Coastal systems and Landscapes

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sediment cell

Sections of the coast bordered by prominent headlands. Within these sections, the movement of sediment is almost contained and the flows of sediment should act in dynamic equilibrium.

dynamic equilibrium

Where a natural system tries to achieve a balance by making constant changes in response to a constantly changing system.

coastal inputs - 3 main areas (material or energy)

• marine - waves, tides, salt spray

• atmosphere - sun, air press, wind speed, direction

• humans - pollution, recreation, settlement, defences

coastal outputs - (material or energy)

• ocean currents

• rip tides

• sediment transfer

• evaporation

coastal stores/sinks - (sediment and material)

• Beaches

• Sand Dunes

• Spits

• Bars and Tombolos

• Headlands and Bays

• Nearshore Sediment

• Cliffs

• Wave-cut Notches

• Wave-cut Platforms

• Caves

• Arches

• Stacks

• Stumps

• Salt Marshes

• Tidal Flats

• Offshore Bands and Bars

coastal transfers/flows - process that link inputs, outputs & stores

• 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

coastal energy - (power behind transfers and flows)

• wind

• gravitational

• flowing water

negative feedback loop

lessens change that has occurred within a system

negative feedback loop - example

1. storm erodes large amount of sand from a beach, taking it out of dynamic equilibrium

2. when destructive waves lose their energy excess sediment is deposited as an offshore bar

3. bar dissipates wave energy, protecting beach from erosion

4. bar gets eroded instead of beach

5. once bar has gone, normal conditions occur and goes back to dynamic equilibrium

positive feedback loop

this exaggerates the change, making the system more unstable

positive feedback loop - example

1. people walking on dunes destroys vegetation growth and causes erosion

2. destroying vegetation, increased erosion as roots holding sand together

3. increases rate of erosion

4. sand dunes eventually become completely eroded, destruction of beach

state the 6 sediment sources

1. rivers

2. cliff erosion

3. wind

4. glaciers

5. offshore

6. longshore drift

rivers - sediment source

most sediment in coastal zone is a result of an input from rivers especially in high-rainfall environments

sediment may be deposited in estuaries, important for animal habitats

then transported throughout coastal system by waves

cliff erosion - sediment source

most erosion occurs during winter months due to more frequent storms. coastlines can retreat up to 10m per year

wind - sediment source

can cause sand to be blown along or up a beach

occur where sand dunes are

offshore - sediment source

waves, tides and currents erode offshore sediment sinks such as offshore bars

transported onto beach, help to build it up

storm surges/tsunami waves may transfer sediment into coastal zone

longshore drift - sediment source

moved along beach by prevailing winds which alter direction of the waves

swash approaches coast

backwash pulls sediment back down the beach

what is it called when the waves move up the beach

swash

what is it called when the waves move down the beach

backwash

what wave type is more frequent during the summer months

constructive

what wave type is more frequent during the winter months

destructive

wavelength of constructive waves

long wavelength

formation of constructive waves

by weather systems in open ocean

formation of destructive waves

localised storm events with strong winds close to the coast

wavelength of destructive wave

short wavelength

frequency of constructive waves

6-9 per minute

frequency of destructive waves

11-16 per minute

wave characteristics - constructive

• low waves surge up the beach

• strong swash

• weak backwash

wave characteristics - destructive

• high waves plunge onto beach

• weak swash

• strong backwash

occurrence on beach type - constructive

gently sloped beaches

occurrence on beach type - destructive

steeply sloped beaches

difference in heigh between tides

tidal range

what is responsible for tides

gravity the pull of the sun or moon

what creates the largest possible tidal range

spring tide

explain spring tide

highest high tide and lowest low tide occur when sun and moon are in alignment. gravitational forces combine to pull oceans towards them - creates largest possible tidal range

what creates the smallest possible tide range

neap tide

explain neap tide

lowest high tide and highest low tide occur when sun and moon are perpendicular to each other. gravitational forces act against each other, so pull is minimised at high tide

what is a rip current

powerful underwater currents occurring close to the shoreline

explain rip currents

1. plunging waves cause buildup of water at top of beach

2. backwash forced under surface due to resistance from breaking waves - forms underwater current

3. flows away from shore quickly e.g. due to gap in sandbar

4. results in rip current

when do riptides occur

ocean tide pulls water through small area, e.g. bay/lagoon

characteristics of high-energy coastline

• powerful waves

• large fetch

• rocky headlands & landforms

• destructive waves (mainly)

• rate of erosion exceeds rate of deposition

characteristics of low-energy coastline

• less powerful waves

• sheltered areas

• constructive waves (mainly)

• landforms of deposition

• rate of deposition exceeds rate of erosion

what is wave refraction

process by which waves turn and lose energy around a headland on uneven coastline. slow down in shallow water near headland

erosion - in relation to coasts

the removal of sediment from a coastline

corrasion

breaking waves fling material e.g. rocks, sediment or shells at a cliff face, knocking off material

corrosion

acid in seawater causes erosion and weakening of rock

abrasion

sediment moved along the shoreline causing it to be worn down over time

attrition

rocks and pebbles hit against each other causing erosion and rounding

hydraulic action

pressure of compressed air forced into cracks in a rock face will cause rock to weaken and break apart

wave quarrying

when air is trapped and compressed against a cliff which causes rock fragments to break off the cliff over time

factors effecting erosion

1. waves

2. beaches

3. subaerial processes

4. rock type

5. rock faults

6. rock lithology

waves - factors effecting erosion

main factor affecting rate and type of erosion. most erosion caused in winter months, more destructive

beaches - factors effecting erosion

beach will absorb wave energy reducing affect of erosion. if coastal management to trap sediment, beaches may not build up in other areas, increasing erosion there

subaerial processes - factors effecting erosion

weathering and mass movement weaken cliffs, increased corrasion and abrasion

rock type - factors effecting erosion

sedimentary rock e.g. sandstone more vulnerable to erosion

rock faults - factors effecting erosion

fissures, cracks and joints act as weaknesses within rock, increased surface area, increased erosion. formation of headlands and bays

rock lithology - factors effecting erosion

• granite & basalt - very slow erosion <0.1cm per year

• slate & marble - slow erosion 0.1-0.3 cm per year

  • limestone - very fast erosion 0.5-10 cm per year

name the 4 processes of transportation

• traction

• saltation

• suspension

• solution

traction - method of transportation

large, heavy sediment rolls along sea bed pushed by currents

saltation - method of transportation

smaller sediment pushed by currents along sea bed. the sediment too heavy to be picked up

suspension - method of transportation

small sediment carried within flow of water. greater velocities able to suspend larger pieces of sediment

solution - method of transportation

dissolved material carried within water

longshore (littoral) drift (LSD)

• waves hit beach at angle, direction of prevailing wind

• push sediment in same direction up beach in swash

• wave carries sediment back down in backwash, 90C angle

• moves sediment along beach

deposition

occurs when sediment becomes too heavy or if wave loses its energy

name the 2 types of deposition

• gravity settling

• flocculation

gravity settling

waters velocity decreases so sediment gets deposited

flocculation

clay particles clump together due to chemical attraction and sink due to high density

Mechanical (physical) weathering

the breakdown of rocks due to exertion of physical forces

freeze-thaw - mechanical

water enters the cracks in rocks and freezes overnight during the winter. This water expands increasing the pressure on the rock causing cracks to develop. These cracks grow, making the cliff more vulnerable

wetting and drying - mechanical

clay expands when wet and will contract when drying. these cycles can cause the rock to fracture and break up

chemical weathering

the breakdown of rocks through chemical reactions

carbonation - chemical

rainwater absorbs CO2 = carbonic acid. acid rain reacts with limestone to form calcium bicarbonate, easily dissolved allowing erosion

oxidation - chemical

minerals become exposed to the air due to cracks and fissure, mineral is then oxidised, causing rock to crumble

solution - chemical

when rock minerals e.g. rock salt, are dissolved

bioogical weathering

the breakdown of rocks by organic activity

plant roots - biological

roots grow into cracks, which exerts pressure causing the rock to split

mass movement

movement of material down a slope under the influence of gravity

name the 7 types of mass movement

• soil creep

• solifluction

• mudflows

• rockfall

• landslide

• slump

• runoff

soil creep

particles of soil rise and fall due to wetting and freezing, causing soil to move down the slope, leads to formation of shallow terracettes

mudflows

increase of water in the soil reduces friction of the soil on rock allowing it to flow over underlying bedrock. very fast flowing danger to life

rockfall

occurs on sloped cliffs over 40 degrees when exposed to mechanical weathering - leads to scree (rock fragments)

slump

build up of water pressure leads to the land collapsing under its own weight - terraced appearance

formation of a cave

• faults in headland eroded by hydraulic action and abrasion to create small fissures

• overlying rock of cave may collapse due to repeated erosion, forming a blowhole

• hydraulic action widens the cave

formation of arches

• faults in headland eroded by hydraulic action and abrasion to create small fissures

• overlying rock of cave may collapse due to repeated erosion, forming a blowhole

• hydraulic action widens the cave

• sub-aerial and marine erosion occurs, eroding the other side of the headland creating an arch

formation of a stack

• faults in headland eroded by hydraulic action and abrasion to create small fissures

• overlying rock of cave may collapse due to repeated erosion, forming a blowhole

• hydraulic action widens the cave

• sub-aerial and marine erosion occurs, eroding the other side of the headland creating an arch

• arch continues to widen until it cannot support itself, falling under the weight leaving a stack

formation of a stump

• faults in headland eroded by hydraulic action and abrasion to create small fissures

• overlying rock of cave may collapse due to repeated erosion, forming a blowhole

• hydraulic action widens the cave

• sub-aerial and marine erosion occurs, eroding the other side of the headland creating an arch

• arch continues to widen until it cannot support itself, falling under the weight leaving a stack

• continued erosion will lead to the depletion of rock resulting in a stump. wave cut platform left afterwards

spits

long narrow strip of land formed when longshore drift causes the beach to extend out to sea. allows for the creation of salt marsh due to sheltered environment

ria

narrowing inlet which is formed when sea levels rise causing coastal valleys to flood

isostatic

a change in local coastline or land height relative to sea level

barrier beaches

beach or spit extends across a bay to join together two headlands. traps water behind it leading to a lagoon. low tidal ranges

tombolo

bar or beach connecting mainland to an offshore island - may only be accessible at low tide

offshore bar

offshore region where sand is deposited - may be caused when backwash from destructive waves removes sediment from a beach

state the dune types in order

• embryo dunes

• fore dune

• yellow dunes

• grey dunes

• mature dunes

embryo dunes

sand begins to accumulate around a small obstacle. only a few metres tall

fore dune

flora begins to colonise e.g. Marram grass, Lyme grass and Sea couch grass. This makes the dune more stable and can withstand storms. Composed of white/yellow sand.

yellow dune

Semi-fixed dunes are stable due to the roots of vegetation and can reach heights of up to 20 metres helping to protect the dunes behind them. Composed of yellow sand.

grey dune

usually the largest within the sand dune system and can reach up to 20 metres, they are a thriving habitat of flora and are very stable with less mobile sand. They are found between 50-100m from the backshore

blowouts

caused by wind erosion forming a bowl shape between dunes

dune slacks

occur between dunes low lying hollows created when there is a ridge

mature dunes

large amounts of organic matter which affect the soil type and colouration