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Managing river and coastal environments: A continuing challenge
2.42.4 How do coastalHow do coastal processes shape theprocesses shape the land?land?
Part BPart B
Managing river and coastal environments: A continuing challenge
What landforms are created by coastal processes?A Erosional landforms
Wave-cut platform
Stack
Sea arch
Geo
Sea cave
Sea cliff
Blow-hole
Managing river and coastal environments: A continuing challenge
What landforms are created by coastal processes?B Depositional landforms
Beach
SpitBar
Tombolo
Managing river and coastal environments: A continuing challenge
Is wave action the only factor in shaping the coast?
Is wave action the only factor in
shaping the coast?
Is wave action the only factor in
shaping the coast?
No, there are several factors interacting with
each other to create coastal landforms.
Managing river and coastal environments: A continuing challenge
Is wave action the only factor in shaping the coast?1 Tectonic movement
Tectonic movement can cause land to rise or fall.The uplifting or lowering of the coastline changes the zone of active wave erosion.
Compressionalforce
Sea
Plate
Uplifting (or lowering) of land
Subject to active wave erosion
Managing river and coastal environments: A continuing challenge
Is wave action the only factor in shaping the coast?2 Nature of rocksHorizontal bedding plane
Sea
Wave undercutting enlarges the notch and causes collapse of rock above the notch. Parallel
retreat of cliffs is resulted.
Land
Notch
Managing river and coastal environments: A continuing challenge
Is wave action the only factor in shaping the coast?2 Nature of rocksBedding plane dipping seawards
Sea
Rocks loosened by wave erosion and
mass movement slide down along the bedding plane.
Land
Managing river and coastal environments: A continuing challenge
Is wave action the only factor in shaping the coast?2 Nature of rocksBedding plane dipping landwards
Sea
The slope is more resistant
to wave erosion.
Land
Managing river and coastal environments: A continuing challenge
Is wave action the only factor in shaping the coast?3 Weather and climate
Global warming leads to a rise in sea levels because of the thermal expansion of water and melting of polar ice caps.Changes in sea levels are changing the position of the zone of active wave erosion.
Managing river and coastal environments: A continuing challenge
Is wave action the only factor in shaping the coast?3 Weather and climate
A warmer world would generate more storm surges, thereby affecting coastal landforms.
Managing river and coastal environments: A continuing challenge
Is wave action the only factor in shaping the coast?4 Fluvial processes
Rivers bring sediment to the coast as they flow to the sea.Deposition occurs at the coast where wave action is weak. Sediment may gradually build up to form depositional landform such as a delta.
Delta
The River Nile, Africa (Credit: NASA)
Red Sea
River N
ile
Managing river and coastal environments: A continuing challenge
Is wave action the only factor in shaping the coast?5 Marine organisms
Some marine organisms protect the coast from wave erosion and favour deposition.
For example, coral reefs and mangroves.
Mangroves
Managing river and coastal environments: A continuing challenge
What landforms are created by coastal processes?A Erosional landformsSea cliffs and wave-cut platforms
Waves repeatedly pound against the coast.The waves erode the part of the coast between high tide and low tide.A notch is formed by undercutting.Undercutting continues and the notch is enlarged. The overhanging part above the notch collapses. It forms a sea cliff.
Managing river and coastal environments: A continuing challenge
What landforms are created by coastal processes?A Erosional landformsSea cliffs and wave-cut platforms
Erosion continues, the sea cliff retreats inland.Over time, a gently sloping or flat surface called a wave-cut platform is developed at the base of the sea cliff.
Managing river and coastal environments: A continuing challenge
What landforms are created by coastal processes?A Erosional landformsSea cliffs and wave-cut platforms
Ping Chau in Mirs Bay
Sea cliffWave-cut platform
Managing river and coastal environments: A continuing challenge
What landforms are created by coastal processes?A Erosional landformsSea caves and geos
A line of weakness in the cliff is exposed to waves.Active wave erosion widens the line of weakness to form a sea cave.When waves splash against the roof of a narrow sea cave, the roof may collapse. A geo is formed.
Block diagram Cross-section
Sea
Sea
LandHigh tide level
Low tide level
Land
High tide levelLow tide level
Line of weakness
Sea cave
Sea cave
Collapse ofcave roof
Geo
Managing river and coastal environments: A continuing challenge
What landforms are created by coastal processes?A Erosional landformsSea caves and geos
A sea cave in Sai Kung A geo in Sai Kung
Managing river and coastal environments: A continuing challenge
What landforms are created by coastal processes?A Erosional landformsSea arches and stacks
When a sea cave gets eroded from time to time, it might cut through to form a sea arch.Further erosion may cause the sea arch to collapse. This leaves a mass of rock with steep sides standing offshore. This is the stack.
Managing river and coastal environments: A continuing challenge
What landforms are created by coastal processes?A Erosional landformsSea arches and stacks
A sea arch and a stack in Canada(Credit: Getty Images)
Managing river and coastal environments: A continuing challenge
w
What landforms are created by coastal processes?A Erosional landformsBlow-holes
A sea cave is developed along a horizontal line of weakness.
When waves break into the sea cave, hydraulic action of waves takes place along the vertical weakness in it.
A vertical or near vertical tunnel is formed along the vertical weakness as a blow-hole.
Managing river and coastal environments: A continuing challenge
What landforms are created by coastal processes?A Erosional landformsBlow-holes
During storms, waves breaking into the sea cave may force water or just air out of the blow-hole.
Halona Blow-hole in Hawaii(Credit: Getty Images)
Managing river and coastal environments: A continuing challenge
What landforms are created by coastal processes?B Depositional landformsBeaches
Wave energy is dispersed in sheltered bays. Deposition takes place to form beaches.
Sand and shingle are built up between the lowest and the highest water levels.
Managing river and coastal environments: A continuing challenge
Waikiki Beach, Hawaii
What landforms are created by coastal processes?B Depositional landformsBeaches
Managing river and coastal environments: A continuing challenge
What landforms are created by coastal processes?B Depositional landforms
Materials are transported along the coast by longshore drift.
Where the coastline changes, the materials are deposited in slack water.
The sediment accumulates and builds up into a spit, with one end attached to the land, and the other end extending out to the sea.
The spit extends as sediment continues to accumulate.
LandChange of coastline
Wind direction
Sea
Materials are built up to form
a spit
Longshore drift
Wave crest
Longshore drift
Spit extends
Marshland
Area behind the spit is of low energy, mud and marshland begins to develop
Longshore drift
Spits
Managing river and coastal environments: A continuing challenge
What landforms are created by coastal processes?B Depositional landformsSpits
As the waves are refracted, the end of the spit becomes hooked.
Longshore drift
Sea Longshore drift
MarshlandLand
End of the spit is bent or recurved
Wave crest
A Spit in Greece
spit
(Credit: Corbis)
Managing river and coastal environments: A continuing challenge
What landforms are created by coastal processes?B Depositional landformsBars
When a spit develops and extends across a bay, a bar is formed.
A lagoon is formed behind the bar.
Managing river and coastal environments: A continuing challenge
What landforms are created by coastal processes?B Depositional landformsBars
Chesil Beach in England is formed from a bar
(Credit: Corbis)
Managing river and coastal environments: A continuing challenge
What landforms are created by coastal processes?B Depositional landformsTombolos
When the spit builds up and joins an island to the mainland or two islands together, a tombolo is formed.
Managing river and coastal environments: A continuing challenge
What landforms are created by coastal processes?B Depositional landformsTombolos
The Cheung Chau tombolo is formed when two spits join together.