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coastal landscapes and change - Coggle Diagram
coastal landscapes and change
LANDFORMS AND LANDSCAPES
9.1 MARINE PROCESSES AND WAVES
waves
directly influence erosion, transport and deposition deposition and help shape the coastline
caused by friction between wind and water; the force of the wind creates ripples in the water, which grows into waves if the wind is sustained
wave size depends on: wind strength, duration of wind blows, water depth and wave fetch
wave fetch:
the uninterrupted distance across water over which wind blows
tides
formed by the gravitational pull of the moon acting on water on the Earth's surface
produced by a bulge of water which, as it passes a location on the coast, high tide occurs
large tidal ranges can produce waves capable of erosion, called tidal bores
when storms occur at the same time as spring tides 9 the highest tides ) the risk of coastal flooding is increased
constructive waves
have a low wave height and a long wavelength
also called spilling or surging waves
gentle, flat waves with a strong swash but weak backwash
strong swash pushes sediment up the beach creating a ridge
destructive waves
have a wave height over 1m and a wave length around 20m
common during storms
also called plunging waves
strong backwash that erodes beach material creating an offshore ridge
beach morphology:
the shape of the beach including its width and slope and features such as berms, ridges and runnels. it also includes the type of sediment such as shingle, sand and mud
sediment supply from rivers is reduced, due to the construction of dams
interference in sediment supply along the coast, often as a result of coastal management
changes in climate; stormier winter's may create a more destructive coastline
erosion processes
hydraulic action
air trapped in cracks and fissures is compressed by the force of waves crashing against the cliff face
pressure forces cracks open, often dislodging rocks from the cliff
abrasion
sediment picked up by waves is thrown against the cliff face, chiseling away at the surface, gradually removing smaller pieces
attrition
sediment is moved around by waves, collisions between rocks chipping fragments off, causing sediment to become smaller and more rounded
corrosion
the dissolving of carbonate rocks from the spray of seawater
erosional landforms
blow hole:
forms when a coastal cave turns upwards and breaks through the flat cliff top
wave-cut notch:
eroded material at the base of a cliff by hydraulic action and abrasion
stacks
arches
stumps
caves
cracks
9.2 TRANSPORT AND DEPOSITION
sediment transport
traction
sediment rolls along, pushed by waves
pebbles, cobbles, boulders
saltation
sediment bounces along, due to force of water or wind
sand-sized particles
suspension
sediment is carried in the water column
silt and clay particles
solution
dissolved material carried in the water as a solution
chemical compounds in solution
longshore drift
is a key source of sediment for depositional landforms. sediment is deposited when the force transporting sediment drops
gravity settling
occurs when the energy of transporting water becomes too low to move sediment
flocculation
is a depositional process that is important for very small particles as they remain suspended in water
depositional landforms
spit
sand or shingle beach ridge extending beyond a turn in the coastline
longshore drift spreads out and loses energy leading to deposition
e.g. Spurn Head on the Holderness Coast
tombolo
a sand or shingle bar that attaches the coastline to an offshore island, formed due to wave refraction around an offshore island
an area of calm water and deposition between the island and the coast
e.g. St Ninian's tombolo, Shetland
barrier beach/bar
sand or shingle beach connecting two areas of land with a shallow water lagoon behind
occurs when a spit grows longer so it extends across a bay
e.g. Chesil Beach, Dorset
hooked/recurved spit
a spit whose end is curved landward, into a bay or inlet.
naturally curves into shallower water
made more pronounced by secondary direction of winds
e.g. Hurst Castle Spit, Hampshire
vegetation
plays an important role in stabilizing depositional landforms; plant succession, salt marshes and sand dunes bind the loose sediment together, encouraging further deposition
depositional landforms are therefore at risk when vegetation is damaged due to overgrazing or trampling from tourism and leisure activities
9.3 SUB-AERIAL PROCESSES
mechanical:
breaks down rocks due to the exertion of a physical force - does not involve chemical change
freeze-thaw -
water expands in volume when freezing, exerting a force within cracks and fissures
salt crystalisation -
the growth of salt crystals in cracks and pore spaces can exert a breaking force
chemical:
involves a chemical reaction and the generation of new chemical compounds
carbonation -
the slow dissolution of limestone due to rainfall producing calcium carbonate solution
hydrolysis -
the breakdown of minerals to form new clay minerals due to the effect of water and dissolved CO2
oxidation -
the addition of oxygen to minerals producing iron oxides and increasing volume contributing to mechanical breakdowns
biological:
often speeds up mechanical or chemical weathering through plants, bacteria or animals
plant roots -
tree and plant roots growing in cracks and fissures forcing rocks apart
rock boring -
many species of clams and molluscs bore into rock and may also secrete chemicals that dissolve rocks
COASTAL RISKS
10.1 SEA LEVEL CHANGE
isostatic change =
a local rise or fall in land level
eustatic change =
a rise or fall in water level caused by a change in the volume of water -
a global change
10.2 THE EROSION THREAT
10.3 COASTAL FLOOD RISK
MANAGING RISKS AND CONFLICT
11.1 CONSEQUENCES FOR COMMUNITIES
11.2 HARD, SOFT AND SUSTAINABLE MANAGEMENT
11.3 COASTAL DECISION-MAKING
COASTAL PROCESSES
8.1 THE COASTAL ZONE
the
littoral zone
is the wider coastal zone including adjacent land areas and shallow parts of the sea just offshore
this can be divided into a number of 'sub-zones'...
backshore zone
above high tide level is only affected by waves during exceptionally high tides and major storms
wave processes are normally confined to the
foreshore
between high and low tide marks
shallow water areas close to land are termed the
nearshore
; this area is often one of intense human activity but also forms part of the physical systems of the coastline as it transfers sediment by currents close to the shore
sub-aerial processes
; surface runoff erosion and mass movement ( landslides ) slowly move sediment downslope
weathering
; the chemical, biological and mechanical breakdown of rocks into smaller fragments and new minerals
mass movement
; landslides, slumps and rock falls, which move material downslope under the influence of gravity
surface runoff
; water, usually during heavy rain, flowing down the cliff ad causing erosion of it
primary coasts
are dominated by land-based processes such as deposition at the coast from rivers or new coastal land formed from lava flows
secondary coasts
are dominated by marine erosion or deposition
emergent coasts
where the coasts are rising relative to sea level - tectonic uplift
submergent coasts
are being flooded by the sea due to sea level rising
8.2 GEOLOGICAL STRUCTURE AND LANDSCAPES
concordant vs discordant coasts
concordant or pacific coasts
are generated when rock strata run parallel to the coastline
( Lulworth Cove, Dorset )
hard portland limestone and resistant purbeck beds protect the much softer rocks landward
marine erosion has broken through the resistant rocks, then rapidly eroded the wider coves behind
white chalk behind the coves prevent erosion further inland
discordant or atlantic coasts
form when different rock strata intersect the coast at an angle, so geology varies along the coastline
dominated by headlands and bays
weak rocks have been eroded creating elongated, narrow bays
especially resistant areas remain as detached islands
rias; drowned river valleys
geological structure
the arrangement of rocks in 3 dimensions
strata:
the different layers of rock within an area and how they relate to each other
deformation:
the degree to which rock units have been deformed ( titled or folded ) by tectonic activity
faulting:
the presence of major fractures that have moved rocks from their original positions
cliff profiles
are influenced by several aspects of geology; the resistance of the rocks, and the angle of rock strata to the coastline
faults
are major fractures in rocks produced by tectonic forces and involving the displacement of rock on either side of the fault line
joints
occur in most rocks, often in regular patterns, dividing up rock strata into blocks with a regular shape
fissures
are much smaller cracks in rocks, often only a few centimeters long, which represent weaknesses erosion can exploit
8.3 RATES OF EROSION
rates of erosion
igneous
few joints so limited to weaknesses erosion can exlpoit
interlocking crystals make for strong, hard erosion-resistant rocks
e.g. granite, basalt, dolerite
very slow ( < 1 mm per year )
metamorphic
often folded and heavily fractured, weaknesses erosion can exploit
foliation; crystals orientated in one direction producing weaknesses
e.g. slate, schist, marble
slow ( 1 - 10 cm per year )
sedimentary
many bedding places and fractures are often more vulnerable to erosion
geologically younger rocks meaning they tend to be weaker
e.g. sandstone, limestone, shale
moderate to fast ( 10cm - several meters per year )
permeable rocks
allow water to flow through them, and include many sandstones and limestones
impermeable rocks
do not allow groundwater flow and include clays, mudstones and most igneous and metamorphic rocks
coastal vegetation
e.g. coastal sand dunes, salt marshes, mangrove swamps
roots of plants bind sediment particles together making them harder to erode
when submerged, plants growing in sediment provide a protective layer so the surface isn't directly exposed to moving water
protect sediment from wind erosion by reducing wind speed at the surface due to friction