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Video Transcript - Volcano Geochemistry - Windows to Earth's Interior

Maggy Benson: When you [00:00:30] think of volcanoes you might imagine mountains towering

over the landscape, lava flowing towards villages, and geologists on

mountainsides measuring seismic activity. But, most volcanoes are hidden

thousands of feet under the sea. These volcanoes erupt and eject magma, just

like the volcanoes on land. So how do scientists study them? Geologists must

gather evidence from underwater. Today, we'll see how Smithsonian geologist,

Dr. [00:01:00] Elizabeth Cottrell, uses volcanic rocks from the sea floor to learn

erupt out of volcanoes? [00:01:30] Is it smoke, rocks, glass, mist, lava, or

magma? Take a moment to think about it and put your answer in the window to

the right.

Maggy Benson: While the results are coming in let's go to our special guest. Today we have with

us Dr. Elizabeth Cottrell, geologist here at the Smithsonian's National Museum

of Natural History. Thanks for joining us Liz.

Liz Cottrell: [00:02:00] It's great to be here.

Maggy Benson: So as a geologist here, you're actually more specifically an igneous petrologist,

that's a mouthful. Can you tell us what an igneous petrologist does?

Liz Cottrell: Sure can. As a petrologist I study rocks. Petrology the study of rocks. An igneous

Liz Cottrell: Yeah. Lots of our viewers may have granite countertops right in your kitchen.

Maggy Benson: Great. So let's go to our results. They're kinda split but 50 percent of our viewers

that glass does not erupt out of volcanoes. What do you say?

Liz Cottrell: Glass does erupt from volcanoes, in fact, the thing that does not erupt from

[00:03:00] a volcano is smoke. Smoke does not erupt from volcanoes, though

you can be forgiven for thinking that it does, because of the images we see of

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volcanoes do look like big eruptions with smoke plumes. What I have right here

in this can is the material that came out of Mount St. Helens when it erupted

here in the United States in 1980. Now I'm gonna dump this out on the table.

Maggy Benson: Huh, there's ...

smoke that's generated by fire but if this were to hit you in the face it would

really hurt.

Maggy Benson: Yeah, that would not feel very good.

Liz Cottrell: No, and it's full of glass. Glass that comes out that's really rapidly quenched

magma.

Maggy Benson: Interesting. So [00:04:00] I know that lava definitely does come out of

volcanoes, is that right? And I see a piece that looks familiar here.

Liz Cottrell: Yeah. You might be familiar with this if you've ever been to Hawaii, for example,

this is pahoehoe lava from Kilauea and what we have here is this glassy surface,

the magma comes out of the volcano and then once it does it's lava and can

this planet, but the majority of the planet is solid rock. This solid mantle, that's

the biggest volume of our planet. Now it's solid not because it's cool, [00:05:00]

because it's actually extremely hot. The reason it's solid is that it's under

incredible pressure. So if we're some atoms down in the Deep Earth and we're

pushed together-

Maggy Benson: You go together.

Liz Cottrell: And we're pushed together under great pressure, we're pushed together to

make a solid. Now what's really challenging to understand is that this solid, over

long time scales, flows. But it's incredibly viscous. You can imagine taking a jar of

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honey, for example, and opening it and putting it [00:05:30] upside-down in

your freezer. Now definitely, you might get in trouble with your mom if you do

this at home, but if you do try this experiment you'll see that the honey does

flow over time, even though you could still bang it and crack it with a hammer.

reaches the surface?

Liz Cottrell: Again, it all has to do with pressure. The pressure continues to become less and

less, as you move up. If you've ever been swimming in the bottom of a pool and

you feel that pressure on your ears, you know that when you have the weight of

something above you it puts you under pressure. As this magma comes towards

the surface the pressure is released. So what I have here is a perfect

supermarket [00:06:30] metaphor for a volcano. A great experiment that you

can do at home. We have here seltzer water, and we all know that from having

drunk soda at any time, that the contents are under pressure. It always says,

"Warning, contents under pressure." And the gas, carbon dioxide, is dissolved in

Maggy Benson: It's all right.

Liz Cottrell: But this is exactly how a volcano works, and exactly why you don't want to be

near one. Now, let's take a look inside our bottle here. You can see all these

bubbles desperately trying to get out towards the surface. This, these, carbon

dioxide, in this case, is buoyant, it [00:07:30] nucleates into these bubbles, they

are wanting to escape so quickly that they take the magma, the water, with

them and erupt it out the top. So in a volcano the magma is brought rapidly to

the surface by these bubbles expanding, is ejected from the volcano and the

magma cools very quickly, to a glass. And that's what we have right here, we

have a great example of one here, this is a pumice from a volcano called

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Liz Cottrell: Yep. And what [00:08:00] you can see here, are these big vesicles, these giant

bubbles. These bubbles are trapped gases from in the Earth that have rapidly

expanded and thrown this magma out into the air and it cooled so quickly that it

made a glass. This is volcanic glass, it's called pumice. And so these, these

you can see that glassy crust, you can see that rapidly, what we call, quenched,

rapidly cooled exterior that gives it this appearance, and then what happened is

it cooled quickly and then those gases inside continued to expand. Pushing and

breaking the crust and this is actually called a bread crust bomb. We call it a

bomb because, "kaboom," it's a bomb, but the bread crust is due to that

texture.

Maggy Benson: So these pieces of volcanic glass, can I call them that?

Liz Cottrell: Mm-hmm (affirmative).

Maggy Benson: Look very different than this material that you have here. It's much shinier.

Liz Cottrell: Yes. And this is different. This is really my favorite kind of volcanic rock. This is

[00:09:30] and it's got this shiny look to it because it cooled so rapidly.

Essentially the water on the ocean floor is extremely cold, about 4 degrees

centigrade. This has erupted under pressure, so if we go back to our soda bottle

and we see those bubbles coming out essentially what's happened here is that

we've kept the pressure on a little bit by being on the ocean floor, and a lot of

these gases are still trapped in here cooled really rapidly to make this shiny

glass. It's not so different than window glass actually.

Maggy Benson: [00:10:00] Interesting. So as an igneous petrologist you're really studying these

rocks that come out of volcanoes but by doing that you're also understanding

the inside of the Earth as well.

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Liz Cottrell: That's correct. Volcanoes are really our windows into the Earth's interior. We, as

people, can't get down deep into the Earth to sample. So we are really like

detectives. We're using the clues brought to the surface by volcanoes to try to

understand what was underneath the volcanoes, how our inner Earth is

information.

you jump into a volcano that has no magma and end up in the center of the

have ever drilled or dug is only about fifteen kilometers depth, that's [00:11:00]

on the order of several miles, maybe 5 ... 5 miles. That's because of the

incredible crushing pressure, so when we go down into these really deep mines

it's really hot, and if you go down in the Earth there's no open caverns, it's all

very high pressure. If you were to jump into a volcano you would end up in what

we call the plumbing system. Just like you have under your sink, you have the

volcano and down into these long plumbing system that variably fill with

Maggy Benson: So where do you get these rocks. I know you said they're your favorite, how do

you get them?

Liz Cottrell: You have to get to the middle of the ocean. And so that's really difficult. The

volcanoes are several kilometers depth in the ocean and so I've had the

opportunity to go to see, on a research ship, and go to these long chains of

volcanoes that are all [00:12:00] along the ocean floor, like big mountain ranges.

We know where the volcanoes are and it's pretty low tech, we take a big bucket

you just saw a picture of this kind of big steel bucket we throw it over the back,

we pay out thousands of feet of crane cable, and if you can imagine it's about 10

thousand feet. So imagine a mountain, if you've ever climbed a mountain

10,000 feet high, and many of our viewers at home probably have not climbed a

mountain that high, we drag a bucket along the ocean floor and then we reel it

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Maggy Benson: Interesting. With this methodology [00:12:30] you must be out at sea all the

time collecting these rocks.

Liz Cottrell: Luckily, I work here at the Smithsonian. At the National Museum of Natural

History were we have this incredible collection of volcanic rocks. We have the

world's largest collection of sea floor rocks, about thirteen thousand sea floor

volcanoes sampled in this collection, and the great thing about it is I can go in,

internationally, researchers come and borrow from our collections all the time.

It's an incredible resource, because when we go to sea it costs many millions of

dollars for one of these expeditions, and so we want to be really ... treat these

rocks with care and keep them for all time.

glasses. Now even though it's a rock, when it's that thin it's transparent to light.

We can look right through it-

Maggy Benson: You can actually see right through.

Liz Cottrell: These are some beautiful images you're looking at now of chips of volcanic glass

that are transparent to light. Then we can go and throw an entire analytical

arsenal at these glasses. We'll look with something called an electron

microprobe, which shoots a beam of electrons [00:14:00] down at the sample.

And then x-rays are readmitted, that gives us the chemical composition of our

glasses. We can look at them with infrared spectroscopy to see the dissolved

volatile contents that we were talking about before. The carbon dioxide, the

water. And then we can look with x-rays and even see the speciation of

elements, the valence state of elements in the glass. So we can really hit them

with whatever we've got, once we've got them back on land.

Maggy Benson: So interesting. So I wanna go back to the location of where you find these.

[00:14:30] Why are volcanoes are all over the ocean bottom?

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these large low areas that are the ocean floor and we have down the middle

here-

Maggy Benson: Down here.

look like?

Liz Cottrell: Yes, this is really rare footage actually, of a volcano erupting under [00:15:30]

water. Again, you can see what I was talking about before, you can see that that

magma coming out, cooling very quickly on the ocean floor. Here's a map,

where again, you can see kind of what we saw on the globe. These long chains

of volcanoes running down the center, these long ridges and when that magma

erupts it's generating new ocean crusts and the ocean floor is being resurfaced

all the time. Here in red, that's where the ocean floor is youngest, it gets

progressively older, yellow to green to blue, and older as you move away. And

that's how our ocean floors [00:16:00] are resurfaced. The continents are old

Maggy Benson: All right. So, what causes lines of volcanoes? Is it horizontal lava flows, plate

boundaries, sideways budding of new volcanoes, or volcano cloning? (Music

plays.) [00:17:00] So the results are coming in and the biggest response has

Liz Cottrell: Great answer. Plate boundaries is exactly correct. The plate boundaries are

where tectonic plates on the Earth's surface come together and so ... the mid-

ocean ridge system is an example of a divergent plate margin where, as I said

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example. But as you might have guessed the Earth is not getting bigger and

bigger.

Maggy Benson: No.

generated here, transits the sea floor and generates back down underneath.

And what you can see here on your screen is the ring of fire, these classic

subduction zone locations where ocean floor is subducting beneath the

continents. And similar to what I just showed you with my hands here's a

graphic that shows you ocean crust moving along and subducting down beneath

the continents [00:18:30] and generating volcanoes in that location and so

that's why we get those long subduction zone volcanoes where the crust is

being recycled.

mean the recycling the Earth's crusts so that our Earth is staying the same size

but ...

Liz Cottrell: That's a good thing.

Maggy Benson: I know you're also looking at the chemistry of what is happening inside our

Earth, how does that all connect?

the atmosphere that we breathe. They've created the oceans that make our

planet habitable. So really we owe our lives here to the presence of volcanoes.

That's what makes ... one of the very many things that makes Earth a unique

and habitable planet.

here at the Smithsonian. We have a lot of really great student questions, are

you ready to take them?

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Liz Cottrell: [00:19:30] Sure.

gone to an active volcano?"

Maggy Benson: Cool. All right, so we have another one and this one comes from Dawson. How

understanding what's inside the Earth. So the first thing we've got a magnetic

field, [00:20:30] okay? The magnetic field is generated by liquid iron flowing

around in the outer core, the flow of that liquid iron generates our magnetic

field protects us from cosmic rays thank goodness for volcanoes? Well thank

goodness for for the magnetic field. That's evidence of the liquid core.

passes through, and we can listen to that energy on the other side and map the

interior of our planet using seismic energy. [00:21:00] For example seismic

scientist at the Smithsonian. How does that work-life balance work?

Liz Cottrell: I would strongly encourage our viewers to have work-life balance, but also to

say that you can be a scientist and a parent. You can be a mom, a dad, and a

scientist and find a way to make that work. I have two kids, [00:22:00] a five-

year-old and two-year-old, bring them to school, bring them home. I think my