It's so cool when huge mountains erupt with waves of lava and clouds of ash!

But did you know there are other things that erupt that aren't volcanoes?

They're called geysers, and instead of spewing out lava and ash, they erupt with a big spout

of water and steam!

This is Old Faithful, one of the most famous geysers in the world.

It's in Yellowstone National Park in Wyoming, and thousands of people come to see it erupt

every year.

When a geyser like Old Faithful erupts, it creates an amazing display of water shooting

into the sky.

But Old Faithful is extra special because it erupts on a set schedule!

A lot of geysers only erupt once in a while, and it's hard to know when it's going

to happen.

But Old Faithful erupts about every hour and a half, sending thousands of liters of boiling-hot

water flying up into the air.

[Squeaks squeaks]

Well Squeaks, it doesn't work exactly like a sprinkler.

The water that erupts from geysers is so incredibly hot that you can't touch it without getting

burned.

In fact, all of that water needs to be really hot in order to shoot out of the ground in

the first place.

Geysers form in special places where there are big pools of water underground, called

reservoirs.

Normally, the water in a reservoir is very cold, and there's a thick layer of rock

that separates it from the magma inside the Earth.

Magma is basically rock that's melted into liquid, and it's super hot — much hotter

than the water in the reservoir.

In most places, the rock layer in between the magma and the water is thick enough to

keep the magma's heat from reaching the water.

But in some areas, the rock layer is thin enough that the heat from the magma can get

to the water.

And when you have something very hot near water, the water heats up and boils, just

like in a pot on your stove.

Now, there's something that's different between a pot of cool, calm water and a pot

of boiling hot water — other than the bubbles.

What do you think it is?

[Squeaks squeaks]

That's right, Squeaks!

Boiling water moves around a lot.

That's because when water is boiling, it has a lot of energy from all of that heat,

which makes it move around and bubble.

But when the water in a reservoir boils, there isn't much room in there for it to move

around!

So, the boiling water rises up to the top of the reservoir pool, and it finds any cracks

in the top of the reservoir.

Then, a bunch of things happen very quickly:

The boiling water races through the crack in the reservoir ceiling, and as huge amounts

of hot water flow into that small space, it moves faster and faster.

The water moves so fast, that when it finally reaches the Earth's surface, it shoots out

of the top in a big spout, creating a geyser!

The water in the reservoir under the Old Faithful is almost always very hot, and every hour

and a half or so, there's enough boiling water to cause a huge eruption.

So, there are a lot of things that need to happen for a geyser to form: there needs to

be a reservoir, and magma, and extra-thin rock between them, and a crack for the water

to flow through, all at the right temperatures to cause an eruption.

And that only happens in five countries in the world!

Only the United States, Russia, Chile, New Zealand, and Iceland have geysers.

Geysers around the world can be very different, though.

Some, like the Little Cub Geyser in Yellowstone, aren't very big.

The Little Cub is less than 2 meters high, or just about 5 feet tall — shorter than

most grown-ups.

Others, like the Steamboat Geyser, which is also in Yellowstone, can reach over 120 meters

high, or 400 feet.

Lots of geysers, including Old Faithful and Steamboat, don't have other geysers around them.

But there are some places that have lots of geysers all together.

That can happen where there are a bunch of cracks in the Earth's surface all close

together, so boiling water from a reservoir can erupt from lots of different geysers in

one area.

Like in the Valley of Geysers in Russia!

It has almost a hundred geysers that have erupted over and over, creating really incredible

sights!

[Squeaks squeaks]

Maybe we should go and visit Old Faithful, Squeaks!

It's not very far from where we live.

Would you like to visit a geyser and see it erupt?

What other amazing landforms do you want to learn about?

Ask a grown-up to help you leave a comment below, or send us a message at kids@scishow.com.

We'll see you next time, here at the fort.