Inside Planet Earth

For over 4.5 billion years,

the Earth has been blasted,

burned, ripped, and scoured.

These phenomenal events

have sculpted our planet

through a series

of devastating cataclysms.

Our ancestors thought volcanoes

were the doorways to hell.

We think we know better.

But we still live in a world

driven by natural forces

which we cannot control

and which are indifferent

to our needs.

We live on a restless planet.

We are only just beginning

to understand the awesome power

that can raise mountains,

form the continents,

open and close the seas.

The fragile truce

between man and the Earth

is being broken all the time.

We are learning more about

the forces that drive our Earth

and how to live with them.

But it may be too late.

79 A.D.

Pompeii, Italy.

A peaceful Roman city

was overwhelmed

by pyroclastic fires

from Mount Vesuvius,

a volcano that had slept

through recorded history

until it suddenly exploded.

20,000 people lived in Pompeii.

Very few escaped

the volcanic shroud.

2,000 years later,

the people of Montserrat,

a small Caribbean island,

faced the same threat.

In June 1995,

the volcano of Soufrire

burst into malignant life.

It had been dormant

for 400 years.

19 people have died, and half

the island is uninhabitable.

Where once there was

a green forest

is total devastation--

an ash desert.

Scientists from

all over the world

are trying to forestall

an even greater disaster.

What we're looking at here is

the Soufrire Hills Volcano.

And basically what it is

is this big scooped valley.

And part of this valley is

what we call English's Crater.

And that's

that big amphitheater.

Sitting within the amphitheater

is the present active dome.

The magma is pushed up

from below, and it comes out.

It's exceptionally viscous.

And it just builds up

and up and up,

forming this big dome structure.

It's exceptionally hot.

Very unstable.

And these blocks

that are overhanging

is what usually falls off,

generates the rock avalanches

and then the pyroclastic flows.

Mark Davies can't just watch

from the safety

of the helicopter.

He must get as close as he can

to the flow.

It's incredibly dangerous.

At any moment,

and without warning,

the volcano might erupt again,

and he'd have

no chance of escaping.

We're quite close

to the dome here.

You can feel the heat

coming off it.

So it's not really a place

we want to hang around.

The cracks have opened up

6cm in 3 days.

So we'll have to keep

an eye on them.

A pyroclastic flow

is essentially like

a snow avalanche,

the only difference being

that it's around

about 800 degrees C.

It contains big, huge blocks

within it,

sometimes the size of houses.

It contains

lots of poisonous gases.

And all of that will travel

at around about the speed

of 80 meters per second

in some cases,

sometimes a heck

of a lot faster.

So you can't outrun it.

You can't outdrive it.

And in some cases,

the only thing

that can get you out fast enough

is a helicopter.

Essentially, if you get caught

in a pyroclastic flow,

you really don't know

whether you'll get crushed,

whether you'll suffocate,

whether you'll

burn to death first.

And, frankly, I wouldn't want

to know, myself.

This is how Montserrat used to be

before the catastrophe--

an 8-mile paradise with

green hills and tiny farms

that had crept close

to the mountain.

The towns were full of memories

of the colonial past.

Now all that is gone.

Sometimes ash falls like hail

for a day at a time.

The heat can be felt

a mile away.

The smell of burning sulfur

fills the air.

The sun is obliterated,

and the midday sky

becomes as dark as night.

There is nothing to be done

but take cover.

Plymouth, the capital,

was like Pompeii--

a thriving port,

center of island life.

It, too, lay in the path

of the pyroclastic flow.

Because they had warning,

the people were able to escape.

But slowly their town

is disappearing

under the pitiless flows

and remorseless ash.

A volcano can sit quietly

for centuries

until the pressure from below

becomes too great

and it explodes.

What everyone on Montserrat

wants to know is,

will it explode again

and will it ever stop?

The scientists' best hope

is to monitor the earthquakes

they know will shake

the mountain before an eruption.

24 hours a day,

they listen and watch.

This is the operations center

for the volcano observatory.

It's monitoring

the whole of the volcano.

It's an early-warning system,

if you like.

We have points

all around the volcano.

So if the ground is moving,

then the information

that those machines gather

out on the volcano

is sent back here.

And it's recorded on these pens.

So it's a visual way

of determining

how much motion is occurring.

When the drum and the needle

on the drum and the pen

is going back and forth--

The bigger the earthquake,

the more violent

that pen will move.

And the greater the chance

of a violent eruption.

But the technique

is only a best guess.

It's not foolproof.

Distrusting science to save them

from the force of nature,

the population dwindles daily

as more and more people escape

to the safety

of neighboring islands.

Those who can't leave

eke out a precarious existence

in makeshift camps.

Families are split.

The young see no futures.

The old can only remember

the past.

One in 10 of us live near

an active volcano.

Many choose to

because volcanic soil

is so fertile and productive.

But will the people

of Montserrat ever be able

to return to their fields

and old ways of life?

Or has that gone,

as lost as Pompeii?

People and politicians

would like clear-cut answers.

But scientists know

that's impossible.

If the eruption stops tomorrow,

the dome is still up

on top of the volcano.

It's still unstable, and it will

still retain its heat.

And it might stay like that

for 5 years

after the eruption finishes.

Or it might cool down

exceptionally quickly

and, within one year,

people could move back.

We don't really know.

Montserrat's disaster

is caused by something

that happened

over 4 billion years ago,

when the Earth's crust

broke into gigantic sections,

forming the tectonic plates.

Understanding Earth's

tumultuous history

is like reading

an intricate detective story,

for the Earth is unlike

any other planet.

Its restless surface

is changing constantly,

destroying the evidence

of the past.

But if you know where to look

for them,

the clues are still there.

About 18,000 meteorites

hit the Earth every year,

hurtling down

at 70,000 miles an hour.

Most are small

and do little damage,

but each brings clues

to the catastrophic formation

of our planet.

Geologist Roger Buick is working

in northwestern Australia.

Even though it's just arrived,

this is the oldest thing

on Earth.

It's a chondrite--

a type of stony meteorite--

and it's been wandering

around the solar system

for about 4,500 million years.

It's stuff like this

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