You’re familiar with volcanoes, eruptive vents where hot magma escapes the Earth’s interior – sometimes with disastrous effects. But did you know that volcanoes have shaped many of the planets and moons in the Solar System, not just our own Earth? And just in the last few years astronomers have discovered there are cold volcanoes on some of the icy objects in the outer solar system.
Volcanoes on Earth
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Fraser Cain: Another trip to UK, anything more coming up?
Dr. Pamela Gay: Yeah, this weekend I’m going toin 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?
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.
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?
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 20th 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 ofinto 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.
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