The high andes of Bolivia
ln the 16th century
rumours of fabulous Wealth
dreW Spanish adventurers to this lonely place.
What they found here exceeded their Wildest dreams.
A mountain of silver...
they called the Cerro Rico.
To the Spanish the Cerro Rico Was a gift from God.
The amount of silver Won from this mountain alone
Was truly fantastic.
Perhaps up to 60,000 tons of silver has been Won,
enough to finance the entire Spanish empire,
and indeed the Western World.
lt is estimated that perhaps just as much remains.
So that this mountain, Cerro Ricco,
can truly be said to be the richest silver mine in the World.
As over the centuries prospectors
folloWed the trail of silver and also gold,
it led them to rich deposits
all round the great Pacific Ocean.
ln fact, you might call the rim of the Pacific
'The Ring of Gold',
but it's more usually called 'The Ring of Fire'
because all round the margin of the Pacific Basin
associated With the mineral deposits,
there are huge chains of volcanoes.
At first sight, there might not seem to be
any connection betWeen volcanoes and ineral Wealth,
but in fact there is,
and that link is a clue to one
of the most puzzling mysteries about the earth.
HoW did the dry land -
the continents on Which We live -
hoW did they form?
Only one third of the Earth's surface is dry land.
Most of the planet is covered by Water
John DeWey is a geologist
Who has spent his career looking at the rocks on land,
trying to understand their origin.
Those on the West coast of Scotland
hold a special interest for him;
they're the oldest in the British lsles.
l think you have to remember
that prior to about thirty years ago,
geologists had been mapping the continents
and making very detailed geological maps,
over a period of perhaps a hundred years,
including a beautiful map of this area
made in the last century With exquisite details
of all the rocks:
but of course there Was no ready explanation
to explain all these rocks and geological relationships.
When John DeWey first came here over 30 years ago,
many geologists still saW no distinction
betWeen the rocks on dry land,
and those beneath the sea.
But that soon began to change.
As scientists explored the oceans,
they started to realize that the veil of Water
concealed a fundamental difference
betWeen the continents and the ocean floor.
Unlike the continents,
the deep ocean floor consists almost entirely
of rocks of only one type.
What's more, scientists Worked out
that this rock had all been produced in the same Way -
all erupted by undersea volcanoes
that ran doWn the middle of the oceans.
lt Was a beautifully simple picture.
ln contrast, on the continents
We see a very, very different kind of story.
These rocks have suffered
an immensely complicated histry
over a very long period of time,
in such a Way that these bands,
light and dark bands,
have been folded, sWirled together,
squidged and squashed
at very high temperatures and pressures
in Ways that are typical
in many many parts of the World,
the kind of thing you see in the continents
but never in the oceans.
HoW had rocks like these been created?
Unlike their ocean-going colleagues,
land geologists lacked a simple theory
that could explain the origin of the continental crust.
ln those days, We didn't have it;
We Were simply groping in the dark.
The first glimmer of light
came from the same region
that had enriched the Spanish Empire...
in the high Andes of Bolivia.
Each year the people Who live
at the foot of the Cerro Rico
celebrate the source of their prosperity.
But for many years the region
has also attracted scientists like Rodney Grapes
and Leonore Hoke from NeW Zealand.
Top it up
This year they're being joined
by tWo British geologists...
...Rick Thomas and Catrin Jones.
The team are heading for an area
Which for thirty years scientists have suspected
may hold the key to hoW the continental crust is formed..
OK, so Where are We heading?
l think really We've got to go straight toWards that big volcano
because there's nothing else
that's gonna give us so good a bearing.
So that's 3.10.
We've got ...? behind us, to the right.
We've got this distinctive volcano.
Yes that's this one here.
... What is it - 3.10?
We'll have to rely on your bearing then.
OK, Well then let's go.
Their journey takes them across the Salar,
a dry salt lake...
part of the vast Altiplano...
a 4000 metre-high plateau in the middle of the Andes.
There are the odd pot-holes,
but l think it's the best road in Bolivia -
you go flat out, 120 kilometres,
if the car makes it.
You're still going at sixty are you?
Yeah, Well. Enjoy the vieW.
BetWeen them and the Pacific coast lies their goal -
a chain of active volcanoes,
the highest in the World.
As they near the volcanoes,
the team start to see signs at the surface
of tremendous activity deep beloW them.
l'm familiar With the volcanoes in NeW Zealand,
and it's a real thrill to come here to the Andes,
Where you can see so many more of these volcanoes,
very similar to the ones We have in NeW Zealand.
The rock that's erupted from these volcanoes is
in fact called Andesite, after the Andes,
so if you like this is the home of the Andesite.
Not just the volcanic cones,
but the entire landscape here is made of andesite
and other volcanic rocks.
Since the 1960s,
scientists studying the growth of the continents,
like Rick Thomas,
have been Working out hoW this happens.
Volcanoes in the Andes are notoriously explosive.
They can eject tons of ash
and fragments of volcanic rock into the atmosphere.
The reason for this behaviour is a surprising one.
The liquid rock at depth contains a lot of Water,
and that Water's happily dissolved
When it's doWn deep:
as it comes close to the surface,
it froths up the magma, the liquid rock,
and it causes it to explode,
just like When you uncork a champagne bottle;
same sort of thing's happening here.
Froths up and What We get is fragments of rock
Which are full of bubbles Within the rock
and you get lots of these pumices
Which you can see here.
lf you'd been here during one of these eruptions,
you'd have seen vast billoWing clouds
in the distance coming toWards you,
kilometres aWay,
but in a minute or so, because they travel so fast -
hundreds of miles an hour quite easily -
they Would have engulfed you.
and this ash cloud Would have just blasted on
doWn the valley and just filled most
of What We can see of that plain.
As the clouds of ash and pumice settle,
they compress together to form neW rock layers.
Over time these layers gradually build up.
Water is the key to this process
and it's the Water that's attracted the team
to this remote spot.
Straight ahead of us, is OjagWe
With its fumarole on top.
Yes, a nice conical volcano, that, actually, and you can...
Leonora plans to collect a gas sample
from the active fumaroles at the summit,
Which are continually producing steam
and other vapours.
...quite clearly the fumarole there.
As you come doWn the right shoulder,
and you just might be able to make out lrruputuncu.
And that's Where We're heading.
Back in the Sixties,
scientists searching for the origin of the continents
realised that the explosive process
they could see building up the landscape here
Was not confined to the Andes;
it Was happening elseWhere too.
MattheW ThirlWall has collected rock samples
from volcanoes all over the World.
Of the thousand or so active volcanoes
in the earth at the moment,
some eighty per cent produce these highly explosive eruptions.
This is a sample of pumice from the Andes,
but We can find almsot identical pumice
in several other places on earth.
Here We have pumice almost exactly the same,
With these gas bubbles in it,
from Mount St. Helens in Washington State,
and this is a typical example of Andesite,
the characteristic rock in these areas.
And you can see-
find almost identical Andesites
in several other recent eruptions -
for example, here We have a sample
from Mount Pinatubo in the Phillippines;
very very similar samples
With some four thousand miles of Pacific betWeen them.
ln fact, geologists soon discovered
that most of the volcanoes that surround the Pacific Ocean
produce the same type of rock,
in the same explosive fashion.
We're completely safe from these eruptions in England,
but if you happen to live anywhere
near the edge of the Pacific Ocean,
you can almost certainly drive Within a day
to one of these Andesitic volcanoes.
So the volcanoes of the Ring of Fire are all basically similar.
Hundreds of them are continually erupting
in an extraordinary arc that runs up
the Western coast of the Americas
from Patagonia all the Way to Alaska...
And then continues all the Way around the Pacific Basin.
lt daWned on scientists that in the process,
the volcanoes Were building up a ring
of Andesitic rock all around the Pacific.
And then they discovered a link
betWeen these rocks
and those Which make up the continent as a Whole.
As they analysed thousands of samples,
from all over the World,
a surprisingly simple picture emerged;
though the rocks looked different,
they Were made from basically the same ingredients.
And indeed their average composition hardly varied
at all from continent to continent.
Even more significant, this average composition
Was essentially the same as that of the volcanic rocks
in the Ring of Fire.
lf one Were to take all the continental crust
of the Whole World, grind it up,
then measure its average composition,
it Would be very very similar to that of these rocks,
and it Would consist of three basic minerals;
the very translucent mineral is quartz,
the rather milky mineral is felspar,
and the dark green mineral is hornblende.
And then if one goes to the Andes
and looks at the volcanoes,
and indeed looks at the rocks injected deep
in the crust beneath the volcanoes,
one has the same general composition
as We find here, of quartz, of felspar and of hornblende.
And of course that immediately
begins to give one an inkling that possibly
these rocks Were formed in the same Way.
Andf not only that but much of the continental crust
must have been formed in the same Way
as We see in the Andes in the present day.
So perhaps the continents had all been created
by volcanoes like these,
building up the crust over geological time.
But, What Was creating the volcanoes themselves?
And hoW could something happening around the Pacific
explain the rocks in Scotland?
All this Was a complete mystery.
But then the Ring of Fire provided another vital clue.
The region Was periodically rocked by earthquakes.
ln 1964,
a major one struck Alaska.
l Was leaning in my cabin getting a cigarette,
and all of a sudden it started shaking.
We Was evidently right over the epicentre.
These big sand spouts Were shooting up in the air.
You can't believe hoW that boat shook and rattled.
lt Was scary.
Could l have your attention please?
Alaska Airlines Flight 61 Will be arriving noW.
The day after the earthquake,
a US government geologist fleW in
to investigate What had happened.
George Plafker is still Working in the region.
l Was in Seattle attending a geological conference
When the earthquake struck.
From the initial reports,
We realised it Was a major disaster
and a great earthquake,
and it Was in my field area.
We got some clothing together
and We took the next flight up to Alaska.
Our mission Was to assess the damage.
And of course as a scientist l Was interested
in trying to figure out the cause of this earthquake.
UnknoWn to George at the time,
understanding the cause Would have global implications.
But his immediate problem Was just getting around;
the earthquake had affected a vast and remote region.
When We first came up,
all We had heard Was that the roads
and railroads Were cut
and that there Was a great deal of landsliding
and Wave damage in the coastal areas.
There Was a big...Water out there,
betWeen this island and that mainland over there.
l said; 'oh, my gosh; tidal Wave', and l just kept running -
l didn't even look back.
Amongst all the stories of eye-Witnesses,
confusing reports of sea-level changes
Were also emerging.
Some Witnesses claimed the sea level had dropped,
others that it had risen.
George's hunch Was that something fundamental
had happened to the land itself,
and that Working this out Would lead him
to the cause of the earthquake.
He decided to examine the shore-line in detail.
This is What We had to do to get around this shore-line.
And it Was here that he made his first remarkable discovery.
This Water level is a little bit beloW mean high-tide.
Mean high-tide normally reaches
to about the top of this rock,
and you can see these barnacles on the rock
and seaWeed Which groW up to that level.
Let me shoW you something fascinating noW.
Here is a line of dead barnacles
and this line is about six feet
above the living barnacles.
When l came here in 1964,
some of these barnacles Were still alive.
George realised that during
the feW moments of the earthquake,
the land here had been jacked up six feet.
What Was more, George had found
a Way to measure accurately land level changes
over the Whole enormous area affected.
He visited hundreds of small coves and inlets,
folloWing the line of barnacles.
That big... Wheel going doWn the track
means it's all up and doWn, He ain't coming back,
so l'm moving on,
l'll soon be gone.
You are flying too high for my little old sky,
so l'm moving on.
That big loud Whistle as it bleW and bleW,
Said hello to the south land,
We're coming to you When We're moving on,
Oh hear my song...
NoW there are thirty tWo feet
above the level at Which barnacles live at the present time.
Spent all of the summer of 1964
and most of the summer of 1965
studying a stretch of coast
more than 500 miles from one end to the other.
lt's to find my home, so please listen to me,
'cause l got a pretty mamma....
Where the shore-line Was uplifted,
plants soon colonised the neW land.
Portage is about 270 degrees...
But When he fleW north West,
further inland,
it Was a completely different story.
...go across Naked lsland...
Before the earthquake,
Portage had been a thriving rail stop.
But George learned that it Was noW being flooded at high tides,
and icebergs Were floating up the river into the toWn.
We Were stood over there
Where the railroad station used to be,
and Watched these icebergs
slam into the bar building and bounce off:
they'd slam into the houses and go crunch.
That night, the Water came in
to the top of the bar
Where people sat to drink,
and Was clear up to there.
And old guy that Worked or us stayed in the bar that night:
the rest of us all fled across the street,
and We all go back over to see if he's all right.
And of course he Was; he Was drunk.
George realised that in this region,
land had gone doWn, nearly tWo metres at Portage.
The subsequent inundation of sea Water,
killed large tracts of pine forest.
When George plotted his measurements on a map,
he found that a striking picture emerged.
Along the coastal regions,
an area about the size of Great Britain
had risen during the earthquake up to 12 metres,
While further inland another vast area
had gone doWn about tWo metres.
That Was something
that Was absolutely neW and different;
nobody had ever seen anything like that
before probably on the face of the earth.
George Plafker had discovered movements of the earth's crust
on a totally unprecedented scale,
that accounted for the huge landslides
and the tidal Waves.
What he still had to explain Was Why parts
of the Alaskan crust had risen, Whilst other parts had sunk.
And the explanation he came up With
changed our vieW of the earth for ever.
When George Was Working on the geological effects
of the Alaskan earthquake of 1964,
We already kneW big tilts of the ground
and movements of the ground,
and indeed earthquakes Were the result of slip on faults,
and perhaps the best example in the World
that has been best studied is the San Andreas fault in California.
And here We have a couple of rather nice slides,
Where a large segment of the fault is slipping along,
so quite naturally,
George Was looking for a similar kind of structure,
a steep break in the aearth's crust along the Alaskan region,
to explain the 1964 earthquake.
But in Alaska there Was no sign of a large fault cutting the surface.
Despite all of our efforts,
We didn't find such a fault.
NoW this Was a major puzzle
and something that bothered me for a long time.
But then George started to look elseWhere.
Finally, after much thinking about it,
l realised that the fault We Were looking for
actually underlays the entire region
of uplifted subsidence,
and that We couldn't see it
because it came to the surface out to sea.
George's insight Was that the fault Was underground,
sloping gently beneath the entire region.
Oceanographers had knoWn for some time
about a mysterious deep trench in the sea floor
about a hundred kilometres offshore.
George Was convinced that this Was
Where his gigantic fault reached the surface -
under Water.
So if l draW a cross-section of Alaska -
l come from the north, do the land,
across the volcano and doWn gradually,
steeper and deeper, then doWn into a deep ocean trench,
and l'll draW the sea
in a blue Wavy colour like this.
What George found, you remember, of course,
Was that the great Alaskan earthquake of 1964
Was produced on a fault plane dipping gently
under Alaska like this,
With this sense of motions,
that is the underpart Was slipping doWn under Alaska in that Way.
And of course this is very important because
if one projects that fault out along its length,
lo and behold, it projects to exactly the position
of the oceanic trench.
So We can connect the trench directly
With this plane of earthquakes.
A major fault like this Would have caused repeated earthquakes
and George realised
it Was What happened betWeen earthquakes
as the crust Was squeezed
that could explain Why some places
had gone doWn While others had risen.
l have here a model,
very simplified representation
of the continental margin of Alaska.
This represents the fault.
For several centuries betWeen earthquakes
there is gradual compression
and uplift of the area above that fault,
and at the time of an earthquake it slips suddenly,
causing uplift on the seaWard side,
and subsidence in the area Where there Was a fault.
And this land movement Was not a one-off event.
When he looked,
George found signs of past earthquakes
engraved in the landscape.
This series of steps Was created
as the land Was repeatedly jacked
out of the sea every feW hundred years
by a sudden movement on the fault.
But it Was What Was happening
beneath the fault that Was really significant.
George suggested that With this sense of motion,
the Whole of the Pacific Ocean floor is slipping,
floWing doWn along this inclined plane underneath Alaska.
And of course the expression of this are intermittent earthquakes
about every seven or eight hundred years.
lf you keep on adding up each feW metres of slip
that generates the earthquake
then over a long period of geological time
this Was suggesting
the Whole Pacific Ocean floor Was floWing doWn
along this inclined plane underneath Alaska.
Only then did George Plafker
and his colleagues realise the full significance
of the ocean trench off the coast of Alaska.
Because this trench circled virtually the Whole Pacific margin,
it suggested that the entire floor of the Pacific Ocean
Was sliding back beneath the surrounding continents,
sinking back into the Earth's interior.
And this Was just part of an even bigger picture.
Geologists had already discovered
that the sea floor Was being continually
created along the mid-ocean ridge-
the volcanic mountain chain
that ran up the middle of the oceans.
The ultimate fate of this sea floor Was obvious noW.
As it Was being created in the middle of the oceans,
so it Was being destroyed at the trenches at ocean margins
in What scientists called subduction zones.
And this Was happening all over the planet.
Together the ocean trenches
and the mid-ocean ridges formed a netWork of lines,
boundaries that divided the globe into vast,
sloWly moving regions - the plates.
lt Was an extraordinary revelation -
geologists suddenly realized
that the entire surface of our World Was in constant motion.
And so the theory of plate tectonics Was born,
and scientists started thinking about the earth
in a completely neW Way.
And it's really quite an extraordinary idea,
but remarkably simple.
The surface of the earth consists
of a number of rigid plates
that are moving relative to each other:
and this map here shoWs these plates
in different colours.
And the Pacific region forms
a huge plate Which um is moving relative
to the Australian plate in the NeW Zealand region,
and sliding past the North American plate in California.
The continents move With the plates.
Throughout geological time,
they have completely rearranged themselves,
sometimes coming together
and sometimes splitting apart,
opening and closing oceans,
re-shaping the face of the earth.
What had begun ith a line of dead barnacles
ended With a neW vieW of our planet.
Plate tectonics suddenly arrived as a marvellous theory
because it Was able to suddenly explain lots of things
We Weren't able to explain many years ago.
Back in Bolivia,
scientists began using the theory of plate tectonics
to explain the origin of the Ring of Fire.
Leonore Hoke and the team
believe that it can also throW neW light
on the growth of the continents.
They knoW that deep beneath their feet,
ocean plate is sinking into the earth's interior.
NoW it's very interesting
because We have volcanoes round about
in the position
Where the subducting oceanic plate
is 100 to 120 kilometres beloW the surface
Where We are here noW.
And that's Where We have volcanoes;
and We knoW from looking at the volcanoes
that they produce a lot of molten rock
and they produce a lot of fluids like Water.
Geologists suspect that some of this Water comes directly
from the sinking ocean plate
and may explain Why the volcanoes are here.
Leonore plans to test this idea
by collecting a sample from high on the volcano.
Well, this is my blue barrel
Which contains all the sample equipment Which l need,
and there are all sorts of things in it like this gas mask
Which protects me from noxious gases,
funnels to collect gas bubbles With,
it contains this tubing Which l need,
and it contains these containers,
and l pack them With at sea-level in NeW Zealand,
oops, they pop When you open them
because We are really at high altitude here.
And here are these special glass containers
um into Which l Will suck the gas they evacuated,
and the gases Will tell me an awful lot about processes
Which gave rise to formation of these volcanoes-
volcanoes and processes Which happen at great depth.
Are We ready then?
Como si yama ...?
Benito Velo
Benito. Leonore.
Benito . Se Catrin.
Come stas?
OK?
lt's six a.m. on the Bolivian border With Chile.
Leonore, Catrin and their guide
are on their Way to their chosen sampling area.
They're heading for the crater,
the most dangerous place on the active volcano;
lrruputuncu.
The climbers are folloWing a rarely used footpath,
made by locals to collect sulphur from the summit.
They are climbing to nearly 6000 metres.
At this height oxygen levels
have almost halved making it difficult to breathe.
lt's hard Work isn't it?
Yeah. Biting Wind.
Sulphurous smell's getting stronger as Well.
Well, We're getting closer to the fumarole.
Yup. Another hour or so.
Brilliant vieW.
That's really the reWard of it, isn't it?
Yeah. lts' amazing.
Feel like a bird up here.
The higher they go, the steeper the climb,
as the sticky volcanic rock has built up the slopes of the crater.
After 4 hours they're Within sight of their goal.
This is the solid material that the volcano's made from.
lt's dark, almost black.
But covering all these rocks is sulphur,
Which is coming from the gases
that are coming up from the craters behind me.
Beautiful yelloW crystalline material.
The gases are also containing Water,
and that Water is pervasively reacting
With the rock, and changing it,
so We get this crumbly White material.
lt's this Water,
together With other gases rising through the crater,
that Leonore has come to collect.
l'm taking a condensate sample;
that means l'm collecting the steam
and l guide it through this glass container
Which is immersed in snoW,
and that cools the steam,
and l'm collecting the Water at the bottom of it,
and you Will see later
on there's quite a lot of Water in this steam.
l'm having a look noW hoW much Water there is;
l dig it out of the snoW.
lt's great to get out of that
hot steam; it's hundred and tWenty degrees.
But What l've collected here is some Water;
you can see it in here.
There's quite a lot coming out of this fumarole.
NoW the chemistry of this Water Will tell us
Where this Water's coming from
and it Will be analysed back at the lab.
There's yelloW all over it.
Covered With sulphur. ...your eyes and things.
lt Was kind of like Hell.
The devil Was about to pop his head out any minute.
OK, time to go.
Mm, it's still Warm.
Back in Wellington, NeW Zealand,
Leonore heads straight for her laboratory.
Here l've got the sample
l collected on top of active volcano in Bolivia,
so let's see What's in it.
She's about to measure the composition of the sample
to get an insight into the events taking place
deep beloW the volcano.
You can measure the different gas components
in the sample, and it contains helium,
it contains argon, it contains CO2,
it contains nitrogen
and many other gas components.
But it's the concentratioan of nitrogen
Which catches her attention;
it goes almost off the scale.
That's good.
l have quite a high signal coming from the nitrogen.
Nitrogen is the most common gas in air.
But the proportion in the sample is far too high;
it suggests a completely different source.
Leonara turns her attention to the Water in the sample.
We can also measure the isotypes
of these gas components
by using a mass petrometer
By analysing the atoms in the Water,
Leonore is hoping to test a startling idea.
She suspects that some of the Water
in the sample might come from the sea.
lf so, it Would support her groWing conviction
that the nitrogen could be coming from dead marine organisms
knoWn to be nitrogen rich,
buried in the sea floor.
Could the flask from Bolivia
contain a sample of the Pacific Ocean?
The hydrogen is very close
to the hydrogen isotopes of sea Water.
So that suggests that some component
Within that Water is probably sea Water.
So We can say from that
that a lot of that nitrogen is biogenic nitrogen,
produced in ocean sediments
and released during the subduction process.
So the journey up the volcano
has yielded an amazing result -
high up at the summit are traces of marine life
and thePacific Ocean itself,
Which have completed a long
and extraordinary journey through the Earth.
Good climb?
Excellent.
The Whole story's contained in one glass flask.
You suffered With me!
And of course a large part of this cyclic process
explains the origin - origins of the continents
because We noW see that lovely link
betWeen the origin of volcanoes
and the oceanic trench.
lt's a beautifully linked system.
We noW have the picture of this flux of Wet rock,
oceanic material coming into the subduction zone,
carrying a lot of Water With it,
getting hotter and hotter
and eventually it gets so hot that the Water is expelled...
...and that Water Will arise into the mantle
above and Will act like anti-freeze;
it Will trigger melting.
So Water is the key to the Ring of Fire.
As the ocean floor sinks into the earth,
Water is squeezed out of the rocks.
Like scattering salt on an icy road,
the Water reduces the melting point
of the surrounding rocks
and so they start to melt.
This molten rock rises to the surface,
to erupt as a line of volcanoes.
But these volcanoes are like the tip of an iceberg.
Only a small proportion
of the molten rockever reaches the surface.
Most of it is building the continental crust
beneath our feet.
The surface volcanoes are merely the surface manifestation
of a huge process of the addition of neW hot material to the crust.
And if this has been going on
for some considerable period of time,
Which We knoW it has,
you can actually make very large amounts of continental crust
in this Way.
There's a huge volume of volcanic material
being added to the crust.
BeloW us, We can imagine more molten rock
ponding underneath you at some level.
As you drive along, you're Witnessing
the growth of continental crusts.
lt's quite an exciting thought.
Here is a place Where for millions of years
the continent has been groWing,
and it's going to continue probably
for many more millions of years.
But as the plates have moved through out geological time,
the places Where the continents
groW have shifted over the Earth.
Britain's ancient crust Was built up
in the same Way by volcanoes -
450 million years ago.
As MattheW ThirlWall explains
in the Lake District.
Everything We see over here
Was produced by big eruptions.
BeloW us, there's something like eight thousand metres
of volcanic rock.
We can tell from the andesitic composition of the rocks,
that there Was almost certainly a subduction zone
beneath the Lake District, With an ocean to the north,
and an oceanic plate coming doWn
beneath the Lake District, beneath Wales,
beneath lreland and so on.
And the crust in this area almost certainly
greW as a response to that subduction.
WorldWide, the composition
of the continental crust is andesitic,
right the Way back through time.
Subduction zones Were the sites of continental crust formation,
not just at the present day at the Ring of Fire,
but right the Way back
until the earliest parts of earth history.
As the continents have groWn,
another legacy has been left behind;
the mineral Wealth With Which We have forged civilisation.
The Cerro Rico itself used to be an active volcano
some 16 million years ago.
And the much older volcanoes in the Lake District
have also brought up their oWn rich dividend;
copper.
ln the 19th century,
this area provided much of the copper
for the burgeoning lndustrial Revolution.
The link betWeen volcanoes
and mineral Wealth is another cvonsequence
of Water moving Within the earth.
The connection is that the hot rocks
at depth mobilise Water,
and that Water circulates around the hot rocks, dissolves,
leaches metals from the volcanic rocks,
forces cracks up to the surface,
transports the metals up in these cracks,
and then deposits them as the pressure drops.
lt's really luckythat that's What's actually happened
because if the metals Were not deposited in these veins
it Would take something like the Whole mountainside
to Work to produce a single copper pipe.
The volcanoes provide the Workable deposits.
The people of the Cerro Rico
have long believed the silver is a gift from Patja Mama
their god of the earth.
ln some Ways, they've been proved right.
Scientists noW see hoW,
as the plates of the earth move,
creating the land on Which We live,
our planet also yields up its Wealth.