Inside Planet Earth Page #6

This is the only place

where 2 continental plates

are colliding on such a scale.

And the mountains

are still growing

as a result

of the tectonic squeeze.

Even Everest

is still stretching skywards.

I can't quite feel it

just standing here on a piece

of Himalayan rock--

The earth that I'm standing on

is actually moving up

at about 10mm a year

and is moving to the north at

an even faster rate than that,

maybe 15mm a year.

The reason

why we can measure this

is because of these

fantastic receivers.

They use 4 satellites

up in the sky above me

to solve a simple

triangulation problem.

But they're so accurate that

they can give me something like

1 mm of accuracy

in the horizontal

and more like 5 mm in the vertical.

That way, I can come back

year after year,

we can see that this point,

drilled into this rock--

that's attached somehow to

the root of these mountains

and the continental plate that

they're stuck to-- is moving.

There is another way

that Rebecca Bendick

and her colleagues

can discover exactly

how the Himalayas are growing.

They have found an area

in the foothills,

10 miles south

of the highest peaks,

that is rising even faster

than the mountains.

The clues to the uplift are

found in the fast-flowing rivers

that tumble through

these valleys.

You can think of this river

in 2 different ways.

One is that this land is still

and the river is cutting down.

The other way-- and, I think, a

better way to think about it--

is that the river is staying

at sort of a constant position

with respect to the sea,

way off in the Bay of Bengal,

and the earth around it

is rising up.

So in order for the river

to stay in one place,

it needs to cut down,

like a knife through butter.

But in some places,

the river cannot cut

quickly enough

to maintain

its natural equilibrium.

Here, the land rises faster

than the river erodes it down,

and a giant step is formed,

creating white water and rapids.

We're looking for places

where the river is

a lot steeper

than its average gradient

anywhere along a stretch.

Those steeper places

are corresponding

to places where the uplift is quick;

so quick that the river

can't keep up.

This will give us clues

about places to come back

and do more intensive

GPS research

to try to pin down

the uplift rate.

It seems this area is continuing

to rise faster than the high peaks.

One day this riverbed

will be taller than Everest.

Taking data in this way

is dangerous.

But with a little bit of care,

it's definitely worth

the good information

that we get about the Earth.

That information is vital

for the 100 million people

living in the danger zone

around the Himalayas.

Earthquakes are common.

30,000 people have been killed

in the last century alone.

This area has been quiet

for 700 years,

and a major quake

is long overdue.

Rebecca Bendick's monitoring

shows that the convergence

of India and China

at 2 inches a year

is setting up immense stresses

which must eventually

be released.

A solar-powered GPS station

will send back information

24 hours a day,

hopefully giving

an early warning.

The crux of the matter is

that we need to know

how that total convergence

is partitioned over the faults.

If all 60mm of convergence

has to be accommodated

in one place on one fault--

on this one narrow line--

then the earthquakes we have

there are gonna be big,

and they're gonna happen often.

But if instead

all of that strain

is accommodated

on several different faults,

something like an accordion,

then each fault

can only be expected to fail

less frequently

and less violently.

Earthquakes are appallingly

destructive to human life.

But for scientists,

they have their uses.

The seismic waves

are like sonar.

By listening

as they pass through the earth,

a picture can be built up of

a place no one will ever see.

First, the waves

race through the crust--

the skin

on the planet's surface.

In some places,

only 4 miles separate us

from the intolerable heat

of the mantle

and interior of the Earth.

3,000 miles down,

in the core itself,

the temperature reaches

an unimaginable 7,000 degrees.

It is the ultimate

nuclear reactor,

the engine driving the planet.

Cooling comes

by gigantic convection currents

in the mantle.

And it's that heat

rising with the hot magma

that forces the tectonic plates

to shift.

Earthquakes are

a ferocious manifestation

of the power

of the Earth's plates.

More than 1.5 million people

have been killed by them

in this century alone.

Most quakes occur

along fault lines,

where the plates grind together.

Scientists can't tell us

when this terrifying destruction

is likely to occur.

They can only tell us why.

You can't have an earthquake

without a fault.

And I'm standing right now

on what is perhaps

the most famous fault in the

world, the San Andreas fault,

that extends from Mexico

down south

way up to Oregon in the north.

This is one of the few places

in the world

where you can stand with

one foot on one tectonic plate

and one on another.

In other words, this ground here

is attached

to New York and Iceland.

The ground here is attached

to Hawaii and Japan.

At this part of the fault,

the plates are stuck.

They should be moving

at 2 inches a year.

The last earthquake

was 100 years ago,

and the fault is storing up

the unreleased energy.

The longer the plates

are stuck together,

the larger

the ensuing tremor will be.

Further north,

the plates are sliding

smoothly past each other.

The evidence is clear from

the way this fence has buckled.

We're on the San Andreas fault,

south of San Francisco.

And this is an interesting part

of the fault zone

because the 1906 earthquake

ruptured through

this field here,

across the road,

and stopped about here.

But this fence was built

after the earthquake.

In other words, the fault has

been sliding ever since then.

So, what's going on

in here exactly?

And you can see here

there are cracks in the road.

These have grown

since I was last here.

All over the road here.

And I have a machine

in the field,

and I am absolutely dying

to see what it says.

Let's go have a look.

What we have in the field here

is a creep meter.

A creep meter measures

creep on the fault--

the creep that's caused

the offset of this fence.

It consists of a rod

that is attached firmly

to that side of the fault,

passes through the fault

into the box here.

Inside the box is a computer

that's been measuring things.

Now, I have to be rather careful

because sometimes

there are snakes here.

No, not this time.

Good.

What's left

are black widows and ants.

All right.

So here is a computer that's

been measuring for a year.

It records the movement

of the fault every minute,

to about 1/1,000

of an inch.

So let's download the data

and have a look.

There we are.

Well, it looks

as though we have had

about 7mm of creep,

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