Original subtitles

>> Earth. A 4.5-billion-year-old

planet, still evolving. As

continents shift and clash,

volcanoes erupt, and glaciers

grow and recede, the Earth's

crust is carved in countless,

fascinating ways, leaving a

trail of geological mysteries

behind.

In this episode, Europe's

greatest mountain chain, the

Alps, is explored. Home to some

of Europe's highest peaks,

longest glaciers and sheerest

rock faces, the Alps are one of

the most dynamic and dangerous

mountain ranges on the planet.

A mysterious land where whole

mountains collapse in on

themselves, and where its rock

once lay entombed at the bottom

of the sea. Scientists have been

hunting for clues hidden inside

the rocks, deep within the ice,

and upon some of the most famous

summits in the world to

understand how the Alps formed

and continue to evolve.

Clues which also provide a

window into the formation of

the Earth itself.

S01x13 The Alps Original Air Date on May 12, 2009

== sync, corrected by elderman ==

With more than 100 peaks rising

higher than 12,000 feet, the

majestic Alps tower over Europe.

The mountains are a huge

physical barrier. 750 miles

long, 125 miles wide, and

spanning seven countries,

the Alps divide Northern and

Europe's tallest mountain, Mont

Blanc, the Alps are one of the

world's highest mountain ranges.

But the majority of these peaks

formed only 30 million years

ago, making it one of the

youngest mountain ranges on

Earth. And for centuries,

geologists have red over these

fabulous rock formations to

figure out how mountains are

made.

But the first person to uncover

a crucial clue to the Alps'

formation was, surprisingly, a

16th-century Renaissance man,

Leonardo da Vinci. He was not

only a great artist, he also had

a brilliant scientific mind.

Da Vinci was a natural detective

who saw the world around him as

a huge mystery waiting to be

solved.

He focused his inquisitive,

scientific mind on the Alps at

a time when most scholars

believed the Earth was flat.

Da Vinci had heard tales of an

extraordinary discovery

embedded in the rocks, and in

1510, he trekked high into the

mountains to take a look.

At 7,000 feet, he found what

he'd been looking for.

Fossils. He knew these creatures

came from the sea, that they

could not have lived in the

Alps. So how did they get there,

more than 100 miles from the

nearest ocean and thousands of

feet above sea level?

The 16th-century explanation

provided by the powerful

Catholic Church decreed that the

marine fossils must have been

washed up during the time of

Noah in 2300 BC.

The holy scriptures describe how

God, sickened by the wickedness

of mankind, inflicted a

terrifying deluge of water upon

the Earth. All forms of life

were annihilated, except those

sheltering on Noah's Ark.

The great torrent of water that

flooded the Earth must have

washed some of the sea

creatures 100 miles inland.

But da Vinci did not believe

this explanation and continued

his investigation as to how the

fossils got there.

In the Säntis Mountains,

northern Switzerland, 500 years

later and 7,000 feet above sea

level, it's still possible to

see the fossilized remains of

sea creatures that so intrigued

da Vinci.

>> Here we have a rock which is

almost covered with fossils,

for example, here, a

cross-section of a clam.

Here below, we have the skeleton

of a coral.

>> Poring over the fossils, da

Vinci carried out an ingenious

piece of detective work. He

found the fossilized remains of

two-shelled creatures that

amazingly still had both halves

intact. If the Church's

explanation of a cataclysmic

flood were true, then the

torrent of water would have torn

these delicate creatures apart.

Da Vinci proposed that these

fossils had formed under the

ocean, and that some other force

had brought them high into the

mountains.

Modern-day scientists have

identified the species

fossilized in these rocks, and

can accurately pinpoint when

they lived.

>> The fossils we see here

actually lived 100 million

years ago in a warm, tropical

sea.

>> This ancient, tropical sea

teemed with life and rich coral

reefs. The sea floor was covered

in urchins, clams and other

species, many now extinct.

Just as da Vinci had imagined,

when some of these creatures

died, they were preserved

intact. Their shells then became

buried in the sediments at the

bottom of the sea and preserved

as fossils when the sediment

turned to rock. But what could

these fossils reveal about the

formation of the Alps?

Again, it was da Vinci's

exceptional powers of

observation that helped unravel

the mystery. He noticed that the

spectacular fossil-bearing rock,

known as limestone, was laid

down in layers several thousand

feet deep. 400 years later, it

was discovered that, along with

the fossils, hidden in the

microscopic structure of

limestone is an essential clue

to solving the mystery of how

the Alps formed--remains of

trillions upon trillions of

seashells. Limestone forms as

tiny sea creatures sink to the

bottom of the ocean. Piling on

top of one another, they compact

together under their vast

accumulated weight, forming

layer upon layer of sedimentary

rock. The Säntis Mountains, like

large areas of the Alps, are

made almost entirely of the

shells of dead sea creatures.

Beds of limestone here are

several thousand feet high--

evidence of the extraordinary

amount of sediment that was

laid down on the ancient sea

floor.

>> We have here a massive

package of limestone, layer

above layer of sea floor, and

this was brought up in an

upright position during the

building of the Alpine mountain

chain.

>> Ancient clues reveal the

origin of the Alps.

Marine fossils are evidence that

these rocks were once covered

by a tropical sea.

And rocks made from trillions of

microscopic seashells reveal

how entire mountains formed from

sediments laid down in the

ocean. Da Vinci suspected that

part of the Alps had formed

beneath the ocean, but how had

these originally flat layers

been upended?

>> Leonardo's explanation was

that some kind of force have

brought the fossils high up to

the mountains. But he actually

couldn't explain then the

driving forces of this

movement.

>> After da Vinci, it would take

scientists another 400 years

before that part of the mystery

was solved.

The Alps. This jagged backbone

of Europe was lifted thousands

of feet above sea level and 100

miles inland.

Many of the Alpine rocks once

lay flat on the sea floor. An

extraordinary force twisted,

folded and turned this land

upside down.

But what was this force and how

could it move great swathes of

solid rock? In the 1870s, Swiss

geologist Arnold Escher and his

student Albert Heim were drawn

to a strange line etched in the

Tschingelhorn mountain.

They traced the line for 30

miles.

Out of reach for most of its

range, they found one location

where this line can be examined

in closeup near the village of

Elm, Eastern Switzerland.

The dark line can clearly be

seen here beneath this strange

overhang.

Above it, Escher and Heim

identified a layer of ancient

sedimentary rock. But strangely,

beneath the line they found a

layer of much younger rock.

>> Underneath we have here the

flysch, these are slates which

are about 35 million years old.

And on top we have the

Verrucano, which has formed

about 260, 270 million years

ago.

>> Escher and Heim were

confused. The rock formations

simply did not make sense.

If both layers were formed by

the buildup of sediments, how

could older rock lie above the

younger one?

Studying the twists and folds in

the surrounding mountains,

Escher and Heim came up with a

theory as to how these rocks

switched places.

>> Just imagine we have one big

sheet of sediments. And one part

of the sediment of this sheet is

pushed over the others. That's

the way we get older sediments

on younger sediments.

>> A gigantic horizontal force

pushed these older rocks a

distance of 30 miles over the

younger layers. The line between

them, where the rocks scrape

over each other, is called an

overthrust.

Escher and Heim's discovery

revolutionized our

understanding of how mountains

are made.

>> This outcrop, actually it's a

closeup of maybe the most

famous overthrust in the world,

the so-called Glarus Overthrust.

And there are only a few places

where you can go--uh, go so

close to it.

>> This site is merely a

closeup of a massive

geological phenomenon that

created the Alps. Sitting above

the Glarus Overthrust is a

mountain range with peaks over

11,000 feet high. It's a

reminder that some awesome power

created the Alps, a force that

can literally move mountains.

But what has the power to push

billions of tons of rock?

Scientists now know that such a

colossal process can only

happen when two continents

collide, driven by the forces

of plate tectonics.

Plate tectonics is the process

by which giant plates of the

Earth's crust move slowly across

the planet's surface, propelled

by vast currents of molten rock

deep within the Earth.

As this happens over millions

of years, continents collide

and split apart and oceans form

and disappear.

But if the Alps formed as a

result of a massive collision,

what continent had crashed into

Europe?

The answer lies entombed in one

of the Alps' most famous

landmarks.

Hidden by clouds, it's

frequently hard to see.

>> There it is, finally.

>> The Matterhorn's unique shape

has made it one of the

best-known mountains in the

world. At 14,692 feet, it's one

of the Alps' highest peaks.

Hidden within the body of this

mountain is another major

overthrust. Here, rocks from the

sea floor lie above the European

bedrock.

Taking a closer look at the

layers formed under the sea, Dr.

Hellwig finds a green-tinged

rock.

>> The rocks we're looking at

here are called green schists.

>> These coarse crystals reveal

that this rock erupted as lava

at the bottom of the ocean, 100

million years ago.

But in the early 20th century,

scientists discovered something

even stranger. An unusual layer

of rock caps the mountain.

This upper layer is a gray rock

called gneiss. But when

geologists traced the origin of

this rock, they found it did not

come from Europe, and was 200

million years older than rocks

from the sea floor.

This rock belonged to a

two-billion-year-old continent

600 miles to the south--Africa.

>> The upper section of this

Alpine sandwich, it consists of

rock which come from Africa.

The middle part, um, are the

rocks from the oceanic crust and

the lower part, then, are the

European rocks.

>> This is evidence that the

Alps formed because ancient

Africa collided with Europe.

The result?

This whole mountain is composed

of three rock types.

>> From a geological standpoint,

it nicely combines the whole

Alpine story, so it shows all

the--shows the most important

aspects of the Alpine history,

right there within one mountain.

>> But how exactly did rocks

from the sea floor get

sandwiched between two

continents?

Detailed studies and dating of

the Alpine rocks have revealed

that, 90 million years ago,

Africa pushed towards Europe,

squashing an ancient sea, the

Tethys Ocean, that lay between

them.

>> As Africa ploughed into

Europe, it first destroyed the

ocean that lay between them

and--and piled it up in--in thin

slices, much as a bulldozer

tears up the ground in front of

it. These slices were then piled

in front of the, uh--the

bulldozer that makes up Africa.

So we began to develop this

large pile of deformed rock

that is what today forms the

Alps.

>> The ocean floor was crumpled

in front of the advancing

African continent, bending,

folding and breaking as it went.

30 million years ago, the Alps

were literally pushed up onto

Europe. Africa was thrust over

and above the other layers, to

form the sandwich of rocks that

would become the Matterhorn.

A jumble of rocks had been

folded and molded by violent

processes, and uplifted 22,000

feet, as high as the Himalayas

today.

Scientists investigating how the

Alps rose up off the ocean

floor have uncovered a 30-mile

line in the rocks, the boundary

between older rocks thrust above

younger ones. And gray gneiss

rocks at the top of the

Matterhorn prove that Africa

collided with Europe, creating

the Alps. But for the last 30

million years, some other

monumental force has eaten away

these great peaks. What has

caused this entire mountain

range to lose nearly half its

height?

30 million years ago, the Alps'

highest peaks towered 22,000

feet into the air. Today, the

tallest peaks are almost half

this height.

Unraveling the mystery of why

and how the Alps are

disappearing is important to

the 14 million people who live

in and around them.

Illhorn mountain, an

extraordinary peak in the Swiss

Alps, provides an essential

clue.

This mountain is almost 9,000

feet tall, but hollow at its

centre. Illhorn is rotten to the

core. This massive hole is

forming as the mountain

collapses in on itself.

But what monumental force is

pulling this mountain down?

It's made of a loose, unstable

mixture of rock and mud that

originally came from the ocean

floor. In winter, this mixture

of rock is glued together by

ice, but in the spring thaw, it

becomes loose.

>> Here you can see the fact

that the rocks are very highly

weathered, you can easily, uh,

in fact by hand, pull them

apart, you can imagine that, uh,

in winter when the ice, when the

water goes behind the rocks and

freezes, that it could actually

mechanically, uh, loosen the

rocks, and in the spring they

fall down. The whole mountain is

composed of these rocks, it's

basically just falling apart.

>> A combination of weak rocks

and the natural action of

freezing and thawing has

resulted in a crumbling

mountain. In the last 10,000

years, 100 million tons of

Illhorn mountain has eroded and

in the process hollowed out a

vast new valley, the Illgraben.

But where has all the rock gone?

Dr. McArdell has come to explore

a deep, seemingly dry riverbed,

which runs down from the heart

of the mountain and into the

river Rhone.

The evidence is hidden beneath

the village and vegetation--

a large, fan-shaped platform of

rubble, 1,500 feet deep and

over one mile square.

>> This structure is built from

the sediment delivered by the

Illgraben catchment. All the

sediment that you see has come

down from the mountain.

>> But this dry riverbed

presents a mystery. How did vast

amounts of debris get

transported down from the

mountain? The Swiss village of

Susten, ground zero for the

investigation, is in a constant

state of alert. A few times a

year, the ground shakes here as

if a gigantic freight train is

thundering through the village.

In a flash, this dry channel is

flooded by a river of rock.

Thousands of tons of debris flow

down from the Illhorn mountain.

Anywhere between

three and five times a year,

there's a large wave of sediment

moving downstream at anywhere

from 10 to 20 miles an hour,

with a flow depth on the order

of up to 10 feet. And it moves

down the channel rapidly and

anyone who's in the channel, of

course, is in danger.

>> Every time it rains, debris

cascades down the mountainside,

making this one of the most

active debris flow zones on

Earth.

>> The Alps are basically being

washed down from the mountains,

through the rivers and into the

lakes, into the valleys further

downstream.

>> Illhorn is an extreme case of

an entire mountain in the

process of decay, resulting in

one of the most dangerous

mountain terrains on the planet.

But inherently unstable rocks

are found right across the

Alps, and have created some of

the Alps' best beauty spots.

Oeschinensee lake is a mile

above sea level and half a mile

square.

But in theory, this lake

shouldn't be here.

The streams that pour off the

mountain should run straight

down the valley unobstructed.

A clue to what created this

high-altitude lake can be found

1,000 feet up on the surrounding

slopes.

>>As we look up on the hill

slopes, we see these very large

fans of debris that are coming

down off of these unstable

slopes. Where we see this sort

of smooth bedrock that's dipping

towards us, this is prime

territory for landslides.

>> When these mountains formed,

flat sheets of sedimentary rock

were thrust up to rest at

extreme angles. The joins

between these stressed and

fractured rock layers

frequently fail, causing huge

layers of rock to shear off the

cliff faces.

>> Much of these open slopes are

probably the result of sheets

of rock peeling off and forming

large landslides.

>> It was a catastrophic

landslide that caused this lake

to form 15,000 years ago.

The entire side of the mountain

sheared off, blocking the

valley and causing stream water

to back up and create one of

the Alps' most breathtaking

landscapes.

>> It's all about gravity,

gravity is what--what ultimately

brings down mountains.

Rivers come in, debris flows

form, landslides form, and this

sort of process is very common

throughout the Alps.

>> Steep slopes and unstable

rocks have created a mountain

range that is ever-changing.

In only a few thousand years,

gravity will also destroy

Oeschinensee lake, as debris

flows fill it up.

Over the last 30 million years,

the Alps have fallen down on a

massive scale, in places

decreasing in height by 10,000

feet. So what has happened to

those thousands of feet and

billions of tons of missing

rock?

A clue can be found in the

rolling hills a few miles north

of the Alps.

At Eggiwil, this rock outcrop

contains an extraordinary

collection of stones.

>> These are large cobbles,

stones that have come from all

over the Alps, so if I look at

some of these, for example this

small white and black rock, this

is a granitic rock that comes

from the center of the Alps,

somewhere very close to the

Matterhorn. And we see,

throughout this outcrop, rocks

that come from different parts

of the Alps.

>> Rocks from hundreds of

different scattered locations

have traveled over 150 miles

before being dumped in this

geologic rock graveyard.

But it's the amount of material

here that's mind-boggling.

These hills are made entirely of

rock debris from the nearby

Alps. At 100 miles wide and 500

miles long, they stretch in an

arc round the Alps, running

through France, Switzerland and

Germany. There's enough material

here to cover all of North

America in 100 feet of rubble.

Could this be where the

thousands of feet of missing

Alpine rock have gone?

>> A big mountain range like the

Alps is heavy, and it weights

down the crust, forming a

depression all the way around

the mountain range.

>> A multi-trillion-ton mass of

rock was pushed up on land as

Africa collided with Europe,

creating the Alps. The weight of

the rock caused the European

crust to sink, making a huge

depression, in places over two

and a half miles deep--the

Molasse basin.

>> Now, the importance of this

depression is it's a trap,

all the sediment that we see

eroding off of the Alps is

trapped in this basin and ends

up sitting there.

>> Dating of these pebbles has

revealed that, ever since the

Alps were created, rivers have

washed Alpine debris hundreds

of miles downstream, dumping the

rocks in this gigantic basin.

>> So these rocks that we're

looking at here are the debris,

the detritus that's come off of

the Alps over the last 20, 30

million years, these particular

rocks are almost 25 million

years old. And what we see are

cobbles, we see little pieces of

all the different rocks that we

see throughout the Alps.

>> For 30 million years, the

debris eroded from the Alps has

been dumped in a

30,000-square-mile bowl,

creating this

rolling chain of hills to the

north of the Alps. This is where

the missing mountain rock is.

Put it all back together and

once again, there'd be mountains

as high as the Himalayas.

Scientists have discovered how

the Alps have almost halved in

height and where the missing

rocks have disappeared to.

The clues are, inherently

unstable mixtures of rock,

resulting in whole mountains

falling apart, debris flows on

steep cliffs, proof that

weakened layers of rock shear

off from the mountainsides, and

a graveyard of pebbles from all

over the Alps, evidence that

these mountains have been

washed away.

But then, two million years ago,

the landscape changed

dramatically. Vertical cliffs

were carved into the Alps and

giant spikes of rock poked

through the clouds. Another

mighty force had begun to

resculpt the Alps.

Over the last two million years,

a blink in geologic time,

something has rapidly and

radically transformed the Alps,

gouging giant peaks and sheer

rock faces.

The most notorious rock

formation being the Eiger, in

southern Switzerland.

The infamous north face of the

Eiger is a 6,000 foot vertical

climb. It's a terrifying,

unrelenting ascent. Climbers

face gale-force winds, freezing

fog, rockfalls and avalanche,

giving the Eiger the reputation

as one of the most

formidable climbs in the world.

Nicknamed the Murder Wall,

since 1935, more than 60

climbers have died here.

How giant climbing walls like

this were formed had been a

mystery to geologists until

1837, when Swiss scientist

Louis Agassiz noticed similar

cliffs at lower altitudes, known

to have been made by a colossal

force--glaciers.

Over 1,000 glaciers wind their

way through the Alpine valleys.

Imperceptible to the naked eye,

these giant rivers of ice

slowly flow downhill.

This time-lapse of the Aletsch

glacier, taken over a period of

three years, reveals how

glaciers can move tens of feet

a year. And where two glaciers

meet, a stripe of rock sits on

the surface, proof that

something extraordinary is

happening beneath the ice.

A force which can transform

jagged rock into a surface as

smooth as glass.

>> We see here a smooth rock

face which was formerly covered

by ice. Underneath the ice,

there is this rocks and sand,

and it carries--the ice carries

this stuff with it and it acts

like sandpaper and polished this

rock.

>> But polishing alone cannot

account for the formation of

the Alps' jagged peaks and the

north face of the Eiger, where

the sides of entire mountains

have been ripped off. More

evidence of the awesome power of

glaciers can be found on these

granite slabs. Deep cracks

penetrate the body of the rock.

>> The ice was flowing over this

rock face and the ice could

enter this crack.

>> Meltwater forming beneath the

glacier seeps into the cracks,

refreezes and splits open the

rock. Weakened and fractured,

huge chunks of stone are ripped

from the bedrock. Vast amounts

of rock are plucked and ground

from the mountainsides and

dumped in the lower, warmer

valleys when the ice melts.

>> So here we are at the end,

the snout of the glacier. And

here debris, water, and rock

boulders. This has been eroded

by the glacier, transported and

moved to this place and this is

the essential process, how

glaciers form the landscape.

>> But how could glaciers have

carved the north face of the

Eiger, and other mighty peaks

which rise thousands of feet

out of reach of the abrasive ice

below? Agassiz came up with a

radical theory. He noticed these

high rock faces were scarred and

gnarled. They had clearly been

gouged by ice, like the

glaciated valleys he'd found at

lower altitudes.

Piecing the evidence tether,

he concluded towering cliffs

like the 6,000-foot Eiger were

the handiwork of ancient,

gigantic glaciers.

But if Agassiz was right, where

did the huge glaciers come from?

The evidence lies locked inside

Europe's biggest river of ice,

the Aletsch glacier.

A massive 14 miles long, it

covers an area of more than

45 square miles and is up to

3,000 feet deep. The Aletsch

glacier in southern Switzerland

has helped scientists understand

how all Alpine glaciers form.

The source of the glacier is

high up in the mountains, where

altitude brings freezing

temperatures and heavy snowfall.

To explore how delicate snowfall

becomes a giant slab of ice, Dr.

Bauder ventures deep into the

heart of the glacier.

This frozen passageway,

32 degrees Fahrenheit and 60

feet deep, offers tourists and

scientists a unique window

into the formation of a glacier.

>> Here we can see the inside of

a glacier. We can see inside the

ice. We see here layers of air

bubbles.

And there are different,

distinct layers visible here,

here, here, and they represent

individual years when this,

erm, ice has been formed.

>> The glacier grows by the

buildup of layer upon layer of

snow. The newly fallen snow

traps pockets of air between the

individual snowflakes, forming

layers of bubbles. As more snow

settles, the flakes beneath

become squashed, making

them stick together to form ice.

Forming over thousands of years,

the amount of ice contained in

a single glacier can be

staggering. It's been estimated

that the Aletsch glacier holds

27 billion tons of water, enough

to provide every human on Earth

with two pints of water a day

for the next six years.

It's the air bubbles, trapped

inside the ice thousands of

years ago, that hold the key to

what carved the Alps'

distinctive shape.

>> In the air bubbles, air is

stored from the time when the

air bubbles have been formed.

So we can analyze the chemical

composition inside there and

learn about the climatic

condition at that time.

>> When scientists analyzed

miniature time capsules like

these, they found air over

12,000 years old, with

surprisingly low levels of the

greenhouse gas carbon dioxide.

This meant that more heat was

escaping from the Earth's

atmosphere, causing global

temperatures to plummet.

Similar studies have revealed

that, for the last two million

years, the Earth has been

gripped by a series of ice ages.

Agassiz' theory was confirmed.

Two million years ago, an

enormous ice sheet engulfed the

Earth's northern hemisphere.

The Alps were buried in ice

almost two miles thick.

It was so deep that only the

tips of the mountains poked out

above the ocean of ice.

As the ice moved, it whittled

lone peaks and tore steep rock

faces high in the Alps, leaving

its legacy on the landscape.

It was during this time that

giant glaciers carved the

infamous north face of the

Eiger.

In their mission to discover how

the Eiger and other great peaks

in the Alps formed, scientists

have found cracks in granite

bedrock, evidence that glaciers

cleave masses of rock from the

mountainsides, and low levels of

carbon dioxide, trapped inside

ice bubbles, prove that giant

glaciers once carved immense

rock walls and pinnacles, which

now tower over the landscape.

10,000 years ago, the great ice

sheets melted, leaving their

mark on the Alps. But today, the

Alps are falling down at a

phenomenal rate. Something has

propelled them into a new and

violent phase of their

evolution.

The Alps are falling down at an

accelerated rate, and millions

of tons of rock are crashing to

Earth.

A clue to what strange force is

at work here can be found high

up in the mountains, where the

remnants of the last ice age

lurk. Alpine glaciers physically

prop up mountains, binding the

rock together. But these icy

rivers are changing shape.

>> Well, what we see in the

background here are glaciers

which are separated, uh, by

rocky surfaces which are looking

very fresh because they have

been ice covered in the last,

uh, few hundred, uh, years.

Uh, if you look across here to

Theodul glacier, we can see

that actually, right next to the

ice, uh, there is some, uh,

grayish material next to the

brownish material. That's

exactly the limit up to where

the glacier was, uh, in 1874.

So you see how much of this ice

has melted down in these 130

uh, years.

>> Scientists believe global

warming is melting the ice

fast than at any other time in

the Alps' history. And as the

glaciers shrink, they expose

steep, unsupported cliffs that

are prone to fall do,

increasing the risks of

landslides.

But scientists have discovered

another way melting glaciers

are weakening the Alps.

When these frozen reservoirs

melt, millions of gallons of

water gush downhill, feeding the

great rivers of Europe.

Like liquid sandpaper, this

torrent scrapes over the rocks,

hollowing out the land at an

accelerated rate.

The dramatic evidence of this

dynamic process can be found in

the valley of Lauterbrunnen.

Echoing through this valley

is the sound of one of the

loudest and most spectacular

water features in the Alps,

Trümmelbach Falls.

>> You can just feel the pulsing

of the water. This is--the name

Trümmelbach actually means drum

sound, and this is reflecting

this, this pulsing, throbbing

that we can hear and feel from

the water flowing down through

these caves.

>> Trümmelbach is a spectacular

glacial waterfall. Over 5,000

gallons of meltwater a second

hurtle down from glaciers on the

nearby Eiger and Jungfrau

mountains. Over hundreds of

years, this abrasive jet-stream

has sliced through the mountain,

creating a narrow canyon.

Each year, from the Swiss Alps

alone, there's enough rock

removed by the glacial

meltwaters to create a mountain

more than half a mile high.

But Trümmelbach, like other

Alpine waterfalls, is living on

borrowed time.

As meltwater thunders down the

waterfalls, it cuts into the

rock, weakening it.

Over time, these steep cliffs

left by the glaciers crumble,

replaced by ever deepening river

valleys.

Today, the rivers

that are now returning are

trying to carve a river valley,

which has a very different shape

and different form, changing

this landscape. All of these

processes come in and destroy

that high relief that the

glaciers have left behind. Very

dynamic processes, very rapid

erosion, very rapid processes

that cannot be sustained over

geologic time.

>> For the last 150 years,

global warming and the

resulting glacial melt has

caused a huge amount of erosion.

Experts warn, if this warming

trend continues, the Alps will

be ice free by the end of the

century and fear these great

mountain peaks will tumble down

even faster. Weakened rocks and

the increased risk of

catastrophic landslides could

spell disaster for villages and

resorts high up in the Alps.

But a look back to ancient times

reveals that the Alps have been

in meltdown before.

In the autumn of 218 BC, the

mighty Hannibal lead an army of

50,000 men and 40 elephants

across the Alps to attack the

Romans. An arduous 15-day trek

across the most treacherous

terrain in Europe. Many men fell

to their deaths along the

perilously narrow tracks.

But Hannibal's audacious plan

paid off. His army pushed on

through Italy to defeat the

Romans.

Today, Hannibal's route is

virtually impassable, blocked by

ice and deep snow. Scientists

realized that when Hannibal

crossed the Alps, the mountain

passes must have been ice free

and the glaciers must have

retreated further back than they

are today.

>> It may have been a bit of a

walk through the forest for

him, at least much of the way,

and certainly a--an easier time

to travel through the Alps than

we would have today, for

example.

>> Past changes in the Earth's

tilt towards the sun have caused

glaciers to melt and refreeze in

response to a fluctuating

climate. If history repeats

itself, glaciers will, sometime

in the distant future, naturally

return to the Alps.

These advances and

retreats of the ice are very

important to the overall rate at

which the Alps are being eroded.

>> It's this natural cycle from

glaciers carving cliffs, to

rivers cutting valleys, and back

again, that has created a

mountain range that is

ever-changing.

And it's this natural process

that will ultimately destroy the

Alps as we know them.

>> The Alps are slowly being

destroyed. We'll probably see

more glacial advances and

retreats that will begin to

erode them down. So, if we were

to come back in ten, 20, maybe

100 million years, we would

still find a mountain range here

today. The Appalachians of

Eastern U.S., for example,

remain a--at least a small,

subdued mountain range, and that

will be the future of the Alps.

>> The Alps will shrink to half

its size and become a mountain

chain less than 6,000 feet high.

Stunted in height, no glaciers

will cap these mountains, nor

feed the great rivers of Europe.

Millions of years from now, the

vast lowlands of France,

Germany and Eastern Europe could

one day be barren and parched.

Scientists have discovered how

the Alps formed and why they're

tumbling down. Marine fossils

and limestone made from

trillions of seashells are proof

that Alpine rocks formed at the

bottom of the sea. Gray gneiss

rocks at the top of the

Matterhorn are evidence

that Africa collided with

Europe, forming the Alps.

Landslides are proof that

sedimentary layers, and

sometimes whole mountains, are

inherently weak and collapsing.

Gases trapped in ancient ice

bubbles reveal that giant

glaciers carved out the rugged

landmarks of the Alps.

And shrinking glaciers and

waterfalls are weakening the

Alps, creating a skyline which

is constantly changing.

Since they were created, the

Alps have continued to evolve.

One of the most varied,

spectacular and intensely

studied mountain ranges on

Earth, understanding how the

Alps were made has unlocked deep

secrets of the powerful forces

that shape our planet.