0:00:50 > 0:00:55Our planet, the Earth, is, as far as we know, unique in the universe.
0:00:55 > 0:01:02It contains life. Even in its most barren stretches, there are animals.
0:01:13 > 0:01:16Around the equator, where those two essentials for life,
0:01:16 > 0:01:21sunshine and moisture, are most abundant, great forests grow,
0:01:21 > 0:01:24and here plants and animals proliferate in such numbers
0:01:24 > 0:01:29that we still have not even named all the different species.
0:01:40 > 0:01:45Here, animals and plants, insects and birds, mammals and man
0:01:45 > 0:01:48live together in intimate and complex communities,
0:01:48 > 0:01:51each dependent on one another.
0:01:51 > 0:01:56Two thirds of the surface of this unique planet are covered by water,
0:01:56 > 0:01:58and it was here indeed that life began.
0:02:11 > 0:02:15From the oceans, it has spread even to the summits of the highest mountains,
0:02:15 > 0:02:20as animals and plants have responded to the changing face of the Earth.
0:02:36 > 0:02:42This river, the Kali Gandaki, has cut its way, in the most remarkable fashion,
0:02:42 > 0:02:46right through the highest range of mountains in the world, the Himalaya.
0:02:46 > 0:02:50To the east of me rises Annapurna, over 26,000 feet high.
0:02:50 > 0:02:53To the west, Dhaulagiri, even higher.
0:02:53 > 0:02:57Their two summits are a mere 22 miles apart,
0:02:57 > 0:03:00and I am four vertical miles below them.
0:03:00 > 0:03:04And that makes this the deepest valley in the world.
0:03:04 > 0:03:08At this altitude, about 7,000 feet, it's quite warm,
0:03:08 > 0:03:14and animal and plant life on the flanks of the valley is both rich and abundant.
0:03:14 > 0:03:17The blossoms on these trees may well look familiar.
0:03:17 > 0:03:20Flowers like them grow in gardens all over the world.
0:03:20 > 0:03:26But these are wild plants and this is their original home. They're rhododendrons.
0:03:29 > 0:03:33And here they are food for monkeys, grey langurs,
0:03:33 > 0:03:36reminders that the hot plains of Southern Nepal and the tropics
0:03:36 > 0:03:38are not far away to the south.
0:03:48 > 0:03:53But they aren't just monkey food. They are the rhododendrons' advertisements,
0:03:53 > 0:03:57attracting birds and insects which will sip their nectar, gather their pollen,
0:03:57 > 0:04:00and so bring about their fertilisation.
0:04:07 > 0:04:12The ring-necked parakeet also comes from the tropics.
0:04:12 > 0:04:15Here, it's at the top of its range.
0:04:15 > 0:04:18Any higher and the weather will be too cold for it.
0:04:18 > 0:04:21Beneath the rhododendrons live several species
0:04:21 > 0:04:24of those most splendid of Asia's birds, the pheasants.
0:04:24 > 0:04:29The blood pheasant, for all its delicate beauty, is a plainer member of the family.
0:04:29 > 0:04:33The cock Tragopan is surely the most magnificent.
0:04:41 > 0:04:46Until, that is, you see a cock Impeyan pheasant,
0:04:46 > 0:04:49with the coronet of a peacock
0:04:49 > 0:04:53and the burnished, metallic iridescence of a tropical butterfly.
0:05:01 > 0:05:06The Impeyan's hen, like those of all pheasants, is comparatively dull.
0:05:19 > 0:05:21This deepest of all valleys in the world
0:05:21 > 0:05:24enables you to walk within a few days
0:05:24 > 0:05:26from the tropics, in its lower reaches,
0:05:26 > 0:05:29to the equivalent of the poles on the slopes high above,
0:05:29 > 0:05:32and to see as you make the journey
0:05:32 > 0:05:34how closely animals and plants
0:05:34 > 0:05:36are matched to the changing circumstances.
0:05:36 > 0:05:41As you walk higher, the rhododendron forest gets thinner and hung with moss.
0:05:41 > 0:05:45The air is moist and it can be quite warm during the day.
0:05:45 > 0:05:48And now, in summer, there are orchids here.
0:05:54 > 0:05:59On the ground beneath, flowers appear in close-packed bunches,
0:05:59 > 0:06:02protecting one another from the night frosts.
0:06:04 > 0:06:10The little Himalayan panda is certainly very well protected against the cold.
0:06:10 > 0:06:13Not only does it have warm, dense fur,
0:06:13 > 0:06:16but, like many animals that spend time in the snow,
0:06:16 > 0:06:19it has hair on the soles of its feet.
0:06:19 > 0:06:26That keeps its feet warm on the snow and stops it from sliding around on ice.
0:06:26 > 0:06:31Now, in the summer, it also helps in getting a grip on wet, slippery branches.
0:06:36 > 0:06:41It's primarily a vegetarian, collecting buds and leaves and fruit,
0:06:41 > 0:06:45but it also takes eggs from a bird's nest, if it can find one.
0:06:49 > 0:06:52On the ground, and scarcely bigger than the panda,
0:06:52 > 0:06:57one of the shyest animals of the Himalayan forests, a musk deer.
0:07:01 > 0:07:05In these tangled trees, antlers would be a considerable handicap,
0:07:05 > 0:07:07and the musk deer doesn't develop them.
0:07:07 > 0:07:10A male fights instead with the short, sharp tusks in his upper jaw.
0:07:10 > 0:07:15They feed on moss, lichen and leaves,
0:07:15 > 0:07:18and are so agile and well-adapted to a mountain life
0:07:18 > 0:07:21that they can climb steep cliffs in search of food.
0:07:24 > 0:07:29When a musk deer or any other animal of any size dies, the vultures come.
0:07:35 > 0:07:37These are griffons,
0:07:37 > 0:07:40very similar to those that circle the skies above Indian villages
0:07:40 > 0:07:42down in the hot foothills.
0:07:42 > 0:07:46They are common in this forest up to 7,000 or 8,000 feet.
0:08:09 > 0:08:14So the lives of all these creatures are connected,
0:08:14 > 0:08:18one with the other, either directly or indirectly,
0:08:18 > 0:08:21and all are ultimately dependent upon the vegetation.
0:08:21 > 0:08:27But of course both animals and plants are also greatly affected by the physical environment.
0:08:27 > 0:08:32I've climbed several thousand feet now and things are beginning to change.
0:08:32 > 0:08:37It's getting colder, and the rhododendrons are giving way to fir trees,
0:08:37 > 0:08:41and that will mean a change in the animals that live here.
0:08:45 > 0:08:49The yellow-throated marten has a broad taste in food.
0:08:49 > 0:08:54It takes fruit on occasion, catches a few insects now and then,
0:08:54 > 0:08:57but it relishes about all, small rodents, like mice and squirrels,
0:08:57 > 0:08:59and there are quite a lot to be found here.
0:08:59 > 0:09:03Even when winter comes, and the forests are deep in snow, it will remain active.
0:09:03 > 0:09:07But it's a great traveller, and if the weather becomes very cold indeed,
0:09:07 > 0:09:11it will descend to lower altitudes for a spell.
0:09:21 > 0:09:25The Himalayan bear is capable of living very high indeed.
0:09:25 > 0:09:29Its thick fur protects it against severe cold,
0:09:29 > 0:09:33but its range is not limited by temperature so much as by food supply.
0:09:33 > 0:09:38In spite of its size, it seldom tackles any animal bigger than a mouse,
0:09:38 > 0:09:42and it lives for most of the time on just ants, grubs, nuts and leaves,
0:09:42 > 0:09:46so it seldom goes any higher than the forest can grow.
0:09:52 > 0:09:59And now, getting on for 10,000 feet up, the forest is beginning to thin.
0:09:59 > 0:10:04In summer, there's not much rain here, for most has fallen at lower altitudes.
0:10:04 > 0:10:06In winter, it gets extremely cold.
0:10:06 > 0:10:13Those conditions don't suit rhododendrons. Here only conifers flourish in large numbers.
0:10:13 > 0:10:18High though we are, the Kali Gandaki is still a very broad river.
0:10:18 > 0:10:20Remarkably, and indeed mysteriously,
0:10:20 > 0:10:26it doesn't rise from the flanks of these giant mountains but cuts right through them.
0:10:26 > 0:10:27The people of the foothills
0:10:27 > 0:10:31have long since recognised the value of this extraordinary corridor
0:10:31 > 0:10:33that leads right through the Himalayas,
0:10:33 > 0:10:37and all summer trains of mules trudge up the valley,
0:10:37 > 0:10:42taking barley and buckwheat to trade with Tibetans for wool and salt.
0:10:44 > 0:10:48All the way up the valley are villages where the muleteers can stay and rest,
0:10:48 > 0:10:51but during the summer few do so.
0:10:51 > 0:10:55Most trudge tirelessly upwards for as long as there's daylight.
0:11:43 > 0:11:45A lammergeier, the bearded vulture,
0:11:45 > 0:11:49a mountain bird that soars around the high valleys of Asia
0:11:49 > 0:11:51and still in a few remote parts of Europe,
0:11:51 > 0:11:54but nowhere higher than this.
0:11:59 > 0:12:03And a sign that now we are getting really high - snow cock.
0:12:03 > 0:12:07Its dappled white plumage gives it camouflage against the broken snow
0:12:07 > 0:12:12that even now, in summer, can fall at these altitudes.
0:12:12 > 0:12:15They forage for seeds and rootlets in the thin turf.
0:12:25 > 0:12:29There are no trees now, just a few small shrubs
0:12:29 > 0:12:30and dry, withered grass.
0:12:30 > 0:12:32But that's enough for the tahr.
0:12:32 > 0:12:37It is neither a true sheep or a true goat, but related equally to them both.
0:12:37 > 0:12:43It will eat almost anything that's green, and is grateful to find it in this bleak land.
0:12:43 > 0:12:45Another typically mountain creature -
0:12:45 > 0:12:48the red-billed chough, a kind of crow.
0:12:48 > 0:12:51They search the rocks for insects, grubs, odd seeds.
0:12:51 > 0:12:53They will take most things.
0:13:00 > 0:13:06Their cousins, yellow-billed choughs, go as high as any bird in the world,
0:13:06 > 0:13:11riding the rising wind currents to the height of the snow peaks themselves.
0:13:36 > 0:13:40Flowers at this altitude can only come from small cushion plants,
0:13:40 > 0:13:43huddled together against the cold.
0:13:43 > 0:13:47Higher still, little can grow except lichens.
0:13:47 > 0:13:51Now it's so cold that growth may only be possible for a few days in the year.
0:13:53 > 0:13:58And yet, in these bleak regions, people live.
0:13:58 > 0:14:01To help plough the fields, they use the yak,
0:14:01 > 0:14:05a domesticated creature that once roamed wild on the plains of Tibet,
0:14:05 > 0:14:09the only large mammal that lives permanently as high as man.
0:14:11 > 0:14:16The people, Bhotias and Sherpas, grow not only barley but potatoes,
0:14:16 > 0:14:20a crop that was first cultivated by the Incas in the Andes
0:14:20 > 0:14:23and was introduced here a century or so ago.
0:14:23 > 0:14:28These highland people are well-adapted to life at these altitudes.
0:14:28 > 0:14:33Their blood contains a particularly high number of red corpuscles
0:14:33 > 0:14:38and so can carry more oxygen in it than a lowlander's can.
0:14:38 > 0:14:43Certainly, when it comes to walking at these high altitudes,
0:14:43 > 0:14:47they're very much better adapted than I am.
0:14:47 > 0:14:56So, all the living creatures in these high valleys are adapted to their environment,
0:14:56 > 0:15:00both their biological environment and their physical environment.
0:15:00 > 0:15:07And yet, in terms of biological history, those adaptations are very recent indeed.
0:15:07 > 0:15:15These immense mountains, the eternal hills, are in fact far from eternal.
0:15:15 > 0:15:20They are younger than the plains of India to the south,
0:15:20 > 0:15:23or the plateau of Tibet to the north.
0:15:23 > 0:15:29They were raised to their present height about 65 million years ago
0:15:29 > 0:15:32from the bottom of the sea.
0:15:32 > 0:15:36And what is the evidence for that extraordinary statement?
0:15:36 > 0:15:40It can be found all over the place, just up here.
0:15:48 > 0:15:51These slopes are littered...
0:15:53 > 0:15:58with fragments like these.
0:15:59 > 0:16:04This is obviously a shell that's been turned to stone, a fossil.
0:16:04 > 0:16:08Although there are no molluscs alive today exactly like this one,
0:16:08 > 0:16:13there are some which are sufficiently similar for us to be sure that it lived
0:16:13 > 0:16:19in water. And if we analyse the rock in which it's embedded,
0:16:19 > 0:16:24it's clear that that was mud laid down at the bottom of a sea.
0:16:24 > 0:16:28But I am as far as possible as it is to be from the sea.
0:16:28 > 0:16:32Not only I am in the middle of Asia, hundreds of miles from the sea,
0:16:32 > 0:16:36but I am over two vertical miles above its level.
0:16:36 > 0:16:41What forces could possibly have raised the seabed to these heights?
0:16:41 > 0:16:45Well, we now know that those forces are still in action,
0:16:45 > 0:16:48that these mountains are still rising
0:16:48 > 0:16:51and that land is still being created.
0:17:14 > 0:17:16I'm in Iceland.
0:17:16 > 0:17:18This fantastic fountain of fire
0:17:18 > 0:17:21rising 200 feet or so into the air behind me
0:17:21 > 0:17:24is molten rock.
0:17:24 > 0:17:27Fine ash is falling all around,
0:17:27 > 0:17:30there are gusts of choking, poisonous gas,
0:17:30 > 0:17:36and it's so hot that this is just about as close as I can get to it.
0:17:49 > 0:17:53The sheer weight of these molten ingots of rock
0:17:53 > 0:17:57prevents them being swept away from the vent by the gale,
0:17:57 > 0:18:00so there's little danger of them suddenly coming our way.
0:18:05 > 0:18:09Less dramatic than the fire fountain, but perhaps more sinister
0:18:09 > 0:18:16is this tide of black slag that is slowly creeping over the surface of the land.
0:18:16 > 0:18:20In parts, it's red-hot and molten and flows like treacle,
0:18:20 > 0:18:25but on the edges it's cooled enough for me to be able to handle it.
0:18:25 > 0:18:29It's black, it's heavy, and it's called basalt.
0:18:29 > 0:18:34Basalt like this has been welling up from deep in the Earth's crust
0:18:34 > 0:18:37over since the beginning of the history of our planet.
0:18:47 > 0:18:51A flow may travel for as much as 25 miles.
0:18:51 > 0:18:55Sometimes it moves no faster than a man can walk,
0:18:55 > 0:18:58but sometimes it races along at an extraordinary speed,
0:18:58 > 0:19:0240 miles an hour, and nothing - nothing - can stop it.
0:19:14 > 0:19:17Sometimes so much lava is produced
0:19:17 > 0:19:20that it accumulates in flows 100 feet or so thick.
0:19:20 > 0:19:26Then the centre layers of it cool exceptionally slowly and very evenly,
0:19:26 > 0:19:28and this is the result.
0:19:29 > 0:19:34Here, at the Giant's Causeway, the top of the lava flow has been eroded away,
0:19:34 > 0:19:38for the eruptions took place 50 million years ago.
0:19:38 > 0:19:42The cooling contractions have produced the effect you see in drying mud,
0:19:42 > 0:19:45though here the cracks extend to a much greater depth
0:19:45 > 0:19:49to produce six-sided columns about a foot and a half across.
0:19:51 > 0:19:57In the Hebrides, there's another lava flow that erupted at about the same time
0:19:57 > 0:20:00and formed Fingal's Cave.
0:20:04 > 0:20:10The blanketing layer of lava that slowed down the cooling of the interior is still uneroded,
0:20:10 > 0:20:15and beneath it the near-perfect basalt columns rise almost 20 feet high.
0:20:37 > 0:20:40Basalt that doesn't contain very much gas
0:20:40 > 0:20:43wells out from below almost quietly.
0:21:13 > 0:21:17But if the lava has been extruded under great pressure,
0:21:17 > 0:21:20it may be full of gas, and then it behaves very differently.
0:21:28 > 0:21:32Sometimes a flow sweeps down over a forest,
0:21:32 > 0:21:34incinerating the trees in its path.
0:21:55 > 0:22:01Most dramatic of all, the lava sometimes wells up inside a crater and can't escape.
0:22:01 > 0:22:06Then it forms that most fearsome of nature's spectacles, a lava lake,
0:22:06 > 0:22:09like this one in Nyiragongo in Africa.
0:22:09 > 0:22:15This lava is over 1,000 degrees centigrade, 2,000 degrees Fahrenheit.
0:22:15 > 0:22:20The bubbles of gas that burst from its surface may be 50 feet across.
0:22:20 > 0:22:24Sometimes, having got rid of much of its gas, like beer losing its fizz,
0:22:24 > 0:22:27it sinks back down the vast pipe up which it rose
0:22:27 > 0:22:31and returns to the lava chamber a mile or so below.
0:22:33 > 0:22:37But lava lakes fed by pipes are not common.
0:22:37 > 0:22:42Basalt more usually comes to the surface of the Earth in a rather different way.
0:22:53 > 0:22:58These Icelandic volcanoes erupt from huge cracks or fissures
0:22:58 > 0:23:05which regularly open up in a line which runs right across the width of the island.
0:23:05 > 0:23:10But that line itself is only the northern end of a huge line of weakness
0:23:10 > 0:23:14that runs for thousands of miles southwards from Iceland
0:23:14 > 0:23:17right round the side of the globe.
0:23:18 > 0:23:23Iceland lies between Norway and Greenland, south of the Arctic Circle.
0:23:23 > 0:23:26The crack, ridged over by lava, is for the most part underwater,
0:23:26 > 0:23:31which is why its existence wasn't known until the beginning of this century.
0:23:31 > 0:23:34From Iceland, it runs midway between Europe and Africa
0:23:34 > 0:23:36to the east and the Americas to the west.
0:23:36 > 0:23:40In places, it rises above the sea to form volcanic islands -
0:23:40 > 0:23:46The Azores, the Cape Verdes, Ascension, St Helena, Tristan da Cunha.
0:23:46 > 0:23:50But below the surface the lava is also continually erupting,
0:23:50 > 0:23:54unseen by human eyes until only a few years ago.
0:24:24 > 0:24:27The clouds of gas come from the lava itself.
0:24:27 > 0:24:30They're not steam. The pressure of the water in these depths
0:24:30 > 0:24:32prevents that from being produced.
0:24:32 > 0:24:36The heat is rapidly absorbed by the vastness of the ocean itself
0:24:36 > 0:24:38so that the lava cools and congeals
0:24:38 > 0:24:41much more quickly than it would do in the air.
0:24:49 > 0:24:54Eruptions like these, at great depths, built the Atlantic ridge.
0:24:54 > 0:24:57But the basalt forms not only the ridge itself
0:24:57 > 0:24:59but the sea floor on either side.
0:24:59 > 0:25:01By dating it chemically,
0:25:01 > 0:25:05we know that the farther it is from the centre of the ridge,
0:25:05 > 0:25:07the older it is.
0:25:07 > 0:25:11This means that basalt is welling up in a molten state at the ridge
0:25:11 > 0:25:15and then, as it solidifies, is moving away on either side.
0:25:15 > 0:25:19We still don't fully understand the forces that power the process,
0:25:19 > 0:25:23but it seems that 50 to 60 miles below the Earth's surface
0:25:23 > 0:25:27it's so hot that the rocks are molten and currents in them
0:25:27 > 0:25:31are welling up beneath the ridge, causing eruptions,
0:25:31 > 0:25:33and then flowing away on either side,
0:25:33 > 0:25:36pulling the great plates of the ocean floor with them.
0:25:36 > 0:25:41It was this movement that dragged apart Africa and South America
0:25:41 > 0:25:44and created the Atlantic Ocean.
0:25:47 > 0:25:49Similar things have happened in the Pacific.
0:25:49 > 0:25:53The great plate that forms the eastern part of the ocean floor
0:25:53 > 0:25:56is moving towards the west coast of America.
0:25:56 > 0:26:00But where it meets the continent, it dives downwards,
0:26:00 > 0:26:03perhaps pulled by the descending current in the crust below,
0:26:03 > 0:26:06producing a deep trench in the ocean floor.
0:26:08 > 0:26:10As it goes down, it takes with it some of the sediments
0:26:10 > 0:26:16that have accumulated at the bottom of the ocean and also some water.
0:26:16 > 0:26:18These new ingredients melt
0:26:18 > 0:26:22and interact with the rocks of the interior
0:26:22 > 0:26:25to produce a mixture that is crucially different from the lava
0:26:25 > 0:26:27that erupted at the ocean's ridge.
0:26:27 > 0:26:33For one thing, it contains much more dissolved gas and steam.
0:26:33 > 0:26:37As it rises up in the cracks on the edge of the continent,
0:26:37 > 0:26:41it cools and solidifies, choking the vents.
0:26:41 > 0:26:45The effect is like screwing down the safety valve of a boiler.
0:27:02 > 0:27:05Mount St Helens on the Pacific coast of North America.
0:27:05 > 0:27:08On May 18th 1980,
0:27:08 > 0:27:11with an explosion 500 times as powerful
0:27:11 > 0:27:13as the atomic blast at Hiroshima,
0:27:13 > 0:27:17it blew away three-quarters of a cubic mile of rock.
0:27:18 > 0:27:22The forests around the mountain were totally destroyed.
0:27:22 > 0:27:26Trees 200 feet tall lay scattered like matchsticks.
0:27:27 > 0:27:29Geologists, weeks beforehand,
0:27:29 > 0:27:33watching a huge bulge develop on the side of the mountain,
0:27:33 > 0:27:36had warned of the coming catastrophe.
0:27:36 > 0:27:40Even so, over 60 people stayed and were killed.
0:27:51 > 0:27:54On the northern side of the volcano,
0:27:54 > 0:27:56there were not even trees to be seen.
0:27:56 > 0:28:00A huge avalanche of rock, blown out by the blast,
0:28:00 > 0:28:05had slid for 15 miles down the side of the mountain, burying everything.
0:28:09 > 0:28:12Behind it, Mount St Helens lay wrecked.
0:28:12 > 0:28:15Its summit was over 1,000 feet lower,
0:28:15 > 0:28:16and at the back of a huge amphitheatre,
0:28:16 > 0:28:19a mile wide from which the rock had come,
0:28:19 > 0:28:22another ominous bulge was developing,
0:28:22 > 0:28:24swathed in jets of steam.
0:28:39 > 0:28:43Almost a century earlier, on the opposite side of the Pacific,
0:28:43 > 0:28:48another catastrophic eruption had taken place on the tiny island of Krakatau,
0:28:48 > 0:28:54in the straits between Java to the east and Sumatra to the west.
0:28:54 > 0:28:59In 1883 it was an island five miles long and three miles wide,
0:28:59 > 0:29:03with three volcanic peaks on it, the highest rising to almost 3,000 feet.
0:29:03 > 0:29:06But those peaks were dormant.
0:29:06 > 0:29:11There had been no sign of any volcanic activity within living memory.
0:29:11 > 0:29:13But in August of that year,
0:29:13 > 0:29:17people on the coast of Java began to hear a series of explosions.
0:29:17 > 0:29:21A great column of smoke rose above Krakatau.
0:29:21 > 0:29:26Pieces of lava the size of a house were being thrown high into the air.
0:29:26 > 0:29:30The explosions continued day after day.
0:29:30 > 0:29:36The column of smoke rose up until it was five miles or so up into the sky.
0:29:36 > 0:29:38Ships that were sailing nearby
0:29:38 > 0:29:41had their decks covered in ash and pumice,
0:29:41 > 0:29:45and at night electric flames played over the rigging.
0:29:45 > 0:29:47Day after day this continued.
0:29:47 > 0:29:52And as it was doing so, it was emptying the lava chamber
0:29:52 > 0:29:54deep in the crust beneath the sea,
0:29:54 > 0:29:58and that was the cause of the greatest catastrophe of all.
0:29:58 > 0:30:03Because on the morning of August 27th, Monday, at 10 o'clock,
0:30:03 > 0:30:07the roof of that lava chamber collapsed.
0:30:07 > 0:30:12Millions of tonnes of sea water poured onto the red-hot lava.
0:30:12 > 0:30:15So did millions of tonnes of rocks.
0:30:15 > 0:30:18And this produced a titanic explosion.
0:30:18 > 0:30:20The noise was almost certainly
0:30:20 > 0:30:24the loudest noise that has ever echoed round the Earth
0:30:24 > 0:30:26in recorded history.
0:30:26 > 0:30:30It was heard 2,000 miles away in Australia.
0:30:30 > 0:30:353,000 miles away on the small island of Rodriguez in the South Atlantic,
0:30:35 > 0:30:38the commander of the garrison heard it
0:30:38 > 0:30:42and thought it was distant gunfire at sea.
0:30:42 > 0:30:46The explosion also produced a tempest of wind,
0:30:46 > 0:30:51which swept out entirely round the globe seven and a half times
0:30:51 > 0:30:54before it finally died away.
0:30:54 > 0:30:59But most catastrophic of all, the explosion produced a tidal wave.
0:30:59 > 0:31:03It swept towards the coasts and as it approached became a wall of water
0:31:03 > 0:31:06over a 100 feet high.
0:31:06 > 0:31:12It crashed into the harbours, it picked up a naval gunboat with a crew of 28
0:31:12 > 0:31:15and lifted it bodily for over a mile inland
0:31:15 > 0:31:17and dumped it on a top of hill.
0:31:17 > 0:31:21And it overwhelmed village after village.
0:31:21 > 0:31:25Over 36,000 people were killed.
0:31:26 > 0:31:30The pall of ash brought darkness
0:31:30 > 0:31:34over an area of 100 miles or so for several days.
0:31:34 > 0:31:41But when it cleared away, the island of Krakatau was unrecognisable.
0:31:41 > 0:31:44Three-quarters of the main island had disappeared.
0:31:44 > 0:31:48The two nearby islets were buried beneath massive deposits of ash.
0:31:48 > 0:31:53And where the tallest peak had stood, the sea was 900 feet deep.
0:31:53 > 0:32:00But not for long. 44 years later another island rose from the boiling sea.
0:32:09 > 0:32:13They called it Anak Krakatau - the child of Krakatau.
0:32:13 > 0:32:15Compared with the explosions of its parent,
0:32:15 > 0:32:19its eruptions are still trivial bubblings.
0:32:44 > 0:32:48Now, after more than 50 years of fitful activity,
0:32:48 > 0:32:52Krakatau's child has built itself a new cone.
0:32:52 > 0:32:56It's still not very big, less than 1,000 feet high.
0:32:56 > 0:32:58Sporadically, it explodes.
0:32:58 > 0:33:02But often it's easy enough to walk round its rim.
0:33:11 > 0:33:13The fumes that boil up from its crater
0:33:13 > 0:33:17are partly steam and partly sulphurous gas,
0:33:17 > 0:33:21and the sulphur condenses on the rocks, coating them yellow.
0:33:23 > 0:33:27All volcanic eruptions spew out sulphur in one form or another,
0:33:27 > 0:33:29including those underwater.
0:33:31 > 0:33:34Here it doesn't form yellow crystals,
0:33:34 > 0:33:39but reacts with the sea water to produce clouds of black sulphides.
0:33:42 > 0:33:46These smokers, nearly two miles deep on the floor of the Pacific,
0:33:46 > 0:33:51are one of the most extraordinary scientific discoveries of recent years.
0:33:51 > 0:33:55The sulphides they produce are food for microscopic bacteria.
0:33:55 > 0:34:01They, in turn, are consumed by a group of creatures unlike any seen before.
0:34:04 > 0:34:07These are giant tube-worms 11 feet long.
0:34:07 > 0:34:12They have neither mouth nor gut but absorb bacteria through their thin skin.
0:34:14 > 0:34:17And these are clams, two feet across.
0:34:17 > 0:34:19They too consume the bacteria.
0:34:19 > 0:34:23The heated water rising above the smokers
0:34:23 > 0:34:25causes currents along the sea bottom
0:34:25 > 0:34:28that sweep small particles to the vents
0:34:28 > 0:34:31so there's a whole community of creatures feeding on them.
0:34:31 > 0:34:36Small, white, blind crabs. Strange fish, hitherto unknown.
0:34:38 > 0:34:41Until this bizarre colony was discovered,
0:34:41 > 0:34:44we had believed that all creatures on Earth
0:34:44 > 0:34:47derived their energy through plants from the sun.
0:34:47 > 0:34:53Even the deep sea creatures fed on fragments falling from the sunlit surface.
0:34:53 > 0:34:56But here were animals that owed nothing to the sun
0:34:56 > 0:35:02and were sustained through bacteria by the chemical energy of volcanoes.
0:35:09 > 0:35:13But volcanoes don't remain active for ever.
0:35:13 > 0:35:17Eventually, there is some shift deep in the Earth's crust
0:35:17 > 0:35:21and the focus of the intense heat moves away slightly
0:35:21 > 0:35:23and the eruptions come to an end.
0:35:23 > 0:35:27But if water should percolate down from the surface through the rocks
0:35:27 > 0:35:29and approach the magma chamber,
0:35:29 > 0:35:34it's still so hot that the water is superheated and forced up again,
0:35:34 > 0:35:37like water in the spout of a boiling kettle.
0:35:37 > 0:35:42On the way, it may dissolve minerals from the rocks through which it passes,
0:35:42 > 0:35:48and then, as it emerges as hot springs, the minerals will be deposited in terraces,
0:35:48 > 0:35:51like these in Rotorua, in New Zealand.
0:36:00 > 0:36:04In some parts, the superheated steam on its way to the surface
0:36:04 > 0:36:09has dissolved the softer rocks through which it passes and brings them up as boiling mud.
0:36:15 > 0:36:19Elsewhere, the boiling water shoots spasmodically into huge fountains,
0:36:19 > 0:36:22and the whole area is wreathed in steam.
0:36:22 > 0:36:27Such a place is typical of land where volcanic fires are on the wane.
0:36:27 > 0:36:31Famous hot springs of Yellowstone in the Rocky Mountains of North America
0:36:31 > 0:36:35are also heated by a vast chamber of molten rock
0:36:35 > 0:36:37some distance down beneath the surface.
0:36:48 > 0:36:52The water welling up from these crystal-clear, chemically rich pools
0:36:52 > 0:36:56is so hot that no creature can live in them.
0:36:56 > 0:36:59When they trickle over the brim, they begin to cool,
0:36:59 > 0:37:04and there rich colonies of bacteria and mats of algae begin to grow.
0:37:04 > 0:37:06In places, they flourish so thickly
0:37:06 > 0:37:09that they break the surface and divert the flow of water
0:37:09 > 0:37:13so that in parts they're cool enough to allow brine flies to settle.
0:37:23 > 0:37:26The flies come to feed on the algae.
0:37:30 > 0:37:33And here, too, they mate.
0:37:47 > 0:37:52They lay their eggs directly in the warm mat of the algae.
0:37:52 > 0:37:56Each has a long white thread to its case, like a seed.
0:38:03 > 0:38:06The eggs, however, are far from safe.
0:38:06 > 0:38:10They're seized by mites that clamber about over the algae.
0:38:20 > 0:38:24Spiders, too, prowl around the grazing herds.
0:38:29 > 0:38:33A slightly larger fly moves among the brine flies.
0:38:33 > 0:38:37It too is a killer, devouring the grubs.
0:38:49 > 0:38:54So the algal mats support a closely-knit interdependent community,
0:38:54 > 0:38:59all nourished by chemicals in the water and energised by the volcanic heat.
0:38:59 > 0:39:02But in the end it's destroyed by its own success.
0:39:02 > 0:39:07Increasing numbers of grubs eat the algae begin to weaken the mat.
0:39:07 > 0:39:13Eventually it gives way, the channel clears and scalding water gushes down,
0:39:13 > 0:39:15killing a generation of grubs
0:39:15 > 0:39:18and many hunters and parasites that live on them.
0:39:21 > 0:39:25Now the process has to start all over again.
0:39:41 > 0:39:44The hot volcanic springs of the Rift Valley in Africa
0:39:44 > 0:39:50also support their own crops of bacteria and the small algae that feed on them.
0:39:50 > 0:39:54But here the creatures that come to harvest them are much bigger.
0:39:54 > 0:39:59Flamingoes, sometimes as many as a million of them on this one lake.
0:40:06 > 0:40:10These lesser flamingoes feed entirely on single-celled algae
0:40:10 > 0:40:15that proliferate in vast quantities in these steaming soda-rich waters.
0:40:15 > 0:40:18Flocks like these remove 150 tonnes
0:40:18 > 0:40:22of these microscopic plants from this lake every day.
0:40:28 > 0:40:30Their bills have sieves inside them
0:40:30 > 0:40:33which strain off the algae as the water passes through them.
0:40:37 > 0:40:40It's easy to see how creatures can benefit
0:40:40 > 0:40:46from the chemical riches of volcanoes dissolved in the waters of hot springs.
0:40:46 > 0:40:49It's more difficult to imagine how any living thing
0:40:49 > 0:40:53could derive nourishment from a basalt lava flow.
0:40:57 > 0:41:02Its surface in many places is as smooth and as hard as glass,
0:41:02 > 0:41:07and neither frost nor roots of plants can initially make any impression on it.
0:41:15 > 0:41:17Centuries may pass after an eruption
0:41:17 > 0:41:22before there's any sign of the surface of such a flow beginning even to weather.
0:41:22 > 0:41:28This flow for example on the flanks of Mount Kilauea in Hawaii is some 3,000 years old,
0:41:28 > 0:41:34and yet still it shows the rippled, ropy surface that formed when it was liquid.
0:41:34 > 0:41:40But in the end the surface does erode and plants do get root in the cracks.
0:41:40 > 0:41:43They in turn can support all kinds of other life,
0:41:43 > 0:41:47and so the lava flow is eventually colonised,
0:41:47 > 0:41:50but not only on its surface but in its depths.
0:41:50 > 0:41:55For these basaltic lava flows are often not as solid as they seem.
0:41:56 > 0:42:00When the lava first flows out of the vent like a river,
0:42:00 > 0:42:05that on the outside of the flow will cool quicker and solidify,
0:42:05 > 0:42:08forming walls on either side of the flow.
0:42:10 > 0:42:16The top too cools quicker, and that causes a crust to form over the flow,
0:42:16 > 0:42:21so that eventually the lava is flowing down a long tunnel.
0:42:21 > 0:42:26When that happens, the walls and ceiling of the tunnel act as insulation,
0:42:26 > 0:42:30keeping the heat in, so that the lava flow remains liquid
0:42:30 > 0:42:33and so continues for mile after mile.
0:42:37 > 0:42:40When eventually the supply of lava stops,
0:42:40 > 0:42:46that tunnel may drain, leaving a long cavern like this one.
0:43:28 > 0:43:32Out of the reach of rain and frost and even dust,
0:43:32 > 0:43:35the surface of the lava looks exactly as it must have done,
0:43:35 > 0:43:38when the last trickle was draining away,
0:43:38 > 0:43:43and the floor was so hot that anything touching it would be turned to a cinder.
0:44:02 > 0:44:07Molten lava had dripped from the ceiling, it had swilled round the sides
0:44:07 > 0:44:11and spurted out in little dribbles from cracks in the newly congealed walls.
0:44:11 > 0:44:15But living organisms have already moved in.
0:44:15 > 0:44:20These roots belong to trees that are growing on the surface of the lava flow.
0:44:20 > 0:44:25They've found their way down through the cracks, and here they dangle,
0:44:25 > 0:44:29catching water as it percolates through the lava and trickles down them.
0:44:29 > 0:44:35Among the rootlets, there are animals that live nowhere else in the world.
0:44:39 > 0:44:43Normally, these creatures are in total darkness.
0:44:43 > 0:44:47Nearly all of them, like this cricket, have lost their pigment.
0:44:47 > 0:44:51Many of them have also lost their wings and their eyes.
0:44:51 > 0:44:55In the blackness, they find their way about by touch,
0:44:55 > 0:45:01and, like many cave insects elsewhere, have developed long legs and antennae.
0:45:08 > 0:45:11Some, like this bug, are scavengers.
0:45:13 > 0:45:16Others, like the centipede, hunt.
0:45:21 > 0:45:24And the millipedes feed on the roots.
0:45:43 > 0:45:47So, in these extraordinary lava caverns,
0:45:47 > 0:45:50there is yet another community of interdependent creatures
0:45:50 > 0:45:54that have come into existence since the volcanoes erupted.
0:46:05 > 0:46:10The colonisation of volcanic ash presents different problems.
0:46:10 > 0:46:13The difficulty here is not the glassy hardness of the rock
0:46:13 > 0:46:18but quite the reverse, its insubstantial dustiness.
0:46:18 > 0:46:21Mount St Helens is still a wasteland.
0:46:23 > 0:46:27It's now, as I speak, some two and a quarter years
0:46:27 > 0:46:30since the volcano erupted.
0:46:30 > 0:46:34I'm some three miles from the crater,
0:46:34 > 0:46:39and still the scene is one of devastation and sterility.
0:46:39 > 0:46:44It's not just that this unweathered ash is not very fertile,
0:46:44 > 0:46:49but it's also that it's so loose that it's difficult for plants to get root.
0:46:49 > 0:46:52But that possibility is always here.
0:46:52 > 0:46:56Here, for example, in this crevice,
0:46:56 > 0:46:59there are the seeds of the willow herb,
0:46:59 > 0:47:03or, as they call it in these parts, fireweed,
0:47:03 > 0:47:06that have been blown up from the valleys below.
0:47:06 > 0:47:10I don't suppose these particular ones will manage to get root here,
0:47:10 > 0:47:13but in the end some plant will,
0:47:13 > 0:47:18and in the end the process of colonisation will begin.
0:47:20 > 0:47:24Krakatau's child is just 57 years old.
0:47:24 > 0:47:27Its flanks too are covered for the most part with ash,
0:47:27 > 0:47:30and they're still buried regularly with new layers from fresh eruptions,
0:47:30 > 0:47:35yet the process of colonisation is already under way.
0:47:35 > 0:47:39Not only are there giant grasses, like this wild sugar cane,
0:47:39 > 0:47:42but trees - a casuarina.
0:47:42 > 0:47:48If you want to see what a century of colonisation by plants can bring about,
0:47:48 > 0:47:53have a look at that fragment of old Krakatau over there.
0:48:01 > 0:48:04We know from first-hand reports that 100 years ago
0:48:04 > 0:48:08there was nothing here but sterile ash many feet deep.
0:48:08 > 0:48:13Within three years, 34 different species of plants had reappeared.
0:48:13 > 0:48:16Ten years later there were twice that number,
0:48:16 > 0:48:20and over 100 species of birds and insects as well.
0:48:20 > 0:48:24Some seeds must have floated here from Java, some 20 miles away,
0:48:24 > 0:48:27and they still continue to do so.
0:48:28 > 0:48:32Other smaller ones were probably carried here by birds,
0:48:32 > 0:48:35either on their feet or in their stomachs.
0:48:46 > 0:48:52But the ash is still here beneath the lattice of roots of the jungle trees.
0:48:56 > 0:49:02Somehow or other, rats and lizards and pythons have all reached here.
0:49:02 > 0:49:05There are now many hundreds of different species of plants,
0:49:05 > 0:49:10and the winds have assisted the passage of a great number of flying insects,
0:49:10 > 0:49:14whose descendants now form large and permanent populations,
0:49:14 > 0:49:17pollinating the flowers, feeding on their fruits,
0:49:17 > 0:49:23collecting their rotting leaves and indeed feeding on one another.
0:49:41 > 0:49:45As yet there are no larger mammals, no monkeys or squirrels,
0:49:45 > 0:49:50no hunting cats or mongoose, as there are in Java or Sumatra.
0:49:50 > 0:49:53But as far as smaller creatures are concerned,
0:49:53 > 0:49:56the number of species is increasing all the time.
0:50:08 > 0:50:12And on the flanks of volcanoes all round the world,
0:50:12 > 0:50:15men clear fields and plant crops,
0:50:15 > 0:50:19even though they know they may be sitting on a time bomb.
0:50:25 > 0:50:30These rice fields lie on the flanks of one of Krakatau's near neighbours,
0:50:30 > 0:50:32Gunung Agung in Bali.
0:50:32 > 0:50:34Only 20 years ago it erupted,
0:50:34 > 0:50:39killing 2,000 people and leaving 150,000 homeless.
0:50:39 > 0:50:43But still the Balinese will not leave fields that are so fertile
0:50:43 > 0:50:48they can produce two or three rich harvests of rice every year.
0:50:49 > 0:50:55Gunung Agung, Krakatau and the rest of the violently explosive volcanoes
0:50:55 > 0:51:00that run in a chain along Sumatra and Java and the Indonesian islands
0:51:00 > 0:51:03stand on the line of the crack in the Earth's crust
0:51:03 > 0:51:07where the basalt plate forming the floor of the Indian Ocean
0:51:07 > 0:51:11meets the partly submerged edge of the continent of Asia.
0:51:11 > 0:51:14This junction already existed 65 million years ago,
0:51:14 > 0:51:18when India was an isolated island in the middle of that ocean.
0:51:18 > 0:51:22Since then, as the ocean floor has continued to spread,
0:51:22 > 0:51:26the continents have shifted and India has moved towards Asia.
0:51:26 > 0:51:29As the two continents approached,
0:51:29 > 0:51:33the sediments between them crumpled and eventually piled up over the junction,
0:51:33 > 0:51:38so instead of the line between them being marked by a chain of volcanoes,
0:51:38 > 0:51:43it's buried deep beneath an immense range of mountains, the Himalaya.
0:51:45 > 0:51:52So these great peaks of sandstone and limestone rising five miles into the sky
0:51:52 > 0:51:56are not only the highest mountains in the world, but among the youngest.
0:51:56 > 0:52:00And the process has not yet come to an end.
0:52:00 > 0:52:05India is still moving north at the rate of two inches a year,
0:52:05 > 0:52:10compacting itself ever more tightly against the continental mass of Asia,
0:52:10 > 0:52:16and the Himalaya are, infinitesimally, getting higher and higher.
0:52:16 > 0:52:20And that is how this ammonite, this sea-living creature,
0:52:20 > 0:52:24came to rest over two miles high in the Himalaya.
0:52:24 > 0:52:28And that too is the explanation of how the Kali Gandaki river
0:52:28 > 0:52:34managed to cut its way clean through the highest range of mountains in the world.
0:52:34 > 0:52:38It was flowing south from the ancient plateau of Tibet
0:52:38 > 0:52:43even before the great mass of India collided with Asia.
0:52:43 > 0:52:48As the sediments between the two land masses buckled and rose over millions of years,
0:52:48 > 0:52:51the river maintained its course,
0:52:51 > 0:52:55cutting down through the rocks as swiftly as they rose.
0:52:55 > 0:52:59And so now it still flows south to the plains of India,
0:52:59 > 0:53:03and does so through the deepest gorge in the world.
0:53:05 > 0:53:08Mountain ranges have been created in this way several times,
0:53:08 > 0:53:10during the history of the Earth
0:53:10 > 0:53:12The Himalaya are just the most recent.
0:53:12 > 0:53:15As they are worn down, so they create different environments
0:53:15 > 0:53:18in which animals and plants can live.
0:53:18 > 0:53:24So we have begun our portrait of the planet up on the roof of the world,
0:53:24 > 0:53:30and we will go from high altitudes to low, from the poles to the equator.
0:53:30 > 0:53:33And in the next programme we'll go even higher,
0:53:33 > 0:53:39to the most inhospitable environment of all, the world of snow and ice.
0:53:54 > 0:53:57Subtitles by Red Bee Media Ltd