This is Geology Bites with Oliver Strimpel.
Water is strongly implicated in many of the most powerful
volcanic eruptions. In this episode, we'll talk
about the two main ways in which this comes about.
The first is when magma comes into contact with external
water, whether from oceans, groundwater, or glaciers.
The second is when water is already present within the
magma. Michael Manga studies how
geological processes affect and are affected by water.
He also studies similar processes on other planets and
on the icy moons of the outer solar system.
He is a professor in the Earth and Planetary Science Department
of the University of California, Berkeley.
Michael Manga. Welcome to Geology Bites.
Oliver, it's a pleasure to join you today.
Let's talk about the first of the two ways that water effects
eruptions, the so-called friato magmatic eruptions, when
external water and hot magma come into contact.
How does this amplify the explosive power of an eruption?
Yeah, you highlighted in that question, Oliver, something
that's really important. Actually, maybe we should define
the word friato magmatic. Friato means water.
Magmatic refers to the melted rock, and the key is that
Magma's hot and water is cold, and so heat is transferred from
hot objects to cold bodies. And so as the magma cools down,
it becomes brittle and it breaks.
And maybe if some of your listeners have had this
unfortunate opportunity of putting some water into hot
glass and it shatters as it cools too quickly.
And so this will make the small pieces of magma that become
volcanic ash that can erupt explosively.
The water in turn, of course, it's cooling the magma, but it's
heating up because it's taking that heat and liquid water
becomes steam, and steam takes up much more space than the
liquid water did. And so that huge volume
expansion, as it expands, carries with it the fragmented
magma, volcanic ash with it as it expands.
You know, most physical systems that we think about, we have
motion that I guess you can think of as being kinetic
energy. When you rub your hands
together, your hands are moving, they have kinetic energy.
And if that energy is dissipated to make heat, when your hands
are rubbing against each other, that's friction.
And so most processes in the Earth take kinetic energy and
convert them into heat. What's special about
freyatomagmatic eruptions is the energy transfer goes the other
way. We can take the heat in the
magma and convert it into kinetic energy to make these
eruptions so explosive. So because, as you said, when
water turns to steam, there's a huge increase in volume, can
steam therefore be generated even when the magma contacts
water at great depths and therefore under great pressure
under the ocean? So as we go deeper inside the
earth or deeper under the surface of the ocean, the
pressure goes up. And as pressure goes up, gases
contract. And this matters for two
reasons. First, liquid water at high
pressures doesn't convert into steam.
It doesn't boil. It becomes a supercritical
liquid. And the second effect of higher
pressure is that the boiling temperature goes up as well.
So at the bottom of the ocean, when water can boil, it can be
as hot as 400°C, and it can be very difficult for magma to heat
water up to that temperature. And so the high pressure inside
the Earth has two effects. It increases the boiling
temperature and in fact can keep boiling from happening.
And if you don't boil water, you don't have the big volume
expansion that drives explosive eruption.
And So what happens instead is that when you get pillow lavas
forming? Yeah.
Pillow lavas. The name is very descriptive.
You see these little blobs of lava that look like pillows,
hence their name. And those are wrapped in a style
we call effusive. Effusive means lava flowing over
the surface in a sort of a coherent, intact manner as
opposed to breaking up into little pieces or fragmenting,
which is what happens for explosive eruptions.
And so pillow lavas form when low viscosity magmas are
extruded onto the bottom of the ocean and they cool pretty
quickly, which is why they get the pillow shape as opposed to
making the very thick lava flows we see on land.
So that interaction with water action in submarine settings to
make pillow lavas is still very important by cooling the outside
of the lava, but it does suppress explosive eruption.
In 2022, we experienced the most powerful eruption in recent
memory, and that was the Hunga Tonga eruption.
Can you describe that eruption and compare it to other
eruptions, just to put it in context, such as the Mount Saint
Helen's eruption in 1980 or Mount Pinatubo 1991?
And I guess water must have been implicated in that one.
Yeah. So the hunger eruption of 2022
was the most powerful volcanic eruption in our lifetimes.
It was so powerful, people in Alaska, 8000 kilometers away
could hear it. And the plume reached a height
of 57 kilometers, which is higher than any eruption we have
documented. Set a record for the number of
lightning strikes. Just like thunderstorms create
lightning, volcanic eruptions will also create lightning by
very rapidly carrying ice and magma to great height.
Also, this eruption created global tsunamis through a
coupling between the atmosphere, the ocean and the solid part of
the earth. And it was, of course,
devastating for the Kingdom nation of Tonga.
So it was an extremely powerful eruption, and much of the power
was because it was a shallow submarine eruption, so that
magma fragmented underwater, and those fragments can interact
with the surrounding liquid water to make steam.
And because the pressure is pretty low, it was a shallow
eruption. A lot of steam could be
generated, and that steam helped power the great energy of the
eruption. You asked about how to put this
in context. You and I were alive during the
1980 Mount Saint Helens eruption.
This eruption was 10 times bigger than Mount Saint Helens
was and was similar to the Pinatubo eruption in the
Philippines. It is small, though, in
comparison with some of the biggest eruptions we know about
what we call super eruptions, the ones that make things like
the big calderas we see in Yellowstone National Park.
About 10 years before the Hunger Tonga eruption, there was
another eruption called the Harva eruption, not too, too far
away, but that had a very different outcome.
Can you tell us about that? Absolutely.
And the Haver submarine eruption occurred South of Hunga Hunga
along a volcanic arc. Volcanic arcs are produced when
plates sink into the Earth's mantle.
And the northern part of the subduction zone is the Tonga
arc. The Kermadec arc is South of
that, just north of New Zealand. And Haver eruption is in the
Kermadec arc and it erupted in 2012.
It was a deeper submarine eruption.
The vent was 900 meters below the ocean surface, and that's
deep enough that the way the volcano erupted was
fundamentally really quite different.
It was also smaller, although bigger than Mount Saint Helens
once again was in 1980. If we call this a deep submarine
eruption, the Haver eruption, it was the largest deep submarine
eruption since 1650, and it created a raft of floating
pumice. Pumice is a volcanic rock full
of bubbles, and there's enough bubbles in this rock that the
fragments can float on the ocean surface.
And it created a huge raft of floating pumice and that
promised because it floats, circumnavigates the planet with
the ocean currents eventually washing up on beaches.
The eruption style, though, is quite different.
The magma as it entered the ocean from the volcanic vent was
full of bubbles, but it hadn't yet fragmented and so it was
extruded or squeezed into the ocean.
There are enough bubbles in it that it's lighter than the
ocean, so the magma floated up to the ocean surface and as it
interacted with the surrounding water, the magma quenched.
It cooled very quickly and broke up into the pieces of pumice
that float on the ocean. Since we're in my office today,
I can show you a piece of the pumice if that would be of
interest. Yeah, please.
So your listeners probably can't see, but these are two pieces I
collected in New Zealand, were transported long distance for a
long time. And unlike most things that
break, they're not angular, but they're rounded on the sides.
And they're rounded because these pieces of pumice, as they
float on the ocean surface, are rubbing against each other, you
know, kind of like pebbles on a beach.
And so they get progressively rounder and smaller as well.
And of course, you can't feel them to see how light they are.
But I do have a container of water.
And if, you know, I put it on, put the piece of pumice on the
water. You can see that it floats.
High and dry. And of course, it has to float
right? It got all the way to New
Zealand from the volcanic vent. And this pumice will float for
years and years. You know, the thing we're
learning about submarine eruptions that I guess we hadn't
properly appreciated, not having had the chance to witness
submarine eruptions and especially deep winds until
2012, is that ocean depth is fundamentally important.
At high depths, you suppress fragmentation, but fragments are
still lighter than water, so they can float on the ocean
surface. At shallow depths you have an
explosive eruption surrounded by liquid water and you can get
very explosive eruptions, more explosive than we had previously
anticipated. Roughly what depth do we switch
over from these highly explosive steam eruptions to the the more
contained ones that either form pillows or the pumice?
Yeah, that's an interesting question that I have actually
tried to think about. How do we map depth onto
eruption style? So let's go from the deepest to
the shallowest. The critical pressure for water
to form steam is about 2200 meters.
So deeper than 2200 meters you should expect mostly effusive
eruptions. And the average depth of mid
ocean Ridge is where oceanic crust is formed is 2500 meters.
The details of what that critical depth is depends on the
eruption rate, how fast the Magma's erupting, and weather
can fragment. But for the Haver eruption in
2012 that formed the raft of floating pumice, if the vent was
probably shallower than two or 300 meters, it probably would
have been an explosive eruption, much like Hunga.
And that's probably useful for hazard assessment.
You can look at the volcanoes around the Earth and identify
those in submarine settings that are below sea level or could
become below sea level if they were to erupt.
Are there some cases where eruptions start below that 2200m
threshold, but because they produce so much lava they build
up a kind of seamount and then get to that critical height and
then stop to become steam driven?
The answer is yes, that any volcano we see poking out of the
ocean had to start its life below sea level.
The islands on Hawaii are good examples where the tops of the
mountains are way above sea level, high enough that there's
even little glaciers on the tallest peaks on on Hawaii.
And so those volcanoes grew from being in a deep submarine
setting to a shallow submarine setting, to being above land.
And the converse is true too, as volcanoes erupt and the flanks
collapse what was once above sea level that then can migrate
below sea level. Yeah, but you're not likely to
go from a great depth to less than 2200 meters of depth in a
single eruption. You're talking about a sequence
of eruptions over many years. Yeah.
To grow a volcano a kilometer in height will take a long time,
probably many eruptions. And I don't know any good
examples where we have documented the detailed growth
of a volcanic edifice under the ocean.
That question highlights one of the challenges in understanding
submarine eruption is that to look at them and observe them,
we have to go under the ocean because our cameras don't look
below the ocean. And that requires sending either
autonomous vehicles or remotely operated vehicles, or using
sonar, some kind of remote mapping technology, to
repeatedly survey the sea floor. It's not something we can
monitor easily and continuously. Is this effect I have magma
contacting external water? Also, what drives geysers, Hot
Springs and mud volcanoes? So geysers are a special type of
hot spring. They erupt boiling water, and
they erupt episodically. And so when they do erupt,
they're erupting a mixture of liquid water and water vapor or
steam. Although actually geyser
eruptions can be energetic enough to carry with them little
fragments of rock. There's almost a continuum
between geyser eruptions and hydrothermal explosions.
Where hydrothermal explosion means hydro water explosion,
things break apart and rock fragments get ejected.
All the geyser fields that we know of, their energy source is
in fact magma underground. So there's no magma directly
erupting in the geyser, but the heat source is in fact Magnus
that are solidifying and cooling underground, transferring their
heat to the groundwater. So.
When you get an intermittent eruption of a geyser, it's the
periodic passage of some water over this magma.
So when we look at a geyser erupting, we're seeing the very
surficial manifestation of that heat transport deeper down.
The groundwater flow that's carrying that heat is probably
much more steady. And the water that's taking the
heat out of the Magnus is probably circulating to depths
of many hundreds of meters to even a few kilometers, and
carrying that heat up to more shallow depths.
Various reservoirs. And actually, from studies of
geysers, direct imaging with cameras or using geophysical
measurements beneath geysers, it looks like there are cavities in
which heat and steam accumulate. In fact, that may be analogous
to the reservoirs in which magma accumulates leading up to
eruption. So actually, there are some
similarities between geyser eruptions and volcanic eruptions
in that they're episodic. They're not erupting
continuously. And there are reservoirs that
are accumulating the gases and the materials that erupt and the
heat. And when the pressure gets big
enough, the eruption begins, the fluids are evacuated, the
eruption ends, and then the process repeats.
But most geysers, many of them are quite irregular.
There's only a very special subset that are truly periodic,
or periodic means the interval between eruptions is always the
same. And even for those that are
periodic, that periodicity varies over time, over decadal
time scales, or can be influenced by earthquakes or
other processes. What about mud volcanoes?
Mud volcanoes also erupt because the pressure in where the mud is
coming from gets too high and so materials are ejected to the
surface, right? So too much pressure underground
mud volcanoes erupts sediment. So this means mud and rock
fragments along with the mixture of water and gas.
And often that gas is methane, natural gas, right?
That methane is produced from the organic material that's
buried with the sediment. And as it's heated to high
enough temperature, that organic materials converted into
methane. Mud volcanoes we often find in
places where we also extract hydrocarbons from the earth, the
oil and gas. And mud volcanoes can erupt this
mixture of fluids, right, water, gas and sediment from as deep as
10 kilometers. And they create land forms that
resemble, in many ways, magmatic volcanoes.
They can erupt sort of explosively.
They can create mud flows. Yeah.
Mud volcanoes can create mountains.
They can create things that look like lava flows.
In fact, I had the great pleasure of going to Azerbaijan,
which is famous for many things, but for many people, the mud
volcanoes are the big tourist attraction in Azerbaijan.
There are fields and mud volcanoes on land as well as
under the sea, under the Caspian Sea.
And the source of the gas in the mud and the fluids are from the
same sedimentary formations from which Azerbaijan is extracting
the oil and gas. And if I was just looking at a
satellite image of the morphology of the flows, I would
not easily be able to tell, maybe not be able to tell at
all, that those were made of mud and not lava.
And they flow downhill. They make long flows.
They look a lot like rhyolite flows, very silica rich flows.
And they can also create spatter, fragmented mud that
falls in the ground. And on Mars, there is debate
about whether some of the landforms that people see little
cones. Are they magmatic cones or are
they produced by mud volcanoes? Presumably mud volcanoes don't
last as long as magmatic wants. They must be very soft and
easily kind of washed away. Yes, on a planet where there's
precipitation, that precipitation will erode the
sediment faster than it would erode lava.
And I guess they're best preserved on land in very dry
places, but also to under the ocean.
A lot of the mud volcanoes on Earth form in submarine settings
and they're they're better preserved.
What happens when there are eruptions on the ice?
Do you get the same amplifying effect?
And can we see this kind of thing happening in Iceland?
In ice is just the solidified form of water.
So in the same way that Magma's, when they interact with water,
can make steam and help Dr. explosive eruptions, the same
process can happen when magma erupts under ice.
But first, you have to melt the ice, and all that melt water
that you're producing does help cool magma and help it solidify.
And so lava flows that erupt under ice often cool fast enough
that they don't erupt explosively.
But there is a distinctive signature of lavas as they cool.
When Magma's cool, they contract.
And when they contract, they will make cracks to accommodate
that change in volume. And maybe some of your listeners
have been to Devil's Causeway in Northern Ireland.
Here in California, there's a place called Devil's Post Pile,
and these are sort of hexagonal vertical columns of lava.
The columns are bounded by what we call cooling joints, the
cracks made as the magma cools, and those cracks propagate
perpendicular to the cooling front.
And so if you cool a flat lava flow underwater, you get
vertical cooling joints. If you're completely surrounded
by ice, those cooling joints will be perpendicular to the ice
lava contact, and so they'll often radiate A distinctive
signature of lavas that cool under ice.
In 2010, you may remember the Afioko eruption happened in
Iceland and closed air traffic in northern Europe.
That was probably the greatest disruption to air traffic in
Europe since World War 2. And there the volcano erupted
under ice, and that melt water flowed into the volcanic vent,
helping to drive the exclusivity of that eruption.
And that water had two effects, right?
The water helped quench the magma to make the volcanic ash,
and the steam generated from that cooling helped power the
eruption. Let's talk about the second
important way in which water effects an eruption, namely when
water is already present in some form within the erupting magma.
How does that amplify eruptions and where exactly does that
water come from? So there are many parts to this
question. Let's start maybe with where the
water comes from and Magma's melted rock.
And when you melt a rock, different elements in the
periodic table either like to stay in the solid that's
leftover or like to go into the melt that's produced.
And water and lots of the other gases prefer to go into the
melt. And so if you take a rock that
has water in it and melt it, most of that water ends up going
into the melt that's produced. And so where's that water coming
from? There can be little bits of
water trapped between crystals inside a rock in the what we
call the pore space. But lots of minerals also
incorporate water directly in the mineral structure.
Clay minerals are an example. There's a mineral called
amphibol that incorporates water in its structure.
And so when you melt a rock that contains amphibol or rocks that
contain clay, the water that was present ends up going into the
melt. And that water that's in the
melt that's formed is fundamentally important for why
we have volcanoes at all. Volcanoes erupt because the melt
that's produced is less dense than the surrounding crust.
So for magma to erupt, we have to make it less dense.
One way to make something less dense is to fill it full of gas,
and at low pressure, the water that was dissolved in the magma
is no longer able to be dissolved.
It comes out of solution and forms bubbles, and it's the
presence of those bubbles that helps Dr. Magma to the surface.
So how do we get all this water into the interior of the earth
in the first place? The process of plate tectonics,
where we create plates at Earth's surface that move
horizontally and then sink into the Earth through a process
called subduction, is a great way to bring water from Earth's
surface, from the oceans into the Earth.
And that water is brought into the Earth through subduction in
two ways. The sediments on top of the
subducting plates, as they sink into the Earth carry with it the
water between the betaments, and the minerals that contain water
also gets abducted as well. And then at high pressure, those
minerals can't hold that water, and they're released into the
overlying part of the Earth we call the mantle.
And that helps drive melting of the mantle.
And when you melt wet rock, the water goes into the melt, it's
carried upwards with that melt, and then powers the volcanic
eruptions we see above subduction zones.
I guess the other concept we should talk about is why is it
that we make bubbles inside magma from that dissolved water?
And the solubility of gases inside liquids increases with
increasing pressure. And your listeners will know
this from their everyday experience.
When you open a carbonated beverage and you take off the
top or you open the can, you decrease pressure and that
carbonated beverage starts to fizz because you've lowered the
pressure. And that's because the
solubility of those gases is lower at low pressure.
And so the water can't dissolve that carbon dioxide and it
starts forming bubbles. And magma does the same thing at
high pressure. It can dissolve a lot of water,
but as the magma rises to shallower depths, the pressure
decreases. The water was dissolved in the
magma forms bubbles, and those bubbles grow.
And if the magma keeps rising, the solubility of those gases
keeps decreasing, and the gases expand.
And it's that rapid expansion of the gas in the formation of
bubbles that drives magma to the surface that makes volcanoes
erupt and erupt explosively. So are we more likely to see wet
magma or the effects of water and the bubbles that you just
described in the tectonic settings where water has just
been subducted, IE in subduction zones or above subduction zones?
Yeah, exactly. Most of Earth's most explosive
volcanic eruptions will happen in places where you can get a
lot of water into magmas. And the best place to do that
are subduction zones where you're bringing water down with
the subductive plate that can enter into the source region for
the magma and then gets carried back up to the surface.
And so mid ocean ridges where plates are being formed.
Those magmas tend to be relatively dry.
At subduction zones, they tend to be quite wet.
I'm not sure if this is related or a separate factor, but I know
that the silica content of the melt is a critical determinant
of viscosity, with the viscosity increasing quite dramatically as
silica content increases. And so since high viscosity
magma tends to block the conduits as it cools, it can
lead to explosive eruptions when the pressure builds up and it
kind of blows its top. Is this silica content
variability independent of the volatile or water content of the
magma? So maybe we should put the
viscosity of magmas in perspective.
The lowest silica content magmas we see, the types of rocks we
call basalts, will have a viscosity or consistency very
similar to something like syrup or honey.
The more silica rich magmas like those we see in volcanic arcs
have a viscosity similar to asphalt, so more than a million
times greater. And the ability to flow is
proportional to viscosity. And so that means the magmas and
volcanic arcs will flow, you know, a million times more
slowly given the same forces driving their motion.
So the amount of silica in magmas has a huge effect on how
they can erupt. So the question was whether
there's a relationship between the amount of water and the
amount of silica observation, if that's the case.
And there's also a reason why. But I should point out actually
that understanding how we make silica rich magmas is still the
subject of quite active research, understanding what
processes dominate and why. But there are two main ways in
which we change the silica content of magmas. 1 is you can
heat the surrounding rock and melt some of it and incorporate
that into the magma sitting in the Crest, and we call that
assimilation, where you incorporate the surrounding
rock. The other process is that as
magma sit in the Crest, they cool and they start to
crystallize as they cool. And those crystals that form can
settle out of the magma and be separated from the remaining
liquid. And we call that fractional
crystallization. Where we crystallize, we remove
some of those crystals and it turns out the first crystals
that form are relatively low in silica.
So that means the magma that's leftover has more silica.
And so through this combination of crystallizing and removing
crystals and assimilating surrounding crust, over time the
magma gets more silica rich. And earlier we talked about the
importance of water liking to stand to melt.
So in the process of melting the surrounding rock or
crystallizing, whatever water was present gets concentrated in
the melt that's leftover. So in the process of enriching
magma and silica, you're also enriching it in water.
And so the two tend to increase over time.
Let's talk about how water is implicated in eruptions
elsewhere in the solar system. Miles, for example, used to have
lots of surface water and has some giant volcanoes.
Can we see evidence of water affecting the volcanic activity
there? Mars used to have abundant
liquid water at surface, and there's still plenty of water on
the surface today. We can see ground ice.
The Phoenix Rover sort of exposed some of it when it dug
into the ground. We can map some of the water
with gamma rays with spacecraft, and they're big ice sheets at
the North and South pole. I mentioned ice because there's
a distinctive landform that's produced when lava flows flow
over ice. We said that magma transfers
heat to the surrounding environment, and if that's
water, it can vaporize that water.
When you flow over ice, you can melt some of that ice, and then
you vaporize that ice. And so now you can imagine a
lava flow flowing on top of ice. It's heating the underlying ice.
That ice could be in the ground. The steam that's generated is
buoyant and expanding, and it blasts its way through the lava
flow, making a little tiny volcano.
We can see fields of these little volcanoes on top of lava
flows in Iceland, and people call them rootless cones,
rootless because there's no actual magma deep underground.
It's just a lava flow on which they're sitting.
And people have mapped out these fields of rootless cones on
Mars, so evidence that lavas flowed over frozen ground.
The youngest volcanism on Mars happened in a place called
Cerberus Fossae, just South of the Elysium volcano.
And there's some long fissures we see on the surface of Mars.
This is also where many of the recent Mars quakes have been
detected from the Insight Lander.
And it looks like there was recent explosive volcanism in
that area that looks like it was generated by magma interacting
with external water, either ice that it melted to incorporate
water like we see in Iceland, or groundwater.
What about some of the icy moons in the outer solar system, such
as Saturn's moon and Solidus? You know, my lifetime, this was
probably one of the most exciting observations from space
exploration is detecting active eruptions on Enceladus.
Enceladus is a small moon of Saturn.
It's got a radius of 250 kilometers.
It's covered with ice, and it's very cold out there.
And so it's hard to imagine 4 1/2 billion years after the
formation of our solar system, something as small as a little
ice ball like Enceladus could be, have both liquid water and
then be erupting that liquid water.
But it is the Cassini spacecraft both imaged that plume and it
flew through the plume and collected ice particles and
measured the composition of those ice particles.
And so now we understand that those eruptions are sourced from
an ocean underneath the ice covered surface, probably a
depth of say 10 kilometers. That ocean is a global ocean in
contact with the rocky interior. We know that because the
eruption is ejecting silica nanoparticles that come from
that interaction with the rocky interior, and those are very
powerful eruptions. They're sending ice particles
into one of the rings of Saturn called the E ring.
Not everything has escape velocity and leaves Enceladus,
so a lot of the erupted material falls back on the surface as
snow. And this actually makes
Enceladus the most reflective object in her solar system from
all that snow. And the eruptions on Enceladus
are interesting. They're probably most like
geysers. Geysers, we said, are boiling
water and liquid water as rises through these cracks at the
South polar region on Enceladus, as it gets to low pressure, that
water also boils. And that volume expansion from
boiling helps drive the eruption.
And once everything enters into space, whatever liquid was there
cools very quickly and forms ice particles.
And the source of that heating to make it boil is tidal
distortion. Yeah.
The source of heating for the oceans in the outer solar
system, ocean worlds is energy from tidal deformation.
The orbits of these satellites around their host planet is not
perfectly circular. And so when the satellite gets
closer to the planet, gravitational attractions bigger
and the planet deforms more. And then when it moves further
away, deforms last, and that squishing and unsquishing the
planet creates heat through friction, and that heat from
friction warms the interior. And for some of these ocean
worlds, that warming is enough to melt the ice to make a liquid
ocean. Europa, which is one of the
Galilean moons of Jupiter, is also covered in ice and it's
crisscrossed with fractures. Do we see water erupting out of
the ice there as well? Yeah.
Whether there are eruptions analogous to those we see on
Enceladus happening at Europa is uncertain, you might almost say
controversial. The Hubble Space Telescope, for
example, saw a plume of, or an anomaly of, of water vapour
above the surface, but it's not detected all the time.
So the question is, was it a false detection or contamination
somehow of some signal? Or it could be the eruptions are
episodic, and so they're on sometimes, not on other times.
From the Galileo mission, it's not obvious that anything they
saw could be attributed to active eruptions.
But certainly when we look at the surface of Europa, we see
features that are most easily explained, I think, by liquid
water being either on the surface or very close to the
surface. There's a type of terrain on
Europa called chaotic terrain, where you see something that
looks like a bunch of icebergs that have been displaced and
rotated a little bit. And that requires mobility of
those blocks of ice. And to enable mobility, it helps
to have a liquid like liquid water.
And we do know that Europa does have a liquid ocean underneath
that ice covered surface. And it's a deep ocean.
It's probably about 100 kilometers deep.
And again, like instead of this tidal deformation heating it up
and causing the water to seep up or blow through the cracks.
Yeah, Jupiter has four big moons.
The Galilean moons IO, Europa, Ganymede and Callisto and
Callisto. Ganymede and Europa are probably
all ocean worlds. What about IO then?
We did an episode earlier. It's the most volcanic object in
the solar system, but is there water involved there?
So IO is the most volcanically active body in our solar system.
And unlike its three neighbors, the ocean worlds covered in ice,
it's closer to Jupiter. It's tidal deformation heating
is much greater, and so it's much hotter.
And it's so warm that all the water that would have been there
has long since boiled away. But to make magmas erupt, you
need something to lower the density.
And so it could be that sulfur on IO plays the role that water
plays with magmas on Earth. So it's the volatile component
that starts forming gases and bubbles that helps drive the
volcanic activity on IO. If you could decide where to
send a new exploratory space mission to learn more about
volcanism in the solar system, especially with regard to the
effect of water, where would you choose?
Enceladus, I think, is an easy choice in part because we can
directly sample the ocean. The eruptions on Enceladus are
delivering that ocean to us above the surface, making it
easy to sample and easy to collect.
And it's a very fresh sample as well.
But I am always reminded that every time we visit a body we
have not gone to before, there are great surprises.
I never would have guessed, until New Horizons flew by Pluto
that Pluto was such an interesting ocean world with
such a rich geological history. I expected it would be a big
ball of ice. And it's anything but.
And I think the same is true for our exploration of Enceladus and
the other moons in the Saturn system.
They turn out to be quite a bit more interesting than we
originally expected, in part maybe because their imagination
is not good enough. Regardless, you know, every
decade or so NASA commissions the National Academy of Sciences
to undertake a decadal survey to identify the highest priority
targets for space exploration. And the most recent NASA
Planetary Science Decadal Survey recommended Uranus Orbiter to
visit Uranus. And Uranus has a number of
interesting moons, and that would be its highest priority
flagship mission, followed by an Enceladus mission.
And so Enceladus and its eruptions are clearly a
community high priority for exploration.
Of course, we have missions on the way.
Let's see. The Dragonfly mission is heading
to Titan. Whether Titan is an ocean world
or not is the subject of some debate.
I think until a year ago we all would have said Titan has an
ocean. There's a paper published in
Nature on December 17th, 2025, arguing in fact that Titan may
not be an ocean world. But it would be an ocean of
methane though. Titan has lakes and rivers and
an atmospheric cycle where there is a liquid and that liquid
would be hydrocarbons, methane, but that's in the very shallow
part of Titan. As we go deeper below the
surface, just like Enceladus or Europa, the interior is probably
mostly water ice, and you get deep enough that water ice can
melt to make a ocean of water. And we used to think Titan had
an ocean. That may not be the case, but we
do have other missions besides Dragonfly that has still to
launch. We have Clipper on its way to
study Europa. The Jupiter Icy Moons Explorer
with the acronym JUICE is on its way to study 3 ocean worlds of
Jupiter, right, Ganymede, Europa and Calista.
So whether or not these new missions will come to fruition,
we have a couple spacecraft on the way.
What are you working on at the moment?
In the last couple years I've had the great pleasure to go on
a couple oceanographic expeditions to study submarine
volcanism. The first was an International
Ocean Discovery Program expedition to the Aegean, part
of the Mediterranean, to study the volcanic history of
Santorini volcano and the nearby Christiana and Colombo volcano,
that whole volcanic field. And its goal was to understand
the interaction between volcanism, tectonics, right the
faulting and rifting to create those basins in which the
volcano set and the evolution of climate.
As sea level goes up and down, that change in pressure
influences the volcanic system. And so in that setting, we can
go all the way back 5 million years and look at the evolution
of that system and sea levels going up and down.
The faults are being activated and the volcanoes are erupting.
And we can do that from the birth of the volcanic centers to
their end in over multiple volcanic cycles.
And so we drilled over 7 kilometers of holes and
recovered thousands of meters of sediment to reconstruct that
volcanic history and also understand the processes that
drive submarine volcanism. And then in September of last
year, I was on the Australian research Vessel investigator
studying the Hunga eruption, recovering samples and mapping
to understand what drove that eruption.
And most of what erupted at Hunga powered that 57 kilometer
high eruption. Most of what erupted collapsed
and went underwater and was not transported in the atmosphere.
And those underwater currents travelled very far and very fast
underwater, snapping the communication cables that
connected Tonga to the outside world.
And so the expedition was aimed at trying to understand how the
volcanic eruption collapsed and what happened to that material,
what governed where it went and how it was transported.
And did you see a caldera that? It was a big eruption, and so it
left behind a hole in the ground.
And one of the questions that motivated that expedition is
understanding what that hole is. Was it a crater?
And a crater is produced by just blowing stuff up.
You can think about an impact. A meteorite hits the surface of
the Earth and excavates a crater from the impact, as opposed to
what we call a caldera, where the ground collapses because the
magma underneath is evacuated and the overlying crust sinks
into what used to be an area filled with magma.
And we're still trying to figure out, do the images we see
support the caldera or crater interpretation, But the
diagnostic signature would be identifying the faults on which
the ground would have collapsed. So hopefully as we continue to
process all our data, we'll be able to resolve all these
interesting open questions. Michael Mango, thank you very
much. Thank you for the time today and
for your listeners who joined for their interest.
You know, volcanoes are really fascinating.
That's a great life to be a volcanologist, and these are
great times to be a volcanologist.
And of course, there's so much still left to learn.
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