The Ethiopian highlands.
The roof of Africa.
30 million years ago,
this was a vast high-altitude plateau the size of Spain.
Since then, the elements have carved the landscape
into Africa's equivalent of the Grand Canyon.
Millions of years of erosion
have created isolated islands of alpine terrain
supporting strange and unique creatures found nowhere else on Earth.
The gelada baboon needs a head for heights,
where a single slip would mean certain death.
Geladas are exclusive to this chilly plateau,
kept warm by a long fur coat.
They are the highest-dwelling primates on the planet,
ranging up to 4, 500 metres.
But what's really surprising is their sheer numbers.
Geladas are the most sociable monkeys on Earth.
Like the game herds of the Serengeti, they are vegetarians.
In these high pastures, they take the place of grazing antelopes.
But geladas aren't the only peculiar creatures up here on the roof of Africa.
This is a giant mole rat...
...a specialised grass-eater that's unique to the Ethiopian highlands.
The mole rat lives underground,
emerging at dawn and dusk to snatch mouthfuls of grass,
which it drags back to its burrow to munch at leisure.
There's every reason to be cautious.
This foxy-looking Ethiopian wolf
preys almost exclusively on giant mole rats.
Despite the wolf's best efforts, mole rats are incredibly common.
It's estimated there may be more than 15, 000 of them
in each square mile of grassland.
Yet despite their high numbers, mole rats and geladas never meet.
So, how can that be?
The answer is this.
Dividing geladas on one side from mole rats on the other,
the Great Rift Valley runs through Ethiopia,
slicing the roof of Africa in two.
But it doesn't stop there.
Extending 3,000 miles further south,
the Great Rift shapes and defines the entire landscape of East Africa,
creating intense hot spots of evolution.
All along the Rift Valley, soaring above the hot, dusty plains,
isolated mountain peaks harbour unique wildlife communities.
A kaleidoscope of strange and remarkable creatures.
As well as extraordinary wildlife,
there's something else that's special about these mountains.
They all share a common origin
that is key to understanding how the rift was formed...
...and why it has had such a far-reaching impact on this part of Africa.
The first clue lies here,
at the very northern margin of the Great Rift Valley.
Ethiopia's Danakil Depression.
This is Erta Ale,
Africa's most active volcano.
It contains the world's only permanent lava lake.
Like a window into the fiery heart of the earth,
Erta Ale provides a terrifying glimpse of the inner workings of our planet.
A cauldron of molten rock beneath our feet.
In geological terms, Erta Ale's volcano is still in its infancy.
But 1, 000 miles to the south,
another Rift Valley volcano has been growing for at least a million years.
Rising to the east of the Great Rift Valley,
snow-capped Kilimanjaro towers nearly four miles high.
It's Africa's loftiest peak
and the tallest free-standing volcano on Earth.
Kilimanjaro and Erta Ale are just two links in a long chain of volcanoes
that runs the length of the Great Rift.
In fact, all the mountains along the rift are volcanic,
born deep beneath the Earth's surface.
Scientists believe that a plume of superhot lava
has been rising up beneath the crust of East Africa
for millions of years.
The thick crust above the plume has been lifted more than a mile high,
causing cracks to appear around its margins.
The Eastern and Western Rift Valleys mark the fractured edges
of the uplifted East African Plateau,
with further branches extending outwards.
And wherever molten rock has seeped through from below,
huge volcanoes have grown up.
It's estimated that over the last 30 million years,
the rift's volcanoes have poured out enough molten rock
to bury an area the size of Wales to a depth of 15 miles.
Mount Kenya's 5,200-metre-high summit is an eroded lava plug,
suggesting it was once even taller.
Below the summit,
a belt of strange and unique alpine plants clings to the slopes.
Even on the equator, mountain weather is unpredictable.
Just a few miles away,
lions and zebra are sweltering under a blazing African sun,
yet here, on Mount Kenya, a sudden squall can bring snow,
creating a winter wonderland.
This extreme climate poses a real challenge
to the mountain's wild inhabitants.
Highland rock hyraxes are found only on Mount Kenya.
High mountain hyraxes have evolved to cope with the cold.
They are much larger than lowland hyraxes
and have exceptionally dense fur,
which allows them to maintain their core temperature
in freezing mountain conditions.
When the sun reappears, the hyraxes save energy by sunbathing.
Giant alpine plants insulate their delicate buds from frost damage
by wrapping them in a protective duvet of leaves,
which unfurl one by one as the temperature rises.
The giant ostrich plume lobelia has evolved a peculiar life cycle.
After several years of growth, it sprouts a huge flower spike,
containing hundreds of tiny flowers swathed in a mass of furry insulation.
Up here, over two and a half miles above sea level,
insect pollinators are scarce,
so the lobelia has developed an alternative partnership.
The plant attracts high-flying sunbirds with a rich supply of nectar.
The sunbirds use the lobelia as a fuelling depot,
a social meeting point
and a sunbathing perch.
In return, the lobelias get pollinated and set seed.
Further down the mountain, at around 3, 000 metres,
lives perhaps Mount Kenya's strangest resident -
the side-striped chameleon.
This cold-blooded reptile is uniquely adapted for mountain life,
far above the altitude where reptiles normally survive.
As dawn breaks, it creeps onto an exposed perch,
where it lines up its body at right angles to the rising sun.
Then, flushing its skin with dark pigment,
it soaks up the rays like a solar panel.
It takes only minutes to raise its temperature 30 degrees Celsius.
Once warmed, it changes to normal daytime colour.
The male chameleon is fiercely territorial.
If another male has the nerve to set foot on his bush,
there's bound to be a fight.
A sneaky bite clinches the bout...
...and the loser slinks off to nurse his bruises.
Further up the mountain,
the hyraxes have also completed their morning sunbathe.
Though it looks like a short-eared rabbit,
the hyrax has some peculiar features
which suggest a much stranger kinship.
The layout of its toes is practically identical to those of an elephant.
Its teeth and bones are also similar, though scaled down a little.
The life of a baby hyrax looks cosy.
But sunbathing out in the open makes them a tempting target for predators.
An augur buzzard.
40 miles west of Mount Kenya,
the Aberdares Mountains are the legacy of an older volcano
that's been severely eroded but still towers over two and a half miles high.
In the frosty alpine grassland, a rare predator is on the prowl.
At lower altitudes, servals have a spotted coat,
but up here, many of them are black.
Some scientists believe
that a dark coat may help the cats to absorb heat on cold, bright days.
In the cool mountain conditions, giant heathers form a dense carpet -
food for Africa's highest resident elephants...
...including one of the biggest tuskers in the world.
Unlike most herbivores, elephants can process almost any plant they find,
including tough heather bushes.
A century ago, elephants migrated freely between the Aberdares and Mount Kenya.
But as the human population has increased locally,
the herd has become marooned in its upland enclave with nowhere to go.
In these mountain forests,
one of Africa's rarest antelopes, the mountain bongo,
is making a last stand.
Bongos are extremely shy and secretive,
staying in dense, shady forest during daylight hours.
Human pressures have now reduced their numbers to around 100
within the Aberdares National Park.
And these have been bred for release into the wild.
The Aberdares lie along the eastern escarpment of the Kenyan Rift Valley,
which here is up to 100 miles across.
Right in the centre of this landscape sits a remarkable volcano,
virtually untouched by the outside world.
Mount Suswa is home to Masai pastoralists,
who graze their herds on the flat crater floor.
But Suswa is no ordinary volcano.
At its centre, steep cliffs plunge 500 metres
into a ring-shaped Rift Valley in miniature.
Around 100 families from the Red Trees Masai community
share the resources of Suswa's grassy crater.
Cattle are at the centre of Masai life - the measure of a family's wealth.
With a six-month dry season
and no permanent streams or lakes anywhere inside the crater,
keeping a supply of drinking water is a constant challenge.
But the Masai have found an ingenious solution to the problem.
A system of metal pipes condenses steam from volcanic vents.
At the centre of the crater,
Mount Suswa's unique circular moat
encloses a lava plateau two miles across -
a miniature lost world protected by a ring of cliffs.
It's thought that Suswa's volcano last erupted
just a couple of hundred years ago,
and parts of the "lost world" are still smouldering.
The Masai consider this wild, tangled jungle a sacred place,
where no hunting or grazing is allowed.
When Suswa's volcano last erupted...
...this moat was a cauldron of molten rock.
The liquid lava has since cooled and solidified,
but along the moat's rim, the volcano still hides a dark secret.
This sunlit boulder pile was formed
when the rock collapsed above an underground cavern,
opening a window into the volcano's main artery,
where molten lava once flowed unseen beneath the skin of the mountain.
Once the volcano stopped erupting and the lava drained away,
it left behind a vast network of empty passages,
some big enough to drive a bus through.
Cave explorers have mapped over six miles of massive tunnels
beneath this single lava flow.
But humans weren't the first creatures to discover this hidden world.
As dusk creeps up the flanks of Mount Suswa,
a troop of baboons is gathering for the night.
Most baboons roost in the treetops
to avoid night-prowling leopards or lions.
But these baboons are heading downwards.
Their destination is an underground chamber
known locally as the baboons' parliament.
As they enter the underworld,
the baboons cross with bats on their way out.
Filming them here requires an infra-red camera
and lights invisible to the baboons.
The walls of the baboon parliament have been worn glassy-smooth
by the hands and feet of generations of baboons.
Rock-climbing in the dark on polished holds
could be considered a hazardous sport,
but presumably, these baboons find it less scary
than sleeping outside with the leopards.
The baboons' final destination
is a series of small ledges high up on the cave wall.
Safe beyond the reach of predators and protected by a roof of solid rock,
the cave dormitory stays warm and dry,
even at the height of the rainy season.
As the last light fades from the sky, the bat exodus intensifies.
This is the world's largest colony of giant mastiff bats.
It's made up entirely of females who have just given birth.
Their pups - thousands of them - can't fly yet
and are completely dependent on their mothers.
But the mother bats must leave their cave to feed.
Packed tightly together for warmth,
the deserted pups are left in a wriggling, squeaking creche.
In all this confusion,
a baby bat has lost its grip and fallen to the cave floor.
The tunnel is alive with creepy creatures of all kinds.
Many are partial to the flesh of a baby bat.
As dawn breaks over the volcano, the baboons leave their sleeping cave.
After a hard night's insect-catching in the skies above the Rift Valley,
the bats return home to roost.
Somehow, in the chaos of fluttering adults
and thousands of squeaking babies,
each mum must track down her own infant to give it its morning feed.
She does this
firstly by remembering where she parked her baby the night before,
then, as she gets closer, by recognising its voice and unique scent.
Like all mammals, baby bats depend on their mothers' milk.
Her little wriggling pup is frantic for its morning feed.
While bats and baboons seek sanctuary
in the protective environment of Mount Suswa's lava caves,
a very different kind of creature has chosen
what must be the Rift Valley's most exposed habitat.
The sheer 500-metre-high cliffs of Mount Ololokwe
are constantly buffeted by strong winds rising from the valley below.
This precarious location
is home to Kenya's largest nesting colony
of Rüppell's griffon vultures.
Vultures thrive in the rift
because the steep valley walls create updraughts,
which they can use to get airborne.
Gliding effortlessly from one thermal to the next,
a vulture can cover 200 miles in a day,
soaring seven miles high with scarcely a wing flap.
From their lofty lookout above the African plains,
nothing escapes their notice.
Out in the Serengeti grassland, the game herds are on the move.
This is what the vultures have been waiting for.
Vultures have a clear pecking order.
The heavy-billed lappet-faced vultures are best equipped to open up a carcass,
so they get the greatest respect.
Once they're finished, the white-backed and griffon vultures pile in
and squabble over the spoils.
The Serengeti is home to the world's greatest game herds.
Most of it lies on the East African Plateau,
perched around a mile above sea level,
the result of uplift by the same lava plume that created the Rift Valley.
But it has another, even more intimate connection
with the rift's fiery origins.
The Serengeti borders Tanzania's most active volcano -
Ol Doinyo Lengai.
In 2007,
Ol Doinyo Lengai produced a spectacular eruption that lasted almost a year...
...throwing out thousands of tons of ash...
...which fell on the surrounding savanna.
As volcanic ash breaks down,
it creates a dense, fertile soil
which is hard for tree roots to penetrate
but is perfect for grass.
The great grass plains of the Serengeti can support over a million wildebeest
only because of the fertility of the vast volcanic ash deposits
on which they grow.
South of the Serengeti, in southern Tanzania,
the Rift Valley's eastern and western branches converge.
Close to their meeting point lies one of the Great Rift's best-kept secrets.
The alpine grassland of the Kitulo Plateau,
known locally as God's Garden.
It provides the stage
for one of Africa's most spectacular floral displays.
The Kitulo meadows are serviced by some unusual insect pollinators.
This is a monkey beetle, a hairy-coated living fossil.
During the ice ages, when Africa was much cooler,
monkey beetles were widespread,
but now they survive only in a few high-altitude meadow lands.
The spectacular plumed mountain marsh widowbird
is another local specialty.
On the slopes of the Kitulo Plateau,
a line of protea sugar bushes marks the transition between meadow and forest.
Their blooms produce a feast of pollen and nectar,
but for the monkey beetles, it's a dangerous prize.
Once in place, the Temple's chameleon,
an insect hunter peculiar to this corner of Tanzania,
hardly needs to move.
Chameleons are unique among reptiles
in having the ability to swivel their eyes independently.
When they line them up,
the stereo image allows them to launch their sticky tongue
exactly the right distance to nail their victim
every time.
Below the line of sugar bushes, where the chameleons stalk their prey,
a belt of dense jungle clings to rain-drenched mountain slopes.
The cool, humid climate fosters ancient tree ferns
and towering hardwood trees.
Isolated from other mountain forests
by the converging arms of the Great Rift Valley,
Mount Rungwe's forests are home to unique creatures.
The area has recently become the focus for scientific research
and new species are being discovered all the time...
...even up in the treetops.
This is a kipunji,
first discovered in 2005 and never filmed before.
In looks and behaviour, the new monkey resembles a mangabey.
But its DNA is similar to a baboon's.
For now, the evolutionary origins of the charismatic kipunji
remain shrouded in mystery.
Kipunjis are particularly fond of this sticky orange cucumber fruit,
which sprouts from vines in the treetops.
They're known to feed on over 100 different plants
and play a crucial role in dispersing their seeds.
But even while scientists begin to uncover their secret lives,
kipunjis are teetering on the verge of extinction.
As the isolated forests around Mount Rungwe
are cleared for farming and firewood...
...the kipunjis' unique forest habitat is shrinking.
With a mere 1, 000 individuals remaining in the wild,
they are already the rarest monkeys in Africa.
There may be little time left to study them.
Fortunately, kipunjis do have friends,
and a project is now under way to safeguard a part of their forest home
and involve local people in their protection.
North-west of the kipunjis' mountain home,
a branch of the Great Rift curves between Tanzania and the Congo.
The valley floor contains vast deepwater lakes,
while to the west lies a series of volcanic mountains
up to three miles high.
And the most spectacular are here,
in the Virungas National Park.
The Virungas volcanoes are home to Africa's largest and rarest great ape...
...the mountain gorilla.
Mountain gorillas evolved from lowland gorillas,
which colonised the Virungas less than half a million years ago,
soon after these volcanoes formed.
They responded to the challenge of high-altitude living
by becoming larger and furrier than their lowland cousins,
enabling them to cope with the permanently cold, miserable weather.
A combination of fertile volcanic soil and two metres of annual rainfall
encourages a profusion of plants on the mountain slopes...
...ideal fodder for giant vegetarian apes.
In response to their fibrous diet,
the gorillas have developed extra-large chewing teeth
and extra-powerful jaw muscles
anchored to a prominent ridge of bone on the crown of their head.
Gorilla society is well ordered,
with each band of females and their young
protected by a huge silver-backed male.
With few natural enemies prepared to brave the wrath of a silverback,
young gorillas can play to their hearts' content.
The unique characteristics
that separate mountain gorillas from their lowland cousins
evolved as a result of their isolation
on just a handful of volcanoes along the Great Rift.
It makes them vulnerable, especially to poaching -
though, fortunately, they have many human allies
fighting to ensure their survival.
Mountain gorillas are, without doubt,
one of the Great Rift's most remarkable creatures,
their evolution uniquely shaped by the volcanic terrain in which they live.
That terrain has itself been moulded and shaped by the fiery rocks beneath,
creating a complex of valleys and volcanoes
spanning the length of East Africa.
For those animals and plants
which were able to adapt to the changing conditions,
the Great Rift has promoted a remarkable burst of evolution.
In this turbulent landscape,
volcanic fire has proved to be less a destroyer,
but more a creator of new life.
And that is what is so special about Africa's Great Rift.
One of the Great Rift team's most difficult assignments
took them deep into Mount suswa's volcanic crater,
home to a troop of very unusual baboons.
Instead of spending the night in trees, they have taken to sleeping down caves.
Cameraman Justin Maguire is here to film them.
Masai elderJeremiah Ole Tanin will be Justin's guide.
He hopes that the baboons will attract visitors to Mount suswa,
generating income for his community.
Wow. That's pretty impressive.
- Yeah. - Fantastic cave.
So, this is where the baboons come and sleep, is it?
Yeah. It is where they spend during the night.
With the baboons out foraging for the day,
Justin has a chance to recce the cave.
Jeremiah warns that when they return at dusk,
they will be wary and easily spooked,
and baboons can be dangerous.
Justin will have to be on his guard.
- So, how many baboons use this cave? - Over 100.
100 baboons? That's incredible. And I'm going to be in there with them?
- So it's going to make 101 baboons? - Oh, yeah. (LAUGHS)
- You think they'll be frightened of me? - Yeah, yeah.
Well, I'm hoping I can be a bit like a baboon and they'll be relaxed with me.
Justin's problem is that if he tries to climb down here at night,
he'll wake any baboons sleeping close to the entrance.
Luckily, Jeremiah has a cunning plan.
The Masai know of a concealed entrance
which should give Justin the chance to sneak in unseen.
Before venturing down at night,
he decides to go for a daylight run-through.
- That is one bendy ladder. - Yeah.
OK. Here goes. Freak!
To film in such a tricky situation, Justin has an experienced team with him.
OK. I'm sending your bag down, OK?
Phil Chapman is the director, but he is also an experienced caver.
Once inside, it becomes apparent
that getting both them and the equipment through the cave
is not going to be as easy as they first thought.
- It looks tiny, Jeremiah. - Yeah.
- Can we really get through there? - Yeah, yeah.
I can hear bats. Are there bats in there?
I do like these things.
OK.
That's quite good. That's fine for them to crawl through.
- Oh, watch your head. - Very sharp stalactites.
Inside, the team find thousands of bats preparing for a night's hunting.
Not only do the bats produce tonnes of droppings,
they also share the cave with less welcome inhabitants.
- Oooh, look. - Look at these millions of fleas.
I can feel them crawling up my trouser leg.
That is quite amazing.
I'm absolutely covered in fleas. Look at my leg.
Finally, they reach the baboons' sleeping chamber,
and Jeremiah was right.
The signs of baboons are everywhere.
As you can just see, all the rocks are smooth.
Very smooth. Shiny.
- Just feel it. - Yeah, that's incredibly smooth.
- Very smooth and shiny. - Yeah.
It's just because of rubbing of their bottom, the...baboons...
Right. So, these have got...
They're smooth because of...
the baboons' bottoms have rubbed on these for many years?
- Yeah, yeah. They've been rubbed... - I can see baboon poo on the top.
- Oh, yeah. See? - OK.
Knowing that baboons are here in numbers is great news for filming,
but poses Justin with another problem.
Baboons could be extremely dangerous in the confined space of the cave,
so Justin needs some way to scare them off if they come too close.
The BBC, in their thoughtfulness, have provided me with a rape alarm,
in case I have trouble with any of the baboons.
There are some big males, aren't there?
- Oh, yeah. - I'm hoping I'm not going to have to...
Ah.
I'm hoping I'm not going to get to the stage they're attacking me.
Oh, yes.
Not only will the team have to build a hide,
they also have to rig up special lights producing infra-red,
which the baboons can't see.
But it's close to sunset, and the baboons are already on their way.
We don't have enough time. That's the big problem.
No, seriously, we're very close to not being able to light this.
We're going to have to start now.
If the baboons return early and find the team,
they may desert the cave, scuppering any chance of filming.
It's 5.50, and the sun will be setting pretty soon.
We've run out of time and we don't want to be here whilst the baboons return.
Phil, I think you guys should really go.
OK.
- Plug that one in. - I'll plug that one in, yeah.
With the lights rigged,
the team leave to allow the baboons to settle in for the night.
We've just got down into the cave now. Um, it's night.
It's one thing walking through the cave with all the guys,
another walking through it at night with 60 baboons,
which I am a little bit nervous about.
Justin is in total darkness,
filming himself in infra-red light,
which neither he nor the baboons can see.
I've found my guide string now,
which leads me to the last bit of the hide.
I think a baboon's seen me.
Right. I've made it into my hide.
And, uh...I've definitely been spotted by one baboon.
I think the baboon that spotted me has fallen asleep, so, hopefully...
No.
He's still barking.
Incredibly quiet. I'm really amazed how quietly they sleep.
The only thing that's changing is the bat sounds.
There's more and more bats in the cave,
which is a clear signal that dawn is approaching,
and soon the baboons are going to wake up, I think.
It seems like a defining sound of the morning are the babies squealing.
It sounds like any... any household, really.
Justin's perseverance has revealed for the first time
the underground behaviour of these unique baboons.
And back at camp, he can share these glimpses with the team.
I have never seen a baboon sleeping.
In the past, baboons were persecuted for killing livestock.
However, attitudes are slowly changing.
They will not be killing them.
We want now to start to conserve them,
to... to get a relationship between baboons and human beings,
because their community can benefit from them.
Justin's filming quest has been a success,
and as interest in Mount suswa increases,
the Masai will be able to share with others
their unique cave-dwelling baboons.