• Waves are the most powerful agents of marine erosion.
• Waves are created by winds sweeping over the water surface, setting up a series of undulating swells surging forward.
• Waves are curved and refracted against the alignment of the coast as they approach shallow water near the shores.
• When the depth of the water is less than the height of the waves, the wave crest curls over and breaks into shore.
• The water rushing up the beach and hurling rock debris against the land is called swash.
• The water that retreats or is sucked back is called backwash.
• An undertow is another element in offshore drift, which flows near the bottom away from the shore.
• The undertow exerts a pulling effect that can be dangerous for sea bathers.

Types of Erosion

• Sea waves, aided by winds, currents, tides, and storms carry on the erosional and depositional processes.
• There are 4 types of erosion:
  • Corrasion or Abrasion:
    • Waves armed with rock debris charge against the base of the cliffs and wear them back by corrosion. 
    • On coming tides and waves complete the work by sweeping the eroded material into the sea.
  • Attrition:
    • The constantly moving waves that transport beach materials also hurl these materials against each other until they are broken into small pieces. 
    • The grinding and polishing of these materials against the cliff faces and against each other is largely responsible for the fine sand which forms the beaches.
  • Hydraulic Action:
    • The erosion that occurs when the motion of water against a rock on the surface produces mechanical weathering.
    • It is a mechanical process, in which the moving water current flows against the banks and bed of a river, thereby removing rock particles.
  • Solvent Action:
    • The solvent or chemical action of waves is another mode of erosion, but it is pronounced only in case of soluble rocks like limestone and chalk. 
    • On limestone coasts, the solvent action of the sea water on calcium carbonate sets up chemical changes in the rocks and disintegration takes place.

Marine transportation

• Solution: minerals are dissolved in the water and carried along in solution.
• Suspension—fine light material is carried along in the water.
• Saltation—small pebbles and stones are bounced along the sea bed.
• Traction—large boulders and rocks are rolled along the sea bed.

Marine Landforms—Erosional

• Headlands and Bays:
  • Cliffs erode at different paces along the coastline
  • Different types of rock can form headlands and bays
  • Soft rock such as clay and sand erodes quickly forming bays
  • Bays are inlets of the sea where land curves inwards, usually with a beach
  • Hard rock such as chalk is more resistant to erosion
  • Soft rock erodes inwards, while hard rock sticks out into the sea forming a headland
  • Headlands are more open to waves and have erosion features such as wave-cut platforms and cliffs
  • Bays are more sheltered with constructive waves which deposit sediment and form a beach.

• Cliffs and Wave-Cut platforms:
  • Cliffs are shaped through erosion and weathering.
  • Soft rock erodes quickly and forms gentle sloping cliffs, while hard rock is more resistant and forms steep cliffs.
  • A wave-cut platform is a wide, gently sloping surface found at the foot of a cliff.
  • A wave-cut platform is formed when the sea attacks the base of the cliff between the high and low water mark.
  • A wave-cut notch is formed by erosional processes such as abrasion and hydraulic action – this is a dent in the cliff usually at the level of high tide.
  • As the notch increases in size, the cliff becomes unstable and collapses, leading to the retreat of the cliff face.
  • The backwash carries away the eroded material, leaving a wave-cut platform.
  • The process repeats, and the cliff continues to retreat.

• Caves, Arches, Stacks, and Stumps:
  • Caves, arches, stacks and stumps are found on a headland due to erosion.
  • Cracks are widened by hydraulic action and abrasion.
  • The widening of the crack forms a cave.
  • The cave grows larger and eventually breaks through the headland, forming an arch.
  • The base of the arch widens through further erosion until it collapses, leaving a stack.
  • A stack is an isolated column of rock.
  • When a portion of the sea arch collapses, the remaining column-like structure is called a stack, skarry, or chimney rock.
  • The stack is undercut at the base until it collapses to form a stump.

• Ria, and Cove:
  • A ria is a coastal inlet formed by the partial submergence of an unglaciated river valley.
  • It is a drowned river valley that remains open to the sea.
  • A cove is a small bay or inlet with a sheltered or restricted entrance.
  • Coves are usually formed by the erosion of soft rock formation.
  • This leaves hard rock that can form a circular or oval bay with a small entrance.
  • A cove is generally less than 1000 feet across and can be much smaller, sometimes less than 100 feet in diameter.
  • Ria:

• Cove:

• Geos and Gloups (blowholes or marine geyser):
  • Waves splashing against the roof of a cave may enlarge the joints when air is compressed and released repeatedly inside them.
  • This can create a natural shaft that may eventually pierce through the surface.
  • When waves break into the cave, they may force water or air out of this hole, which is known as a Gloup or blow hole.
  • The enlargement of blow holes and continual action of waves weakens the cave roof.
  • When the cave roof collapses, a long, narrow creek may develop which is known as a Geos.

• Chasms:
  • Chasms are narrow, deep indentations formed due to headward erosion by wave action through vertical planes of weakness in rocks.
  • Lateral erosion of the chasm mouth widens it till a bay is formed.

• Creek and Inlet:
  • Creeks are natural streams of water tributary to a river or a narrow sheltered waterway or an inlet in a shoreline or channel in a marsh.
  • Inlets are long and narrow indentations of a shoreline that often lead to an enclosed body of salt water such as a bay, lagoon, or marsh.
  • Creek:

• Inlet:

Marine Landforms – Depositional

• When water loses its energy, any sediment it is carrying is deposited. The build-up of deposited sediment can form different features along the coast.

• Beaches:
  • Beaches are formed by eroded material that is transported from elsewhere and then deposited by the sea.
  • Waves must have limited energy for beaches to form in sheltered areas like bays.
  • Constructive waves build up beaches with a strong swash and a weak backwash.
  • Sandy beaches are usually found in bays where the water is shallow and the waves have less energy.
  • Pebble beaches often form where there are higher-energy waves and cliffs are being eroded.
  • The cross-profile of a beach is called the beach profile and has ridges called berms, which show the lines of high tide and storm tides.
  • A sandy beach typically has a gently sloping profile, whereas a shingle beach can be much steeper.
  • The size of the material on the beach is larger at the top due to high-energy storm waves carrying large sediment.
  • The smallest material is found nearest the water as the waves break down the rock through attrition.
• Spits and Hook:
  • A spit is a stretch of sand or shingle jutting into the sea from the land.
  • Spits are formed due to changes in the landscape or river mouth.
  • Longshore drift carries sediment.
  • Deposition occurs when the coastline changes shape.
  • A long, thin ridge of material is deposited, forming the spit.
  • Hooked ends can form due to changes in wind direction.
  • Waves cannot get past a spit, creating sheltered water behind it.
  • Silts are deposited here to form salt marshes or mudflats.

• Bars, Lagoons, and Barriers:
  • Sometimes a spit can grow across a bay and join two headlands together. This landform is known as a bar. They can trap shallow lakes behind the bar; these are known as lagoons. Lagoons do not last forever and may be filled up with sediment.
  • Barrier: It is the overwater counterpart of a bar.

• Tombolos & Dumb Ball:
  • A tombolo is a sandy isthmus. Sometimes, islands are connected with mainland by a bar called tombolo.
  • If two islands are connected to each other by a bar is called Dumb Ball.
• Marine Dunes & Dune Belts:
  • With the force of on-shore winds, a large amount of coastal sand is driven landwards forming extensive marine dunes that stretch into dune belts
  • Their advance inland may engulf farms, roads & even the entire villages;
  • Hence to arrest the migration of dunes, sand binding species of grass & shrubs, such as marram grass & pines are planted.