SOURCE
: NIOS & NCERT
• The
work of sea waves as an agent of gradation includes erosion, transportation and
deposition.
EROSION BY SEA WAVES:
Abrasion:
• When the sea water loaded with rock fragments and
sand attack the coastal rocks it is called abrasion.
Attrition:
• The rock particles present in the water hit
against each other and break into progressively smaller particles. This process
is called attrition.
hydraulic action:
hydraulic action:
• 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:
Important features made through sea wave erosion are mentioned
here:
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.
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.
Sea arches or natural bridges:
• 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.
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 sea stack.
Stumps:
Transportation by Sea Waves:
• Sea waves, currents and tides are the main agents
of transportation of eroded material in the coastal regions.
• 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:
• Removal and transportation, towards the sea, of
the material deposited by river etc. on the coast.
• 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.
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.
Some of these topographical features are discussed here:
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.
• Marina Beach of Chennai and Kovalam Beach of
Thiruvananthapuram are the famous beaches of India.
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.
Spit Earth :
• When one end of a bar is attached to the coast and
other extends into the sea, it is called a spit.
Lagoon :
• 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 northeastern
coast and lake Vembanad on Kerala coast are examples of lagoon lakes in India.
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