Physical Geography - Coasts

the coast

The part of the land near the sea; the edge of the land

Standard Deviation

Calculation that can be used to determine how spread out a sample of data is against the full range of values available

the coastline

is regarded as an open system with inputs, processes and outputs; interacts with surroundings.

Landscape

consists of a constantly changing assemblage of erosional and depositional landforms: they are the result of continuous change in elements of the coastal system

Landform

a natural feature of the Earth's surface

Storm surge

The pushing of water against a coastline to abnormally

high levels, usually a combination of extreme low pressure

and high tides.

Ocean current

Large scale movement of water in the oceans

Tidal range

The vertical difference in height of sea level between high

and low tide.

Spring tide

Tides that occur twice a month when the sun and moon

align on the same side of the Earth.

Neap tide

Tides that occur twice a month when the Sun and Moon

are at right angles to the Earth.

ocean currents

are large scale movements of water in the oceans measured in metres per second or knots.

thermohaline circulation

A process driven by density differences in water due to temperature and salinity variations in different parts of the ocean. These currents occur at deep and shallow ocean levels and more slower than tidal or surface currents

waves

Caused by surface of sea exerting frictional drag on lowest layer of wind so higher layers move faster over the lower levels and fall forward

tides

Controlled by gravitational pull of moon and of sun slightly

sediment cell

is a stretch of coastline, usually bordered by two prominent headlands, where the movement of sediment is more or less contained.

Inputs (sources)

these are primarily derived from the river, coastal erosion and offshore sources, such as bars or banks.

Stores (Sinks)

These include the beach, sand dunes and offshore deposits (bands and bars)

Outputs

Material within the cell may be swept out to sea to act as an output from the system. This may occur as a result of a severe storm event.

Transfers (flows)

these involve littoral drift together with onshore and offshore processes such as rip currents.

Sediment budget

For a beach to exist, sediment has had to come from somewhere and the combination of wave, current and tide action ensures this. It is best thought of as being similar to a bank account, and is defined as the balance between sediment being added to and removed from the coastal system, that system being defined within each sediment cell.

discordant coastline

a coast where bands of different rock type run at right angles to the coast. The differing resistance to erosion leads to the formation of headlands and bays.

concordant coastline

A coast where layers of differing rock types run parallel to the coast. The outer hard rock provides a protective barrier to erosion of the softer rocks further inland. Coves may form if erosion occurs.

Morphology

is the shape of the landscape features and is determined by geology (rock type) and lithology.

Strata

layers of rock

Bedding planes

horizontal, natural breaks in strata, caused by haps in time during periods of rock formation.

Joints

vertical fractures caused either by contraction as sediments dry out, or by earth movements during uplift.

Folds

formed by pressure during tectonic activity, which makes rocks buckle and crumple

faults

formed when the stress or pressure to which a rock is subjected, exceeds its internal strength (causing it to fracture). The faults then slip or move along fault planes.

Dip

refers to the angle at which rock strata lie (horizontally, vertically, dipping towards the sea or dipping inland)

differential erosion

It is the different rates of erosion that occur along a coastline due to geological factors such as the resistance of the rock and structural weaknesses (faults, joints, bedding planes)

Swash aligned

beaches produced where waves break in line (parallel) with the coast. They make smoothly curved, concave beaches, beach face is orientated parallel to the fronts of dominant waves

Drift aligned

beaches produced where waves break at an angle to the coast, so swash is at an angle and backwash is perpendicular to the beach so material is transported along the beach via longshore drift

Spit

a long, narrow beach of sand or shingle with one end attached to the shore and the other extending into the sea or estuary.

distal point

the furthest point of the spit that extends from the headland

Proximal point

where the spit joins to the mainland

Compound spit

A spit that shows evidence of a series of sequential growth and recurvature is known as a compound spit.

bar

form when a spit grows across a bay and connects with another headland.

tombolo

Where a spit forms on a coastline where there is a small offshore island and the ridge of beach sediment is deposited towards and joins the small island

barrier islands

A long thin sandy stretch of land oriented parallel to the mainland coast that protects the coast from full force of powerful storm waves. between barrier islands and mainland is a calm protected water body eg bay or lagoon. may have formed when low lying areas of spit were breached by sea.

sand dunes

Depositional landforms. Accumulations of sand shaped

into mounds by the wind. They are dynamic ecosystems

called psammoseres.

Climatic climax community

achieved when a stable situation is reached

salt marshes

Halosere environments (tolerant of salty conditions) Tidal landform consisting of silt and mud. Coastal ecosystem in the upper coastal intertidal zone between land and open salt water

Eustatic change

a global change in sea level resulting from an actual fall or rise in the level of the sea itself

Isostatic change

local changes in sea level resulting from the land rising or falling relative to the sea.

Emergent Coastline

A coastline exhibiting features associated with falling sea levels e.g. raised beaches and relict cliffs

Relict cliffs

Where land has risen from the sea in the past as a result of isostatic processes (when land subsides, rises or tilts), degraded cliffs can often be seen that are no longer reached by the sea.

Submergent Coastline

A coastline exhibiting features associated with rising sea levels e.g. Rias and Fjords.

rias

This is a drowned river valley. As sea levels rise they flood the river valleys, leaving only the highland visible.

Fjords

This is a drowned glacial valley. As sea levels rise, U-shaped valleys left by glaciers are submerged.

Dalmatian coasts

form in areas of the world where valleys (especially glacial valleys) lie parallel to each other.mWhen 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.

Hard engineering

involves the building of entirely ARTIFICIAL structures using various materials such as rock, concrete and steel to reduce or stop the impact of coastal processes.

Soft Engineering

involves a 'softer', more environmentally friendly, approach. It often uses natural materials, and tries to work with natural processes.

Holistic

meaning an interconnected approach.

Hold the line

maintaining the current position of the coastline (often using hard-engineering methods)

Advance the line

extending the coastline out to sea (by encouraging the build-up of a wider beach, using beach-nourishment methods and groyne construction.

Managed retreat/strategic realignment

allowing the coastline to retreat in a managed way (e.g. creating salt-marsh environments by deliberately breaching flood banks that protect low-quality farmland.

Do nothing/no active intervention

letting nature takes its course and allowing the sea to erode cliffs and flood low-lying land and allowing existing defenses to collapse.

physical weathering

the break up of rocks without any chemical changes taking place

chemical weathering

involves a chemical reaction where salts may be dissolved or a clay-like deposit may result which is then easily eroded

biological weathering

breakdown of rocks by organic activity

wetting and drying

(physical) rock  alternates between being wet and dry. Some rocks such as shale expand when they are wet and contract when they are dry causing cracks to form in the rocks.

exfoliation

(physical) rock may expand as it is heated by the sun and contracts when it cools. This can cause cracks to form in the rock.

crystallisation

(physical) the high salt content of sea water can lead to the growth of salt crystals within the rock that exert pressure on joints and lead to fracturing.

freeze-thaw

(physical) water that fills cracks in the rock freezes when temperatures drop. The ice expands and exerts pressure within the rock, enlarging cracks.

carbonation

(chemical) coastlines composed of chalk or limestone are dissolved by acidic rain and seawater.

oxidation

(chemical)  rocks containing iron compounds experience oxidation (rusting) when exposed to oxygen and water from the air and the sea. This causes disintegration.

examples of biological weathering

• The roots of plants on cliff tops can create and expand tiny fissures. Sub surface seaweed can also attach to rocks and weaken them during movement.

• Surface animals such as puffins may excavate nesting burrows in cliffs. Sub surface creatures such as limpets may also remove rock when they attach to it.

erosion

 is the breakdown and subsequent removal and transportation of material. It is usually caused by the direct action of the sea on the shore.

weathering

is the disintegration of rock in situ. There are three main types of weathering

hydraulic action

When a wave advances air can be trapped and compressed  in joints in the rock or between the breaking wave and the cliff. When it retreats the compressed air expands, the continuous process can weaken joints/cracks in the cliff causing pieces to break off

cavitation

Bubbles formed in the water may implode under high pressure generating tiny jets of water which will erode the rock over time.

abrasion

involves a sandpapering effect as sediment is dragged up/down/across the shoreline eroding and smoothing rocky surfaces. important in the formation of a wave-cut platform

quarrying

the action of waves breaking against unconsolidated material eg sands/gravels. waves scoop out the loose material in a similar way to a digger in a quarry.

solution

Weak acids can dissolve alkaline rock e.g. chalk/limestone or the alkaline sediment that bonds rock particles together.

attrition

the gradual wearing down of rock particles by impact and abrasion as the pieces of rocks are moved by waves,tides,currents. this process gradually makes stones rounder and smoother.

mass movement

is the movement of consolidated material (solid rock) and unconsolidated material (clay and soil) due to gravity.

rockfall

sudden collapse of individual rock fragments at a cliff faces often steep/vertical resistant rock. Rocks fall to form scree or tallus at cliff foot. triggered by mechanical weathering/earthquakes.

landslides

a block of rock moving rapidly downhill, mobing material remains largely intact. triggered by earthquakes/heavy rainfall when slip surface is lubricated and friction is reduced.

runoff

when overland flow occurs down a slope/cliff small particles are moved to enter the littoral zone forming input into sediment cell - can be considered a flow that transfers water and sediment from rock face to beach/sea. toxic chemicals can contaminate water and threaten coastal ecosystems (link between water cycle + coastal system)

mudflows

involves earth and mud flowing downhill usually over unconsilidated or weak bedrock eg clay after heavy rainfall. water gets trapped in rock increasing pore water pressure forcing rock particles apart leading to slope failure. pore water pressure is a form of energy within the slope system and is extremely important factor in determing slope instability

slumping

when the slide surface is curved rather than flat. occur in weak and unconsilidated clays and sands when permeable rock overlies impermeable rock which causes a build-up of pore water pressure. characterised by a sharp break of slope and the formation of a scar, multiple landslips can result in a terraced appearance on the cliff face.

soil creep

slow movement of individual soil particles downhill. Involves particles rising towards the ground surface due to wetting or freezing and then returning vertically to the surface in response to gravity as the soil dries out or thaws (zigzag movement similar to that of longshore drift)  It can't be seen operation but its action can be implied by the formation of shallow terracets, the build-up of soil on the upslope side of walls and the bending of tree trunks.

traction

the rolling of coarse sediment along the sea bed that is too heavy to be picked up and carried by the sea

saltation

sediment bounces along the seabed, light enough to be picked up or dislodged but too heavy to remain within the flow of water

suspension

smaller lighter sediment picked up and carried within the flow of water

solution

chemicals dissolved in the water, transported and precipitated elsewhere. Plays an important role in the carbon cycle, transferring and redepositing carbon in the oceans.

deposition

once the energy flow that is moving material declines, then deposition is likely to occur. this may be on the seabed, as extensions to exisiting coastal features, on the shore or along estuaries.