Convergent boundary

Do you remember when we played with two toy cars and made them crash into each other? That's kind of what happens when two big rocks in the Earth's crust (the outside layer of the Earth) are pushing towards each other. This is called a convergent boundary.

Imagine that the Earth's crust is made out of different layers, just like a sandwich. The top layer is called the lithosphere and it's the rocky part that we can see. Underneath that, there is a layer called the asthenosphere which is hot and gooey like melted cheese. When two pieces of the lithosphere push towards each other at a convergent boundary, they start to sink into the asthenosphere.

Now, when two cars crash into each other, they usually get all smashed up and don't move anymore. But when two tectonic plates (the big pieces of lithosphere) collide, some pretty amazing things can happen. Sometimes, the edge of one plate will slip under the other one and this is called subduction. This creates a really big trench in the ocean (like a canyon but underwater) because the sinking plate takes a bunch of ocean floor with it.

Another thing that can happen is that both plates are really strong and they don't want to sink. So they just keep pushing and pushing against each other. This can make the rocks on top buckle and fold up like a big crumpled piece of paper. When this happens, it creates really tall mountains, like the Himalayas in Asia.

So, in short, a convergent boundary is when two pieces of the Earth's crust are crashing into each other and sometimes it can create giant mountains or deep trenches in the ocean.