Mass motions (also called mass-wasting) is the down-slope activity of Regolith (loose uncemented mixture the soil and also rock particles that covers the Earth"s surface) through the force of gravity without the aid of a transporting medium such as water, ice, or wind. Still, together we shall see, water dram a crucial role.

Mass motions are component of a continually of erosional processes in between weathering and stream transport. Fixed movement reasons regolith and rock to relocate down-slope wherein sooner or later the loosened particles will be choose up by another transporting agent and also eventually moved to a site of deposition such as an ocean container or lake bed.

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Mass movement processes are arising continuously on every slopes; part act very slowly, others occur an extremely suddenly, regularly with destructive results.

In this discussion, we hope to answer the following questions:

What determines whether or not a steep is steady or unstable? exactly how are the various mass activity processes classified? exactly how are fixed movement events triggered? What observations might suggest the the area is unstable and also may start to move? How can we mitigate versus mass motion hazards?

We begin with a discussion of the pressures acting at the surface that reason mass movements.


Gravity is the main force responsible for mass movements.

Gravity is a pressure that acts all over on the Earth"s surface, pulling everything in a direction towards the center of the Earth. ~ above a level surface, parallel to the Earth"s surface, the force of gravity acts downward. So long as the material remains top top the flat surface it will certainly not relocate under the pressure of gravity. Of course if the material creating the flat surface becomes weak or fails, climate the unsupported assistance mass will relocate downward.
On a slope, the pressure of gravity can be resolved right into two components: a component acting perpendicular to the slope, and a component acting parallel come the slope.


The perpendicular ingredient of gravity, gp, helps to host the object in place on the slope. The component of gravity acting parallel to the slope, gs, reasons a shear stress and anxiety parallel to the slope and also helps to move the object in the down-slope direction. ~ above a steeper slope, the shear stress and anxiety component the gravity, gs, increases, and also the perpendicular component of gravity, gp, decreases. an additional force resisting activity down the slope is group under the hatchet shear strength and also includes frictional resistance and also cohesion amongst the corpuscle that comprise the object. when the sheer stress becomes better than the combination of forces holding the object on the slope, the object will relocate down-slope. Thus, down-slope movement is favored through steeper slope angles (increasing the shear stress) and anything that reduces the shear stamin (such together lowering the cohesion among the corpuscle or lowering the friction resistance. for unconsolidated material, the edge that creates a steady slope is called the angle that repose.

The function of Water

Although water is not constantly directly involved as the transporting tool in mass motion processes, that does play vital role. Addition of water native rainfall or eye melt adds load to the slope. Water have the right to seep into the floor or rock and replace the wait in the pore an are or fractures.Since water is heavier 보다 air, this boosts the weight of the soil.If the material becomes saturated through water, vibrations could cause liquifaction come occur, similar to often happens during earthquakes. Water deserve to reduce the friction follow me a sliding surface.Water has actually the ability to change the edge of repose (the slope edge which is the secure angle for the slope).

Think around building a sand castle on the beach. If the sand is entirely dry, that is difficult to develop a heap of sand v a steep face like a castle wall. If the sand is rather wet, however, one can construct a vertical wall. If the sand is too wet, climate it flows like a fluid and also cannot remain in position as a wall.

dry unconsolidated grains will form a pile v a steep angle identified by the angle that repose. The edge of repose is the steepest angle at i beg your pardon a pile of unconsolidated grains stays stable, and is controlled by the frictional contact between the grains. In general, for dry materials the edge of repose increases with raising grain size, yet usually lies between around 30 and also 45 o. Coarser grained and angular particles have a steeper edge of repose 보다 fine grained and also rounded particles.


Another product that shows comparable swelling and also compaction together a an outcome of enhancement or remove of water is peat. Peat is organic-rich material built up in the bottoms of swamps as decaying vegetable matter.

perceptible Soils - In some soils the clay minerals are arranged in arbitrarily fashion, with lot pore an are between the individual grains.This is often referred to as a "house that cards" structure. Often the grains are organized in this position by salts (such together gypsum, calcite, or halite) precipitated in the pore an are that "glue" the corpuscle together.As water infiltrates into the pore spaces, as questioned above, it can both be soaked up onto the clay minerals, and can dissolve far the salts holding the "house the cards" together.


Compaction the the soil or shaking of the soil deserve to thus cause a rapid change in the structure of the material. The clay minerals will certainly then heat up v one another and also the open space will be reduced.

But this may reason a loss in shear stamin of the floor and result in slippage down slope or liquefaction.

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some water saturated clays are stable so lengthy as castle aren’t disturbed, but when shiver occurs, just like sands, they can turn right into a runny fluid. This are referred to as quick clays.

Weak Materials and Structures

Rocks frequently contain planar frameworks that end up being slippage surfaces if load is included or support is removed.