What is Mass Movement?
Mass movement is the downslope movement of slope material such as soil, mud and rock under the pull of gravity. Rainwater adds weight to the material and reduces friction between particles, making movement easier. Mass movement can be slow or rapid. The moving material is called regolith, the layer of weathered rock lying on the bedrock.
Types of Mass Movement
- Soil creep — the slowest movement; tilted poles, bent trees and cracked walls are its signs.
- Slumping — material slides in a rotational way along a curved surface, common on clay slopes and coastal cliffs.
- Landslide — the rapid, sudden sliding of a mass of rock and soil down a steep slope.
- Mudflow — the fast flow of water-saturated soil, often after prolonged heavy rain.
Key idea
Mass movement is controlled by gravity, slope steepness and water content; it moves faster as the slope gets steeper and the soil gets wetter.
Factors and Effects
Steep slopes, heavy rain, weak rock, lack of vegetation and deforestation raise the risk of mass movement. Human activities such as cutting slopes for construction and farming on hillsides are also major causes. Effects include destroyed buildings, blocked roads, ruined crops and loss of life, as in the Highland Towers tragedy in Selangor. Control measures include replanting trees, building retaining walls and installing slope drainage. Warning signs and slope monitoring also help to reduce the risk of disaster.