Coastal Systems and landscapes AQA A-Level Geography

What type of system are coastal systems?

Open - both matter and energy can enter and leave the system (sediment and energy in this case which create distinctive landscapes)

What are examples of inputs for a coastal system?

Energy from: Wind, waves, tides and currents

Sediment from: waves, tides and currents bringing in offshore currents, crushed shells and marine organisms, flooded river valleys (estuaries), coastal erosion of cliffs & sea level change

What are examples of flows/transfers in coastal systems?

longshore drift, weathering, mass movement, erosional processes, deposition & transportational processes

What are examples of stores in a coastal systems?

spits, beaches, dunes, offshore bars, tombolos (spits that connect an island to a beach)

What are examples of outputs in a coastal system?

sediment washed out to sea and deposited further along the coast, dissipation of wave energy, accumulation of sediment above the tide limit

What is an example of negative feedback in a coastal system?

1. A beach in dynamic equilibrium before a storm

2. Sediment is eroded from the beach during a storm due to strong backwash

3. Sediment is deposited offshore forming an offshore bar

4. Waves are forced to break before reaching beach - dissipating energy and reducing further erosion after reaching the beach

5. When the storm calms, normal wave conditions rework sediments from the offshore bar back to the beach

What is an example of positive feedback in a coastal system?

1. global temperature rise warms the oceans

2. increased oceanic temperatures

3. warm water is less able to dissolve gas

4. dissolved CO2 is released by oceans

5. More CO2 back into atmosphere which acts as a greenhouse gas

6. increases global temperature more

7. ice melts

8. sea levels rise

Why do coastal systems landforms constantly change?

Coastal landscapes change due to erosion and deposition which changes as they are driven by inputs of energy

What is the backshore?

the area between the high water mark (HWM) and the landward limit of marine activity (Changes usually take place only during a storm)

What is the foreshore?

the area between the HWM and the low water mark (LWM). The most important zone for marine processes when the area is not influenced by a storm

What is the inshore?

the area between the LWM and the point where the waves don’t have influence on the land beneath them

What is the offshore?

the area beyond the point where waves don’t have anymore influence on the seabed and in which activity is limited to deposition of sediments

What is the nearshore?

the area extending in the direction of the sea from the HWM to the area where waves break

What three zones are included in the nearshore?

Swash zone, surf zone and breaker zone

What is the swash zone?

the area where a turbulent layer of water washes up the beach after a wave has broken

What is the surf zone?

the area between where the waves break, forming a foamy surface, and where the waves move up the beach as swash

What is the breaker zone?

the area where waves approaching the coastline begin to break (water depth is usually 5-10m)

What is erosion?

The wearing away of the Earth’s surface by the mechanical action of river, wave and wind processes

What is the fetch?

the distance of open water that wind blows over uninterrupted by land obstacles.

The length of the fetch helps to determine the magnitude and energy of the wave

What is mass movement?

The movement of material downhill under the influence of gravity (can be assisted by rainfall)

What is weathering?

The breakdown or decay of rock at or near the Earth’s surface (mechanical, biological or chemical)

What is the energy needed to drive coastal systems provided by?

waves, wind, tides and currents

Why is wind a vital input to coastal systems?

it is a primary source of energy for other processes and an important agent of erosion and transport

Where do spatial variations in energy result from?

Variations in the strength and duration of the wind.

If wind speed is persistently high and uninterrupted, wave energy is higher

local weather patterns may influence short-term wind speed changes and direction, but most coastlines have a prevailing wind direction (so wind usually reaches coast from one direction) - this also controls the direction material is transported

Why does wind play a vital role in wave formation?

Waves are created by the transfer of energy from the wind over the sea (the ‘frictional drag’)

The energy required by waves is dependent on the strength of the wind, the length of time it is blowing and the fetch

How does wind act as an agent of erosion?

it can pick up and remove sediment from the coast (e.g. sand) and use it to erode other features

most common type of wind erosion = abrasion

is also an important agent of moving sediment along the coast, inland and beyond the tidal zone

How are waves formed?

wind drags water forming lumps called capillary waves transferring energy becoming bigger ‘swells’. The wind is transferred into the water by friction and the orbital motion keeps it moving and expanding

Why do waves break onto the shore?

1. The water becomes shallower and the circular orbit of water particles changes into an elliptical shape

2. The wavelength and velocity decrease and the wave height increases - causing more water to rise to a point where the wave breaks (wavelength ratio of 1:7 = breaks)

3. water rushes up the beach as swash and returns as backwash

What are constructive waves?

waves with a low wave height, long wavelength and low frequency of around 6-8/min. Powerful swash and weaker backwash = beach material build up

What happens as a constructive wave approachs a beach?

the wave front steepens slowly, giving a gentle spill onto the beach surface

swash rapidly loses volume and energy as water percolates through beach material = weak backwash (insufficient force to pull sediment back)

so material is constantly moved up the beach forming ridges (berms)

What are destructive waves?

waves with a high wave height and a steep form, high frequency (10-14/min) Strong backwash, weak swash = more sediment is removed than added

What happens when a destructive wave approaches the beach?

• rapidly steepen and plunge downwards when breaking

• this creates a powerful backwash and inhibits swash for the next wave

• very little material is moved up the beach so more material can be pulled back down the beach

• commonly associated with steeper beach profiles

• the force of each wave might project shingle up the beach forming a ridge called a ‘storm beach’

What type of waves do most beaches experience?

most beaches experience alternating cycles of constructive and destructive waves

What is the negative feedback loop associated with constructive and destructive waves?

• constructive waves build up the beach and make it steeper which encourages destructive waves

• overtime destructive waves move material back down the beach reducing the beach angle encouraging constructive waves

What happens when waves approach topography that is not a regular shape?

waves are refracted

How do waves refract?

1. wave drags in the shallow water

2. The part of the wave in the deeper water moves forward faster which makes the wave bend

3. Overall effect = wave energy becomes concentrated on the headland = greater erosion

4. Low energy waves spill into the bay = deposition

What are tides?

periodic rise and fall in the level of the sea caused by gravitational pull of the sun and moon (moon has greater influence because it is nearer)

The moon pulls water towards it, creating a high tide, creating a compensatory bulge on the opposite side of Earth

What is a spring tide?

the highest tidal range caused by the sun, earth and moon aligning. The sun and moon’s gravitation forces combine so there is more pull creating a more extreme tidal range

What is a neap tide?

the lowest tidal range caused by the sun and earth aligning with the moon perpendicular. The sun and moon are at right angles so the gravitation pulls work against each other, pulling less water

Apart from the moon and sun, what other factors can impact the regular pattern of tides?

morphology of the seabed, proximity of land masses and the impact of the spinning forces of Earth (coriolis force)

What can the tidal range be a significant factor in the development of?

the coastline

What is the tidal range and what do they determine?

difference in height of water at high and low tide (this is not fixed)

• they determine upper and lower limits of erosion and deposition

• the amount of time each day is in the littoral zone (i.e. longshore drift zone)and is exposed to sub-aerial weathering

What are the results of a low tidal range?

e.g. Mediterranean

restricts waves to a narrow width in the coastal line

What are the results of a high tidal range?

e.g. British Isles

wide zone for wave attack

formations of wide wave-cut platforms

Which areas are exposed to the highest energy waves?

areas exposed to large fetches and strong winds (e.g Portugal and California)

What is a landscape?

the visible features on land

What is a landform?

the shape and character of the land surface

What are moderate energy, tide dominated coastal features?

mudflats, sand marshes, sandflats, mangroves, deltas

What are high energy, wave dominated coastal features?

shore platforms, cliffs, beaches, spits, tombolos, deltas

What are wind dominated, low energy coastal features?

sand dunes

What is a current?

a permanent or seasonal movement of surface water

What are longshore currents (littoral drift)?

• occur as most waves hit the coastline at an angle

• This generates a flow of water (current) running parallel to shoreline

• this moves water along surf zone and transports sediment

When do rip currents form?

• they are strong currents moving away from the shoreline

• form when seawater is piled up by incoming waves

• current may initially run parallel to shoreline but a headland or change of coastal direction might change this

• hazardous

What is the upwelling movement?

the movement of cold water from deep in the ocean towards the surface

• more dense cold water replaces warmer surface water = creates nutrient-rich cold ocean currents

• can form part of the pattern of global ocean circulation currents

How do currents form?

• wind and breaking waves push water towards land (causes a rise in water level)

• excess water flows back to sea

• if there is coral or a deeper depth, water flows offshore easier - initiates rip current

What are tidal surges (storm surges)?

occasions when meteorological conditions give rise to strong winds which can produce really high water levels (higher than levels of a high tide)

What is an area affected by tidal surges?

North sea (tidal surge 1953) and east coast of Britain (December 2013 and January 2014)

• Depressions (intense low pressure weather) over the North Sea produce low pressure conditions that can raise sea levels (1 cm for every 1 millibar drop in pressure)

• Strong winds drive waves ahead of the storm and push the sea water towards coast = piling up of water on the coast effect

• Due to the North Sea’s shape, water is usually concentrated into smaller spaces (funnelling) - spring tides intensify this effect

What are high energy coasts?

coastlines where:

• strong steady prevailing winds create high energy waves

• rate of erosion is higher than deposition

• typical landforms: headlands, cliffs, wave cut platforms

• e.g. Cornish coast

Low energy coasts?

coastlines where:

• low inputs of wind energy

• wave energy is low

• rate of deposition exceeds erosion

• typical landforms: beaches and spits

• e.g. Severn Estuary

What does coastal sediment come from?

streams, rivers, estuaries, cliff erosion, offshore sand banks, material from biological origin (crushed shells, marine organism skeletons)

What are sediment cells?

a distinct area of coastlines separated by distinct barriers like headlands with balanced inputs and outputs

11 in england and wales e.g. Portland Bill, Selsey Bill, Land’s End

In theory = closed systems. However, fine sediments can get into neighbouring cells

What is a sub cell?

smaller sections of sediment cells - allow closer study and management

e.g. the sub cell operating between Flamborough Head and Humber estuary

What is a coastal sediment budget?

the balance between sediment being added to and removed from the coastal system

What happens when more material is added than removed to a sediment budget?

• a net accretion of material

• positive budget or surplus

• shoreline builds towards the sea

What happens when more material is removed than added to a sediment budget?

• negative budget or deficit

• shoreline retreats landward

What do the coastal erosion processes control concerning the sediment budget?

the level of deficit

What can the sediment budget be used to identify?

the sources that deliver sediment to the cell and to the sites where sediment is stored, or sediment sinks.

Calculating a cell’s sediment budget requires identification of all sediment sources and sinks and an estimation of all sediment removed and added each year - extremely difficult and expensive

What are sediment cell inputs?

sediment deriving from coastal erosion, rivers and offshore sources (bars and banks)

What are sediment cell outputs?

material within cell swept out to sea - could be a result of a strong storm

What are sediment cell transfers?

littoral (sideways) drift, onshore and offshore processes e.g. rip currents

What are sediment cell stores?

beaches, sand dunes, offshore deposits

What creates a positive sediment budget (coastline builds)?

• beach nourishment (adding new sediment to beach through soft engineering)

• deforestation (roots are removed = more soil and sediment erode into sea)

• sea level rise (more erosion = more sediment is added to system)

• rockfall in upland area

What creates a negative sediment budget (coastline retreats)?

• dam built along river (blocks water and traps sediment)

• dredging (removing sediment so less is deposited on the beach)

• creation of sea wall (flat sea walls = waves crash into sea wall and quarry = takes away sediment in backwash)

What are marine processes?

the processes that operate on a coastline connected with the sea e.g. waves and tides

what are sub-aerial processes?

operate on land but affect the shape of coastline e..g weathering and run-off

What is erosion?

the break down and removal of rock and sediment by agents that move e.g waves

What is transportation?

the movement of sediment by water

What is deposition?

when energy levels decrease in environments like bays and estuaries - sediment is dropped due to gravity

What is hydraulic action?

the force of waves exerted on rocks that weakens them

What is abrasion?

material picked up by the sea wearing away rocks = damages cliff face

What is attrition?

rocks in the sea that carry out abrasion being slowly worn down into smaller pieces

What is solution/corrosion?

the dissolving of calcium-based rocks (limestone) in the sea

seawater itself does not cause (7-8.5 pH)

What is wave quarrying?

when breaking waves trap air when hitting cliff face and the force of water compresses the air into a gap, creating pressure

when water pulls back the pressure is released which weakens the cliff

What is lithology?

the characteristics of rocks (resistance and permeability)

very resistant rock like granite will be eroded slower than weaker materials like clay

some rocks like limestone are well-jointed so the sea can penetrate along lines of weakness = more vulnerable to erosion

what is differential erosion?

variation in rates of erosion

What other features of rocks also affect erosion?

structure and variation

What is a concordant coastline?

when rocks run parallel to the coast

form coves

• areas of weakness are infiltrated by the sea (hydraulic action)

• erosion focuses on the weakness

• soft rock erodes faster than hard rock

• cove is formed e.g Lulworth Cove

what are discordant coastlines?

when rocks are perpindicular to the coastline

form headlands and bays

• hard rock erodes slower and hard rock erodes quicker

• hard rocks form headlands

• soft rocks form bays

• wave refraction and differential erosion occur

• e.g Swanage Bay

Why is the dip of a rock a major factor?

steepest cliffs = rocks with horizontal strata or which dip gently inland

rocks that dip towards coast = more gently sloped

What is traction?

large stones and boulders are rolled along seabed and beach by moving seawater (high energy environments)

what is suspension?

very small particles of sand and silt are carried by moving water (can cause murky water appearance)

What is saltation?

small stones bounce along seabed and beach

relatively high energy conditions

can end up dislodging more particles

What is solution?

dissolved materials are transported within the mass of moving water

When does deposition occur?

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

What is gravity settling?

the water’s velocity has decreased so sediment is dropped

What is flocculation?

an important process in salt and tidal marshes. Clay particles clump together due to chemical attraction and then sink due to high density

What is longshore drift?

• occurs when waves approach the beach at an angle due to direction of prevailing wind

• material is pushed up by swash at angle and dragged down by backwash perpendicular (gravity)

• this continues overtime in a zigzag pattern, transporting sediment along coast (can become more rounded and smaller)

What can interfere with longshore drift?

groynes and piers lead to entrapment of beach material as sediment accumulates on windward side

deposition of this material takes place in sheltered locations such as bays

What is marine deposition?

sediment carried by seawater is deposited (when waves lose energy or rapid coastal erosion provides an abundant supply of sediment

• when sand and shingle accumulate

• as waves slow after breaking

• as water pauses at the top of swash

• when water percolates into beach material as backwash

What is aeolian deposition?

sediment carried by wind is deposited