Yellowstone National Park
is an incredibly beautiful place,
visited by millions of people
every year.
Its popularity is surprising,
considering it sits
on a massive volcano.
Heat from underground
has created hot springs,
and geysers, where the water
is so hot it changes state
to a gas.
Thankfully,
the Yellowstone volcano
has not had an eruption
for over 600,000 years.
Other active volcanoes
erupt more frequently.
In a volcano
there is so much heat energy
that even solid rock
can change state to liquid
and gas.
Deep underground,
heat and pressure build up.
Eventually, the solid rock
absorbs so much energy
that it becomes a liquid.
When this molten rock
is underground we call it magma.
The magma forces its way
to the surface,
and explodes out of the volcano.
[volcano explodes]
boom!
Once expelled from the volcano,
this flowing river
of red-hot rock is called lava.
At the same time,
enormous amounts of gas
are released high
into the atmosphere.
Gases like water vapor,
carbon dioxide
and sulfur dioxide,
that smells like rotten eggs!
Over time, the volcanic materials
lose heat energy
and change state once again.
The water vapor cools
and will fall to Earth as rain,
and the lava solidifies back
into rock.
The volcano will be calm,
until the next eruption!
