Original subtitles

Human beings venture into the highest parts of our planet at their peril.

Some might think that by climbing a great mountain they have somehow conquered it,

but we can only be visitors here.

This is a frozen, alien world.

This is the other extreme.

One of the lowest, hottest places on Earth.

It's over a hundred metres below the level of the sea.

But here, a mountain is in gestation.

Pools of sulphuric acid are indications that deep underground

there are titanic stirrings.

This is the Danakil Depression in Ethiopia,

lying within a colossal rent in the Earth's surface

where giant land masses are pulling away from one another.

Lava rises to the surface through this crack in the crust,

creating a chain of young volcanoes.

This one, Erta-Ale, is today the longest continually-erupting volcano on the planet.

A lake of lava that has been molten for over 100 years.

These same volcanic forces

also created Ethiopia's highlands.

Seventy million years ago, this land was just as flat and as deep as the Danakil Depression.

Molten lava, rising from the Earth's core,

forced up a huge dome of rock 500 miles wide.

The Roof of Africa.

Over millennia, rain and ice carved the rock into a landscape of spires and canyons.

These summits, nearly three miles up,

are home to some very remarkable mountaineers.

Gelada baboons.

They are unique to the highlands of Ethiopia.

The cliffs where they sleep are for expert climbers only.

And geladas certainly have the right equipment,

the strongest fingers of any primate and an utterly fearless disposition.

But you need more than a head for heights to survive up here.

A day in the geladas' life reveals how they've risen to the challenge.

For all monkeys, morning is grooming time,

a chance to catch up with friends.

But unlike other monkeys, geladas chatter constantly while they do it.

It's a great way to network while your hands are busy.

But these socials can't go on for too long.

Geladas have a busy daily schedule and there's work to be done.

Most monkeys couldn't live up here.

There's no fruit and few insects to feed on.

But geladas are unique.

They're the only monkeys in the world to live almost entirely on grass.

They live in the largest assemblies formed by any monkeys.

Some groups are 800 strong and they crop the high meadows like herds of wildebeest.

The geladas graze alongside walia ibex,

which are also unique to these highlands.

These rare creatures are usually very shy,

but they drop their guard when the geladas are around.

You might expect that grazers would avoid each other's patch,

but this is a special alliance from which both partners benefit.

It's not so risky to put your head down if others are on the lookout.

Ethiopian wolves.

They won't attempt an attack in broad daylight.

But at dusk, the plateau becomes a more dangerous place.

With the grazing largely over,

there's a last chance to socialise before returning to the sleeping cliffs.

An early warning system puts everyone on the alert.

Their day ends as it began, safe on the steep cliffs.

The Ethiopian volcanoes are dormant

but elsewhere, others still rage.

Volcanoes form the backbone of the longest mountain chain on our planet,

the Andes of South America.

This vast range stretches 5, 000 miles from the equator down to the Antarctic.

It formed as the floor of the Pacific Ocean

slid beneath the South American continent, buckling its edge.

At the southern end stand the mountains of Patagonia.

It's high summer.

But the Andes have the most unstable mountain weather on the planet

and storms can erupt without warning.

Temperatures plummet and guanacos and their newborn young

must suddenly endure a blizzard.

Truly, all seasons in one day.

A puma, the lion of the Andes.

Pumas are usually solitary and secretive.

To see a group walking boldly in the open is extremely rare.

It's a family, a mother with four cubs.

She has just one brief summer

in which to teach them their mountain survival techniques.

Rearing four cubs to this age is an exceptional feat,

but she does have an excellent territory, rich in food and water.

Although the cubs are now as large as their mother,

they still rely on her for their food.

It will be another year before the cubs can hunt for themselves.

Without their mother's skill and experience,

they would never survive their first winter.

Battered by hurricane-force winds, these slopes are now lifeless.

Further north, they hold other dangers.

Moving at 250 miles an hour,

an avalanche destroys everything in its path.

In the American Rockies, 100, 000 avalanches devastate the slopes every winter.

This huge mountain chain continues the great spine

that runs from Patagonia to Alaska.

The slopes of the Rockies, bleak though they are,

provide a winter refuge for some animals.

A mother grizzly emerges from her den after six months dozing underground.

Her two cubs follow her and take their first steps in the outside world.

These steep slopes provide a sanctuary for the cubs.

A male bear would kill and eat them given the chance

but big animals find it difficult to get about here.

Males may be twice the size of a female and even she can have problems.

Her cubs, however, make light of the snow and of life in general.

But the mother faces a dilemma.

It's six months since she last fed and her milk is starting to run dry.

She must soon leave the safety of these nursery slopes

and lead her cubs away from the mountain.

If she delays, the whole family will risk starvation.

Summer reveals the true nature of the Rockies.

Stripped of snow, the peaks bare their sculpted forms.

Only now can mountaineers reclaim the upper reaches.

Two miles up, the crumbling precipices seem devoid of life.

But there are animals here.

A grizzly bear.

It seems to be an odd creature to find on these high rocky slopes.

It's hard to imagine what could have attracted it here.

At this time of the year, bears should be fattening up for the winter,

yet they gather in some numbers on these apparently barren slopes.

They're searching for a rather unusual food.

Moths.

Millions have flown up here to escape the heat of the lowlands

and they're now roosting among the rocks.

Moths may seem a meagre meal for a bear,

but their bodies are rich in fat

and can make all the difference in a bear's annual struggle for survival.

Another battle is being waged here but on a much longer time scale.

These loose boulders are the mountains' crumbling bones.

The Rockies are no longer rising but slowly disintegrating.

All mountains everywhere are being worn down by frost, snow and ice.

The Alps were raised some 15 million years ago

as Africa, drifting northwards, collided with the southern edge of Europe.

These spires are the eroded remains of an ancient seabed

that once stretched between the two continents.

But these are just the Alpine foothills.

The range at its centre rises to three miles high

and is crowned with permanent snows.

The Matterhorn, its summit too steep to hold a snowfield.

Mont Blanc, the highest peak in Western Europe.

The distinctive jagged shapes of the Alps

were carved by those great mountain sculptors,

the glaciers.

Immense rivers of moving ice, laden with rock,

grind their way down the mountains, gouging out deep valleys.

They're the most powerful erosive force on our planet.

A moulin, a shaft in the ice opened by meltwater

as it plunges into the depths of the glacier.

Like the water running through it, the ice itself is constantly moving,

flowing down the valley with unstoppable force.

Alpine glaciers may seem immense,

but they're dwarfed by those in the great ranges

that divide the Indian subcontinent from Tibet.

This is the boulder-strewn snout of the giant Baltoro Glacier

in the Karakoram Mountains of Pakistan.

It's the biggest mountain glacier on Earth,

43 miles long and over three miles wide.

This huge, ice-filled valley is so large it's clearly visible from space.

This is the greatest concentration of peaks over five miles high

to be found anywhere on Earth.

They're the most dangerous mountains of all.

K2 and her sister peaks have claimed more lives than any others.

The peaks here rise so precipitously,

the glaciers are so steep and crevassed,

that few except the most skilled mountaineers can penetrate these ranges.

Markhor gather for their annual rut.

Males must fight for the right to breed,

but on these sheer cliffs, any slip by either animal could be fatal.

A snow leopard, the rarest of Himalayan animals.

It's a female returning to her lair.

These are the first intimate images of snow leopard ever filmed in the wild.

She greets her one-year-old cub.

Her den is well chosen.

It has exceptional views of the surrounding cliffs.

On these treacherous slopes,

no hunter other than the snow leopard

would have a chance of catching such agile prey.

A female with young makes an easier target.

Her large paws give an excellent grip

and that long tail helps her balance.

Silently she positions herself above her prey.

She returns with nothing.

Golden eagles patrol these cliffs

in search of the weak or injured.

With a two-metre wingspan,

this bird could easily take a young markhor.

Eagles hunt by sight and the thickening veil of snow forces them to give up.

For the leopard, the snow provides cover and creates an opportunity.

The worsening weather dampens the sound of her approach,

allowing her to get within striking distance.

It was an act of desperation to try and catch such a large animal.

Wolves have made a kill, giving other hunters a chance to scavenge.

The worst of the blizzard brings success for the snow leopard.

But having descended so far to make the kill,

she has a gruelling climb to get back to her lair.

The cub must be patient.

It will be a year before it has the strength and skill

to kill for itself on these difficult slopes.

The snow leopard is an almost mythical creature,

an icon of the wilderness,

an animal few humans have ever glimpsed

for its world is one we seldom visit.

The Karakoram lie at the western end of a range

that stretches across a tenth of our planet,

the Himalayas.

These, the highest mountains in the world,

like other great ranges, were created by the collision of continents.

Some 50 million years ago, India collided with Tibet,

thrusting up these immense peaks which are still rising.

This vast barrier of rock and ice is so colossal

it shapes the world's climate.

Warm winds from India, full of moisture, are forced upwards by the Himalayas.

As the air rises, so it cools, causing clouds to form

and the monsoon is born.

At high altitudes, the monsoon rains fall as snow.

Here, at the far eastern end of the range in China,

one inhabitant endures the bitter winters out in the open.

Most other bears would be sleeping underground by now

but the giant panda can't fatten up enough to hibernate.

Its food, bamboo, on which it totally relies,

has so little nutritional value

that it can't build up a store of fat like other bears.

Most of the creatures here move up or down the slopes with the seasons,

but the panda is held captive by its diet,

for the kind of bamboo it eats only grows at this altitude.

But these forests hold fewer challenges for the more mobile.

The golden snub-nosed monkey,

like the giant panda, lives only in China.

Their thick fur allows them to survive at greater altitudes than any other monkey.

And when the cold bites, they have these upper slopes to themselves.

Even if you have a warm coat,

it apparently helps to surround yourself with as many layers as possible.

But at least these monkeys have a choice.

If they tired of tree bark and other survival food,

they can always descend to lower, warmer altitudes

and not return until spring.

As the snows retreat, trees come into bloom.

Cherry blossom.

Rhododendrons. Here in their natural home,

they form great forests and fill the landscape with the colours of a new season.

These forests are host to a rich variety of springtime migrants.

Beneath the blooms, another display.

It's the mating season for oriental pheasants,

Himalayan monal,

tragopan and blood pheasant.

Musk deer make the most of a short flush of spring foods.

This male smells a potential mate.

The red panda, rarely glimpsed in the wild.

It was once considered a kind of raccoon

but is now believed to be a small mountain bear.

By midsummer, its larger more famous relative

has retreated into a cave.

A giant panda nurses a tiny week-old baby.

Her tender cleaning wards off infection.

She won't leave this cave for three weeks.

Not while her cub is so utterly helpless.

Progress is slow, for milk produced on a diet of bamboo is wretchedly poor.

Four weeks old and the cub is still blind.

Its eyes do not fully open until three months after birth.

But the chances of the cub reaching adulthood are slim.

The struggle of a giant panda mother to raise her cub is a touching symbol

of the precariousness of life in the mountains.

On the highest summits of our planet, nothing can live permanently.

The highest peak of all, Mount Everest.

Five and a half miles above sea level and still rising.

The roof of our world.

Of those humans who've tried to climb it, 1 in 10 have lost their lives.

Those that succeed can stand for only a few moments on its summit.

The Nepalese call it, "A mountain so high no bird can fly above it."

But each year, over 50, 000 demoiselle cranes

set out on one of the most challenging migrations on Earth.

To reach their over-wintering grounds in India, they must cross the Himalayas.

By late morning, ferocious winds are roaring past the peaks.

The cranes must gain height to avoid the building storm.

They've hit serious turbulence.

They must turn back or risk death.

A new day and a new opportunity.

The flock stay in close contact by calling to one another.

Weak from lack of food and water,

they use thermals, rising columns of warm air, to gain height.

For many, this is their first journey across the Himalayas.

For some, it will be their last.

The golden eagles have been expecting them.

The eagles work in pairs to separate a young crane from the flock.

It escapes the clutches of one and is caught by another.

But even a young crane is a heavy prize

and the eagle has to struggle to control it.

The mother can wait no longer.

This is a desperate race against worsening weather.

The rest of the flock battle on.

In the final ascent, every wing-beat becomes an exhausting struggle.

At last, they are over the highest barrier that lies in their way.

But like all who visit the world of the high mountains,

they dare not linger.