Mass movement is the downslope movement of the rock debris in response to gravity without the direct aid of other media such as air, water, ice, and ground shaking (still these factors contribute to the process of mass movement). Downslope movement occurs when the gravitational driving force exceeds the frictional resistance of the material resting on the slope. The ultimate driving force of mass movement is gravity. At any point on the earth’s surface, gravity (Fg) acts vertically downwards towards the Earth’s centre but can be resolved into two components on a sloping surface, one parallel to the slope surface (Fp) and one perpendicular (“normal”) to it (Fn).
Orders of Landforms:
Mass wasting occurs in all environments:
Almost in all types of the environment, a mass movement is common, but very large landslides are most common in tectonically active upland areas, where they are favoured by the lethal combination of;
• steep slopes.
• rapidly incising rivers.
• glaciers on valley floors (glacial transport).
• severe physical weathering producing jointed and fractured rock.
• fluctuating groundwater pressure.
• episodes of intense rainfall.
•On lower slopes and lowland areas, most landslides occur as a result of water pressure increases during heavy rain or snowmelt.
Landforms produced by Mass Movement:
The landform can also be divided into three types according to their constructional, depositional and destructional nature.
(1). Constructional Landforms: These are of three types as detailed below:
- Due to Earth movement: Fault mountains, garbens, fold mountains, down-wraped basins and the dome mountains.
- Due to Volcanic Activities: Lava plains, calderas crater lakes, cinder cones and volcanic cones.
- Due to Weathering: Talus, rock glaciers and landslide acumulations.
(2). Depositional Landforms: These are of five types:
- Fluvial; Fans, cones, deltas, and flood plains.
- Glacial; Drumlind, Eskers, Moraines, and outwash plains.
- Eolian or wind; Loess plains and sand dunes
- Littoral or waves; Beaches, offshore bars and spits.
- Organic; Coral reefs.
(3). Destructional Landforms: These are of five categories.
- Fluvial; Valley, monadnocks, and paneplains.
- Glacial; Coles, Troughs, cirques, aretes and horns.
- Eolian; Deflation hollows, yardages.
- Littoral; Sea cliffs, terraces sea stacks.
- Underground Water; Sinds and natural brides.