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- Earth is constantly changing
the way it looks,

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and there's more happening
beneath our feet

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than you might expect.

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[dramatic music]

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Can you tell the difference
between these two mountains?

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The difference
is Earth-shattering.

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- The difference between
a mountain and a volcano

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is that volcanoes

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are formed from lava,

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whereas mountains are not
necessarily formed from lava.

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Volcanism changes and shapes
our planet

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by giving us new landmasses
such as Hawaii,

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such as Iceland,

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and it also builds these tall,
mountain-like structures

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on the surface of our planet.

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And in many cases,
it actually helps

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to make the ground
more fertile for planting

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of different types of crops.

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- Volcanoes are places
on the Earth or other planets

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where molten material
from the inside comes up

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and flows out or explodes out
onto the surface.

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Volcanoes will form anywhere

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that the material
from the inside

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can make its way
to the surface.

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Sometimes the material
will just shove its way up

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and makes its own pathway.

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Other times, it'll follow
a fracture or a crack

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through the rocks
at the surface.

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- Faults are just cracks
in Earth's crust

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that form the boundaries
for Earth's tectonic plates.

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- One of the things you can
actually tell right away

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from looking at a volcano
is if you look at its slope,

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if you just look
at the volcano as a whole,

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it's just the height
divided by the width.

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A shallow-sloped volcano
was one that was formed

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by magma that had a
low viscosity, that was runny,

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and a steep-sloped volcano

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is one that was formed
by a magma that was sticky.

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When magma moves around, it
has to push the rocks around.

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And one way
that we can measure that

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is through the breaking
of the rocks

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using seismometers.

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- Volcanoes play a role
in how Earth looks today,

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but did you know that volcanoes
are on other worlds

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in our solar system?

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You didn't?
Well, that's not your fault.

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- Mars has volcanoes.

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Actually, the largest volcano
in our solar system,

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Olympus Mons, is on Mars.

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Venus has volcanoes,

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Jupiter's moon, Io, has lots
and lots of volcanoes.

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And there are hundreds
of volcanoes on Io's surface

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and they erupt daily.

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- Not all planetary bodies
are made of rocks,

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and in fact,

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the outer solar system,

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the majority
of the bodies out there are--

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have an icy surface.

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And so through heating
and other mechanisms,

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you can melt ice
just like you can melt rocks.

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- And so when we have
volcanism on these moons,

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instead of taking the form
of hot rock or lava

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that erupts onto the surface,

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we have slush
that erupts onto the surface.

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What we call this
cold volcanism,

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or this icy volcanism,
is cryovolcanism.

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You have a planet that
has a very smooth surface,

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then you know that volcanoes
or cryovolcanoes

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have been active.

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You know that
there's been some fluid,

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whether that be lava,

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or when you're talking
about icy volcanism,

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icy lava or a cryolava that's
erupted onto the surface

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and it smoothed
the surface out.

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- Cryovolcanoes?
Cool.

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So there are different types
of volcanoes

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and they can be found
all over our solar system.

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But how do we know this?

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- So the technology that's used
to explore volcanoes

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that I use the most
is basically

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data that comes back
from robotic spacecraft.

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So NASA has sent spacecraft

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to many planets and moons.

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From these pictures,
we're able to determine

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how tall these volcanoes are,
how wide they are.

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These spacecraft also have
instruments that tell us about

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the composition
of those volcanoes.

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What we're able
to do with that information

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is we're able to use,
then, computer models

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and mathematical equations

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to try to figure out
how these volcanoes formed,

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how runny the lava was
that formed them.

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- Other ways that we can
monitor volcanoes include

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paying attention to gases
coming out of fractures

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around the volcanoes.

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A really big volcanic eruption
can have global effects.

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Something big
like Mt. Pinatubo

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puts so much ash into the air

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that it actually cooled
the Earth off

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for a little while.

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- It's important
to study volcanoes

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because they teach us a lot

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about the interior properties
of planets and moons.

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So, if we see volcanoes on the
surface of a planet or a moon,

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we know at one time or another

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that the interior
was warm enough

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to sustain that type
of activity.

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When we think of our own
planet, Earth,

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volcanism has been
very important.

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We have this very nice
atmosphere that, you know,

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full of nitrogen and oxygen
that we breathe here.

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Early Earth's atmosphere
was actually formed

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from gases that erupted
from volcanoes.

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- It's important
to study volcanoes

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no matter where they are,

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and thanks to NASA,
we know more about volcanoes

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on our planet and
in our solar system.

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Talk about explosive science.

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For "Real World,"
I'm Mishay.