Sorry about the last post that you couldn't open..Here it is again..Al

Yellowstone Park  
transcript of radio talk show regarding the potential for a super eruption
Supervolcanoes BBC2 9:30pm Thursday 3rd February 2000 

NARRATOR (SINÉAD CUSACK): Yellowstone is America's first and most famous National Park. Every year over 3 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 

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 fossilized 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 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 

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 

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 

BILL McGUIRE: 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 McGUIRE: 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 McGUIRE: 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 McGUIRE: 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 

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

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 

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 

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: 

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 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 

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 

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 McGUIRE: 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 

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 

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 

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

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 McGUIRE: 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 McGUIRE: 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.