coasts

is the coast an open or closed system and why

open system because it receives inputs from outside the system and transfers outputs away from the coast and into other systems. These systems may be terrestrial, atmospheric or oceanic, and can include rock, water and carbon cycles

what are sediment cells

• sections of the coast that are often bordered by prominent headlands

• within sediment cells, the movement of sediment is almost contained and the flows of sediment act in dynamic equilibrium

• within each sediment call there are smaller ‘subcells’. Often the smaller subcells are used when planning coastal management projects

define dynamic equilibrium

the maintenance of a balance in a natural system, despite being in a constant state of the change. Inputs and outputs are constantly changing to maintain the balance 

simply, how could dynamic equilibrium be interrupted 

• on the long term, it may. e upset by human interventions 

• in the short term, it may be interrupted by natural variations 

list some inputs in the coastal system 

• marine; waves, tides, salt spray

• atmosphere; sun, air pressure, wind speed and direction 

• humans; pollution, recreation, settlement, defences 

list some outputs in the coastal system

• ocean currents

• rip tides

• sediment transfer

• evaporation

list some stores/sinks of sediment and material

• beaches, sand dunes, spits, bars and tombolos, headlands and bays, cliffs, wave-cut notches, wave-cut platforms, caves, arches, stacks, stumps, salt marshes, tidal flats, offshore banks and bars

list some transfers/ flows within the coastal system 

• wind-blown sand

• mass movement processes 

• longshore drift

• weathering

• erosion; hydraulic action, corrosion, attrition, abrasion

• transportation; bedload, in suspension, traction, in solution 

• deposition; gravity settling, flocculation

list some sources of sediment

• rivers

• cliff erosion

• wind

• offshore (e.g. waves, tides and currents erode sediment sinks such as offshore bars)

• longshore drift

describe the process of longshore drift

• the swash approaches the coast at an angle due to the prevailing winds, transferring sediment along the beach.

• the backwash pulls the sediment directly back down the beach at a right angle due to gravity

• this transfers sediment along the coastline and the process repeats

what are sediment budgets 

• they use data of inputs, outputs, stores and transfers to assess the gains and losses of sediment within a sediment cell

• in principle, a system will operate in a. state of dynamic equilibrium where inputs and outputs of sediment are equal, however human actions and natural variation can disrupt the equilibrium

how are waves formed

• winds move across the surface of the water, causing frictional drag which creates small ripples

• leads to circular orbital movement of water particles

• as the seabed becomes shallower, the wave height increases but the wavelength and velocity both decrease

• this causes water to back up from behind the wave, until the wave breaks.

give some factors affecting wave energy

• strength of the wind; stronger wind means stronger waves

• duration of the wind; if the wind is active for longer periods of time, then the energy of the waves will build up and increase

• size of the fetch; the fetch is the distance over which the wind blows and the larger it is, the more powerful the waves will be. (also is the distance to the nearest land mass in a particular direction)

compare constructive and destructive waves

• constructive have long wavelength whereas destructive have short wavelength 

• constructive have long waves which surge up the beach whereas destructive have high waves which plunge onto the beach

• constructive have strong swash and weak backwash whereas destructive have weak swash and strong backwash 

• constructive occurs on gently sloped beaches whereas destructive occur on steeply sloped beaches 

describe the negative feedback system between waves and beaches

• the presence of constructive waves causes deposition on the beach, which in turn leads to the beach profile becoming steeper

• steeper beaches favour the formation of destructive waves which are then more likely to occur

• the destructive waves erode the beach, reducing the beach profile and leading to the formation of constructive waves.

describe the negative feedback system between seasons and waves

• constructive waves occur more frequently in summer when there are fewer storms, which means that the beach profile is more gentle in summer

• steeper beach profile during the winter months when destructive waves are more common

• this should lead to a state of dynamic equilibrium, but in reality this doesn’t occur due to external factors such as wind strength and direction

how are tides caused

when the gravitational pull of the sun or moon changes the water levels of the seas and oceans (this idea shows how gravity is a key source of energy at the coast)

what is the spring tide

• when the sun and moon are in alignment

• both of their gravitational forces combine to effectively pull the oceans towards them, causing the highest and lowest tides

• it causes the largest possible tidal range

what is a neap tide

• when the sun and the moon are perpendicular to each other

• their gravitational forces act against each other, so the overall pull is minimised.

• creates the smallest possible tidal range

what are rip currents 

• powerful underwater currents occurring in areas close to the shoreline 

• the backwash of waves is forced under the surface due to resistance from breaking waves, forming an underwater current 

• a gap in a sandbar could cause it to flow away from the shore more quickly, creating a ripcurrent 

• riptides are different to ripcurrents- riptides occur when the ocean tide pulls water through a small area such as a bay or lagoon. They are an energy source in a coastal environment, and can lead to outputs of sediment from the beach area 

what are high energy coastlines

• associated with more powerful waves (destructive) , so they occur when there is a large fetch

• they typically have rocky headlands and landforms

• rate of erosion exceeds rate of deposition

what are low energy coastlines

• have less powerful waves (constructive) and occur in sheltered areas

• often result in sandy areas

• landforms of deposition since the rates of deposition exceed the rate of erosion

what happens in the process of wave refraction 

• waves slow down in shallow water near a headland due to friction with seabed

• this causes the wave to bend 

• this causes them to concentrate their energy on headlands and dissipate it in bays 

describe a negative feedback system to do with headlands, bays, rock types and wave refraction

1. due to different rock strengths, erosion leads to the formation of headlands where resistant rocks exists, and bays where uncol=nsolidated rocks and clays exist

2. due to wave refraction, this increases forces of erosion on the headlands and reduced erosion in the bays.

3. eventually, the headlands are worn away, which again increases erosion within the bays

4. this would lead to dynamic equilibrium if conditions stayed constant

define the process of corrasion

sand and pebbles are picked up by the sea and hurled against cliffs at high tide.

define the process of abrasion 

sediment grinds against rock surfaces  and wears them away

define attrition

wave action causes rocks and pebbles to hit against each other, wearing each other down and becoming rounder in shape.

define hydraulic action

as a wave crashes onto a rock of cliff face, air is forced into cracks, joints an faults within the rock. The high pressure causes the cracks to force apart and widen. Over time this causes the rock to fracture

define corrosion (solution)

the mildly acidic seawater causes alkaline rock (such as limestone) to be eroded (process is very similar to carbonation weathering)

CAN LINK THIS WITH CARBON CYCLE AND GLOBAL WARMING 

how do waves affect erosion

• they affect the rate and type of erosion

• as a result, most erosion occurs during the winter months when waves are more likely to be destructive and more powerful due to storms

how do beaches affect erosion

• a beach infant of a cliff will absorb wave energy and thus reduce the effects of erosion.

• therefore if coastal management such as groins are used which trap sediment, this can lead to beaches not building up in other areas and could increase rate of erosion there

how do subaerial processes affect erosion 

• weathering and mass movement processes such as landslides weaken cliffs.

• rock fragments as a result of these processes may lead to increased corrosion and abrasion 

how can rock type/ lithology affect erosion

• sedimentary rocks (e.g. sandstone) are more vulnerable to erosion

• igneous and metamorphic rocks are more resistant to erosion

how do rock faults affect erosion

• fissures, cracks and joints are all types of weaknesses within the rock

• the more there are, the quicker erosion will occur

• they also increase the rock surface area, further promoting erosion

• large faults in the rock can lead to formation of headlands and bays due to the favourable conditions for erosion they create

list the four main processes of transportation 

1. traction

2. saltation

3. suspension

4. solution 

define traction

large, heavy sediment rolls along the sea bed pushed by currents

define saltation

smaller sediment bounces along the seabed, being pushed by currents. The sediment is too heavy to be picked up by the flow of water

define suspension

small sediment is carried within the flow of the water.

define solution 

dissolved material is carried within the water, potentially in a chemical form.

when does deposition occur 

when sediment becomes too heavy for the water to carry, or if the wave loses energy

define flocculation

• clay particles clump together due to chemical attraction and then sink due to their high density.

• important process in salt and tidal marshes

define weathering

the breakdown of rocks (mechanical, biological or chemical) over time

define mechanical weathering and give examples

• the breakdown of rocks due to exertion of physical forces

• e.g. freeze thaw- water enters cracks in rocks and water freezes and expands, causing cracks to develop.

define chemical weathering and give an example 

• the breakdown of rocks through chemical reactions 

• carbonation- rainwater reacts with CO2 in the air to create a weak carbonic acid. Dissolves limestone 

• oxidation- when minerals become exposed to the air through cracks and fissures, the mineral will become oxidised which increases its volume and causes the rock to crumble. e.g. iron is oxidised to iron oxide and turns rusty orange colour.

• solution- when rock minerals such as rock salt are dissolved

define biological weathering and give an example

• the breakdown of rocks by organic activity

• plant roots- roots of plants grow into the cracks or rocks, which exerts pressure, eventually splitting the rocks.

define mass movement and list the four types

the movement of material down a slope under the influence of gravity

creeps, flows, slides, falls

what factors affect the type of mass movement 

cliff slope/angle, rock type, rock structure, vegetation, saturation of ground, presence weathering 

define soil creep

• the slowest but most continuous form of mass movement.

• movement of soil particles downhill

• particles rise and fall due to wetting and freezing

define solifluction

• occurs mainly in tundra areas where the land is frozen

• as the top layers flaw during summer, the surface layers flow over the frozen layers

• forms solifluction layers

define mudflows 

• an increase in the water content in soil can reduce friction, leading to earth and mud flowing over underling bedrock.

define rockfall

• occurs on sloped cliffs when exposed to mechanical weathering, though mostly occurs on vertical cliff faces.

• leads to scree building up at the base of the slope.

define a landslide 

• heavy rainfall leads to water between joints in cliffs, which can reduce friction and lead to a landslide.

• a block of intact rock moved down the cliff face along a flat slope. 

• can be very dangerous 

define a slump

• contrary to a landslide, the slope is curved, so often occur in weak and unconsolidated clay and sands areas.

define runoff

• it is an example of a link between the water cycle and the coastal system

• the water in the form of overland flow may erode the cliff face and pick up sediment (sediment is transported in water via suspension)

• it may also be responsible for increasing pollution in coastal areas if it picks up water or excess chemicals

explain the formation of caves, arches, stacks and stumps 

• initially, faults in the headland are eroded by hydraulic action and abrasion to create small caves

• marine erosion widens the faults at the base of the headland, widening over time to create a cave

• the cave will widen due to both marine erosion and sub-aerial processes, eroding through to the other side of the headland, creating an arch

• the arch continues to widen until it is able to support itself, falling under its own weight through mass movement, leaving a stack as one side of the arch becomes detached from the mainland

• with marine erosion attacking the base of the stack, eventually it will collapse into a stump

• a wave-cut platform will be left afterwards.

how are wave-cut notches and platforms created

• this sequence occur on steep cliffs

• 1. when waves erode a cliff, the erosion is mostly concentrated around the high-tide line. the main processes of hydraulic action and corrosion create a wave-cut notch

• as the notch becomes deeper, (and sub-aerial weathering weakens the cliff from the top) the cliff face becomes unstable and falls under its own weight through mass movement

• this leaves behind a platform of the unaffected cliff base beneath the wave-cut notch

• over time the same processes repeat leading to a wave-cut platform being formed, which is normally exposed at high-tide

how are spits formed

1. when longshore drift causes the beach to extend out to sea, usually due to a change in direction of the coastline

2. this sediment protection can create a salt marsh due to the sheltered, saline environment, where water flow speed is lower, allowing deposition of finer sediments

3. the length of the spit depends on any changing currents or rivers, which will prevent sediment from being deposited. (this means a spit can never extend across an estuary)

4. a change in wind direction or wave direction can cause the end of the spit to curve (known as a recurved end)

how is a bar formed

• a spit extends across a bay to join two headlands

• this traps water behind it ,leading to the formation of a lagoon which is separated from the sea.

what is a tombolo

• a bar or beach that connects mainland to an offshore island

• they may be covered at high tide if they are low lying

what are offshore bars

• an offshore region where sand is deposited, as the waves don’t have enough energy to carry the sediment to shore.

define vegetation succession 

a plant community that changes over time

what happens in a sand dune succession

1. pioneer species such as sea rocket are resistant and able to survive in salty sand, with its roots helping to bind the dunes together

2. decaying organic matter adds nutrients and humus to the soil, allowing marram grass to grow

3. larger plants are able to colonise the area and the climax community occurs when trees are able to colonise the area

give some features of Marram Grass

• it is tough and flexible, so can cope with being blasted with sand

• it has adapted to reduce water loss through transpiration

• their roots grow up to 3 metres deep and can tolerate temperatures of up to 60*C

explain the salt marsh succession

1. algal stage- Gut Weed and algae establish as they can grow on bare mud, which their roots help to bind together

2. Pioneer stage- Cord grasses and Glasswort grow, their roots begin to stabilise the mud

3. Establishment stage- Salt marsh grass grow, creating a carpet of vegetation and so the height of the salt marsh increases

4. stabilisation- Sea Thrift, Scurvy Grass and Sea Lavender grow, and so salt rarely ever gets submerged beneath the marsh

5. climax vegetation- Rush and Red Fescue grass grow since the salt marsh is only submerged once or twice a year.

how does coastal vegetation help to stabilise sediment

• lots of plants bind soil together which helps to reduce erosion

• plants reduce the wind speed at the surface and so less wind erosion occurs

list different types of dunes

• embryo dunes- upper beach area where sand stars to accumulate round a small obstacle (e.g. driftwood)

• yellow dunes- as more sand accumulates and the dune grows, vegetation may develop on the upper and back dune surfaces, which stabilises the dune. The tallest of the dune successions

• grey dunes- sand develops into soil with lots of moisture and nutrients, as vegetation dies, enabling more varied plant growth.

• dune slack- the water table rises closer to the surface, allowing the dvelopment of moisture-loving plants (e.g. willow grass)

• heath and woodland- sandy soils develop as there is a greater nutrients content. trees such as willow, oak grow. the coastal woodland becomes a natural windbreak to the mainland behind.

what happens in isostatic change

• when the land rises or falls relative to the sea

• post-glacial rebound- the land that was covered by thick ice sheets during the last ice age is still slowly rising as it rebounds from the weight being removed

• plate tectonics and volcanic activity can also cause land to rise or fall, affecting local sea levels.

what happens during Eustatic change 

• Eustatic change is a global rise or fall in sea level caused by a change in the amount of water in the oceans.

• Eustatic affects Everywhere 

• during glacial periods- water is stored in ice sheets and glaciers, decreasing volume of water in oceans 

• in interglacial periods- ice sheets and glaciers melt and the water flows back into the oceans 

since 1880 and the Industrial Revolution, how much have sea levels increased

since 1880 and the Industrial Revolution, sea levels have increased by around 235m

define coastalisation

the process by which the coast is being developed and people are moving to the coast, increasing the number of people at risk from marine related environmental activity.

what is a storm surge 

• it is a result of the low pressure created by large weather events such as tropical storms. It raises the sea level and poses a significant flooding risk.

• has the potential to inundate flood defences 

how could the risk of a storm surge be exacerbated

1. removing natural vegetation- mangroves provide protection against extreme weather events such as cyclones (e.g. in the Bay of Bengal). However, due to pressure for land space, many mangrove forests are destroyed to make space for tourism, local industry and housing. mangroves trap sediment leading to accretion on he coastline, helping protect communities from the potential impacts of climate change

2. global warming- as the surface of the oceans get warmer, it is predicted that the frequency and intensity of storms will increase, and so the severity of storm surges and flooding is also expected to increase.

what are the consequences of storm surges for coastal communities

• reduced house and land prices (as the area is at significant risk), leading to economic loss for homeowners and local economies. (e.g. in the UK insurers don’t provide home insurance for people living along coastlines at extreme risk of storm surges)

• damage to the environment- destroying plant successions and damaging many coastal landforms (e.g. in 2013 the spit ‘Spurn Head’ was destroyed by a storm surge.)

give a fact that relates to a spit being destroyed by a storm surge 

Spurn Head was destroyed by a storm surge in 2013

evaluate hard engineering methods

• involves man made structures that aim to prevent erosion

• often very effective at preventing erosion in the desired area, but at a high cost

evaluate sea walls

• effective erosion protection

• promenade has tourists benefits 

• visually unappealing 

• wave energy reflected elsewhere, with impacts on erosion rates 

evaluate rock armour (rip rap)

• cost effective

• rocks are sourced from elsewhere, so do not fit in with local geology

• pose a hazard if climbed upon

evaluate revetments

( wooden or concrete ramps that help absorb wav energy)

• cost effective

• visually unappealing

• can need constant maintenance which creates an additional cost

evaluate soft engineering 

• aims to work with the physical environment

• natural methods of coastal defence

• useful for protecting against sea level change and coastal erosion

evaluate beach nourishment

• sediment is taken from offshore sources to build up the existing beach

• builds up beach, protecting cliff and increasing tourist potential

• cost effective and looks natural

• needs constant maintenance

• dredging may have consequences on local coastal habitats

Bay of Bengal (Odisha), exmoor mires project, river exe 

evaluate dune regeneration

• marram grass is planted. The roots help to bind the dunes, protecting land behind.

• cost effective and creates an important wildlife habitat

• planting is time consuming