Landslides Fierce Earth


Landslides

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On today's Fierce Earth...

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When the ground lets us down.

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Danger from above!

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The island being eaten away by the sea.

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Danger from below.

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Exploring the secret world of the sinkhole.

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Danger all around!

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Look out for the landslide!

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What happens when the ground shakes, the seas rise up

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and the air tears itself apart?

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The Fierce Earth team move in,

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taking on the most powerful forces on the planet.

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Get ready for Fierce Earth -

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the Earth and how to survive it.

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Rock, earth, debris...

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a landslide is any or all of these things,

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moving down a slope, en masse.

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Landslides can be big, they can be small.

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They can happen slowly or be over in seconds.

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One thing is for certain, though -

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if you're above, or if you're below, landslides can mean big trouble.

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Houses, roads, people - they're all at risk

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when the solid ground we take for granted gives way.

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Today, we're going to find out

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exactly why the earth can suddenly move,

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and how humans survive in the shadow of the landslide.

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There are four main types of landslides.

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The fall, where material breaks off from a cliff, or a steep slope,

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and tumbles down.

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The topple, where a big chunk falls forward

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from the top of a slope.

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Next, we have the slide, a mass of material slides down the slope

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along a clean break.

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And, finally, the flow.

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Material flows down the slope as a liquid, like mudflows.

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Landslides occur all over the world

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and are often triggered as a result of earthquakes or volcanoes.

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But there is one country with no volcanoes

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and few earthquakes that is still at risk from landslides,

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a country usually spared the worst of the Fierce Earth.

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And that country is the United Kingdom.

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Whoo!

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The UK is under attack from all sides by the sea.

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Lashed by the wind from the Atlantic,

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enduring snow and ice every winter.

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And let's not forget the rain.

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All these things create erosion, one of the major causes of landslides.

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In the UK, they tend to be slow moving and rarely cause injuries,

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but landslides can still be seriously destructive.

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And there's one little island here that really takes a battering.

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This is the Isle of Wight in the English Channel.

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It's like the UK in miniature,

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surrounded by 100 kilometres of coastline.

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No-one lives very far from the water

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and because of that, landslides have become a part of life.

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The Needles are the Isle of Wight's most famous landmark -

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a series of chalk stacks rising out of the sea.

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The Needles are absolutely stunning,

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but they're the clearest example

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that erosion is slowly shrinking the island

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and causing landslides.

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Once upon a time, the Needles would have been arches

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and, before that, cliffs.

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Like the rest of the UK, the coastline here is always changing.

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Roads might have to be re-routed,

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houses abandoned and demolished before they fall into the sea,

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but it's the same story across much of the UK.

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So what's going on?

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Coastal erosion is what's going on.

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The sea attacking the land and it never gives up.

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The sea is moving constantly, isn't it?

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Every day, every night, wearing away at the cliffs

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that make up the coast.

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As bits fall off the cliff, they're washed back again by the waves,

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acting like giant sandpaper, scouring away.

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The waves undercut the rock at sea level,

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and the land above gives way - a landslide.

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They say an Englishman's home is his castle,

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but he'd better watch out where he builds it.

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The softer the rock, the more at risk it is from erosion,

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and there's a lot of soft, white chalk on the Isle of Wight.

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But tougher rock is no match for water, either,

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and erosion causes rock falls all over the UK.

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Leo is in Scotland to find out how.

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The River Spean in the West Highlands.

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It wends its way through spectacular gorges cut through solid rock.

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Gorges cut by the power of water,

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but not just this bit of water, that kind of water.

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My kind of water.

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Flowing water erosion has caused rock falls

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and landslips that have left the river bed littered with debris -

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anything from small stones to huge boulders.

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They churn up the water

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and create some of the most spectacular rapids in the UK.

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And I'm going to take on those rapids in this...

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Here we go.

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..a River Bug.

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This tiny, white-water raft will let me really experience

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the fierce power of the water as it races through the rock.

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Rapids are dangerous,

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so I'll be watched over every splash of the way

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by white-water specialist Joe.

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So it's quite a rocky river.

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What happens if I'm going to crash into a big rock?

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If you're going backwards, that's fine,

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this big air packet behind you, this air bag, acts a bit like a cushion.

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If you're going forward, however, you get your legs out in front

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but keep your knees soft.

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-So you can fend yourself off?

-Exactly.

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If you come across a boulder, just push off with your feet

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and push yourself back into the flow, where the water's nice and deep.

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-Ready to rock'n'roll?

-Let's do this!

-Excellent.

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I'm going to have to get good at this fast, but, remember,

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I've had training from an expert. Never attempt this on your own.

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Agh!

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Ah!

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Not exactly the line I was hoping for!

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Agh!

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A slight lack of control, but really good fun.

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Rapids show us that a gentle river can suddenly gain dangerous power -

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a good reason never to explore rivers unaccompanied.

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But water doesn't have to flow quickly to erode.

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Even the tiniest particles carried along in the water

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help scour away the rock.

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This is how the river could have looked thousands of years ago.

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And this is how it looks now.

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Even now, when the water seems quite calm,

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it's working its way slowly, slowly,

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eating away at the rock, carving its way deeper.

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In millions of years, who knows how deep it will be?

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I hear rapids!

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Sounds terrifying!

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Rivers that descend steeply tend to erode downwards

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and cut high, V-shaped banks.

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Landslides are more likely to occur here than on gentler,

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wider rivers with more sideways erosion.

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The eroded rocks, close up, are almost alien.

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They're smooth and fluid,

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and look like a frozen version of the water that has shaped them.

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You see these deep channels that have been cut down into the rock?

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Well, these pebbles scoured them out

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over thousands and thousands of years.

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You know when you pull a plug out of your bath tub?

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It makes those little whirlpools.

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That's kind of what happens in the river - they're called eddies.

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These pebbles go round and round

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and scour out these beautiful channels.

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It's been a real privilege to travel this gorge,

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going with the flow

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like one of the billions of tiny floating particles,

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dwarfed by the very cliffs they help create.

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2012 was wet.

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It rained and it rained

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and it rained.

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By December, it had been officially declared

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the second wettest year since records began.

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And then, at Christmas, this happened.

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A massive landslide tore a huge chunk of land

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off the north coast of the Isle of Wight.

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It destroyed the concrete sea wall

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that was protecting the slope from wave erosion.

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So if the sea didn't cause this landslide, what did?

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Everyone who grows up on the Isle of Wight knows the warning signs

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to look for. Danny and Kieran live nearby.

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You start to see sort of cracks

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and, occasionally, some rocks tumbling down,

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so it gradually slips away.

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Eventually, it just goes.

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Also, when just little chunks

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of rock fall down

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and they're soft, so as they're falling down,

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they break into littler bits.

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That's also a sign that the land could go any minute.

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If you feel how soft the rock is.

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That's really quite soft.

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That would give way quite easily.

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That's basically what we're walking along.

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At the top, it's the mud that's just dried up

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that makes it hard and seem like it's all right.

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But, underneath, it's really soft.

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We have special permission to visit

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the foot of the recent giant landslide, now thought to be stable.

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The same can't be said for the path.

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I can't believe... This path, you used to be able to walk along it,

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but the full force pushed this pathway right out into the sea.

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It used to be a straight path.

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It used to have no cracks.

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It used to be good for walking, cycling, running.

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-It was never an empty path.

-It is really scary.

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If you look, at the earth that was there, now,

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it used to be up on that thing.

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We didn't actually put the cracks and all the things together

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to come up with the idea of a landslide, so we were like, "What?!"

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This all sounds quite scary to me,

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but Danny and Kieran have grown up with landslides.

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If you're a bit worried about it, don't worry,

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cos it will come down, usually, quite slowly,

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so you should be able to get away.

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Also, the best safety precautions are put in place,

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so if there is any risk of a landslide,

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the path will be sealed off,

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so there's no risk that anybody can get hurt.

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After safety checks,

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I'm allowed to walk out further onto the landslide itself.

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It really brings home the forces locked within the land.

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Forces that a sea wall is powerless to control.

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Standing here on the landslide,

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you can really feel the power of the rocks

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that must have forced their way down,

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pushing the concrete path there out,

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like it was a piece of paper. So what happened?

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The landslide started behind the sea wall,

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so it couldn't have been caused by sea erosion from the waves.

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But 2012 was the second wettest year on record.

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Here's the monthly rainfall.

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And, according to the

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British Geological Survey,

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there were way more landslides

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than usual,

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shown here in green. In December,

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around five times as many.

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If you compare the monthly rainfall

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with the number of landslides,

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they follow the same pattern,

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so the record rain is causing the record landslides.

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With the help of Kieran, Danny and his mates,

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I am going to show you how rain can cause landslides

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even miles away from the sea. But first, we have to build a hill.

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On your way, guys!

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'The ground we stand on is made up of different sorts of material.'

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We're building our hill on a rock which is impermeable,

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which means it doesn't soak up water.

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But some rock is permeable, which means it does soak up water,

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just like this sand.

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These different types of rock can make a big difference

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when it comes to landslides.

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So, thanks to these guys, I've got my hill

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and I've learned my lesson from last time,

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so I built the castle on top of it.

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But, oh, no, this is the UK

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and the one thing we can rely on is the rain.

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-Oh!

-SHE LAUGHS

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As the rain falls on the hills, some water runs off as rivers.

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But if the ground is permeable, it soaks up the rain

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and starts to get heavier, like our sand here.

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Add in other danger factors, like a steep slope,

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weaker or impermeable rock below,

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and you have the perfect recipe for instability.

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Our wet, heavy, rock begins to slide.

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ALL: Yes!

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-Yes!

-Nearly, nearly!

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The Isle of Wight has it tough, with both the sea

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and weather causing landslides.

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But stick around because the islanders are fighting back.

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Later in the show, I'll be taking the battle against landslides

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to new heights. Plus, the amusement park

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where the ground itself is a white-knuckle ride.

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But first, Dougal is in Yorkshire to find out how underground water

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creates the most feared land

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movement of them all.

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This is a sinkhole.

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Houses, cars,

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even whole street blocks, have been damaged

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when the ground suddenly gives way.

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And if you want to know what causes these awesome phenomena, you can

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find them right here in the UK, where they're not quite as scary -

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unless you're hanging over the edge of one.

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This is Alum Pot, a gigantic sinkhole

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in the Yorkshire Dales that's 80m deep.

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You could fit Nelson's Column in there.

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It's beautiful from here, but a little scary from the edge.

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But like everything on our fierce Earth,

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sinkholes are a lot less scary when you understand them.

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Woo!

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This area in the Yorkshire Dales is what's known as a karst landscape,

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a type of land recognisable by its pitted surface

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and numerous sinkholes.

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Karst formations can be found across the UK

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and they're all made of the same type of rock - limestone.

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Here is a stunning example of a limestone pavement.

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The rocks beneath my feet are riddled with holes,

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a bit like a wood-infested floorboard,

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and it's this landscape that holds the key to sinkholes.

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This amazing eroded rock only hints at the fierce forces

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at work in these peaceful valleys.

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The real action is deep underground.

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This is how sinkholes happen.

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Here is a mini-version of the landscape that's all around us.

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The sugar cubes beneath

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are the limestone that you can see that I am sitting on,

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and the sand above is the soil on top.

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Just like the limestone, the sugar cubes are strong,

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but they can also be dissolved in water.

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Mmm. Tasty.

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So what happens when it rains?

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As the water pours down on to the soil, it filters down through,

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until it hits the limestone - the sugar cubes in this example.

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There, it can start to dissolve the limestone.

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Rainwater is naturally acidic and this aids that process.

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The limestone dissolves, the sugar cubes dissolve,

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they leave hollows

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and the ground literally falls from underneath your feet.

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That's how you make a sinkhole.

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This erosion is exactly what created Alum Pot.

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The underground water here has built a cave system that will lead me

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right into the centre of the giant sinkhole itself.

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You should never, ever enter caves unaccompanied,

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so I've got expert caver, Jane, as my guide.

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One of the underground streams breaks the surface

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a couple of hundred metres from the pot.

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This is our entrance into the secret world of sinkholes.

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As the stream enters the cave system,

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you can see how it's opening out the cracks,

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dissolving, carving, sculpting the rock

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as it plunges further and further into the Earth,

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and that's where we're going to follow it.

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There you go. Down you go. Don't fall in,

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but, if you do, don't worry.

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There is a very cold pool at the bottom to catch you.

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-There's a cold pool to stop me.

-Very cold.

-Oh!

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-Hold on tight!

-OK.

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The path of the stream soon splits and becomes harder to follow.

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The cave system is like a maze built by water, as it squeezes

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and eats its way relentlessly through the limestone.

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It's getting really tight now.

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'Things are about to get a lot tighter.'

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They call this gap the Cheese Press.

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Apparently, I've got to squeeze through this

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to get to the other side.

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I don't even think my helmet can make it through.

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You might have to take your helmet off, but you can get through.

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Wish me luck.

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HE LAUGHS This is incredible!

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Phew!

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Now I know why they call it the Cheese Press! Oh!

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I really hope there's another way out of here.

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Just look at this!

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You can actually see the cracks and joints in the rock

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where the water's percolating through and dissolving it.

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And, here...

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Here's a big chunk of rock that's fallen from just up there. Bang!

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There's thousands of tonnes of rock above our head

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and the river is still going deeper and deeper into the Earth.

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This process has been happening for thousands and thousands of years

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and it's still happening today.

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Wow!

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Not many people get to crawl through the secret plumbing of the Earth.

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The water that is endlessly at work is leading us closer to our goal -

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a view of the giant Alum Pot sinkhole that few ever see.

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One last obstacle remains.

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It has to be the thinnest ladder I've ever been on.

0:20:110:20:14

Light at the end of the tunnel!

0:20:140:20:16

And what a light it is.

0:20:170:20:20

The stream has brought me back to where my journey began,

0:20:200:20:24

to the incredible sinkhole the water itself created - Alum Pot.

0:20:240:20:28

Ominous from above,

0:20:290:20:31

a wondrous secret world from below.

0:20:310:20:34

That's amazing! Wow!

0:20:380:20:42

I started my journey just up there, skipped down waterfalls,

0:20:450:20:49

literally been squeezed through the Earth

0:20:490:20:51

and I've come here to see Alum Pot in its full glory.

0:20:510:20:54

I just want to go one stage further.

0:20:540:20:57

My final goal is suspended in the very middle of the abyss...

0:21:010:21:05

..a precarious, fallen boulder.

0:21:060:21:08

My journey to this spot has been tough

0:21:120:21:15

and not something you should ever attempt without an expert guide.

0:21:150:21:19

But standing in the centre of this incredible sinkhole,

0:21:190:21:22

it's been more than worth it.

0:21:220:21:24

The powerful forces that cause landslides

0:21:340:21:36

are never going to go away.

0:21:360:21:39

So how do humans deal with the risk?

0:21:390:21:42

Here on the Isle of Wight,

0:21:420:21:43

islanders know better than most people

0:21:430:21:46

that what goes up

0:21:460:21:48

must come down!

0:21:480:21:51

Whoo-hoo!

0:21:510:21:53

Blackgang Chine is the oldest amusement park in the world.

0:22:000:22:05

It first opened in 1843

0:22:050:22:07

and generations of families have come here

0:22:070:22:10

since the island became fashionable in Victorian times.

0:22:100:22:13

The park has changed a lot since then,

0:22:130:22:16

but so has the very land it sits on.

0:22:160:22:19

The chine that gives Blackgang its name

0:22:190:22:22

came close to destroying it.

0:22:220:22:24

A chine is a narrow gorge on the coast, formed by water erosion.

0:22:270:22:32

The small chine at Blackgang

0:22:320:22:34

has grown into a vast gash in the coastline,

0:22:340:22:37

with landslides sitting on top of landslides.

0:22:370:22:41

Erosion rates average four metres a year,

0:22:410:22:43

but heavy rains have seen losses of up to 40 metres in one year.

0:22:430:22:48

The park is being eaten away.

0:22:480:22:51

The last major landslide here was in 1994,

0:22:510:22:54

when a third of the existing park moved.

0:22:540:22:58

If you look really carefully, you can see the remains

0:22:580:23:01

of the old Wild West-themed area that had to be abandoned.

0:23:010:23:05

Was Blackgang Chine about to go the way of dinosaurs?

0:23:150:23:20

You don't keep going for 170 years without learning a few tricks.

0:23:200:23:25

The chine is constantly monitored for movement,

0:23:250:23:27

so nobody was hurt when the Wild West finally slipped away.

0:23:270:23:31

The owners of the park did what they had always done - regrouped,

0:23:310:23:35

re-planned and rebuilt.

0:23:350:23:38

This is the new Wild West area, built on higher, more stable ground.

0:23:380:23:42

In summer, 5,000 people a day come here,

0:23:420:23:45

most of them oblivious to the challenges

0:23:450:23:47

that winter rains bring to Blackgang Chine.

0:23:470:23:50

An amusement park that has adapted to the times and landslides.

0:23:500:23:54

Just along the coast from Blackgang Chine,

0:23:570:24:00

a very 21st-century battle against landslides is taking place,

0:24:000:24:05

and the islanders are winning.

0:24:050:24:07

Work is going on all across the Isle of Wight

0:24:080:24:10

to make sure the coast is safe.

0:24:100:24:12

It's happening above me right now -

0:24:120:24:14

it's called landslide mitigation - and it's a massive job.

0:24:140:24:18

After all, they're holding a cliff together.

0:24:180:24:21

The clifftop path here is popular with local walkers,

0:24:230:24:26

but a recent landslip means it's too dangerous to use.

0:24:260:24:30

And the Hideaway Cafe is in danger of slipping away.

0:24:300:24:34

In the past, the path might have been left to disappear,

0:24:340:24:37

but modern techniques mean there's hope for the cafe yet.

0:24:370:24:41

The council has called in an expert landslide mitigation team

0:24:410:24:45

to make the cliff safe over a sheer drop 40 metres above the beach

0:24:450:24:49

and I'm the newest recruit.

0:24:490:24:51

-You feel nice and snug?

-Yes.

-OK, brilliant. Come round here. OK?

0:24:510:24:56

-'Simon shows me the ropes...'

-Right, you can pull across this way.

0:24:560:24:59

'..and pulleys...'

0:24:590:25:00

-That's you descending.

-'..and levers.'

0:25:000:25:02

If you want to stop, you can let go of everything

0:25:020:25:04

-and that pulls tight.

-Good.

0:25:040:25:07

-That's nice and secure. You do have to trust this kit.

-You do.

0:25:070:25:11

If I step down here, and then you can follow me down.

0:25:110:25:15

-Lovely!

-Whoo, incoming!

-Yeah, no problem.

0:25:150:25:18

'The wooden wall is the first step in making the coastal path safe.

0:25:180:25:22

'It will reinforce the path foundations by stopping them

0:25:220:25:25

'from sliding in wet weather, so it has to be very secure.'

0:25:250:25:29

And we are pretty much ready to go.

0:25:290:25:31

Whoo!

0:25:310:25:32

-We are just going to let the drill do the work.

-Yep.

0:25:340:25:36

OK, pull backwards.

0:25:390:25:41

'Longer and longer drill bits are added

0:25:420:25:44

'as we drill deeper and deeper.'

0:25:440:25:46

We are going to go back in again.

0:25:460:25:49

'It's a tough job drilling two metres into the sticky, wet clay.'

0:25:490:25:53

Woo!

0:25:530:25:55

-OK.

-'Two-metre hole drilled.'

0:25:560:25:59

'Time to insert a two-metre reinforced steel bolt

0:25:590:26:02

'to hold up the wood that's holding up the earth

0:26:020:26:05

'that's holding up the path!'

0:26:050:26:07

-That's right.

-OK.

-He's going to sit over the end.

-There we go.

0:26:070:26:11

-Fantastic.

-How long do you think this will last,

0:26:110:26:13

-a structure like this?

-More than our lifetime, hopefully.

-Wow!

0:26:130:26:17

'The path is on its way to being rebuilt.

0:26:170:26:19

'Next job is to secure the loose earth below with plastic mat

0:26:190:26:23

'and wire netting.

0:26:230:26:25

'The holes allow plants to regrow through into the slope

0:26:250:26:28

'and bind the earth together with their roots.

0:26:280:26:31

'Stability with a little help from mother nature.'

0:26:310:26:35

You can't even see the rock netting now

0:26:350:26:36

and that's what we want. We want lots of vegetation

0:26:360:26:39

to help stick everything on the top together.

0:26:390:26:42

Nice and tight on there.

0:26:440:26:45

-This is the final one.

-Lovely. I'll just put my foot on there.

-Yep.

0:26:480:26:51

And we'll feed him round and underneath.

0:26:510:26:54

'Since the early 1990s, the council here has spent

0:26:540:26:57

'over £5 million on cliff stabilisation.'

0:26:570:27:00

Landslides will always be with us here in the UK.

0:27:000:27:03

The waves will always pound at the coast

0:27:030:27:05

and, let's face it, the rain will always fall.

0:27:050:27:09

But the human ingenuity

0:27:090:27:10

in the face of the Fierce Earth will always remain.

0:27:100:27:14

Although landslides that injure people are rare,

0:27:150:27:18

they are one threat that will never go away.

0:27:180:27:21

But we can learn to live alongside them,

0:27:210:27:24

analysing the ground, controlling the risks

0:27:240:27:29

and rebuilding when needed.

0:27:290:27:32

This is how we maximise our chances of surviving the Fierce Earth.

0:27:320:27:37

Next time, things are hotting up underground.

0:27:390:27:42

And I dive to the spot where the Earth tears itself apart.

0:27:440:27:47

Wish me luck.

0:27:470:27:48

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