Question

What process is involved in the formation of a waterfall, when a stream flows from an area of harder to softer rock?

Answer 1

erosion

Mountain streams may erode waterfalls. A waterfall forms where a stream flows from an area of harder to softer rock   Figure below  . The water erodes the softer rock faster than the harder rock. This causes the stream bed to drop down, like a step. This creates a waterfall. As erosion continues, the waterfall gradually moves upstream.