Book 5, Question 71 · Video
Underground Worlds! Why Do Caves Form?
Rainwater picks up a little acid from the air and soil. Where the rock is limestone, that slightly acidic water can slowly dissolve the rock and carve out empty spaces underground.
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What Crafty Clover says in this video
Intro
Hi! I'm Crafty Clover! Let's discover something amazing. Why do caves form?
The Big Idea
Deep under the ground, there are huge rooms of rock, called caves! Many caves start with rainwater. Rain picks up a little acid, and slowly eats away some kinds of rock, like limestone, along cracks. Rain plus time can eat a room in the rock! Let's see how.
Step 1
Step one: rain picks up a little acid. As rain falls and soaks through soil, it picks up carbon dioxide. That makes it a very weak acid, like fizzy water. It's much too weak to hurt you.
Step 2
Step two: the water finds a crack. Limestone has tiny cracks. The slightly acid water trickles down into them. It slowly dissolves the rock around the crack.
Step 3
Step three: a room grows. Over thousands and thousands of years, the crack widens into tunnels, and then into a big open chamber. Later, drips can build stone icicles inside!
A Closer Look
Let's peek inside a cave. The thin opening at the top is a crack in the limestone. The big open room is the chamber. Stalactites hang from the ceiling. Stalagmites rise from the floor.
Quick Facts
Quick facts! A stalactite hangs from the ceiling, and a stalagmite grows up from the floor. A tip: stalactites hold tight to the ceiling! Stalagmites grow very slowly, often only about a centimeter every hundred years. Each drip leaves behind a tiny bit of mineral, and that slowly builds the stone icicles. Grown-up note: caves are dark, wet, and easy to get lost in. Only visit with a trained guide.
Think Like a Scientist
Now, think like a scientist! Try this with a grown-up. Put a piece of chalk in a little vinegar, and watch the bubbles. The acid slowly eats the chalk, just like rain eats limestone. Why does a cave need so much time?
Outro
So caves form when slightly acid rain slowly dissolves rock, over a very long time. Amazing, right? Crafty Clover can be found on Amazon Books, Google Bookstore, and Apple Books. Available for purchase or download! Bye for now!