Why is a valley so low between the hills?

Have you ever stood on a hill and looked down? Feel the wind on your cheeks. Far below, the ground dips low, like the inside of a big bowl. At the bottom of many valleys, a little river shines in the sun.

The hills stand tall all around the valley. So why is the valley so low? Let's find out together.

It all starts with rain. When rain falls on the hills, the water does not stay up top. The Earth pulls it down, so it runs downhill.

Little trickles of water run down from every slope. They meet in a small dip between the hills and join together. Now they make a river, and it flows there day and night.

The river runs over its riverbed, which means the ground right under the water. The water rushes over the riverbed, fast and strong.

The rushing water pushes sand and little stones along. They bump and scrape the riverbed, again and again. Little by little, they wear away the riverbed, which means they rub off tiny bits of it. Where do you think all those tiny bits go?

The river carries them away! It sweeps the tiny bits along with it, far from the hills. So each day, the riverbed gets a tiny bit lower.

This takes a very, very long time, much longer than anyone can remember. Bit by bit, the river cuts deeper and deeper into the ground.

The hills on each side stay high, because the river does not flow over their tops. Only the low middle keeps getting worn away. So the river's path turns into a deep, low valley between them.

Rain makes a river, and the river wears away its riverbed, bit by bit. So the ground between the hills gets lower and lower, while the hills stay high.

Down at the bottom of the valley, the little river still shines in the sun. Its water flows along, carrying sand and stones, all day and all night.