Mass Movement, Meaning , Causes, Types, in Geography

Mass Movement

Mass Movements can be defined as the transferring of mass of rock and debris down the slopes under the direct influence of gravity.The speed of mass movement might be slow or fast. Gravity facilitates mass motions, which are unaffected by geomorphic factors such flowing water, glaciers, wind, waves, etc. Even though there is a change in the materials, erosion is not a category that applies to mass movement. Mass movement is a function of force of gravity and not any geomorphic agents like running water, wind, waves, etc. Hence, it can be safely assumed that weathering is not a prerequisite for mass movement though it aids mass movements.

Mass Movement is a common phenomenon in areas with unconsolidated materials, thinly bedded rocks, faults, abundant precipitation, scarcity of vegetation, etc. There are a number of mass movement activating factors like removing support from below through natural and artificial means, increase in gradient or slope, heavy earthquakes, natural seepage, removal of natural vegetation, etc.

Mass Movement Modes

The Mass Movement is followed by different modes of movement downhill, like slide, flow, and heave.

1. Slide

In slide movement, the maximum motion is found along the base of the moving mass. A clear visible layer divides the mobile upper layer and stable lower mass, and the plane separating is called a shear plane. Sliding may occur under dry conditions, but the presence of water provides a greater speed to sliding.

2. Flow

In flow movement the material above the shear plane reaches the maximum speed at top, while rate of movement diminishes with increasing depth till it reaches zero along the shear plane. Water also aids the flow movement further.

3. Heave

This type of mechanism moves particles ranging from the size of fine clay to large boulders. A very slow rate is maintained.

Types of Mass Movements in Geography

Types of Mass Movements are classified based on the rate at which mass movements occur. They range from slow mass movement to rapid mass movement.

1. Solifluction

In the solifluction process the soil flow covers the surface with water saturated mass. The flow is completely water dependent. As water content increases soil cover changes from soggy matter and loses cohesive strength. The frictional force acting decreases enabling gravity to move the weathered layer on the slope. Solifluction is a slow process as compared to other types of mass movement. The ground that experiences solifluction  is broken into gentle, terrace-like features.

2. Soil Creep

This is a widespread mass movement that can be found everywhere across the Earth’s surface. The surface requires minimum support; the surface should be very steep to experience soil creep. The soil creep can involve any kind of debris, and it is not moisture dependent; hence, any kind of climate is suitable.

Surfaces experiencing soil creep can be easily identified with trees having downward bend at their trunks, tilt in exposed rock beds, etc. In mountainous areas heaps of weathered matter are collected at the base of slopes, this is one of the examples of soil creep.

3. Mudflow and Earthflow

The process of earthflow and mudflow is very similar to that of other mass weathering phenomena. The mudflow occurs on a large scale. On the contrary, earth flow happens on any surface in a localised manner. Mud flow is characteristic to valleys and has very rapid movement. Absence of vegetation and heavy rainfall further aids the mud flow.

4. Landslide

Landslides are the most devastating, sudden rapid slide movements capable of transporting and burying settlements and destroying the ecosystem for a very long time. It is most common in areas that have steep slopes and unconsolidated soil surfaces. Triggering factors are heavy rainfall and earthquakes. The landslides are also experienced with debris and rockfall. Anthropogenic activities like constructing railway lines on high mountains on unconsolidated platforms, quarrying, and excavating further increase the risk of vulnerable places.

5. Liquefaction

Solid surfaces shake during earthquake tremors. This allows clay rich rocks to behave like plastic matter, thus causing liquefaction. It can uproot buildings and their foundations altogether.

6. Avalanche

Any sudden and disastrous landslides may be called an avalanche. It is a phenomenon in humid regions. It involves rapid weathered rock mass movement.

Difference between Weathering, Erosion and Mass Movement

The table shows the difference between Weathering, Erosion and Mass Movement

Mass Movement UPSC

Mass Movement is a common phenomenon in areas with unconsolidated materials, thinly bedded rocks, faults, abundant precipitation, scarcity of vegetation, etc. There are a number of mass movement activating factors like removing support from below through natural and artificial means, increase in gradient or slope, heavy earthquakes, natural seepage, removal of natural vegetation, etc.

These notes  are of immense importance for UPSC IAS aspirants. This article discusses about mass movements.

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