Shownotes

• History of the Theory of Plate Tectonics — Berkeley
• Alfred Wegener
• Plate Tectonics, mechanisms — Berkeley
• Plate Tectonics animation — Berkeley
• Plate Tectonics
• Online version of "This Dynamic Earth: The Story of Plate Tectonics" by Jacquelyne Kious and Robert  Tilling — USGS
• Paleomap project (with the goal of illustrating the plate tectonic development of the ocean basins and continents, as well as the changing distribution of land and sea during the past 1100 million years) — Christopher Scotese
• Continental Drift – USGS
• Pangaea — Wiki
• Why Does Earth's Magnetic Field Flip — National Geographic
• "When North Goes South" -- 3-D simulation of geomagnetic field reversal — Los Alamos National Lab
• Earth's plates are moving between 1-10 cm a year – Enchanted Learning
• Lithosphere — USGS
• Asthenosphere — USGS
• Convection-driven plate tectonics and the everyday example of convection: boiling custard — Imperial College (this post also discusses plate tectonics on Venus)
• The Great Rift Valley between Africa and Saudi Arabia – Plate Tectonics.com
• San Andreas Fault – Geology.com
• Ep. 110 — Search for Extraterrestrial life and the  Drake Equation (planet habitability might depend on plate tectonics)
• Plate Tectonics on Venus? Rising temps on a planet like Venus could shut them down — Universe Today
• Evidence of past plate tectonics on Mars — Geology.com

Transcript: Plate Tectonics

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Fraser Cain: Hey Pamela, are you enjoying your summer so far?

Dr. Pamela Gay: I’m traveling my little luggage back off right now. [Laughter]

Fraser: Right so whatever you see from the inside of an airplane that is your summer.

Pamela: You know the inside of an airplane can let you see some pretty cool things.

Fraser: That’s true. I know you’re going to be in Seattle, the UK, in China.

Pamela: [Laughter] Then I am going to South America – 3 continents, one of them twice, in addition to our own so that makes 4 continents in one summer.

Fraser: Good. Alright the surface of the Earth feels solid under your feet but you’re actually standing on a plate of the Earth’s crust. The plate is slowly shifting around across the mantle of the Earth.

Over geologic time scales plate tectonics has totally resurfaced our planet bringing continents together and tearing them apart. We know we have plate tectonics here on Earth but what about other worlds in the solar system?

Plate tectonics is one of the coolest stories. It is the lone scientist railing against the establishment proving the theory, bringing the evidence and turning everyone’s minds to the new theory.

Pamela: And it is a theory that is younger than you and I.

Fraser: So tell it! Tell the story! [Laughter]

Pamela: There is a lone scientist as you quite elegantly put it whose name was Alfred Lothar Wegener. He like a lot of other people looked at a globe and went hmm you really can just sort of take South America and fit it very nicely into Africa.

In fact if you have a globe you really hate and you need to do this with a 3-dimensional globe not with a map that has a Mercator projection. Find yourself a really old globe – one that has all the nations of Eastern Europe and Africa completely wrong so you don’t feel bad about destroying it.

Fraser: Right, something with Yugoslavia on it. [Laughter]

Pamela: Right, Czechoslovakia. Take a razor blade to the globe and cut out the land. You can actually rearrange the land masses to more or less form one large mega-continent. This had been noticed by Magellan.

Pretty much as long as we’ve been able to get all the way around the planet in one piece we’ve known that the continent is fit together in a kind of weird way. People looked at fossils in South America and Africa and discovered that on the eastern coast of South America and on the western coast of Africa, two places separated by a whole lot of ocean, we have the exact same fossils.

It wasn’t like it is easy for a hedgehog to hop in the ocean and swim across the Atlantic Ocean. Somehow we were able to get fossils on the same side of both continents or at least on facing sides of the two continents even though the continents were far apart. Coincidentally the continents when cut out of the globe fit together like puzzle pieces.

Fraser: There are mineral deposits that start on one continent and then continue on the other continent. Yeah, it is amazing.

Pamela: Alfred put forward the idea of continental drift that once upon a time, long, long, long ago, like order of 225-250 million years ago back in the Permian Period maybe all the continents formed one giant continent called Pangaea.

Maybe for reasons that he wasn’t completely sure how to explain he said continental drift but there weren’t any forces driving this drift at that period. Something caused the land to tear itself apart and start pulling itself into the continents we know today.

During WW II we as a society set up seismic monitors all over the planet. We increased the seismic monitors as the cold war progressed because you can use seismology to detect something under the ground being blown up.

We would be able to go investigate this and if you scatter seismometers all over the planet you can do 3-dimensional mapping to figure out exactly where underground either an earthquake originated or a nuclear bomb was tested which was the real reason they paid for the technology.

Fraser: How were Wegener’s theories received? He says, knowing the answer.

Pamela: No one believed Alfred. They mocked him openly.

Fraser: Yeah.

Pamela: The planet was the way it was and this is after we’d already accepted things like evolution. This was after we had already accepted things like Earth goes around the sun, sun goes around the galaxy. We understood that the big bang existed.

Fraser: The Milky Way was one galaxy and that those were other galaxies that were moving apart from each other.

Pamela: Exactly, right.

Fraser: We knew about how old the universe and the galaxy were.

Pamela: Yeah, yet poor Alfred Wegener was mocked. People made fun of him. They said he was wrong. He plugged away at it looking for evidence. He looked at well look at all the seismology; there are clear lines of anger on our planet where we have volcanoes and earthquakes originating.

The whole ring of fire – he was able to mark out all these different plate boundaries. If you look at mountain ranges, you can see the different levels of the planet upwelling in these great amazing rifts. You see these when you fly over the continent.

He was able to just look at all these different lines of evidence including things like the flipping of the magnetic field of the Earth in some of these levels. Over time slowly he swayed people to believe him.

Nowadays with GPS we can look out and go aha, England is moving away at a rate of roughly 3 centimeters a year. This is similar to the rate at which your fingernails grow. Now we believe him but like many new ideas.

Fraser: How long did it take?

Pamela: It took about a decade. We’re kind of slow to come around to new things occasionally.

Fraser: It took about a decade for scientists to go from openly mocking him [laughter] to most scientists being onboard with the theory. Why was it so successful?

Pamela: It explained it.

Fraser: It explained it and amazing wonderful evidence.

Pamela: What’s cool is now we can look at maps that are based in part on where we find fossils. We’re able to say we know these continents touched up until the Jurassic Period. We know these continents touched up until the Cretaceous Period.

We’re able to follow – thanks to the fossil record – the divergence of the continents. We’re able to basically figure out well go back to the Permian it’s all one continent.

Over time things migrated out to being what they are today. Even today we can see Saudi Arabia is working on tearing itself apart right now toward becoming its own land mass separate from Asia.

Fraser: Now we have a much better scientific understanding of exactly what’s going on with plate tectonics. What is the story? What’s causing the drift?

Pamela: It’s basically we have a hot planet. Things circulate. As the planet is trying to give off its heat we have this layer of liquid rock basically. We have very heavy lithosphere down at the bottoms of the ocean and much lighter materials making up the continents.

The continents are able to kind of float around atop of a partial melt called the asthenosphere. We have plates made up as lithosphere with the heavy ones down at the bottom of the ocean. All of this is floating on top of this partially melted layer that is moving very slowly at geologic time scales.

We have circulating hot liquid rock underneath. As the heat is released we have the plates moving relative to one another and heat bubbling out in the form of volcanoes at different places along the boundaries of the plates. It’s sort of like you can imagine you have a crusty material on top of a lava lamp.

Fraser: You should really just refer to the boiling custard that we all make, right? [Laughter]

Pamela: Right we found and example the other day online that this is clearly like everyday boiling custard of which I still haven’t seen what boiling custard looks like. I’m going to imagine a big giant lava lamp with crusty nastiness on top of it.

As chunks of the thick part of the lava lamp come up to the surface and well back down, the stuff floating on top of that lava lamp is getting moved around. It’s getting broken apart so that heat can escape.

Fraser: Right and this is just a result of the fact that there’s still a lot of heat escaping from the Earth. Even though the Earth is cooling there’s still a ton of heat down there.

Pamela: Over time the heat that’s being generated from radioactive decays is going to slowly go away as the radioactive material finally uses itself up. Over time the heat that’s still left over from when the planet was formed is going to radiate away.

Eventually our continents are going to lock themselves down in a given place. For now, everything is moving around.

Fraser: We’ve got sort of two situations, right? We’ve got the places where the plates are coming together and we’ve got the places where the plates are coming apart. Why don’t we talk a bit about that?

Pamela: We also have the places where the plates are just rubbing up side-by-side.

Fraser: Let’s look at those 3 examples then. Where do we have them coming apart?

Pamela: Saudi Arabia is one example of places coming apart. We also have the mid-ocean ridge out in the Atlantic Ocean where everything is completely coming apart.

There are all sorts of neat basically black smokers and colonies of really weird critters living down purely off of the heat that’s coming out of this divide down at the bottom of the Atlantic Ocean.

Fraser: It kind of looks like a crease where Earth is coming out and going in both directions. [Laughter] Right, Pamela?

Pamela: Exactly.

Fraser: It’s almost like fresh materials. That’s what it is, fresh materials just spreading out from those creases. Then you’ve got the situations where they’re coming together so what’s going on there?

Pamela: Where the plates are coming together is where we start getting mountain ranges formed. Currently the Himalayas are still in the process of forming. India is still plowing its way northward.

What’s cool is we can actually age where different parts of the planet careened into each other by the height of mountains. The Himalayan Mountains are the tallest mountains in the world and they are the youngest mountains in the world.

India is still moving, still creating these mountains very, very slowly. This is where you have the convergence, you have mountains.

Fraser: Right. Everest is still getting bigger.

Pamela: Everest is still getting bigger.

Fraser: You have situations where you get them sliding side-by-side, just rubbing past each other.

Pamela: This is one of the problems that we have here in America. The whole western coast of California is trying to move. As California attempts to become more equatorial, you end up with all sorts of earthquakes.

Basically the continents build up pressure, build up pressure and we have all kind of experienced this trying to move heavy objects across the floor.

You have a heavy cardboard box filled with stuff on the asphalt of your driveway where there’s a lot of friction. You push and push and eventually it just gives and it slides.

Occasionally you fall on your knees as it suddenly slides way more than you expected. That’s what happens when you have some of these earthquakes.

You have along the fault line pressure building, pressure building and all of a sudden the pressure overcomes the frictional forces between the two plates and the plates slide. You get destruction.

Fraser: I actually live on that same fault. I’m a little more north but pretty much right along that ring of fire right along the coast of the Pacific plate.

We have the exact same risk up here in Canada where we can have really awful huge earthquakes every few hundred years.

Pamela: If you look at a map of the planet that tracks where all of the different motions are going on you have much of America is actively attempting to go west and then California itself is trying to move in new and interesting directions.

We have Australia working on trying to move itself north. We have India still working on trying to move itself. Europe is moving over toward Asia. This is where you have the Euro Mountains and the Alps all along in there.

The Andes Mountains is where you have the edge of a crust trying to move inland essentially.

All these different mountain ranges, all of this is caused by the motions of the plates. It leads to some rather traumatic things both under water and above land that we can see.

Fraser: When we did our show quite awhile ago we talked about the Drake equation. If we were talking about how to expand the Drake equation one of the things that you proposed is whether or not a planet had plate tectonics. That could be necessary for life. I was just wondering why that is.

Pamela: Plate techtonics aren’t so much a requirement for life but a diagnostic of things that are required for life. We have plate tectonics because our planet still has a molten moving circulating core.

It’s these motions inside of our planet that create our magnetosphere, that create the magnetic field around the planet Earth that is able to protect us from incoming cosmic rays. It protects us from the sun and a whole lot of things that could kill us.

Fraser: It also runs the carbon cycle.

Pamela: Right, we have the circulation of it rains, things die, and things end up in the ground. Over time we’re actually flipping over layers of our planet just like you might till a garden.

Fraser: So if we didn’t have the plate tectonics going on the carbon would just all remain on the surface and build up and build up. That sounds kind of familiar. [Laughter] Sounds like some other planet in the solar system.

Pamela: Without being able to sequester carbon away underground first of all we wouldn’t have oil. Second of all we kind of would have a runaway greenhouse effect.

One of the problems that we’re running into right now is we’re circumventing our planet’s carbon cycle. In a perfect solar system things would die on the surface of the planet and the planet would eventually bury them very deep.

It would eventually turn them into things like coal and oil and petrified wood and all sorts of cool things that are far, far away from the surface of the planet. More importantly, they aren’t part of the atmosphere.

Fraser: We’re just pulling them under as one plate goes under another plate. Just take it back down under the crust.

Pamela: Without this we end up with things like carbon monoxide and carbon dioxide and methane and other complex organic badness building up in our atmosphere. Methane conveniently breaks down in sunlight but carbon monoxide and carbon dioxide don’t.

If you get too much of them in the atmosphere the planet will slowly heat up. Right now we’re taking all of that nice friendly sequestered carbon-based material and burning it in power plants. That includes the engine of your car. That’s just a really small power plant.

We’re releasing things that should be buried underground back into our atmosphere and we’re causing our planet – at least in part – to slowly heat up. This is bad.

Fraser: Right. We know we have plate tectonics here on Earth but what about other places in the solar system?

Pamela: When we look at other planets, like Mars and Venus, we don’t see plate tectonics that we recognize. We don’t see the big mid-ocean rifts because they don’t exactly have oceans.

We don’t see the giant mountain ranges that are created from plates colliding so we don’t see basically the diverging and converging plates that we see here on the planet Earth.

We do see evidence for motion. We do see they don’t have perfectly smooth surfaces and not every mountain is caused by a crater. Not every mountain is caused by a volcano.

We do look at these two worlds and see evidence that in the past they did have some level of geologic activity. They may not have had the giant plates that we have but their surfaces certainly moved themselves around and their surfaces certainly were different in the past.

It’s just that the majority of the restructuring happened due to volcanism which we talked about in our last episode.

Fraser: Right but we talked about the carbon cycle here on Earth and we know that Venus has no plate tectonics so is that part of the problem for Venus?

Pamela: Venus is just a whole variety of badness.

Fraser: It’s closer to the sun.

Pamela: It’s close to the sun. Once upon a time it had water on it but that water got too hot and ended up becoming water vapor. Water vapor is a greenhouse gas.

The carbon on the planet ended up in the atmosphere. Now it has an atmosphere that is rich in organics that trap the heat on the planet. It rains sulphuric acid which is just a whole new form of badness.

It has hydrochloric acid. It has basically acid in liquid form falling out of the sky. The thick impermeable layer of clouds that we can’t look through in the optical, those clouds also trap infrared heat.

Sunlight goes through the clouds and heats up the planet. The rock of the surface of the planet tries to radiate away that heat in the form of infrared.

The infrared just basically reflects back off of the clouds building up so that you end up with Venus hotter than the planet Mercury.

Fraser: But that heat contributes to the fact that it has no continental drift, right?

Pamela: Actually that is part of what’s going on with Venus. You don’t have the same huge temperature gradient that we have here on Earth. On Earth we have circulating hot liquid rock deep in our planet. As it rises, gives off its heat and settles back down it’s this convective process that is driving plate tectonics.

On Venus you don’t have the huge temperature gradient as you come up through the rock and then hit really hot atmosphere; really hot surface of planet.

Without the huge temperature gradients that you have here on the planet Earth you don’t have any circulation. You don’t have the driving forces that cause the plates to move.

Instead you just end up with occasionally the entire planet resurfaces itself all at once as it gives off its heat.

Fraser: You have no more carbon cycle so no way trap the heat back under. Things just stay the way they are.

Pamela: You end up with a planet that we have trouble landing robots on because they’d melt quickly.

Fraser: [Laughter] Yeah, then what about Mars?

Pamela: Mars is tiny. People really don’t I think in general understand how small Mars is. Because it is tiny it never really held onto its heat.

It’s sort of the difference between taking a giant loaf of bread out of the oven and taking a completely flat pan of cake out of the oven. That really thin flat pan of cake is going to cool off much faster than the big loaf of bread just because it has more surface area compared to the volume. It can radiate its heat through that surface area much faster.

Mars just cooled off. It did have some heat, some liquid rock in its center. It just wasn’t enough to get the whole surface of the planet moving around. We can see evidence that it once had liquid rock in the form of the Olympus Mons volcanoes.

We have giant volcanoes all in one place all on the surface of Mars, not that they’d be anywhere other than the surface of Mars. They’re all in one clustered area. They were able to grow to be some of the biggest mountains in the solar system.

Fraser: Right that’s the Tharsis Bulge.

Pamela: Yeah, one giant hot spot on the planet just fed and fed the growth of this mountain set.

Fraser: Okay like here on Earth we’ve got the Hawaiian hot spot. You’ve got this long mountain chain or island chain of volcanic islands and that’s one hot spot. You’ve got the continental plate floating over the top of this hot spot and moving.

You get cracks in the surface makes an island and then the plate moves and you get another island and so on. I guess on Mars it just never moved. It just kept going and going and going for billions of years.

Pamela: What’s really cool is like what we said in the last episode the giant valley set that’s beside Olympus Mons – this is Valles Marineris – was formed with well if you relieve the pressure underneath the crust, if you remove all of the liquid rock from underneath the crust, it’s going to slump. It’s going to crack.

That was enough to start this valley. The valley was also cut by water and it’s a complex geologic feature that people are still working to fully understand but I just love the idea that you grow the planet in one place and you have to shrink it in another.

Fraser: Last week we talked about cryo-volcanism. Is there sort of similar things happening with like Europa?

Pamela: One of the really cool things about Europa is you can actually see how the different parts of its crust move around. You can see the cracking, the striations; you can see the places where the different sections of the ice move apart from one another.

You end up with upwelling of fluid. This is very much like the diverging areas that we have at the bottom of our ocean except it is occurring at the surface of a planet that we can conveniently image much more conveniently than we can image the bottom of our own ocean.

Fraser: Right and there are big long cracks where you can see the new materials come up from underneath and it is spreading.

Pamela: You can see the effects of where different places move relative to one another where you can actually see where a crack used to be a straight line.

Two separate sections of ice moved parallel to one another and that crack got split and now one section of the crack is further north than the other section of the crack.

Fraser: I think about when you break through or maybe you’re walking through a really thin ice puddle with boots on and the pieces of ice crack open. Chunks of ice floats slide across the top of other ones. It’s sort of a very similar situation going on but it’s with water and ice not rock.

I guess the underlying mechanisms are all just the same. You’ve got a difference of energy, you’ve got liquid, and you’ve got solids.

Pamela: You have circulation. You have convection. The physics is the same and what’s cool is by changing how much gravity there is and how viscous the material is, you’re going from lava to water.

You’re also going from high gravity Earth to low gravity Europa. You can end up with very similar physics. It’s not identical, but it’s close and it’s cool.

Fraser: It’s really cool. I think that covers our journey into plate tectonics, way out of your field Pamela. [Laughter] But thanks a lot for.

Pamela: I’ve been hanging out with some really cool geophysicists periodically. If you ever want to meet really cool scientists who aren’t astronomers, go hang out with a geophysicist.

Fraser: I guess the funny thing sort of is that – a friend of mine was talking to me about this – he says you guys go everywhere because it’s all connected. You have to.

We’ve got a bunch of shows planned on biology because it is connected to astronomy, to the search for life and exploration of the solar system and plate tectonics, geology, and all that stuff and physics, quantum mechanics. It’s all connected.

Pamela: This is where the word universe comes in because everything is included.

Fraser: Right, you talk about everything in the universe. Exactly, I hope the listeners appreciate the wide range of topics we get to choose from.

This transcript is not an exact match to the audio file. It has been edited for clarity. Transcription and editing by Cindy Leonard.

Shownotes

Volcanoes on Earth

• USGS Volcanoes website
• Volcano World (latest eruption info, FAQs, lesson plans) — Oregon State
• Volcano.com – (images, info)
• Magma – molten rock found beneath the surface of Earth — Wiki
• Lava – molten rock expelled by volcanic eruption — Wiki
• Lithosphere – USGS
• Asthenosphere – USGS
• Shield Volcanoes -- USGS
• Volcanism in Iceland
• Mount St. Helens
• Krakatau Volcano, Indonesia
• Santorini Volcano, Greece– NASA Earth Observatory
• Santorini and the "Atlantis" eruption — National Geographic
• Mt. Vesuvius and Pompeii
• Mt. Pelee, West Indies
• Hawaiian Island Volcanoes – USGS
• Hydrothermal Vents and Life in the Ocean
• "Ring of Fire" — USGS
• Pyroclastic Flows — MTU

Volcanoes in the Solar System

• Io; "Alien Volcano" — NASA
• Volcanoes on Venus — Oregon State
• Venus' Volcanoes — Universe Today's Guide to Space
• Good imagery of Venus' volcanoes — GSU
• Volcanoes on the Moon — Universe Today's Guide to Space
• Volcanoes Rocked the Far Side of the Moon – Nat Geo
• Volcanism on Mars — Oregon State
• Olympus Mons Flyover — Goddard Space Flight Center
• Vallis Marineris — GSFC
• Volcanoes on Mars — Universe Today's Guide to Space
• Possible Cryovolcanoes on Titan — Universe Today
• Cryovolcanoes on Europa and Triton -- Absolute Astronomy
• "Enceladus South Polar Stipes Spew Warm Water" – The Planetary Society
• Ammonia Volcanoes on Charon — The Planetary Society
• Possible Volcanoes on Pluto — Space.com

Transcript: Volcanoes, Hot and Cold

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Fraser Cain: Another trip to UK, anything more coming up?

Dr. Pamela Gay: Yeah, this weekend I’m going to ConvergenceCon in Minneapolis and then I’m going to the Microsoft Faculty Summit and then I’m going to the ‘Eclipse of the Century Cruise’ in Asia. Then I’m going to the International Astronomical Union in Brazil.

Fraser: I think I’m just going to cry. [Laughter] People are like what’s going on with the crazy schedule? This is why.

Pamela: We’re so sorry guys. My dogs have started to hate my luggage. They know what it is now.

Fraser: Oh really?

Pamela: Yeah.

Fraser: But we’re here, we’re recording so let’s get on with our show. You’re familiar with volcanoes’ erupt events where hot magma escapes the Earth’s interior, sometimes with disastrous affects. Did you know that volcanoes have shaped many of the planets and moons in the solar system and not just our own Earth?

Just in the last few years astronomers have discovered that there are cold volcanoes in some of the icy objects in the outer solar system. I guess we should just start with the familiar volcanoes that we’re well aware of.

When we see a volcano with lava and [laughter] rocks and ash coming out, what’s the process that’s going on?

Pamela: For one of many different reasons there is typically a thin spot in the mantle of the Earth. Magma is able to flow up and flow towards the surface. Depending on how viscous it is, how easily it flows or not you either end up with this very thick sludgy material building up and building up until it explodes like Mount St. Helens did. Or you end up with it just kind of leaking through the surface and spreading out making nice friendly volcanic islands like we see in Hawaii.

Fraser: Where is the magma, the lava coming from? Is there just like some vast ocean of rock inside the Earth?

Pamela: Not the way most people think of it. There are many different layers to the Earth. There is indeed a deep down layer where everything is pretty much molten rock.

Above that we have two different layers. At the very top which is pretty much where we live we have the lithosphere which consists of the crust and the upper part of the mantle.

The crust and the upper part of the mantle are floating essentially on top of – and I apologize to the geophysics community for my pronunciation – the asthenosphere which is pretty much solid but if you look at it in geological time scales it is slowly flowing.

As these two things move and flex and so on, they occasionally end up with thin spots. These thin spots between these two different layers allow magma to come up. You can get this in a variety of different ways. You can have places where the plates are diverging or converging and in the process you get cracks and weaknesses.

You can also end up with what we refer to as magma plumes. This is where you end up with this single hot spot that wields itself all the up to the surface like what causes the Hawaiian Islands.

Fraser: Right and those could be almost anywhere.

Pamela: Those can be absolutely anywhere. We in fact have one here in North America underneath Yellowstone that’s forming one of the big calderas in North America.

Fraser: Okay so you’ve got this hot magma coming up from the mantle making its way through the crust and you had said that the viscosity of the magma has an effect on what kind of volcano you get?

Pamela: Depending on how you end up with either a large magma chamber under the surface or a nice steady flow from lower levels and the composition as well you end up with magma – you end up with lava – of different compositions and different viscosities.

Just like corn syrup will flow down the counter on a cold day in a very different way from water that isn’t frozen, lava depending on its consistency will also flow and erupt differently.

You can also end up with different amounts of gas trapped inside of the lava. It’s that heated gas that at times can make the most explosive eruptions.

Fraser: Let’s look at a couple of volcanoes. Some of the ones that we’re familiar with is the Hawaiian Islands as we mentioned before.

All of the observatories are up on Kilauea with its lava fountains and pouring into the ocean. What’s going on there?

Pamela: In general the Hawaiian Islands and in fact also the volcanoes on Iceland are shield volcanoes. They have the low viscosity lava.

Lava comes up through the surface, flows down the sides of the volcano building it up and up until you end up with these beautiful basically mountainous volcanoes like we’ve all seen in the pictures with the observatories.

Fraser: I’ve actually been on the big island of Hawaii and stood on some of the lava flows. It’s quite amazing. It looks like someone took a river and froze it with like streams and rivulets.

It’s quite amazing. There is this other stuff which is sharper and jagged which looks like sort of a crumbling pile as it goes down the hill. It’s quite amazing to see this stuff and touch it, it’s so smooth. You can imagine it’s flowing so fast, not like water but it’s still flowing rather quickly.

Pamela: Part of what makes up these differences is how much silica is in it. When you see the sharp glassy – in fact you can even get volcanic glasses – when you see this, that’s when you have more silica in one part of the flow.

In general with the shield we get a lot less silica. That’s where you end up with these nice beautiful experiences like the one you were able have.

Fraser: I highly recommend that. If anyone has never been to see the volcano observatory on the big island of Hawaii, it’s one of those places you’ve got to go at least once in your life.

Pamela: I have to admit this is where you’re the expert and I’m not.

Fraser: Aha!

Pamela: I’ve never been there. I’ve been to Hawaii but I never really got to leave the conference facility.

Fraser: Oh no. That’s right that was a couple of years ago at the AAS meeting that was on Hilo, right?

Pamela: Right.

Fraser: Oh, you should have gone. Okay, I won’t berate you this episode. Then how is that different from Mount St. Helens?

Pamela: Mount St. Helens is more of a high viscosity mountain. This is where it is really cool to watch the past six years of gallery images that have been taken from the volcano observatory.

There’s actually a webcam that allows you to watch Mount St. Helens from day to day. It’s a much higher viscosity and you end up with these building slowly growing at basically truckload a minute in some cases worth of lava bulges. These bulges build and build until the pressure beneath builds to the point that it explosively erupts.

Back in 1980 we essentially had a third of the mountain just decide it was going to go up into the atmosphere. It was going to rain itself down across North America and all due do this high viscosity lava that just built up over time.

Fraser: I’m sure a certain portion of our listening audience will have Mount St. Helens memories or I guess of Pinatubo memories. I live on the west coast near Vancouver and that’s pretty close to Mount St. Helens and a lot of people remember the bang.

They could hear the bang and within a couple of days we were getting lava in the rain coming down – not lava but ash landing. It was covering the cars so we had like this powder of ash everywhere.

I have some family down near Portland and after the big eruption they went down and scooped up a jar full of ash and pumice stones and gave it to me. I’ve still got a jar filled with bits of Mount St. Helens. The kids really like it. It’s quite neat stuff to play with.

Pamela: That was one that I remember as a little tiny kid living down in the Newberry Park part of southern California near Los Angeles. We actually had a layer of dust on our cars. The effects of these volcanoes can be continent-ranging in some cases.

While Mount St. Helens didn’t significantly damage the environment or the ability of anyone to live, it just made everything a little bit dirty and a little bit colder. In the past these giant eruptions have actually been blamed potentially for different extinctions.

Fraser: What are some examples of a bigger eruption? I guess Krakatoa, right?

Pamela: Right, so there’s Krakatoa that happened in the Indonesian Islands. There are also the islands of Crete where you can see half the islands in that area that disappeared.

It is rumored that some of the myth of Atlantis is actually tied to having a volcano go off and having an entire civilization that was living on that island destroyed during the eruption.

On a city scale we can look at Pompeii and Herculaneum and how they were destroyed by Mount Vesuvius going off and pyroclastic flows flowing over the cities and filling in the buildings while people ran for their lives.

Fraser: Okay so what’s a pyroclastic flow?

Pamela: This is where you end up with mud and lava and ash forming this very fast flowing sludge down the side of the mountain that then will actually solidify encapsulating and protecting everything that’s inside of it.

These are extremely dangerous because they flow so quickly. You can’t escape them. It’s not like getting hit with an avalanche where once the avalanche has run over you, you have some chance of swimming up to the surface. This just kills you.

Fraser: Right it’s like a thousand degrees and you just get cooked just like that by hot mud. Ugh, way to go.

Pamela: Yeah, it’s sort of like the asphalt truck getting you at the end of the day.

Fraser: I know that there was an island in the Caribbean where about 30,000 people died the beginning of the 20^th century. Mount Pelee I think and it was the same situation.

It just killed 30,000 people just in about ten minutes and the whole city was gone. That’s one of the greatest risks from volcanoes these pyroclastic flows.

Once again, the universe has figured all kinds of innovative ways to kill us so this is just one of them. [Laughter]

Pamela: One of the problems that we face today is we can never say for certainty when any given volcano is going to be completely extinct or when it is going to decide to do like Mount St. Helens did and just send large chunks of mountain into the atmosphere and cascading down the sides of what’s left of the mountain.

Human beings live near volcanoes. Mexico City is in danger; Seattle is in a certain amount of danger. There are cities in Africa and in Indonesia that are all in danger from various volcanoes that while not too active still have the potential to just suddenly rear their ugly heads and destroy a few thousand people’s homes or a few hundred thousand people’s homes.

Fraser: What are the – this is going to lead on to us taking this conversation out to the solar system – how do volcanoes shape the evolution of a planet over the long term?

Pamela: It’s part of the whole plate tectonics process which we’re going to talk about more in our next episode. At the bottoms of the oceans we have great trenches that are part of the continental plates pulling themselves apart.

Where the plates are pulling themselves apart you end up with magma bubbling up. You end up with these great smoky regions with amazing life that requires no sunlight to thrive.

It’s all living off of the thermal energy coming out of these magma escapees I guess, these regions where the planet is recreating itself, resurfacing itself at the bottom of the ocean.

Now at the other side you also end up with places where one plate is plunging underneath another plate. Here you also can end up with as gases are escaping, as everything is heated up and rubbing together and where you end up with thin areas in the mantle you can also end up with volcanic activity.

This is what actually creates the whole ring of fire area that starts with Indonesia, works its way up the eastern coast of Asia round Japan, cuts across to Alaska and then comes back down across the Seattle mountains, the Vancouver ones that you’re dealing with.

Fraser: Uh-Oh. [Laughter]

Pamela: Yeah it’s all part of the ring of fire. This is just all active movement of the Earth’s plates. Like I said we also do end up with these isolated hot spots that are a bit harder to understand.

Why is it that right in the middle of the plate you end up with a particularly thin spot? Occasionally you’ll hear geophysicists saying maybe that’s where a really big asteroid hit the planet and it just hasn’t quite healed itself.

In general we think this is from magma plumes where you just end up with a nice really, really hot convective cell inside the planet that has hot magma flowing up and circulating. Eventually it wears away at the crust until it is able to escape out and forms large chambers.

The chambers build and build until you end up with some sort of either an explosion or a gentle flowing. This is where we can end up with the Snake River Range through the Rockies which you can look at the mountains and see this area has been completely filled in.

Fraser: I guess we want to take this out to the solar system. Where are some places that are actively volcanic right now but not on Earth?

Pamela: Io is probably the most dramatic example. This is a moon of Jupiter that is in an orbit that is in a unique resonance. It’s getting basically pulled into an elliptical orbit that it can’t escape because it’s getting yanked about by the other Galilean moons. It’s getting yanked around by Ganymede and by Europa.

Through this process it’s constantly getting flexed. It’s like taking a basketball and bouncing yourself up and down on it so that it constantly gets a little bit flatter, rebounds to its normal shape. It gets a little bit flatter, rebounds to its normal shape.

The constant flexing heats up the interior of Io and that heat has to escape. The way it escapes is through massive volcanoes. This little tiny moon, it is a little bit smaller than Earth’s own moon, actually has mountains on it larger that Mt. Everest.

These mountains are all volcanically built. When we look at it we can’t find craters without looking really, really hard because the surface is constantly getting renewed by all these lava flows.

Fraser: Then there are several volcanoes going off right now?

Pamela: At any given moment, every time we look at this planet we’re able to see new changes to its surface. It’s really the most exciting if toxic surface in the solar system.

Fraser: There are some amazing pictures of volcanic plumes hundreds of kilometers into space raining down lava around the moon. These awful bruises where fresh material has come out from the moon and spread out and resurfaced an area, Io is off the charts. To think that we’re volcanic, that’s nothing.

Pamela: It’s not the only dramatic activity that goes on. When we look at the planet Venus, it was originally thought that we don’t see anything that looks like the rift valleys that we see here on Earth.

We don’t see anything that looks like mid-ocean trenches we have on Earth. People said we don’t see the plates therefore it must not have plate tectonics.

Then we started counting craters. You can judge the age of a surface by looking at how many craters are on it. The older the surface is, the more craters it has and the younger the surface the fewer craters it has.

Venus’ surface isn’t entirely old. It is actually only a few hundred million years old. What we think happened was the heat inside Venus built up and built up until essentially the entire surface restructured itself in a massive many different volcanic eruptions.

We do see the signs of volcanoes. We do see the signs of collapsed calderas. We do see the signs of the types of rifts you get associated with volcanoes. It’s just a different type of volcanism that’s present on Venus.

Fraser: Right, you’re not seeing this sort of gradual volcanism like we have here on Earth. It was almost like it was something catastrophic that hit a large part of the planet at roughly the same time and then it was done. Maybe it had several of these events in the past.

Pamela: That’s what is thought. In reading up for this show one of the analogies I saw was that it’s like the everyday boiling of custard. I have to admit that I took exception with this analogy because I don’t boil custard every day and in fact have never boiled custard.

For those of you who have boiled custard the way you get these churning nodules of stuff rising and settling, that apparently resembles how Venus resurfaces itself.

Fraser: Hmm, I’ve never boiled custard so I really don’t know. [Laughter]

Pamela: Well apparently there is a geophysicist out there that thinks everyone boils custard every day.

Fraser: [Laughter]. And then so it’s a very familiar thing, right? Now there’s Venus and what about the moon? Is there any volcanism on the moon?

Pamela: Not today. When we do study the moon and we look at what its surface composition is made of and in fact look at its surface in detail, we do see many of the same features that we see here on Earth tied up with volcanoes.

We do see volcanic events. We do see tongues of lava. So in the distant past when it was still a much more liquidy world it did have magma escaping through its surface.

It does have the basaltic material that is characteristic of lava. In fact a lot of the dark stuff in the moon is from stuff that escaped in the past from inside of the moon.

Fraser: A lot of those seas, right the Mare (Maray)? Is that how you say that? They are volcanic events and those are different from the craters.

Pamela: The other most notable example in our solar system probably of lava escaping is on Mars where we have the Olympus Mons complex of volcanoes.

Fraser: Right, no question that’s a volcano.

Pamela: The flyovers are spectacular because even from the spacecraft you can see wow that’s big. Anytime a mountain is impressive in size while you’re orbiting the planet that’s a big mountain.

Fraser: Well the biggest mountain in the solar system is Olympus Mons.

Pamela: Right and the pressure of the lava escaping and in fact the effects of the surface slumping as the lava escaped is thought to be part of what caused the Valles Marineris Rift Valley.

There are canyons that are due to water but we think that some of the starting of these things was caused by the rifts, the tearing apart of the surface as the magma moved from being inside the planet to building up the Olympus Mons volcanoes.

Fraser: Mars is a lot smaller than Earth so how is it possible that Mars has a much bigger volcanic mountain than we have on Earth?

Pamela: That’s actually the reason it can be bigger is it’s smaller. Here on the planet Earth as the lava escapes gravity pulls it down. Gravity itself limits how high mountains can get by essentially causing them to crumple under their own weight if they get too big.

On Mars where you have less gravity, and even on Io where you have much, much less gravity, you’re able to get these huge volcanoes because you don’t have gravity pulling all the material down and flattening the mountains if they try to get too tall.

Fraser: I know that with the Hawaiian Islands they are constantly sinking because the weight of the mountain is sort of saddling into the Earth, except for the ones that still have lava coming out of them.

They’re still growing because amount of lava coming out is faster than they’re settling down and causing this big depression around them. With Olympus Mons I guess there’s so less gravity they can just get taller.

Pamela: Right this is where some of the Pacific Atolls, the big doughnuty coral reefs are the mounds of extinct volcanoes. It’s not just that erosion destroyed them they also just sank into the ocean.

Fraser: Hmm. There’s Olympus Mons and there are a few other large volcanoes on Mars. Is there any evidence that there is volcanism happening today?

Pamela: Yes and no. In terms of big flashy volcanoes there’s no evidence. Just like you can end up with small steam vents you can end up with areas of hot springs which are again related to volcanic-type activities.

A lot of times these smaller events release methane. On Mars we do see that methane in the atmosphere. We think it’s due to some sort of still active geology on this planet.

Fraser: Or life.

Pamela: Or life but being ever skeptical as we’re supposed to be.

Fraser: Yeah, let’s say it is volcanoes. Okay are there any other interesting places, Europa?

Pamela: Well yeah and this is where we left out some of the coolest of the cool because we have ice volcanoes as well, cryo-volcanoes.

Fraser: That’s not what’s going on with Europa is it?

Pamela: Europa is actually cryo-volcanism. This is where you have a silica-based world with an iron core but it’s coated in water. As it gets flexed through the same affects that are affecting Io its watery surface is constantly cracking and resurfacing.

Occasionally you’ll end up with geysers of water as well. All of this is going on as a form of cryo-volcanism but some of the flashiest examples of cryo-volcanism actually aren’t here but rather are orbiting instead around Neptune and Saturn.

Fraser: Is it almost like on Europa where it may have this ocean with this crust of ice around it, it’s almost it’s the same thing. The crust is cracking open and water is coming out and it’s just like lava except it is water.

Pamela: That’s exactly what it is.

Fraser: That’s really cool.

Pamela: The first example we actually had of cryo-volcanism wasn’t the big ice Europa but instead it was Neptune’s moon Triton. When Voyager flew past it, it saw these strange geysers of icy materials being sent off into space.

Since then we’ve found this in more and more different places. Saturnian’s moon Enceladus is perhaps one of the coolest examples of this. Its geysers actually appear to be part of what’s constantly restocking Saturn’s moon with small icy bits.

In these cases you have a crust of some sort of solid material like water and beneath it you have volatiles and you have liquid water. The volatiles and the liquid water force their way up through the surface and erupt just like lava erupts through much more rocky-based volcanoes here on the planet Earth.

As the material shoots off into space it starts out hundreds to sometimes thousands of degrees warmer than the icy surface. It then freezes rapidly. When it doesn’t have escape velocities it rains down as chunks of ice.

The force of the explosion can actually send this material into the space between the moon and the planet that it is orbiting around creating rains and debris trails. This is just another way to pollute the space but in a very cool way.

Fraser: Right and we have evidence of Saturn’s Enceladus also possibly a couple of other of Saturn’s moons as well might be contributing material in this way.

Don’t astronomers think that maybe even Pluto and Charon have ice volcanoes as well?

Pamela: Yes. Here we think Pluto and Charon and even other Quiper Belt objects. There are now people playing with the idea that with some of these icy chunks of stuff that people are arguing if they are planets or minor planets or plutinos or dwarf planets – choose whatever name you want – these icy bits in the outer solar system are mostly ice.

They do have rocky cores. They do have radioactive materials within them. Just like the planet Earth has its molten core – because we have so much heat being released through radioactive decay – there are people who think that with some of these Quiper Belt objects radioactive decay of material within them can lead to cryo-volcanism.

You don’t necessarily have to have tidal flexing like we see with Enceladus or Europa. It could be that just having a normal mix of radioactive material within one of these icy bodies can lead to cryo-volcanism in the outer solar system.

Fraser: Hmm. I can just imagine as astronomers start to find some extrasolar planets, like Earthlike worlds, I’m sure they’ll start to find super heavy worlds orbiting their suns very close in sort of in the same way they started to find the hot Jupiters.

You can just imagine the tidal forces that would be going on in some of those worlds. They must just be in constant states of eruption like Io.

Pamela: You can imagine something the size of Earth or Venus that is undergoing the same flexures as Io and the same dramatic volcanism as Io.

A planet that is basically nothing more than a slab of stuff attempting so solidify its crust that’s constantly getting overwritten with explosive magma.

Fraser: As you said next week we’re going to talk about plate tectonics and sort of study what it is here on Earth.

Then once again we’ll try and look around the solar system to figure out where else plate tectonics have had a role and why not if it’s not there.

This transcript is not an exact match to the audio file. It has been edited for clarity. Transcription and editing by Cindy Leonard.