Inside Planet Earth Page #5

They go with a bang.

The old ocean floor carries

water into the mantle,

which mixes with the magma.

When the pressure

can no longer be contained,

it explodes in that most awesome

of natural events,

a volcanic eruption.

Most of the world's volcanoes

are in subduction zones,

but there are exceptions.

Kilauea is on

the Big Island of Hawaii,

part of a chain of islands in

the middle of the Pacific Ocean,

thousands of miles away

from any subduction zone.

But the whole chain is formed

entirely from volcanoes

whose rivers of fire

heave and bubble

at temperatures

of 2,000 degrees.

What provides the furnace

for all this outpouring

if it's not the crashing

of the tectonic plates?

The volcanologists

have an explanation.

The lava that's flowing

and spattering behind me

is the surface manifestation

of a thermal anomaly,

or a hot spot,

that's deep within the earth

beneath my feet.

Where we are now--

on Kilauea Volcano

on the Big Island of Hawaii--

is at the southeast end of

a 6,000-kilometer-long chain

of seamounts and volcanic

islands that have formed

as the Pacific plate

has moved north and westward

over the last

80 million years or so

at a rate of around

9 or 10cm per year.

So as the plate

moves over this hot spot,

you burn through

the lithosphere,

forming a volcanic island.

And then the plate moves on,

and a new island forms

further to the southeast.

The hot spot has made Kilauea

the tallest mountain

in the world--

30,000 feet

from its base on the seafloor.

Taller even than Everest.

It's also one of

the most studied.

But scientists can't always wait

for the lava to come to them.

They must catch it as it bursts

through the crust.

Carl Thornber often goes fishing

with a cable in a red-hot pond.

And sometimes

he has to get even closer.

It's extremely dangerous.

At any moment, the lava may

spurt out unexpectedly,

leaving Thornber

with nowhere to run.

Behind me is a perched lava pond

that's being fed from a vent

off to my left.

You can see

that there's lava spattering

and overflowing on its edges.

I'm gonna attempt to scoop

a sample of molten lava--

hopefully with a hammer

so I won't have to use

a long cable to throw it in.

And it'll be extremely hot.

We have to worry about gases.

And we have to worry

about breakouts

near the edge of the pond.

So we'll see how it goes.

Thornber is risking his life.

But unless scientists can learn

how to forecast eruptions,

volcanoes will continue to be

an uncontrollable threat.

Okay, we'll take this sample

back to the USGS observatory,

and we'll prepare it

for chemical analysis.

The chemistry

of Hawaiian basalts is unique

compared to volcanic deposits

near subduction zones

or near mid-ocean ridges.

And that will be reflected

in the chemistry that we see.

More importantly,

we're looking at very subtle

variations in chemistry

that can be correlated

with the eruptive history

of this volcano.

So it will allow us to predict

what may happen next.

High on Maui,

the next island in the chain,

NASA scientists at the satellite

laser ranging station

are preparing

for a long night's work.

They're setting up to fire

a laser beam

at a satellite target

orbiting the Earth.

The information they gain

will tell them, to the inch,

how fast the island, and the

Pacific plate on which it rests,

are moving across the ocean.

They have to time

the firing exactly

to be sure

that no planes are passing.

The laser beam would blind

any pilot

who might look at it directly.

Okay, we're at 227 Azimuth.

18 degrees ''L''.

This is starlit.

Culmination's at 74 degrees.

We're rotating clockwise.

Okay, you'll be clear to fire.

We're at 21.

Going down.

The laser beam flashes out

and bounces back,

pinpointing their location.

22 years of calculations confirm

that Maui and the Pacific plate

are moving northwest at the

rate of 2.5 inches a year--

amazingly fast.

This is the absolute proof

that the surface of our planet

is in constant motion.

Tectonic theory says that the

volcanoes of the Hawaiian chain

should get progressively older

and become more eroded

the further they travel

from the hot spot.

And they do.

One day,

the raging fires of Kilauea

will be as silent and cold

as these dead cones.

But the heir to them all

is already emerging.

As one island dies,

a new one is formed.

The hot spot is currently moving,

or manifesting itself,

at Lo'ihi,

which is a submarine seamount

to the south

of the Big Island of Hawaii

and still more than 3,000 feet

beneath the surface

of the ocean.

It may be another 100,000 years

before we see Lo'ihi surface.

At the same time,

the hot spot is causing

destruction elsewhere,

the pressure of the continual

input of magma from below

is bulldozing open

this great crack

which stretches across

the length of the island.

It is more than 80 feet deep,

and it's splitting away

at 3 inches a year.

Eventually, the whole side

of the mountain will fail

and collapse into the sea.

It will send a giant wave

racing away to the Pacific Rim,

to reach the west coast

of the Americas in a few hours,

causing massive destruction.

We can't predict or prevent

these catastrophes.

The geological truce

between ourselves

and our restless planet

may be coming to an end.

Cataclysms may have caused

extinctions and disasters,

but they have also shaped

the Earth

and produced an environment

in which human life

could flourish--

the air breathable,

the seas are warm,

climate mild, the ice rooted

firmly at the poles.

In fact, a geological truce.

But that truce

may be coming to an end.

The forces that drive the Earth

are impervious to our needs.

With man so widely spread

across the planet,

cataclysms of nature will turn

into human catastrophes.

Every movement of the plates

brings the danger

of disaster nearer.

50 million years ago,

the Asian and Indian plates

were about to clash.

Separated by a dying ocean,

they collided

with fantastic force.

Neither would give way,

and the land had

only one way to go-- up.

This is the world's highest

mountain range, the Himalayas.

This entire area was uplifted

from sea level

to over 5 miles high

in less than 30 million years.

How do the scientists know?

From the evidence of the rocks.

There's dramatic evidence

for this uplift

right in the face of Everest,

in Lhotse.

The famous yellow band

that you can see cutting across

is actually a marine limestone.

It was formed

in the bottom of the ocean.

So 50 million years ago,

the tops of these mountains

were at the bottom of the sea.

It's hard to believe.

We have similar evidence

from Tibet,

Where we find things

like this--

ammonite fossils

of marine creatures

that now are more than

4,000 meters above sea level.

Certainly these tell us

that plate tectonics

supplies enough force

to lift things

from the bottom of the ocean

all the way to here,

the top of the world.

Rate this script:0.0 / 0 votes