,967
CATHEY: So this is travelling
at very high velocity, um,

243
00:19:28,967 --> 00:19:31,167
easily over 100 miles per hour,

244
00:19:31,167 --> 00:19:35,487
across the land surface
and obliterating everything in its path.

245
00:19:35,487 --> 00:19:37,887
NASH: It was extremely hot
when it arrived here,

246
00:19:37,887 --> 00:19:42,607
and... perhaps as hot as... as
1,500 degrees Fahrenheit, two...

247
00:19:42,607 --> 00:19:45,167
...twice a pizza oven,
I mean, it's just very hot.

248
00:19:46,207 --> 00:19:49,167
So what would it have been
like to be standing on this spot

249
00:19:49,167 --> 00:19:51,687
hundreds of thousands of years ago,

250
00:19:51,687 --> 00:19:56,317
on the day when the Yellowstone
ash cloud roared over the horizon?

251
00:19:57,567 --> 00:20:01,607
The... the impact of this would... would
be, uh, absolutely unimaginable.

252
00:20:01,607 --> 00:20:03,087
It would be...
CATHEY: Yeah.

253
00:20:03,087 --> 00:20:06,767
I think you would be disarticulated,
burned and... and unrecognisable,

254
00:20:06,767 --> 00:20:09,201
and it would be very difficult
to find any of you.

255
00:20:13,367 --> 00:20:16,367
All of the evidence about the size
of the supereruption

256
00:20:16,367 --> 00:20:20,007
helped solve the mystery
of the missing volcano.

257
00:20:20,007 --> 00:20:24,327
Scientists realised that the supereruption
was so enormous

258
00:20:24,327 --> 00:20:27,687
that it must have blown
the volcano to pieces.

259
00:20:27,687 --> 00:20:31,077
(ROARING AND EXPLOSIONS)

260
00:20:33,327 --> 00:20:37,007
Swarms of mosquitoes show
that explosive rhyolite lava

261
00:20:37,007 --> 00:20:39,607
underlies parts of the park.

262
00:20:39,607 --> 00:20:43,647
Obsidian glass 60 miles away
reveals that ash flows spread

263
00:20:43,647 --> 00:20:46,647
for miles around Yellowstone.

264
00:20:46,647 --> 00:20:50,687
And thick layers of debris
confirm how gigantic an explosion

265
00:20:50,687 --> 00:20:52,166
this must have been.

266
00:20:53,887 --> 00:20:59,207
The problem now is the explosive legacy
that the supervolcano left behind.

267
00:20:59,207 --> 00:21:05,157
Because a deadly danger still lurks here,
hidden deep under the ground.

268
00:21:11,127 --> 00:21:15,287
For nearly a century after Yellowstone
National Park was established,

269
00:21:15,287 --> 00:21:18,757
nobody realised one astonishing fact.

270
00:21:20,407 --> 00:21:26,721
That the park is located inside one of
the biggest volcano craters on Earth.

271
00:21:28,287 --> 00:21:30,407
It wasn't until the late 1960s

272
00:21:30,407 --> 00:21:33,927
that American geophysicist
Robert Christiansen realised

273
00:21:33,927 --> 00:21:37,807
that rock formations he had
been studying for several years

274
00:21:37,807 --> 00:21:44,155
all around the edges of the park
in fact formed a giant circular ridge.

275
00:21:45,687 --> 00:21:49,887
He compared his findings on the ground
with a series of NASA pictures

276
00:21:49,887 --> 00:21:53,567
taken between 1966 and 1970,

277
00:21:53,567 --> 00:22:02,123
confirming that the ring was the rim
of a giant crater, 45 miles across.

278
00:22:03,727 --> 00:22:07,727
Parts of the crater rim
are still clearly visible today,

279
00:22:07,727 --> 00:22:11,356
but the other edge
is almost out of sight.

280
00:22:16,727 --> 00:22:20,567
Finding the crater coincided
with another scientific discovery

281
00:22:20,567 --> 00:22:23,365
in a totally different part of the country.

282
00:22:25,887 --> 00:22:30,607
In California, scientists identified
a strange, thin layer of ash

283
00:22:30,607 --> 00:22:34,567
buried underneath the modern-day soil.

284
00:22:34,567 --> 00:22:38,367
The ash matched material
from the Yellowstone crater.

285
00:22:38,367 --> 00:22:45,247
Dating the soil layers proved
that the ash arrived 640,000 years ago.

286
00:22:45,247 --> 00:22:50,640
Scientists at last had a date
for the Yellowstone supereruption.

287
00:22:56,687 --> 00:23:00,047
Ash was later found
all over the western US,

288
00:23:00,047 --> 00:23:03,403
confirming the huge size of the eruption.

289
00:23:05,367 --> 00:23:09,127
At least 80 times the size
of the 1883 explosion

290
00:23:09,127 --> 00:23:12,836
that destroyed the island of Krakatoa.

291
00:23:21,087 --> 00:23:27,640
And 2,500 times bigger than the
1980 eruption of Mount St Helens.

292
00:23:31,047 --> 00:23:34,527
The almost unimaginable size
of the Yellowstone blast

293
00:23:34,527 --> 00:23:38,759
means that scientists now call it
a supervolcano.

294
00:23:43,807 --> 00:23:46,047
But that creates another mystery.

295
00:23:46,047 --> 00:23:48,167
In this peaceful landscape,

296
00:23:48,167 --> 00:23:54,487
where is the steaming hot crater that
the volcano must have left behind?

297
00:23:54,487 --> 00:23:57,687
Today, when you're looking out
across the landscape,

298
00:23:57,687 --> 00:24:01,327
you see rolling hills and... and trees,

299
00:24:01,327 --> 00:24:04,487
so, obviously, there's not
a big hole left in the ground,

300
00:24:04,487 --> 00:24:07,607
um, from the eruption of the...
of the Yellowstone volcano.

301
00:24:07,607 --> 00:24:10,247
So something else has happened.

302
00:24:10,247 --> 00:24:15,767
One of the first processes was infilling
with all sorts of volcanic lava flows,

303
00:24:15,767 --> 00:24:18,767
and if you look just down from
the landscape toward those trees,

304
00:24:18,767 --> 00:24:23,207
you'll see one of the oldest lava flows
that happened

305
00:24:23,207 --> 00:24:26,279
after the 640,000-year eruption.

306
00:24:27,287 --> 00:24:31,127
Over hundreds of thousands of years
this flow has weathered into soil

307
00:24:31,127 --> 00:24:33,960
and been covered with trees.

308
00:24:36,287 --> 00:24:40,447
But elsewhere in the park are
a different type of lava deposit,

309
00:24:40,447 --> 00:24:44,807
still bare of vegetation because
this lava was still erupting

310
00:24:44,807 --> 00:24:47,480
up until about 100,000 years ago.

311
00:24:49,287 --> 00:24:55,522
The later lava was far less explosive
and more runny, and cooled slowly.

312
00:24:57,367 --> 00:25:00,287
It smoothed the harsh,
volcanic landscape

313
00:25:00,287 --> 00:25:03,643
into Yellowstone's softer countryside.

314
00:25:09,447 --> 00:25:13,486
That made Yellowstone, at first,
more tranquil.

315
00:25:16,287 --> 00:25:20,447
But there's evidence here that
the land was soon buried once again,

316
00:25:20,447 --> 00:25:24,201
this time by freezing snow and ice.

317
00:25:25,687 --> 00:25:28,997
The ice that polished the rocks
has a story to tell.

318
00:25:30,767 --> 00:25:36,399
It offers crucial evidence about volcanic
forces still shaping the park to this day.

319
00:25:40,327 --> 00:25:43,524
Its tale unfolds
through the tiniest of clues.

320
00:25:44,887 --> 00:25:48,926
Scratches on the rocks reveal
which way the ice was moving.

321
00:25:51,207 --> 00:25:54,367
They show that glaciers always
slid the same way,

322
00:25:54,367 --> 00:25:59,600
outwards and downwards from
an icecap at the heart of the park.

323
00:26:01,527 --> 00:26:05,887
The only conclusion is that something
pushed up Yellowstone Park

324
00:26:05,887 --> 00:26:10,756
so much higher than the surrounding
hills that glaciers formed on the top.

325
00:26:22,327 --> 00:26:25,407
But what force could
possibly be powerful enough

326
00:26:25,407 --> 00:26:28,877
to have raised Yellowstone's peaks
up into the air?

327
00:26:39,247 --> 00:26:41,447
The first clue to help answer
that question

328
00:26:41,447 --> 00:26:44,767
comes from Yellowstone's
numerous earthquakes.

329
00:26:44,767 --> 00:26:50,127
When the ground deforms, it creaks
and groans like a Stradivarius violin.

330
00:26:50,127 --> 00:26:52,038
And the creaks and groans
are essentially earthquakes.

331
00:26:53,167 --> 00:26:56,204
The quakes are recorded by
seismometers all over the park.

332
00:26:58,927 --> 00:27:01,567
The earthquake monitoring
is a critical part of the picture

333
00:27:01,567 --> 00:27:06,447
because it's basically... it's the
stethoscope that we have to really see

334
00:27:06,447 --> 00:27:09,405
and sense the... the heartbeat
of the system.

335
00:27:15,847 --> 00:27:20,125
Smith is investigating
a puzzling geological mystery.

336
00:27:22,807 --> 00:27:25,887
Yellowstone has up to
5,000 earthquakes a year,

337
00:27:25,887 --> 00:27:31,166
even though it's in the stable heart
of the North American continent.

338
00:27:32,367 --> 00:27:35,647
Scientists needed to know what
was happening underground

339
00:27:35,647 --> 00:27:37,842
to shake the park so much.

340
00:27:39,807 --> 00:27:44,247
To find out, they plotted the precise
locations and depths of earthquakes

341
00:27:44,247 --> 00:27:45,885
under the ground.

342
00:27:51,447 --> 00:27:54,041
So, why are there so many quakes?

343
00:27:58,647 --> 00:28:01,287
The answer had to wait
until the mid-1980s,

344
00:28:01,287 --> 00:28:06,680
when ever more powerful computers
first let scientists see into the Earth.

345
00:28:07,687 --> 00:28:11,847
Seismic waves spreading out
from earthquakes travel rapidly

346
00:28:11,847 --> 00:28:16,727
through cold rock, but slow down
when the rocks are hot.

347
00:28:16,727 --> 00:28:20,207
The varying wave speeds
can be translated by computers

348
00:28:20,207 --> 00:28:26,407
into colour 3D images, revealing exactly
where hot rock lies under the ground.

349
00:28:26,407 --> 00:28:28,327
Seismic waves propagate
through the Earth

350
00:28:28,327 --> 00:28:31,127
just like X-rays go through a body,

351
00:28:31,127 --> 00:28:36,727
and so we use the same physics to
reconstruct the structure of the geol...

352
00:28:36,727 --> 00:28:38,247
...of the Earth beneath us.

353
00:28:38,247 --> 00:28:42,567
The seismic waves have outlined
the park's underground structures,

354
00:28:42,567 --> 00:28:46,321
revealing a graphic history
of what's happened under Yellowstone.

355
00:28:48,327 --> 00:28:51,727
They reveal this gigantic reservoir
of molten rock

356
00:28:51,727 --> 00:28:55,007
which created Yellowstone's crater
when lava erupted out,

357
00:28:55,007 --> 00:29:00,286
and the ground above collapsed
into the space left behind.

358
00:29:01,967 --> 00:29:05,807
And the seismic waves still slow
down under Yellowstone today,

359
00:29:05,807 --> 00:29:10,167
showing that the magma chamber
still lurks under the park.

360
00:29:10,167 --> 00:29:16,047
It's more than 30 miles long,
25 miles wide and ten miles in depth.

361
00:29:16,047 --> 00:29:21,087
But its size alters from year to year
as it fills or empties

362
00:29:21,087 --> 00:29:25,647
with semi-liquid rock at
an incredible 1,500 degrees Fahrenheit.

363
00:29:25,647 --> 00:29:29,567
This is the hidden,
beating heart of Yellowstone Park.

364
00:29:29,567 --> 00:29:32,207
The way it moves
deforms the ground above,

365
00:29:32,207 --> 00:29:36,727
explaining the fault lines
and the earthquakes they produce.

366
00:29:36,727 --> 00:29:39,207
And its heat ultimately powers

367
00:29:39,207 --> 00:29:43,086
all of Yellowstone's hot water pools
and geysers.

368
00:29:48,807 --> 00:29:52,687
Subterranean Yellowstone
is giving up its secrets.

369
00:29:52,687 --> 00:29:57,407
Seismographs record thousands
of earthquakes in the park.

370
00:29:57,407 --> 00:29:59,847
And the evidence of earthquake waves

371
00:29:59,847 --> 00:30:04,477
reveals a massive magma chamber
miles under Yellowstone's surface.

372
00:30:05,727 --> 00:30:09,807
But the Yellowstone investigation
is far from finished,

373
00:30:09,807 --> 00:30:15,127
because there's evidence of another,
even more monstrous sized structure

374
00:30:15,127 --> 00:30:17,800
under the park.

375
00:30:24,607 --> 00:30:27,287
By the beginning of the 21 st century,

376
00:30:27,287 --> 00:30:30,127
scientists investigating
how Yellowstone was made

377
00:30:30,127 --> 00:30:33,517
had images of what lay under the park.

378
00:30:34,527 --> 00:30:36,807
But there was a problem.

379
00:30:36,807 --> 00:30:41,127
Technology only allowed a view
of a few miles below the surface.

380
00:30:41,127 --> 00:30:46,407
Then, as more and more data was fed
into more and more powerful computers,

381
00:30:46,407 --> 00:30:49,001
there was a breakthrough.

382
00:30:50,047 --> 00:30:55,527
In April 2006, geologists published
new diagrams of hot structures,

383
00:30:55,527 --> 00:30:57,687
far deeper under the park

384
00:30:57,687 --> 00:31:02,327
and computers painted
more detailed pictures.

385
00:31:02,327 --> 00:31:04,443
The results were startling.

386
00:31:07,127 --> 00:31:09,647
Investigators saw for the first time

387
00:31:09,647 --> 00:31:13,765
the sleeping monster
that lies below Yellowstone Park.

388
00:31:17,367 --> 00:31:20,807
Snaking down hundreds of miles
into the Earth,

389
00:31:20,807 --> 00:31:24,687
far deeper than
the relatively shallow magma chamber,

390
00:31:24,687 --> 00:31:28,362
is a colossal volcanic pipe.

391
00:31:32,367 --> 00:31:35,127
Nobody's certain how deep it goes,

392
00:31:35,127 --> 00:31:38,847
but they can picture it
down to 400 miles or more -

393
00:31:38,847 --> 00:31:43,159
twice the distance between
Washington and New York.

394
00:31:47,447 --> 00:31:53,127
Smith makes an educated guess about
what the underground plume is like.

395
00:31:53,127 --> 00:31:56,367
Our best estimates now
as we start doing the physics

396
00:31:56,367 --> 00:32:00,087
and the dynamics of these things,
it's like a conduit of melted rock,

397
00:32:00,087 --> 00:32:02,127
like a chimney.

398
00:32:02,127 --> 00:32:06,167
That chimney, called a hotspot,
pumped up enough heat

399
00:32:06,167 --> 00:32:10,607
to melt the rocks of the crust
and fill the overlying magma chamber,

400
00:32:10,607 --> 00:32:15,123
which then erupted to blast out
Yellowstone's vast crater.

401
00:32:20,247 --> 00:32:23,727
Understanding how the crater formed
was an important moment

402
00:32:23,727 --> 00:32:25,797
for the investigation.

403
00:32:28,047 --> 00:32:33,127
Because there was evidence that
similar eruptions had happened before.

404
00:32:33,127 --> 00:32:35,038
Many times before.

405
00:32:46,127 --> 00:32:48,007
Throughout the 1960s,

406
00:32:48,007 --> 00:32:49,887
various teams of geologists

407
00:32:49,887 --> 00:32:51,647
studied the Snake River Plain,

408
00:32:51,647 --> 00:32:53,367
to the southwest of Yellowstone Park,

409
00:32:53,367 --> 00:32:54,887
and found traces

410
00:32:54,887 --> 00:32:57,481
of ancient volcanic craters.

411
00:32:58,727 --> 00:33:01,327
The crater rims had long been eroded,

412
00:33:01,327 --> 00:33:04,007
but their outlines were confirmed
by aerial pictures

413
00:33:04,007 --> 00:33:06,396
over the following decade.

414
00:33:08,967 --> 00:33:12,087
They ran in a straight line
along the plain,

415
00:33:12,087 --> 00:33:15,007
heading for the heart
of Yellowstone Park.

416
00:33:15,007 --> 00:33:21,047
On average, each crater was a couple
of million years older than its neighbour.

417
00:33:21,047 --> 00:33:22,647
Investigators realised

418
00:33:22,647 --> 00:33:26,887
that these are the remnants of
earlier supervolcano explosions,

419
00:33:26,887 --> 00:33:31,483
an unbroken chain stretching
far back into geological history.

420
00:33:37,167 --> 00:33:39,567
It seemed clear
that, time after time,

421
00:33:39,567 --> 00:33:44,607
the hotspot had blasted out
a supereruption and then moved on.

422
00:33:44,607 --> 00:33:49,362
The hotspot appeared
to have travelled hundreds of miles.

423
00:33:51,647 --> 00:33:54,487
But that posed yet another riddle.

424
00:33:54,487 --> 00:34:00,039
How could a hotspot anchored
to the core of the planet be moving?

425
00:34:08,847 --> 00:34:12,287
An important clue
had been found in 1985

426
00:34:12,287 --> 00:34:15,484
by American volcanologist William Scott.

427
00:34:17,007 --> 00:34:20,527
He realised that plotting the location
of 30,000 earthquakes

428
00:34:20,527 --> 00:34:24,566
around Yellowstone
produced an amazing pattern.

429
00:34:25,967 --> 00:34:31,200
The quakes traced out a giant V-shape
on the surface of the Earth.

430
00:34:32,887 --> 00:34:36,163
The V-shape wrapped
around the hotspot's location.

431
00:34:37,407 --> 00:34:41,687
It seemed, at first, to confirm
that the hotspot was still moving,

432
00:34:41,687 --> 00:34:45,127
rippling up the land around it
with fault lines

433
00:34:45,127 --> 00:34:47,436
and tens of thousands of earthquakes.

434
00:34:53,807 --> 00:34:57,927
But the real answer lay with
the theory of plate tectonics.

435
00:34:57,927 --> 00:35:03,797
It showed that it's the American
continent, not the hotspot, that's moving.

436
00:35:05,327 --> 00:35:08,367
And the chain of craters on
Snake River Plain is there

437
00:35:08,367 --> 00:35:12,687
because for millions of years,
the moving American continent

438
00:35:12,687 --> 00:35:18,047
has continually pushed new land
over the stationary hotspot.

439
00:35:18,047 --> 00:35:22,127
SMITH: But, as the North American
Plate moved across this source of heat,

440
00:35:22,127 --> 00:35:27,047
it pops through the lid
and creates the hotspot track.

441
00:35:27,047 --> 00:35:28,647
That's the Snake River Plain.

442
00:35:28,647 --> 00:35:30,922
Yellowstone is just the
active component today.

443
00:35:32,007 --> 00:35:36,876
The repeated hotspot explosions
on land have made Yellowstone unique.

444
00:35:39,367 --> 00:35:42,767
Other hotspots have been
identified around the world,

445
00:35:42,767 --> 00:35:46,007
like the one that has created
the island chain of Hawaii,

446
00:35:46,007 --> 00:35:50,407
but Yellowstone is the only place
where a hotspot has erupted

447
00:35:50,407 --> 00:35:52,875
in the middle of a continent.

448
00:35:55,687 --> 00:36:00,647
Each of the earlier explosions
blew the original mountains to pieces.

449
00:36:00,647 --> 00:36:05,367
Then, the land smoothed over
with later flows of more runny lava

450
00:36:05,367 --> 00:36:08,916
that was released
from deep under the Earth's crust.

451
00:36:15,127 --> 00:36:16,967
Multiple strands of evidence

452
00:36:16,967 --> 00:36:19,687
combine to reveal
Yellowstone's slumbering monster,

453
00:36:19,687 --> 00:36:24,247
the gigantic hotspot plume
lying under the park.

454
00:36:24,247 --> 00:36:28,240
Earthquake maps
show the hotspot's location.

455
00:36:29,447 --> 00:36:33,360
Seismic waves reveal
the depth of the plume.

456
00:36:34,447 --> 00:36:40,447
And earlier craters prove regular
supereruptions over millions of years.

457
00:36:40,447 --> 00:36:44,127
All of which leads to the most
frightening question of all.

458
00:36:44,127 --> 00:36:47,767
When will Yellowstone erupt again?

459
00:36:47,767 --> 00:36:50,839
(RUMBLING AND EXPLOSIONS)

460
00:36:59,047 --> 00:37:02,127
Measuring the amount and
geographical spread of ashfall

461
00:37:02,127 --> 00:37:06,647
from Yellowstone's supereruptions
produced some terrifying figures.

462
00:37:06,647 --> 00:37:08,887
(EXPLOSIONS)

463
00:37:08,887 --> 00:37:11,527
640,000 years ago,

464
00:37:11,527 --> 00:37:16,007
the eruption poured out around
240 cubic miles of material -

465
00:37:16,007 --> 00:37:22,887
enough to bury the whole of New York
State tens of feet deep in ash.

466
00:37:22,887 --> 00:37:26,567
If it happens again,
thousands will die

467
00:37:26,567 --> 00:37:32,367
and vast areas of the United States
will be buried in volcanic debris.

468
00:37:32,367 --> 00:37:35,484
But when will Yellowstone erupt again?

469
00:37:39,607 --> 00:37:41,807
One clue to when that next eruption

470
00:37:41,807 --> 00:37:46,358
will happen comes from investigating
the eruptions of the past.

471
00:37:48,527 --> 00:37:51,487
The hotspot punches out
a supereruption, on average,

472
00:37:51,487 --> 00:37:54,126
every 600,000 years.

473
00:37:55,687 --> 00:38:00,636
And the last one
was 640,000 years ago.

474
00:38:02,487 --> 00:38:05,607
But geologists expect that
there will be warning signs

475
00:38:05,607 --> 00:38:08,167
before Yellowstone explodes again.

476
00:38:11,287 --> 00:38:13,847
Volcanic eruptions are usually preceded

477
00:38:13,847 --> 00:38:16,407
by an increasing number
of earthquakes.

478
00:38:18,007 --> 00:38:21,527
The quakes are a sign that
underground volcanic chambers

479
00:38:21,527 --> 00:38:25,007
are filling with molten rock and
expanding to stretch and deform

480
00:38:25,007 --> 00:38:27,521
the land up above.

481
00:38:36,407 --> 00:38:38,887
Yellowstone Park usually experiences

482
00:38:38,887 --> 00:38:42,927
an average of 12 tiny
earthquake tremors every day.

483
00:38:42,927 --> 00:38:46,007
Most are too weak to be felt by tourists

484
00:38:46,007 --> 00:38:49,967
and register only on the
most sensitive seismometers.

485
00:38:49,967 --> 00:38:52,407
But in early 2009,

486
00:38:52,407 --> 00:38:57,007
more than four times as many quakes
started striking every day.

487
00:38:57,007 --> 00:39:00,887
Over one ten-day period,
there were more than 500 quakes,

488
00:39:00,887 --> 00:39:06,207
some of them up to magnitude 3.9,
powerful enough to frighten the visitors

489
00:39:06,207 --> 00:39:08,038
and put the scientists on alert.

490
00:39:09,727 --> 00:39:13,356
There's a second indicator
of increasing volcanic activity.

491
00:39:14,887 --> 00:39:19,087
If more molten rock does inflate
the underground chamber,

492
00:39:19,087 --> 00:39:23,239
the ground above will rise.

493
00:39:25,687 --> 00:39:29,646
And that, too, seems to be
happening right now.

494
00:39:32,567 --> 00:39:36,527
Unusual evidence to prove it
comes from an unlikely source,

495
00:39:36,527 --> 00:39:39,519
the waters of Yellowstone Lake.

496
00:39:40,927 --> 00:39:44,967
Around 100 years ago,
small steamships carried tourists

497
00:39:44,967 --> 00:39:47,167
on sightseeing trips
across the lake.

498
00:39:47,167 --> 00:39:49,327
But one of the ships caught fire

499
00:39:49,327 --> 00:39:52,239
and sank forever
below the surface of the lake.

500
00:39:53,887 --> 00:39:56,927
But now, Yellowstone's
astonishing geological forces

501
00:39:56,927 --> 00:40:01,000
have resurrected the ship's remains
from their watery grave.

502
00:40:02,127 --> 00:40:05,967
Here we have a boat
which burnt down to water level

503
00:40:05,967 --> 00:40:12,567
and so this tells us something about
the deformation of Yellowstone,

504
00:40:12,567 --> 00:40:17,407
and basically, what's happened
is that the floor of the lake has risen,

505
00:40:17,407 --> 00:40:20,126
bringing the boat out of water.

506
00:40:21,247 --> 00:40:25,167
The reappearance of the wreck shows
that land under and around the lake

507
00:40:25,167 --> 00:40:29,718
is rising because of the expansion
of the magma chamber.

508
00:40:31,727 --> 00:40:36,767
Even more alarmingly, the rate at
which it's rising seems to be increasing.

509
00:40:36,767 --> 00:40:41,607
In geological terms,
a huge area of Yellowstone Park

510
00:40:41,607 --> 00:40:46,840
is positively soaring up into the air,
faster than it's ever done before.

511
00:40:56,167 --> 00:40:59,447
The biggest uplift of all has
been recorded just a few miles

512
00:40:59,447 --> 00:41:02,567
from the shore of the lake.

513
00:41:02,567 --> 00:41:04,607
There's a GPS system here,

514
00:41:04,607 --> 00:41:08,680
a much more sophisticated version
of the one in your car.

515
00:41:09,687 --> 00:41:12,327
It measures not only its surface position,

516
00:41:12,327 --> 00:41:16,240
but also its exact altitude
to within fractions of an inch.

517
00:41:17,847 --> 00:41:21,807
There's a small radio antenna, about
the size of your thumb, that sits on top

518
00:41:21,807 --> 00:41:25,567
of this steel rod,
and it is anchored in two to thr...

519
00:41:25,567 --> 00:41:28,527
...about three or four feet,
so if the ground moves up and down,

520
00:41:28,527 --> 00:41:30,245
the antenna moves up and down.

521
00:41:32,327 --> 00:41:36,639
The GPS and the land on which
it's anchored are moving upwards.

522
00:41:37,967 --> 00:41:43,527
We're above the magma chamber
and, beginning in late 2006,

523
00:41:43,527 --> 00:41:48,567
this whole area of ground
started to rise, uh,

524
00:41:48,567 --> 00:41:51,927
at the order of two
to three inches per year.

525
00:41:51,927 --> 00:41:58,087
And as of today, this whole system
right here has risen about that much,

526
00:41:58,087 --> 00:42:00,047
and it's still moving today,

527
00:42:00,047 --> 00:42:03,967
and so we're measuring and keeping
close track of the deformation,

528
00:42:03,967 --> 00:42:07,198
the... of the uplift
that we're seeing at this station.

529
00:42:08,207 --> 00:42:11,847
But does the uplift mean
that Yellowstone's supervolcano

530
00:42:11,847 --> 00:42:14,122
is threatening to erupt once again?

531
00:42:15,127 --> 00:42:19,727
The question of what lies
in Yellowstone's geologic future

532
00:42:19,727 --> 00:42:21,407
is fascinating,

533
00:42:21,407 --> 00:42:28,404
and I and all of my colleagues would love
to know the answer to that question.

534
00:42:29,407 --> 00:42:33,116
The scientists keep a careful watch
on the volcano's activity.

535
00:42:35,607 --> 00:42:38,927
The idea of science
is to understand the process

536
00:42:38,927 --> 00:42:43,607
and so we have a responsibility
to see how this system is deforming,

537
00:42:43,607 --> 00:42:45,887
and how it's working,
hence we have to be aware

538
00:42:45,887 --> 00:42:49,567
there is still a possibility of... of
volcanic eruptions or earthquakes.

539
00:42:49,567 --> 00:42:51,447
After all, that's what made this system,

540
00:42:51,447 --> 00:42:54,803
and, uh, there is no reason
to think that volcanism has stopped.

541
00:42:56,847 --> 00:42:58,927
The Yellowstone investigation
has shown

542
00:42:58,927 --> 00:43:01,767
that the park's sleeping supervolcano

543
00:43:01,767 --> 00:43:04,520
is still alive, and dangerous.

544
00:43:05,527 --> 00:43:09,607
Old Faithful's underground
plumbing reveals volcanic heat.

545
00:43:09,607 --> 00:43:12,767
Obsidian glass tells
of a massive eruption.

546
00:43:12,767 --> 00:43:17,287
Seismographs record
thousands of earthquakes,

547
00:43:17,287 --> 00:43:21,687
while the earthquake waves reveal
terrifying underground chambers.

548
00:43:21,687 --> 00:43:27,000
And the reappearance of a sunken boat
shows that the land is rising.

549
00:43:28,327 --> 00:43:31,847
And yet, the ultimate
Yellowstone geological question

550
00:43:31,847 --> 00:43:33,967
remains to be answered.

551
00:43:33,967 --> 00:43:38,647
When will the supervolcano
erupt once again?

552
00:43:38,647 --> 00:43:41,407
HEASLER: We know
there's enough magma left,

553
00:43:41,407 --> 00:43:42,967
we know there's enough heat,

554
00:43:42,967 --> 00:43:46,807
we know that there will be
future eruptions in Yellowstone.

555
00:43:46,807 --> 00:43:52,200
But we don't know if there will ever be
another catastrophic eruption.

556
00:43:55,727 --> 00:44:00,567
So the investigation is left
with a deadly serious warning.

557
00:44:00,567 --> 00:44:03,887
On the timescale
that geologists work to,

558
00:44:03,887 --> 00:44:08,767
a coming supereruption in Yellowstone
may well be right around the corner.

559
00:44:08,767 --> 00:44:13,927
That corner could be 10,000
or 100,000 years in the future.

560
00:44:13,927 --> 00:44:16,887
Or it could be tomorrow.

561
00:44:16,887 --> 00:44:21,087
A new and devastating chapter
in the ever-changing story

562
00:44:21,087 --> 00:44:23,885
of how the Earth was made.