The sand castle will begin to disintegrate and crumble as water is poured over it till there remains nothing but a shallow pile of sand. Ask the students to compare this activity to rainfall and the effect it has over mountains and hills over a long period of time. Landslides can be caused by prolonged rainfall over hills and mountains. Over a period of time, erosion can wear away a mountain until it is level with the plains. Short term effects of erosion are evident in river cutbanks, hillsides, and gullies.
Erosion can strip the earth of valuable mineral-laden top soil, which harms agriculture.
The more that students know about the causes and prevention of erosion, the more they can do to wisely use the land and not destroy or misuse it.