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Earth, a 4.5- Billion-year-old planet,
still evolving.

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As continents shift and clash, volcanoes
erupt, and glaciers grow and recede,

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the Earth's crust is carved
in countless, fascinating ways,

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leaving a trail
of geological mysteries behind.

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In this episode, Europe's greatest
mountain chain, the Alps, is explored.

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Home to some of Europe's
highest peaks, longest glaciers

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and sheerest rock faces,
the Alps are one of the most

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dynamic and dangerous
mountain ranges on the planet.

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A mysterious land where whole
mountains collapse in on themselves,

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and where its rocks once lay entombed
at the bottom of the sea.

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Scientists have been hunting for clues
hidden inside the rocks,

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deep within the ice, and upon some of
the most famous summits in the world

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to understand how the Alps formed
and continue to evolve.

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Clues which also provide a window

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into the formation of the Earth itself.

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With more than 100 peaks
rising higher than 12,000 feet,

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the majestic Alps tower over Europe.

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The mountains
are a huge physical barrier.

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750 miles long, 125 miles wide,
and spanning seven countries,

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the Alps divide Northern
and Southern Europe.

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Home of the iconic Matterhorn and
Western Europe's tallest mountain,

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Mont Blanc, the Alps are one of the
world's highest mountain ranges.

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But the majority of these peaks
formed only 30 million years ago,

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making it one of the youngest
mountain ranges on Earth.

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And for centuries, geologists have pored
over these fabulous rock formations

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to figure out how mountains are made.

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But the first person to uncover
a crucial clue to the Alps' formation

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was, surprisingly, a 16th-century
Renaissance man, Leonardo da Vinci.

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He was not only a great artist,
he also had a brilliant scientific mind.

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Da Vinci was a natural detective
who saw the world around him

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as a huge mystery waiting to be solved.

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He focused his inquisitive,
scientific mind on the Alps

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at a time when most scholars
believed the Earth was flat.

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Da Vinci had heard tales
of an extraordinary discovery

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embedded in the rocks,

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and in 1510, he trekked high
into the mountains to take a look.

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At 7,000 feet,
he found what he'd been looking for.

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Fossils.

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He knew these creatures
came from the sea,

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that they could not have lived in the Alps.

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So how did they get there,

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more than 100 miles
from the nearest ocean

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and thousands of feet above sea level?

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The 16th-century explanation provided
by the powerful Catholic Church

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decreed that the marine fossils
must have been washed up

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during the time of Noah in 2300 BC.

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The holy scriptures describe how God,

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sickened by the wickedness
of mankind,

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inflicted a terrifying deluge of water
upon the Earth.

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All forms of life were annihilated,
except those sheltering on Noah's Ark.

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(THUNDER)

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The great torrent of water
that flooded the Earth

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must have washed some of the
sea creatures 100 miles inland.

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But da Vinci did not believe
this explanation

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and continued his investigation
as to how the fossils got there.

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In the S�ntis Mountains,
northern Switzerland, 500 years later

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and 7,000 feet above sea level, it's still
possible to see the fossilised remains

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of sea creatures
that so intrigued da Vinci.

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Here we have a rock
which is almost covered with fossils,

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for example, here,
a cross-section of a clam.

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Here below,
we have the skeleton of a coral.

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Poring over the fossils, da Vinci carried
out an ingenious piece of detective work.

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He found the fossilised remains
of two-shelled creatures

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that amazingly still had
both halves intact.

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If the Church's explanation
of a cataclysmic flood were true,

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then the torrent of water would have torn
these delicate creatures apart.

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Da Vinci proposed that these fossils
had formed under the ocean,

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and that some other force had
brought them high into the mountains.

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Modern-day scientists have identified
the species fossilised in these rocks,

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and can accurately pinpoint
when they lived.

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The fossils we see here
actually lived 100 million years ago

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in a warm, tropical sea.

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This ancient, tropical sea
teemed with life and rich coral reefs.

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The sea floor was covered in urchins,
clams and other species,

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many now extinct.

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Just as da Vinci had imagined,

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when some of these creatures died,
they were preserved intact.

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Their shells then became buried in
the sediments at the bottom of the sea

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and preserved as fossils
when the sediment turned to rock.

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But what could these fossils reveal
about the formation of the Alps?

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Again, it was da Vinci's
exceptional powers of observation

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that helped unravel the mystery.

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He noticed that the spectacular
fossil-bearing rock,

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known as limestone, was laid down
in layers several thousand feet deep.

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400 years later, it was discovered
that, along with the fossils,

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hidden in the microscopic structure
of limestone is an essential clue

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to solving the mystery
of how the Alps formed -

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remains of trillions upon trillions
of seashells.

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Limestone forms as tiny sea creatures
sink to the bottom of the ocean.

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Piling on top of one another,

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they compact together under
their vast accumulated weight,

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forming layer upon layer
of sedimentary rock.

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The S�ntis Mountains,
like large areas of the Alps,

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are made almost entirely of the shells
of dead sea creatures.

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Beds of limestone here are
several thousand feet high -

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evidence of the extraordinary amount
of sediment

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that was laid down
on the ancient sea floor.

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We have here
a massive package of limestone,

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layer above layer of sea floor,

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and this was brought up
in an upright position

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during the building
of the Alpine mountain chain.

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Ancient clues reveal the origin
of the Alps.

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Marine fossils are evidence that
these rocks were once covered

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by a tropical sea.

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And rocks made from trillions
of microscopic seashells

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reveal how entire mountains formed
from sediments laid down in the ocean.

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Da Vinci suspected that part of the Alps
had formed beneath the ocean,

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but how had these originally flat layers
been upended?

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Leonardo's explanation
was that some kind of force

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have brought the fossils
high up to the mountains.

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But he actually couldn't explain then
the driving forces of this movement.

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After da Vinci, it would take
scientists another 400 years

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before that part of the mystery
was solved.

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The Alps.

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This jagged backbone of Europe was
lifted thousands of feet above sea level

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and 100 miles inland.

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Many of the Alpine rocks
once lay flat on the sea floor.

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An extraordinary force twisted,
folded and turned this land upside down.

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But what was this force and how could
it move great swathes of solid rock?

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In the 1870s, Swiss geologist Arnold
Escher and his student Albert Heim

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were drawn to a strange line etched
in the Tschingelhorn mountain.

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They traced the line for 30 miles.

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Out of reach for most of its range,
they found one location

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where this line can be examined
in close-up

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near the village of Elm,
Eastern Switzerland.

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The dark line can clearly be seen here
beneath this strange overhang.

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Above it, Escher and Heim identified
a layer of ancient sedimentary rock.

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But strangely, beneath the line they
found a layer of much younger rock.

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Underneath we have here

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the flysch, these are slates

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which are about 35 million years old.

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And on top we have the Verrucano,

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which has formed about
260, 270 million years ago.

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Escher and Heim were confused.

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The rock formations
simply did not make sense.

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If both layers were formed
by the build-up of sediments,

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how could older rock
lie above the younger one?

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Studying the twists and folds
in the surrounding mountains,

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Escher and Heim came up with a theory
as to how these rocks switched places.

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Just imagine we have
one big sheet of sediments.

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And one part of the sediment of
this sheet is pushed over the others.

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That's the way we get older sediments
on younger sediments.

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A gigantic horizontal force pushed these
older rocks a distance of 30 miles

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over the younger layers.

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The line between them,
where the rocks scrape over each other,

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is called an overthrust.

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Escher and Heim's discovery
revolutionised our understanding

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of how mountains are made.

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This outcrop, actually it's a close-up

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of maybe the most famous overthrust
in the world,

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the so-called Glarus Overthrust.

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And there are only a few places
where you can go... uh, go so close to it.

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This site is merely a close-up
of a massive geological phenomenon

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that created the Alps.

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Sitting above the Glarus Overthrust
is a mountain range

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with peaks over 11,000 feet high.

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It's a reminder that some
awesome power created the Alps,

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a force that can literally
move mountains.

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But what has the power to push
billions of tons of rock?

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Scientists now know that such
a colossal process can only happen

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when two continents collide,
driven by the forces of plate tectonics.

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Plate tectonics is the process
by which giant plates of the Earth's crust

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move slowly across the planet's surface,
propelled by vast currents of molten rock

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deep within the Earth.

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As this happens over millions
of years, continents collide

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and split apart
and oceans form and disappear.

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But if the Alps formed as a result
of a massive collision,

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what continent
had crashed into Europe?

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The answer lies entombed in one
of the Alps' most famous landmarks.

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Hidden by clouds,
it's frequently hard to see.

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There it is, finally.

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The Matterhorn's unique shape

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has made it one of the best-known
mountains in the world.

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At 14,692 feet, it's one
of the Alps' highest peaks.

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Hidden within the body of this mountain
is another major overthrust.

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Here, rocks from the sea floor
lie above the European bedrock.

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Taking a closer look at the layers
formed under the sea,

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Dr Hellwig finds a green-tinged rock.

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The rocks we're looking at here
are called green schists.

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These coarse crystals reveal
that this rock erupted as lava

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at the bottom of the ocean,
100 million years ago.

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But in the early 20th century,

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scientists discovered something
even stranger.

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An unusual layer of rock
caps the mountain.

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This upper layer is a grey rock
called gneiss.

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But when geologists
traced the origin of this rock,

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they found it did not come from Europe,

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and was 200 million years older
than rocks from the sea floor.

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This rock belonged to
a two-billion-year-old continent

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600 miles to the south - Africa.

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The upper section
of this Alpine sandwich,

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it consists of rock
which come from Africa.

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The middle part, um, are the rocks
from the oceanic crust

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and the lower part, then,
are the European rocks.

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This is evidence that the Alps formed

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because ancient Africa
collided with Europe.

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The result?

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This whole mountain is composed
of three rock types.

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From a geological standpoint,

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it nicely combines the whole
Alpine story, so it shows all the...

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...shows the most important aspects
of the Alpine history,

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right there within one mountain.

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00:15:28,784 --> 00:15:32,205
But how exactly did rocks
from the sea floor get sandwiched

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between two continents?

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Detailed studies and dating
of the Alpine rocks

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00:15:40,798 --> 00:15:43,593
have revealed that, 90 million years ago,

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Africa pushed
towards Europe,

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squashing an ancient sea,

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the Tethys Ocean,
that lay between them.

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As Africa ploughed
into Europe,

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it first destroyed the ocean

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that lay between them

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and... and piled it up
in... in thin slices,

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much as a bulldozer
tears up

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00:16:01,031 --> 00:16:02,658
the ground in front of it.

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These slices were then piled
in front of the, uh... the bulldozer

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00:16:05,870 --> 00:16:07,539
that makes up Africa.

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So we began to develop this
large pile of deformed rock

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that is what today forms the Alps.

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The ocean floor was crumpled in front
of the advancing African continent,

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bending, folding
and breaking as it went.

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30 million years ago, the Alps
were literally pushed up onto Europe.

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Africa was thrust over
and above the other layers,

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to form the sandwich of rocks
that would become the Matterhorn.

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A jumble of rocks had been folded
and moulded by violent processes,

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and uplifted 22,000 feet,
as high as the Himalayas today.

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Scientists investigating how
the Alps rose up off the ocean floor

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00:17:03,147 --> 00:17:07,152
have uncovered a 30-mile line
in the rocks,

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the boundary between older rocks
thrust above younger ones.

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And grey gneiss rocks
at the top of the Matterhorn

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prove that Africa collided with Europe,
creating the Alps.

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But for the last 30 million years, some
other monumental force has eaten away

233
00:17:25,049 --> 00:17:26,383
these great peaks.

234
00:17:26,383 --> 00:17:32,725
What has caused this entire mountain
range to lose nearly half its height?

235
00:17:35,436 --> 00:17:41,360
30 million years ago, the Alps' highest
peaks towered 22,000 feet into the air.

236
00:17:42,403 --> 00:17:45,782
Today, the tallest peaks
are almost half this height.

237
00:17:47,868 --> 00:17:52,456
Unravelling the mystery of why and how
the Alps are disappearing

238
00:17:52,456 --> 00:17:57,296
is important to the 14 million people
who live in and around them.

239
00:17:58,882 --> 00:18:02,635
Illhorn mountain,
an extraordinary peak in the Swiss Alps,

240
00:18:02,635 --> 00:18:05,348
provides an essential clue.

241
00:18:08,601 --> 00:18:14,067
This mountain is almost 9,000 feet tall,
but hollow at its centre.

242
00:18:16,110 --> 00:18:18,489
Illhorn is rotten to the core.

243
00:18:18,489 --> 00:18:23,202
This massive hole is forming
as the mountain collapses in on itself.

244
00:18:25,038 --> 00:18:29,210
But what monumental force
is pulling this mountain down?

245
00:18:31,504 --> 00:18:35,258
It's made of a loose, unstable
mixture of rock and mud

246
00:18:35,258 --> 00:18:38,095
that originally came from the ocean floor.

247
00:18:38,095 --> 00:18:42,558
In winter, this mixture of rock
is glued together by ice,

248
00:18:42,558 --> 00:18:45,980
but in the spring thaw, it becomes loose.

249
00:18:48,983 --> 00:18:52,446
Here you can see the fact
that the rocks are very highly weathered,

250
00:18:52,446 --> 00:18:55,199
you can easily, uh, in fact
by hand, pull them apart,

251
00:18:55,199 --> 00:18:57,327
you can imagine that, uh...

252
00:18:57,327 --> 00:18:58,870
...in winter when the ice,

253
00:18:58,870 --> 00:19:01,248
when the water goes behind the rocks
and freezes,

254
00:19:01,248 --> 00:19:05,127
that it could actually mechanically,
uh, loosen the rocks,

255
00:19:05,127 --> 00:19:07,047
and in the spring they fall down.

256
00:19:07,047 --> 00:19:09,133
The whole mountain
is composed of these rocks,

257
00:19:09,133 --> 00:19:10,759
it's basically just falling apart.

258
00:19:19,312 --> 00:19:23,900
A combination of weak rocks and the
natural action of freezing and thawing

259
00:19:23,900 --> 00:19:27,280
has resulted in a crumbling mountain.

260
00:19:27,280 --> 00:19:31,993
In the last 10,000 years, 100 million tons
of Illhorn mountain has eroded

261
00:19:31,993 --> 00:19:38,168
and in the process hollowed out
a vast new valley, the lllgraben.

262
00:19:38,168 --> 00:19:41,463
But where has all the rock gone?

263
00:19:41,463 --> 00:19:46,511
Dr McArdell has come to explore
a deep, seemingly dry riverbed,

264
00:19:46,511 --> 00:19:49,264
which runs down from the heart
of the mountain

265
00:19:49,264 --> 00:19:50,891
and into the river Rhone.

266
00:19:52,935 --> 00:19:57,899
The evidence is hidden beneath
the village and vegetation -

267
00:19:57,899 --> 00:20:01,737
a large, fan-shaped platform of rubble,

268
00:20:01,737 --> 00:20:06,785
1,500 feet deep
and over one mile square.

269
00:20:09,831 --> 00:20:14,211
This structure is built from the sediment
delivered by the lllgraben catchment.

270
00:20:14,211 --> 00:20:17,548
All the sediment that you see
has come down from the mountain.

271
00:20:17,548 --> 00:20:21,803
But this dry riverbed
presents a mystery.

272
00:20:21,803 --> 00:20:26,559
How did vast amounts of debris get
transported down from the mountain?

273
00:20:26,559 --> 00:20:31,065
The Swiss village of Susten,
ground zero for the investigation,

274
00:20:31,065 --> 00:20:33,692
is in a constant state of alert.

275
00:20:33,692 --> 00:20:36,696
A few times a year,
the ground shakes here

276
00:20:36,696 --> 00:20:40,576
as if a gigantic freight train
is thundering through the village.

277
00:20:40,576 --> 00:20:42,202
(RUMBLING)

278
00:20:42,202 --> 00:20:46,208
(SIREN WAILS)

279
00:20:53,091 --> 00:20:57,930
In a flash, this dry channel
is flooded by a river of rock.

280
00:21:01,642 --> 00:21:06,273
Thousands of tons of debris flow
down from the Illhorn mountain.

281
00:21:07,275 --> 00:21:09,319
McARDELL: Anywhere between
three and five times a year,

282
00:21:09,319 --> 00:21:12,030
there's a large wave of sediment
moving downstream

283
00:21:12,030 --> 00:21:14,116
at anywhere
from 10 to 20 miles an hour,

284
00:21:14,116 --> 00:21:16,703
with a flow depth on the order
of up to 10 feet.

285
00:21:16,703 --> 00:21:20,123
And it moves down the channel rapidly
and anyone who's in the channel,

286
00:21:20,123 --> 00:21:21,751
of course, is in danger.

287
00:21:24,879 --> 00:21:29,301
Every time it rains,
debris cascades down the mountainside,

288
00:21:29,301 --> 00:21:34,224
making this one of the most
active debris flow zones on Earth.

289
00:21:36,310 --> 00:21:39,354
The Alps are basically being
washed down from the mountains,

290
00:21:39,354 --> 00:21:44,111
through the rivers and into the lakes,
into the valleys further downstream.

291
00:21:44,111 --> 00:21:49,242
Illhorn is an extreme case of an entire
mountain in the process of decay,

292
00:21:49,242 --> 00:21:53,789
resulting in one of the most dangerous
mountain terrains on the planet.

293
00:21:55,249 --> 00:21:58,920
But inherently unstable rocks
are found right across the Alps,

294
00:21:58,920 --> 00:22:02,800
and have created some of
the Alps' best beauty spots.

295
00:22:05,136 --> 00:22:09,140
Oeschinensee lake is a mile
above sea level and half a mile square.

296
00:22:11,351 --> 00:22:14,355
But in theory, this lake shouldn't be here.

297
00:22:16,399 --> 00:22:18,235
The streams
that pour off the mountain

298
00:22:18,235 --> 00:22:21,656
should run straight down
the valley unobstructed.

299
00:22:23,992 --> 00:22:27,329
A clue to what created this
high-altitude lake can be found

300
00:22:27,329 --> 00:22:30,249
1,000 feet up on the surrounding slopes.

301
00:22:31,793 --> 00:22:33,504
As we look up on the hill slopes,

302
00:22:33,504 --> 00:22:36,006
we see these very large
fans of debris

303
00:22:36,006 --> 00:22:38,635
that are coming down off
of these unstable slopes.

304
00:22:40,261 --> 00:22:44,600
Where we see this sort of smooth
bedrock that's dipping towards us,

305
00:22:44,600 --> 00:22:47,645
this is prime territory for landslides.

306
00:22:47,645 --> 00:22:49,398
When these mountains formed,

307
00:22:49,398 --> 00:22:54,069
flat sheets of sedimentary rock
were thrust up to rest at extreme angles.

308
00:22:55,113 --> 00:22:59,326
The joins between these stressed
and fractured rock layers frequently fail,

309
00:22:59,326 --> 00:23:04,207
causing huge layers of rock
to shear off the cliff faces.

310
00:23:05,375 --> 00:23:08,796
Much of these open slopes are
probably the result of sheets of rock

311
00:23:08,796 --> 00:23:11,507
peeling off and forming large landslides.

312
00:23:13,427 --> 00:23:15,971
It was a catastrophic landslide

313
00:23:15,971 --> 00:23:20,560
that caused this lake
to form 15,000 years ago.

314
00:23:20,560 --> 00:23:24,815
The entire side of the mountain
sheared off, blocking the valley

315
00:23:24,815 --> 00:23:26,775
and causing stream water to back up

316
00:23:26,775 --> 00:23:30,656
and create one of the Alps'
most breathtaking landscapes.

317
00:23:32,741 --> 00:23:34,285
It's all about gravity,

318
00:23:34,285 --> 00:23:36,371
gravity is what ultimately
brings down mountains.

319
00:23:36,371 --> 00:23:40,834
Rivers come in, debris flows form,
landslides form,

320
00:23:40,834 --> 00:23:43,713
and this sort of process is very common
throughout the Alps.

321
00:23:44,714 --> 00:23:48,928
Steep slopes and unstable rocks
have created a mountain range

322
00:23:48,928 --> 00:23:50,430
that is ever-changing.

323
00:23:50,430 --> 00:23:52,348
In only a few thousand years,

324
00:23:52,348 --> 00:23:57,688
gravity will also destroy Oeschinensee
lake, as debris flows fill it up.

325
00:23:59,065 --> 00:24:03,945
Over the last 30 million years, the Alps
have fallen down on a massive scale,

326
00:24:03,945 --> 00:24:08,451
in places decreasing
in height by 10,000 feet.

327
00:24:08,451 --> 00:24:12,206
So what has happened
to those thousands of feet

328
00:24:12,206 --> 00:24:15,543
and billions of tons of missing rock?

329
00:24:17,628 --> 00:24:22,969
A clue can be found in the rolling hills
a few miles north of the Alps.

330
00:24:26,306 --> 00:24:31,729
At Eggiwil, this rock outcrop contains
an extraordinary collection of stones.

331
00:24:33,564 --> 00:24:37,819
These are large cobbles, stones
that have come from all over the Alps,

332
00:24:37,819 --> 00:24:41,866
so if I look at some of these, for
example, this small white and black rock,

333
00:24:41,866 --> 00:24:44,620
this is a granitic rock that comes
from the centre of the Alps,

334
00:24:44,620 --> 00:24:46,747
somewhere very close to the Matterhorn.

335
00:24:46,747 --> 00:24:48,791
And we see, throughout this outcrop,

336
00:24:48,791 --> 00:24:51,420
rocks that come from different parts
of the Alps.

337
00:24:52,420 --> 00:24:55,341
Rocks from hundreds of
different scattered locations

338
00:24:55,341 --> 00:24:57,844
have travelled over 150 miles

339
00:24:57,844 --> 00:25:02,141
before being dumped
in this geologic rock graveyard.

340
00:25:03,434 --> 00:25:07,480
But it's the amount of material
here that's mind-boggling.

341
00:25:07,480 --> 00:25:12,445
These hills are made entirely of
rock debris from the nearby Alps.

342
00:25:12,445 --> 00:25:18,410
At 100 miles wide and 500 miles long,
they stretch in an arc round the Alps,

343
00:25:18,410 --> 00:25:22,039
running through France,
Switzerland and Germany.

344
00:25:22,039 --> 00:25:28,297
There's enough material here to cover all
of North America in 100 feet of rubble.

345
00:25:28,297 --> 00:25:33,720
Could this be where the thousands of
feet of missing Alpine rock have gone?

346
00:25:33,720 --> 00:25:36,182
A big mountain
range like the Alps is heavy,

347
00:25:36,182 --> 00:25:38,100
and it weights down the crust,

348
00:25:38,100 --> 00:25:40,728
forming a depression all the way
around the mountain range.

349
00:25:41,730 --> 00:25:45,443
A multi-trillion-ton mass of rock
was pushed up on land

350
00:25:45,443 --> 00:25:48,988
as Africa collided with Europe,
creating the Alps.

351
00:25:50,074 --> 00:25:53,243
The weight of the rock caused
the European crust to sink,

352
00:25:53,243 --> 00:25:58,000
making a huge depression, in places
over two and a half miles deep -

353
00:25:58,000 --> 00:26:00,460
the Molasse basin.

354
00:26:02,422 --> 00:26:05,008
Now, the importance of this depression
is it's a trap,

355
00:26:05,008 --> 00:26:07,386
all the sediment that we see
eroding off of the Alps

356
00:26:07,386 --> 00:26:10,514
is trapped in this basin
and ends up sitting there.

357
00:26:10,514 --> 00:26:15,020
Dating of these pebbles has revealed
that, ever since the Alps were created,

358
00:26:15,020 --> 00:26:19,818
rivers have washed Alpine debris
hundreds of miles downstream,

359
00:26:19,818 --> 00:26:23,488
dumping the rocks in this gigantic basin.

360
00:26:23,488 --> 00:26:27,117
So these rocks that we're
looking at here are the debris,

361
00:26:27,117 --> 00:26:31,248
the detritus that's come off of the Alps
over the last 20, 30 million years,

362
00:26:31,248 --> 00:26:34,085
these particular rocks
are almost 25 million years old.

363
00:26:34,085 --> 00:26:37,714
And what we see are cobbles, we see
little pieces of all the different rocks

364
00:26:37,714 --> 00:26:40,676
that we see throughout the Alps.

365
00:26:40,676 --> 00:26:44,847
For 30 million years, the debris eroded
from the Alps has been dumped

366
00:26:44,847 --> 00:26:50,020
in a 30,000-square-mile bowl,
creating this rolling chain of hills

367
00:26:50,020 --> 00:26:52,231
to the north of the Alps.

368
00:26:52,231 --> 00:26:56,403
This is where
the missing mountain rock is.

369
00:26:56,403 --> 00:26:58,614
Put it all back together and once again,

370
00:26:58,614 --> 00:27:01,534
there'd be mountains
as high as the Himalayas.

371
00:27:03,161 --> 00:27:07,333
Scientists have discovered how
the Alps have almost halved in height

372
00:27:07,333 --> 00:27:10,169
and where the missing rocks
have disappeared to.

373
00:27:10,169 --> 00:27:14,257
The clues are, inherently
unstable mixtures of rock,

374
00:27:14,257 --> 00:27:19,306
resulting in whole mountains falling
apart, debris flows on steep cliffs,

375
00:27:19,306 --> 00:27:23,519
proof that weakened layers of rock
shear off from the mountainsides,

376
00:27:23,519 --> 00:27:26,481
and a graveyard of pebbles
from all over the Alps,

377
00:27:26,481 --> 00:27:30,069
evidence that these mountains
have been washed away.

378
00:27:32,071 --> 00:27:36,702
But then, two million years ago,
the landscape changed dramatically.

379
00:27:36,702 --> 00:27:39,747
Vertical cliffs were carved into the Alps

380
00:27:39,747 --> 00:27:43,084
and giant spikes of rock
poked through the clouds.

381
00:27:43,084 --> 00:27:48,507
Another mighty force
had begun to resculpt the Alps.

382
00:27:50,385 --> 00:27:54,556
Over the last two million years,
a blink in geologic time,

383
00:27:54,556 --> 00:27:58,436
something has rapidly
and radically transformed the Alps,

384
00:27:58,436 --> 00:28:02,899
gouging giant peaks
and sheer rock faces.

385
00:28:05,987 --> 00:28:11,618
The most notorious rock formation
being the Eiger, in southern Switzerland.

386
00:28:13,371 --> 00:28:19,128
The infamous north face of the Eiger
is a 6,000 foot vertical climb.

387
00:28:19,128 --> 00:28:22,090
It's a terrifying, unrelenting ascent.

388
00:28:22,090 --> 00:28:28,388
Climbers face gale-force winds,
freezing fog, rockfalls and avalanche,

389
00:28:28,388 --> 00:28:32,936
giving the Eiger the reputation as one of
the most formidable climbs in the world.

390
00:28:35,189 --> 00:28:36,858
Nicknamed the Murder Wall,

391
00:28:36,858 --> 00:28:42,739
since 1935, more than
60 climbers have died here.

392
00:28:48,621 --> 00:28:53,001
How giant climbing walls like this were
formed had been a mystery to geologists

393
00:28:53,001 --> 00:28:59,885
until 1837, when Swiss scientist
Louis Agassiz noticed similar cliffs

394
00:28:59,885 --> 00:29:06,518
at lower altitudes, known to have been
made by a colossal force - glaciers.

395
00:29:07,686 --> 00:29:12,525
Over 1,000 glaciers wind their way
through the Alpine valleys.

396
00:29:13,735 --> 00:29:19,784
Imperceptible to the naked eye, these
giant rivers of ice slowly flow downhill.

397
00:29:21,369 --> 00:29:25,624
This time-lapse of the Aletsch glacier,
taken over a period of three years,

398
00:29:25,624 --> 00:29:30,588
reveals how glaciers
can move tens of feet a year.

399
00:29:30,588 --> 00:29:35,636
And where two glaciers meet,
a stripe of rock sits on the surface,

400
00:29:35,636 --> 00:29:40,892
proof that something extraordinary
is happening beneath the ice.

401
00:29:40,892 --> 00:29:47,734
A force which can transform jagged rock
into a surface as smooth as glass.

402
00:29:47,734 --> 00:29:52,364
We see here a smooth rock face
which was formerly covered by ice.

403
00:29:53,992 --> 00:29:59,623
Underneath the ice, there is this
rocks and sand, and it carries...

404
00:29:59,623 --> 00:30:02,294
...the ice carries this stuff with it

405
00:30:02,294 --> 00:30:07,132
and it acts like sandpaper
and polished this rock.

406
00:30:07,132 --> 00:30:12,138
But polishing alone cannot account for
the formation of the Alps' jagged peaks

407
00:30:12,138 --> 00:30:14,391
and the north face of the Eiger,

408
00:30:14,391 --> 00:30:17,270
where the sides of entire mountains
have been ripped off.

409
00:30:18,980 --> 00:30:21,191
More evidence of the awesome power
of glaciers

410
00:30:21,191 --> 00:30:23,736
can be found on these granite slabs.

411
00:30:23,736 --> 00:30:27,616
Deep cracks penetrate
the body of the rock.

412
00:30:31,245 --> 00:30:37,252
The ice was flowing over this rock face
and the ice could enter this crack.

413
00:30:37,252 --> 00:30:41,048
Meltwater forming beneath the glacier
seeps into the cracks,

414
00:30:41,048 --> 00:30:44,302
refreezes and splits open the rock.

415
00:30:44,302 --> 00:30:49,934
Weakened and fractured, huge chunks
of stone are ripped from the bedrock.

416
00:30:49,934 --> 00:30:54,648
Vast amounts of rock are plucked
and ground from the mountainsides

417
00:30:54,648 --> 00:30:57,860
and dumped in the lower,
warmer valleys when the ice melts.

418
00:30:59,613 --> 00:31:05,328
So here we are at the end,
the snout of the glacier.

419
00:31:05,328 --> 00:31:10,250
And here debris, water,
and rock boulders.

420
00:31:10,250 --> 00:31:15,173
This has been eroded by the glacier,
transported and moved to this place

421
00:31:15,173 --> 00:31:20,178
and this is the essential process,
how glaciers form the landscape.

422
00:31:22,598 --> 00:31:26,019
But how could glaciers have carved
the north face of the Eiger,

423
00:31:26,019 --> 00:31:29,232
and other mighty peaks
which rise thousands of feet

424
00:31:29,232 --> 00:31:31,443
out of reach of the abrasive ice below?

425
00:31:32,652 --> 00:31:35,906
Agassiz came up with a radical theory.

426
00:31:35,906 --> 00:31:40,203
He noticed these high rock faces
were scarred and gnarled.

427
00:31:40,203 --> 00:31:43,206
They had clearly been gouged by ice,

428
00:31:43,206 --> 00:31:47,044
like the glaciated valleys
he'd found at lower altitudes.

429
00:31:49,213 --> 00:31:50,674
Piecing the evidence together,

430
00:31:50,674 --> 00:31:54,428
he concluded towering cliffs
like the 6,000-foot Eiger

431
00:31:54,428 --> 00:31:58,392
were the handiwork
of ancient, gigantic glaciers.

432
00:31:59,893 --> 00:32:04,190
But if Agassiz was right, where
did the huge glaciers come from?

433
00:32:06,026 --> 00:32:11,115
The evidence lies locked inside
Europe's biggest river of ice,

434
00:32:11,115 --> 00:32:12,575
the Aletsch glacier.

435
00:32:14,244 --> 00:32:19,876
A massive 14 miles long, it covers
an area of more than 45 square miles

436
00:32:19,876 --> 00:32:22,462
and is up to 3,000 feet deep.

437
00:32:22,462 --> 00:32:25,424
The Aletsch glacier
in southern Switzerland

438
00:32:25,424 --> 00:32:30,430
has helped scientists understand
how all Alpine glaciers form.

439
00:32:32,849 --> 00:32:35,519
The source of the glacier
is high up in the mountains,

440
00:32:35,519 --> 00:32:39,399
where altitude brings freezing
temperatures and heavy snowfall.

441
00:32:40,817 --> 00:32:45,156
To explore how delicate snowfall
becomes a giant slab of ice,

442
00:32:45,156 --> 00:32:48,994
Dr Bauder ventures
deep into the heart of the glacier.

443
00:32:50,955 --> 00:32:55,793
This frozen passageway, 32 degrees
Fahrenheit and 60 feet deep,

444
00:32:55,793 --> 00:32:59,465
offers tourists and scientists
a unique window

445
00:32:59,465 --> 00:33:01,509
into the formation of a glacier.

446
00:33:01,509 --> 00:33:05,389
Here we can see
the inside of a glacier.

447
00:33:05,389 --> 00:33:11,771
We can see inside the ice.
We see here layers of air bubbles.

448
00:33:14,817 --> 00:33:19,614
And there are different,
distinct layers visible here, here, here,

449
00:33:19,614 --> 00:33:25,037
and they represent individual years
when this ice has been formed.

450
00:33:26,497 --> 00:33:31,420
The glacier grows by the build-up
of layer upon layer of snow.

451
00:33:31,420 --> 00:33:36,593
The newly fallen snow traps pockets of
air between the individual snowflakes,

452
00:33:36,593 --> 00:33:38,136
forming layers of bubbles.

453
00:33:38,136 --> 00:33:42,391
As more snow settles,
the flakes beneath become squashed,

454
00:33:42,391 --> 00:33:45,687
making them stick together to form ice.

455
00:33:47,272 --> 00:33:49,108
Forming over thousands of years,

456
00:33:49,108 --> 00:33:52,863
the amount of ice contained in
a single glacier can be staggering.

457
00:33:54,239 --> 00:34:00,204
It's been estimated that the Aletsch
glacier holds 27 billion tons of water,

458
00:34:00,204 --> 00:34:04,126
enough to provide every human on
Earth with two pints of water a day

459
00:34:04,126 --> 00:34:06,754
for the next six years.

460
00:34:07,797 --> 00:34:11,426
It's the air bubbles, trapped
inside the ice thousands of years ago,

461
00:34:11,426 --> 00:34:15,974
that hold the key to what carved
the Alps' distinctive shape.

462
00:34:15,974 --> 00:34:17,600
In the air bubbles,

463
00:34:17,600 --> 00:34:21,605
air is stored from the time when
the air bubbles have been formed.

464
00:34:21,605 --> 00:34:26,611
So we can analyse
the chemical composition inside there

465
00:34:26,611 --> 00:34:30,282
and learn about the climatic condition
at that time.

466
00:34:30,282 --> 00:34:33,619
When scientists analysed
miniature time capsules like these,

467
00:34:33,619 --> 00:34:37,041
they found air over 12,000 years old,

468
00:34:37,041 --> 00:34:41,880
with surprisingly low levels of
the greenhouse gas carbon dioxide.

469
00:34:41,880 --> 00:34:45,426
This meant that more heat was
escaping from the Earth's atmosphere,

470
00:34:45,426 --> 00:34:47,971
causing global temperatures
to plummet.

471
00:34:50,140 --> 00:34:53,894
Similar studies have revealed
that, for the last two million years,

472
00:34:53,894 --> 00:34:57,565
the Earth has been gripped
by a series of ice ages.

473
00:35:00,778 --> 00:35:03,280
Agassiz' theory was confirmed.

474
00:35:03,280 --> 00:35:05,241
Two million years ago,

475
00:35:05,241 --> 00:35:09,329
an enormous ice sheet engulfed
the Earth's northern hemisphere.

476
00:35:09,329 --> 00:35:14,544
The Alps were buried in ice
almost two miles thick.

477
00:35:14,544 --> 00:35:17,088
It was so deep that
only the tips of the mountains

478
00:35:17,088 --> 00:35:19,884
poked out above the ocean of ice.

479
00:35:19,884 --> 00:35:23,305
As the ice moved,
it whittled lone peaks

480
00:35:23,305 --> 00:35:26,267
and tore steep rock faces
high in the Alps,

481
00:35:26,267 --> 00:35:29,896
leaving its legacy on the landscape.

482
00:35:31,898 --> 00:35:33,442
It was during this time

483
00:35:33,442 --> 00:35:37,697
that giant glaciers carved
the infamous north face of the Eiger.

484
00:35:45,748 --> 00:35:48,752
In their mission to discover how
the Eiger and other great peaks

485
00:35:48,752 --> 00:35:55,009
in the Alps formed, scientists
have found cracks in granite bedrock,

486
00:35:55,009 --> 00:35:59,390
evidence that glaciers cleave masses
of rock from the mountainsides,

487
00:35:59,390 --> 00:36:03,603
and low levels of carbon dioxide,
trapped inside ice bubbles,

488
00:36:03,603 --> 00:36:09,569
prove that giant glaciers once carved
immense rock walls and pinnacles,

489
00:36:09,569 --> 00:36:13,281
which now tower over the landscape.

490
00:36:13,281 --> 00:36:16,035
10,000 years ago,
the great ice sheets melted,

491
00:36:16,035 --> 00:36:18,287
leaving their mark on the Alps.

492
00:36:19,289 --> 00:36:23,460
But today, the Alps are falling down
at a phenomenal rate.

493
00:36:23,460 --> 00:36:28,675
Something has propelled them into a
new and violent phase of their evolution.

494
00:36:31,803 --> 00:36:35,683
The Alps are falling down
at an accelerated rate.

495
00:36:37,811 --> 00:36:41,273
And millions of tons of rock
are crashing to Earth.

496
00:36:44,068 --> 00:36:46,739
A clue to what strange force
is at work here

497
00:36:46,739 --> 00:36:49,033
can be found high up in the mountains,

498
00:36:49,033 --> 00:36:52,119
where the remnants
of the last ice age lurk.

499
00:36:52,119 --> 00:36:58,169
Alpine glaciers physically prop up
mountains, binding the rock together.

500
00:36:58,169 --> 00:37:01,172
But these icy rivers are changing shape.

501
00:37:01,172 --> 00:37:03,926
Well, what we see in the background
here are glaciers

502
00:37:03,926 --> 00:37:10,768
which are separated, uh, by rocky
surfaces which are looking very fresh

503
00:37:10,768 --> 00:37:17,275
because they have been ice covered
in the last, uh, few hundred, uh, years.

504
00:37:17,275 --> 00:37:20,696
Uh, if you look across here
to Theodul glacier, we can see

505
00:37:20,696 --> 00:37:25,994
that actually, right next to the ice, uh,
there is some, uh, greyish material

506
00:37:25,994 --> 00:37:27,788
next to the brownish material.

507
00:37:27,788 --> 00:37:35,255
That's exactly the limit up to where
the glacier was, uh, in 1874.

508
00:37:35,255 --> 00:37:41,054
So you see how much of this ice has
melted down in these 130, uh, years.

509
00:37:42,263 --> 00:37:45,601
Scientists believe global warming
is melting the ice

510
00:37:45,601 --> 00:37:48,729
faster than at any other time
in the Alps' history.

511
00:37:48,729 --> 00:37:53,819
And as the glaciers shrink,
they expose steep, unsupported cliffs

512
00:37:53,819 --> 00:37:58,324
that are prone to fall down,
increasing the risks of landslides.

513
00:38:00,243 --> 00:38:01,996
But scientists have discovered

514
00:38:01,996 --> 00:38:05,416
another way melting glaciers
are weakening the Alps.

515
00:38:07,836 --> 00:38:10,089
When these frozen reservoirs melt,

516
00:38:10,089 --> 00:38:13,342
millions of gallons
of water gush downhill,

517
00:38:13,342 --> 00:38:16,137
feeding the great rivers of Europe.

518
00:38:19,517 --> 00:38:23,313
Like liquid sandpaper,
this torrent scrapes over the rocks,

519
00:38:23,313 --> 00:38:26,901
hollowing out the land
at an accelerated rate.

520
00:38:31,239 --> 00:38:34,785
The dramatic evidence of this
dynamic process can be found

521
00:38:34,785 --> 00:38:37,455
in the valley of Lauterbrunnen.

522
00:38:40,124 --> 00:38:43,421
Echoing through this valley
is the sound of one of the loudest

523
00:38:43,421 --> 00:38:48,677
and most spectacular water features
in the Alps, Tr�mmelbach Falls.

524
00:38:54,016 --> 00:38:56,645
You can just feel
the pulsing of the water.

525
00:38:56,645 --> 00:38:58,855
This is... the name Tr�mmelbach

526
00:38:58,855 --> 00:39:00,608
actually means drum sound,

527
00:39:00,608 --> 00:39:06,782
and this is reflecting this, this pulsing,
throbbing that we can hear and feel

528
00:39:06,782 --> 00:39:09,785
from the water flowing down
through these caves.

529
00:39:11,830 --> 00:39:15,834
Tr�mmelbach
is a spectacular glacial waterfall.

530
00:39:15,834 --> 00:39:20,882
Over 5,000 gallons of meltwater
a second hurtle down from glaciers

531
00:39:20,882 --> 00:39:23,802
on the nearby Eiger
and Jungfrau mountains.

532
00:39:23,802 --> 00:39:27,098
Over hundreds of years,
this abrasive jet-stream

533
00:39:27,098 --> 00:39:31,103
has sliced through the mountain,
creating a narrow canyon.

534
00:39:31,103 --> 00:39:34,941
Each year, from the Swiss Alps alone,
there's enough rock removed

535
00:39:34,941 --> 00:39:39,780
by the glacial meltwaters to create
a mountain more than half a mile high.

536
00:39:42,825 --> 00:39:48,582
But Tr�mmelbach, like other Alpine
waterfalls, is living on borrowed time.

537
00:39:51,711 --> 00:39:54,548
As meltwater thunders down
the waterfalls,

538
00:39:54,548 --> 00:39:57,134
it cuts into the rock, weakening it.

539
00:39:58,219 --> 00:40:02,391
Over time, these steep cliffs
left by the glaciers crumble,

540
00:40:02,391 --> 00:40:06,103
replaced by ever deepening river valleys.

541
00:40:06,103 --> 00:40:08,064
WILLOTT: Today,
the rivers that are now returning

542
00:40:08,064 --> 00:40:09,775
are trying to carve a river valley,

543
00:40:09,775 --> 00:40:13,904
which has a very different shape and
different form, changing this landscape.

544
00:40:13,904 --> 00:40:17,158
All of these processes
come in and destroy that high relief

545
00:40:17,158 --> 00:40:19,161
that the glaciers have left behind.

546
00:40:19,161 --> 00:40:23,040
Very dynamic processes,
very rapid erosion, very rapid processes

547
00:40:23,040 --> 00:40:25,460
that cannot be sustained
over geologic time.

548
00:40:25,460 --> 00:40:30,716
For the last 150 years, global warming
and the resulting glacial melt

549
00:40:30,716 --> 00:40:33,053
has caused a huge amount of erosion.

550
00:40:34,721 --> 00:40:38,225
Experts warn,
if this warming trend continues,

551
00:40:38,225 --> 00:40:41,062
the Alps will be ice free
by the end of the century

552
00:40:41,062 --> 00:40:45,359
and fear these great mountain peaks
will tumble down even faster.

553
00:40:45,359 --> 00:40:50,407
Weakened rocks and the increased risk
of catastrophic landslides

554
00:40:50,407 --> 00:40:55,621
could spell disaster for villages
and resorts high up in the Alps.

555
00:40:55,621 --> 00:40:57,832
But a look back to ancient times

556
00:40:57,832 --> 00:41:01,003
reveals that the Alps
have been in meltdown before.

557
00:41:02,797 --> 00:41:05,049
In the autumn of 218 BC,

558
00:41:05,049 --> 00:41:09,554
the mighty Hannibal led an army
of 50,000 men and 40 elephants

559
00:41:09,554 --> 00:41:12,683
across the Alps to attack the Romans.

560
00:41:13,768 --> 00:41:19,400
An arduous 15-day trek across
the most treacherous terrain in Europe.

561
00:41:19,400 --> 00:41:24,531
Many men fell to their deaths
along the perilously narrow tracks.

562
00:41:27,618 --> 00:41:30,371
But Hannibal's audacious plan paid off.

563
00:41:30,371 --> 00:41:35,002
His army pushed on through Italy
to defeat the Romans.

564
00:41:36,880 --> 00:41:39,799
Today, Hannibal's route
is virtually impassable,

565
00:41:39,799 --> 00:41:43,387
blocked by ice and deep snow.

566
00:41:43,387 --> 00:41:46,933
Scientists realised that
when Hannibal crossed the Alps,

567
00:41:46,933 --> 00:41:49,686
the mountain passes
must have been ice free

568
00:41:49,686 --> 00:41:53,565
and the glaciers must have retreated
further back than they are today.

569
00:41:55,443 --> 00:41:57,904
It may have been a bit of a walk through
the forest for him,

570
00:41:57,904 --> 00:42:00,742
at least much of the way,
and certainly a... an easier time

571
00:42:00,742 --> 00:42:04,078
to travel through the Alps than
we would have today, for example.

572
00:42:04,078 --> 00:42:07,249
Past changes
in the Earth's tilt towards the sun

573
00:42:07,249 --> 00:42:10,503
have caused glaciers
to melt and refreeze

574
00:42:10,503 --> 00:42:13,339
in response to a fluctuating climate.

575
00:42:13,339 --> 00:42:18,680
If history repeats itself, glaciers
will, sometime in the distant future,

576
00:42:18,680 --> 00:42:21,891
naturally return to the Alps.

577
00:42:21,891 --> 00:42:24,603
WILLOTT: These advances
and retreats of the ice

578
00:42:24,603 --> 00:42:29,026
are very important to the overall rate
at which the Alps are being eroded.

579
00:42:30,444 --> 00:42:35,616
It's this natural cycle from glaciers
carving cliffs, to rivers cutting valleys,

580
00:42:35,616 --> 00:42:40,665
and back again, that has created
a mountain range that is ever-changing.

581
00:42:42,625 --> 00:42:44,711
And it's this natural process

582
00:42:44,711 --> 00:42:47,756
that will ultimately destroy the Alps
as we know them.

583
00:42:51,844 --> 00:42:54,431
The Alps are
slowly being destroyed.

584
00:42:54,431 --> 00:42:58,185
We'll probably see more glacial
advances and retreats

585
00:42:58,185 --> 00:42:59,521
that will begin to erode them down.

586
00:42:59,521 --> 00:43:03,274
So, if we were to come back
in 10, 20, maybe 100 million years,

587
00:43:03,274 --> 00:43:05,820
we would still find a mountain range
here today.

588
00:43:05,820 --> 00:43:08,447
The Appalachians of Eastern U.S.,
for example,

589
00:43:08,447 --> 00:43:11,118
remain a... at least a small,
subdued mountain range,

590
00:43:11,118 --> 00:43:13,120
and that will be the future of the Alps.

591
00:43:13,120 --> 00:43:15,873
The Alps will shrink to half its size

592
00:43:15,873 --> 00:43:19,670
and become a mountain chain
less than 6,000 feet high.

593
00:43:21,130 --> 00:43:24,509
Stunted in height, no glaciers
will cap these mountains,

594
00:43:24,509 --> 00:43:27,095
nor feed the great rivers of Europe.

595
00:43:29,014 --> 00:43:32,435
Millions of years from now,
the vast lowlands of France,

596
00:43:32,435 --> 00:43:37,066
Germany and Eastern Europe
could one day be barren and parched.

597
00:43:39,735 --> 00:43:42,572
Scientists have discovered
how the Alps formed

598
00:43:42,572 --> 00:43:44,908
and why they're tumbling down.

599
00:43:45,951 --> 00:43:51,583
Marine fossils and limestone made
from trillions of seashells are proof

600
00:43:51,583 --> 00:43:55,045
that Alpine rocks formed
at the bottom of the sea.

601
00:43:55,045 --> 00:43:58,966
Grey gneiss rocks at the top
of the Matterhorn are evidence

602
00:43:58,966 --> 00:44:02,513
that Africa collided with Europe,
forming the Alps.

603
00:44:03,848 --> 00:44:06,601
Landslides are proof
that sedimentary layers,

604
00:44:06,601 --> 00:44:11,398
and sometimes whole mountains,
are inherently weak and collapsing.

605
00:44:11,398 --> 00:44:14,235
Gases trapped in ancient
ice bubbles reveal

606
00:44:14,235 --> 00:44:18,698
that giant glaciers carved out
the rugged landmarks of the Alps.

607
00:44:20,493 --> 00:44:26,041
And shrinking glaciers and waterfalls are
weakening the Alps, creating a skyline

608
00:44:26,041 --> 00:44:27,793
which is constantly changing.

609
00:44:29,545 --> 00:44:33,675
Since they were created,
the Alps have continued to evolve.

610
00:44:34,760 --> 00:44:37,180
One of the most varied,
spectacular

611
00:44:37,180 --> 00:44:40,183
and intensely studied
mountain ranges on Earth,

612
00:44:40,183 --> 00:44:42,311
understanding how the Alps were made

613
00:44:42,311 --> 00:44:44,271
has unlocked deep secrets

614
00:44:44,271 --> 00:44:47,317
of the powerful forces
that shape our planet.