Tunnel valley

Have you ever played with sand on the beach and made little tunnels in it? A tunnel valley is kind of like a big version of that, but it's made of dirt and rocks deep underground.

A long, long time ago - even before dinosaurs - parts of the Earth were covered in ice. These icy sheets were really heavy and pushed down on the ground like a roller. It made the ground go down, then go up again, like a rollercoaster.

When it started to get warm again, the ice melted and ran off the top of the hills like water from a bathtub. This melted water went down into the valleys and made rivers. But it also made little tunnels in the dirt and rocks, like the ones you made on the beach.

Over lots and lots of time, these tunnels got bigger and bigger as more and more water flowed through them. And that's how tunnel valleys were formed! Now we can find them deep underground, and scientists study them to learn more about what happened a long, long time ago.