Introduction

Exogenic forces cause the landform evolution by acting on the topmost layer of the earth’s crust. The fundamental work of these forces is to change the uneven landscapes into smooth ones, therefore, very often these forces are called forces of gradation. The work is done by the gravity forces and sunlight in the forms of the rivers, airflow, glaciers, etc. In this chapter, we will mainly be focusing on mass wasting which is also known as a mass movement. Mass wasting is the movement of soil and rocks down the slope of a hill or of a steep land due to gravity. Mass wasting can be considered as the subsequent step of weathering.

Types of mass wasting

Though there are numerous types of Mass wasting, we can classify them into three sections. They are i.) mass flow and ii.) mass sliding and iii.) mass falls.

1.Mass flow

1.1. Slow flow

• Soil creep: Soil creep, a phenomenon where the eroded and decayed soils slowly come down the slope of a hill due to gravity. It occurs on gentle slopes and is distinguished by the wavy surface it creates. As the weight of water drags the damp earth down the slope, it goes slowly. Soil grains may be released by rain splashes and fall further downslope.
• Rock creep & Talus creep: It is also a slow mass flowage process. The downstream bending of layers of layered or foliated rock, as well as the slow downslope migration of massive slabs of rock away from their parent outcrop. Rocks and Talus are considerably large types (pieces) of dehydrated mass. Being dried, cracks take place, and taluses are formed which come down from the top.
• Frost heaving: In freezing conditions, if somehow water gets trapped in the cracks of a hill, after freezing the volume of the trapped water increases and causes bigger cracks. As a result of that, bulks of rocks are produced and they come through the cracks.
• Solifluction: solifluction is the movement of damp soil down an inclined slope. Because permafrost is water-impervious, the soil above it may get oversaturated and slide downslope under gravity’s pull. The most sensitive soil is that which has been loosened and damaged by frost. Moving at a maximum rate of a few inches every day, the slopes gradually become smooth, soft, and concave. If not destroyed, the soil’s original stratifications become twisted.

1.2. Rapid flow

The rapid flow of mass depends on the water content of the rocks and soil. The aforementioned elements come down the steep slope rapidly if the inclined plane is lubricated by their moisture content. Earthflow and Mudflow are examples of rapid mass flow.

2.Mass slide

The phrase “mass slide” refers to several different processes that result in the downhill and outwards movement of hillside elements such as soil, rock, artificial fill, or a combination of these.  The materials may collapse, topple, slide, spread, or flow as they move. There are two types of landslide they are-

2.1. Block Glide

When a large layer of soil or rock slides on the inclined plane it is called a block glide. This type of landslide is extremely dangerous. 

2.2. Slump

 It’s a form of slide in which rock rotates downward along a concave-upward curved surface. The upper surface of each slump block, as well as the individual blocks, remain largely undamaged. On the hillside, slumps leave arcuate scars or depressions. Slumps can be found in small clusters or enormous complexes spanning hundreds of square meters. Slumps can also be triggered by heavy rainfall or earthquakes.

3.Mass falls

When the mass wasting takes place on a very steep place that is undercut by river flow or airflow, the piece of rocks and soil falls straight on the base of the cliff. 

3.1. Rock falls

Rock particles can be easily broken off from steep bedrock slopes, most typically due to frost-wedging in places with frequent freeze-thaw cycles. You could have heard rock fragments fall onto a talus slope if you’ve ever climbed along a steep mountain trail on a cool morning. This occurs because the water between fissures freezes and swells overnight, and when the same water thaws in the morning sun, the ice-pushed shards fall down the slope below.

3.2. Earth falls

Instead of rocks, if soil bulk, alluvium (mixture of soil and rock) fall freely from the cliff then the incident is called earth fall. 

3.3. Debris falls

If earth elements like sediments and rocks along with trees, houses, and other kinds of stuff fall freely on the base of a hill, the phenomenon is recognized as debris fall.

Conclusion:

Mass wasting is a geology phrase that refers to all gravity-driven downhill rock and soil movement. When a slope is too steep to stay stable with the material and circumstances available, mass wasting occurs. During a mass-wasting event, loose rock and soil, known as regolith, often shift. The angle of the slope and the shear strength of the accumulating materials are the two parameters that define slope stability. Changes that overstepped slope angles and reduce slope stability, such as quick snowmelt, severe rainfall, earthquake shaking, volcanic eruption, storm waves, stream erosion, and human activities, are all examples of mass-wasting events.  The most prevalent cause is excessive precipitation. The type of movement and material used in mass-wasting events are categorized, and they all have similar morphological surface traits. Rockfalls, slides, flows, and creep are the most typical types of mass-wasting occurrences.