Erg (landform)

Okay, imagine you're playing with a bunch of sand on the beach. You make little mountains and valleys with your hands, right? An erg is like a really big version of those mountains and valleys - but instead of sand, it's made out of tiny bits of rock and sand.

Now, the really cool thing about an erg is that it's constantly changing shape! This is because the wind blows the little bits of rock and sand around, making them shift and move. That's why ergs look different every time you see them - the wind has changed where all the little bits are.

People who study ergs call them "dunes," which is a fancier word that means the same thing. Just like how you can run up and down the little sand hills on the beach, people can climb up and slide down the dunes in an erg too! But you have to be careful, because the sand can be really hot during the day and really cold at night.

So, an erg is basically a giant mountain and valley made out of tiny rocks and sand that the wind blows around, and it's always changing shape.