[♪ INTRO]
It was really nice of Sam to invite us over!
Hi there, we just got back from visiting Sam the Bat.
Sam invited us to explore the cave where his family lives.
So Squeaks and I have been learning all about caves!
That’s true.
Sam the Bat’s cave looked pretty different from
some of the other caves we’ve looked at in pictures.
While they all have some things in common,
there are actually many different kinds of caves, and they all look unique.
Let’s start with things they have in common.
Caves are really just large spaces underground or in a hard surface like rock.
Actually, yes, the Fort is a cave!
This part of the Fort is in the basement, which is underground.
But before we decorated it all nice and comfy, there was a cave here!
Most caves are made by nature, instead of being dug by people.
The different natural materials that make caves are
one of the things that can make them different from each other.
And the reason why there are so many different kinds of caves is
because of the different places and the ways nature makes them.
One of the most common tools nature uses to build caves is found all over,
in oceans, lakes, coming out of your sink…
Yes, you’re right!
Water!
When water washes against rocks, it wears away at them.
This is called erosion.
And over time, water can transform rocks in big ways,
including turning them into caves!
Limestone caves are made when water goes down through the ground,
and mixes with different parts of the ground to make acid,
a liquid that can break down a kind of rock called limestone.
The watery acid eats away at the rock, leaving behind empty spaces.
That means it’s a kind of erosion.
When the water and acid have eroded enough rock,
the empty space left behind can become a new cave!
But there are many other ways, and many other places, where caves can form.
Sometimes, where the ocean meets the land, there are cliffs in between.
And the ocean waves wash up against those cliffs, again and again and again.
Those cliffs sometimes have small cracks or breaks in them.
And water gets into the small cracks in the rocky cliffs,
and then begins breaking off and carrying away tiny pieces of rock.
So more erosion happens in the side of the cliff.
More and more pieces get taken away, until eventually,
there’s a huge hole in the side of the cliff.
We call caves like these sea caves.
Ooh, interesting question, Squeaks.
It actually takes a really long time for water to erode limestone or cliffsides.
It can take millions of years for caves to form like this.
Some caves around today probably started forming
before there were any people around!
However, water can work a little faster to make caves
if it’s in something other than rock.
Glacier ice caves are made during warmer months,
when part of giant glaciers made of ice start to melt into water.
A glacier is like a big ice blanket that sometimes sits over mountains.
The solid ice can start to melt into liquid water when it gets warm.
The water melts more and more of the ice around it as it flows through the glacier.
That hollows out big spaces in the glacier that stay behind
during the colder months, when liquid water freezes into ice again.
People can actually explore some glacier ice caves,
but it’s really, really cold in there!
But I can think of one type of cave that forms quickly,
and with something much warmer than ice or water.
Lava caves!
Lava caves, or lava tubes, are made when a volcano erupts,
and lava flows down across the ground.
Lava is the liquid form of rock, just like water is the liquid form of ice.
So the lava can flow like a river of water does.
The top layer of that lava gets cooled by the air touching it,
hardening the lava into a crust of rock over the rest of the lava river.
When the rest of the lava flows down a hill and away, that rocky crust layer is
left behind, with an empty tube underneath where the lava had been.
It does look a bit like the inside of a straw!
But this tube also has a lot of rocky ledges, and sometimes twists and turns.
Lava caves form much faster than limestone caves, sea caves, or glacier caves;
but even though they’re very different, they’re still caves.
Yes, it is amazing how things as different as
water and lava can end up both making caves!
Learning about all the different types of caves can show us how nature can
change really slowly, like with limestone caves, or really quickly, like the lava caves.
Which is your favorite type of cave, Squeaks?
Aww, the Fort is probably my favorite cave, too.
Any cave that I get to share with my friends is a great cave.
What kinds of caves would you want to explore?
Can you think of anything else that could help to build a cave?
Remember to hit the subscribe button to continue learning with Squeaks, me,
and all of our friends, and we’ll see you next time, here at the Fort.
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