Here's why:

* Faults are fractures in the Earth's crust where rocks have moved past each other. They can be caused by:

* Earthquakes: The sudden movement of rocks along a fault is what causes earthquakes.

* Tectonic forces: The slow, continuous movement of tectonic plates can create faults.

* Erosion: Rivers can sometimes carve through rock formations, creating faults.

* Cracks are a more general term for any break in a material. While a fault is technically a crack, the term "fault" is used specifically to describe breaks in the Earth's crust where there has been movement.

So, a large crack in the earth formed by a river or earthquake is called a fault.