Chapter 20 Chapter 20

Coastal Processes and Coastal Processes and TerrainTerrain

Coastal Processes and TerrainCoastal Processes and Terrain

Coastal ProcessesCoastal Processes– Forces That Shape CoastlinesForces That Shape Coastlines– Coastal Sediment TransportCoastal Sediment Transport– Coastal DepositionCoastal Deposition

Coastal LandformsCoastal Landforms– Depositional LandformsDepositional Landforms– Shorelines of SubmergenceShorelines of Submergence– Coral CoastsCoral Coasts

What are coastlines?What are coastlines?

Coastlines are the transition from land Coastlines are the transition from land to waterto water

Not permanent featuresNot permanent features Always subject to erosion & depositionAlways subject to erosion & deposition They are at the interface of the 3 major They are at the interface of the 3 major

components of Earth’s environment:components of Earth’s environment:– HydrosphereHydrosphere– LithosphereLithosphere– AtmosphereAtmosphere

Coastal ProcessesCoastal Processes

WindWind is a major force – it moves the is a major force – it moves the water, creating waves and currentswater, creating waves and currents

Waves & currents shape coastlines Waves & currents shape coastlines and create topographic featuresand create topographic features

Waves = erosion = headlandsWaves = erosion = headlands Currents = deposition = beaches & Currents = deposition = beaches &

sandbarssandbars

Coastal ProcessesCoastal Processes

TidesTides Diastrophic EventsDiastrophic Events

– EarthquakesEarthquakes– VolcanoesVolcanoes

Sea or lake level changeSea or lake level change– Tectonic forcesTectonic forces– Eustatic changeEustatic change

Exceptions to Lakeshore ChangeExceptions to Lakeshore Change

Tidal range is insignificantTidal range is insignificant Water level rise/fall different processWater level rise/fall different process Coral reefs occur only in tropical or Coral reefs occur only in tropical or

sub-tropical sub-tropical oceansoceans.. Force of ocean water creates more Force of ocean water creates more

dramatic topographic featuresdramatic topographic features

WavesWaves

Waves are agents of erosion

Headlands are promontories of sloping land projected into the sea

WavesWaves

Appear to move but don’t, except Appear to move but don’t, except when they breakwhen they break

Energy passes through the water, Energy passes through the water, causing the water to undulatecausing the water to undulate

Most are wind generated – action of Most are wind generated – action of friction of wind moving across waterfriction of wind moving across water

Transfer of energy from wind to Transfer of energy from wind to water initiates wave actionwater initiates wave action

Small number of waves from volcanic Small number of waves from volcanic or diastrophic activityor diastrophic activity

Development of WavesDevelopment of Waves

Wave RefractionWave Refraction

Eustatic Sea Level ChangeEustatic Sea Level Change

Sea level change due to amount of Sea level change due to amount of water in sea/oceanwater in sea/ocean

Related to action Related to action of continental ice of continental ice sheetssheets

Ellesmere Island, Canada

TidesTidesCavendish Beach, PEI

Bay of Fundy, NS

Tidal CharacteristicsTidal Characteristics

Not significant agents of erosionNot significant agents of erosion Significant erosion only in narrow Significant erosion only in narrow

bays, margins of shallow seas, and bays, margins of shallow seas, and passages between islandspassages between islands

Normal High TidesNormal High Tides

What you should know about tides:

The Moon pulls at Earth – the Sun pulls at Earth and this is what causes tides

Position of Sun, Moon & Earth cause variation in tides

Highest Tidal RangesHighest Tidal Ranges

Stream OutflowStream Outflow

Madagascar

Stream outflow is a major contributor of sediment to oceans

This sediment is then transported by coastal waters

Erosion – Rocky CoastlineErosion – Rocky Coastline

Port Campbell, Australia

Most erosion along the coast is due to wave action

Air is forced into cracks in the rocks as the wave hits the shore

When the wave recedes, the air expands loosening the sections of rock

This is a major process of erosion

Erosion – Cliff CoastlineErosion – Cliff CoastlineWave Cut Notch

b) Erosion at sea level or just above

c) As notch is cut, cliff is undercut and falls away

d) The cliff face retreats, until it reaches bedrock - then you have a headland

Formation of ArchesFormation of Arches

Victoria, Australia

1985

1992

Continuous pounding wave action

Erosion - SandErosion - Sand

Currents and tides cause erosionCurrents and tides cause erosion Storms accelerate erosionStorms accelerate erosion A major storm can remove an entire A major storm can remove an entire

beach in a few hours – eroding down beach in a few hours – eroding down to the bedrockto the bedrock

Sediment TransportSediment Transport Nearly all sediment transport on Nearly all sediment transport on

coastlines is accomplished by wave coastlines is accomplished by wave action and action and locallocal currents currents

Mechanisms:Mechanisms: Longshore CurrentsLongshore Currents strike at an strike at an

angle almost parallel to the shore - angle almost parallel to the shore - “along the shore”“along the shore”

Beach DriftingBeach Drifting is downwind is downwind displacement of particles along coastdisplacement of particles along coast

Movement with ebb and surge of tide Movement with ebb and surge of tide tumbles particles and reduces sizetumbles particles and reduces size

Coastal Coastal Sediment Sediment TransportTransport

Longshore Current

DepositionDeposition

Most coastal deposition is of fine Most coastal deposition is of fine sand particlessand particles

During storms larger particles/pieces During storms larger particles/pieces can be moved and depositedcan be moved and deposited

Sediment BudgetSediment Budget is the balance of is the balance of eroded and deposited materialeroded and deposited material

Coastal LandformsCoastal Landforms

Depositional LandformsDepositional Landforms– BeachesBeaches– Barrier Islands/LagoonsBarrier Islands/Lagoons– SpitsSpits

Shorelines of SubmergenceShorelines of Submergence– Fjorded CoastsFjorded Coasts– Wave-Cut Cliffs and PlatformsWave-Cut Cliffs and Platforms– Marine TerracesMarine Terraces

Coral CoastsCoral Coasts

BeachesBeachesAn exposed deposit of loose sediment adjacent to a body of water

Backshore: landward of HWL

Foreshore: zone of tidal rise & fall

Offshore: zone always underwater

Barrier Barrier IslandsIslands

Long narrow sandbars built up in shallow offshore water

Usually parallel to shore

Barrier Islands Barrier Islands and Lagoonsand Lagoons

Water is isolated between barrier islands and main land

Eventually merge with barrier and mainland if sediment deposit not interrupted

SpitsSpitsLinear deposit attached to land at one end and extending into open water in down current direction

Coral CoastsCoral Coasts

Great Barrier Reef, Australia

In tropical oceans, most continents and islands are fringed with coral reefs

The coral is composed of polyps – tiny marine animals

They secrete external skeletons of calcium carbonate

Fringing Fringing ReefsReefs

Attached to the coast of volcano

Barrier Reefs and AtollsBarrier Reefs and Atolls

Atoll is a ring shaped coral structure surroundig a landless lagoon

Usually just at sea level

Barrier reef is aging fringe reef

Volcano is sinking and lagoon forms between reef and volcano

Coral Reefs of the WorldCoral Reefs of the World