Back-arc basin

Okay kiddo, imagine you have two pieces of bread that you put together to make a sandwich. Now imagine that one piece of bread is a big piece of land and the other piece of bread is a big piece of water.

Now, sometimes when the land is moving around a lot, like when two pieces of land are crashing into each other (like when you play bumper cars), it can push down on the big piece of water and make a new area where the water is deeper.

This new area where the water is deeper is called a back-arc basin. It's kind of like a little pool that forms behind the big piece of land.

These back-arc basins usually happen when two pieces of land are colliding and one piece of land is getting pushed down under the other piece. This can cause volcanoes to form along the edge of the land, and sometimes hot water and gas can come up from the ocean floor.

So a back-arc basin is like a little pool of deep water that forms behind two pieces of land that are crashing into each other. It's where volcanoes can form and hot water can come out of the ocean floor!