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>> Earth--a unique planet--

restless and dynamic

Continents shift and clash.

volcanoes erupt, glaciers grow

and recede. Titanic forces that

are constantly at work, leaving

behind a trail of geological

mysteries.

One of earth's most intriguing

mysteries is the presence of

a huge arc of geological

destruction surrounding the

Pacific.

It is known as the Ring of Fire.

Three-quarters of earth's

volcanoes are situated here...

And 90% of all earthquakes also

occur along this line.

Over the last 200 years,

disasters here have claimed over

one million lives.

Now scientists set out to

discover why these volcanoes

and quakes occur all around the

margins of the Pacific Ocean and

to find out what powers them.

Unlocking the mysteries of this

awesome force of geology will

bring the scientists one step

closer to understanding

How the Earth was Made.

S02x07 Ring of Fire Original Air Date on January 22, 2009

-- Sync, corrected by elderman -- -- for MY-SUBS.com ---

The Ring of Fire is one of

the most extensive zones of

destruction on planet earth.

Its most visible features are

the hundreds of volcanoes that

line the shores of the Pacific

Ocean. They form an arc

which extends 25,000 miles,

from South America

along America's northwest coast

to Alaska and then down

through Russia, Japan, and

Southeast Asia

all the way to New Zealand.

Cataclysmic eruptions have

occurred here throughout

history.

August, 1883. Indonesia.

The krakatoa volcano blew itself

to pieces, creating the loudest

sound in recorded history.

June, 1991. The philippines.

Mount Pinatubo blasted debris

22 miles into the atmosphere.

Suffocating ash swamped over

2,500 square miles.

And in may 1980,

Mount St. Helens caused

$1 billion of damage.

The ever-present threat from

these volcanoes makes it

essential for scientists to

understand the forces that

power them. The investigation

begins here in Alaska.

This land of rugged beauty

marks the most northern extreme

of the Ring of Fire.

75% of all the volcanoes in the

United States are situated in

Alaska, making it a perfect

laboratory for volcanologists.

The first step is to discover

how the Ring of Fire's giant

volcanoes form.

>> We're headed to

Augustine Volcano, which lies in

Cook Inlet, and it's part of the

chain of volcanoes that extends

all the way down into the

Aleutian Islands.

>> It's a 60-mile journey out

across the frigid Alaskan water.

In the distance, the volcano

soon appears.

>> There's Augustine Volcano

over there. It's gonna

be a perfect day to visit.

>> From high above the clouds,

Dr. Bull can gain a clear view

of the volcano's distinctive

outline.

Augustine is a stratovolcano--

the type of volcano found all

around the Ring of Fire.

>> Stratovolcanoes are

quite unique in that they are

shaped as beautiful cones. And

Augustine is a perfect example

of that.

>> Augustine last exploded in

January 2006--the most recent

of 7 eruptions here since 1935.

Over the years, solidified lava

flows have gradually built up

on the volcano's flanks.

To investigate what makes these

volcanoes dangerous, Dr. Bull

climbs high up on the side of

one of these lava flows.

>> This lava is made up

of blocks. There's bits that

are a little denser than others.

And you can see there's a lot

of different pieces to it. So we

call this a blocky lava flow.

>> This blocky lava provides

a crucial clue as to why

the Ring of Fire volcanoes

can be so deadly.

>> This lava is more thick when

it comes out of the volcano.

And its thickness will have

an effect on how it runs down

the slope.

The thickness or viscosity of

lavas can be shown in a number

of ways.

Hawaii lavas are quite runny.

Honey is a perfect example of

that. If you have a volcano

putting out Hawaii-like lava,

it's gonna run quite easily

down the rock whereas if you

have something more like

these blocky lavas,

they're gonna be a little bit

more like peanut butter.

And they'll still run, but

the viscosity is much greater.

>> The viscosity of lava is

primarily determined by the

amount of silica it contains.

Silica is the most abundant

mineral in earth's crust.

>> The more silica,

the thicker or more viscous

the lava is likely to be.

>> Hawaiian lava contains little

silica, so it's runny and

produces a relatively flat

landscape, but Ring of Fire

lavas are rich in silica,

making them sticky

and less able to flow, creating

tall, cone-shaped

stratovolcanoes.

During the 2006 eruption of

Augustine, thermal imaging

cameras were used to study the

volcano.

They show this sticky lava

building up

layer upon layer.

But the thickness of this

lava also makes these volcanoes

lethal.

>> Because these volcanoes have

lava that is thick,

things don't move

through them very well and

bubbles of gases can build up.

>> Deep in the earth under

immense pressure, molten rock

called magma contains dissolved

gas. But as this magma rises,

yhe pressure decreases.

This drop in pressure means

bubbles of the gas begin to

appear just like opening

a bottle of soda.

If the magma is runny, these

gases can safely escape.

But in sticky, silica-rich Ring

of Fire magma, the gases can get

trapped, often with terrible

consequences.

>> It's like trying to

have a bubble move through

peanut butter. It won't happen

quite so easily, so there's

a lot of pressure that builds

up. And once that pressure

builds up, it reaches a point

where it can't take all that

pressure any more.

>> The result--giant explosions

caused by the catastrophic

build-up of gas inside the

molten rock.

This is the reason Ring of Fire

volcanoes can be so dangerous.

But it's not usually the

initial explosion that kills.

It's what happens next.

>> Those explosive eruptions

can create plumes

that go up for tens of miles.

>> When these plumes run out of

energy, they can collapse back

down the sides of the volcano

in a superheated avalanche of

ash and gas.

With temperatures of 1,300

degrees fahrenheit and speeds

over 100 miles per hour, these

flows destroy everything in

their path--a terrifying

consequence of the explosive

eruptions caused by gases

building up inside thick lava.

In the next stage of her

investigation, Dr. Bull searches

for clues as to how this sticky

lava forms. On Augustine's lower

slopes, she hunts for lava

samples from inside the volcano.

This giant block of solidified

sticky lava was once molten

magma, deep underground.

It was blasted out here during

an eruption. And it came with

some intriguing evidence.

>> So what I'm seeing in

this rock is a lot of minerals

and a little bit in some cases

of hornblende.

>> The presence of these

hornblende crystals provides

a crucial clue to how the magma

formed.

>> This is important in

telling us something about

magma conditions where the

hornblende crystallized.

Hornblende is a mineral that

only forms in the presence of

water.

>> These hornblendes show water

exists deep in the earth.

Scientists suspect this water

plays a crucial role in creating

the magma that powers volcanoes.

Deep underground, rocks are hot

and semi-solid.

It might seem that the presence

of water would cool them down,

but that's not what happens.

This water, which is under huge

pressure, alters the rocks'

structure and causes them to

melt, forming plumes of magma.

This molten rock soars up to

the surface, building giant

volcanoes.

Without water causing magma

formation deep underground,

these Ring of Fire volcanoes

would simply not exist.

>> A lot of this process

we're still working on and we

don't understand, but there's

a fair amount of it that we do.

And water has a very

significant role in when and

how rocks melt.

>> The investigation into why

the Ring of Fire is so dangerous

has uncovered two important

pieces of evidence.

Blocky lava flows are

evidence of thick, viscous

magma which traps gases inside

volcanoes, leading to explosive

eruptions.

And hornblende crystals reveal

that water deep underground

encourages the formation of the

magma that powers the volcanoes.

Next, the geology detectives

figure out how this water gets

underground and make

a remarkable discovery--

The chemical signature of

microscopic organisms inside

the volcanoes.

>> All around the Ring of Fire,

explosive magma is forming deep

underground, fuelled by water.

Solving the mystery of where

this water comes from is

the key to how scientists will

figure out why the Ring of Fire

is so dangerous.

The investigation now turns to

Mount Lassen--an active volcano

in Northern California.

Surrounding the volcano are

bubbling hot springs, boiling

mud, and volcanic vents called

fumaroles belching superheated

steam and gas.

All this thermal activity is

driven by the immense heat

rising from magma deep

underground.

By sampling the gas coming from

these fumaroles, scientists

hope to discer the source of

the water which causes the

magma to form.

>> This device measures

the temperature; the

temperature of this fumarole is

92.5 degrees "c",

about 200 degrees fahrenheit.

So just about at the boiling

point for this elevation.

And that's what we want for

a good gas sample--

a good boiling fumarole.

So you can see what's happening

at the surface here--all this

steam coming out of the ground.

But it's the gases that are

along with this steam that we

look at closely.

And the composition of those

gases tell us about what's

happening at various depths

beneath the ground where we

can't see.

>> Tests on these gases,

xollected from volcanoes all

around the Pacific Ring of Fire,

have revealed something

surprising--the gases contain

carbon-12, a type of carbon that

comes from living organisms.

The specific levels of c-12

found here are the unique

signature of tiny sea organisms

called phytoplankton.

Billions of phytoplankton live

in the Ocean.

As they grow, they absorb

carbon-12 into their cells.

When they die, they fall to the

bottom, forming layers of

sediment.

In this way, their carbon-12 is

transferred to the seafloor.

Intriguingly, scientists have

found this same carbon-12

pouring out of volcanoes all

around the Ring of Fire.

>> Volcanoes of the Cascade

Range have carbon dioxide

that's very rich in carbon-12,

And it's almost like

you're cooking Oceanic sediments

that are rich in

phytoplankton down deep

beneath these volcanoes to

generate the carbon dioxide you

see coming out the top.

That links this carbon dioxide

to organic sediments way

offshore in the Ocean.

The organic matter that was

originally phytoplankton

becomes carbon dioxide that we

see at the surface.

>> Seafloor sediments are

getting into volcanoes.

And these sediments contain

seawater.

This is the water that causes

the rocks to melt below

the volcanoes, forming magma.

But a mystery remains.

The magma plumes feeding

the volcanoes lie sometimes

hundreds of miles from the

ocean. The scientists now have

to figure out how the sediments

loaded with seawater are moving

so far inland. To find out,

the investigation heads for

Alaska's Chugach Mountains.

The research here begins with

an analysis of the local rocks.

>> Oh, this is

a really neat boulder that's

right here. And what you can

see in it is that there's this

whole mixture of rock types.

You can see that there's

this black stuff which would

originally have been mud.

There's several different

colors of kind of greenish

rocks which would be kind of

different flavors of volcanics.

Oh, here it looks like

there's limestone,

and I'm gonna put some acid

here. And if it fizzes, it's

limestone.

Yeah, sure enough that's what

it is.

And this would have formed

in the Ocean. And so this is

made up of the bodies of little

critters that got incorporated

into this rock, and now it's up

here in the Chugach Mountains.

>> The presence of jumbled

oceanic rocks 20 miles from the

sea is evidence that something

remarkable is happening at

the bottom of the Ocean.

>> The fact that you have

this mixture of rock types here

is evidence for

the seafloor moving.

>> Geologists know that only

an enormous process called

subduction could shift these

mixed Ocean sediments here.

Subduction occurs when the

seafloor moves and slides down

under the land.

As it descends, the top

sediment layers are scraped off

by the land like a snow plow

scoops up snow.

They're pushed up into a huge

mound of mixed-up rocks.

The Chugach Mountains were

formed in this way.

The seafloor, loaded with

water, now continues down into

the earth.

This is how seawater gets deep

underground where it creates

the magma plumes that build

the Ring of Fire's explosive

volcanoes.

>> Where we're at right now,

the Pacific is subducting

beneath us to the northwest

at this northern part

of the Ring of Fire.

It's about 20 miles beneath our

feet right here, but if we were

to go off that way where the

volcanoes are, it's about

60 miles beneath our feet there.

And so as it goes to the

northwest, it subducts and then

brings water and sediment into

the earth that ends up causing

melting in the mantle, and then

that melt rises as magma to

volcanoes.

>> The investigation to discover

how water is getting down below

Ring of Fire volcanoes has

turned up intriguing clues:

Carbon-12 samples indicating

fhat Ocean sediments are getting

deep below the Ring of Fire's

volcanoes and mixed rocks

in the Chugach Mountains

20 miles inland from the Ocean

are evidence that

the whole seafloor is on the

move, sliding deep under the

land. This process is the engine

that powers the Ring of Fire's

killer volcanoes.

But deep underground,

the Ring of Fire hides another

even more deadly secret--

earthquakes that can destroy

entire cities.

>> The Ring of Fire--a lethal

line of volcanoes--

75% of all the volcanoes on

the planet.

These fiery peaks encircling

the Pacific Ocean are built by

tremendous forces deep in the

Earth. Eruptions here have taken

many thousands of lives and

destroyed billions of dollars

of property.

But an even bigger killer is

present on the Ring of Fire...

Earthquakes.

90% of the world's quakes occur

in this narrow band around the

Pacific often with disastrous

results.

Sumatra, September 2009.

A giant earthquake left more

than a thousand people dead.

Mexico, September 1985.

More than 9,000 people were

killed by a massive, magnitude 8

quake that shook Mexico City.

And Alaska, March 1964,

North America's greatest-ever

recorded earthquake, near

Anchorage.

This quake was so powerful,

ground movements were observed

4,000 miles away in Florida.

Such awesome power drives

scientists on to discover why

these deadly quakes occur all

around the Ring of Fire.

The investigation moves to

Prince William Sound, 36 miles

from the epicenter of the

1964 Alaskan disaster.

>> We're at the northern edge

of the Ring of Fire,

and we're gonna be looking

at evidence for how geologically

active this area is today.

>> Haeussler heads for

Montague Island--a place that's

permanently scarred by

the powerful forces which shape

this entire region.

On land, he finds a rugged

boulder-strewn shoreline.

>> So you can see we're at

the edge of the Ocean.

We're in a high energy

environment. There's boulders

all over the place, and we're

at the top of the beach.

Waves have been crashing here

and basically getting rid of the

little tiny rocks, leaving only

boulders behind.

And then right here, you can see

that these boulders are kind of

lined up against each other

like dominoes. And so it takes

big waves to sort of flip these

over and line them up kind of

like dominoes

Like that right here.

>> But it's not this rocky beach

that reveals how violent

Ring of Fire quakes can be.

The real evidence lies 1/4 mile

inland.

Haeussler hunts through

the thick undergrowth.

Hidden by the trees is a

near-identical line of boulders.

>> We've hiked in,

thrashed through the alders,

the Alaskan jungle up to here.

We're probably 25 or 30 feet

above sea level at this point,

and what we have here is

a beach. I mean, this is

basically a perfectly preserved

high energy beach environment

like we were looking at down

on the shoreline.

And you can see here once again

there is these big boulders

that are sort of laid over

in this domino-like fashion

sort of pointing uphill

as a result of this big wave

energy, big waves pounding

on the beach flipping the

boulders over, pointing in

the uphill direction.

>> This inland raised shoreline

runs for hundreds of yards

parallel with the Ocean.

It's a key piece of evidence.

And it can only mean one thing--

the land itself must have

recently risen up

out of the Ocean, taking

the entire shoreline with it.

>> It means that there was

an event that was essentially

an instant in which this region

was uplifted to this elevation

and made this here.

This has to have been

a result of a big earthquake.

Really cool.

What we're looking at here is

a result of the 1964

great Alaska earthquake.

Pretty much right here

where we're at is where

there was the largest uplift

that occurred.

The massive earthquake here not

only lifted the land out

of the sea,

it also caused a wave of

destruction, devastating

nearby Anchorage.

>> It was a magnitude 9.2.

It was the second largest

earthquake ever recorded on

Earth. It was just enormous. It

lasted 4 1/2 minutes

of ground shaking.

>> What happened throughout this

region offers evidence of

the type of quake that makes

the Ring of Fire so dangerous.

>> So we know from this kind of

earthquake that occurred here in

1964 that this was

a thrust-type earthquake or

even there was a fancy term,

megathrust earthquake, because

it was so big that occurred

right here.

And this is a result of the

slippage of one piece of rock

over another or one underneath

the other.

>> Megathrust quakes like this

are the most powerful on earth

and are one of the great

dangers of the Ring of Fire.

If they occur under the Ocean,

they can generate killer waves

called Tsunamis.

The great Alaskan earthquake

of 1964 caused a tsunami over

200 feet high.

Waves traveled over 1,700

miles, claiming lives as far

away as California.

But this disaster was nothing

compared to what happened

compared to what happened in 2004.

On December 26th, tragedy

struck when an enormous

underwater megathrust

earthquake off the Asian coast

generated monster waves.

The coastlines of 14 countries

were swamped, killing more than

200,000 people.

The vast scale of this disaster

was a brutal indication of the

power of megathrust earthquakes.

And it's given urgency to

finding out why these quakes

happen all around

happen all around the Ring of Fire.

Once again, the Alaskan

landscape is the perfect

geological laboratory.

>> So we're headed to

a seismic station in

south-central Alaska near

the tip of the Kenai Peninsula.

>> Millions of years of the Ring

of Fire's volcanic activity and

rippling earthquakes have given

Alaska an incredibly rugged

landscape. It's not easy to find

a flat spot to land.

>> It's clear on my side.

>> High on the hillside lies

West's seismic station,

protected under the yellow

cover from the elements and

the local bears.

>> So this is the vault

where one of our seismic

stations lives. This is one of

the many seismic stations that

dot the state of Alaska.

>> Several thousand seismic

stations like this exist, all

the way from Alaska down to

California.

>> This whole system

together monitors any kind of

seismic activity, any sort of

warthquakes throughout this

whole area.

It's part of a whole network on

all of the volcanoes around

here, on the mainland, and

throughout this whole area.

So the seismic data can be used

not only to judge the severity

of the earthquake

or the magnitude, but also

when taken across a number of

stations to pinpoint the

location of that earthquake.

In Alaska, we're looking at

about 1,500 earthquakes

every month.

And you take all of those

together, and you start to see

patterns. They map out

a ribbon of earthquake activity

that follows all along the

coast.

>> This ribbon of earthquake

activity extends all around

the Ring of Fire.

But it is what scientists can

see below the surface that is

most revealing.

>> If you look at it

from the side, you see that

actually the earthquakes that

are happening close to the

ocean tend to be shallow, but

as you go inland, they're deeper

and they create this dipping

feature that starts out in

the Ocean and then dips down

beneath the continent.

>> This giant dipping feature

provides conclusive evidence

for how the megathrust

earthquakes are generated.

The earthquake epicenters

exactly follow the path taken

by the seafloor as it moves

down underneath the volcanoes.

Earthquakes are triggered as

the rocks slide past each other

down into the earth.

It is this subduction of the

seafloor beneath the land which

creates the Ring of Fire's

lethal megathrust quakes

and builds its explosive

stratovolcanoes.

>> So all of these

observations--the volcanoes,

the line of seismic activity,

the big earthquakes at the

interface--all of those are

part of one system.

They all tie together and are

interrelated.

>> The investigation into why

the Ring of Fire is prone to

such lethal earthquakes

reveals...

A raised shoreline--

evidence that the Ring of Fire

suffers the most violent

megathrust earthquakes.

And seismic data shows that

these killer quakes are caused

by subduction, the movement of

the seabed, which also builds

the Ring of Fire's giant

volcanoes.

To discover exactly where

this awesome process of

subduction occurs,

oceanographers search for the

deepest and most inaccessible

places on the entire planet.

>> The journey to understand why

the Pacific Ring of Fire is

so volatile has revealed

the critical role of subduction,

which pushes the seabed deep

down into the earth.

In Alaska's Prince William

Sound, investigators search for

where the seafloor is vanishing

below the land.

>> There are ridges,

outcrops, canyons, gullies,

mountains underwater.

And so the ability to make

a continuous map of the

seafloor, get a full picture of

it gives you the ability to

understand how the seafloor's

put together and what it has to

do with the way the Earth

functions.

>> Reynolds is using high-tech

echo-sounding technology to

monitor the exact depth of the

seafloor. A sound wave is sent

from beneath the ship.

The time it takes to reach

the seafloor and return gives

an accurate reading of depth.

Reynolds' research shows that

all around the Alaskan coast,

the seabed is relatively

shallow. But farther out towards

the open Ocean, the readings

change dramatically.

>> So in general

around the world when

you go out from land, you cross

over a relatively flat shelf,

down the slope,

and into the deep Ocean basin

which is very flat.

But around the Ring of Fire as

you go out from land across the

shelf, down the slope, instead

of going directly into a flat

ocean basin, you go across

a very deep trench.

These trenches are the deepest

areas on the planet, and the one

around Alaska reaches

approximately 21,000 feet.

>> These giant features are

called subduction trenches.

The largest are deep enough to

swallow all of Mount Everest.

They mark the exact spot where

the seafloor disappears down

into the earth--the process

that jolts the land in

megathrust earthquakes and

forms the volcanoes that make

the Ring of Fire so dangerous.

>> The Ring of Fire is named for

these volcanoes that circle the

Pacific Ocean, but offshore of

the volcanoes--wherever you have

a chain of volcanoes, you also

have one of these deep Ocean

trenches.

>> The location and shape of the

Ring of Fire is determined not

by its famous volcanoes but by

the position of these deep

subduction trenches miles out

in the Ocean.

And by mapping the location

of all the trenches in the

Pacific Ocean, scientists have

made a further, even more

significant, discovery.

High-tech imaging has made it

possible for scientists to

visualize the earth drained of

its Oceans.

This reveals that these deep

trenches outline the edge of

a giant rock slab, or plate,

that makes up the entire floor

of the Pacific Ocean.

This huge Pacific plate is

one of 14 plates which cover the

entire surface of the planet.

Subduction occurs where this

plate rubs against one of its

neighbors, producing the line

of volcanoes which extends all

around the Pacific.

But the investigation isn't

finished. Experts journey

to Tiger Mountain in

Washington State to figure out

how such huge plates can be

shifted against each other.

>> The gps that you use to

drive around can tell you where

you're at on a city block or on

a street to within a meter or

so. But in geology,

we're interested

in centimeter to millimeter

accuracy so that we can track

the changing of the land.

It's much more subtle.

>> High on the mountainside,

Flake has set up a gps marker

point.

>> Here we are on Tiger

Mountain.

This is our gps unit.

What we have is these metal

rods going into solid bedrock,

cemented in so that there's

no motion.

This gps antenna allows us to

measure point positions per day

of where this spot is.

>> A network of these gps

antennas across North America

provides evidence for the

monumental forces which power

the Ring of Fire.

>> This is just

a single antenna. There's

hundreds all across the western

United States to give us

a better picture of what's going

on with the ground surface.

By combining all the data

of these gps, we're able to see

that North America

is actually moving.

>> The entire continent is

moving westwards at about

3 inches per year.

This movement is possible

because the earth's crust rides

upon a hot, soft layer of rock

called the mantle.

>> Well, the mantle is so hot

and at such a high pressure,

and the temperature is hotter

as you get towards the center

of the earth, that's gonna want

to move out and convect just

like a boiling pot of water.

And so it creates a convection

current coming up to the surface

which then drags along

those plates on top.

>> These phenomenal convection

currents force the Pacific

Plate into its neighbors,

driving the process of

subduction.

>> As the plates get

dragged by the mantle

convection currents, they impede

upon other plates.

One has to give, so one dives

down underneath another.

And then the trapped water from

its Ocean sediment escapes and

melts the upper-lying mantle.

And that creates hot magma that

rises to the surface and

creates the volcanoes that form

around the Ring of Fire.

>> The investigation into the

forces that drive the Ring of

Fire has now found

subduction trenches that reveal

the shape of the entire

Pacific Plate

And gps data providing evidence

for the convection currents

which force this giant plate

against its neighbors.

It is this movement of the

entire Pacific plate and the

resulting subduction of the

seafloor down the trenches that

shapes and builds

the Ring of Fire.

But one final mystery remains.

Vast sections of the seafloor

are constantly being destroyed.

But despite millions of years

of subduction down these

trenches, the planet's seafloors

have never been eradicated.

The geology detectives

can now reveal why.

>> All around the Ring of Fire,

enormous volcanoes dot

a landscape warped by violent

earthquakes. Offshore,

the seafloor is swallowed down

giant subduction trenches.

But despite millions of years

of subduction, the area of

seafloor remains roughly the

same.

Geologists could only assume

one thing: Somewhere far out

in the Ocean, volcanic activity

must be creating new seafloor

rocks, replacing those destroyed

here during subduction.

Beginning in 1977, a series of

expeditions set out to

investigate where this occurred.

Scientists realized that if

volcanic activity was

constructing new seabed, the

surrounding water should be

warm. The Alvin Submersible was

equipped with high-tech sensors

to discover where this warm

water existed.

To begin with, the crew searched

the seafloor without any luck.

But then they hit the jackpot--

A column of rock pumping out

superheated water.

This is a black smoker.

Measurements of the water

around these features have

found temperatures in excess of

750 degrees fahrenheit.

This heat comes from magma

welling up from inside the

Planet. It was a discovery that

provided the evidence

the scientists needed.

These volcanic marvels mark

the location of giant features

called mid-Ocean ridges.

At these ridges on the bottom

of the Ocean, powerful

convection currents in the

mantle separate Earth's plates,

allowing lava to spill out

onto the seabed.

>> New Oceanic crust is

constantly being formed out in

the mid-Ocean ridges.

That crust moves away from those

ridges towards the edge

of the continents,

where we're located now.

>> In this way, the seafloor is

constantly renewed, replacing

material destroyed by subduction

at the edges of the Ocean.

These mid-Ocean ridges exist

at the bottom of every Ocean on

Earth.

They provide a never-ending

supply of new rock, keeping

alive the entire plate tectonic

cycle.

>> Well, this is

a planetary scale process,

this is the planet itself

circulating. And the rock and

the magma from deep inside the

Earth welling up to the surface

forming this crust.

And then that crust dives back

down into the earth

at the subduction zones,

at the trenches. And it's mixed

back into the solid earth.

>> So great is the power driving

this system that experts see

no end to the constant movement

of plates around the planet.

>> The forces involved

with plate tectonics caused by

the heating from the inner core

of the Earth is so astronomical

that there is

nothing that will stop it.

>> It seems like

the Ring of Fire will go on for

some period of time.

It looks as if we've been

having subduction here

underneath southern Alaska on

the order of 200 million years.

And it looks like--

There's no evidence that it's

gonna stop any time soon.

>> But over the coming billions

of years, the ongoing movement

of plates will redraw the map

of the world.

>> The Pacific Plate is

moving, and things on it ride

with the plates that

are being subducted. So for

example, the Hawaiian Islands

are moving up here to Alaska,

parts of California are moving

up here to Alaska,

Baja California is moving north

here to Alaska. So apparently

Alaska's a popular place to be.

It'll be the resting-place of

all these things.

>> So the map of the Pacific

will slowly change driven by

the immense force of subduction.

This is the real story of the

Ring of Fire.

Subduction creates the magma

plumes which build the region's

explosive volcanoes.

Subduction powers the violent

megathrust earthquakes that

shake the region, leveling

whole cities in seconds

and causing killer tsunamis.

>> This process of subduction

just releases

an enormous amount of energy

through both earthquakes,

through building these

mountains, through volcanoes.

It's just really inconceivably

huge.

>> This is what makes the Ring

Of Fire the most geologically

active and most deadly place

on the entire planet.

>> And you see the whole

picture of creation

and destruction of a plate in

the Pacific Ocean. And the Ring

Of Fire is the boundary of that

cycle, and it's the place where

all the destruction is

happening.

>> Geology detectives have now

pieced together the evidence

for what makes the Ring of Fire

so dangerous, and discovered

what powers it.

Violent eruptions of explosive

blocky lava build the Ring of

Fire's famous volcanoes.

Mixed rocks from the seafloor

found miles inland are evidence

for the process of subduction

that builds the volcanoes.

Raised shorelines are evidence

for giant megathrust

earthquakes caused deep

underground by subduction.

And gps plots provide evidence

for the immense convection

currents deep in the earth

which drive the entire system.

These giant forces have built

the Ring of Fire.

>> The energy that drives

rhis whole convective system

is really without parallel

on the earth. There's

nothing else that we can

compare it to as far as the

amount of energy and the force

that moves the continents

around, compresses them against

one another, drags one down

beneath the other.

Really just awesome forces.

>> These forces are unstoppable.

And while the shape of the

Pacific will slowly change, for

millions of years to come,

explosive volcanoes will

continue to line its shores--

Dynamic proof that the earth

is never at rest.

-- Sync, corrected by elderman -- -- for MY-SUBS.com ---