存储在岩浆是什么气体?

Chris - You're listening to the Naked Scientists and my name Chris Smith and we're live at the Cambridge Science Centre where we are talking extreme geology this week. Our guests this evening are James Jackson, Tehnuka Ilanko and also Arwen Deuss. They're all earth scientists and Tehnuka, you work on volcanoes. Tell us about what you do.

Tehnuka - I'm a volcanologist working on volcanic gases and most of my work is done on gases from Mount Erebus volcano in Antarctica. So, what we do is set up an instrument on the crater of the volcano. Inside the crater, there's an active lava lake and these are quite unusual. An active lava lake is sort of a pond of lava that, for some reason, is connected to the source of the lava. And so, there's fresh magma coming up. So, the hot stuff is coming up and the lake is turning over. All of this time, it's emitting gases. Now, the thing about these gases is, they're always in the magma when the magma is at depth. It's a bit like a bottle of coke. You've got no bubbles in it when it's sealed as far as you can see. But there's carbon dioxide inside the bottle and it's all dissolved because the bottle is sealed. When you open the bottle, you're releasing some of the pressure out and suddenly, all of these bubbles start forming and stuff comes out of the top. It's the same thing inside a volcano. What we're trying to do is measure the gases and to find out where they come from, and how that's driving their lava movement inside the volcano.

Chris - Quick practical question, why Antarctica? I mean, I know you get to go to Antarctica which I'd love to do, but does that not limit how often you can go there?

Tehnuka - It does mean we can only go down there once a year. And this year, we can't actually go down there at all because we're going with the US Antarctic Programme and unfortunately, things have shut down there.

Chris - They're closed for business at the moment aren't they? So that's scuppered your expedition then.

Tehnuka - But normally, there's very good fieldwork support and like I said, lava lakes like the one at Erebus are quite unusual. So, the opportunity to work there makes it worth the effort.

Chris - How big is this thing?

Tehnuka - When I was last there, it was probably about 30 metres across - the lava lake itself. The volcano is nearly 4,000 metres high.

Chris - And how hot is that lava lake?

Tehnuka - That's a good question and it's one of the things we've been trying to figure out, but approximately a thousand degrees Celsius.

克里斯-哇!所以,你我不会持续很长时间f you took a dip.

Tehnuka - No.

Chris - What does that do to the ice in the environment?

Tehnuka - The crater itself closest to the lava lake is empty of ice, but they're on the volcano. It's still covered in ice and snow.

Chris - In terms of actually what this volcano is, volcanoes come in different flavours. So, if we look in different parts of the world, they behave very differently from each other. What determines that and what sort of flavour of volcano is Erebus?

Tehnuka - So, some of it is to do with sort of deeper parts of the Earth - so, what's underneath the volcano and to do with how the plates which are underneath the volcano are interacting which maybe you might hear more about from Arwen. Erebus is quite a runny magma relatively speaking and so, it's got this active lava lake. Some other volcanoes might be more explosive. They might get blocked that bit more easily and you get bigger explosions.

Chris - What are you learning from the gases?

Tehnuka - The gases show some interesting patterns. So, when we get big bubble burst explosions from the lava lake, they're often quite rich in carbon dioxide. Sometimes we see very cyclic changes in the gas coming out and we're still trying to figure out what's causing this.

Chris - We're going to come your questions in just a tick so have your thinking caps on. I got loads of emails on volcanoes here, so let's take the first one. This is from Dreamcatcher37 on Twitter who says, "How much effect does volcanic activity have on global warming? What's their pollution impact?"

Tehnuka - That's a very good question. One of the main things people say about volcanoes' impact on the climate is the sulphur dioxide that they output is that in effect it can have the effect of masking the Earth from incoming radiation. And so, actually promoting cooling.

Chris - Got an email here from a listener who has actually said that if you look at history, there's evidence for some massive eruptions millions of years ago which were covering an area of the size of North America with ash and things. They go on to say, "Well, isn't there a massive hole left underground when all this stuff has come out?"

Tehnuka - I guess there would be, yeah.

Chris - Any questions?

Jonathan - Hello. I'm Jonathan from Cambridge. I understand the caldera in the Yellowstone Park is quite dangerous. How dangerous is it? Is it likely to erupt at any time?

Tehnuka - So, that actually kind of flows on from the previous question. One of the things that can happen and I think this will be demonstrated to you later - after a big eruption is that the hole and the stuff that was underneath the volcano has somehow emptied out and that leaves a space which means the stuff on top can collapse in. So, a caldera forms usually when a big magma chamber, the source of all the stuff that erupted has emptied and leaves a space.

Chris - And if that thing goes off, what will be the effect?

Tehnuka - Very big.

Chris - Bad! Any other questions?

Aaron - Hi. I'm Aaron from Hardwick here. Could you just sum up the gases that come up when volcano erupts?

Tehnuka - So, there can be a lot of different gases that come out. Most of what we see is water and carbon dioxide. Sulphur dioxide can be another big one and then I could go on forever, but some of the other main ones are carbon monoxide, hydrogen chloride, hydrogen fluoride, H2S which is the stuff that gives off the funny smell.

Chris - I've got two emails - one from Devin and one from Richard Roberts. They both emailedchris@thenakedscientists.com. They say, "Do volcanoes cause global warming or global cooling?"

Tehnuka - That's another very good question and I'm not sure it's the one I can answer directly. The historical record of big eruptions, for example, there's a big eruption in Iceland called 'Blacky' in human history. So, we know that it had crazy effects on the climates in different parts of the world. What we tend to see is extremes of weather, but how that effect is felt in different places will vary.

James - We have some well-known causes. There's one in 1811 or 1812 in Indonesia and that created famously the year without a summer which caused all the crops to fail in northeast United States and which started the great migration to the west countries - so Oregon and so on. And they didn't know at that time what caused it, but it was a massive eruption in Indonesia, producing a huge amount of dusts in the upper atmosphere and what that does is shield the atmosphere from sunlight and it cools. The other one closer to modern times was in 1990. In the Philippines, a big mountain, Mt. Pinatubo exploded and that reduced global temperature by half a degree for 2 years. And that doesn't sound like much - half a degree - until you realise that actually, even in the last Ice Age when the ice was maximum, there were global temperatures of only 4 degrees colder than it is today. So, messing about with global temperature at a few degrees level is quite a dangerous thing to do. But mostly, it's cooling that I know about from historical records.

Ben - Hi. I'm Ben from Cambridge. I was just wondering whether new volcanoes can form and how frequently that happens.

Tehnuka - Depends on where you're looking. In some ways, you can say that new volcanoes are forming all the time. Usually, they tend to be ocean. There are plates where the ground is moving it at and these are called divergent plate margins. Along these, you've got magma coming up and I guess in a way, you could call these volcanoes that are constantly forming. Volcanoes can always form. There was a famous case of a Mexican cornfield where this farmer looked at one day and saw a volcano is starting to form.

Chris - The email from Bryan Houser, Tehnuka who says, "How do islands get produced in ocean?" That's also often a volcanic phenomena isn't it?

Tehnuka - That's right and again, it's just the volcano forming, but they've been building up from the seafloor. So, a lot of these volcanoes are much bigger than the ones we see in the end, for example in Hawaii.

Brendan - Hi. I'm Brendan from Cambridge. How likely do you think we are to see another Pinatubo type eruption which cause the climate to change in sort of our lifetimes?

Tehnuka - That's a good question, but it's not one I know an easy answer for. Unfortunately, forecasting of volcanic activity is still quite difficult.

Arwen - It's really difficult to make predictions. It's very difficult to forecast earthquakes and it's also very difficult to forecast volcanoes. At least with volcanoes, sometimes we have a little bit of warning. The volcanoes that are close to cities like Vesuvius, I continuously monitored. And we hope that we will notice the vibrations, the small earthquakes that will start happening in a few days, leading up to the volcanic eruption. So hopefully, with volcanoes, we'll have a little bit of warning. The question is, will we be able to evacuate people? Is it possible to actually evacuate a city like Naples in just a few days? I'm not sure. It's a very massive city. Earthquakes is a completely different story. I'm not sure we'll be able to predict those. The only thing we might be able to do is get a feeling for how big earthquake will be, once it has started. There's work being done in the United States and if you would know after you've just felt few shakings, if you have a computer programme that can then say, "This is just going to be a small earthquake. No worries" or, "This is going to be a big one." Then the really destructive waves will come maybe 20 seconds later. You'll have 20 seconds to do some important things - maybe turn on some emergency equipment, warn people that they can just move from where - if they're in a more dangerous place, go and be in a more safer place. That will not be a proper prediction, days in advance, but it might give us a little bit of extra safety and just prevent some of the major disasters happening, potentially killing slightly less people than what's happening nowadays.

Fergul - This is Fergul from Cambridge. I wonder if it's possible to tell from the nature of the volcanic gases, what their original origin is, if they're from some chemical reactions with the geology or if they can be traced somehow back to atmospheric gases, way back in geological history or perhaps ground water?

Tehnuka——因此,一些工作我做的是尝试to model where the gases I measured came from but just within the volcano. So, some of this has to do with how soluble a gas is. So, how much it wants to be dissolved inside the magma. Some gases like water are quite soluble. Other gases like carbon dioxide aren't. So, it might not be that unusual for a volcano to be emitting carbon dioxide even though nothing is about to hit then. But when you start seeing for example a lot of sulphur dioxide coming out, that can be a warning sign that the magma has reached the higher level inside the volcano. So, more soluble gas like sulphur dioxide that usually like staying dissolved has depressurised so that the stuff that's keeping it dissolved inside the magma has lessened and it's also starting to come out and that can be a warning sign of an eruption.

Chris - Tehnuka Ilanko.