Jane: This is But Why: A Podcast for Curious Kids from Vermont
Public. I'm Jane Lindholm. On this show, we take questions
from curious kids just like you, and we find answers. You know,
it's been a big summer for volcanoes. You might have heard
that back in July, a volcano erupted in Iceland, and then in
August, a big earthquake struck off the coast of Russia,
triggering multiple volcanic eruptions in the region. While
the eruption in Iceland was related to a couple of years of
ongoing volcanic activity in that region, the one in Russia
had been dormant - inactive, quiet - for hundreds of years.
And as we're putting this episode out in September of
2025, an active volcano in Japan has been spewing ash into the
air. The Smithsonian Institution's National Museum of
Natural History in the United States keeps a list of all the
active volcanoes and volcanic activity in the world, and says
that at any given time there are typically 40 to 50 continuing
eruptions, and out of those, generally around 20 will be
actively erupting on any particular day. I did not
realize there was that much volcanic activity all the time.
You definitely don't want to be near a volcano while it's
erupting, but if you ever get a chance to view it from a safe
distance, volcanic eruptions are fascinating. You might see
bright, hot, orange lava flowing down mountain slopes, making
really cool patterns, and when you look up into the sky, you
could see giant plumes of smoke filling the air. Melody, Joey
and I were kind of hoping to get that safe viewpoint to watch an
eruption while we were in Iceland earlier this summer. And
it turns out we just missed one. It was only a couple weeks after
we left that Iceland's Sundhnúkur Crater row erupted
right near where we had been. If you don't live in an area with
volcanoes, they can seem really mysterious. Why do they erupt
and how? And how can we know in advance so we can make sure to
stay safe? If you live in areas that are very volcanically
active, you may already know a lot about volcanoes and how to
stay safe around them. You've sent us a lot of volcano
questions over the years, and since Iceland has so much
ongoing volcanic activity, we figured while we were there,
whether we could see a live eruption or not, we should find
someone who studies volcanoes in Iceland who could answer all of
your questions.
Freysteinn Sigmundsson: My name is Freystein Sigmundsson. I work
at University of Iceland. We do research to better understand
how our planet is working. And I study volcanoes.
Jane: Does that mean you're a volcanologist?
Freysteinn Sigmundsson: Yes, volcanology is a very broad
field. You can study the rocks on a volcano. What I try to do
is to study what is inside the volcanoes.
Jane: Iceland has about 30 volcanic systems with about 130
volcanoes within those systems. You can think of a volcanic
system as a network of volcanoes. So it's a good place
to be if you're a volcanologist. And living so close to so many
volcanoes when he was youngmade Professor Sigmundsson really
curious.
Freysteinn Sigmundsson: When I was a young kid, there was a
period of very high activity of eruptions here in Iceland. So I
saw a lot of coverage of that, and I guess that pushed me into
the study of volcanoes.
Jane: I did not see volcanoes growing up in New England, the
northeastern part of the US. And there's a reason for that. Most
volcanoes form at the boundaries of Earth's tectonic plates,
these large pieces of the outer shell, the lithosphere of the
earth. Iceland sits right on top of the Mid-Atlantic Ridge, where
the North American and Eurasian tectonic plates are slowly
drifting apart. And Iceland is a hot spot, meaning the underlying
ground is warmer than the surface area above. These
factors make for a lot of volcanic activity. But to get
volcanic activity, you have to have a volcano. And what's a
volcano?
Freysteinn Sigmundsson: A volcano is, in essence, a crater
that has erupted a magma, and in most cases we would expect it to
have erupted more than once, so it builds up some kind of a
mountain.
Jane: The crater is at the top of the volcanic mountain, but
it'll look a little bit like somebody's taken a big scoop
out, leaving a bowl-shaped, round hole right at the top.
That's the crater. Do you know what magma is? I. Here's how
Professor Sigmundsson explains it.
Freysteinn Sigmundsson: What is inside volcanoes. We call it
magma, molten rock. You can think of it as a human body. We
have blood inside our human body. Volcanoes have magma.
Jane: This molten rock, magma, is extremely hot. So hot that it
has become liquefied. It gets that hot because the core of the
Earth is really, really hot. An eruption happens when more and
more magma accumulates under the surface, building pressure. The
magma can move upwards through cracks or weakness in the
material around it, making its way up and then breaking through
the top layer of the Earth's surface, and boom! That liquid
rock plus gas and ashes come out onto the surface in an eruption.
Freysteinn Sigmundsson: We have basically two types of volcanic
eruptions. In one type of eruption, magma comes out of
volcano and flows on the surface of the Earth like a liquid. The
magma changes into lava, and it just solidifies as black rock on
the surface. The other type of eruption is explosive, and they
are often more dangerous. Liquid that is inside the volcanoes,
when it comes to the surface of the Earth, it explodes into tiny
particles and goes up into the air. And it can stop air
traffic. And there can be so much of this particles that it
becomes completely dark.
Fritz: My name is Fritz. I am five years old, and I live in
Fairview Park, Ohio. What was the first ever volcano to
explode and turn into magma?
Luca: I'm Luca from Pasadena. How many years did volcano
starting existed?
Jane: Luca is wondering how many years ago did volcanoes start
existing? And Fritz is wondering if we know what the first ever
volcano to explode was.
Freysteinn Sigmundsson: The existence and evolution of our
planet is all about volcanoes. So the first volcanoes were
really born when the planet was forming. We don't have a name
for the first volcano, so we cannot say what was the first
volcano, but we can ask other questions, like, if you are in
some specific region, we can ask, when did the first
volcanoes form in this region? And often the time scale, or the
time for that is measured in millions of years. Like, I live
in Iceland. Iceland is an island in the middle of the ocean, and
the reason Iceland exists are volcanoes. And Iceland started
to form as an island about 20 million years ago. That is when
the first volcanoes appeared here. And typically a volcano
here in Iceland is about half a million years. So mankind, we
are very small in comparison to the lifetime of volcanoes.
Navy: My name is Navy. I live in Meridian. How do volcanoes
erupt?
Boaz: My name is Boaz. I'm from Israel. I'm eight years old.
What is the pressure that makes a volcano erupt?
Oliver: My name is Oliver. I live in Watertown,
Massachusetts, and I'm six years old. How do volcanoes erupt?
Zoe: My name is Zoe. I'm seven years old, and I live in
Singapore. How do volcanoes erupt?
Rosemary: My name is Rosemary. I live in Canada. I'm six years
old. Why do volcanoes form?
Jane: How do volcanoes form? And how do they erupt?
Freysteinn Sigmundsson: Volcanoes form because of this heat that
needs to escape from the interior of the Earth. So there
is somewhere rock is melted, there's a liquid inside the
Earth. This liquid wants to rise up to the surface because it is
buoyant. It is less dense. It is like if you jump into a swimming
pool, you float up. The same is happening with the magma inside
the Earth. And therefore they form because this liquid is
coming towards the surface of the Earth. And often when there
has been sort of one path for magma, it is utilized by more
magma. So there are repeated outflow of this liquid and the
eruptions, when do they occur, exactly? Well, pressure is
building up inside where magma is accumulating in a very
similar manner as what happens if you, if you have a balloon
and you blow air into it, and you continue to blow, you see,
it gets always more and more difficult. That's because there
is more pressure inside the balloon. Same happens with
volcanoes. More new liquid that flows into a volcano, the
pressure increases. But if you continue very hard to blow into
your balloon, it may explode. That is the same thing that
happens for a volcano. The eruption starts when the
pressure is too much inside the balloon that is collecting magma
inside the volcano, and there we go. We have an eruption.
Theodore: My name is Theodore. How does the volcano rise up
inside the sea?
Jane: Can you talk a little bit about volcanoes that form
underwater?
Freysteinn Sigmundsson: Yes, we have super many volcanoes in the
oceans, underwater. Lots of submarine volcanoes, underwater.
What happens is, inside the volcano, the process is very
similar, but the eruptions are different. Often we form both
lava similar as on the surface, but the lava will be of a little
different types. If the eruptions happen in shallow
water or water depth of a few hundred meters, it becomes
explosive. So what happens then is that the lava, when it comes
into the ocean, it can explode into fine particles, similar as
an explosive eruption, and then it can pile off. And eruptions
can create mountains. And we have had new island created off
the coast of Iceland in an eruption that was first under
ocean water, and the volcano rose out of the sea.
Calvin: My name is Calvin. I'm five years old. I live in New
York City. Which one's hotter, the sun or a volcano?
Freysteinn Sigmundsson: The red glow of this liquid that comes
out of the volcano means it is very hot, 1,000 degrees Celsius.
This is about 1,800 degrees Fahrenheit. So it is super hot.
But inside the sun, it is much hotter.
Jane: Scientists say the core of the Sun is as hot as 15 million
degrees Celsius. That's 27 million degrees Fahrenheit. So
the heat from underneath the earth is definitely hot. But if
we're comparing about 1,000 degrees in a volcano to 15
million degrees in the core of the Sun, the Sun is much, much
hotter. Coming up, how do we know when a volcano is going to
erupt?
This is But Why. I'm Jane Lindholm, and today on the show,
we're learning all about volcanoes with University of
Iceland professor and volcanologist Freysteinn
Sigmundsson. So as we just heard, when a volcano erupts,
magma, or hot, molten rock, flows onto the Earth's surface.
And at that point, we give it a new name: lava. We've got some
questions about lava and how it forms.
Alana: Hi, my name is Alana, and I'm eight years old, and I live
in Norwalk, California. And my question is, why do volcanoes
have lava in them, and how does the lava even get in there?
Landis: My name is Landis. I'm seven years old. I live in San
Antonio, Texas. Where do volcanoes get their lava from?
Charlie: My name is Charlie. I live in New Zealand. I am six
years old. What is lava made out of?
Freysteinn Sigmundsson: Lava is made out of rock that has become
so hot that it melts. And you'll see many of the features of
volcanoes can be explained by this heat. So the volcano
scattered magma initially, that is when the lava is inside the
volcano. Because of heat, the rock started to melt and form
liquid. So the liquid inside the volcano comes to the surface,
and then we call it lava. So it is a hot liquid. And many
volcanoes have a lot of hot liquid inside them, and that's
when we have an eruption. This liquid comes to the surface and
we have lava. So that's the story, basically, of the lava.
It's all about the Earth trying to release heat from its
Trixie: My name is Trixie. I'm four. I live in Virginia. Why
interior.
are volcano lava is orange?
Jane: Why is lava orange?
Freysteinn Sigmundsson: Yeah, similar reasons the sun is
yellow. It is transmitting energy. It is so hot that it
starts to radiate energy. The sun is radiating energy that is
still hotter than the lava that is yellow. The orange color is
simply radiation from a different temperature.
Jane: When melody, Joey and I were in Iceland, we didn't see
an eruption, but we did visit a solidified lava field from
volcanoes that had already erupted just a few years ago.
The lava there was no longer bright orange because it had
cooled and hardened back into rock. But I could see the
different textures and patterns of the lava as it had flowed
across the surface. And I was really surprised to see that
there was still smoke coming out of the solidified lava field,
even though it had been more than a year since the last
eruption. We even saw signs warning people not to walk on it
because it might still be very hot underneath. So I asked
Professor Sigmundsson how long can it be hot underneath that
hard surface, and how long can a lava field be dangerous after an
eruption.
Freysteinn Sigmundsson: For... for years. Because it takes a
long time to cool a lava field. It depends, of course, how thick
it is, but if it is like few meters...
Jane: As tall as an adult.
Freysteinn Sigmundsson: Yes, or twice or three times that. That
is maybe typical for lava fields here in Iceland, they can have
really liquid magma inside them for possibly for months or
years. But there is also another danger simply related to the
rocks. You know, it is liquid that is transforming into rock
again on the surface of the Earth. And the structure of lava
fields is very intriguing. Many of the lava fields here in
Iceland are very irregular on the surface. So you also have
the danger of just falling. So they are dangerous, yes. So you
need to be aware of that.
Harper: My name is Harper, and I am five years old, and I live in
Scottsdale, Arizona. Why can't we live on volcanoes?
Freysteinn Sigmundsson: Lots of people live on volcanoes, and
lots of people live close to volcanoes. Here in Iceland, we
live quite close to volcanoes. I mean, the capital of Iceland,
Reykjavik, is not far from volcanoes. Here in Iceland,
there are two villages that are practically on a volcano. But
worldwide, there are many people that live on volcanoes. And the
reason people live on volcanoes, like in Indonesia, is because
the the soil on a volcano can be very fertile, and you can grow
crops there.
Jane: Professor Sigmundsson says living close to volcanoes can
come with other great benefits. In Iceland, for example,
geothermal energy powers about 70% of the country.
Freysteinn Sigmundsson: We have cold winters, but we heat most
of the houses in Iceland by water that comes from the
volcanoes, hot water, and it just goes into a radiator
directly from volcano and heats our houses. We have very hot
houses here in Iceland, even if the winters are cold
Jane: And many volcanoes stay dormant, which means they're
inactive, kind of asleep for hundreds or even thousands of
years. So it's entirely possible for someone to live close to an
inactive volcano their whole life and not experience an
eruption. The tricky thing, though, is that volcanoes don't
always stay asleep.
Freysteinn Sigmundsson: If they can talk about the volcanoes as
a living creature, in their lifetime, most of the time they
are sleeping. So they only wake up occasionally. Some of the
work I do is try to understand what happens when a volcano is
trying to wake up. And yeah, it is difficult to forecast. For
example, if you're sick, if you do not feel very well in your
stomach, you may need to throw up occasionally. And forecasting
when you will throw up if you have a stomach disease may be
difficult. You almost throw up, but then suddenly it comes, and
maybe we are not prepared. The same is with volcanoes. It is
difficult to forecast when they throw up.
Jane: I like that way of thinking about it. And yes, in
my experience, sometimes you think: Oh, I don't feel good. Oh
my gosh, now I'm throwing up. It can be a very surprising thing.
Freysteinn Sigmundsson: Same for volcanoes. What volcanologists
are trying to do, some of our work is to forecast the activity
and better prepare society. That you're listening to this podcast
is very good, because we need to more people that understand what
volcanoes are doing.
Soleil: Hello. My name is Soleil and I live in Hamden,
Connecticut, and I'm five years old and about to be 60,
volcanoes erupt in the winter?
Freysteinn Sigmundsson: What you know about volcanoes is that
they are very irregular. They can erupt any time of the year.
Volcanoes are not like a clock.
Jennifer: My name is Jennifer, and seven years old. I'm from
Ohio. How do volcanologists know a volcano is going to erupt?
Freysteinn Sigmundsson: That is my job, part of my job, to
understand what happens before this, yeah. So we need to
measure their activity, and we can measure what is happening
inside the volcano with different techniques, mainly
three techniques. We can study earthquakes, how the ground is
shaking in a volcano, because the waves from earthquakes come
to the surface. And we can measure the waves and then
figure out what is happening inside. Or we can measure how
the ground of a volcano is moving, and thereby, maybe, try
to understand how the pressure is building up, like in a
balloon. Or we can measure what we can call volcanic gas. That
is like if you smell something is burning in your stove, then
something serious may happen unless you stop the process.
It's basically the same thing we can try to sense or sniff, in a
sense, what the gas that is coming out of a volcano.
Jane: When something is burning in your stove, that's a very
familiar smell. Like I can picture the smell of burning
toast. The smell of a volcano that is getting active, what is
that smell? Is that a sulfuric smell, which sometimes people
describe as kind of like rotten eggs?
Freysteinn Sigmundsson: It can be increased in that. It can
also be increase in gas types that has no smell that we need
special instruments to measure. So we need some technology.
Normally, we cannot use our nose for it.
Jane: Are there things that you can look at? If I was looking at
a volcano, and say, oh, something is happening? Or do
you need special tools and special maybe even computer
models to be able to understand what's happening?
Freysteinn Sigmundsson: Sometimes we can see it with our eyes. For
example, if there is new, hot liquid coming into a volcano,
the heat of the rock around it can increase, and we can start
to have more geothermal activity, or basically steaming
from a volcano. So we can get visual steam from a volcano,
basically meaning it is hotter. But we typically need equipment.
We need to study the earthquakes. We need to see how
the ground is moving, or we need to measure the gases that come
out. And typically, to understand how volcanoes behave,
both in this time period before an eruption and during eruption,
we need this monitoring data, and we take it all together and
try to understand what is happening inside the volcano
during an eruption. And often we need a computer model for that.
So even if I'm a volcanologist, most of the time I'm in front of
a computer.
Jane: Scientists have been studying volcanic activity for a
long time, but there's still a lot we don't know about how they
work. For Professor Sigmundsson, he says his goals are to keep
learning more about what's inside volcanoes and how that
might help him understand better the warning signs volcanoes are
giving. That way, people could be informed before a volcano
erupts. That's especially important for people who live
close by, of course. Volcanic eruptions are a forceful release
of extreme heat and energy. They can destroy homes, they can make
nearby towns unsafe, require residents to evacuate, or leave.
Sometimes, all the ash from an eruption gets high up into the
atmosphere and causes problems like planes needing to find new
routes or not being able to fly at all. And remember our recent
episode about smoke traveling from forest fires. Ash from
volcanoes can, of course, also get into the atmosphere and go
very, very far from where the volcano has originally erupted.
Given all of that, it makes sense that we often think of
volcanoes as something kind of scary and unpredictable and
dangerous and bad. But Professor Sigmundsson says it's important
to be respectful of the power and destruction of volcanic
activity, but to also recognize the beauty.
Freysteinn Sigmundsson: If you look at some photographs or
videos of volcanoes, it's a beautiful thing to see a small
eruption. You sese some nice red magma being thrown up into the
air and flowing. So, so I was a young kid that had the
opportunity to see eruptions and hear about them. They caught my
interest. They are beautiful, spectacular, and if you stare at
them for a long time, stare into the red glow, you can be
charmed.
Jane: And volcanoes are also very important. Not only did
they shape the landscape we know today on Earth, but they
continue to do that. New islands and new terrain is constantly
being formed by volcanic eruptions. Plus, volcanoes are
important for things like geothermal energy, how we can
heat and cool our homes and buildings. And they can create
very fertile soils, meaning it's easier to grow things like
fruits and vegetables. So volcanoes are all of those
things at once: a little bit mysterious, maybe scary
sometimes, occasionally dangerous, but also beautiful,
interesting and important. Thanks to Professor Freysteinn
Sigmundsson at the University of Iceland for speaking with us
about volcanoes and answering your question. As always, if you
have a question about anything, have an adult record you asking
it on a smartphone. You can use an app like voice memos or
recorder. Then have your adult email the file to
questions@butwhykids.org. But Why is produced by Melody
Bodette, Sarah Baik and me Jane Lindholm at Vermont Public and
distributed by PRX. Our video producer is Joey Palumbo, and
our theme music is by Luke Reynolds. If you like our show,
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episode. Until then, stay curious.