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Ali Bux Wassan Department of Mining Engineering MUET,Jamshoro

EROSION

Definition:

“It is the transportation of weathered material” OR

“EROSION is the break up and removal of rock by moving natural agents like wind, water and

glacier”.

Agents of Erosion/Erosional Agents:

Erosion is caused mainly by three agents:

1) Wind (Blowing Air)

2) Water (Running Water)

3) Glacier(Moving ice)

Out of these three, the 1st agent i.e. water is the most important and it is responsible for the

maximum havoc .Moreover, it is considered to be the most powerful agent, especially in times

of flood.

It may act in three forms:

1. Falling Rain drops

2. Running Rivers and Streams

3. Running Overland Flow

A. Erosion by Running Water (River):

River erode their bed by several processes, thus rate of erosion depended upon:

1) Velocity of River

2) Nature of bed rock

3) Sediments’ load

Thus river does erosion in 4 ways:

I. Chemical Action: (water is Universal Solvent)

It includes the solvent and chemical action of water on country rocks e.g. It has been

observed that whenever water containing CO2 comes in contact with Limestone ,it gets

dissolved into the water easily.

II. Hydraulic Action:

Rapid flowing water hammers the uneven faces of rocks exposed along its channel and

rock fragments.

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Ali Bux Wassan Department of Mining Engineering MUET,Jamshoro

III. Abrasion: The flowing water uses the pebble, gravels etc as a tool for scratching and

breaking the sides and floor of the channel.

IV. Attrition:

It is the breaking of the transported material due to mutual collusion; as a result the rock

particles became more rounded and smaller in size.

Transportation by River:

A river carries enormous amount of soil and rock material, this sedimental material flowing in a

river is called its “LOAD”,

This can be classified into three types:

1) DISSOLVED LOAD: is the water soluble material

2) BED LOAD: is that heavier material which moves along the bed of the river with occasional

jumps

3) SUSPENDED LOAD: consists of finer material, which is kept in suspension by the turbulence

of flowing water e.g. clay particle

The deposit formed by running water is called ALLUVIAL deposit.

B. Erosion by Wind:

The air in motion is called “Wind”. It is an important Erosional agent; its work is

particularly seen in arid region. It is quite an effective agent of erosion in deserts and

dry areas.

Wind erosion is generally caused by three main processes:

1) Deflation:

It is process of simply removing the loose sand and dust from an area by fast

moving winds. Deflation is the very effective process of wind erosion at places where the

land is dry as in deserts.

2) Abrasion:

The blowing winds generally pick up sand particles from the earth’s surface and

then move as sand laden wind, when this wind strikes the rocks or other structures in their

way, they will cause them to erode by the rubbing and grinding action of the moving sand

particles.

3) Attrition:

The particles that travel with wind collide against one another .These mutual

collisions lead to their further break down and the process is called attrition.

3 | P a g e E r o s i o n

Ali Bux Wassan Department of Mining Engineering MUET,Jamshoro

Transportation by Sediments by Wind:

The total sediments load carried by wind can be divided into:

I. Bedded Load:

The larger and heavy particles such as sands and gravel constitute the

bed load. These particles move in a series of rolls and jumps along the bed.

II. Suspended Load:

The finer clay or dust particles, which are lifted by the moving

winds by s distance of hundred of meters above the earth, is called suspended load.

C. Erosion by Glacier:

A glacier is a “mass of moving ice”. This causes erosion of the

surfaces over which it moves. OR

Glaciers are the rivers of ice which moves over the ground under the influence of gravity.

All the rock material carried by a Glacier is called “MORAINE”.

About 10% of our present world is covered by glacier.

The y are slow erosive agents as compared to water and wind

The work of Erosion, by GLACIERS is done in following ways:

a) Plucking:

Particles ranging in size from fine powder to giant boulders are picked up by the

glacier from its valley floor through which it moves, and carries them along.

b) Abrasion:

The moving ice grinds, scratches and polishes the rock with help of rock

fragments which are held firmly within the body of a glacier.

Transportation by Glaciers

The material carried by glacier ,is transported entirely in an embedded state in its body.

The size of such material ranges from the finest clay to boulders of many tons. The loose

rock materials deposited by the ice are called “Glacial Deposits”