Erosion occurs when natural forces alter a landscape. What does it mean to alter a landscape

w

The question is asking "erosion occurs when natural forces alter a landscape. What does it mean to alter a landscape " - and the answer is that it means that something is changing how the landscape looks like. For example, a river would make a valley deeper through carrying stones with the water and removing sand from the bottom of the river, and so the valley would be altered, that is changed.