Mass movement is responsible for the redistribution and movement of a lot of material on the coastline.
Put simply, mass movement is the downhill movement of material, influenced by gravity. There are four types of mass movement, each caused by different factors:
Rockfall occurs when pieces of rock fall away from the cliff face due to weathering, especially with freeze-thaw weathering.
The slopes are steep, and the movement of material is rapid. Rockfall can also happen with earthquakes, or other extreme weather such as very heavy rain.
Flow is usually associated with the process known as mudflow. The soil becomes saturated with water and flows down a slope. This flow is a massive movement of material, which can carry rocks and vegetation with it.
Normally preceded by the word ‘land’ for a landslide, this is the movement of material as a whole, which remains intact until it reaches the bottom of the slope. Slides can be dangerous for people and animals, as the movement can be rapid and involve large blocks of rock that slide down a slope.
Slump is the process of weaker rocks becoming saturated and heavy, sliding their way down the slope in one mass. This is common on the coast and is also known as a rotational slip. The mass of land leaves behind a curved, scooped-out surface as it moves toward the foot of the slope.
Mass movement is a crucial process in shaping the coast. When a coastal cliff is subjected to extensive weathering and erosion, it becomes weaker and is unable to support the material above it. If a cliff is weakened, it is more easily influenced by gravity and mass movement.
The more frequent or more dramatic the mass movement, the more impact it will have. As coastal slopes and cliffs are subject to falls, flows, slides and slumps, they lose material, and the cliff line retreats (moves backwards). Mass movement is a process that works to change the landscape alongside other processes; if there are higher levels of erosion or weathering, then mass movement will have a more significant impact.
Mass movement also poses a threat to human activity. People can be injured by fast-moving masses such as through landslides, and property or land can be damaged or lost in the process.