DC_Amazing Earth_2of9_Amazing Earth The Violent Present
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00:00For over 4.5 billion years, the Earth has been blasted, burned, ripped and scoured.
00:15These phenomenal events have sculpted our planet through a series of devastating cataclysms.
00:37Our ancestors thought volcanoes were the doorways to hell.
00:41We think we know better, but we still live in a world driven by natural forces which
00:46we cannot control and which are indifferent to our needs.
00:52We hope the Earth beneath our feet is still, but that is a deception.
00:56We live on a restless planet.
01:01We're only just beginning to understand the awesome power that can raise mountains, form
01:09the continents, open and close the seas.
01:22We are learning more all the time about the forces that drive our Earth and how to live
01:27with them.
01:28But it may be too late.
01:30The geological truce between ourselves and our restless planet may be coming to an end.
01:4279 A.D.
01:43Pompeii, Italy.
01:44A peaceful Roman city was overwhelmed by pyroclastic fires from Mount Vesuvius, a volcano that
01:51had slept through recorded history until it suddenly exploded.
01:5720,000 people lived in Pompeii.
02:00Very few escaped the volcanic shroud.
02:112,000 years later, the people of Montserrat, a small Caribbean island, face the same threat.
02:18In June 1995, the volcano of Soufrière burst into malignant life.
02:24It had been dormant for 400 years.
02:3919 people have died and half the island is uninhabitable.
02:43Where once there was a green forest is total devastation, an ash desert.
02:50Scientists from all over the world are trying to forestall an even greater disaster.
03:20Mark Davies can't just watch from the safety of the helicopter.
03:44He must get as close as he can to the flow.
03:47It's incredibly dangerous.
03:48At any moment, and without warning, the volcano might erupt again and he'd have no chance
03:53of escaping.
03:54We're quite close to the dome here.
03:55You can feel the heat coming off it.
03:56So it's not really a place we want to hang around.
03:57The cracks have opened up to six centimetres in three days.
03:58So we'll have to keep an eye on them.
03:59A pyroclastic flow is essentially like a snow avalanche.
04:27The only difference being that it's around about 800 degrees C.
04:31It contains big, huge blocks within it, sometimes the size of houses.
04:34It contains lots of poisonous gases and all of that will travel at around about a speed
04:40of 80 metres per second, in some cases, sometimes a heck of a lot faster.
04:44So you can outrun it, you can outdrive it, and in some cases the only thing that can
04:48get you out fast enough is a helicopter.
04:55Essentially, if you get caught in a pyroclastic flow, you really don't know whether you'll
04:59get crushed, whether you suffocate, whether you burn to death first, and frankly, I wouldn't
05:04want to know myself.
05:22This is how Montserrat used to be before the catastrophe, an eight-mile paradise with green
05:27hills and tiny farms that had crept close to the mountain.
05:34The towns were full of memories of the colonial past.
05:37Now all that is gone.
05:40Sometimes ash falls like hail for a day at a time.
05:43The heat can be felt a mile away.
05:45The smell of burning sulphur fills the air.
05:52The sun is obliterated and the midday sky becomes as dark as night.
05:58There's nothing to be done but take cover.
06:06Plymouth, the capital, was like Pompeii, a thriving port, centre of island life.
06:15It too lay in the path of the pyroclastic flow.
06:23Because they had warning, the people were able to escape, but slowly their town is disappearing
06:28under the pitiless flows and remorseless ash.
06:39A volcano can sit quietly for centuries until the pressure from below becomes too great
06:43and it explodes.
06:45What everyone on Montserrat wants to know is, will it explode again and will it ever
06:49stop?
06:55The scientists' best hope is to monitor the earthquakes they know will shake the mountain
06:59before an eruption.
07:01Twenty-four hours a day they listen and watch.
07:07This is the operation centre for the volcano observatory.
07:11It's monitoring the whole of the volcano.
07:13It's an early warning system, if you like.
07:17We have points all around the volcano, so if the ground's moving, then the information
07:23that those machines gather out on the volcano is sent back here and it's recorded on these
07:29pens so it's a visual way of determining how much motion is occurring.
07:36When the drum and the needle on the drum and the pen is going back and forth, the bigger
07:42the earthquake, the more violent that pen will move.
07:46And the greater the chance of a violent eruption.
07:49But the technique is only a best guess, it's not foolproof.
07:54Distrusting science to save them from the force of nature, the population dwindles daily
07:59as more and more people escape to the safety of neighbouring islands.
08:11Those who can't leave eke out a precarious existence in makeshift camps.
08:16Families are split, the young see no futures.
08:19The old can only remember the past.
08:29One in ten of us live near an active volcano.
08:32Many choose to because volcanic soil is so fertile and productive.
08:37But will the people of Montserrat ever be able to return to their fields and old ways
08:41of life, or has that gone, as lost as Pompeii?
08:52People and politicians would like clear-cut answers, but scientists know that's impossible.
08:58No one can tell what a volcano is going to do next.
09:02If the eruption stops tomorrow, the dome is still up on top of the volcano.
09:07It's still unstable, and it'll still retain its heat, and it might stay like that for
09:11five years after the eruption finishes.
09:14Or it might cool down exceptionally quickly, and within one year people could move back.
09:18We don't really know.
09:22Montserrat's disaster is caused by something that happened over four billion years ago,
09:26when the Earth's crust broke into gigantic sections, forming the tectonic plates.
09:32They drift endlessly around the globe like giant bumper cars, joining and separating,
09:37carrying with them all the continents and oceans.
09:41The crust that forms on lava ponds behaves much like the plates.
09:45There are nine huge ones, many thousands of miles wide, and it's at their boundaries that
09:50catastrophes occur.
09:52Montserrat sits on the boundary of the Caribbean and North American plates, where volcanoes
09:56erupt and earthquakes shudder.
10:04When they clash, new landscapes are created.
10:07Oceans shift, and mountains soar into the sky.
10:21Fifty million years ago, the Asian and Indian plates were about to clash.
10:26Separated by a dying ocean, they collided with fantastic force.
10:30Neither would give way, and the land had only one way to go, up.
10:44This is the world's highest mountain range, the Himalayas.
10:53This entire area was uplifted from sea level to over five miles high in less than thirty
10:58million years.
11:02How do the scientists know?
11:04From the evidence of the rocks.
11:08There's dramatic evidence for this uplift right in the face of Everest in Lhotse.
11:13The famous yellow band that you can see cutting across is actually a marine limestone.
11:17It was formed in the bottom of the ocean.
11:22So fifty million years ago, the tops of these mountains were at the bottom of the sea.
11:27It's hard to believe.
11:29We have similar evidence from Tibet, where we find things like this, ammonite fossils
11:35of marine creatures at now more than four thousand meters above sea level.
11:41Can any of these tell us that plate tectonics supplies enough force to lift things from
11:46the bottom of the ocean all the way to here, the top of the world?
11:52This is the only place where two continental plates are colliding on such a scale, and
11:57the mountains are still growing as a result of the tectonic squeeze.
12:02Even Everest is still stretching skywards.
12:08I can't quite feel it, just standing here on a piece of Himalayan rock, but my research
12:14and the research of the University of Colorado team, setting up a network of global positioning
12:19system stations all over Nepal, they're telling us that the earth that I'm standing on is
12:24actually moving up at about ten millimeters a year, and is moving to the north at an even
12:30faster rate than that, maybe fifteen millimeters a year.
12:33The reason why we can measure this is because of these fantastic receivers.
12:39They use four satellites up in the sky above me to solve a simple triangulation problem,
12:45but they're so accurate that they can give me something like one millimeter of accuracy
12:50in the horizontal, and more like five millimeters in the vertical.
12:54That way I can come back year after year, we can see that this point drilled into this
12:58rock that's attached somehow to the root of these mountains and the continental plate
13:04that they're stuck to is moving.
13:07There is another way that Rebecca Bendik and her colleagues can discover exactly how the
13:11Himalayas are growing.
13:13They have found an area in the foothills ten miles south of the highest peaks that is rising
13:19even faster than the mountains.
13:21The clues to the uplift are found in the fast flowing rivers that tumble through these valleys.
13:29You can think of this river in two different ways.
13:44One is that this land is still and the river is cutting down.
13:49The other way, and I think a better way to think about it, is that the river is staying
13:54at sort of a constant position with respect to the sea, way off in the Bay of Bengal,
13:59and the earth around it is rising up.
14:02So in order for the river to stay in one place, it needs to cut down like a knife through butter.
14:08But in some places, the river cannot cut quickly enough to maintain its natural equilibrium.
14:13Here, the land rises faster than the river erodes it down, and a giant step is formed,
14:19creating white water and rapids.
14:23We're looking for places where the river is a lot steeper than its average gradient
14:28anywhere along a stretch.
14:30Those steeper places are corresponding to places where the uplift is quick,
14:36so quick that the river can't keep up.
14:39This will give us clues about places to come back and do more intensive GPS research
14:45to try to pin down the uplift rate.
14:50It seems this area is continuing to rise faster than the high peaks.
14:54One day, this river bed will be taller than Everest.
15:07Taking data in this way is dangerous, but with a little bit of care,
15:11it's definitely worth the good information that we get about the earth.
15:17That information is vital for the hundred million people living in the danger zone
15:22around the Himalayas.
15:24Earthquakes are common.
15:2630,000 people have been killed in the last century alone.
15:29This area has been quiet for 700 years, and a major quake is log overdue.
15:36Rebecca Bendick's monitoring shows that the convergence of India and China
15:40at two inches a year is setting up immense stresses,
15:44which must eventually be released.
15:47A solar-powered GPS station will send back information 24 hours a day,
15:52hopefully giving an early warning.
15:57The crux of the matter is that we need to know how that total convergence
16:02is partitioned over the fault.
16:04If all 60 millimeters of convergence has to be accommodated in one place
16:09on one fault, on this one narrow line,
16:13then the earthquakes we have there are going to be big,
16:16and they're going to happen often.
16:18But if instead all of that strain is accommodated on several different faults,
16:23something like an accordion,
16:25then each fault can only be expected to fail less frequently and less violently.
16:40Earthquakes are appallingly destructive to human life,
16:44but for scientists they have their uses.
16:47The seismic waves are like sonar.
16:49By listening as they pass through the Earth,
16:52a picture can be built up of a place no one will ever see.
16:57First, the waves race through the crust, the skin on the planet's surface.
17:02In some places, only four miles separate us
17:05from the intolerable heat of the mantle,
17:07and interior of the Earth.
17:10The temperature is nearly 3,000 degrees,
17:13so intense the rocks are partially melted.
17:183,000 miles down in the core itself,
17:21the temperature reaches an unimaginable 7,000 degrees.
17:24It is the ultimate nuclear reactor, the engine driving the planet.
17:37Cooling comes by gigantic convection currents in the mantle,
17:41and it's that heat rising with the hot magma
17:44that forces the tectonic plates to spread apart.
17:53Until recently, scientists had never visited the place
17:56where this spreading occurred.
17:58It was hidden under the waves.
18:03Now even the depths are giving up their secrets.
18:08Alvin, the world's first deep-sea submersible,
18:12led the way to this unexplored terrain.
18:20One of the first regions visited was the East Pacific Rise,
18:24part of the spreading area called the Mid-Ocean Ridge.
18:28They expected to find evidence of the Earth at work.
18:37But what they actually discovered lay beyond imagination.
18:51From this pioneering work, scientists worldwide
18:54are able to study the extraordinary geological systems
18:57four miles beneath our feet.
19:00Lindsay Parson heads a team
19:02at the Southampton Oceanographic Centre.
19:06These are really some of the most amazing images
19:09that I think we have of the ocean floor.
19:12They're taken from about 3,000 metres down.
19:16They're in some of the deepest parts of the ocean floor.
19:21And we're here looking at hydrothermal systems
19:24where bottom water for the sea is being sucked into the ocean floor,
19:29it's being heated from the heat engine inside the Earth,
19:33and it's being delivered out into the ocean floor again
19:36once it's dissolved and leached out minerals
19:39and chemical compounds from the rock itself,
19:42which is why the smokers, as we call them,
19:45are black and densely coloured here.
19:47The pressure is an immense 2 tonnes per square inch.
19:51Water is superheated to over 700 degrees.
19:54It's highly acidic, full of hydrogen sulphide and heavy metals.
19:58The equivalent volume of the world's oceans
20:01is siphoned through the vent systems every 30 million years.
20:08Samples prove that the sea floor along the ridges
20:11is the youngest on Earth, endlessly reborn.
20:20But an even greater surprise lay in store.
20:24Even in this harshest of terrain, life takes hold.
20:28The black smokers are warm-water oases
20:31around which familiar species,
20:33shrimps, footlong clams and mussels,
20:36thrive alongside more bizarre forms,
20:39six-foot-long tube worms and strange fish.
20:46The majority of the life forms here
20:48depend not on light to maintain their existence.
20:51They absorb and fix chemicals from the hydrothermal vents
20:55to keep them alive.
20:57They are chemosynthetic communities
20:59rather than photosynthetic communities.
21:02Far from the sun and the air,
21:04these creatures have evolved in a self-contained environment
21:08separated from the rest of the biosphere.
21:11They have managed to survive the endless geological upheavals
21:14that rack the world above them.
21:16Maybe one day, long after we are gone,
21:19they will inherit the Earth.
21:27Here, scientists can also watch the extraordinary process
21:30of the seabed actually creating itself.
21:35The hydrothermal systems lie along the mid-ocean ridge.
21:38The mid-ocean ridge is the line
21:41along which the tectonic plates move apart from one another,
21:45allowing hot molten rock from the interior of the Earth
21:49to well up and to form new ocean floor,
21:51the youngest part of the world as we know it.
21:54The mid-ocean ridge is the Earth's crust factory.
21:57New molten magma endlessly emerges
22:00to force the cold, older lava away from the ridges.
22:03Enough lava is created each year
22:06to bury New York a hundred feet deep.
22:10And this unrelenting pressure is like a wedge
22:12between the plate boundaries,
22:14driving them and their continents on their unstoppable journey.
22:21Accurate mapping of the sea floor is now possible
22:23and crucial to understanding the system on a grand scale.
22:27By careful monitoring, scientists can calculate
22:30just how fast the sea floor is spreading and the plates moving.
22:34A sonar sledge is towed across the ocean bed.
22:38Individual snapshots are processed by computer
22:41and a photomontage created.
22:45That information is turned into three-dimensional maps.
22:54What emerges is that the sea floor is full of great valleys
22:58and deep trenches, and that here is the largest
23:01and tallest range of volcanic mountains on Earth,
23:0440,000 miles long, sometimes five miles high,
23:08stretching around the globe like a seam on a baseball.
23:14Oceanographic research is difficult,
23:16but there is a country that might have been designed
23:18as a geological laboratory,
23:20the one place where the Mid-Atlantic Ridge
23:22becomes exposed on land,
23:26Iceland.
23:34The land here is being torn apart.
23:36The rift shows exactly where the plates are being forced away
23:40from each other at about an inch per year,
23:43and Iceland is in the middle.
23:51The land is continually reshaped through eruption and rifting.
23:55The lava from the flows forms vertical dikes
23:58and horizontal beds, just as it does on the ocean floor.
24:15Geysers and mud pools are evidence of the heat and pressure
24:19just beneath the surface, continually seeking a way to escape.
24:25Ice Age
24:48The glaciers inch forward,
24:50and a new Ice Age seems to wait in the wings.
25:10Ice and fire is a deadly mixture.
25:13In 1996, part of the Mid-Ocean Ridge erupted under the ice cap.
25:21It rapidly melted its way through 300 feet of ice,
25:25forming a deep gorge.
25:32The meltwater raced away to fill a subglacial lake
25:35until it could no longer be contained.
25:38In the catastrophic flood that followed,
25:40ten square miles of land was drowned.
25:50This time, the damage was only to roads and bridges,
25:53but in Iceland, the earth is always menacing.
25:58In 1975, the Kofla Volcanic Eruptions began,
26:02lasting nine years.
26:04Fourteen square miles of basalt spewed out,
26:07in some places widening the land itself by 28 feet.
26:14In 1973, the town of Heimi was almost overwhelmed
26:18when a nearby volcano woke from a 5,000-year sleep.
26:22Five months later, the lava and ash had destroyed 300 houses,
26:26reshaped the harbor, and added nearly a square mile of new land.
26:35Living in a laboratory can be hard.
26:49But if new land is continually being made
26:52at the crust factory along the ridges,
26:54why isn't the world itself constantly expanding?
27:00The reason is subduction,
27:02the giant recycling process that has been going on
27:05since the world began,
27:07and which causes most volcanoes and earthquakes.
27:13Subductions are a natural process
27:17Subduction zones are the graveyards of the old, dense oceanic floor.
27:22Where it collides with the lighter continental crust,
27:25it's forced down.
27:29It pulls the rest of the plate with it
27:31to be melted in the ferocious furnace of the inner earth.
27:37The plates don't die peacefully.
27:39They go with a bang.
27:40The old ocean floor carries water into the mantle,
27:43which mixes with the magma,
27:45and when the pressure can no longer be contained, it explodes
27:49in that most awesome of natural events,
27:52a volcanic eruption.
28:10Most of the world's volcanoes are in subduction zones,
28:14but there are exceptions.
28:16Kilauea is on the Big Island of Hawaii,
28:18part of a chain of islands in the middle of the Pacific Ocean,
28:21thousands of miles away from any subduction zone.
28:26But the whole chain is formed entirely from volcanoes,
28:30whose rivers of fire heave and bubble at temperatures of 2,000 degrees.
28:35What provides the furnace for all this outpouring
28:37if it's not the crashing of the tectonic plates?
28:41The volcanologists have an explanation.
28:44The lava flows from the so-called small Milky Way,
28:47down this crater.
28:49The lava flows from the lake,
28:51down here,
28:52down there,
28:53down here,
28:54down here,
28:55down here.
28:56the furnace for all this outpouring if it's not the crashing of the tectonic
29:00plates. The volcanologists have an explanation. The lava that's flowing and
29:05spattering behind me is the surface manifestation of a of a thermal anomaly
29:10or a hotspot that's deep within the earth beneath my feet. Where we are now
29:15on Kilauea Volcano on the Big Island of Hawaii is at the southeast end of a
29:206,000 kilometer long chain of seamounts and volcanic islands that have formed as
29:26the Pacific plate has moved north and westward over the last 80 billion years
29:32or so at a rate of around 9 or 10 centimeters per year. So as the plate
29:37moves over this hotspot you burn through the lithosphere forming a volcanic
29:42island and then the plate moves on and a new island forms further to the
29:46southeast. The hotspot has made Kilauea the tallest mountain in the world
29:5230,000 feet from its base on the seafloor, taller even than Everest. It's
29:59also one of the most studied but scientists can't always wait for the
30:04lava to come to them.
30:08They must catch it as it bursts through the crust. Carl Thornburgh often goes
30:18fishing with a cable in a red-hot pond
30:24and sometimes he has to get even closer. It's extremely dangerous. At any moment
30:29the lava may spurt out unexpectedly leaving Thornburgh with nowhere to run.
30:37Behind me is a perched lava pond that's being fed from a vent off to my left. You
30:43can see that there's lava spattering and overflowing on its edges. I'm going to
30:47attempt to scoop a sample of molten lava hopefully with a hammer so I won't
30:52have to use a long cable to throw it in and it'll be extremely hot we have to
30:57worry about gases and we have to worry about breakouts near the edge of the
30:59pond so we'll see how it goes. Thornburgh is risking his life but
31:05unless scientists can learn how to forecast eruptions volcanoes will
31:09continue to be an uncontrollable threat.
31:22Okay we'll take this sample back to the USGS observatory and we'll prepare it
31:27for chemical analysis. The chemistry of Hawaiian basalts is unique compared to
31:32volcanic deposits near subduction zones or near mid-ocean ridges and that will
31:37be reflected in the in the chemistry that we see. More importantly we're
31:42looking at very subtle variations in chemistry that can be correlated with
31:47the eruptive history of this volcano so it will allow us to predict what may
31:51happen next. High on Maui, the next island in the chain, NASA scientists at the
31:57Satellite Laser Ranging Station are preparing for a long night's work.
32:01They're setting up to fire a laser beam at a satellite target orbiting the
32:06earth. The information they gain will tell them to the inch how fast the
32:10island and the Pacific plate on which it rests are moving across the ocean. They
32:16have to time the firing exactly to be sure that no planes are passing. The
32:21laser beam would blind any pilot who might look at it directly.
32:36Okay you'll be clear to fire.
32:45The laser beam flashes out and bounces back pinpointing their location.
32:5022 years of calculations confirm that Maui and the Pacific plate are moving
32:55northwest at the rate of two and a half inches a year, amazingly fast. This is the
33:01absolute proof that the surface of our planet is in constant motion.
33:08Tectonic theory says that the volcanoes of the Hawaiian chain should get
33:12progressively older and become more eroded the further they travel from the
33:17hotspot, and they do.
33:23One day the raging fires of Kilauea will be as silent and cold as these dead
33:29cones. But the air to them all is already emerging. As one island dies, a new one is
33:38formed. The hotspot is currently moving or manifesting itself at Loihi, which is
33:47a submarine seamount to the south of the Big Island of Hawaii and still more than
33:523,000 feet beneath the surface of the ocean. Maybe another hundred thousand
33:56years before we see Loihi surface.
34:08At the same time, the hotspot is causing destruction elsewhere. The pressure of
34:29the continual input of magma from below is bulldozing open this great crack
34:34which stretches across the length of the island. It is more than 80 feet deep
34:41and it's splitting away at three inches a year. Eventually the whole side of the
34:46mountain will fail and collapse into the sea. It will send a giant wave racing
34:51away to the Pacific Rim to reach the west coast of the Americas in a few
34:55hours, causing massive destruction.
35:04We can't predict or prevent these catastrophes. The fragile truce between
35:14man and the earth is being broken all the time.
35:19Earthquakes are a ferocious manifestation of the grumbling power of
35:37the earth's tectonic plates. More than one and a half million people have been
35:43killed by them in this century alone. Most quakes occurred along fault lines
35:50where the plates grind together, but scientists can't tell us when this
35:54terrifying destruction is likely to occur. They can only tell us why. You
36:00can't have an earthquake without a fault and I'm standing right now on what is
36:04perhaps the most famous fault in the world, the San Andreas fault that extends
36:07from Mexico down south way up to Oregon in the north. This is one of the few
36:14places in the world where you can stand with one foot on one tectonic plate and
36:18one on another. In other words this ground here is attached to New York and
36:25Iceland, the ground here is attached to Hawaii and Japan. Faults are places of
36:34great danger, but they are also geological safety valves. The fault is
36:40the place where two plates slide past each other. If the fault slides smoothly
36:47you don't get earthquakes, but if the fault gets stuck inevitably you get
36:50earthquakes. At this part of the fault the plates are stuck, they should be
36:54moving at two inches a year. The last earthquake was 100 years ago and the
36:59fault is storing up the unreleased energy. The longer the plates are stuck
37:03together the larger the ensuing tremor will be.
37:09Further north the plates are sliding smoothly past each other. The evidence is
37:13clear from the way this fence has buckled.
37:20We're on the San Andreas fault south of San Francisco and this is an interesting
37:26part of the fault zone because the 1906 earthquake ruptured through this field
37:32here across the road and stopped about here, but this fence was built after the
37:38earthquake. In other words the fault has been sliding ever since then. So one of
37:43the interesting things about this is what's going on here exactly and you can
37:48see here there are cracks in the road. These have grown since I was last here
37:52all over the road here and I have a machine in the field and I am absolutely
37:57dying to see what it says. Let's go have a look.
38:02What we have in the field here is a creep meter. A creep meter measures creep on the fault,
38:08the creep that's caused the offset of this fence. It consists of a rod that is
38:13attached firmly to that side of the fault, passes through the fault into the box here.
38:18Inside the box is a computer that's been measuring things. Now I have to be
38:23rather careful because sometimes there are snakes here. Not this time. Good.
38:30What's left are black widows and ants. All right. So here is a computer that's
38:38been measuring for a year. It records the movement of the fault every minute to
38:44about a thousandth of an inch. So let's download the data and have a look.
38:52Ah, there we are. Well it looks as though we've had about seven millimetres of
38:58creep like this site usually has. But the interesting thing is it's all limited to
39:03a very short period of time. If you look here you can see the fault has been
39:07locked for most of the year but suddenly in the middle of September it takes off
39:12and it slips about five millimetres in the space of a couple of hours and it
39:16continues to slip in the next few days. In other words, a whole year's budget of
39:20slip occurs within the space of a few days. That might not seem much, five
39:26millimetres, but it's affecting a long section of the fault, maybe five miles
39:31long, involving millions of tons of rock. Now it really doesn't matter here. This
39:36is a nice little field, there aren't any people, but further north this creep
39:40process and the things that are happening beneath the earth are far more
39:44sinister. San Francisco is home to two and a half million people and lies
39:50right on the Hayward Fault. In its 200 years history it's been hit by three
39:55killer quakes. Scientists know the slippage on the fault has begun to slow
40:00down, a warning sign. But when will it strike?
40:08In 1989, 67 people died in an earthquake at Loma Prieta, part of San Francisco. No
40:15one had foreseen it coming.
40:26Earthquakes are an inevitable consequence of the movement of plates. We
40:31cannot stop plate motions and therefore we cannot stop earthquakes, but we can
40:36begin to live with them. And the first thing we must learn to do is to build
40:42our cities better. As the world population grows, so does the danger.
40:47There are now more than a hundred cities around the world with population of over
40:51two million and more than half of those are on plate boundaries or places where
40:56earthquakes have already struck.
41:07Los Angeles is the most vulnerable of all the places on the West Coast fault
41:12line. This stretch of road shows why. Not only is it on the San Andreas, but here
41:18the fault is being forced around a bend. Where this happens, the rocks get
41:22compressed with enormous force. They cannot go sideways, so they go up. The
41:28movement curls the rocks, bends, folds and crunches them, faulting and distorting
41:33the land. Many faults never surface, although scientists know they're there.
41:41Known as blind faults, they are probably the most dangerous of all.
41:48You come down the hills here until you hit the plains, the flat area where 11 million people live,
41:54and across there, far behind the tall buildings of downtown LA, we think
42:02there's a fault right there, right underneath the center of LA.
42:08At 4.24 in the morning on the 17th of January 1994, the suburb of Northridge
42:14was shaken to its foundations. A blind fault had fractured 11 miles down,
42:19causing some of the most intense ground shaking ever recorded. Ground
42:25acceleration exceeded gravity, throwing buildings, furniture and people into the
42:29air. 61 died, 9,000 were injured. Buildings, roads and bridges were destroyed.
42:36Damages ran to 20 billion dollars, and the aftershocks went on for days.
42:44There are two things an earthquake can do. When it goes, like Northridge did,
42:55seismic waves are spread all over the basin, there's big ripples shaking all the
43:00buildings, everyone feels it. But there are certain locations where the shaking
43:04is much worse, and that occurs through a process of seismic waves that are
43:09reflected from from the mountains. It's exaggerated where the sediments are
43:14concentrated in the basin here, because the basin is completely flat, and it's flat
43:18because it's washed in there from the mountains by water, so we have saturated
43:24sediments. When the sand and water combination is shaken together, as in an
43:28earthquake, it turns liquid for five minutes after the shocks, causing tall
43:33buildings to destabilize and fall. It's called liquefaction, and presents an
43:38enormous and unpredictable danger.
43:44And there is another geological trap waiting to spring. The San Gabriel
43:49Mountains stretch from the San Andreas Fault down to the Los Angeles Basin. As
43:54the earthquakes crack and shudder along the faults, they are being inched towards
43:59the city. Here the fault is pink, and the mountains in yellow. This is how they
44:05have swung so far. In some distant geological future, they will cover the
44:10city completely.
44:16What does the geological future look like? What clues are hidden in the
44:21mountains, deserts, and seas? Human time span is so short, it's hard to understand
44:27that we will be undone by forces that play out over millions of years. It's
44:32difficult to grasp that the march of the earth is unstoppable.
44:42We've been very lucky because modern society is actually developed at a time
44:46when very little has been happening geologically, so we've been in a period
44:50of geological quiescence. Now this isn't going to last. We know that there are
44:53going to be major global catastrophes occurring in the future, gigantic tsunami,
44:58big volcanic eruptions, more impact events, and on that basis we know that
45:02we're all living on this planet simply by geological consent.
45:16Asteroids are a very real threat. They've been hitting the earth since it began
45:21its journey through space and time. 200 space rocks large enough to cause global
45:27devastation are known to be on earth-crossing orbits, and there may be
45:31many more. In 1996, one missed us by 300,000 miles and astronomers hair's
45:38breadth away. The geological record shows impacts brought catastrophe and
45:43devastation which wiped out many species. A direct hit could extinguish us just as
45:50it did the dinosaur.
45:57Impact destruction may seem a remote concern, but there is a more immediate
46:06threat. Ice is crucial in helping to keep the earth's climate mild enough for life
46:11to survive, but worldwide the temperature is rising and the ice is melting.
46:27If this keeps happening, sea levels will rise. A rise of only 15 inches would spell
46:34catastrophe for low-lying countries and low-lying cities.
46:42Major sea level rise in itself may be catastrophic for the planet, but actually
46:46there are unexpected effects as well, and that is that rising sea levels may
46:50trigger volcanic eruptions.
46:54We know this because we've been looking at the relationship between changing sea
47:00levels and volcanic eruptions in the Ice Age, when we had changes of a hundred or
47:04two hundred meters in sea level over a few tens of thousands of years.
47:09Maguire's new work on Etna seems to show that the more rapidly sea level rises or
47:14falls, the more violently the volcano tends to explode. When sea levels rise
47:19around coastal volcanoes such as Etna, they have a rather interesting effect. If
47:23you imagine the volcano sitting on a plate with Etna here, if you then load
47:27the other half of the plate by a sea level change of 100 meters or so, it
47:31has the effect of bending it, and what that does is set up tensional stresses
47:35within the volcano, and any magma sitting there will burst its way out as in the
47:39form of an explosive eruption.
47:42In modern times, we haven't really experienced the full terror of volcanic
47:54catastrophe. If Bill Maguire's theory is right, such an event could hurry in the
47:59new Ice Age, because nature can wield a two-edged sword.
48:06Rising sea levels could cause volcanoes to erupt, spewing debris and sulfur into
48:13the atmosphere. That will cut out the heat from the Sun, so the earth will cool.
48:19That will make the ice form again, freezing the oceans so sea levels drop
48:24once more. And that sudden fall may trigger more volcanic activity, pumping
48:31more material into the atmosphere, making the earth even colder, ushering in the
48:38dark, and the ice, and the long winter.
48:51In some places, the future is already here. The small mining town of Coleman's
48:57Kop, abandoned just a few decades ago, is already being invaded by the sand dunes.
49:02Eventually, it'll be entirely covered. If we turn our back for one moment, the
49:08geological cycle of erosion and deposition will take over.
49:12Professor Rampino knows from his work in the Namibian desert how the tectonic
49:17dance will end. Scientists may argue about the short and medium term, but the
49:22further ahead they look, the clearer the vision becomes. The sand in this dry
49:27riverbed in Namibia is part of an endless cycle of erosion and deposition.
49:31The sand is carried downstream by rivers to the coast and picked up by ocean
49:36currents, moved along the Namibian shore to form the long beaches of Namibia.
49:41Some of the sand is blown inland to form dunes. The sands can be consolidated into
49:51sandstone, and then be eroded again to form new sands. Part of a cycle from
49:56granite, to sands, to sandstone, and back to sand again. On a human timescale, not
50:03much happens, but on a geological timescale, all that we have done and all
50:07that we have made will be destroyed.
50:13So, at the end, Earth has no future. Through millennia to come, the unfamiliar
50:20continents will form and move on as the plates continue their wanderings. Rivers
50:28will change their courses, oceans will empty and fill, and mountains erode and
50:34rise again.
50:36But our Sun is aging. In five billion years, it will run out of energy. As
50:49gravity tightens its grip, it will collapse on itself, the temperature
50:54rising to 100 million degrees. It will expand uncontrollably, engulfing Mars,
51:02Venus, and the Earth.
51:07The seas will boil away, the atmosphere evaporate, as Earth becomes a charred
51:13ember.
51:16Then the Sun will cease all nuclear fusion, and die. It will be the end of
51:23our amazing Earth.