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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 Säntis 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 Säntis 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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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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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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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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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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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

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these great peaks.

234
00:17:26,287 --> 00:17:32,601
What has caused this entire mountain
range to lose nearly half its height?

235
00:17:35,327 --> 00:17:41,243
30 million years ago, the Alps' highest
peaks towered 22,000 feet into the air.

236
00:17:42,287 --> 00:17:45,677
Today, the tallest peaks
are almost half this height.

237
00:17:47,767 --> 00:17:52,327
Unravelling the mystery of why and how
the Alps are disappearing

238
00:17:52,327 --> 00:17:57,196
is important to the 14 million people
who live in and around them.

239
00:17:58,767 --> 00:18:02,527
Illhorn mountain,
an extraordinary peak in the Swiss Alps,

240
00:18:02,527 --> 00:18:05,246
provides an essential clue.

241
00:18:08,487 --> 00:18:13,959
This mountain is almost 9,000 feet tall,
but hollow at its centre.

242
00:18:16,007 --> 00:18:18,367
Illhorn is rotten to the core.

243
00:18:18,367 --> 00:18:23,077
This massive hole is forming
as the mountain collapses in on itself.

244
00:18:24,927 --> 00:18:29,079
But what monumental force
is pulling this mountain down?

245
00:18:31,367 --> 00:18:35,127
It's made of a loose, unstable
mixture of rock and mud

246
00:18:35,127 --> 00:18:37,967
that originally came from the ocean floor.

247
00:18:37,967 --> 00:18:42,447
In winter, this mixture of rock
is glued together by ice,

248
00:18:42,447 --> 00:18:45,837
but in the spring thaw, it becomes loose.

249
00:18:48,847 --> 00:18:52,327
Here you can see the fact
that the rocks are very highly weathered,

250
00:18:52,327 --> 00:18:55,087
you can easily, uh, in fact
by hand, pull them apart,

251
00:18:55,087 --> 00:18:57,207
you can imagine that, uh...

252
00:18:57,207 --> 00:18:58,727
...in winter when the ice,

253
00:18:58,727 --> 00:19:01,127
when the water goes behind the rocks
and freezes,

254
00:19:01,127 --> 00:19:05,007
that it could actually mechanically,
uh, loosen the rocks,

255
00:19:05,007 --> 00:19:06,927
and in the spring they fall down.

256
00:19:06,927 --> 00:19:09,007
The whole mountain
is composed of these rocks,

257
00:19:09,007 --> 00:19:10,645
it's basically just falling apart.

258
00:19:19,167 --> 00:19:23,767
A combination of weak rocks and the
natural action of freezing and thawing

259
00:19:23,767 --> 00:19:27,127
has resulted in a crumbling mountain.

260
00:19:27,127 --> 00:19:31,847
In the last 10,000 years, 100 million tons
of Illhorn mountain has eroded

261
00:19:31,847 --> 00:19:38,047
and in the process hollowed out
a vast new valley, the lllgraben.

262
00:19:38,047 --> 00:19:41,327
But where has all the rock gone?

263
00:19:41,327 --> 00:19:46,367
Dr McArdell has come to explore
a deep, seemingly dry riverbed,

264
00:19:46,367 --> 00:19:49,127
which runs down from the heart
of the mountain

265
00:19:49,127 --> 00:19:50,765
and into the river Rhone.

266
00:19:52,807 --> 00:19:57,767
The evidence is hidden beneath
the village and vegetation -

267
00:19:57,767 --> 00:20:01,607
a large, fan-shaped platform of rubble,

268
00:20:01,607 --> 00:20:06,635
1,500 feet deep
and over one mile square.

269
00:20:09,687 --> 00:20:14,047
This structure is built from the sediment
delivered by the lllgraben catchment.

270
00:20:14,047 --> 00:20:17,407
All the sediment that you see
has come down from the mountain.

271
00:20:17,407 --> 00:20:21,647
But this dry riverbed
presents a mystery.

272
00:20:21,647 --> 00:20:26,407
How did vast amounts of debris get
transported down from the mountain?

273
00:20:26,407 --> 00:20:30,927
The Swiss village of Susten,
ground zero for the investigation,

274
00:20:30,927 --> 00:20:33,527
is in a constant state of alert.

275
00:20:33,527 --> 00:20:36,567
A few times a year,
the ground shakes here

276
00:20:36,567 --> 00:20:40,407
as if a gigantic freight train
is thundering through the village.

277
00:20:40,407 --> 00:20:42,047
(RUMBLING)

278
00:20:42,047 --> 00:20:46,040
(SIREN WAILS)

279
00:20:52,927 --> 00:20:57,796
In a flash, this dry channel
is flooded by a river of rock.

280
00:21:01,487 --> 00:21:06,117
Thousands of tons of debris flow
down from the Illhorn mountain.

281
00:21:07,127 --> 00:21:09,167
McARDELL: Anywhere between
three and five times a year,

282
00:21:09,167 --> 00:21:11,887
there's a large wave of sediment
moving downstream

283
00:21:11,887 --> 00:21:13,967
at anywhere
from 10 to 20 miles an hour,

284
00:21:13,967 --> 00:21:16,527
with a flow depth on the order
of up to 10 feet.

285
00:21:16,527 --> 00:21:19,967
And it moves down the channel rapidly
and anyone who's in the channel,

286
00:21:19,967 --> 00:21:21,605
of course, is in danger.

287
00:21:24,727 --> 00:21:29,127
Every time it rains,
debris cascades down the mountainside,

288
00:21:29,127 --> 00:21:34,076
making this one of the most
active debris flow zones on Earth.

289
00:21:36,167 --> 00:21:39,207
The Alps are basically being
washed down from the mountains,

290
00:21:39,207 --> 00:21:43,967
through the rivers and into the lakes,
into the valleys further downstream.

291
00:21:43,967 --> 00:21:49,087
Illhorn is an extreme case of an entire
mountain in the process of decay,

292
00:21:49,087 --> 00:21:53,638
resulting in one of the most dangerous
mountain terrains on the planet.

293
00:21:55,087 --> 00:21:58,767
But inherently unstable rocks
are found right across the Alps,

294
00:21:58,767 --> 00:22:02,646
and have created some of
the Alps' best beauty spots.

295
00:22:04,967 --> 00:22:08,960
Oeschinensee lake is a mile
above sea level and half a mile square.

296
00:22:11,167 --> 00:22:14,204
But in theory, this lake shouldn't be here.

297
00:22:16,247 --> 00:22:18,047
The streams
that pour off the mountain

298
00:22:18,047 --> 00:22:21,483
should run straight down
the valley unobstructed.

299
00:22:23,807 --> 00:22:27,167
A clue to what created this
high-altitude lake can be found

300
00:22:27,167 --> 00:22:30,079
1,000 feet up on the surrounding slopes.

301
00:22:31,607 --> 00:22:33,327
As we look up on the hill slopes,

302
00:22:33,327 --> 00:22:35,847
we see these very large
fans of debris

303
00:22:35,847 --> 00:22:38,441
that are coming down off
of these unstable slopes.

304
00:22:40,087 --> 00:22:44,407
Where we see this sort of smooth
bedrock that's dipping towards us,

305
00:22:44,407 --> 00:22:47,487
this is prime territory for landslides.

306
00:22:47,487 --> 00:22:49,207
When these mountains formed,

307
00:22:49,207 --> 00:22:53,883
flat sheets of sedimentary rock
were thrust up to rest at extreme angles.

308
00:22:54,927 --> 00:22:59,127
The joins between these stressed
and fractured rock layers frequently fail,

309
00:22:59,127 --> 00:23:04,042
causing huge layers of rock
to shear off the cliff faces.

310
00:23:05,207 --> 00:23:08,607
Much of these open slopes are
probably the result of sheets of rock

311
00:23:08,607 --> 00:23:11,326
peeling off and forming large landslides.

312
00:23:13,247 --> 00:23:15,807
It was a catastrophic landslide

313
00:23:15,807 --> 00:23:20,367
that caused this lake
to form 15,000 years ago.

314
00:23:20,367 --> 00:23:24,647
The entire side of the mountain
sheared off, blocking the valley

315
00:23:24,647 --> 00:23:26,607
and causing stream water to back up

316
00:23:26,607 --> 00:23:30,486
and create one of the Alps'
most breathtaking landscapes.

317
00:23:32,567 --> 00:23:34,087
It's all about gravity,

318
00:23:34,087 --> 00:23:36,167
gravity is what ultimately
brings down mountains.

319
00:23:36,167 --> 00:23:40,647
Rivers come in, debris flows form,
landslides form,

320
00:23:40,647 --> 00:23:43,525
and this sort of process is very common
throughout the Alps.

321
00:23:44,527 --> 00:23:48,727
Steep slopes and unstable rocks
have created a mountain range

322
00:23:48,727 --> 00:23:50,247
that is ever-changing.

323
00:23:50,247 --> 00:23:52,167
In only a few thousand years,

324
00:23:52,167 --> 00:23:57,480
gravity will also destroy Oeschinensee
lake, as debris flows fill it up.

325
00:23:58,887 --> 00:24:03,767
Over the last 30 million years, the Alps
have fallen down on a massive scale,

326
00:24:03,767 --> 00:24:08,247
in places decreasing
in height by 10,000 feet.

327
00:24:08,247 --> 00:24:12,007
So what has happened
to those thousands of feet

328
00:24:12,007 --> 00:24:15,363
and billions of tons of missing rock?

329
00:24:17,447 --> 00:24:22,760
A clue can be found in the rolling hills
a few miles north of the Alps.

330
00:24:26,127 --> 00:24:31,520
At Eggiwil, this rock outcrop contains
an extraordinary collection of stones.

331
00:24:33,367 --> 00:24:37,607
These are large cobbles, stones
that have come from all over the Alps,

332
00:24:37,607 --> 00:24:41,687
so if I look at some of these, for
example, this small white and black rock,

333
00:24:41,687 --> 00:24:44,407
this is a granitic rock that comes
from the centre of the Alps,

334
00:24:44,407 --> 00:24:46,567
somewhere very close to the Matterhorn.

335
00:24:46,567 --> 00:24:48,607
And we see, throughout this outcrop,

336
00:24:48,607 --> 00:24:51,201
rocks that come from different parts
of the Alps.

337
00:24:52,207 --> 00:24:55,127
Rocks from hundreds of
different scattered locations

338
00:24:55,127 --> 00:24:57,647
have travelled over 150 miles

339
00:24:57,647 --> 00:25:01,925
before being dumped
in this geologic rock graveyard.

340
00:25:03,247 --> 00:25:07,287
But it's the amount of material
here that's mind-boggling.

341
00:25:07,287 --> 00:25:12,247
These hills are made entirely of
rock debris from the nearby Alps.

342
00:25:12,247 --> 00:25:18,207
At 100 miles wide and 500 miles long,
they stretch in an arc round the Alps,

343
00:25:18,207 --> 00:25:21,847
running through France,
Switzerland and Germany.

344
00:25:21,847 --> 00:25:28,087
There's enough material here to cover all
of North America in 100 feet of rubble.

345
00:25:28,087 --> 00:25:33,527
Could this be where the thousands of
feet of missing Alpine rock have gone?

346
00:25:33,527 --> 00:25:35,967
A big mountain
range like the Alps is heavy,

347
00:25:35,967 --> 00:25:37,887
and it weights down the crust,

348
00:25:37,887 --> 00:25:40,526
forming a depression all the way
around the mountain range.

349
00:25:41,527 --> 00:25:45,247
A multi-trillion-ton mass of rock
was pushed up on land

350
00:25:45,247 --> 00:25:48,762
as Africa collided with Europe,
creating the Alps.

351
00:25:49,847 --> 00:25:53,047
The weight of the rock caused
the European crust to sink,

352
00:25:53,047 --> 00:25:57,767
making a huge depression, in places
over two and a half miles deep -

353
00:25:57,767 --> 00:26:00,235
the Molasse basin.

354
00:26:02,207 --> 00:26:04,807
Now, the importance of this depression
is it's a trap,

355
00:26:04,807 --> 00:26:07,167
all the sediment that we see
eroding off of the Alps

356
00:26:07,167 --> 00:26:10,287
is trapped in this basin
and ends up sitting there.

357
00:26:10,287 --> 00:26:14,807
Dating of these pebbles has revealed
that, ever since the Alps were created,

358
00:26:14,807 --> 00:26:19,607
rivers have washed Alpine debris
hundreds of miles downstream,

359
00:26:19,607 --> 00:26:23,287
dumping the rocks in this gigantic basin.

360
00:26:23,287 --> 00:26:26,887
So these rocks that we're
looking at here are the debris,

361
00:26:26,887 --> 00:26:31,007
the detritus that's come off of the Alps
over the last 20, 30 million years,

362
00:26:31,007 --> 00:26:33,847
these particular rocks
are almost 25 million years old.

363
00:26:33,847 --> 00:26:37,487
And what we see are cobbles, we see
little pieces of all the different rocks

364
00:26:37,487 --> 00:26:40,447
that we see throughout the Alps.

365
00:26:40,447 --> 00:26:44,607
For 30 million years, the debris eroded
from the Alps has been dumped

366
00:26:44,607 --> 00:26:49,807
in a 30,000-square-mile bowl,
creating this rolling chain of hills

367
00:26:49,807 --> 00:26:52,007
to the north of the Alps.

368
00:26:52,007 --> 00:26:56,167
This is where
the missing mountain rock is.

369
00:26:56,167 --> 00:26:58,407
Put it all back together and once again,

370
00:26:58,407 --> 00:27:01,319
there'd be mountains
as high as the Himalayas.

371
00:27:02,927 --> 00:27:07,087
Scientists have discovered how
the Alps have almost halved in height

372
00:27:07,087 --> 00:27:09,927
and where the missing rocks
have disappeared to.

373
00:27:09,927 --> 00:27:14,007
The clues are, inherently
unstable mixtures of rock,

374
00:27:14,007 --> 00:27:19,087
resulting in whole mountains falling
apart, debris flows on steep cliffs,

375
00:27:19,087 --> 00:27:23,287
proof that weakened layers of rock
shear off from the mountainsides,

376
00:27:23,287 --> 00:27:26,247
and a graveyard of pebbles
from all over the Alps,

377
00:27:26,247 --> 00:27:29,842
evidence that these mountains
have been washed away.

378
00:27:31,847 --> 00:27:36,447
But then, two million years ago,
the landscape changed dramatically.

379
00:27:36,447 --> 00:27:39,527
Vertical cliffs were carved into the Alps

380
00:27:39,527 --> 00:27:42,847
and giant spikes of rock
poked through the clouds.

381
00:27:42,847 --> 00:27:48,285
Another mighty force
had begun to resculpt the Alps.

382
00:27:50,127 --> 00:27:54,327
Over the last two million years,
a blink in geologic time,

383
00:27:54,327 --> 00:27:58,207
something has rapidly
and radically transformed the Alps,

384
00:27:58,207 --> 00:28:02,678
gouging giant peaks
and sheer rock faces.

385
00:28:05,727 --> 00:28:11,359
The most notorious rock formation
being the Eiger, in southern Switzerland.

386
00:28:13,127 --> 00:28:18,887
The infamous north face of the Eiger
is a 6,000 foot vertical climb.

387
00:28:18,887 --> 00:28:21,847
It's a terrifying, unrelenting ascent.

388
00:28:21,847 --> 00:28:28,127
Climbers face gale-force winds,
freezing fog, rockfalls and avalanche,

389
00:28:28,127 --> 00:28:32,678
giving the Eiger the reputation as one of
the most formidable climbs in the world.

390
00:28:34,927 --> 00:28:36,607
Nicknamed the Murder Wall,

391
00:28:36,607 --> 00:28:42,477
since 1935, more than
60 climbers have died here.

392
00:28:48,367 --> 00:28:52,767
How giant climbing walls like this were
formed had been a mystery to geologists

393
00:28:52,767 --> 00:28:59,647
until 1837, when Swiss scientist
Louis Agassiz noticed similar cliffs

394
00:28:59,647 --> 00:29:06,280
at lower altitudes, known to have been
made by a colossal force - glaciers.

395
00:29:07,447 --> 00:29:12,282
Over 1,000 glaciers wind their way
through the Alpine valleys.

396
00:29:13,487 --> 00:29:19,517
Imperceptible to the naked eye, these
giant rivers of ice slowly flow downhill.

397
00:29:21,127 --> 00:29:25,367
This time-lapse of the Aletsch glacier,
taken over a period of three years,

398
00:29:25,367 --> 00:29:30,327
reveals how glaciers
can move tens of feet a year.

399
00:29:30,327 --> 00:29:35,367
And where two glaciers meet,
a stripe of rock sits on the surface,

400
00:29:35,367 --> 00:29:40,647
proof that something extraordinary
is happening beneath the ice.

401
00:29:40,647 --> 00:29:47,487
A force which can transform jagged rock
into a surface as smooth as glass.

402
00:29:47,487 --> 00:29:52,117
We see here a smooth rock face
which was formerly covered by ice.

403
00:29:53,727 --> 00:29:59,367
Underneath the ice, there is this
rocks and sand, and it carries...

404
00:29:59,367 --> 00:30:02,047
...the ice carries this stuff with it

405
00:30:02,047 --> 00:30:06,887
and it acts like sandpaper
and polished this rock.

406
00:30:06,887 --> 00:30:11,887
But polishing alone cannot account for
the formation of the Alps' jagged peaks

407
00:30:11,887 --> 00:30:14,127
and the north face of the Eiger,

408
00:30:14,127 --> 00:30:17,005
where the sides of entire mountains
have been ripped off.

409
00:30:18,727 --> 00:30:20,927
More evidence of the awesome power
of glaciers

410
00:30:20,927 --> 00:30:23,447
can be found on these granite slabs.

411
00:30:23,447 --> 00:30:27,326
Deep cracks penetrate
the body of the rock.

412
00:30:30,967 --> 00:30:36,967
The ice was flowing over this rock face
and the ice could enter this crack.

413
00:30:36,967 --> 00:30:40,767
Meltwater forming beneath the glacier
seeps into the cracks,

414
00:30:40,767 --> 00:30:44,047
refreezes and splits open the rock.

415
00:30:44,047 --> 00:30:49,647
Weakened and fractured, huge chunks
of stone are ripped from the bedrock.

416
00:30:49,647 --> 00:30:54,367
Vast amounts of rock are plucked
and ground from the mountainsides

417
00:30:54,367 --> 00:30:57,564
and dumped in the lower,
warmer valleys when the ice melts.

418
00:30:59,327 --> 00:31:05,047
So here we are at the end,
the snout of the glacier.

419
00:31:05,047 --> 00:31:09,967
And here debris, water,
and rock boulders.

420
00:31:09,967 --> 00:31:14,887
This has been eroded by the glacier,
transported and moved to this place

421
00:31:14,887 --> 00:31:19,915
and this is the essential process,
how glaciers form the landscape.

422
00:31:22,327 --> 00:31:25,727
But how could glaciers have carved
the north face of the Eiger,

423
00:31:25,727 --> 00:31:28,967
and other mighty peaks
which rise thousands of feet

424
00:31:28,967 --> 00:31:31,162
out of reach of the abrasive ice below?

425
00:31:32,367 --> 00:31:35,607
Agassiz came up with a radical theory.

426
00:31:35,607 --> 00:31:39,927
He noticed these high rock faces
were scarred and gnarled.

427
00:31:39,927 --> 00:31:42,927
They had clearly been gouged by ice,

428
00:31:42,927 --> 00:31:46,761
like the glaciated valleys
he'd found at lower altitudes.

429
00:31:48,927 --> 00:31:50,407
Piecing the evidence together,

430
00:31:50,407 --> 00:31:54,127
he concluded towering cliffs
like the 6,000-foot Eiger

431
00:31:54,127 --> 00:31:58,120
were the handiwork
of ancient, gigantic glaciers.

432
00:31:59,607 --> 00:32:03,919
But if Agassiz was right, where
did the huge glaciers come from?

433
00:32:05,727 --> 00:32:10,807
The evidence lies locked inside
Europe's biggest river of ice,

434
00:32:10,807 --> 00:32:12,286
the Aletsch glacier.

435
00:32:13,967 --> 00:32:19,567
A massive 14 miles long, it covers
an area of more than 45 square miles

436
00:32:19,567 --> 00:32:22,167
and is up to 3,000 feet deep.

437
00:32:22,167 --> 00:32:25,127
The Aletsch glacier
in southern Switzerland

438
00:32:25,127 --> 00:32:30,121
has helped scientists understand
how all Alpine glaciers form.

439
00:32:32,567 --> 00:32:35,207
The source of the glacier
is high up in the mountains,

440
00:32:35,207 --> 00:32:39,120
where altitude brings freezing
temperatures and heavy snowfall.

441
00:32:40,527 --> 00:32:44,847
To explore how delicate snowfall
becomes a giant slab of ice,

442
00:32:44,847 --> 00:32:48,681
Dr Bauder ventures
deep into the heart of the glacier.

443
00:32:50,647 --> 00:32:55,487
This frozen passageway, 32 degrees
Fahrenheit and 60 feet deep,

444
00:32:55,487 --> 00:32:59,167
offers tourists and scientists
a unique window

445
00:32:59,167 --> 00:33:01,207
into the formation of a glacier.

446
00:33:01,207 --> 00:33:05,087
Here we can see
the inside of a glacier.

447
00:33:05,087 --> 00:33:11,481
We can see inside the ice.
We see here layers of air bubbles.

448
00:33:14,527 --> 00:33:19,327
And there are different,
distinct layers visible here, here, here,

449
00:33:19,327 --> 00:33:24,720
and they represent individual years
when this ice has been formed.

450
00:33:26,207 --> 00:33:31,127
The glacier grows by the build-up
of layer upon layer of snow.

451
00:33:31,127 --> 00:33:36,287
The newly fallen snow traps pockets of
air between the individual snowflakes,

452
00:33:36,287 --> 00:33:37,847
forming layers of bubbles.

453
00:33:37,847 --> 00:33:42,087
As more snow settles,
the flakes beneath become squashed,

454
00:33:42,087 --> 00:33:45,397
making them stick together to form ice.

455
00:33:46,967 --> 00:33:48,807
Forming over thousands of years,

456
00:33:48,807 --> 00:33:52,561
the amount of ice contained in
a single glacier can be staggering.

457
00:33:53,927 --> 00:33:59,887
It's been estimated that the Aletsch
glacier holds 27 billion tons of water,

458
00:33:59,887 --> 00:34:03,807
enough to provide every human on
Earth with two pints of water a day

459
00:34:03,807 --> 00:34:06,446
for the next six years.

460
00:34:07,487 --> 00:34:11,127
It's the air bubbles, trapped
inside the ice thousands of years ago,

461
00:34:11,127 --> 00:34:15,647
that hold the key to what carved
the Alps' distinctive shape.

462
00:34:15,647 --> 00:34:17,287
In the air bubbles,

463
00:34:17,287 --> 00:34:21,287
air is stored from the time when
the air bubbles have been formed.

464
00:34:21,287 --> 00:34:26,287
So we can analyse
the chemical composition inside there

465
00:34:26,287 --> 00:34:29,967
and learn about the climatic condition
at that time.

466
00:34:29,967 --> 00:34:33,287
When scientists analysed
miniature time capsules like these,

467
00:34:33,287 --> 00:34:36,727
they found air over 12,000 years old,

468
00:34:36,727 --> 00:34:41,567
with surprisingly low levels of
the greenhouse gas carbon dioxide.

469
00:34:41,567 --> 00:34:45,087
This meant that more heat was
escaping from the Earth's atmosphere,

470
00:34:45,087 --> 00:34:47,647
causing global temperatures
to plummet.

471
00:34:49,807 --> 00:34:53,567
Similar studies have revealed
that, for the last two million years,

472
00:34:53,567 --> 00:34:57,242
the Earth has been gripped
by a series of ice ages.

473
00:35:00,447 --> 00:35:02,967
Agassiz' theory was confirmed.

474
00:35:02,967 --> 00:35:04,927
Two million years ago,

475
00:35:04,927 --> 00:35:09,007
an enormous ice sheet engulfed
the Earth's northern hemisphere.

476
00:35:09,007 --> 00:35:14,207
The Alps were buried in ice
almost two miles thick.

477
00:35:14,207 --> 00:35:16,767
It was so deep that
only the tips of the mountains

478
00:35:16,767 --> 00:35:19,567
poked out above the ocean of ice.

479
00:35:19,567 --> 00:35:22,967
As the ice moved,
it whittled lone peaks

480
00:35:22,967 --> 00:35:25,927
and tore steep rock faces
high in the Alps,

481
00:35:25,927 --> 00:35:29,556
leaving its legacy on the landscape.

482
00:35:31,567 --> 00:35:33,127
It was during this time

483
00:35:33,127 --> 00:35:37,359
that giant glaciers carved
the infamous north face of the Eiger.

484
00:35:45,407 --> 00:35:48,407
In their mission to discover how
the Eiger and other great peaks

485
00:35:48,407 --> 00:35:54,687
in the Alps formed, scientists
have found cracks in granite bedrock,

486
00:35:54,687 --> 00:35:59,047
evidence that glaciers cleave masses
of rock from the mountainsides,

487
00:35:59,047 --> 00:36:03,247
and low levels of carbon dioxide,
trapped inside ice bubbles,

488
00:36:03,247 --> 00:36:09,247
prove that giant glaciers once carved
immense rock walls and pinnacles,

489
00:36:09,247 --> 00:36:12,927
which now tower over the landscape.

490
00:36:12,927 --> 00:36:15,687
10,000 years ago,
the great ice sheets melted,

491
00:36:15,687 --> 00:36:17,962
leaving their mark on the Alps.

492
00:36:18,967 --> 00:36:23,127
But today, the Alps are falling down
at a phenomenal rate.

493
00:36:23,127 --> 00:36:28,326
Something has propelled them into a
new and violent phase of their evolution.

494
00:36:31,447 --> 00:36:35,326
The Alps are falling down
at an accelerated rate.

495
00:36:37,447 --> 00:36:40,917
And millions of tons of rock
are crashing to Earth.

496
00:36:43,727 --> 00:36:46,407
A clue to what strange force
is at work here

497
00:36:46,407 --> 00:36:48,687
can be found high up in the mountains,

498
00:36:48,687 --> 00:36:51,767
where the remnants
of the last ice age lurk.

499
00:36:51,767 --> 00:36:57,807
Alpine glaciers physically prop up
mountains, binding the rock together.

500
00:36:57,807 --> 00:37:00,807
But these icy rivers are changing shape.

501
00:37:00,807 --> 00:37:03,567
Well, what we see in the background
here are glaciers

502
00:37:03,567 --> 00:37:10,407
which are separated, uh, by rocky
surfaces which are looking very fresh

503
00:37:10,407 --> 00:37:16,927
because they have been ice covered
in the last, uh, few hundred, uh, years.

504
00:37:16,927 --> 00:37:20,327
Uh, if you look across here
to Theodul glacier, we can see

505
00:37:20,327 --> 00:37:25,647
that actually, right next to the ice, uh,
there is some, uh, greyish material

506
00:37:25,647 --> 00:37:27,447
next to the brownish material.

507
00:37:27,447 --> 00:37:34,887
That's exactly the limit up to where
the glacier was, uh, in 1874.

508
00:37:34,887 --> 00:37:40,678
So you see how much of this ice has
melted down in these 130, uh, years.

509
00:37:41,687 --> 00:37:45,007
Scientists believe global warming
is melting the ice

510
00:37:45,007 --> 00:37:48,167
faster than at any other time
in the Alps' history.

511
00:37:48,167 --> 00:37:53,247
And as the glaciers shrink,
they expose steep, unsupported cliffs

512
00:37:53,247 --> 00:37:57,763
that are prone to fall down,
increasing the risks of landslides.

513
00:37:59,647 --> 00:38:01,407
But scientists have discovered

514
00:38:01,407 --> 00:38:04,843
another way melting glaciers
are weakening the Alps.

515
00:38:07,247 --> 00:38:09,487
When these frozen reservoirs melt,

516
00:38:09,487 --> 00:38:12,767
millions of gallons
of water gush downhill,

517
00:38:12,767 --> 00:38:15,565
feeding the great rivers of Europe.

518
00:38:18,927 --> 00:38:22,727
Like liquid sandpaper,
this torrent scrapes over the rocks,

519
00:38:22,727 --> 00:38:26,322
hollowing out the land
at an accelerated rate.

520
00:38:30,647 --> 00:38:34,207
The dramatic evidence of this
dynamic process can be found

521
00:38:34,207 --> 00:38:36,880
in the valley of Lauterbrunnen.

522
00:38:39,527 --> 00:38:42,847
Echoing through this valley
is the sound of one of the loudest

523
00:38:42,847 --> 00:38:48,080
and most spectacular water features
in the Alps, Trümmelbach Falls.

524
00:38:53,407 --> 00:38:56,047
You can just feel
the pulsing of the water.

525
00:38:56,047 --> 00:38:58,247
This is... the name Trümmelbach

526
00:38:58,247 --> 00:39:00,007
actually means drum sound,

527
00:39:00,007 --> 00:39:06,167
and this is reflecting this, this pulsing,
throbbing that we can hear and feel

528
00:39:06,167 --> 00:39:09,204
from the water flowing down
through these caves.

529
00:39:11,247 --> 00:39:15,247
Trümmelbach
is a spectacular glacial waterfall.

530
00:39:15,247 --> 00:39:20,287
Over 5,000 gallons of meltwater
a second hurtle down from glaciers

531
00:39:20,287 --> 00:39:23,207
on the nearby Eiger
and Jungfrau mountains.

532
00:39:23,207 --> 00:39:26,487
Over hundreds of years,
this abrasive jet-stream

533
00:39:26,487 --> 00:39:30,487
has sliced through the mountain,
creating a narrow canyon.

534
00:39:30,487 --> 00:39:34,327
Each year, from the Swiss Alps alone,
there's enough rock removed

535
00:39:34,327 --> 00:39:39,162
by the glacial meltwaters to create
a mountain more than half a mile high.

536
00:39:42,207 --> 00:39:47,998
But Trümmelbach, like other Alpine
waterfalls, is living on borrowed time.

537
00:39:51,087 --> 00:39:53,927
As meltwater thunders down
the waterfalls,

538
00:39:53,927 --> 00:39:56,521
it cuts into the rock, weakening it.

539
00:39:57,607 --> 00:40:01,767
Over time, these steep cliffs
left by the glaciers crumble,

540
00:40:01,767 --> 00:40:05,487
replaced by ever deepening river valleys.

541
00:40:05,487 --> 00:40:07,447
WILLOTT: Today,
the rivers that are now returning

542
00:40:07,447 --> 00:40:09,167
are trying to carve a river valley,

543
00:40:09,167 --> 00:40:13,287
which has a very different shape and
different form, changing this landscape.

544
00:40:13,287 --> 00:40:16,567
All of these processes
come in and destroy that high relief

545
00:40:16,567 --> 00:40:18,567
that the glaciers have left behind.

546
00:40:18,567 --> 00:40:22,447
Very dynamic processes,
very rapid erosion, very rapid processes

547
00:40:22,447 --> 00:40:24,847
that cannot be sustained
over geologic time.

548
00:40:24,847 --> 00:40:30,087
For the last 150 years, global warming
and the resulting glacial melt

549
00:40:30,087 --> 00:40:32,442
has caused a huge amount of erosion.

550
00:40:34,127 --> 00:40:37,607
Experts warn,
if this warming trend continues,

551
00:40:37,607 --> 00:40:40,447
the Alps will be ice free
by the end of the century

552
00:40:40,447 --> 00:40:44,727
and fear these great mountain peaks
will tumble down even faster.

553
00:40:44,727 --> 00:40:49,807
Weakened rocks and the increased risk
of catastrophic landslides

554
00:40:49,807 --> 00:40:55,007
could spell disaster for villages
and resorts high up in the Alps.

555
00:40:55,007 --> 00:40:57,207
But a look back to ancient times

556
00:40:57,207 --> 00:41:00,404
reveals that the Alps
have been in meltdown before.

557
00:41:02,167 --> 00:41:04,447
In the autumn of 218 BC,

558
00:41:04,447 --> 00:41:08,927
the mighty Hannibal led an army
of 50,000 men and 40 elephants

559
00:41:08,927 --> 00:41:12,044
across the Alps to attack the Romans.

560
00:41:13,167 --> 00:41:18,767
An arduous 15-day trek across
the most treacherous terrain in Europe.

561
00:41:18,767 --> 00:41:23,887
Many men fell to their deaths
along the perilously narrow tracks.

562
00:41:27,007 --> 00:41:29,727
But Hannibal's audacious plan paid off.

563
00:41:29,727 --> 00:41:34,357
His army pushed on through Italy
to defeat the Romans.

564
00:41:36,247 --> 00:41:39,167
Today, Hannibal's route
is virtually impassable,

565
00:41:39,167 --> 00:41:42,767
blocked by ice and deep snow.

566
00:41:42,767 --> 00:41:46,287
Scientists realised that
when Hannibal crossed the Alps,

567
00:41:46,287 --> 00:41:49,047
the mountain passes
must have been ice free

568
00:41:49,047 --> 00:41:52,926
and the glaciers must have retreated
further back than they are today.

569
00:41:54,807 --> 00:41:57,287
It may have been a bit of a walk through
the forest for him,

570
00:41:57,287 --> 00:42:00,127
at least much of the way,
and certainly a... an easier time

571
00:42:00,127 --> 00:42:03,447
to travel through the Alps than
we would have today, for example.

572
00:42:03,447 --> 00:42:06,607
Past changes
in the Earth's tilt towards the sun

573
00:42:06,607 --> 00:42:09,887
have caused glaciers
to melt and refreeze

574
00:42:09,887 --> 00:42:12,687
in response to a fluctuating climate.

575
00:42:12,687 --> 00:42:18,047
If history repeats itself, glaciers
will, sometime in the distant future,

576
00:42:18,047 --> 00:42:21,247
naturally return to the Alps.

577
00:42:21,247 --> 00:42:23,967
WILLOTT: These advances
and retreats of the ice

578
00:42:23,967 --> 00:42:28,404
are very important to the overall rate
at which the Alps are being eroded.

579
00:42:29,807 --> 00:42:34,967
It's this natural cycle from glaciers
carving cliffs, to rivers cutting valleys,

580
00:42:34,967 --> 00:42:40,041
and back again, that has created
a mountain range that is ever-changing.

581
00:42:41,967 --> 00:42:44,087
And it's this natural process

582
00:42:44,087 --> 00:42:47,124
that will ultimately destroy the Alps
as we know them.

583
00:42:51,207 --> 00:42:53,807
The Alps are
slowly being destroyed.

584
00:42:53,807 --> 00:42:57,527
We'll probably see more glacial
advances and retreats

585
00:42:57,527 --> 00:42:58,887
that will begin to erode them down.

586
00:42:58,887 --> 00:43:02,647
So, if we were to come back
in 10, 20, maybe 100 million years,

587
00:43:02,647 --> 00:43:05,167
we would still find a mountain range
here today.

588
00:43:05,167 --> 00:43:07,807
The Appalachians of Eastern U.S.,
for example,

589
00:43:07,807 --> 00:43:10,487
remain a... at least a small,
subdued mountain range,

590
00:43:10,487 --> 00:43:12,487
and that will be the future of the Alps.

591
00:43:12,487 --> 00:43:15,247
The Alps will shrink to half its size

592
00:43:15,247 --> 00:43:19,035
and become a mountain chain
less than 6,000 feet high.

593
00:43:20,487 --> 00:43:23,847
Stunted in height, no glaciers
will cap these mountains,

594
00:43:23,847 --> 00:43:26,441
nor feed the great rivers of Europe.

595
00:43:28,367 --> 00:43:31,767
Millions of years from now,
the vast lowlands of France,

596
00:43:31,767 --> 00:43:36,397
Germany and Eastern Europe
could one day be barren and parched.

597
00:43:39,087 --> 00:43:41,927
Scientists have discovered
how the Alps formed

598
00:43:41,927 --> 00:43:44,236
and why they're tumbling down.

599
00:43:45,287 --> 00:43:50,927
Marine fossils and limestone made
from trillions of seashells are proof

600
00:43:50,927 --> 00:43:54,407
that Alpine rocks formed
at the bottom of the sea.

601
00:43:54,407 --> 00:43:58,327
Grey gneiss rocks at the top
of the Matterhorn are evidence

602
00:43:58,327 --> 00:44:01,876
that Africa collided with Europe,
forming the Alps.

603
00:44:03,207 --> 00:44:05,927
Landslides are proof
that sedimentary layers,

604
00:44:05,927 --> 00:44:10,727
and sometimes whole mountains,
are inherently weak and collapsing.

605
00:44:10,727 --> 00:44:13,567
Gases trapped in ancient
ice bubbles reveal

606
00:44:13,567 --> 00:44:18,038
that giant glaciers carved out
the rugged landmarks of the Alps.

607
00:44:19,847 --> 00:44:25,367
And shrinking glaciers and waterfalls are
weakening the Alps, creating a skyline

608
00:44:25,367 --> 00:44:27,119
which is constantly changing.

609
00:44:28,887 --> 00:44:33,005
Since they were created,
the Alps have continued to evolve.

610
00:44:34,087 --> 00:44:36,527
One of the most varied,
spectacular

611
00:44:36,527 --> 00:44:39,527
and intensely studied
mountain ranges on Earth,

612
00:44:39,527 --> 00:44:41,647
understanding how the Alps were made

613
00:44:41,647 --> 00:44:43,607
has unlocked deep secrets

614
00:44:43,607 --> 00:44:46,644
of the powerful forces
that shape our planet.