changing landscapes

weathering definition

a range of processes that break up rock, active on a stretch of coastline above the tide line

whats an input

energy from wind, waves and tides; sediment from weathering and erosion processes

whats an output

sediment removed by longshore drift and sediments deposited as landforms, such as dunes.

what does open system mean

energy and sediment can move from the boundary of the system into the environment around it.

coastal sediment budget

the balance between the input, store and output of sediment.

when is the sediment budget balanced

when input=output.

in a steady- state equilibrium

sediment cells in uk

there are 11 major cells for England and Wales which are divided into smaller- sub cells.

sediment can be lost from cells, making them open systems.

sediment cell definition

a stretch of coastline where the sediment budget is self-contained. also known as a littoral cell.

steady state equilibrium

changes in energy and the resulting change in coastlines do not vary much from from the long-term average conditions.

e.g. beach profiles adjusts in summer and winter as wave energy changes, but the average gradient stays the same.

metastable equilibrium

the coastal zone changes from one state of equilibrium to another due to an event causing a change in conditions.

e.g. sediment removal due to dredging changes the beach profile, or it disappears. There is a new equilibrium with a reduced beach.

dynamic equilibrium

the state of equilibrium changes over a longer timescale than metastable equilibrium

e.g. climate change causing rising sea level allows new areas of land to be influenced by wave attack, resulting in a change in cliff profile

positive feedback

increases the initial change that occurred.

negative feedback

reduces the effect of the change, helping the coast return to its original condition.

tides

created by the gravitational effect of the moon, which pulls water on earth towards it to create high tides, with a balancing increase in sea level on the opposite side of the earth.

spring tides

twice a month the earth, moon and sun are aligned, so the gravitational pull is greatest, creating higher than average tides.

neap tides

when the sun and moon are at right angles to each other the gravitational pull is weaker, creating lower than average tides.

tidal range

difference in height between high and low water during the monthly tidal cycle.

constructive wave

less than 1 metre high

long- up to 100m between crests

wave period- 6-8 breaking each minute.

gentle steepness- tends to spill over

low wave energy

stronger swash

material moves up the beach to form a berm

increase beach gradient

more frequent in summer

destructive waves

greater than 1 metre high

shorter- 20 metres between crests

shorter period- 10-14 breaking each minute

steep- plunging

high energy

stronger backwash

material moves down beach

steeper upper beach, gentle lower beach.

more frequent in winter, with stormier weather.

wave length

the horizontal distance between wave crests

wave height

the vertical distance between crest and trough

wave period

the time interval for the wave motion from trough to trough, or crest to crest, in seconds. sea waves have wave periods between 1 and 20 metres

high- energy coastal environments

these are erosive, rocky coastlines. processes affecting them include:

• physical, chemical and biological weathering.

• mass movements, e.g. rock falls

• transportation processes moving material from or along the coastline.

low energy coastal environments

deposition is the dominant process, creating sandy coastlines and associated features such as sand dune, spits and bars. estuarine coastlines are low-energy.

sub-aerial processes

physical/mechanical weathering

chemical weathering

biotic weathering

mass movement

Marine erosion processes

hydraulic action

corrasion/ abrasion

attrition

corrosion

freeze-thaw

repeated freezing and thawing of water results in the expansion of cracks in rocks, causing small fragments to break off.

salt crystallisation

sea water evaporates from cracks, allowing salt crystals to grow, exerting pressure and causing pieces of rock to break off.

water- layer weathering

constant wetting and drying causes clay-rich rock to expand and contract, resulting in cracks, which aid physical weathering processes.

solution

the removal of rock dissolved in acidic rain water

oxidation

oxygen dissolved in water reacts with minerals, causing oxidation

hydration

minerals in rocks absorb water, which weakens their structure, making them susceptible to weathering

hydrolysis

breakdown of rock by acidic water produces clay and soluble salts, especially feldspar in granite.

carbonation

carbon dioxide dissolved in rain water creates weak carbonic acid, which dissolves calcium carbonate in limestone- this process plays an important role in the carbon cycle.

landslide

rocks affected by physical weathering or marine erosion collapse downwards.

rockslide

rocks slide down a cliff face when the bedding planes dip towards the sea

rotational slip

softer rocks give way, moving downhill in one mass along a concave slip surface.

slump/mudslide

saturated soft rock flows downhill

soil creep

soil particles move downslope, aided by rain drop impact.

solifluction

movement of wet soil downslope caused when underlying layers are frozen.

traction

sediment rolls or slides along the seabed

saltation

sediment is bounced along the seabed

suspension

small particles are held and moved in the water

solution

material dissolves in the water and is moved by the sea.

flocculation

occurs where fresh water mixes with sea water, such as in a river estuary. clay particles coagulate due to chemical reactions to form flocs, which are heavier and more likely to be deposited.

tombolo

a spit or bar that joins the mainland to an island, for example the eastern end of Chesil Beach, where it joins the isle of portland.

cuspate foreland

a triangular-shaped projection from the shoreline made up of a series of ridges created by longshore drift from opposing directions. a famous example is Dungeness in kent

aeolian processes

the wind activity and how the wind erodes, transports and deposits sediments.

sand dunes- ridges

lines of dunes parallel to the coast

sand dunes- slacks

hollows found between the dune ridges

grey dunes

older dunes where decomposing organic matter creates a humus layer on the surface, making the dunes appear grey.

yellow dunes

younger dunes with no humus layer

embryo dunes

youngest dunes in the early stages of formation

fore dunes

dune ridges closest to the sea.

blow-out

an area of dune that has been eroded by the wind, often due to its protective cover of vegetation being removed by animal or human activity.

rills

shallow channels cut by the action of running water.

salt marshes

• gently sloping

• found in low-energy, sheltered areas

• important wildlife habitats

coral reefs

best conditions for them to grow are:

• clear water, allowing light penetration

• seawater temperatures 23-29 degrees

• shallow water- less than 100m deep

• wave activity

mangroves

• an ecosystem of small trees along tropical coastlines.

• vegetation is salt tolerant

• stilt roots

seasonal changes- summer

• fewer storms

• less frequent high wind speeds

• lower-energy waves

• waves constructive

• sediment moved onshore

seasonal changes- winter

• more storms

• high winds more frequent

• higher-energy waves

• destructive waves more frequent

• sediment moved offshore

eustatic change

• global change in the volume of water in the oceans

• during a glaciation period more water is frozen, resulting in less liquid in the oceans, so sea level falls.

• global warming, melting of ice sheets, adding water to the oceans and raising the sea level.

isostatic change

• localised change in the relative sea level caused by the upward or downward movement of land masses.

• during glacial periods the weight of ice causes the land to sink into the crust, making sea level appear relatively higher.

• melting ice removes the weight and the land very slowly rises, causing a relative fall in sea level.

management strategies- do nothing

allows natural processes such as coastal erosion to continue

managed retreat or realignment

allows the shoreline to move inland by erosion or flooding to a new line of defence.

hold the line management

the present shoreline is protected by a variety of hard and soft engineering solutions.

advance the line management

the shoreline is moved seawards either using hard engineering structures or by encouraging sand dune growth

limited intervention management

deals with the problem to some extent, for example by encouraging the growth of salt marsh or sand dunes that reduce the impact of wave energy; it can also involve raising buildings to cope with flooding due to rising sea levels.

Cost- benefit analysis (CBA)

Divides the value of benefits (e.g property protection and employment) by costs. Benefits should outweigh costs for the adoption of a strategy.

What does the choice of management strategy depend on?

• feasibility- technical aspects

• Cost-benefit analysis- divers the value of benefits buys costs

• Environmental impact analysis- effects on the environment

• Risk assessment

Sea walls

Hard engineering

Concrete structures at the cliff foot to absorb wave energy

Rock armour (rip-rap)

Hard engineering

Large rocks placed to absorb wave energy

Revetments

Hard engineering

Wooden or concrete structures that absorb wave energy while allowing some flow of sediment

Groynes

Hard engineering

Wooden structures jutting into the sea to trap longshore drift

Offshore bars

Islands of boulders offshore to absorb the force of the waves before they reach land

Beach nourishment (replenishment)

Soft engineering

Sand or shingle is added, extending the beach or replacing eroded material

Beach reprofiling

Soft engineering

Beach shape is changed to absorb more energy, reducing erosion

Positive impacts of humans activity on coastal landscapes

• adoption of sustainable management

• Increasing use of integrated shoreline management strategies

Conservation strategies

• world heritage sites e.g Great Barrier Reef, Australia

• National marine reserves

• Sites of Special Scientific Interest(SSSI)

Offshore dredging

The extraction of sand and gravel from the seabed for use in construction.

Negative effects:

• destruction of seabed habitats and the marine food wed

• Changes to wave types and sediment flows, resulting in changes in the beach profile.

Erosion of sand dunes

• conversion

• Removal

• Overuse

• External factors

Integrated coastal zone management (ICZM)

• Form of sustainable management

• Tried to balance environmental, economic, social, cultural and recreational needs

• Involves the participation of all stakeholders in the coastal zone

• Uses defence methods

eustatic change

changes in the absolute sea water level

isostatic changes

changes in the absolute level of land

causes of eustatic change

• glacio-eustatic change (major)

• thermal expansion (minor)

isostatic rebound

where ice sheets melt and the underlying crust pushes back up

Flandrian transgression

• rapid sea level rise between 11,500 years ago and 6000 years ago

• associated with the melting of bulk ice caught up in the pleistocene ice age

coastlines of emergence

more isostatic rebound than eustatic

• raised beaches

• raised cliffs and shore platforms

coastlines of submergence

more eustatic change than isostatic

• rias

• fjords

Rias

• formed by the drowning of the lower reaches of a river valley and its tributaries

• more common on discordant coastlines

• example: Milford Haven, Pembrokeshire

formation of a rias

1. original river valley formed from fluvial processes overtime

2. during the flandrian transgression there was rapid sea level rise. lower tributaries flooded and became much wider

3. eustatic is happening more than isostatic because the sea level rises

Fjords

• drowning of a U-shaped valley

• e.g west coast Norway

• similar to rias

raised beaches

• wave cut platforms and fossil beaches eroded during periods with higher sea level, which are now above the current beach level.