Coastal landscape development (Factors influence the rate of retreat:…
Coastal landscape development
Coastal landforms and landscape:
is the 'big picture'. It refers to the whole coastline that is being viewed and includes the coast and countryside linked to it. It is the broader picture and is made up from different features.
E.g. The Jurassic Coastline
is an individual component of the coastal landscape. They are a distinct part of the wider coastal landscape but must be viewed individually.
E.g. A stack
E.g. Durdle Door is a landform which created and adds to a landscape.
wave- cut platform
cave, arch, stack, stump
is when the cliff naturally goes backwards.
hydraulic action, undercutting. High amplitude destructive waves.
notch, unsupported. Cliff above unsupported.
sub- aerial weathering. Undercut further pronounced by hydraulic action.
retreat collapses. Attrition removes the sediment.
Wave- cut platform:
at the base of the cliff
can be seen at low tide
rock pools- abraded by the rocks being dragged out to sea
when waves break against the foot of a cliff, hydraulic action and solution/ corrosion is concentrated close to the high- tide line.
this creates a wave- cut notch.
as the notch gets bigger due to continued erosion, the cliff is undercut and the rock above it becomes unstable, eventually collapsing.
as these erosional processes are repeated, the notch migrates inland and the cliff retreats.
leaving behind a wave- cut platform, which is usually only exposed at low tide.
wave- cut platforms rarely extend more than a few hundred meters, because a wave will break earlier and it's energy will be dissipated before it reaches the cliff, thus reducing the rate of erosion, limiting the further growth of the platform.
Headland and bays:
protudes (sticks out), all different shapes and sizes, often rocky, high energy, destructive waves refract around the headland, hard more resistant rock, eroded at a much slower rate.
semi- circular inlet, often with a beach, deposition, constructive waves, low energy- deposit material, soft/ less resistant rock, erodes at a much quicker rate.
depositional, constructive waves, low energy environments, beaches, high rate or erosion originally, soft rock, inlet, cove.
bands of hard and soft rock.
discordant coastlines, hydraulic action, abrasion, concordant coasts.
on discordant coastlines bands of hard and soft rock run perpendicular to the sea. There is a differential rate of erosion along the coast because of this. Hydraulic action and abrasion therefore force the soft rock to retreat in land forming bays. The harder rock is left protruding out as a headland because it erodes slowly. Eventually, wave refraction concentrates energy on the headland and leaves the bay with depositional constructive waves.
sheer force of the water eroding the base of the cliff.
rocks/ material scraping the base of the cliff; being hurled at the cliff.
rocks colliding with each other to create smaller, smoother rocks.
acid water that dissolve fragments of rock. Water becomes chemical by pollution.
coastal morphology is related not only to the underlying geology, or rock type, but also to it
the geologic structure of a rock.
layers of rock
horizontal, natural breaks in the strata caused during the formation of the rock
verticle fractures caused either by contraction as sediments dry out, or by earth movements during uplift.
refers to the angle at which rock strata lie (horizontally, vertically, dipping towards the sea or dipping in land.)
formed when the stress or pressure to which a rock is subjected exceeds it's internal strength (causing it to fracture.) The faults then slip or move along fault planes.
formed by pressure during tectonic activity, which makes rocks, buckle, and crumple.
Influence of lithology on erosion:
joints and faults are weaknesses that make the rock more susceptible to erosion.
rocks that dip inland produce a stable, steep cliff profile.
rocks that dip towards the sea are prone to slumping and are much weaker.
strong resistant rock- igneous and metamorphic, sedimentary rocks that are dipping steeply or even vertically, long fetch and high energy waves that encourage erosion and undercutting by the sea.
weak, unconsolidated rocks which are prone to slumping, rocks that are dipping towards the sea, a sheltered location with low- energy waves and a short fetch will result in sub- aerial debris building up at the foot of the cliff preventing undercutting and steepening.
Factors influence the rate of retreat:
type of erosion
rising sea levels
joints and faults:
prime sight of erosion, weaknesses, sea attacks the cliff causing and forcing air and water into faults and joints causing more pressure, hydraulic action, abrasion, chemical action, Green Bridge of Wales, Pembrookeshire.
cave -> arch:
eroded further by hydraulic action break through to the back of the cliff.
arch -> stack:
rock at the top unsupported, repeated erosion, top of arch collapses.
stack -> stump:
base prone to hydraulic action and abrasion, worn down by waves and weather, keep getting eroded until you can only see it at low tide.
abrasion and hydraulic action using the weaknesses to compress the air and water into the faults and joints.
Durdle Door, Green Bridge of Wales, the repeated process of hydraulic action through the cave to the other side of the cliff.
Old Harry, undercutting the top of the stack becomes unstable so collapses due to hydraulic action and abrasion.
still eroded until it can only be seen at low tide.
Sea level change:
in the last 20,000 years, sea levels have increased, relative to today's sea level. The difference is about 120m.
we are said to be still coming out of the last ice age, 20,000 years ago.
last ice- age water cycle slows down and increased storage as ice.
ice advantages from both poles.
less water is reaching the sea, not being replenished by rivers because they have dried up.
in the last 20,000 years the water cycle has started to increase. The increase in temperature, means the water held as ice floods rivers.
climatic change warming leads to release of water from ice storage.
projected rise in the future due to global warming -> humans fault not natural (ice age.)
the level of the sea changes daily due to the gravitational pull of the moon and sun (tides) but if we take an average of the level of the sea in relation to the land it has constantly changed throughout history.
changes of sea level in relation to the land, water moving.
land moving in relation to the sea e.g. fold mountains.
eustatic changes (global) :
these are when sea levels rise and fall due to inputs of water e.g. melting of glaciers results in eustatic rise whereas the formation of glaciers and increased water storage results in eustatic fall. It is when the sea moves relative to the land.
isostatic change (localised) :
these occur as a result of changes to landmass heights in relation to the sea. Tectonic activity can force the crust upwards thus having an overall lowering effect on the sea level. Another example linked to 'ice age' is the weight of the cold perued and bounce back during warming. These both result in isostatic changes to sea levels.
and/ or the reduced weight of glacial ice leading to crustal
gives us isostatic sea level fall.
ice age thawing:
glacial melt water feeds seas.
thermal expansion and increased glacial melt.
as the name suggests these are coastlines that have been 'drowned' by 'eustatic sea level rise. Two main landforms are associated with submergent coastlines -> rias and fjords.
Fowey estuary in Cornwall is a good example of eustatic sea level rise resulting in a drowned river valley or ria. It has a typical long and cross profile similar to that of a river It is much deeped at the mouth of the estuary and shallower in land e.g. Dart Estuary.
fjords are similar to rias in terms of thier formation. However, eustatic sea level rise results in the drowning of deep, glaciated U shaped valleys as opposed to river valleys. Accompanying this drowning is the isostatic uplift of the earths crust as the weight of the melting glaciers is reduced. The result of the bounce back and drowning are the spectacular, very deep, flooded valleys with very steep sides found in coastal areas of Norway, New Zealand and Chile.
these form in areas of the world where valleys (especially glacial valleys) lie parallel to each other. When the valleys are flooded by the rise in sea level, the tops of the valleys remain above the surface of the sea and appear to be a series of islands that run parallel to the coastline. The best example of a dalmation coastline is the one from which they get their name, Dalmatian coast in Croatia.
coastlines of emergence:
isostaic uplift of the crust has forced the land to rise or 'emerge' from the sea. They also occur from eustatic fall in sea level. The main landform associated with emergent coastlines is the raised beach.
a raised beach coastline on the Isle of Arram, West Scotland. Here, a raised beach can be seen due to relative sea level fall. After the ice melted at the end of the last Ice Age, isostatic readjustment of the crust in this area of Western Scotland took place. As a result, the crust bounced back and relative sea fell, leaving former coastal features above the new sea level.
impacts of rising sea level:
increased erosive power of the sea- accelerated erosion on the Holderness coast, more homes, businesses, farmland at risk so the greater need for costly hard engineering.
salt marsh ecosystems are threatened:
SSSI behind Spurn Head in danger of being lost as the spit is eroded and shrinking due to sediment starvation because of hard engineering needed to protect the coast from increased erosion.
coastal settlements at risk of flooding:
New Orleans 2006, the Maldives have lost over 5m of beachfront in 20years, 1m rise would inundate 25% of Bangladesh areas of the UK around the Humber, wash and Thames Estuary would be flooded- huge cost implication for defence and /or displacement of people.
greater emphasis on management:
hard vs soft debate.
Estuarine mudflats and salt marshes:
are formed along depositional coastlines, in low energy environments, sediment is deposited, coagulates and mud builds up over time at low tide --> after a certain amount of time, mudflats are created which are raised above the high tide level due to sedimentation and accretion --> various seeds are transferred by the wind and the sea water and pioneer plants are glasswort and sea blite germinate as they halophytic --> root systems help consolidate soils and decomposed plant matter add humus aiding bioconstruction --> incrased oxygen levels in the soils and improved nutrient content enable plants like sea pursland and sea lavender to flourish and secceed the pioneer grasses --> eventually, the community stabilises and climaxes. Here rushes and reeds proliferate and the ecosystems is said to be in a state of equilibrium --> the succession of vegetation on a salt marsh is called a halosere.
formation of a spit:
Longshore drift moves material along the coastline.
A spit forms when the material is deposited.
Over time, the spit grows and develops a hook if wind direction changes further out.
Waves cannot get past a spit, which creates a sheltered area where silt is deposited and mud flats or salt marshes form.
Hurst Castle spit is east of Bournemouth.
are formed by the wind. They normally develop where a) there is a strong onshore wind; b) there is a large supply of sand; c) a large- intertidal range so that large expanses of sand regularly dry out.
the wind moves sand dried out at low tide inland by saltation --> an obstacle (driftwood) will halt saltation and result in the accumulation of sand --> pioneer plants (marram grass) can tolerate the harsh consitions and begin to colonise the area- this encourages further depostion and the growth of the dunes --> another dune forms on the seaward sied of the original dunes (sheltering the original dune and resulting in changing environmental conditions) --> a sequence of dunes forms (oldest inland) amd environmental conditions continue to change due to the presence of vegetation (simple soils from due to decaying vegetaion) --> number and diversity of plant species on teh dunes increases- eventually the climax community is reached.
definitions/ plants/ grasses:
bars: constructive waves - low energy - positive budget, adding sediment - where a spit grows across a
, joining the two
. Behind the bar, a
is created where water has been
and the lagoon may gradually be infilled as a
develops due to it being a
low energy zone
, which encourages
- e.g. Loe bar, Helston, Cornwall.
if the extension of material joins to an offshore island it is know as a tombolo.
coastal dunes psammosere:
succession of plants- following on from each other, plant - tree.
essentially a muddy sea shore with vegetation growing on it. It is a low energy area that forms a transitional zone between land and salty (or brackish) water.
behind a spit, river estuary, behind a headland, bay