Formation of potholes in river beds is an example of?

Potholes in river beds are formed due to cavitation. Cavitation is the formation of vapor bubbles in a liquid due to a sudden decrease in pressure. This can occur when water flows over a rock or other obstacle in the river bed. As the water flows over the obstacle, the pressure decreases and the water vaporizes. The vapor bubbles then collapse, creating a shock wave that erodes the rock or other material. Over time, this can create potholes in the river bed.