Chapter 20 Coastal Processes and Terrain. Coastal Processes –Forces That Shape Coastlines...
-
Upload
andrea-wilcox -
Category
Documents
-
view
229 -
download
5
Transcript of Chapter 20 Coastal Processes and Terrain. Coastal Processes –Forces That Shape Coastlines...
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