Mass movements are the movement of masses of bodies of mud, bedrock, soil, and rock debris caused by gravitational pull along steep-sided hills and mountains. It is also known as slope movements or mass wasting. It can be slow or fast, influencing shallow to deep columns of material and working creep, flows, slide, and fall. Gravity aids mass movements, and no geomorphic agents such as running water, glaciers, wind, waves, or currents participate in the process. This article will explain to you about Mass Movements - Denudational Processes which will be helpful in Geography preparation for the UPSC Civil service exam.

What is Mass Movement?

• Mass movement is the movement of weathered material down a slope due to gravitational forces.
• The movement may be gradual or sudden, depending on the gradient of the slope, the weight of weathered debris, the presence of lubricating moisture, etc.
• Mass movement is erosion, transport, and accumulation processes that occur on both gentle and steep slopes, mostly due to gravitational forces.
• As a result of mass movements, landscapes are leveled and formed.
• Mudslides, landslides, and avalanches are examples of mass movements that involve the sliding of massive amounts of soil and rock.
• Air, water, and ice do not transport debris from one location to another; however, debris may transport water, ice, or air.
• These are more active on weathered slopes than unweathered materials.
• Though there is a shift of materials from one location to another, mass movements are not erosion.

Mass Movements - Classification

The mass movements are often classified into two major classes:

• Slow movements
• Rapid movements

Mass Movements

Slow Movements

Creeping

• It occurs on moderately steep, soil-covered slopes (and does not require water lubrication as solifluction does).
• Except by prolonged observation, the movement is exceedingly slow and unnoticeable.
• We may have seen that several of our region's electric posts in sloppy regions have drifted from their horizontal linearity. This is a creep effect.

Soil Creeping

Solifluction

• It's the gradual downslope movement of water-saturated or lubricated soil mass or fine-grained rock debris.
• It's a kind of creep in which the movement is influenced by lubricated water.
• Because groundwater strata are occupied in between permanently frozen soil and rocks in permafrost zones, it primarily occurs there.

Solifluction

Rapid Movements

Earthflow

• It is the downslope movement of water-saturated clay or silt along a hill.
• Depending on the steepness of the slope, even the soft sedimentary bedrocks can also slide down in case of a higher slope.
• Deeply weathered igneous rocks can also slide down.

Earthflow

Mudflow

• A mudflow occurs when thick layers of weathered materials become saturated with water and flow down along definite pathways in the absence of vegetation and cover, and when significant rainfall occurs.

Mudflow

Debris Avalanche

• It occurs more frequently in humid areas with or without vegetation.
• It is similar to a snow avalanche and happens in narrow pathways on steep mountains.

Debris Avalanche

Landslides

• Regardless of the above-mentioned rapid mass motions, the materials involved in landslides are rather dry.
• Slump, debris slide, rockslide are the forms of landslides.

Landslides

• Slump: A form of landslide in which many units of rock debris slide backward in relation to the slope over which the movement occurs.
• Debris slide: There is no backward rotation in this sort of landslide. The drop is nearly vertical.
• Rockslide: It refers to the movement of individual rock masses.

Major Causes of Mass Movements

• Gravity: The fundamental driving force behind all mass movements. It constantly pulls materials downward, with steeper slopes generally being more susceptible to mass wasting.
• Saturation from Water: Water infiltrating the ground can increase pore pressure in between soil and rock particles, reducing their friction and cohesion.
• Oversteepening of Slopes: Human activities, such as road construction and mining, or natural processes, like river erosion, can oversteepen slopes making them unstable and more prone to collapsing.
• Removal of Vegetation: Deforestation, forest fires, or human construction can remove this protective cover, making slopes more vulnerable to mass movements.
• Earthquakes: The shaking from seismic activities can dislodge rocks and soil, especially on steep slopes, triggering landslides and rockfalls.
• Volcanic Activity: Eruptions can lead to the rapid melting of snow and ice on volcanoes, producing lahars – a type of mudflow or debris flow.
• Weathering: Chemical and physical weathering weaken rocks, making them more susceptible to being dislodged and moved by gravity.
• Freeze-thaw Cycles: In colder climates, the repeated freezing and thawing of water in cracks can weaken rocks, leading to rockfalls.
• Human Activities: Excavation, loading of slopes, artificial vibration, and other human-induced factors can contribute to slope instability.

Conclusion

Mass movements can occur due to natural phenomena such as earthquakes, volcanic eruptions, and floods, but gravity is the driving force. It is mainly influenced by the strength and adhesion of the slope material as well as the frictional force acting on the material. Human activities such as mining, highway construction, or shopping malls can also contribute to mass wastage.