Coasts - Coastal Landscape Development Flashcards
What three factors determine coastal landscape development?
1) Coastal geology and lithology.
2) Climate.
3) Nature of tides and waves.
What are the three classifications of coastline?
1) Concordant or discordant.
2) A cliffed coast, flat coast or graded shoreline.
3) Emergent or submergent coastline.
What three factors determine the particular coastal landscape?
1) A high or energy coastline.
2) Dominated by processes of erosion or deposition.
3) More or less intensely managed by people.
Describe the formation of headlands and bays.
1) Headlands and bays form along discordant coastline, where there are alternating bands of more and less resistant rock which lay at right angle to the beach or coastline.
2) Initially erosional processes predominate in areas with less-resistant rock, forming bays, leaving the more resistant rock protruding out to sea as headlands.
3) Because of the refraction, the headlands then receive the highest energy waves and are more vulnerable to the forces of erosion than the bays.
Describe the formation of cliffs and wave cut platforms.
1) At high energy coastlines, hydraulic action and abrasion cause the formation of wave-cut platforms.
2) Powerful destructive waves attack the base of the cliff at high tide.
3) The hydraulic action and abrasion create a wave-cut notch which over time increases in size, this is called undercutting.
4) Eventually the overhang created by the undercutting collapses due to weathering and gravity.
5) Backwash transports material from the cliff’s base leaving a wave cut platform.
Describe the formation of caves, arches, stacks and stumps.
1) Wave refraction concentrates wave energy onto the headland and can contribute to the formation of caves, arches, stacks and stumps.
2) Joints in the headland are susceptible to erosion by hydraulic action.
3) Over time the joints widen forming a cave which is enlarged by hydraulic action and abrasion.
4) Eventually erosion cuts through the headland forming an arch.
5) The roof of the cave will eventually collapse due to gravity and the lack of support.
6) This leaves a stack which will over time be eroded by weathering, abrasion and hydraulic action to form a stump.
Describe the formation of beaches.
1) Drift-aligned beaches form where longshore drift moves the sediment along the beach as waves approach at an oblique angle. This will often culminate in a spit where the coastline changes direction.
2) Swash-aligned beaches form where the energy is low. The waves are more parallel to the shore in swash-aligned environments so there is very little horizontal or lateral movement of sediment.
Describe the formation of simple and compound spits.
1) Longshore drift transports sediment along the coastline, in the dominant wind direction.
2) If a change in the direction of the coastline occurs, material continues to be transported following the direction of LSD rather than the coastline and so material is transported and the distal end of the spit will extend across the sea.
3) Deposition of sediment occurs when there is a decrease in the water’s velocity, commonly at estuaries as the flow of water into the sea is stronger than the drift and sediment is forcefully deposited, causing the build up of sediment and therefore the growth of the spit.
What is the difference between simple and compound spits?
1) Simple spits are either straight or recurved and do not have minor spits, or recurved ridges, along their landward. Compound spits may have similar features to simple spits and they have a number of recurved ridges, or minor spits, along their landward side, possibly marking the position where they terminated in the past.
2) Changes in the direction of prevailing winds will coincide with the direction of fetch and wave direction; therefore, the direction of transported material and the development of a re-curved distal end.
Describe the formation of tombolos.
A tombolo is a spit connecting an island to the mainland or another island. Due to sediment deposition, it is formed when a spit extends from the mainland to an island or between two islands. The process is the same as that which forms spits, but the offshore island changes the wave conditions to promote deposition between the island and the mainland.
Describe the formation of offshore bars.
A bar is another coastal landform created by deposition. It is similar to a spit, but instead of projecting out into the sea, it runs parallel to the coast, connecting two headlands and enclosing a body of water behind it, forming a lagoon or bay. Bars are formed when a spit grows across a bay or when there is significant sediment deposition between two headlands due to wave action and longshore drift.
Describe the formation of barrier beaches and islands.
1) A barrier beach is usually formed as an extension to a spit.
2) Longshore drift moves sediment along the coastline until there is a change in the direction of the coastline. A spit develops, usually in a bay and once the spit develops across the whole bay, a barrier beach forms. Barrier beaches are unlikely to form in estuaries as the outcoming force of freshwater will always keep part of the estuary clear.
3) Colonisation by vegetation can stabilise the barrier beach and trap further sediment keeping the barrier beach above sea even at high tide (barrier island).
4) Depending upon the climate the landward side may be colonised by mangroves in the still lagoon, which adds further stability.
Describe the formation of sand dunes.
1) Deposition can also lead to the formation of sand dunes.
2) Sand dunes are formed in areas where there is a large quantity of sand, a large tidal range and onshore prevailing winds.
3) When sand is trapped towards the back of the beach due to an obstacle dunes will develop.
4) Pioneer plant species hold the sand together and stabilise the dune.
5) Other plants are then able to thrive in the environment which leads to the development of the dune ecosystem, this is called plant succession.
Describe the formation of estuarine mudflats and saltmarsh environments.
1) Saltmarshes tend to develop in sheltered estuaries behind spits. As the spit develops, the area behind it becomes sheltered.
2) Silt is deposited by the river which gradually builds up to form an intertidal mudflat. The mudflat continues to build and rise above sea level with the addition of further silt.
3) Vegetation which is highly adapted to environment colonises the mud which itself traps further sediment.
4) The salt marsh environment is colonised by halophytic vegetation.
What is eustatic change?
Eustatic change occurs when there is a change in the volume of water in the ocean basins.
What are the causes of eustatic change?
1) Changing amounts of ice: melting ice caps or water being locked away when ice forms.
2) Thermal expansion: occurs when water warms and this takes up more volume.
3) Tectonics: Magma rising to the surface lifts the crust and reduces the capacity of the oceans causing sea levels to rise.
What is isostatic change?
Isostatic change occurs when the height of the land changes relative to the water level.
What are the causes of isostatic change?
1) Post glacial adjustment: during a period of glaciation extremely heavy ice sheets weigh land down, when the glacial period ends and the ice melts the land will rebound to a higher level, lowering sea level in a process known as isostatic recovery/readjustment.
2) Accretion: within the sediment cell there are areas of net deposition causing land to build up.
3) Subsidence: caused by the lowering of the water table or increased deposition weighing down the sediment.
4) Tectonics: the folding of the sedimentary rock, lava and ash from volcanoes increases the height of the land relative to the sea level.
What are raised beaches?
Raised beaches are beaches which are above high tide level, they are flat and covered by sand/pebbles and experience succession.
Describe the formation of rias.
Rias are formed when rising sea levels flood narrow winding inlets and river valleys. They are deeper at the mouth of the inlet, with the water depth decreasing further inland.
Describe the formation of fjords.
1) Fjords are an example of coastal landforms of submergence. They are primarily a product of glacial erosion. As glaciers advanced towards coastal location in Norway, for example, they carved out vast glacial troughs, through processes such as abrasion and plucking. A combination of localised isostatic re-adjustment and global eustatic sea level change has led to the flooding of these valleys.
2) An example is Sogne Fjord in Norway.
3) An interglacial period also leads to the formation of fjords.
Describe the formation of dalmatian coasts.
Dalmatian Coasts occur when valleys running parallel to the coast become flooded as a result of sea level change. This leaves a series of narrow, long and rugged islands.
