Landslides Fierce Earth

On today's Fierce Earth...

When the ground lets us down.

Danger from above!

The island being eaten away by the sea.

Danger from below.

Exploring the secret world of the sinkhole.

Danger all around!

Look out for the landslide!

What happens when the ground shakes, the seas rise up

and the air tears itself apart?

The Fierce Earth team move in,

taking on the most powerful forces on the planet.

Get ready for Fierce Earth -

the Earth and how to survive it.

Rock, earth, debris...

a landslide is any or all of these things,

moving down a slope, en masse.

Landslides can be big, they can be small.

They can happen slowly or be over in seconds.

One thing is for certain, though -

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

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

when the solid ground we take for granted gives way.

Today, we're going to find out

exactly why the earth can suddenly move,

and how humans survive in the shadow of the landslide.

There are four main types of landslides.

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

and tumbles down.

The topple, where a big chunk falls forward

from the top of a slope.

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

along a clean break.

And, finally, the flow.

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

Landslides occur all over the world

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

But there is one country with no volcanoes

and few earthquakes that is still at risk from landslides,

a country usually spared the worst of the Fierce Earth.

And that country is the United Kingdom.

Whoo!

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

Lashed by the wind from the Atlantic,

enduring snow and ice every winter.

And let's not forget the rain.

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

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

but landslides can still be seriously destructive.

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

This is the Isle of Wight in the English Channel.

It's like the UK in miniature,

surrounded by 100 kilometres of coastline.

No-one lives very far from the water

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

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

a series of chalk stacks rising out of the sea.

The Needles are absolutely stunning,

but they're the clearest example

that erosion is slowly shrinking the island

and causing landslides.

Once upon a time, the Needles would have been arches

and, before that, cliffs.

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

Roads might have to be re-routed,

houses abandoned and demolished before they fall into the sea,

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

So what's going on?

Coastal erosion is what's going on.

The sea attacking the land and it never gives up.

The sea is moving constantly, isn't it?

Every day, every night, wearing away at the cliffs

that make up the coast.

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

acting like giant sandpaper, scouring away.

The waves undercut the rock at sea level,

and the land above gives way - a landslide.

They say an Englishman's home is his castle,

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

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

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

But tougher rock is no match for water, either,

and erosion causes rock falls all over the UK.

Leo is in Scotland to find out how.

The River Spean in the West Highlands.

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

Gorges cut by the power of water,

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

My kind of water.

Flowing water erosion has caused rock falls

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

anything from small stones to huge boulders.

They churn up the water

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

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

Here we go.

..a River Bug.

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

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

Rapids are dangerous,

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

by white-water specialist Joe.

So it's quite a rocky river.

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

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

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

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

but keep your knees soft.

-So you can fend yourself off?

-Exactly.

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

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

-Ready to rock'n'roll?

-Let's do this!

-Excellent.

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

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

Agh!

Ah!

Not exactly the line I was hoping for!

Agh!

A slight lack of control, but really good fun.

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

a good reason never to explore rivers unaccompanied.

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

Even the tiniest particles carried along in the water

help scour away the rock.

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

And this is how it looks now.

Even now, when the water seems quite calm,

it's working its way slowly, slowly,

eating away at the rock, carving its way deeper.

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

I hear rapids!

Sounds terrifying!

Rivers that descend steeply tend to erode downwards

and cut high, V-shaped banks.

Landslides are more likely to occur here than on gentler,

wider rivers with more sideways erosion.

The eroded rocks, close up, are almost alien.

They're smooth and fluid,

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

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

Well, these pebbles scoured them out

over thousands and thousands of years.

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

It makes those little whirlpools.

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

These pebbles go round and round

and scour out these beautiful channels.

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

going with the flow

like one of the billions of tiny floating particles,

dwarfed by the very cliffs they help create.

2012 was wet.

It rained and it rained

and it rained.

By December, it had been officially declared

the second wettest year since records began.

And then, at Christmas, this happened.

A massive landslide tore a huge chunk of land

off the north coast of the Isle of Wight.

It destroyed the concrete sea wall

that was protecting the slope from wave erosion.

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

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

to look for. Danny and Kieran live nearby.

You start to see sort of cracks

and, occasionally, some rocks tumbling down,

so it gradually slips away.

Eventually, it just goes.

Also, when just little chunks

of rock fall down

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

they break into littler bits.

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

If you feel how soft the rock is.

That's really quite soft.

That would give way quite easily.

That's basically what we're walking along.

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

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

But, underneath, it's really soft.

We have special permission to visit

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

The same can't be said for the path.

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

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

It used to be a straight path.

It used to have no cracks.

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

-It was never an empty path.

-It is really scary.

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

it used to be up on that thing.

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

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

This all sounds quite scary to me,

but Danny and Kieran have grown up with landslides.

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

cos it will come down, usually, quite slowly,

so you should be able to get away.

Also, the best safety precautions are put in place,

so if there is any risk of a landslide,

the path will be sealed off,

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

After safety checks,

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

It really brings home the forces locked within the land.

Forces that a sea wall is powerless to control.

Standing here on the landslide,

you can really feel the power of the rocks

that must have forced their way down,

pushing the concrete path there out,

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

The landslide started behind the sea wall,

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

But 2012 was the second wettest year on record.

Here's the monthly rainfall.

And, according to the

British Geological Survey,

there were way more landslides

than usual,

shown here in green. In December,

around five times as many.

If you compare the monthly rainfall

with the number of landslides,

they follow the same pattern,

so the record rain is causing the record landslides.

With the help of Kieran, Danny and his mates,

I am going to show you how rain can cause landslides

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

On your way, guys!

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

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

which means it doesn't soak up water.

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

just like this sand.

These different types of rock can make a big difference

when it comes to landslides.

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

and I've learned my lesson from last time,

so I built the castle on top of it.

But, oh, no, this is the UK

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

-Oh!

-SHE LAUGHS

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

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

and starts to get heavier, like our sand here.

Add in other danger factors, like a steep slope,

weaker or impermeable rock below,

and you have the perfect recipe for instability.

Our wet, heavy, rock begins to slide.

ALL: Yes!

-Yes!

-Nearly, nearly!

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

and weather causing landslides.

But stick around because the islanders are fighting back.

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

to new heights. Plus, the amusement park

where the ground itself is a white-knuckle ride.

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

creates the most feared land

movement of them all.

This is a sinkhole.

Houses, cars,

even whole street blocks, have been damaged

when the ground suddenly gives way.

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

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

unless you're hanging over the edge of one.

This is Alum Pot, a gigantic sinkhole

in the Yorkshire Dales that's 80m deep.

You could fit Nelson's Column in there.

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

But like everything on our fierce Earth,

sinkholes are a lot less scary when you understand them.

Woo!

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

a type of land recognisable by its pitted surface

and numerous sinkholes.

Karst formations can be found across the UK

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

Here is a stunning example of a limestone pavement.

The rocks beneath my feet are riddled with holes,

a bit like a wood-infested floorboard,

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

This amazing eroded rock only hints at the fierce forces

at work in these peaceful valleys.

The real action is deep underground.

This is how sinkholes happen.

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

The sugar cubes beneath

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

and the sand above is the soil on top.

Just like the limestone, the sugar cubes are strong,

but they can also be dissolved in water.

Mmm. Tasty.

So what happens when it rains?

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

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

There, it can start to dissolve the limestone.

Rainwater is naturally acidic and this aids that process.

The limestone dissolves, the sugar cubes dissolve,

they leave hollows

and the ground literally falls from underneath your feet.

That's how you make a sinkhole.

This erosion is exactly what created Alum Pot.

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

right into the centre of the giant sinkhole itself.

You should never, ever enter caves unaccompanied,

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

One of the underground streams breaks the surface

a couple of hundred metres from the pot.

This is our entrance into the secret world of sinkholes.

As the stream enters the cave system,

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

dissolving, carving, sculpting the rock

as it plunges further and further into the Earth,

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

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

but, if you do, don't worry.

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

-There's a cold pool to stop me.

-Very cold.

-Oh!

-Hold on tight!

-OK.

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

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

and eats its way relentlessly through the limestone.

It's getting really tight now.

'Things are about to get a lot tighter.'

They call this gap the Cheese Press.

Apparently, I've got to squeeze through this

to get to the other side.

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

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

Wish me luck.

HE LAUGHS This is incredible!

Phew!

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

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

Just look at this!

You can actually see the cracks and joints in the rock

where the water's percolating through and dissolving it.

And, here...

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

There's thousands of tonnes of rock above our head

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

This process has been happening for thousands and thousands of years

and it's still happening today.

Wow!

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

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

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

One last obstacle remains.

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

Light at the end of the tunnel!

And what a light it is.

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

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

Ominous from above,

a wondrous secret world from below.

That's amazing! Wow!

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

literally been squeezed through the Earth

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

I just want to go one stage further.

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

..a precarious, fallen boulder.

My journey to this spot has been tough

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

But standing in the centre of this incredible sinkhole,

it's been more than worth it.

The powerful forces that cause landslides

are never going to go away.

So how do humans deal with the risk?

Here on the Isle of Wight,

islanders know better than most people

that what goes up

must come down!

Whoo-hoo!

Blackgang Chine is the oldest amusement park in the world.

It first opened in 1843

and generations of families have come here

since the island became fashionable in Victorian times.

The park has changed a lot since then,

but so has the very land it sits on.

The chine that gives Blackgang its name

came close to destroying it.

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

The small chine at Blackgang

has grown into a vast gash in the coastline,

with landslides sitting on top of landslides.

Erosion rates average four metres a year,

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

The park is being eaten away.

The last major landslide here was in 1994,

when a third of the existing park moved.

If you look really carefully, you can see the remains

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

Was Blackgang Chine about to go the way of dinosaurs?

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

The chine is constantly monitored for movement,

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

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

re-planned and rebuilt.

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

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

most of them oblivious to the challenges

that winter rains bring to Blackgang Chine.

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

Just along the coast from Blackgang Chine,

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

and the islanders are winning.

Work is going on all across the Isle of Wight

to make sure the coast is safe.

It's happening above me right now -

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

After all, they're holding a cliff together.

The clifftop path here is popular with local walkers,

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

And the Hideaway Cafe is in danger of slipping away.

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

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

The council has called in an expert landslide mitigation team

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

and I'm the newest recruit.

-You feel nice and snug?

-Yes.

-OK, brilliant. Come round here. OK?

-'Simon shows me the ropes...'

-Right, you can pull across this way.

'..and pulleys...'

-That's you descending.

-'..and levers.'

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

-and that pulls tight.

-Good.

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

-You do.

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

-Lovely!

-Whoo, incoming!

-Yeah, no problem.

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

'It will reinforce the path foundations by stopping them

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

And we are pretty much ready to go.

Whoo!

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

-Yep.

OK, pull backwards.

'Longer and longer drill bits are added

'as we drill deeper and deeper.'

We are going to go back in again.

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

Woo!

-OK.

-'Two-metre hole drilled.'

'Time to insert a two-metre reinforced steel bolt

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

'that's holding up the path!'

-That's right.

-OK.

-He's going to sit over the end.

-There we go.

-Fantastic.

-How long do you think this will last,

-a structure like this?

-More than our lifetime, hopefully.

-Wow!

'The path is on its way to being rebuilt.

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

'and wire netting.

'The holes allow plants to regrow through into the slope

'and bind the earth together with their roots.

'Stability with a little help from mother nature.'

You can't even see the rock netting now

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

to help stick everything on the top together.

Nice and tight on there.

-This is the final one.

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

-Yep.

And we'll feed him round and underneath.

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

'over £5 million on cliff stabilisation.'

Landslides will always be with us here in the UK.

The waves will always pound at the coast

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

But the human ingenuity

in the face of the Fierce Earth will always remain.

Although landslides that injure people are rare,

they are one threat that will never go away.

But we can learn to live alongside them,

analysing the ground, controlling the risks

and rebuilding when needed.

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

Next time, things are hotting up underground.

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

Wish me luck.