ICSE Class 9 Answered

Four rapid mass movements are:

1. Landslides: This is the most common of all the mass movements. When the surface of the rock breaks off, rock is displaced from its place and a heavy movement of rock and mud takes place. The downwards slope of the rock takes place in two main ways:
1. Fall: When the fragments of rocks fall down through steep slopes, fall takes place.
2. Slide: When a rock along with mud comes down a slope in a fixed path, the movement is called a slide.
2. Earth Flow: When fine grained materials which have been saturated with water, come down a slope due to the pull of gravity, it is known as anearth flow. It generally occurs in areas which have alluvium soil, and in hilly regions.
3. Mud Flow: When water flows with many particles like silt, down a slope, it is called mud flow. In mud flow, the quantity of water is more than in an earth flow. It generally takes place in areas where vegetation is sparse and slopes are steep.
4. Sheet Wash: When the entire piece of land is covered with a thick layer of mud, soil and water, it is called a sheet wash. This occurs in the absence of natural vegetation. Many parts of the world have been affected due to sheet wash.