On Fri, 28 Nov 2003 22:17:47 -0000, "The Rifleman"
wrote:

Supervolcanoes
BBC2 9:30pm Thursday 3rd February 2000

NARRATOR (SINÉAD CUSACK): Yellowstone is America's first and most
famous National Park. Every year over three million tourists visit this
stunning wilderness, but beneath its hot springs and lush forests lies a
monster of which the public is ignorant.

PROF ROBERT CHRISTIANSEN (US Geological Survey): Millions of people
come to Yellowstone every year to see the marvellous scenery and the
wildlife and all and yet it's clear that, that very few of them really
understand that they're here on a sleeping giant.

NARRATOR: If this giant were to stir, the United States would be
devastated and the world would be plunged into a catastrophe which could
push humanity to the brink of extinction.

PROF ROBERT SMITH (University of Utah): It would be extremely
devastating on a scale that we've probably never even thought about.

PROF BILL McGUIRE (Benfield Greig Centre, UCL): It would mean absolute
catastrophe for North America and the problem is we know so little about
these phenomena.

NARRATOR: In 1971 heavy rain fell across much of east Nebraska. In the
summer palaeontologist Mike Voorhies travelled to the farmland around the
mid-west town of Orchard. What he was to discover exceeded his wildest
dreams.

PROF MIKE VOORHIES (University of Nebraska): Well I was walking up
this gully looking for fossils, the way I'd walked up a thousand gullies
before, keeping my eye on the ground looking for pieces of fossils that
might have washed down in the rain the previous night and I scrambled up to
the top and I saw something that completely astounded me, a sight that no
palaeontologist has ever seen.

NARRATOR: It was a sight of sudden, prehistoric disaster. Voorhies's
digging revealed the bones of 200 fossilised rhinos, together with the
prehistoric skeletons of camels and lizards, horses and turtles. Dating
showed they had all died abruptly 10 million years ago.

MIKE VOORHIES: It suddenly dawned on me that this was a scene of a
mass catastrophe of a type that I'd never, never encountered before.

NARRATOR: The cause of death, however, remained a mystery. It was not
from old age.

MIKE VOORHIES: I could tell by looking at the teeth that these animals
had died in their prime. What was astounding was that here were young
mothers and their, and their babies, big bull rhinos in the prime of life
and here they were dead for no, no apparent reason.

NARRATOR: For the animals at Orchard death had come suddenly. There
was another strange feature to the skeletons, an oddity which offered a
crucial clue about the cause of the catastrophe.

MIKE VOORHIES: We saw that all of these skeletons were covered with
very peculiar growth, soft material that I first thought was a mineral
deposit. Then we noticed that it was cellular. It's biological in origin so
there was something actually growing on those bones. I had no idea what that
stuff was, never seen anything like it.

NARRATOR: A palaeo-pathologist, Karl Reinhard, was sent a sample of
the bones.

PROF KARL REINHARD (University of Nebraska): This specimen is typical
of the rhino bones. You see this material, in this case it's a whitish
material that's deposited on the surface of the original bone. This is
peculiar to me, but as I thought back in my experience I realised that this
was similar to something that turns up in the veterinary world, a disease
called Marie's disease.

NARRATOR: Marie's is a symptom of deadly lung disease. Every animal at
Orchard seemed to be infected.

KARL REINHARD: One of the clues was that all of the animals had it.
Now that is a very important observation for all the diseases, all the
animals to exhibit this disease there had to be some universal problem.

NARRATOR: Scientists discovered the universal problem was ash. 10
million years ago ash had choked them to death.

KARL REINHARD: It may have been a bit like pneumonia with the lungs
filling with fluid, except in this case the fluid would have been blood for
the ash is very sharp. There'd be microscopic shards of ash lacerating the
lung tissue and, and causing the bleeding. I would imagine these animals as
stumbling around the thick ash, spitting up blood through their mouths and
gradually dying in a most miserable way.

NARRATOR: Only a volcano could have produced so much ash, yet the wide
flat plains of Nebraska have no volcanoes.

MIKE VOORHIES: I remember some of my students and I sitting around
after a day's digging and just speculating where did this stuff come from?
There, there are no volcanoes in Nebraska now. As far as we know there never
have been. We, we obviously had to have volcano somewhere that, that
produced enough ash to completely drown the landscape here, but where that
was really was anybody's guess.

NARRATOR: One geologist in Idaho realised there had been a volcanic
eruption which coincided with the disaster at Orchard 10 million years ago,
but the site was halfway across North America.

PROF BILL BONNICHSEN (Idaho Geological Survey): It seemed like a
really fascinating story which made me think, because I had been working on
volcanic rocks in south-western Idaho that potentially could make lots of
ash and, and there was some age dates on that that were around 10 million
years and I began to wonder wow, could this situation in Nebraska have
really been caused by some of these large eruptions that evidently had
happened in south-western Idaho.

NARRATOR: The extinct volcanic area, Bruneau Jarbridge, was 1600
kilometres away, a vast distance. How could this eruption have blasted so
much ash so far? Bonnichsen was sceptical.

BILL BONNICHSEN: Volcanoes will spew ash for a few tens or maybe a few
hundreds of miles. This ash, and it's like two metres thick, in Nebraska is
1600 kilometres or more away from its potential source, so that's an amazing
thing. There really had been no previous documentation, to my knowledge, of
phenomenon like that.

NARRATOR: Despite his doubts Bonnichsen decided to compare the
chemical content of ash from the two sites. He analysed samples from both
Bruneau Jarbridge and Orchard and plotted their mineral composition on a
graph looking for similarities.

BILL BONNICHSEN: if you have a group of rocks that are very similar to
one another they should be a closely spaced cluster of pods. We had these
analyses come out from the Orchard site and I thought I'd try the clock
again and see how close they were to one another. By golly, they fall right
in the same little trend as the Bruneau Jarbridge samples.

NARRATOR: Bonnichsen's hunch had proved correct. Bruneau Jarbridge was
responsible for the catastrophe at Orchard. An eruption covering half of
North America with two metres of ash was hundreds of times more powerful
than any normal volcano. It seemed almost unbelievable, but then Bruneau
Jarbridge was that rarest of phenomena which scientists barely understand
and the public knows nothing about: a supervolcano.

ROBERT SMITH: Supervolcanoes are eruptions and explosions of
catastrophic proportions.

BILL McGUI When you actually sit down and think about these things
they are absolutely apocalyptic in scale.

PROF MICHAEL RAMPINO (New York University): It's difficult to conceive
of a, of an eruption this big.

NARRATOR: Scientists have never witnessed a supervolcanic eruption,
but they can calculate how vast they are.

BILL McGUI Super eruptions are often called VEI8 and this means
that they sit at point 8 on what's known as a volcano explosivity index. Now
this runs from zero up to 8. It's actually a measure of the violence of a
volcanic eruption and each point on it represents an eruption 10 times more
powerful than the previous one, so if we take Mount St. Helens, for example,
which is a VEI5, we can represent that eruption by a cube of this sort of
size, this represents here the amount of material ejected during that
eruption. If you go up step higher and look at a VI6, something of the
Santorini size for example, then we can represent the amount of material
ejected in Santorini by a cube of this sort of size, but if we go up to VEI8
eruptions then we're dealing with something on an altogether different
scale, a colossal eruption and you can represent a VI8, some of the biggest
VI8 eruptions by a cube of this, this sort of size. It's absolutely
enormous.

NARRATOR: Normal volcanoes are formed by a column of magma, molten
rock, rising from deep within the Earth, erupting on the surface and
hardening in layers down the sides. This forms the familiar dome or
cone-shaped mountains.

BILL McGUI Most people's idea of a volcano is a lovely symmetrical
cone and this involves magma coming up, reaching the surface, being extruded
either as lava or as explosive eruptions as, as ash and these layers of ash
and lava gradually accumulate until you're left with a, a classic cone
shape.

NARRATOR: Vulcanologists know this smooth flowing magma contains huge
quantities of volcanic gases, like carbon dioxide and sulphur dioxide.
Because this magma is so liquid these gases bubble to the surface, easily
escaping. There are thousands of these normal volcanoes throughout the
world. Around 50 erupt every year, but supervolcanoes are very different in
almost every way.

First, they look different. Rather than being volcanic mountains,
supervolcanoes form depressions in the ground. Despite never having seen a
supervolcano erupt, by studying the surrounding rock scientists have pieced
together how supervolcanoes are formed. Like normal volcanoes they begin
when a column of magma rises from deep within the Earth. Under certain
conditions, rather than breaking through the surface, the magma pools and
melts the Earth's crust turning the rock itself into more thick magma.

Scientists don't know why, but in the case of supervolcanoes a vast
reservoir of molten rock eventually forms. The magma here is so thick and
viscous that it traps the volcanic gases building up colossal pressures over
thousands of years. When the magma chamber eventually does erupt its blast
is hundreds of times more powerful than normal draining the underground
reservoir. This causes the roof of this chamber to collapse forming an
enormous crater. All supervolcano eruptions form these subsided craters.
They are called calderas.

BILL McGUI The main factor governing the size of eruptions is
really the amount of available magma. If you've accumulated an enormous
volume of magma in the crust then you have at least a potential for a very,
very large eruption.

NARRATOR: The exact geological conditions needed to create a vast
magma chamber exist in very few places, so there are only a handful of
supervolcanoes in the world. The last one to erupt was Toba 74,000 years
ago. No modern human has ever witnessed an eruption. We're not even sure
where all the supervolcanoes are. Yellowstone National Park, North America.
Ever since people began to explore Yellowstone the area was known to be
hydrothermal. It was assumed these hot springs and geysers were perfectly
harmless, but all that was to change.

ROBERT CHRISTIANSEN: I first came to Yellowstone in the mid-1960s to
be a part of a major restudy of the geology of Yellowstone National Park,
but at that point I had no idea of what we were to find.

NARRATOR: When geologist Bob Christiansen first began examining
Yellowstone rocks he noticed many were made of compacted ash. But he could
see no extinct volcano or caldera crater, there was no give-away depression.

ROBERT CHRISTIANSEN: We realised that Yellowstone had been an ancient
volcanic system. We suspected that it had been a caldera volcano, but we
didn't know where the caldera was or specifically how large it was.

NARRATOR: As he searched throughout the Park looking for the volcanic
caldera Christiansen began to wonder if he was mistaken. Then he had a
stroke of luck. NASA decided to survey Yellowstone from the air. The Space
Agency had designed infrared photography equipment for the moon shot and
wanted to test it over the Earth. NASA's test flight took the most revealing
photographs of Yellowstone ever seen.

ROBERT CHRISTIANSEN: What was so exciting about looking at the remote
sensing imagery was the sense that showed it in one, one sweeping view of
what this truly was.

NARRATOR: Christiansen hadn't been able to see the ancient caldera
from the ground because it was so huge. It encompassed almost the entire
Park.

ROBERT CHRISTIANSEN: An enormous feature. 70 kilometres across, 30
kilometres wide. This had been a colossal supervolcano. Certainly one of the
largest known anywhere on earth.

NARRATOR: Bob Christiansen was determined to find out when Yellowstone
had last erupted. He began examining the sheets of hardened ash, dozens of
metres thick blasted from the ground during the eruption. What he found was
3 separate layers. This meant there had been 3 different eruptions. When
Christiansen and his team dated the Yellowstone ash he found something
unexpected. The oldest caldera was formed by a vast eruption 2 million years
ago. The second eruption was 1.2 million years old and when he dated the
third and most recent eruption he found it occurred just 600,000 years ago.
The eruptions were regularly spaced.

ROBERT CHRISTIANSEN: Quite amazingly we realised that there was a
cycle of caldera-forming eruptions, these huge volcanic eruptions about
every 600,000 years.

NARRATOR: Yellowstone was on a 600,000 year cycle and the last
eruption was just 600,000 years ago. Yet there was no evidence of volcanic
activity now. The volcano seemed extinct. That reassuring thought was about
to change. There was another geologist who was fascinated by Yellowstone's
volcanic history. Like Bob Christiansen, Professor Bob Smith has been
studying the Park for much of his career. In 1973 he was doing field work,
camping at one end of Yellowstone Lake.

ROBERT SMITH: I was working at the south end of this lake at a place
called Peal Island. I was standing on the island one day and I noticed a
couple of unusual things. The, the boat dock that we normally would use at
this place seemed to be underwater. That evening as I was looking over the
expanse of the south end of the lake I could see trees that were being
inundated by water. I took a look at these trees and they were be, being
inundated with water a few inches, maybe a foot deep and it was very unusual
for me to see that because nowhere else in the lake would the lake level
have really changed. What did it mean? We did not know.

NARRATOR: Smith commissioned a survey to try to find out what was
happening at Yellowstone. The Park had last been surveyed in the 1920s when
the elevation, the height above sea-level, was measured at various points
across Yellowstone. 50 years later, Smith surveyed the same points.

ROBERT SMITH: The idea was to survey their elevations and to compare
the elevations in the mid-70s to what they were in 1923 and the type of
thing that we did is to make recordings at a precision level of, of a few
millimetres.

NARRATOR: The two sets of figures should have been similar, but as the
survey team moved across the Park, they noticed something unexpected: the
ground seemed to be heaving upwards.

ROBERT SMITH: The surveyor said to me there's something wrong and he
said it's not me, it's got to be something else, so we went through all the
measurements again trying to be very careful and the conclusion kind of hit
me in the face and said this caldera has uplifted at that time 740
millimetres in the middle of the caldera.

NARRATOR: As the measuring continued, an explanation for the submerged
trees began to emerge. The ground beneath the north of Yellowstone was
bulging up, tilting the rest of the Park downwards. This was tipping out the
sound end of the lake inundating the shoreside trees with water. The
vulcanologist realised only one thing could make the Earth heave in this
way: a vast living magma chamber. The Yellowstone supervolcano was alive and
if the calculations of the cycle were correct, the next eruption was already
overdue.

ROBERT CHRISTIANSEN: Well this gave us a real shiver of nervousness if
you will about the fact that we have been through this 600,000 year cycle
and that the last eruption was about 600,000 years ago.

ROBERT SMITH: I felt like telling people, that is we basically have on
our hands a giant.

NARRATOR: The scientists had found the largest single active volcanic
system yet discovered. There were many things they needed to find out. How
big was the magma chamber deep underground, how widespread would the effects
of an eruption be and crucially, when would it happen? To answer any of
these questions vulcanologists knew they first had to understand
Yellowstone's mysterious magma chamber.

ROBERT SMITH: It's incredibly important to understand what's happening
inside of the magma chamber because that pressure and that heat, the fluid
is what's triggering the final eruption. It's like understanding the primer
in a bullet.

NARRATOR: Understanding the magma chamber would be very difficult.
Smith and his team needed to discover the size of something 8 kilometres
below the ground. They began harnessing information from an ingenious
source: earthquakes.

ROBERT SMITH: Well, what we have here is a seismometer. This is the
working end of a seismograph, the device that's used to record earthquakes.
It is able to pick up the smallest of earthquakes in, in Yellowstone plus it
picks up moderate to large earthquakes around the world, it is so sensitive.
This forms one of a network of 22 seismograph stations in Yellowstone that
is used for monitoring and all the data are transmitted to a central
recording fcility at the University of Utah.

NARRATOR: Like many thermal areas, Yellowstone has hundreds of tiny
earth tremors each year. They are harmless, but in his seismographic lab
Smith has been using them to trace the size of the magma chamber.

ROBERT SMITH: Earthquakes are essentially telling you the pulse. They
tell you the real time pulse of how the caldera is deforming, of how faults
are fracturing.

NARRATOR: Bob Smith's 22 permanent seismographs are spread across the
Park. They detect the sound-waves which come from earthquakes deep
underground. These waves travel at different speeds depending on the texture
of what they pass through. Soundwaves passing through solid rock go faster
than those travelling through molten rock or magma. By measuring the time
they take to reach the seismographs Smith can tell what they've passed
through. Eventually this builds up a picture of what lies beneath the Park.

ROBERT SMITH: The magma chamber we found extends basically beneath the
entire caldera. It's maybe 40-50 kilometres long, maybe 20 kilometres wide
and it has a thickness of about 10 kilometres. So it's a giant in volume and
essentially encompasses a half or a third of the area beneath Yellowstone
National Park. NARRATOR: The magma chamber was enormous. If it erupted it
would be devastating. To discover the extent of the devastation scientists
had to understand the force of the eruption. The clues to this could be
found in a much smaller volcano halfway across the world: the Greek island
of Santorini. The eruption here 3,500 years ago, although not VEI8 in scale,
did have a small magma chamber. Professor Steve Sparks has spent much of his
career studying Santorini.

PROF STEVE SPARKS (University of Bristol): When I first came to
Santorini and started to look at the pumice deposits from these caldera
forming eruptions I found evidence of a dramatic change in the power and
violence of the eruption.

NARRATION: By examining the layers of Santorini pumice Sparks
discovered magma chambers could erupt with almost unimaginable force and
spread their devastation widely.

STEVE SPARKS: There's dramatic evidence of a sudden increase in the
power. Huge blocks about 2 metres in diameter were hurled out of the volcano
reaching 7 kilometres and smashing into the ground and to do that the blocks
must have been thrown from the volcano at hundreds of metres per second,
about the speed of Concorde and you can imagine this enormous red rock
crashing in and breaking up on impact.

NARRATOR: To understand why caldera volcanoes could erupt with such
power Sparks replicated their violence at one trillionth of the scale.

STEVE SPARKS: OK, so we need this.

NARRATOR: In the lab he modelled a reaction which occurs in the magma
chamber of an erupting caldera.

STEVE SPARKS: The problem is we can't go into a magma chamber so the
next best thing to do is to go to the laboratory and try and simulate what
happens in the magma chamber and in the pathway to the surface.

NARRATOR: Sparks believed escaping volcanic gas trapped in the magma
might be responsible for the violence of the eruptions. Into a glass flask -
the magma chamber - he poured a mixture of pine resin and acetone. the pine
resin mimicked the magma, the acetone modelled trapped volcanic gases like
carbon dioxide and sulphur dioxide.

STEVE SPARKS: Pine resin is a very sticky, stiff material so it has
some properties which are rather like magma and we thought that if we could
get a, a gas which dissolved in pine resin, like acetone, then we could get
a, a laboratory system which would represent the, the natural case.

NARRATOR: Sparks then created a vacuum above the flask to mimic the
depressurisation that occurs in the magma chamber when a supervolcano begins
its eruption and the dissolved volcanic gas can expand. When the vacuum
reached the liquid it caused a dramatic change. The dissolved acetone
suddenly became a gas. This made the resin expand causing violent frothing
and blasting the contents out of the chamber.

STEVE SPARKS: These experiments give us tremendous insight into the
tremendous power of gases coming out of solution and enabled to drive these
very dramatic explosive flows.

NARRATOR: Unlike supervolcanoes, normal volcanoes don't have this vast
reservoir of magma and trapped volcanic gases and don't have the potential
for such powerful eruptions. But experiments in the laboratory cannot answer
the biggest question of all surrounding Yellowstone: when will it next
erupt? Scientists face a problem. They have never seen a supervolcano erupt.
Until a VEI8 eruption is observed and analysed no-one knows what the
telltale precursors would be to a Yellowstone eruption.

BILL McGUI We can actually model volcanoes and their activity. We
can do it in the laboratory on computer, but we need observational data in
order to make those models realistic.

ROBERT SMITH: What the precursors might be for a giant volcanic
eruptions they've never been observed scientifically and they've never been
documented, so we don't know what to look for.

ROBERT CHRISTIANSEN: Nobody wants to see a global disaster of course
and yet we'll never really fully understand the processes involved in these
supervolcanic eruptions until one of them happens.

NARRATOR: A terrible truth underlies all mankind's efforts to
understand the vast mechanisms which drive VEI8 eruptions. Ultimately trying
to find out what makes supervolcanoes work may be pointless. Consider the
last one. 74,000 years ago a supervolcano erupted here in Sumatra. It would
have been the loudest noise ever heard by man. It would have blasted vast
clouds of ash across the world.

The resultant caldera formed Lake Toba, 100 kilometres long, 60
kilometres wide. it was, in short, colossal. Scientists are only now
beginning to understand the effects of so much ash on the planet's climate.
This is the ocean core repository at Columbia University in America. It
contains thousands of drill samples from seabeds round the world, a
historical keyhole through which scientists, like Michael Rampino can view
volcanic history.

MICHAEL RAMPINO: The size of the Toba eruption was enormous. We're
talking about, about 3,000 cubic kilometres of material coming out of that
volcano. That's about 10,000 times the size of the 1980 Mount St. Helens
eruption which people think of as a large eruption, a truly super eruption.

This is an ocean drilling core from the central Indian Ocean. It's
about 2,500 kilometres from the Toba volcano and here are 35 centimetres of
ash deposited after the Toba eruption. It shows that this Toba eruption was
a supervolcanic event, it was much, much bigger than any other volcanic
eruption we see in the geological record. Chemical analysis of the ash tells
us that this eruption was rich in sulphur, would have released a tremendous
amount of sulphur dioxide and other gases into the stratosphere which would
have turned into sulphuric acid aerosols and affected the climate of the
Earth for years.

NARRATOR: For a long time scientists have known that volcanic ash can
affect the global climate. The fine ash and sulphur dioxide blasted into the
stratosphere reflects solar radiation back into space and stops sunlight
reaching the planet. This has a cooling effect on the Earth. In the year
following the 1991 eruption of Mount Pinatubo for instance the average
global temperature fell by half a degree Celsius. By comparing the amount of
ash ejected by past volcanoes with their effect on the Earth's temperature,
Rampino has estimated the impact of the Toba eruption on the global climate
74,000 years ago.

MICHAEL RAMPINO: I'm plotting a simple graph where one side there's
sulphur released in millions of tons by volcanic eruptions and on the other
side there's a cooling in degree Celsius that we saw after these volcanic
eruptions. I'm plotting as points the historical eruptions like Mount St.
Helens, Krakatoa, Pinatubo, Tambora. There's a nice correlation between the
sulphur released into the atmosphere and the cooling.

NARRATOR: Because of this relationship between the sulphur released by
large volcanoes and global cooling, Rampino can calculate the drop in
temperature caused by the Toba eruption.

MICHAEL RAMPINO: We can see this kind of plot predicts that the Toba
eruption was so large that the temperature change after Toba in degrees
Celsius would have been about a 5 degree global temperature drop, very
significant, very severe global cooling. NARRATOR: Five degrees Celsius
average drop in global temperature would have been devastating causing
Europe's summers to freeze and triggering a volcanic winter.

MICHAEL RAMPINO: Five degrees globally would translate into 15 degrees
or so of summer cooling in the temperate to high latitudes. The effects on
agriculture, on the growth of plants, on life in the oceans would be
catastrophic.

NARRATOR: This global catastrophe would have continued for years,
dramatically affecting life on Earth, but what impact did it have on humans?
The answer may be buried not inside the ancient rocks, but deep within us
all. Lynn Jorde and Henry Harpending are scientists specialising in human
genetics. Since the early 1990s they have been studying mitochondrial DNA
using the information to investigate mankind's past. Most of our genetic
information is stored in the nuclei of our cells, but a small, separate
quantity exists in another component, the part which produces the cells'
energy, the mitochondria.

PROF LYNN JORDE (University of Utah): Mitochondria have their own
genes. It's a small number of genes, a small amount of DNA, but it's
distinct from the rest of the DNA in the cell and because of the way
mitochondria are transmitted from one generation to the next, they're,
they're inherited only from the mother so they give us a record of the
maternal lineage of a population.

NARRATOR: Mitochondrial DNA is inherited only by the mother. All
mutations are passed on from mother to child, generation after generation at
a regular rate. Over time, the number of these mutations accumulate in a
population.

LYNN JORDE: Every event that takes place in our past, every major
event, a population increase, a population decrease, or the exchange of
people from one population to another changes the composition of the
mitochondrial DNA in that population, so what happens is that we have a
record of our past written in our mitochondrial genes.

NARRATOR: By knowing the rate of mutation of mitochondrial DNA and by
a complex analysis of the distribution of these mutations, the geneticists
can estimate the size of populations in the past. Several years ago they
began seeing a strange pattern in their results.

LYNN JORDE: We expected that we would see a pattern consistent with a
relatively constant population size. Instead, we saw something that departed
dramatically from that expectation. We saw a pattern much more consistent
with a dramatic reduction in population size at some point in our past.

NARRATOR: This confirmed what other geneticists have noticed. Given
the length of time humans have existed, there should be a wide range of
genetic variation, yet DNA from people throughout the world is surprisingly
similar. What could have caused this? The answer is a dramatic reduction of
the population some time in the past: a bottleneck.

LYNN JORDE: We imagine the population diagrammed like this. In the
distant past back here we have a large population, then a bottleneck looking
like this and then a subsequent enlargement of population size again, so we
would have families of people in the distant past with a significant amount
of genetic diversity, but when the bottleneck occurs, when there's a
reduction in population size perhaps only a few of those families would
survive the bottleneck.

We have a dramatic reduction in genetic diversity during this time
when the population is very small and then after the bottleneck the people
who would we, who we would see today would be descendants only of those who
survived, so they're going to be genetically much more similar to one
another reducing the amount of genetic variation.

NARRATOR: Human DNA is so similar the scientists concluded the
population reduction had been catastrophic. PROF HENRY HARPENDING
(University of Utah): It seemed so incredible, you know the idea that all of
us, now there's 6 billion people on Earth, and what the data were telling us
was that we, you know our species was reduced to, you know, a few thousand.
Suddenly it hit us, we had something to say about human history.

LYNN JORDE: Our population may have been in such a precarious position
that only a few thousand of us may have been alive on the whole face of the
Earth at one point in time, that we almost went extinct, that some event was
so catastrophic as to nearly cause our species to cease to exist completely.

NARRATOR: It is an astonishing revelation, but the key was to find out
when and why it happened. Because mitochondrial DNA mutates at an average
rate these scientists believe, controversially, that they can narrow down
the date of the bottleneck.

LYNN JORDE: Mutations in the mitochondria take place with clocklike
regularly, so the number of mutations give us a clock essentially that we
can use to approximately date the major event. In the case of a population
bottleneck we think that this would have occurred roughly 70-80,000 years
ago, give or take some number of thousands of years. So then the real
question is: what could have caused such a reduction, an extreme reduction,
in the human population down to as few as 5 or 10,000 individuals?

NARRATOR: As for what caused this dramatic reduction in population the
geneticists had no idea. Henry Harpending began touring universities to talk
about the bottleneck. He was invited by anthropologist Stanley Ambrose to
give a lecture to his students.

HENRY HARPENDING: Well Stanley is full of ideas, he's the kind of
scientist that plucks things from all over and puts them together.

PROF STANLEY AMBROSE (University of Illinois): I sat in on the lecture
and he start4ed talking about this human population bottleneck and I thought
what could have caused it and at that point I broke out into a sweat. I
went up to Henry and said I've just read a paper, and it's on the top of my
desk now, that may have an explanation for why this population bottleneck
occurred.

HENRY HARPENDING: I didn't read it till a week later and when I read
it you know it was like somebody kicking you in the face. There it was.

STANLEY AMBROSE: The paper was about the super eruption of a volcano
called Toba in Sumatra.

NARRATOR: This team of scientists believe the bottleneck occurred
between 70 and 80,000 years ago, although this date is hotly debated. Toba
erupted in the middle of this period, 74,000 years ago. If there really is a
connection this research has terrifying implications for a future
Yellowstone eruption. It could well be of a similar size and ferocity to
Toba. Like Toba, it would have a devastating impact, not just on the
surrounding region, North America, but on the whole world.

MICHAEL RAMPINO: If Yellowstone goes off again, and it will, it'll be
disastrous for the United States and eventually for the whole world.

NARRATOR: Vulcanologists believe it would all start with the magma
chamber becoming unstable.

BILL McGUI You'd start seeing bigger earthquakes, you may see parts
of Yellowstone uplifting as magma intrudes and gets nearer and nearer the
surface.

ROBERT SMITH: And maybe an earthquake sends a rupture through the
brittle layer, you've broken the lid of the pressure cooker.

BILL McGUI This would generate sheets of magma which will be
probably rising up to 30, 40, 50 kilometres sending gigantic amounts of
debris into the atmosphere.

ROBERT CHRISTIANSEN: Where we are right now would be gone. We would be
instantly incinerated.

MICHAEL RAMPINO: Pyroclastic flows will cover that whole region, maybe
kill tens of thousands of people in the surrounding area.

BILL McGUI You're getting a, an eruption which we can barely
imagine. We've never seen this sort of thing. You wouldn't be able to get
within 1,000 kilometres of it when it was going like this.

ROBERT CHRISTIANSEN: The ash carried in the atmosphere and deposited
over large areas of the United States, particularly over the great plains,
would have devastating effects.

BILL McGUI The area that would be affected is, is the bread basket
of North America in effect and it produces an enormous amount of grain on a
global scale really. That's, that's, that's the problem and you would see
nothing. The harvest would vanish virtually overnight.

ROBERT CHRISTIANSEN: All basic economic activity would certainly be
impacted by this and let alone changes in the climate that could possibly be
induced.

MICHAEL RAMPINO: The climatic effects globally from that eruption will
be produced by the plume of material that goes up into the atmosphere.
That'll spread worldwide and will have a cooling effect that will probably
knock out the growing season on a global basis. We can't really overstate
the effect of these huge eruptions. Civilisation will start to creak at the
seams in a sense.

ROBERT SMITH: The fact that we haven't seen one in historic time or
documented means the human race really is not attuned to these things
because they're such a rare event.

MICHAEL RAMPINO: It's really not a question of if it'll go off, it's a
question of when because sooner or later one of these large super eruptions
will happen.

Back to Supervolcanoesprogramme page.









"The British attitude is to treat society like a game preserve where a
certain percentage of the 'antelope' are expected to be eaten by the
"lions".
Christopher Morton

Better buy that new lathe now before it's to late
Don Warner
---------
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...
On Fri, 28 Nov 2003 22:17:47 -0000, "The Rifleman"
wrote:

Supervolcanoes
BBC2 9:30pm Thursday 3rd February 2000

NARRATOR (SINÉAD CUSACK): Yellowstone is America's first and most
famous National Park. Every year over three million tourists visit this
stunning wilderness, but beneath its hot springs and lush forests lies a
monster of which the public is ignorant.

PROF ROBERT CHRISTIANSEN (US Geological Survey): Millions of people
come to Yellowstone every year to see the marvellous scenery and the
wildlife and all and yet it's clear that, that very few of them really
understand that they're here on a sleeping giant.

NARRATOR: If this giant were to stir, the United States would be
devastated and the world would be plunged into a catastrophe which could
push humanity to the brink of extinction.

PROF ROBERT SMITH (University of Utah): It would be extremely
devastating on a scale that we've probably never even thought about.

PROF BILL McGUIRE (Benfield Greig Centre, UCL): It would mean
absolute
catastrophe for North America and the problem is we know so little about
these phenomena.

NARRATOR: In 1971 heavy rain fell across much of east Nebraska. In
the
summer palaeontologist Mike Voorhies travelled to the farmland around the
mid-west town of Orchard. What he was to discover exceeded his wildest
dreams.

PROF MIKE VOORHIES (University of Nebraska): Well I was walking up
this gully looking for fossils, the way I'd walked up a thousand gullies
before, keeping my eye on the ground looking for pieces of fossils that
might have washed down in the rain the previous night and I scrambled up
to
the top and I saw something that completely astounded me, a sight that no
palaeontologist has ever seen.

NARRATOR: It was a sight of sudden, prehistoric disaster.
Voorhies's
digging revealed the bones of 200 fossilised rhinos, together with the
prehistoric skeletons of camels and lizards, horses and turtles. Dating
showed they had all died abruptly 10 million years ago.

MIKE VOORHIES: It suddenly dawned on me that this was a scene of a
mass catastrophe of a type that I'd never, never encountered before.

NARRATOR: The cause of death, however, remained a mystery. It was
not
from old age.

MIKE VOORHIES: I could tell by looking at the teeth that these
animals
had died in their prime. What was astounding was that here were young
mothers and their, and their babies, big bull rhinos in the prime of life
and here they were dead for no, no apparent reason.

NARRATOR: For the animals at Orchard death had come suddenly. There
was another strange feature to the skeletons, an oddity which offered a
crucial clue about the cause of the catastrophe.

MIKE VOORHIES: We saw that all of these skeletons were covered with
very peculiar growth, soft material that I first thought was a mineral
deposit. Then we noticed that it was cellular. It's biological in origin
so
there was something actually growing on those bones. I had no idea what
that
stuff was, never seen anything like it.

NARRATOR: A palaeo-pathologist, Karl Reinhard, was sent a sample of
the bones.

PROF KARL REINHARD (University of Nebraska): This specimen is
typical
of the rhino bones. You see this material, in this case it's a whitish
material that's deposited on the surface of the original bone. This is
peculiar to me, but as I thought back in my experience I realised that
this
was similar to something that turns up in the veterinary world, a disease
called Marie's disease.

NARRATOR: Marie's is a symptom of deadly lung disease. Every animal
at
Orchard seemed to be infected.

KARL REINHARD: One of the clues was that all of the animals had it.
Now that is a very important observation for all the diseases, all the
animals to exhibit this disease there had to be some universal problem.

NARRATOR: Scientists discovered the universal problem was ash. 10
million years ago ash had choked them to death.

KARL REINHARD: It may have been a bit like pneumonia with the lungs
filling with fluid, except in this case the fluid would have been blood
for
the ash is very sharp. There'd be microscopic shards of ash lacerating
the
lung tissue and, and causing the bleeding. I would imagine these animals
as
stumbling around the thick ash, spitting up blood through their mouths
and
gradually dying in a most miserable way.

NARRATOR: Only a volcano could have produced so much ash, yet the
wide
flat plains of Nebraska have no volcanoes.

MIKE VOORHIES: I remember some of my students and I sitting around
after a day's digging and just speculating where did this stuff come
from?
There, there are no volcanoes in Nebraska now. As far as we know there
never
have been. We, we obviously had to have volcano somewhere that, that
produced enough ash to completely drown the landscape here, but where
that
was really was anybody's guess.

NARRATOR: One geologist in Idaho realised there had been a volcanic
eruption which coincided with the disaster at Orchard 10 million years
ago,
but the site was halfway across North America.

PROF BILL BONNICHSEN (Idaho Geological Survey): It seemed like a
really fascinating story which made me think, because I had been working
on
volcanic rocks in south-western Idaho that potentially could make lots of
ash and, and there was some age dates on that that were around 10 million
years and I began to wonder wow, could this situation in Nebraska have
really been caused by some of these large eruptions that evidently had
happened in south-western Idaho.

NARRATOR: The extinct volcanic area, Bruneau Jarbridge, was 1600
kilometres away, a vast distance. How could this eruption have blasted so
much ash so far? Bonnichsen was sceptical.

BILL BONNICHSEN: Volcanoes will spew ash for a few tens or maybe a
few
hundreds of miles. This ash, and it's like two metres thick, in Nebraska
is
1600 kilometres or more away from its potential source, so that's an
amazing
thing. There really had been no previous documentation, to my knowledge,
of
phenomenon like that.

NARRATOR: Despite his doubts Bonnichsen decided to compare the
chemical content of ash from the two sites. He analysed samples from both
Bruneau Jarbridge and Orchard and plotted their mineral composition on a
graph looking for similarities.

BILL BONNICHSEN: if you have a group of rocks that are very similar
to
one another they should be a closely spaced cluster of pods. We had these
analyses come out from the Orchard site and I thought I'd try the clock
again and see how close they were to one another. By golly, they fall
right
in the same little trend as the Bruneau Jarbridge samples.

NARRATOR: Bonnichsen's hunch had proved correct. Bruneau Jarbridge
was
responsible for the catastrophe at Orchard. An eruption covering half of
North America with two metres of ash was hundreds of times more powerful
than any normal volcano. It seemed almost unbelievable, but then Bruneau
Jarbridge was that rarest of phenomena which scientists barely understand
and the public knows nothing about: a supervolcano.

ROBERT SMITH: Supervolcanoes are eruptions and explosions of
catastrophic proportions.

BILL McGUI When you actually sit down and think about these
things
they are absolutely apocalyptic in scale.

PROF MICHAEL RAMPINO (New York University): It's difficult to
conceive
of a, of an eruption this big.

NARRATOR: Scientists have never witnessed a supervolcanic eruption,
but they can calculate how vast they are.

BILL McGUI Super eruptions are often called VEI8 and this means
that they sit at point 8 on what's known as a volcano explosivity index.
Now
this runs from zero up to 8. It's actually a measure of the violence of a
volcanic eruption and each point on it represents an eruption 10 times
more
powerful than the previous one, so if we take Mount St. Helens, for
example,
which is a VEI5, we can represent that eruption by a cube of this sort of
size, this represents here the amount of material ejected during that
eruption. If you go up step higher and look at a VI6, something of the
Santorini size for example, then we can represent the amount of material
ejected in Santorini by a cube of this sort of size, but if we go up to
VEI8
eruptions then we're dealing with something on an altogether different
scale, a colossal eruption and you can represent a VI8, some of the
biggest
VI8 eruptions by a cube of this, this sort of size. It's absolutely
enormous.

NARRATOR: Normal volcanoes are formed by a column of magma, molten
rock, rising from deep within the Earth, erupting on the surface and
hardening in layers down the sides. This forms the familiar dome or
cone-shaped mountains.

BILL McGUI Most people's idea of a volcano is a lovely
symmetrical
cone and this involves magma coming up, reaching the surface, being
extruded
either as lava or as explosive eruptions as, as ash and these layers of
ash
and lava gradually accumulate until you're left with a, a classic cone
shape.

NARRATOR: Vulcanologists know this smooth flowing magma contains
huge
quantities of volcanic gases, like carbon dioxide and sulphur dioxide.
Because this magma is so liquid these gases bubble to the surface, easily
escaping. There are thousands of these normal volcanoes throughout the
world. Around 50 erupt every year, but supervolcanoes are very different
in
almost every way.

First, they look different. Rather than being volcanic mountains,
supervolcanoes form depressions in the ground. Despite never having seen
a
supervolcano erupt, by studying the surrounding rock scientists have
pieced
together how supervolcanoes are formed. Like normal volcanoes they begin
when a column of magma rises from deep within the Earth. Under certain
conditions, rather than breaking through the surface, the magma pools and
melts the Earth's crust turning the rock itself into more thick magma.

Scientists don't know why, but in the case of supervolcanoes a vast
reservoir of molten rock eventually forms. The magma here is so thick and
viscous that it traps the volcanic gases building up colossal pressures
over
thousands of years. When the magma chamber eventually does erupt its
blast
is hundreds of times more powerful than normal draining the underground
reservoir. This causes the roof of this chamber to collapse forming an
enormous crater. All supervolcano eruptions form these subsided craters.
They are called calderas.

BILL McGUI The main factor governing the size of eruptions is
really the amount of available magma. If you've accumulated an enormous
volume of magma in the crust then you have at least a potential for a
very,
very large eruption.

NARRATOR: The exact geological conditions needed to create a vast
magma chamber exist in very few places, so there are only a handful of
supervolcanoes in the world. The last one to erupt was Toba 74,000 years
ago. No modern human has ever witnessed an eruption. We're not even sure
where all the supervolcanoes are. Yellowstone National Park, North
America.
Ever since people began to explore Yellowstone the area was known to be
hydrothermal. It was assumed these hot springs and geysers were perfectly
harmless, but all that was to change.

ROBERT CHRISTIANSEN: I first came to Yellowstone in the mid-1960s
to
be a part of a major restudy of the geology of Yellowstone National Park,
but at that point I had no idea of what we were to find.

NARRATOR: When geologist Bob Christiansen first began examining
Yellowstone rocks he noticed many were made of compacted ash. But he
could
see no extinct volcano or caldera crater, there was no give-away
depression.

ROBERT CHRISTIANSEN: We realised that Yellowstone had been an
ancient
volcanic system. We suspected that it had been a caldera volcano, but we
didn't know where the caldera was or specifically how large it was.

NARRATOR: As he searched throughout the Park looking for the
volcanic
caldera Christiansen began to wonder if he was mistaken. Then he had a
stroke of luck. NASA decided to survey Yellowstone from the air. The
Space
Agency had designed infrared photography equipment for the moon shot and
wanted to test it over the Earth. NASA's test flight took the most
revealing
photographs of Yellowstone ever seen.

ROBERT CHRISTIANSEN: What was so exciting about looking at the
remote
sensing imagery was the sense that showed it in one, one sweeping view of
what this truly was.

NARRATOR: Christiansen hadn't been able to see the ancient caldera
from the ground because it was so huge. It encompassed almost the entire
Park.

ROBERT CHRISTIANSEN: An enormous feature. 70 kilometres across, 30
kilometres wide. This had been a colossal supervolcano. Certainly one of
the
largest known anywhere on earth.

NARRATOR: Bob Christiansen was determined to find out when
Yellowstone
had last erupted. He began examining the sheets of hardened ash, dozens
of
metres thick blasted from the ground during the eruption. What he found
was
3 separate layers. This meant there had been 3 different eruptions. When
Christiansen and his team dated the Yellowstone ash he found something
unexpected. The oldest caldera was formed by a vast eruption 2 million
years
ago. The second eruption was 1.2 million years old and when he dated the
third and most recent eruption he found it occurred just 600,000 years
ago.
The eruptions were regularly spaced.

ROBERT CHRISTIANSEN: Quite amazingly we realised that there was a
cycle of caldera-forming eruptions, these huge volcanic eruptions about
every 600,000 years.

NARRATOR: Yellowstone was on a 600,000 year cycle and the last
eruption was just 600,000 years ago. Yet there was no evidence of
volcanic
activity now. The volcano seemed extinct. That reassuring thought was
about
to change. There was another geologist who was fascinated by
Yellowstone's
volcanic history. Like Bob Christiansen, Professor Bob Smith has been
studying the Park for much of his career. In 1973 he was doing field
work,
camping at one end of Yellowstone Lake.

ROBERT SMITH: I was working at the south end of this lake at a
place
called Peal Island. I was standing on the island one day and I noticed a
couple of unusual things. The, the boat dock that we normally would use
at
this place seemed to be underwater. That evening as I was looking over
the
expanse of the south end of the lake I could see trees that were being
inundated by water. I took a look at these trees and they were be, being
inundated with water a few inches, maybe a foot deep and it was very
unusual
for me to see that because nowhere else in the lake would the lake level
have really changed. What did it mean? We did not know.

NARRATOR: Smith commissioned a survey to try to find out what was
happening at Yellowstone. The Park had last been surveyed in the 1920s
when
the elevation, the height above sea-level, was measured at various points
across Yellowstone. 50 years later, Smith surveyed the same points.

ROBERT SMITH: The idea was to survey their elevations and to
compare
the elevations in the mid-70s to what they were in 1923 and the type of
thing that we did is to make recordings at a precision level of, of a few
millimetres.

NARRATOR: The two sets of figures should have been similar, but as
the
survey team moved across the Park, they noticed something unexpected: the
ground seemed to be heaving upwards.

ROBERT SMITH: The surveyor said to me there's something wrong and
he
said it's not me, it's got to be something else, so we went through all
the
measurements again trying to be very careful and the conclusion kind of
hit
me in the face and said this caldera has uplifted at that time 740
millimetres in the middle of the caldera.

NARRATOR: As the measuring continued, an explanation for the
submerged
trees began to emerge. The ground beneath the north of Yellowstone was
bulging up, tilting the rest of the Park downwards. This was tipping out
the
sound end of the lake inundating the shoreside trees with water. The
vulcanologist realised only one thing could make the Earth heave in this
way: a vast living magma chamber. The Yellowstone supervolcano was alive
and
if the calculations of the cycle were correct, the next eruption was
already
overdue.

ROBERT CHRISTIANSEN: Well this gave us a real shiver of nervousness
if
you will about the fact that we have been through this 600,000 year cycle
and that the last eruption was about 600,000 years ago.

ROBERT SMITH: I felt like telling people, that is we basically have
on
our hands a giant.

NARRATOR: The scientists had found the largest single active
volcanic
system yet discovered. There were many things they needed to find out.
How
big was the magma chamber deep underground, how widespread would the
effects
of an eruption be and crucially, when would it happen? To answer any of
these questions vulcanologists knew they first had to understand
Yellowstone's mysterious magma chamber.

ROBERT SMITH: It's incredibly important to understand what's
happening
inside of the magma chamber because that pressure and that heat, the
fluid
is what's triggering the final eruption. It's like understanding the
primer
in a bullet.

NARRATOR: Understanding the magma chamber would be very difficult.
Smith and his team needed to discover the size of something 8 kilometres
below the ground. They began harnessing information from an ingenious
source: earthquakes.

ROBERT SMITH: Well, what we have here is a seismometer. This is the
working end of a seismograph, the device that's used to record
earthquakes.
It is able to pick up the smallest of earthquakes in, in Yellowstone plus
it
picks up moderate to large earthquakes around the world, it is so
sensitive.
This forms one of a network of 22 seismograph stations in Yellowstone
that
is usedfor monitoring and all the data are transmitted to a central
recording facility at the University of Utah.

NARRATOR: Like many thermal areas, Yellowstone has hundreds of tiny
earth tremors each year. They are harmless, but in his seismographic lab
Smith has been using them to trace the size of the magma chamber.

ROBERT SMITH: Earthquakes are essentially telling you the pulse.
They
tell you the real time pulse of how the caldera is deforming, of how
faults
are fracturing.

NARRATOR: Bob Smith's 22 permanent seismographs are spread across
the
Park. They detect the sound-waves which come from earthquakes deep
underground. These waves travel at different speeds depending on the
texture
of what they pass through. Soundwaves passing through solid rock go
faster
than those travelling through molten rock or magma. By measuring the time
they take to reach the seismographs Smith can tell what they've passed
through. Eventually this builds up a picture of what lies beneath the
Park.

ROBERT SMITH: The magma chamber we found extends basically beneath
the
entire caldera. It's maybe 40-50 kilometres long, maybe 20 kilometres
wide
and it has a thickness of about 10 kilometres. So it's a giant in volume
and
essentially encompasses a half or a third of the area beneath Yellowstone
National Park. NARRATOR: The magma chamber was enormous. If it erupted it
would be devastating. To discover the extent of the devastation
scientists
had to understand the force of the eruption. The clues to this could be
found in a much smaller volcano halfway across the world: the Greek
island
of Santorini. The eruption here 3,500 years ago, although not VEI8 in
scale,
did have a small magma chamber. Professor Steve Sparks has spent much of
his
career studying Santorini.

PROF STEVE SPARKS (University of Bristol): When I first came to
Santorini and started to look at the pumice deposits from these caldera
forming eruptions I found evidence of a dramatic change in the power and
violence of the eruption.

NARRATION: By examining the layers of Santorini pumice Sparks
discovered magma chambers could erupt with almost unimaginable force and
spread their devastation widely.

STEVE SPARKS: There's dramatic evidence of a sudden increase in the
power. Huge blocks about 2 metres in diameter were hurled out of the
volcano
reaching 7 kilometres and smashing into the ground and to do that the
blocks
must have been thrown from the volcano at hundreds of metres per second,
about the speed of Concorde and you can imagine this enormous red rock
crashing in and breaking up on impact.

NARRATOR: To understand why caldera volcanoes could erupt with such
power Sparks replicated their violence at one trillionth of the scale.

STEVE SPARKS: OK, so we need this.

NARRATOR: In the lab he modelled a reaction which occurs in the
magma
chamber of an erupting caldera.

STEVE SPARKS: The problem is we can't go into a magma chamber so
the
next best thing to do is to go to the laboratory and try and simulate
what
happens in the magma chamber and in the pathway to the surface.

NARRATOR: Sparks believed escaping volcanic gas trapped in the
magma
might be responsible for the violence of the eruptions. Into a glass
flask -
the magma chamber - he poured a mixture of pine resin and acetone. the
pine
resin mimicked the magma, the acetone modelled trapped volcanic gases
like
carbon dioxide and sulphur dioxide.

STEVE SPARKS: Pine resin is a very sticky, stiff material so it has
some properties which are rather like magma and we thought that if we
could
get a, a gas which dissolved in pine resin, like acetone, then we could
get
a, a laboratory system which would represent the, the natural case.

NARRATOR: Sparks then created a vacuum above the flask to mimic the
depressurisation that occurs in the magma chamber when a supervolcano
begins
its eruption and the dissolved volcanic gas can expand. When the vacuum
reached the liquid it caused a dramatic change. The dissolved acetone
suddenly became a gas. This made the resin expand causing violent
frothing
and blasting the contents out of the chamber.

STEVE SPARKS: These experiments give us tremendous insight into the
tremendous power of gases coming out of solution and enabled to drive
these
very dramatic explosive flows.

NARRATOR: Unlike supervolcanoes, normal volcanoes don't have this
vast
reservoir of magma and trapped volcanic gases and don't have the
potential
for such powerful eruptions. But experiments in the laboratory cannot
answer
the biggest question of all surrounding Yellowstone: when will it next
erupt? Scientists face a problem. They have never seen a supervolcano
erupt.
Until a VEI8 eruption is observed and analysed no-one knows what the
telltale precursors would be to a Yellowstone eruption.

BILL McGUI We can actually model volcanoes and their activity.
We
can do it in the laboratory on computer, but we need observational data
in
order to make those models realistic.

ROBERT SMITH: What the precursors might be for a giant volcanic
eruptions they've never been observed scientifically and they've never
been
documented, so we don't know what to look for.

ROBERT CHRISTIANSEN: Nobody wants to see a global disaster of
course
and yet we'll never really fully understand the processes involved in
these
supervolcanic eruptions until one of them happens.

NARRATOR: A terrible truth underlies all mankind's efforts to
understand the vast mechanisms which drive VEI8 eruptions. Ultimately
trying
to find out what makes supervolcanoes work may be pointless. Consider the
last one. 74,000 years ago a supervolcano erupted here in Sumatra. It
would
have been the loudest noise ever heard by man. It would have blasted vast
clouds of ash across the world.

The resultant caldera formed Lake Toba, 100 kilometres long, 60
kilometres wide. it was, in short, colossal. Scientists are only now
beginning to understand the effects of so much ash on the planet's
climate.
This is the ocean core repository at Columbia University in America. It
contains thousands of drill samples from seabeds round the world, a
historical keyhole through which scientists, like Michael Rampino can
view
volcanic history.

MICHAEL RAMPINO: The size of the Toba eruption was enormous. We're
talking about, about 3,000 cubic kilometres of material coming out of
that
volcano. That's about 10,000 times the size of the 1980 Mount St. Helens
eruption which people think of as a large eruption, a truly super
eruption.

This is an ocean drilling core from the central Indian Ocean. It's
about 2,500 kilometres from the Toba volcano and here are 35 centimetres
of
ash deposited after the Toba eruption. It shows that this Toba eruption
was
a supervolcanic event, it was much, much bigger than any other volcanic
eruption we see in the geological record. Chemical analysis of the ash
tells
us that this eruption was rich in sulphur, would have released a
tremendous
amount of sulphur dioxide and other gases into the stratosphere which
would
have turned into sulphuric acid aerosols and affected the climate of the
Earth for years.

NARRATOR: For a long time scientists have known that volcanic ash
can
affect the global climate. The fine ash and sulphur dioxide blasted into
the
stratosphere reflects solar radiation back into space and stops sunlight
reaching the planet. This has a cooling effect on the Earth. In the year
following the 1991 eruption of Mount Pinatubo for instance the average
global temperature fell by half a degree Celsius. By comparing the amount
of
ash ejected by past volcanoes with their effect on the Earth's
temperature,
Rampino has estimated the impact of the Toba eruption on the global
climate
74,000 years ago.

MICHAEL RAMPINO: I'm plotting a simple graph where one side there's
sulphur released in millions of tons by volcanic eruptions and on the
other
side there's a cooling in degree Celsius that we saw after these volcanic
eruptions. I'm plotting as points the historical eruptions like Mount St.
Helens, Krakatoa, Pinatubo, Tambora. There's a nice correlation between
the
sulphur released into the atmosphere and the cooling.

NARRATOR: Because of this relationship between the sulphur released
by
large volcanoes and global cooling, Rampino can calculate the drop in
temperature caused by the Toba eruption.

MICHAEL RAMPINO: We can see this kind of plot predicts that the
Toba
eruption was so large that the temperature change after Toba in degrees
Celsius would have been about a 5 degree global temperature drop, very
significant, very severe global cooling. NARRATOR: Five degrees Celsius
average drop in global temperature would have been devastating causing
Europe's summers to freeze and triggering a volcanic winter.

MICHAEL RAMPINO: Five degrees globally would translate into 15
degrees
or so of summer cooling in the temperate to high latitudes. The effects
on
agriculture, on the growth of plants, on life in the oceans would be
catastrophic.

NARRATOR: This global catastrophe would have continued for years,
dramatically affecting life on Earth, but what impact did it have on
humans?
The answer may be buried not inside the ancient rocks, but deep within us
all. Lynn Jorde and Henry Harpending are scientists specialising in human
genetics. Since the early 1990s they have been studying mitochondrial DNA
using the information to investigate mankind's past. Most of our genetic
information is stored in the nuclei of our cells, but a small, separate
quantity exists in another component, the part which produces the cells'
energy, the mitochondria.

PROF LYNN JORDE (University of Utah): Mitochondria have their own
genes. It's a small number of genes, a small amount of DNA, but it's
distinct from the rest of the DNA in the cell and because of the way
mitochondria are transmitted from one generation to the next, they're,
they're inherited only from the mother so they give us a record of the
maternal lineage of a population.

NARRATOR: Mitochondrial DNA is inherited only by the mother. All
mutations are passed on from mother to child, generation after generation
at
a regular rate. Over time, the number of these mutations accumulate in a
population.

LYNN JORDE: Every event that takes place in our past, every major
event, a population increase, a population decrease, or the exchange of
people from one population to another changes the composition of the
mitochondrial DNA in that population, so what happens is that we have a
record of our past written in our mitochondrial genes.

NARRATOR: By knowing the rate of mutation of mitochondrial DNA and
by
a complex analysis of the distribution of these mutations, the
geneticists
can estimate the size of populations in the past. Several years ago they
began seeing a strange pattern in their results.

LYNN JORDE: We expected that we would see a pattern consistent with
a
relatively constant population size. Instead, we saw something that
departed
dramatically from that expectation. We saw a pattern much more consistent
with a dramatic reduction in population size at some point in our past.

NARRATOR: This confirmed what other geneticists have noticed. Given
the length of time humans have existed, there should be a wide range of
genetic variation, yet DNA from people throughout the world is
surprisingly
similar. What could have caused this? The answer is a dramatic reduction
of
the population some time in the past: a bottleneck.

LYNN JORDE: We imagine the population diagrammed like this. In the
distant past back here we have a large population, then a bottleneck
looking
like this and then a subsequent enlargement of population size again, so
we
would have families of people in the distant past with a significant
amount
of genetic diversity, but when the bottleneck occurs, when there's a
reduction in population size perhaps only a few of those families would
survive the bottleneck.

We have a dramatic reduction in genetic diversity during this time
when the population is very small and then after the bottleneck the
people
who would we, who we would see today would be descendants only of those
who
survived, so they're going to be genetically much more similar to one
another reducing the amount of genetic variation.

NARRATOR: Human DNA is so similar the scientists concluded the
population reduction had been catastrophic. PROF HENRY HARPENDING
(University of Utah): It seemed so incredible, you know the idea that all
of
us, now there's 6 billion people on Earth, and what the data were telling
us
was that we, you know our species was reduced to, you know, a few
thousand.
Suddenly it hit us, we had something to say about human history.

LYNN JORDE: Our population may have been in such a precarious
position
that only a few thousand of us may have been alive on the whole face of
the
Earth at one point in time, that we almost went extinct, that some event
was
so catastrophic as to nearly cause our species to cease to exist
completely.

NARRATOR: It is an astonishing revelation, but the key was to find
out
when and why it happened. Because mitochondrial DNA mutates at an average
rate these scientists believe, controversially, that they can narrow down
the date of the bottleneck.

LYNN JORDE: Mutations in the mitochondria take place with clocklike
regularly, so the number of mutations give us a clock essentially that we
can use to approximately date the major event. In the case of a
population
bottleneck we think that this would have occurred roughly 70-80,000 years
ago, give or take some number of thousands of years. So then the real
question is: what could have caused such a reduction, an extreme
reduction,
in the human population down to as few as 5 or 10,000 individuals?

NARRATOR: As for what caused this dramatic reduction in population
the
geneticists had no idea. Henry Harpending began touring universities to
talk
about the bottleneck. He was invited by anthropologist Stanley Ambrose to
give a lecture to his students.

HENRY HARPENDING: Well Stanley is full of ideas, he's the kind of
scientist that plucks things from all over and puts them together.

PROF STANLEY AMBROSE (University of Illinois): I sat in on the
lecture
and he start4ed talking about this human population bottleneck and I
thought
what could have caused it and at that point I broke out into a sweat. I
went up to Henry and said I've just read a paper, and it's on the top of
my
desk now, that may have an explanation for why this population bottleneck
occurred.

HENRY HARPENDING: I didn't read it till a week later and when I
read
it you know it was like somebody kicking you in the face. There it was.

STANLEY AMBROSE: The paper was about the super eruption of a
volcano
called Toba in Sumatra.

NARRATOR: This team of scientists believe the bottleneck occurred
between 70 and 80,000 years ago, although this date is hotly debated.
Toba
erupted in the middle of this period, 74,000 years ago. If there really
is a
connection this research has terrifying implications for a future
Yellowstone eruption. It could well be of a similar size and ferocity to
Toba. Like Toba, it would have a devastating impact, not just on the
surrounding region, North America, but on the whole world.

MICHAEL RAMPINO: If Yellowstone goes off again, and it will, it'll
be
disastrous for the United States and eventually for the whole world.

NARRATOR: Vulcanologists believe it would all start with the magma
chamber becoming unstable.

BILL McGUI You'd start seeing bigger earthquakes, you may see
parts
of Yellowstone uplifting as magma intrudes and gets nearer and nearer the
surface.

ROBERT SMITH: And maybe an earthquake sends a rupture through the
brittle layer, you've broken the lid of the pressure cooker.

BILL McGUI This would generate sheets of magma which will be
probably rising up to 30, 40, 50 kilometres sending gigantic amounts of
debris into the atmosphere.

ROBERT CHRISTIANSEN: Where we are right now would be gone. We would
be
instantly incinerated.

MICHAEL RAMPINO: Pyroclastic flows will cover that whole region,
maybe
kill tens of thousands of people in the surrounding area.

BILL McGUI You're getting a, an eruption which we can barely
imagine. We've never seen this sort of thing. You wouldn't be able to get
within 1,000 kilometres of it when it was going like this.

ROBERT CHRISTIANSEN: The ash carried in the atmosphere and
deposited
over large areas of the United States, particularly over the great
plains,
would have devastating effects.

BILL McGUI The area that would be affected is, is the bread
basket
of North America in effect and it produces an enormous amount of grain on
a
global scale really. That's, that's, that's the problem and you would see
nothing. The harvest would vanish virtually overnight.

ROBERT CHRISTIANSEN: All basic economic activity would certainly be
impacted by this and let alone changes in the climate that could possibly
be
induced.

MICHAEL RAMPINO: The climatic effects globally from that eruption
will
be produced by the plume of material that goes up into the atmosphere.
That'll spread worldwide and will have a cooling effect that will
probably
knock out the growing season on a global basis. We can't really overstate
the effect of these huge eruptions. Civilisation will start to creak at
the
seams in a sense.

ROBERT SMITH: The fact that we haven't seen one in historic time or
documented means the human race really is not attuned to these things
because they're such a rare event.

MICHAEL RAMPINO: It's really not a question of if it'll go off,
it's a
question of when because sooner or later one of these large super
eruptions
will happen.

Back to Supervolcanoesprogramme page.









"The British attitude is to treat society like a game preserve where a
certain percentage of the 'antelope' are expected to be eaten by the
"lions".
Christopher Morton