Mass Movement

Mass Movements, also called Mass Wasting, is the movement of a massive amount of materials down the slope under the direct influence of gravity. The material moved can be rocks, soil, or even snow and ice, but water and air are not very effective agents to move these masses. Some examples of mass movements are a creep, flow, slide, and fall in western ghats, the Himalayas, etc. These mass movements may vary from slow to rapid affecting shallow to deep columns of materials. The Geography Class 11: Mass Movement chapter also mentions the following. 

• Gravity has an effect on all stuff, even bedrock and weathered materials. Weathering is not a need for large movements, but it does help mass movements
• Overworn slopes, mass movements are particularly vigorous
• Gravity aids radical movements and no geomorphologic agents such as flowing water, mountains, wind, tides, glaciers, or wave action play a role in the process
• Though a transfer (assisted by gravity) of materials from one point to another, mass motions are not subject to erosion
• Components on the slopes have their very own resistance to unsettling pressures and will give up only after the force exceeds the materials’ shear resistance
• Mass movements are favoured by weak unconsolidated components, thinly layered stones, cracks, sedimentary rock beds, sheer cliffs or steep terrain, heavy precipitation and torrential showers, and a lack of vegetation, among other factors

Activating causes of Mass Movements

• Natural or artificial ways of transferring support from below to materials above
• Increase in slope grade and height
• Overloading occurs when materials are added naturally or artificially
• Over saturation and lubricating of slope materials owing to severe rains
• Material or load is removed from the original slope surfaces
• Earthquakes and explosions are common
• Natural seepage is excessive
• Excessive water withdrawal from lakes, dams, and rivers causes a gradual discharge of water from under slopes and riverbanks
• Destruction of the natural vegetation on an indiscriminate basis

Types of Movements

• Heave (heaving up of soils due to frost growth and other causes)
• Flow
• Slide

Landslides

• These are relatively quick and noticeable motions
• The materials in question are relatively dry
• The size and morphology of something like the detached mass are determined by the type of the rock discontinuities, the amount of erosion, and the slope’s angle of inclination

Types of Landslides based on types of movement

• Slump landslides: The retrograde rotation of one or more pieces of rock debris concerning the slope across which the movement occurs
• Debris landslides: It is defined as the quick-rolling or sliding of earth debris without any bulk rotation in the reverse direction
• Debris fall: Earth debris is almost entirely free to tumble down a vertical or overhanging cliff in the Debris fall
• Sliding: Rockslide is the term used to describe the movement of individual rock masses along the substrate, joint, or fault surfaces. Rock sliding on steep slopes is rapid and damaging
• Rockfall: Rockfall refers to the free fall of rock blocks down a steep slope while staying clear of the slope. Rockfalls occur from the rock face’s surface layers, separating them from rockslides, which influence materials to a significant depth

Debris Avalanche and Landslides in India

In the Himalayas:

• Tectonically, in the Himalayas, landslides are pretty active
• Sedimentary rocks and poorly consolidated and semi-consolidated deposits make up the majority of them
• The incline is steep in the Himalayas

In the Western Ghats

• The Nilgiris border Tamil Nadu, Kerala, Karnataka, and the Western Ghats on the west coast, is tectonically stable and primarily made up of some mighty rocks, yet debris eruptions and landslides do occur
• Many slopes in Western Ghats and Nilgiris are steeper, with virtually vertical cliffs and escarpments