A Perfect Planet (2021) s01e01 Episode Script
Volcano
1
DAVID ATTENBOROUGH: A Perfect Planet.
There is only one planet in the universe, as far as we know, where there is life.
The Earth.
Our home.
The perfect planet.
Life here is only possible because of a unique balance of natural forces.
Energy from the sun powers the living world.
Weather systems transport fresh water around the globe.
And powerful ocean currents circulate life's essential nutrients.
This series will reveal how these global forces have worked together to create our planet's fragile life-support system.
One of these forces is so important that life would never have even started without it.
Across the surface of our planet, there are over 1,500 active volcanoes.
This is the most active - Kilauea in Hawaii.
Here, magma - liquid rock from the planet's hot interior - bursts out through fractures in the Earth's crust.
And it's been flowing for months.
Nothing can stand in the lava's way.
Volcanoes are certainly destructive, but without these powerful underground forces, there would be no breathable atmosphere.
No oceans.
No land.
No life.
We can't control volcanoes, but they're vital for all living things on Planet Earth.
This is Ol Doinyo Lengai in Tanzania.
It's one of Africa's most active volcanoes, and has erupted over 15 times in the last hundred years.
On its northern flank lies Lake Natron, 400 square miles in extent, and one of the world's most corrosive bodies of water.
The water wells up from deep below, carrying such a concentration of chemicals that it can burn skin.
But one animal thrives here.
Volcano birds.
Nearly two million lesser flamingos live in East Africa and all of them come here to breed.
But they can only nest here when the lake's level drops so far that in the centre its bed is exposed.
And that rare moment is now.
How they know when the conditions are right is a mystery.
But some have flown thousands of miles to be here.
The flamingos head for the middle of the lake, where the intense evaporation has created islands of salt.
It's here that the birds build their nests, over three miles from the lake's edge and safe from land predators, which are unable to cross the surrounding moat of caustic soda.
The single egg is laid on a mount of hardened salt built by the adults, its height an insurance against a sudden rise in water level which often happens on Lake Natron.
As the centre dries and enlarges, more and more flamingos arrive to nest on it.
In good years, such as now, as many as half a million pairs breed here.
After 28 days of incubation, a chick emerges into Natron's harsh glare.
Here, temperatures can rise to 55 degrees Celsius.
Mother's wing, however, can serve as a sun-shield.
The chick is fed a rich liquid made of the lake's barely digested algae and traces of its parent's blood.
After a few days, the chick is strong enough to stretch its legs.
It then joins a growing crèche made up of chicks of different ages.
Soon, the need for fresh water will force the infant birds to trek to springs on the lake's edge a journey they have to make on foot, as their flight feathers have yet to develop.
Every day, the adults fly to these springs to feed.
Here, on the lake's margins, they collect algae that flourish in the volcanic water - vital food for the flamingos.
It's the algae that turn the flamingos' feathers pink.
It even colours their eyes.
The adults spend most of their day at the springs, and now their chicks are going to join them there.
No-one wants to get left behind.
It's a three-mile march over razor-sharp flakes of soda and sticky, caustic mud a life-threatening trial, especially for the youngest chicks.
The groups merge into one giant crèche.
For some, the challenges are just too great.
Exhaustion overcomes the weakest.
And now there is yet another threat.
Marabou storks.
They have long legs like a flamingo, but a beak like a Roman sword.
And they are patient, waiting for an easy target.
Their very presence creates panic among the chicks.
The smallest avoid being trampled underfoot by travelling on the outside of the group.
But that exposes them to attack.
Their only defence is to run.
But you have little chance when you're barely ankle-high to your pursuer.
Stragglers will almost certainly be taken.
But there comes a point when every stork has had its fill.
This little chick is very lucky.
At last, the youngsters reach the freshwater springs at the lake's margin to rejoin their parents.
Almost unbelievably, each chick has a unique call that its parent can recognise.
It's not just lesser flamingos that depend on volcanoes.
Ultimately, so do all living things.
Over 80% of the Earth's surface is the result of magma bursting up from the molten interior.
The process started four billion years ago and it still continues today.
When lava cools, it solidifies into rock and eventually weathers into land that can support life.
All the Galápagos Islands in the Pacific are volcanic, and Fernandina is the youngest of them and still growing.
At its centre, a volcanic crater four miles wide and over 800 metres deep.
It seems dormant, but it was erupting only two weeks ago.
Even so, there are some who depend on the heat from this volcano.
A female land iguana, heavy with eggs, approaches the crater's rim.
It took her ten days to climb up here, but the toughest part of her journey is still ahead.
She's going to descend into the crater itself.
Frequent tremors make the crater walls unstable.
More people have travelled in space than have visited the bottom of Fernandina's crater.
But instinct drives her on.
The warm volcanic ash on the crater floor has the perfect temperature for incubating her eggs.
But there are no clear paths down.
Any made last year have been destroyed by rockfalls.
The slope is steep and unstable.
Tumbling rocks quickly become an avalanche.
With the boulders falling down away from her, she's not in immediate danger.
But behind her, higher up, two other females have also started the descent.
And now she is in the firing line.
She's safe.
Others before her haven't been so lucky.
But she's undeterred.
At last, after an eight-hour descent, she reaches the crater floor.
Now she must find a suitable place to dig her nest.
The best sites are already taken.
And nesting females are very aggressive.
A nodding head means keep away.
Push off! Ignored warnings are met with force.
But she's come a long way, and she's not going to give up now.
She, too, starts to dig a hole in which to lay her eggs.
That done, she will head back, leaving the volcano to provide the warmth her eggs need if they are to hatch.
Sometimes, of course, the volcano erupts and destroys not only eggs, but many nesting adults.
But for the iguanas, the benefits of nesting in the crater are so great that it's worth all the risks.
Volcanic islands make up just 5% of the planet's land, but they're home to nearly 20% of its species.
Animals often evolve very swiftly on islands, cut off from their mainland relatives and faced with the challenges of isolation.
This is Wolf, an extinct volcano and one of the most remote islands of the Galápagos, 800 miles from the nearest large landmass and over a million years old.
A finch.
A female.
Its ancestors doubtless were blown here by storms many centuries ago.
Like most finches, they feed on seeds, nectar and insects.
But there's little food of any kind on Wolf.
And since they aren't strong enough fliers to leave the island, they've had to find food from a very unusual source.
They depend on another of the island's inhabitants.
Nazca boobies.
Every day, these seabirds commute between the island and their fishing grounds out in the open ocean.
Each time a pair meet, they renew their bond and then catch up with the neighbours.
Now is the time to hop into action.
Blood.
They are vampire finches.
These little birds have become one of the world's newest species.
She cuts the quill of a large flight feather, and the blood flows.
The sight of it attracts the attention of others.
Blood is very nutritious - worth fighting for.
So, with this never-ending supply of food, the vampire finches can flourish on an island where otherwise they could not survive.
Why the boobies don't object, nobody knows.
Perhaps the finches' behaviour started when they helped the boobies to remove parasites from their plumage.
Maybe the boobies think that the little vampires are still providing a service.
Who can tell? Volcanic islands don't last forever.
Changes deep in the Earth's crust bring their eruptions to an end, and the forces of erosion then begin to wear them down.
But the coral around them continues to grow, sea levels change, and eventually all that is left is a ring-shaped island of coral rock surrounding a lagoon.
An atoll.
There are hundreds of atolls in tropical seas, all remnants of vanished volcanoes.
This is one of the largest and most pristine - Aldabra, in the Indian Ocean.
20 million years ago, it was an island with a volcanic crater in its centre.
Now it's an atoll.
Mangroves took root and seabirds came to nest.
One land animal in particular reached here before man.
A giant tortoise.
These creatures can float and live without food or fresh water for long periods of time.
This isolated atoll is the perfect refuge.
Their only enemy is the sun.
Without shade, a tortoise risks being boiled in his shell.
So, after feeding in the cool of the morning, and before the sun becomes too crushingly hot, they have to find cover.
All of them.
There is very little vegetation, but caves in the coral rock can provide the shade they so badly need.
He's nearly there.
All that is left is a white-knuckle ride to the bottom.
And he's in.
Thousands of others are still out in the sun.
This tree could shade a couple of hundred, if they pack tight.
It's bumper-to-bumper parking.
Within an hour or so, all must find shade of some sort if they're to survive.
Safe.
But the future for Aldabra's tortoises is far from certain.
The climate is changing, sea levels are rising, and Aldabra's tortoises may soon have to find a new refuge or drown.
In some places, volcanoes erupt not in the ocean, but in the very middle of a continent.
North America, and in its very heart, a volcanic hot spot - Yellowstone.
The last major eruption here came to an end about 650,000 years ago, but this volcano is only sleeping.
Not far below ground, there is still magma.
And that heats the groundwater to boiling point.
Geysers.
Some spout boiling water and steam to heights of 90 metres or so.
Elsewhere, the scalding waters liquefy the ground sediments, creating pots of boiling mud.
And this underground heating has proved a lifeline for some.
River otters.
They need a constant supply of food if they're to keep warm in these freezing temperatures.
And this close-knit family know exactly where to find it.
The springs are so hot that the rivers never freeze, even in the coldest winters so the otter family can fish the year round.
Trouble.
This coyote knows that in the middle of winter a thermal river means otters, and otters mean fish.
The question is how to steal their catch? Perhaps the thing to do is to pretend you're not interested and hope that they wander close enough for a snatch-and-run raid.
It seems the cool-under-fire otters can outwit the not-so-wily coyote.
Many animals benefit from the volcanic heat coming up from below.
And we do as well, but not nearly as much as we could.
The volcanic heat could provide us with much of the energy that we need, and then we could stop burning gas and coal that is now changing the climate worldwide.
Deep in the Earth's crust, below both the oceans and the continents, there are lines of weakness along which rises liquid rock.
The Kamchatka Peninsula in the north-west Pacific lies along one of them.
There are only a thousand known geysers in the world, and many of them are here in this isolated valley.
Steam from superheated water fills the air.
But the danger from the scalding pools does little to deter Kamchatka's most famous residents.
In May, when the rest of Kamchatka is still covered by snow, this valley is free of it, and bears, having just woken up from their winter sleep, know that.
The grass is fertilised by mineral-rich water spraying from the geysers much-needed forage for a large male bear that hasn't eaten for several months.
And he's not the only one.
The bears haven't seen one another for seven months, since the start of winter.
And it seems that right now they would prefer to keep it that way.
Nothing should come between a bear and his first meal of the year.
And in one place, Kamchatka's underground forces provide its bears with even more nutritious meals.
Kurile Lake lies within the crater of an immense volcano that long ago produced one of the greatest eruptions in the planet's history.
The lake is still circled by active vents and mineral-rich ash from their regular eruptions has made these waters particularly fertile.
Millions of salmon come here from the Pacific Ocean in order to spawn in these fertile waters, which will provide their newly hatched young with abundant food so grass soon ceases to be top of the menu for Kamchatka's bears.
By the time spring has turned to summer, Kurile Lake contains the most dense assembly of bears to be found anywhere on Earth all hungry for salmon.
But this early in the season, the fish are still strong and swift.
Nothing seems to work.
But one old bear knows that right now there is an easier meal to be had.
He remembers that if he paddles out into the lake, away from the shoals of newly arrived salmon, there's food that doesn't need chasing.
Some of the first fish to arrive have died, and their bodies can be easily collected from the bottom of the lake.
Diving for them at leisure doesn't use many calories.
And he can take his time.
A couple of weeks later, the salmon are beginning to spawn and are less wary.
Now it's worth running.
The fish are so abundant that there is plenty for all even those with no previous experience.
There are now so many fish, it's difficult to know which one to chase.
In a single day, a bear can consume 100,000 calories, 50 times more than the average human being does.
And one part is particularly delicious.
Caviar.
80 calories in every mouthful.
By supporting huge concentrations of salmon, mineral ash from Kurile Lake's volcanoes has made life surprisingly easy for these bears.
Our planet depends on minerals brought up by volcanoes from the Earth's molten core.
A single ash cloud can carry billions of tonnes of minerals.
And as a consequence, the lands surrounding volcanoes are among the world's most fertile.
Those in East Africa's Rift Valley support the most dynamic ecosystem on Earth.
The Serengeti.
This is the most productive of all natural grasslands anywhere.
Every year, over a million wildebeest assemble in this particular corner of the Serengeti to feed on grass specially rich in calcium and phosphorus - essential minerals for the pregnant females.
In just three weeks, half a million calves are born on these ash-rich plains.
That's 24,000 a day, a thousand an hour.
Calves stand up within a few minutes of being born though some need a little more time to find their feet.
But a mother won't let her calf suckle until it's mastered a few physical skills.
Walking.
Trotting.
And running.
Wildebeest calves must run if they're to stay alive for these plains also support the greatest assembly of hunters on the planet.
Each species has its own special hunting technique.
But all have the same aim to make the most of this brief super-abundance of life.
Only one in ten wildebeest calves will survive to adulthood.
But that is enough to maintain the million-strong herd of wildebeest and the planet's highest density of predators.
Volcanoes fertilise the planet, but they're the source of something else so important that life could not have started without it.
The first carbon dioxide in the Earth's atmosphere was brought by volcanoes from deep in the Earth's crust.
And this gas is the foundation of life.
Every plant needs it to grow, and absorbs it from the air.
Volcanoes continue to release carbon dioxide today, and for the last 10,000 years its presence in the atmosphere has suited life perfectly.
Its greenhouse properties have kept our planet's climate stable and warm.
But too much carbon dioxide would make the planet's temperature rise to levels that would upset the Earth's long-established ecological balances.
Today, humanity itself has become a new kind of supervolcano.
Now, every year, we ourselves release 100 times more carbon than all the Earth's volcanoes combined.
And that has brought climate chaos.
We can't control volcanoes.
But we can limit the amount of carbon dioxide that we produce.
And if we do that, there will still be time to restore the ecological balance that once made this Earth our perfect planet.
DAVID: Lake Natron in Tanzania is one of the world's most toxic bodies of water.
Yet once every few years, when the centre dries out, it's brought to life by thousands of breeding flamingos.
But to reach the colony, there's only one way to cross this soft soda sludge.
DARREN WILLIAMS: It's finally here.
Our secret weapon is a hovercraft.
And it's beautiful.
Having shipped it from the UK, Darren's keen to test that all systems are go.
Getting it off the trailer is one thing, but at least the hovercraft's fans, that give it lift, are working well enough.
DARREN: Well, guys, what do you think? We know she works, but maybe some of these guys' lungs don't now.
125 miles away, on the edge of Lake Natron, cameraman Matt Aeberhard is trying to camouflage his hides.
MATT: Those are our blinds.
So, you can't camouflage those on the flats, and the best thing that we can do is actually turn them into a little cluster of flamingos.
It's pretty cool, huh? Hide complete, all that's needed is transport out to the colony.
And after a ten-hour cross-country journey, Darren arrives with his secret weapon, and it's an instant hit.
It's a new local tourist attraction.
You like it? The first job is to get the hovercraft into service and plot a route out to the nesting flamingos.
The volcanic spring water is soon replaced by a crust of razor-sharp salt crystals.
And for a machine that relies on a delicate blow-up bottom, that's a problem.
DARREN: So what we have here are the plates of dried-out soda which form on the mud substrate underneath, and it just batters the hovercraft.
We just cannot travel across this stuff.
It's impossible.
If I was to skim my hand across that, I would cut it to shreds.
But crossing the soda crust is the only way out to the colonies.
So Matt and Darren have to hope for the best.
Unfortunately for Matt, the best position for his flamingo-covered hide has a rather soggy floor.
MATT: When the mud dries, it leaves massive amounts of salt, very scratchy, nasty and aggressive salts.
But sitting shin-deep in toxic sludge is a price worth paying for the view.
And Matt is soon rewarded with the birth of a chick right in front of his hide.
The daily commute, however, is taking its toll on the hovercraft.
Oh, come on! And its blow-up bottom is literally being ripped apart.
We've trashed 52 of these, that now need to be repaired.
It's like travelling over sandpaper.
So what do you do when your hovercraft needs replacement skirts, and you're in the middle of nowhere? Enter the local Maasai tribe, well known for their needlework skills.
There are only a few places in the world that specialise in hovercraft maintenance, and Lake Natron is now officially one of those hot spots.
So if you're in the need of any hovercraft services, you know where to go.
Two days later, and after a lot of serious sewing, the hovercraft is ready to ride again.
DARREN: You look like the new Tanzanian bobsleigh team! And getting back on the lake couldn't have come at a better time, as the chicks are now on the move.
Sadly, the new hide position is no drier.
MATT: We have an enormous crèche of hundreds of thousands of birds just pouring into the lagoon from the salt mud, just constantly chatting to each other.
But the massive crèche attracts some unwelcome visitors predators - marabou storks.
MATT: These marabous, they know exactly what they are doing.
Soon, thousands of panicked chicks are on the move, desperately trying to avoid the predators.
And it's a scene that will live long in Matt's memory.
I mean, it was literally like war had been declared.
I mean, that's one of thethe most amazing and frightening and freaky wildlife scenes I've ever, ever seen.
And believe me, I've seen a few.
And few places are more challenging than Lake Natron, but, to quote Matt, if you can deal with the acrid and sulphurous stink of the soda, the stinging eyes and the chemical attack on your legs, then you could be rewarded with one of the greatest spectacles on Earth.
There is only one planet in the universe, as far as we know, where there is life.
The Earth.
Our home.
The perfect planet.
Life here is only possible because of a unique balance of natural forces.
Energy from the sun powers the living world.
Weather systems transport fresh water around the globe.
And powerful ocean currents circulate life's essential nutrients.
This series will reveal how these global forces have worked together to create our planet's fragile life-support system.
One of these forces is so important that life would never have even started without it.
Across the surface of our planet, there are over 1,500 active volcanoes.
This is the most active - Kilauea in Hawaii.
Here, magma - liquid rock from the planet's hot interior - bursts out through fractures in the Earth's crust.
And it's been flowing for months.
Nothing can stand in the lava's way.
Volcanoes are certainly destructive, but without these powerful underground forces, there would be no breathable atmosphere.
No oceans.
No land.
No life.
We can't control volcanoes, but they're vital for all living things on Planet Earth.
This is Ol Doinyo Lengai in Tanzania.
It's one of Africa's most active volcanoes, and has erupted over 15 times in the last hundred years.
On its northern flank lies Lake Natron, 400 square miles in extent, and one of the world's most corrosive bodies of water.
The water wells up from deep below, carrying such a concentration of chemicals that it can burn skin.
But one animal thrives here.
Volcano birds.
Nearly two million lesser flamingos live in East Africa and all of them come here to breed.
But they can only nest here when the lake's level drops so far that in the centre its bed is exposed.
And that rare moment is now.
How they know when the conditions are right is a mystery.
But some have flown thousands of miles to be here.
The flamingos head for the middle of the lake, where the intense evaporation has created islands of salt.
It's here that the birds build their nests, over three miles from the lake's edge and safe from land predators, which are unable to cross the surrounding moat of caustic soda.
The single egg is laid on a mount of hardened salt built by the adults, its height an insurance against a sudden rise in water level which often happens on Lake Natron.
As the centre dries and enlarges, more and more flamingos arrive to nest on it.
In good years, such as now, as many as half a million pairs breed here.
After 28 days of incubation, a chick emerges into Natron's harsh glare.
Here, temperatures can rise to 55 degrees Celsius.
Mother's wing, however, can serve as a sun-shield.
The chick is fed a rich liquid made of the lake's barely digested algae and traces of its parent's blood.
After a few days, the chick is strong enough to stretch its legs.
It then joins a growing crèche made up of chicks of different ages.
Soon, the need for fresh water will force the infant birds to trek to springs on the lake's edge a journey they have to make on foot, as their flight feathers have yet to develop.
Every day, the adults fly to these springs to feed.
Here, on the lake's margins, they collect algae that flourish in the volcanic water - vital food for the flamingos.
It's the algae that turn the flamingos' feathers pink.
It even colours their eyes.
The adults spend most of their day at the springs, and now their chicks are going to join them there.
No-one wants to get left behind.
It's a three-mile march over razor-sharp flakes of soda and sticky, caustic mud a life-threatening trial, especially for the youngest chicks.
The groups merge into one giant crèche.
For some, the challenges are just too great.
Exhaustion overcomes the weakest.
And now there is yet another threat.
Marabou storks.
They have long legs like a flamingo, but a beak like a Roman sword.
And they are patient, waiting for an easy target.
Their very presence creates panic among the chicks.
The smallest avoid being trampled underfoot by travelling on the outside of the group.
But that exposes them to attack.
Their only defence is to run.
But you have little chance when you're barely ankle-high to your pursuer.
Stragglers will almost certainly be taken.
But there comes a point when every stork has had its fill.
This little chick is very lucky.
At last, the youngsters reach the freshwater springs at the lake's margin to rejoin their parents.
Almost unbelievably, each chick has a unique call that its parent can recognise.
It's not just lesser flamingos that depend on volcanoes.
Ultimately, so do all living things.
Over 80% of the Earth's surface is the result of magma bursting up from the molten interior.
The process started four billion years ago and it still continues today.
When lava cools, it solidifies into rock and eventually weathers into land that can support life.
All the Galápagos Islands in the Pacific are volcanic, and Fernandina is the youngest of them and still growing.
At its centre, a volcanic crater four miles wide and over 800 metres deep.
It seems dormant, but it was erupting only two weeks ago.
Even so, there are some who depend on the heat from this volcano.
A female land iguana, heavy with eggs, approaches the crater's rim.
It took her ten days to climb up here, but the toughest part of her journey is still ahead.
She's going to descend into the crater itself.
Frequent tremors make the crater walls unstable.
More people have travelled in space than have visited the bottom of Fernandina's crater.
But instinct drives her on.
The warm volcanic ash on the crater floor has the perfect temperature for incubating her eggs.
But there are no clear paths down.
Any made last year have been destroyed by rockfalls.
The slope is steep and unstable.
Tumbling rocks quickly become an avalanche.
With the boulders falling down away from her, she's not in immediate danger.
But behind her, higher up, two other females have also started the descent.
And now she is in the firing line.
She's safe.
Others before her haven't been so lucky.
But she's undeterred.
At last, after an eight-hour descent, she reaches the crater floor.
Now she must find a suitable place to dig her nest.
The best sites are already taken.
And nesting females are very aggressive.
A nodding head means keep away.
Push off! Ignored warnings are met with force.
But she's come a long way, and she's not going to give up now.
She, too, starts to dig a hole in which to lay her eggs.
That done, she will head back, leaving the volcano to provide the warmth her eggs need if they are to hatch.
Sometimes, of course, the volcano erupts and destroys not only eggs, but many nesting adults.
But for the iguanas, the benefits of nesting in the crater are so great that it's worth all the risks.
Volcanic islands make up just 5% of the planet's land, but they're home to nearly 20% of its species.
Animals often evolve very swiftly on islands, cut off from their mainland relatives and faced with the challenges of isolation.
This is Wolf, an extinct volcano and one of the most remote islands of the Galápagos, 800 miles from the nearest large landmass and over a million years old.
A finch.
A female.
Its ancestors doubtless were blown here by storms many centuries ago.
Like most finches, they feed on seeds, nectar and insects.
But there's little food of any kind on Wolf.
And since they aren't strong enough fliers to leave the island, they've had to find food from a very unusual source.
They depend on another of the island's inhabitants.
Nazca boobies.
Every day, these seabirds commute between the island and their fishing grounds out in the open ocean.
Each time a pair meet, they renew their bond and then catch up with the neighbours.
Now is the time to hop into action.
Blood.
They are vampire finches.
These little birds have become one of the world's newest species.
She cuts the quill of a large flight feather, and the blood flows.
The sight of it attracts the attention of others.
Blood is very nutritious - worth fighting for.
So, with this never-ending supply of food, the vampire finches can flourish on an island where otherwise they could not survive.
Why the boobies don't object, nobody knows.
Perhaps the finches' behaviour started when they helped the boobies to remove parasites from their plumage.
Maybe the boobies think that the little vampires are still providing a service.
Who can tell? Volcanic islands don't last forever.
Changes deep in the Earth's crust bring their eruptions to an end, and the forces of erosion then begin to wear them down.
But the coral around them continues to grow, sea levels change, and eventually all that is left is a ring-shaped island of coral rock surrounding a lagoon.
An atoll.
There are hundreds of atolls in tropical seas, all remnants of vanished volcanoes.
This is one of the largest and most pristine - Aldabra, in the Indian Ocean.
20 million years ago, it was an island with a volcanic crater in its centre.
Now it's an atoll.
Mangroves took root and seabirds came to nest.
One land animal in particular reached here before man.
A giant tortoise.
These creatures can float and live without food or fresh water for long periods of time.
This isolated atoll is the perfect refuge.
Their only enemy is the sun.
Without shade, a tortoise risks being boiled in his shell.
So, after feeding in the cool of the morning, and before the sun becomes too crushingly hot, they have to find cover.
All of them.
There is very little vegetation, but caves in the coral rock can provide the shade they so badly need.
He's nearly there.
All that is left is a white-knuckle ride to the bottom.
And he's in.
Thousands of others are still out in the sun.
This tree could shade a couple of hundred, if they pack tight.
It's bumper-to-bumper parking.
Within an hour or so, all must find shade of some sort if they're to survive.
Safe.
But the future for Aldabra's tortoises is far from certain.
The climate is changing, sea levels are rising, and Aldabra's tortoises may soon have to find a new refuge or drown.
In some places, volcanoes erupt not in the ocean, but in the very middle of a continent.
North America, and in its very heart, a volcanic hot spot - Yellowstone.
The last major eruption here came to an end about 650,000 years ago, but this volcano is only sleeping.
Not far below ground, there is still magma.
And that heats the groundwater to boiling point.
Geysers.
Some spout boiling water and steam to heights of 90 metres or so.
Elsewhere, the scalding waters liquefy the ground sediments, creating pots of boiling mud.
And this underground heating has proved a lifeline for some.
River otters.
They need a constant supply of food if they're to keep warm in these freezing temperatures.
And this close-knit family know exactly where to find it.
The springs are so hot that the rivers never freeze, even in the coldest winters so the otter family can fish the year round.
Trouble.
This coyote knows that in the middle of winter a thermal river means otters, and otters mean fish.
The question is how to steal their catch? Perhaps the thing to do is to pretend you're not interested and hope that they wander close enough for a snatch-and-run raid.
It seems the cool-under-fire otters can outwit the not-so-wily coyote.
Many animals benefit from the volcanic heat coming up from below.
And we do as well, but not nearly as much as we could.
The volcanic heat could provide us with much of the energy that we need, and then we could stop burning gas and coal that is now changing the climate worldwide.
Deep in the Earth's crust, below both the oceans and the continents, there are lines of weakness along which rises liquid rock.
The Kamchatka Peninsula in the north-west Pacific lies along one of them.
There are only a thousand known geysers in the world, and many of them are here in this isolated valley.
Steam from superheated water fills the air.
But the danger from the scalding pools does little to deter Kamchatka's most famous residents.
In May, when the rest of Kamchatka is still covered by snow, this valley is free of it, and bears, having just woken up from their winter sleep, know that.
The grass is fertilised by mineral-rich water spraying from the geysers much-needed forage for a large male bear that hasn't eaten for several months.
And he's not the only one.
The bears haven't seen one another for seven months, since the start of winter.
And it seems that right now they would prefer to keep it that way.
Nothing should come between a bear and his first meal of the year.
And in one place, Kamchatka's underground forces provide its bears with even more nutritious meals.
Kurile Lake lies within the crater of an immense volcano that long ago produced one of the greatest eruptions in the planet's history.
The lake is still circled by active vents and mineral-rich ash from their regular eruptions has made these waters particularly fertile.
Millions of salmon come here from the Pacific Ocean in order to spawn in these fertile waters, which will provide their newly hatched young with abundant food so grass soon ceases to be top of the menu for Kamchatka's bears.
By the time spring has turned to summer, Kurile Lake contains the most dense assembly of bears to be found anywhere on Earth all hungry for salmon.
But this early in the season, the fish are still strong and swift.
Nothing seems to work.
But one old bear knows that right now there is an easier meal to be had.
He remembers that if he paddles out into the lake, away from the shoals of newly arrived salmon, there's food that doesn't need chasing.
Some of the first fish to arrive have died, and their bodies can be easily collected from the bottom of the lake.
Diving for them at leisure doesn't use many calories.
And he can take his time.
A couple of weeks later, the salmon are beginning to spawn and are less wary.
Now it's worth running.
The fish are so abundant that there is plenty for all even those with no previous experience.
There are now so many fish, it's difficult to know which one to chase.
In a single day, a bear can consume 100,000 calories, 50 times more than the average human being does.
And one part is particularly delicious.
Caviar.
80 calories in every mouthful.
By supporting huge concentrations of salmon, mineral ash from Kurile Lake's volcanoes has made life surprisingly easy for these bears.
Our planet depends on minerals brought up by volcanoes from the Earth's molten core.
A single ash cloud can carry billions of tonnes of minerals.
And as a consequence, the lands surrounding volcanoes are among the world's most fertile.
Those in East Africa's Rift Valley support the most dynamic ecosystem on Earth.
The Serengeti.
This is the most productive of all natural grasslands anywhere.
Every year, over a million wildebeest assemble in this particular corner of the Serengeti to feed on grass specially rich in calcium and phosphorus - essential minerals for the pregnant females.
In just three weeks, half a million calves are born on these ash-rich plains.
That's 24,000 a day, a thousand an hour.
Calves stand up within a few minutes of being born though some need a little more time to find their feet.
But a mother won't let her calf suckle until it's mastered a few physical skills.
Walking.
Trotting.
And running.
Wildebeest calves must run if they're to stay alive for these plains also support the greatest assembly of hunters on the planet.
Each species has its own special hunting technique.
But all have the same aim to make the most of this brief super-abundance of life.
Only one in ten wildebeest calves will survive to adulthood.
But that is enough to maintain the million-strong herd of wildebeest and the planet's highest density of predators.
Volcanoes fertilise the planet, but they're the source of something else so important that life could not have started without it.
The first carbon dioxide in the Earth's atmosphere was brought by volcanoes from deep in the Earth's crust.
And this gas is the foundation of life.
Every plant needs it to grow, and absorbs it from the air.
Volcanoes continue to release carbon dioxide today, and for the last 10,000 years its presence in the atmosphere has suited life perfectly.
Its greenhouse properties have kept our planet's climate stable and warm.
But too much carbon dioxide would make the planet's temperature rise to levels that would upset the Earth's long-established ecological balances.
Today, humanity itself has become a new kind of supervolcano.
Now, every year, we ourselves release 100 times more carbon than all the Earth's volcanoes combined.
And that has brought climate chaos.
We can't control volcanoes.
But we can limit the amount of carbon dioxide that we produce.
And if we do that, there will still be time to restore the ecological balance that once made this Earth our perfect planet.
DAVID: Lake Natron in Tanzania is one of the world's most toxic bodies of water.
Yet once every few years, when the centre dries out, it's brought to life by thousands of breeding flamingos.
But to reach the colony, there's only one way to cross this soft soda sludge.
DARREN WILLIAMS: It's finally here.
Our secret weapon is a hovercraft.
And it's beautiful.
Having shipped it from the UK, Darren's keen to test that all systems are go.
Getting it off the trailer is one thing, but at least the hovercraft's fans, that give it lift, are working well enough.
DARREN: Well, guys, what do you think? We know she works, but maybe some of these guys' lungs don't now.
125 miles away, on the edge of Lake Natron, cameraman Matt Aeberhard is trying to camouflage his hides.
MATT: Those are our blinds.
So, you can't camouflage those on the flats, and the best thing that we can do is actually turn them into a little cluster of flamingos.
It's pretty cool, huh? Hide complete, all that's needed is transport out to the colony.
And after a ten-hour cross-country journey, Darren arrives with his secret weapon, and it's an instant hit.
It's a new local tourist attraction.
You like it? The first job is to get the hovercraft into service and plot a route out to the nesting flamingos.
The volcanic spring water is soon replaced by a crust of razor-sharp salt crystals.
And for a machine that relies on a delicate blow-up bottom, that's a problem.
DARREN: So what we have here are the plates of dried-out soda which form on the mud substrate underneath, and it just batters the hovercraft.
We just cannot travel across this stuff.
It's impossible.
If I was to skim my hand across that, I would cut it to shreds.
But crossing the soda crust is the only way out to the colonies.
So Matt and Darren have to hope for the best.
Unfortunately for Matt, the best position for his flamingo-covered hide has a rather soggy floor.
MATT: When the mud dries, it leaves massive amounts of salt, very scratchy, nasty and aggressive salts.
But sitting shin-deep in toxic sludge is a price worth paying for the view.
And Matt is soon rewarded with the birth of a chick right in front of his hide.
The daily commute, however, is taking its toll on the hovercraft.
Oh, come on! And its blow-up bottom is literally being ripped apart.
We've trashed 52 of these, that now need to be repaired.
It's like travelling over sandpaper.
So what do you do when your hovercraft needs replacement skirts, and you're in the middle of nowhere? Enter the local Maasai tribe, well known for their needlework skills.
There are only a few places in the world that specialise in hovercraft maintenance, and Lake Natron is now officially one of those hot spots.
So if you're in the need of any hovercraft services, you know where to go.
Two days later, and after a lot of serious sewing, the hovercraft is ready to ride again.
DARREN: You look like the new Tanzanian bobsleigh team! And getting back on the lake couldn't have come at a better time, as the chicks are now on the move.
Sadly, the new hide position is no drier.
MATT: We have an enormous crèche of hundreds of thousands of birds just pouring into the lagoon from the salt mud, just constantly chatting to each other.
But the massive crèche attracts some unwelcome visitors predators - marabou storks.
MATT: These marabous, they know exactly what they are doing.
Soon, thousands of panicked chicks are on the move, desperately trying to avoid the predators.
And it's a scene that will live long in Matt's memory.
I mean, it was literally like war had been declared.
I mean, that's one of thethe most amazing and frightening and freaky wildlife scenes I've ever, ever seen.
And believe me, I've seen a few.
And few places are more challenging than Lake Natron, but, to quote Matt, if you can deal with the acrid and sulphurous stink of the soda, the stinging eyes and the chemical attack on your legs, then you could be rewarded with one of the greatest spectacles on Earth.