In Our Time - Vulcanology

Episode Date: July 3, 2003

Melvyn Bragg and guests discuss the formation of volcanoes. In 79AD Mount Vesuvius erupted on the Bay of Naples, buried Pompeii in ash and drowned nearby Herculaneum in lava. The great letter writer Pliny the Younger was staying with his uncle in Misenum and was a witness to the cataclysm. He described it to the historian Tacitus, It seemed as though the sea was being sucked backwards, as if it were being pushed back by the shaking of the land. Certainly the shoreline moved outwards, and many sea creatures were left on dry sand. Behind us were frightening dark clouds, rent by lightning twisted and hurled, opening to reveal huge figures of flame. These were like lightning but bigger. This eruption, which claimed the life of Pliny's uncle, is one of about 500 volcanoes to have erupted in the last two thousand years, some of which are now categorised by vulcanologists as Plinian, after Pliny's famous description.What causes volcanoes? What role do they play in the formation and maintenance of our planet? And is it ever possible to predict when and where they are about to erupt?With Hilary Downes, Professor of Geochemistry at Birkbeck, University of London; Steve Self, Professor of Vulcanology at the Open University; Bill McGuire, Benfield Professor of Geophysical Hazards at University College London.

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or wherever you get your pods. Thanks for downloading the In Our Time podcast. For more details about In Our Time and for our terms of use, please go to BBC.co.com.uk forward slash Radio 4. I hope you enjoy the program. Hello. In AD 79, Mount Vesuvius erupted on the Bay of Naples. Buried Pompeian ash and drowned nearby Herculaneum in lava. The great letter writer Pliny the Younger was staying with his uncle in Misenum

and was a witness to the cataclysm. He described it to the historian Tacitus as, quote, It seemed as though the sea was being sucked backwards, as if it were being pushed back by the shaking of the land. Certainly the shoreline moved outwards, and many sea creatures were left on dry land. Behind us were frightening dark clouds, rent by lightning, twisted and hurled,

opening to reveal huge figures of flame. These were like lightning, but bigger. This eruption, which claimed the life of Pliny's uncle, is one of about 500 volcanoes to have erupted in the last 2,000 years, some of which are now categorized by volcanologists as Plinion. What causes volcanoes? What role do they play in the formation and maintenance of our planet? And is it ever possible to predict when and where they're about to erupt?

With me to discuss the state of the art of volcanology is Hilary Downs, Professor of Geochemistry at Birkbeck University of London, Steve Self, Professor of Volcanology at the Open University, and Bill McGuire, Benfield Professor of Geophysical Hazards at University College London. And Hilary Downs, before we get to the detail of types of volcano and how they erupt, would you give us a brief description of the composition of the Earth with its main geological components? So we know, as it were, what the initial setup is. Yes, the Earth is something rather like a gobstopper.

An old-fashioned gobstopper, you think of one of those. We have the crust at the very outer edge of the Earth. That's where we live. If we go down into the earth about 50 kilometres, plus or minus a bit, we reach an area called the mantle. This is a very thick shell. It goes down to about 3,000 kilometres. And it's made out of minerals like olivine and silicate minerals like that.

After that, deep in the earth you have the earth's core, which is essentially made of iron and nickel. The outer part of the core is liquid, and the inner part of the core has crystallized as a solid nickel-iron ball. And magnetism occurs at the surface of the earth due to perturbations within the earth, particularly in the mantle. And that gap between the crust and the mantle, what did you say 30-50 kilometres,

that's called the lithosphere, isn't it? What happens there? The lithosphere is composed of the earth's crust and a little bit of underlying mantle, if you like, has frozen onto the base of the earth's crust. And that's where the plate tectonic activity takes place. The lithosphere, the lithospheric plates move around the surface of the earth due to the convection in the mantle.

So we've got this core, which is exceedingly hot. Then we've got this mantle, 3,000 kilometres around it, and then we've got the lithosphere, which I mispronounced there on, and then on top of that is the crust on which we are existing at this very moment. You talked about magmatism. Now, people might have thought you were mispronouncing a word, but you weren't. Can you just explain what you mean by magnetism? Well, magnetism is anything that relates to the formation of magma.

Magma is liquid, molten rock. As it comes to the surface, we see it as lava flows, but it may also not reach the surface. The magma may simply crystallize inside the crust, giving us, when it gets eroded, giving us big granite plutons, as we have in, say, southwest England.

So the heat is pushing stuff up all the time towards the crust, is that right? And this stuff turns into magma. This could be far too crude, so you're going to enlighten it? Well, in order to get magma, you have to melt the mantle. The mantle has to undergo a certain amount of melting.

There's 3,000 deeps. Not the whole lot, no, no. No, just near the surface in the top 100 kilometres or so. And there are different ways to get the mantle to melt. One way is to heat it up, and that can happen by heat coming from the inner parts of the earth. You can also get the mantle to melt if you decompress it. So if you reduce the pressure, it melts, unlike ice, which does the opposite. it. And the third way is to add another substance to the mantle, and the most common one would be

water. And this does happen in several places around the earth where water is taken down into the mantle in subduction zones. So there are the three ways of getting the mantle to melt, and in each case it produces magma. And then that magma can rise up through the lithosphere and either crystallize in the crust or erupt as a volcano. Thank you very much. Steve Self, most volcanoes that we're talking about rising up, when they rise up, they rise up at junctions between tectonic plates. Can you briefly just tell us what tectonic plates are and why do magmas, molten magma, why do they seek these and how do they find these gaps?

Well, tectonic plates are, as Hillary said, composed of the lithosphere with the crowsy. riding on top and they change in composition from heavier material at the bottom to lighter material at the top and any magma that comes up to a tectonic plate is molten and therefore it has a lower density than the bottom of the lithosphere therefore it tries to rise through the lithosphere and it has to find a way of doing that and obviously where there's a break is the easiest place for it to rise. So although there's probably magma under large parts of the earth,

lithosphere, it's only where there's a break created by being a junction between two plates where they're spreading or where they're coming together and subducting one underneath another, that the magma finds it easiest to rise to the surface. So we're looking at the surface of our planet as like a cracked eggshell into about 12 different plates, oceanic plates and other tectonic plates

which are gradually coming together or gradually going apart about two centimetres here but that's the surface it isn't a smooth egg shell this is cracked eggshell and in those cracks there are the possibilities for eruptions to take place and subdux one is when they come apart that leaves a gap free to get through

ones when they come together that's subduction that drives the thing down that that's water in the ciliary we're saying in both cases it allows this molten what's it magma to come out not right yeah that's right Yes, and it will collect, it will pond at the bottom of the lithosphere, and then rise up a little way, and then find a place of weakness or a horizon of the same density,

and it will spread out there and spend a little time there and undergo some crystallization, and once a big enough blob of it forms, then it will take off towards the surface again and gradually work its way up to the surface of the earth to erupt and form a volcanic eruption, and a volcano. So this is ceaselessly happening.

This is what's happening our planet as we're sitting here every day, has happened for millions of years, we'll keep happening for millions of years, this is the deal.

Yes, just going on all the time. Can you tell us the difference between, and the relationship between effusive volcanoes and explosive volcanoes? Effusive volcanoes

are those that produce mainly lava flows. Examples are the Hobayan shield volcanoes, the great big shields like Malmalaura and Malnkaya. What do you mean by a shield?

They're called shield volcanoes, I suppose, because the shape of the volcano was like the shields that used to be carried by ancient warriors and laid on the ground. Low, whale-backed sort of shape. Like hills in the borders. Yes. And the lava comes out from a central vent

or from a line called a fisher. and gradually builds up these low-angle shield volcanoes, if it's low viscosity, runny type of lava. There are other types of lava volcanoes that are made of much more sticky toothpaste-like, crusty toothpaste-like magma that erupts at the surface and forms very blobby-looking mounds of lava.

And these are another type of effusive volcano, usually made of a magma type called rilite or day site. When the, is it, the magma turns into lava when it comes out, is that the idea? The magma is a liquid. The lava is a liquid. And the liquid gradually solidifies by freezing and crystallizing. And so the, there's not a change of, well, the only change of state is from liquid to solid. as the magma comes out, forms a lava flow and freezes on the surface.

So I have these superating volcanoes where this lava comes out and forms these great shields. You talked about the Hawaiian shield, these massive formations there. And there's one mountain, if you start at the bottom of the sea, it's much, much higher than Everest, and that's a volcanic mountain. And the eruptive forms, I mean, when we think of volcanoes, we think Vesuvius, Krakatoa, Etna, and they operate in a different way. Well, Aetna's an effusive volcano dominantly. It's growing and growing and growing.

And it erupts very frequently and I'm sure Bill knows only too well. This works on Mount Etna. It's been erupting on and off for most of the last century. And the other type of activity that you mentioned, explosive activity, the magma starts off in the same way in the magma chamber. It's a liquid and it's rising towards the surface. but something happens on the way to the surface to break up the magma into pieces

and that's due to the expansion of gases in the magma. Do you want to take that on, Bill, on this eruptive volcanoes? Yes, well, I mean, the first thing to say about explosive volcanoes is that they're much more dangerous, generally speaking, to human life and to property. What happens is that as the magma rises up the conduit of the volcano, you have gas in the magma which expands, it tears the magma apart and as this tearing apart of the magma accelerates it up the conduit

when it reaches the surface it's blasted out as fragments so it doesn't flow out nice and quietly as a lava flow but it's blasted high up into the atmosphere sometimes 10, 20, 30 kilometres up. Can you give us some idea of what you know historically of the force that these things, these volcanoes erupted, pertain can assume? The forms? The force.

The force. Well, one thing that people don't appreciate, I think, is how incredibly powerful volcanic eruptions and other natural phenomena in general are. Quite often people say to me, can't you stop volcanoes erupted by maybe drilling a hole in them and letting off steam, which is, it just shows that people don't understand that the energy produced in some of the biggest volcanic eruptions is comparable to hundreds, if not thousands of nuclear explosions. The force is incredible. And the biggest volcanic eruptions can send clouds of ash to the edge of space effectively and transport across millions of square kilometres of the Earth's surface.

So enormous forces involved. Are those forces still possible? The last one of that, the size that you're talking about was, as I understand it, 73,000 years ago. But there have been some pretty big ones since then. Again, as I was saying earlier, is that the condition of the planet we're on? Those are going to come around, are they? Well, absolutely. I mean, you're talking about the last so-called superruption,

which was at Toba in Indonesia, something that Steve has worked on. it's estimated that these eruptions on this scale occur perhaps a couple of times every 100,000 years. But that's pretty much normal behaviour for the Earth. So we are going to see one of these things again in the future. They're not going to stop happening just because we're here. Most people listening will know when they say volcano, and one place they'll go in their minds is Vesuvius. So it's a useful example.

Can you just give us an example before we move on to Wajun about what happened in Vesuvius, AD 79? and we're very lucky to have extremely good descriptions left, some by plenty of the elder, some by his adoptive nephew, Pliny the younger, and so that's a good starting point. What happened there and what was the force of it? Well, this was, you can actually categorise volcanic eruptions on a scale, rather like the Richter scale, the volcanic explosivity index, again, something that Steve has been very much involved with.

It runs from zero to eight, it's logarithmic, so each point on it represents an eruption ten times more, powerful say than the one before. The eruption of Vesuvius in 79 AD was a score about a six on that. Super eruption is an eight. So it's a sort of moderate to large explosive eruption. Of course, the people in Pompey and Herculane were living very close to that volcano. It blasted a huge cloud of ash into the atmosphere.

It also sent down what we call pyroclastic flows, which are these hurricane blasts of super-eated volcanic gases and magma droplets and blocks the size of houses sometimes. Are these pyroclastic flows, are these comparable to hundreds of nuclear bombs that you're talking about? Is that where we see that force in the pyroclastic flows? The force, really, the big forces that I'm talking about are really associated with the blast. Many pyroclastic flows, most pyroclastic flows, are driven by gravity rather than anything else. It's simply gravity that as material is ejected out of the volcanic vent and piles up around the vent,

gravity just causes it to continue to slide down the size of the volcanoes, effectively, as almost like. turbulent landslides, if you like. So it's gravity that's the main force there rather than the upward blast. Is Vesuvius useful as an example in any other ways? I mean, we all know about it, as it were, so it's useful for us to have a way into volcanoes. But can you draw anything else for a bit

that's of greater significance than the thing itself? Well, my interest in Vesuvius and many of my colleagues is in the future, because it's in terms of volcanic hazard, in terms of the threat of a volcanic eruption in the future, Vesuvius is a really big problem. There are 600,000 people living on the flanks of that volcano. It's done nothing for 60 years.

Nobody really knows when the next eruption is going to occur. It could be this year. It could be a few centuries down the line. And because the air is now so densely populated, it is going to be a really big problematic issue in getting people out before something serious happens. And I think that's our main concern. Have you got it?

One hopes it's rather closely monitored this. It's very closely monitored, but monitoring isn't everything. Are we going to come back to that in a minute? Let's talk about the Hawaiian volcano, which is part of the biggest individual rock formation on Earth, and that's been producing lava for 20 years or so. Now, is that a hazard? You're in the business of hazards.

What does that tell us? Well, this is an eruption which, as you say, has been going on for a couple of decades now. It is producing lava flows. It has been producing them over that time. Most of that lava has been either entering the sea or just forming flatest plains of lava. Occasionally eruptions on Hawaii.

why do threaten towns and small settlements, they will damage property, they will cover agricultural land, etc., but they won't kill people. These things move much too slowly. Unless you're nail to the floor, there's no way you're going to die by means of a lava flow. So, you know, they're not a threat to life,

but they're a threat to property. Hilary Downes, the centre of the earth, as you've said, is still hot, retaining energy and heat and so on. Can you see, do we see volcanoes as part of the process of the earth, cooling. How do they fit in with the sort of history of the planet? Yes, well the Earth's been cooling down

ever since it was formed and the heat has got to come out of the Earth. It's conducted away. If you go down a mine, it gets hotter inside the Earth. But if you think of volcanoes as a

sort of heat valve they allow some of this energy, some of this heat from the Earth to be dissipated. Do we also see volcanoes in some way as affecting the atmosphere in which we live? There's a theory that I read in preparing for this, that in fact the atmosphere that we have owes a lot to what came out of the centre of the earth by way of volcanic activity?

Yes. Can you give us some detail of that? Well, much of the gas that comes out of volcanoes is water, also a little carbon dioxide, and we think that the nitrogen that we find, in the atmosphere also came out of the earth. The only thing that's in the atmosphere that doesn't seem to owe its existence to volcanoes

is oxygen and that owes its existence to plants and that's a whole different discussion. So volcanoes at one stage added to the atmosphere and made the atmosphere the one we have which made life possible, life's in it. And the oceans, the water in the oceans as well. So that all came from that. But now have we sort of, have we sort of?

have settled that question and do the volcanoes now start to interfere with what they once got right as it were yes volcanoes can put a lot of gas into the atmosphere sulphur dioxide in particular which gives rise to acid rain of course and but they do continue to add to the atmosphere but but i think the earth is the atmosphere is not going to change greatly um due to volcanism at the moment but on an individual volcanic basis, yes, it will that the volcanoes still put a lot of gas into the Earth's atmosphere. Well, your reassurance

that it isn't going to change very much at the moment it's very much at odds with Bill's view that Vesuvius could be going off as we sit and speak, because the predicting in this business seems to be to be completely non-existent, and that seems to be the deal around the table, but can you just tell us what happens in the

atmosphere? This stuff comes out, and the blast is hundreds of atom bombs, of hydrogen. Up it goes. And what happens up there in the atmosphere? Can you give us a description of it? Well, the volcanic cloud is blown around by the wind. And depending on which way the wind's blowing, you'll get a large volcanic plume of ash and dust. This will start to fall out of the atmosphere

and it will blanket the whole area beneath the volcanic plume. And these plumes can blanket areas of many thousands of square miles and at a great distance from the actual volcano. An example is the ash plume that came out of Mount St. Helens 20, 30 years ago. And that ash plume went all over the western states of North America

down into Montana and Wyoming. And yet that was a very small volcanic eruption. that we have much more, and we have evidence of much bigger volcanic eruptions that had much larger ash clouds that covered much larger areas. Steve, do you want to add to that, Steve, what happens in the eruptions,

how do they affect the atmosphere and the weather? Yes, I think we can add a slightly different perspective to this. Bill mentioned the incredible energy of the eruptions. Much of this energy is actually heat energy and the way that the volcanic eruption columns and clouds go very high into the atmosphere, penetrate up into the mid to upper stratosphere, so that's up to about 55 kilometres height

above the surface of the earth, is due to the heat energy. It's due to convection. There's a giant convection cell. And the actual blast from the volcano only drives the volcanic plume the first few kilometers. And then because the atmosphere's quite dense and viscous near the surface of the earth,

the drag on that plume, the aerodynamic drag, is huge, and it slows down. But because it's so hot, then it becomes a convective cell, and that's what drives it up. And then, as Hillary said, the ash falls out very quickly within a few hours to a few days, and what's left up in the atmosphere is gas. And especially the high plumes, the ones that penetrate the stratosphere,

they will take water, and carbon dioxide and sulphur dioxide up into the stratosphere where the stratosphere is essentially dry, there's not much water, we don't get many clouds in the stratosphere. Think when you're settling back in the aeroplane that's just taken off from Heathrow and the captain says we've now reached cruising altitude and you look out of the window, there's no clouds up there, so there's no water, you're looking into the stratosphere then.

And at a volcanic eruption... Clouds underneath us. There's clouds underneath you, but there's not clouds up there. The aeroplanes levelling off in the bottom of the stratosphere usually. So you're looking at the clean stratosphere, and a volcanic eruption dumps all this gas and up into the stratosphere. So clouds may form in the stratosphere due to volcanic eruptions where there aren't normally clouds. And the effect of this could be, as Hillary said,

on large swathes of land, the weather of large slays of land, quite a long way away. It can be quite a long way away. And violent effects, yeah. Well, Mount Penituba erupted in 1991. Within two or three months, a whole veil of sulfuric acid aerosol droplets, basically smog up in the stratosphere, had spread over the whole earth. And that, of course, reduces the amount of sunlight that comes in from outer space, reduces the amount of solar energy reaching the surface of the earth,

and you get cooling. And it also changes the dynamics of the stratosphere, the air circulation in the stratosphere. And you get peculiar weather. And that's why many eruptions are associated with deterioration in climate for a few years after the eruption and periods of really strange, wacky weather, anomalous weather, snow in July and things like that in many parts of the world.

And with other problems, I mean, fallouts from Iceland resulted in marked great deterioration health of people in this country. I mean, very serious deterioration of health, respiratory diseases and so on and so forth. Do you think that volcanoes, this is very simply, I'm very sorry about this, the volcanoes were once extremely useful, got the whole thing going, but now they've entered into the sort of debit side. Obviously people die as a result of the volcanic eruptions, about 80,000 in the last century,

maybe a quarter of a million since the 17th century, but they also do a lot of good. and for example they provide power in certain countries in Iceland and New Zealand, etc. More than that, though, they provide very fertile agricultural soil. And if we take Mount Etna, for example, every point in Etna is covered on average every 400 years by lava. That means you can live there or a family can live there for 15 generations, having a great life growing oranges and vines and olives from the fantastic fertile source before they get hit by lava.

And then the government will compensate them and they can build a new house. From that point of view, bearing mind that lava flows do not kill people but just damage property, it's still a great life. So volcanoes do some good as well. And lava, of course, turns can settle and not be at all, not harm you at all, can't it really? What parts of the earth are there and helpful as a result of volcanoes? What part of the crust, besides the lava banks on the immediate side of volcanoes? Well, generally speaking, this fertile soil business is really quite important because countries like Indonesia and others in Southeast Asia rely on the fact that they have lots of volcanoes to produce their fertile soils.

But it's not the lava really. That takes many, that solidifies as a solid carapace and it takes centuries at least to break down. It's the volcanic ash and the fine material which contains all the minerals that plants need to grow. That breaks down to soil very, very quickly. So some of these countries have lots of volcanoes on the negative side. they lose lives as a result of that, also have very fertile soles right across the country as well. So there's a plus and minus there.

Besides people living, what other pluses do you think there are for volcanoes now? Tourism is a big one. No, seriously. Mount Etna, for example, is a major tourist resort in Sicily. The local people there have found a way to avoid the lava flow problem because if you go up, for example,

at the bottom of the cable car, which takes you up to the volcano, all the souvenir shops there are on wheels. So if there are any lava flows head in their direction, they can attach vehicles and drive them off. But tourism, seriously, is a big plus for volcanoes. Iceland, for example. People go to Iceland either to see the glasses or to see the volcanoes.

New Zealand is well known for its hydrothermal pools, Yellowstone for its geese. So tourism generally is a big industry, and the volcanic aspect of it is also very strong. It's interesting, isn't it? Making a sort of, let's go and have a holiday, besides something kind of blows to Smith, I suppose it's been going in for a long time.

Has it? Is that a new phenomenon? I mean, people didn't... In Pliny's Day, a couple of thousand years ago, they didn't say, let's go and build a place at Pompeii because we might get blown up, will that make it more exciting? Nobody even knew it was a volcano then, but if we come onto the 18th century, for example,

when William Hamilton worked there, who was the husband of Emma, he was really the first field volcanologist. He spent all his time up this volcano, dodging volcanic bombs, studying how it worked, whatever. People came to visit him. They were fascinated by Vassu. Vesuvius, because it was always erupting then.

People were coming along, visiting it, going up, seeing how it went on. Of course, his wife and Hamilton were doing something entirely different at the same time. His wife and Nelson. His wife and Nelson, yes. He was giving him the courage to save the nation. Exactly. 100%. Something like that.

But tourism, you know, even then volcanoes attracted people. They've always fascinated people. And you can really see as part of the grand tour, I suppose, Vesuvius and Naples was one of the areas people like to go to. Well, I'm a bit worried that we've only been going for half and I've reduced these massive things that can wipe the earth out to blooming tourist attractions. So I'm going to get back from Steve's self. We know that the role of volcanoes have had, or we know, you know, in things which are called extinction events in our planet. Now, can you describe the last, and the one such extinction event was about 65 million years ago, an asteroid, massive asteroid hit the planet.

and all sorts of life was destroyed. It's supposed to where we kicked off then because of the dinosaurs. And so and so forth. It was an extinction event. It's self-explanatory. Now, can you give us an example of a volcanic extinction event? What happened and how likely is it to occur again? There have been seven, well, depending on how you count them,

seven to 12 major mass extinctions in the last 300 million years of, geological time. And the most famous one that you've mentioned, the Cretaceous tertiary boundary mass extinction, the one that I put it. The one that wiped out the dinosaurs and 75% of all other living species is the only one that coincides with meteorite impact.

Proven, as proven today, by the current scientific research. The other seven uncannily, interestingly, all more or less coincide with what are called flood basalt events, which are flood lavas, types of eruptions that aren't occurring on Earth at the moment of a much bigger scale, lava effusive producing eruptions. But of a scale that we haven't had on earth for the last 15 million. years. They occur roughly every 30 million years. And Hillary can make some comments about why they might do that later perhaps. But nearly every one of these other mass extinctions has coincided by the limits of our present understanding and our present ability to age date these events with one of these huge lava-forming events. And so it's very interesting what these

events might have done in the past to life on earth and what part they play in the whole of the evolution of life leading up to our existence. Well, if you can describe what a flood basalt is and does, and then Hillary can describe that when they occur and, as it were, why they occur, will be a bit wiser. So, right. Okay. A flood lava eruption, its average size is something in the order of, you know, a small Mount Tober eruption, this 75,000-year super eruption,

are 50 times bigger than the largest lava eruptions that we've had recently, which occurred in Iceland, 934 AD and 1783 AD. So they produce lava flows hundreds of kilometres long. In fact, the limitation on the size of lava flows on Earth is the size of the continents. There are lava flows that have essentially crossed continents and eventually on our earth they flow into the sea. But if continents were bigger and the volcanoes were further away from the coast,

I'm sure we could have lava flows on Earth two or three thousand kilometres long. And I'm sure there have been in the past lava flows during flood-besort events that are that long. So you get these enormously long, wide-spreading lavas erupted over what I've some what contentiously suggested as lasting for periods of decades to maybe centuries. So lava's continuously pumped out of the earth in a whole

series of eruptions over a short period of geological time, about a million years. And these are extinction events, are they? Well, the only viable connection is by the release of gas from these eruptions, even though

they would affect a big area underneath the lava flows covered by lava. That's not going to create extinctions. You've got to do something globally. And the only global connection that I can see to the sort of affecting life on Earth is by gas release. So you've got to release the gas at the vents

and we're beginning research. We've got a few case studies done that convincingly show this has happened. Enormous amounts of sulfur dioxide gas are released by these events. They go to middle heights in the atmosphere and possibly get circulated all the way around the earth. And so there are these whole series of massive climate-inducing

and acid rain-type events. And this may, although it needs a lot more research, may be connected with mass extinctions. Would you like to develop that, Hillary? Well, I think we're very fortunate not to be living in a period of flood basalt eruptions. they are enormous and we think that they're formed

our best guess is that they're formed by a mantle plume a plume of hot rock welling up from the very deeper parts of the earth towards the surface as it comes towards the surface it decompresses and that's where we get a large volume of magma being produced whether they are produced in a

regular fashion or whether they're random, I don't think we really know yet. But they are, they have been occurring for as long as we have geological records going back into the early times of the earth. We know that there are old lava eruptions there may be eroded away now so that all we see are the little feeder vents, which we call dikes. But nevertheless, those feeder, events, even in the very ancient part of the earth, are many hundreds of miles long, which indicates that the lava flows would have been of the same kind of magnitude as Steve has described. And yes, they probably have had the same kind of effect on the Earth's climate. Each time there has been one of these eruptions. And they aren't confined just to the continents. We

we are now starting to appreciate that there are two or three submarine plateaus which are basically enormous piles of basaltic lava and so we need to take those into account as well as the ones that we can see on the continents. Again I'm going to turn to Bill now

but again there's a slight contradiction I'm sure you don't see any contradiction but I do that you say I'm glad we're not in a period of flood basalts as if as it were you can predict these things but what I've got you're shaking ahead we can't predict these things so you don't know. We might be in the fear of flood vessels. So can I turn to you, Bill?

I've been reading for this that only one-tenth a volcanoes are monitored, and they're very difficult to predict. Can you just give us some idea of the, well, of the unpredictability, and why only one-tenth are monitors, and what that means? Well, the consequences of that are. Yeah, there have been about maybe 600 volcanoes

or so that have erupted in historic times, but there might be another, at least that many again, maybe up to 3,000 volcanoes in total that are either active or potentially active. So that's a lot of volcanoes to monitor. Many of these are in developing countries. They don't have the expertise. They don't have the financial backing to monitor them.

I think that's the big problem. Where we do monitor them closely, they are, in fact, relatively easy to predict. No volcano ever erupts without precursory signs, without warning signs, because as the magma forces its way to the surface, to break the rock, that generates swarms of earthquakes. It also swells the volcano up, so we see the ground deforming.

So we know if a volcano is going to do something. The difficulty is predicting exactly when the eruption is going to start, how big it's going to be, when the climax is going to be, because sometimes eruptions last for weeks or months. So those are the difficult points, but there is new research going on at the moment. In fact, some of my colleagues at UCL have a new model, which has successfully looked back at eruptions of Montserrati over the last 10 years, looked at Pinatubo,

and has been able to develop a model that predicts maybe four or five days ahead very accurately when the start of an eruption will occur, looking at how the numbers of earthquakes increase or how the ground swelling increases. So no volcano ever erupts without warning signs, and we're getting better at pinpointing the start of these things. But nevertheless, we're still, we, I mean, the human, are still only able to monitor one tenth. Well, that's a big problem. I mean, we should monitor, we need to monitor many more volcanoes. The volcanoes that are best monitored are in the countries that can best cope with the disasters if they happen. Vesuvius, Aetna, the Hawaiian volcanoes, there are many much more dangerous volcanoes around the Pacific Rim in South America, Central America, which nobody's looking at. And one of the ways we can improve that, I think, is by using satellite technology,

because satellites can monitor many more volcanoes more frequently without having to go there on foot and spend a lot of time and effort and instrumentation actually looking at them. Steve, so for you convinced of the predictability of volcanoes because there was that volcano in Colombia, which had an ice cap on top, was thought to be extinct, and that wiped out 29,000 people, didn't it? The mud that came after the explosion, which lifted the ice cap, went for 50 kilometres, which nobody really expected,

and wiped out a whole town. So do you think that's predictable as Bill says they are? Well, Bill's right. If the volcano is closely monitored, then the behaviour is predictable. the problem for humankind is all those volcanoes that either we still don't recognize a volcanoes it's notable that in the last 20, 30 years

there have been three major volcanic eruptions, one of the ones you mentioned Ruiz, but two others, Pinatubo in 1991 and El Chichon in Mexico in 1982, both of which were insignificant, inactive volcanoes before they erupted. and the secret there lies in the fact that these are volcanoes that perform erupt only every few hundred or few thousand years and therefore our what would you call it corporate history

our memory of activities from those volcanoes doesn't exist and it's not even written in the legends of the people who live around there because they've been dormant since people have started to live in the area and have recorded anything. And they're the real problems. I'm sure that one of the next major eruptions to occur will be from a volcano that we currently don't even recognize as a volcano or has been mapped many, many years ago as a volcano and then forgotten about

because it's not currently active. There's no attention placed on it. You deal very much in the area of hazards, Bill Maguire. Is there any, from what you can tell, I mean, see if, just given us the comfort that something's on a blurb that we know absolutely nothing about now that does everybody else. But insofar as you know a lot about it, what do you see as sort of, what it forced imminent as they might say on that, on the news. I knew you're going to ask that question.

Yeah, well, there you go. You should be prepared for it. I am. But the first thing to say is that, just to reinforce Steve's comment, three quarters of all the big eruptions of the last couple of centuries have occurred at volcano, have been the first recorded eruptions at those volcanoes. So whatever I say, now are probably going to be wrong. The next eruption is going to be somewhere we've never thought of. But there are places in the world that people are concerned about. There's Vesuvius, as I've mentioned. There's Long Valley, Mammoth Mountain in California, which is one of these what's so-called restless cold-eer is a huge volcanic crater that's going up and down,

swelling, subsiding, earthquakes going on. That has been, is a potential erupting volcano in the next few decades. Dominica, the island and the Caribbean, has been suffering earthquake swarms beneath the volcanic area. People are just crossing this off their holiday spots as we go. And of course the area we've been working very much in the last few years is the island of La Palma and the Canaries, which has the whole western flank of the volcano, is slowly sliding into the sea at the moment,

and that thing eventually will go plunge straight in within a few minutes and cause all sorts of problems, these huge tsunami tidal waves. Well, you think more imminently than eventually, don't you, in La Palma, and when that happens, a hundred metre high wave will hit America, meter high wave, we'll hit what the tsunami is. Yeah, and then that'll be

some carry on, right it? It will be, I mean, you would need to evacuate something like 100 million people probably from the east coast of the US, the Caribbean, etc. If this happened, but the trouble is you wouldn't have time. Once this huge landslide, which is about the volume of the Isle of Man, goes into the sea,

it will reach the US and the Caribbean in 12 hours. And you do think, I mean, I'm being a bit jerky about this because I think it's very difficult to imagine. You actually do think this is bound to happen. It's on the cards. It's going to happen sooner on it. It will happen. It could be next year. It could be a couple of thousand years down the line. But it's normal behaviour for these volcanoes. They get bigger and bigger and bigger and then they collapse. There are lots of examples. Hilary, Danz, finally, do you think there's any, there is going to be found a way to control volcanic activity of this sort?

No, I don't think you can control volcanic activity. It's just too great. The forces are too enormous. the only thing you can do is have good monitoring, the sort of thing that Bill does, good models to see how a volcano is likely to erupt, and good evacuation plans. Well, thank you very much. The world feels a little less sife than it did at the start of the programme.

Thanks to Hilary Downs, Steve Self and Bill Maguire. We will try to bring a little healing to the world next week, and I'll be talking about the philosophy. of nature. Thanks for listening. We hope you've enjoyed this Radio 4 podcast. You can find hundreds of other programmes about history, science and philosophy at BBC.com.uk forward slash radio 4.