The eruption of a volcano The erosion of the walls of a canyon The uplifting of mountain ranges The forming of dunes or mounds in a desert
I gave my students this multiple choice question: Roger poured water over a pile of sand. Some of the sand washed away. This process is similar to which of the following?

Only one answer is correct among these 4 choices:
- The eruption of a volcano
- The erosion of the walls of a canyon
- The uplifting of mountain ranges
- The forming of dunes or mounds in a desert

Could you tell me which one is correct?

The erosion of the walls of a canyon