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.