Saturday, 16 April 2016


·  The work of sea waves as an agent of gradation includes erosion, transportation and deposition.


·  Sea waves have a great erosive force.
·  In their role of an erosional agent they perform four functions.
·  When the sea water loaded with rock fragments and sand attack the coastal rocks it is called abrasion.

·  The rock particles present in the water hit against each other and break into progressively smaller particles. This process is called attrition.
·  Thirdly the broadening of cracks and crevices in the cliffs along the coast due to the attack of the sea waves is called the hydraulic action.
·  The rocks made up of limestone are subjected to solution action by the sea waves.
·  All these processes help in formation of new features on the coastal margins.

Landforms Produced by sea Wave Erosion :
·  Waves, like streams erode the coastal rocks with the help of rock fragments present in the water.
·  important features made through sea wave erosion are mentioned here:

(i) Sea Cliff
·  The maximum impact of the sea waves is observed on the lower part of the coastal rocks and consequently the lower part of the rocks is eroded more rapidly than the upper part.
·  This results in the formation of a hollow under the rock and with the passage of time this excavation in the lower part of the rock keeps on becoming larger.
·  The upper part of the rock is thus left projecting out towards the sea.
·  After sometime, this projecting part fall into the sea under its own weight. As a result a vertical wall is left. This vertical wall is called a cliff.
·  In India a number of sea cliffs are found along the Konkan Coast of India.

(ii) Sea Caves :
·  When the upper part of the coastal rock is hard and the lower part is soft, the erosion is not uniform.
·  The lower part of the rock in such circumstances is eroded much faster than the upper part.
·  Due to differential erosion a hollow is created in the lower part of the rock.
·  When the waves pound against this hollow, air present
in the hollow gets compressed.
·  When the wave comes out of the hollow, the pressure on air is also released and it expands.
·  Due to continuous compression of the air in the hollow, the rocks are subjected to a great pressure and they break.
·  In this process, the hollows in the lower part of the rock keep on enlarging.
·  With passage of time they attain the form of caves and are known as sea caves.

(iii) Sea Arches :
·  When a part of coast extends to some distance into the sea, sea waves working from opposite directions cut a passage through the soft rocks.
·  In the initial stages, this passage is a narrow hole but it enlarges into a broad arch.
·  These broad doorlike features are called sea arches or natural bridges.

(iv) Sea Stacks :
·  When the roof of an arch is broken by erosion or under its own weight or due to any other reason a part of the original rock remains standing as a solitary mass.
·  It may be the rock forming the side of the arch. This type of a feature is called a seastack.
·  Sometimes they take the shape of islands but such islands are not
·  Small underwater stacks are known as stumps.

(B) Transportation by Sea Waves :
·  Sea waves, currents and tides are the main agents of transportation of eroded material in the coastal regions.
·  However, the role of waves is more important in connection with the formation of coastal relief features.
·  The material deposited on the coasts by the rivers and glaciers etc. is removed and transported by the waves.

Transportation by sea waves is carried out in two ways:
(i) Removal and transportation, towards the sea, of the material deposited by river etc. on the coast.
(ii) Carrying of material found in the sea to the coastal areas. During this process, the oceanic materials like pearls, conches and other shells are brought to the coast.

(C) Deposition by Sea Waves :
·  Sea waves are helpful in the deposition of the material eroded from the coastal areas.
·  Oceanic current are also helpful in deposition of the transported material.
·  Deposition of the material along the coast is selective.
·  The larger particles are deposited first therefore they are found near the coast.
·  On the other hand, the finest particles are deposited last and they are deposited generally away from the coast.
·  This selective deposition is sometimes altered or affected by a change in the intensity or force of the waves.
·  Thus it is sometimes possible to find very fine particles deposited near the coast where generally larger particles are deposited.
·  A number of topographical features are formed due to deposition by waves and currents.

Some of these topographical features are discussed here:

(i) Beach :
·  Most of the material eroded and picked up by the waves is deposited near the coast.
·  Due to this deposition, the sea becomes shallow and a part of the coastal area is raised above the water level.
·  This raised portion is almost like a flat plain of a platform formed of gravel and sand.
·  This type of depositional features along the coast is called a beach. Beaches are centres of tourist attraction.
·  Marina Beach of Chennai and Kovalam Beach of Thiruvananthapuram are the famous beaches of India.

(ii) Sand Bar :
·  Sometimes the deposits of sand and gravel laid down by waves and currents form embankment, separating shoreline from the sea.
·  They thus form barriers between the sea and the mainland.
·  Such deposits are called sand bars.
·  They sometime pose difficulties in navigating.

(iii) Spit Earth :
·  When one end of a bar is attached to the coast and other extends into the sea, it is called a spit.
·  These spits are formed by the accumulation of materials brought by waves like sand and gravel.

·  Sometimes due to deposition of waves and currents both the ends of the bar join to enclose a part of the sea water between the coast and the bar.
·  This enclosed part of the sea forms a lake of saline water.
·  This saline water lake is called a lagoon.
·  Sometimes the lagoons are formed due to wave erosion also.
·  A lagoon is generally connected with the sea through a narrow passage. The Chilka and Pulicate lakes on the north-eastern coast and lake Vembanad on Kerala coast are examples of lagoon lakes in India.
·  Topographical features like beaches, bars, spits and lagoons are formed by the action of waves.

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