Coastal Geomorphology:Coastal Geomorphology:The Oceans, Coastal The Oceans, Coastal

Processes, and LandformsProcesses, and Landforms

Chapter 12Chapter 12

Currents: SurfaceCurrents: SurfaceDriven by temperature differences, wind, coriolis Driven by temperature differences, wind, coriolis forceforce

TidesTides

•A “bulge” in the A “bulge” in the world’s oceans, world’s oceans, caused by the caused by the gravitational pull of gravitational pull of the moon and sunthe moon and sun

FFgg = = G mG m11 m m22

dd22

TidesTides• Tidal range—the difference Tidal range—the difference

between high and low tidebetween high and low tide• Affected by the shape of the Affected by the shape of the

coastline and seafloorcoastline and seafloor• Spring tides—highest tides, Spring tides—highest tides,

strong and quickstrong and quick– Occur when sun, moon, and Occur when sun, moon, and

Earth line up (the sea “springs” Earth line up (the sea “springs” up and back)up and back)

• Neap tides—lowest tidesNeap tides—lowest tides– Sun and moon at right angles Sun and moon at right angles

with respect to Earthwith respect to Earth– Neap = A low incline of bend Neap = A low incline of bend

(when graphed)(when graphed)

Monthly Tidal CycleMonthly Tidal Cycle

Extreme High TidesExtreme High Tides

• The Bay of Fundy

• A 50’ (15m) tidal fluctuation is common (x2)

•A tidal bore (several in. to several ft. high) rushes miles up the Petitcodiac River in New Bruswick

Landforms shaped by extreme Landforms shaped by extreme tidestides

88

Extreme tides: Mont Saint Michel, Extreme tides: Mont Saint Michel, FranceFrance

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Low tide High tide

Waves and Wave DynamicsWaves and Wave Dynamics

Waves and Wave DynamicsWaves and Wave Dynamics

•Period—The time it takes two Period—The time it takes two successive waves (from crest to crest, successive waves (from crest to crest, or from trough to trough) to pass a or from trough to trough) to pass a given pointgiven point

•Fetch—The distance over which the Fetch—The distance over which the wind blows, creating waveswind blows, creating waves

Waves and Wave DynamicsWaves and Wave Dynamics

•Factors affecting open ocean waves:Factors affecting open ocean waves:–FetchFetch

•The greater the distance over which the wind The greater the distance over which the wind blows, the larger the wavesblows, the larger the waves

–Wind strengthWind strength•The stronger the wind, the larger the wavesThe stronger the wind, the larger the waves

–Wind durationWind duration•The longer the wind blows, the more waves The longer the wind blows, the more waves will be createdwill be created

Wave Base = Wave Base = 11//22 wave length wave length

Wave base

Waves of Oscillation vs. Waves of Oscillation vs. TranslationTranslation

Waves of oscillation

Waves of translation

Waves of Oscillation (Transition) Waves of Oscillation (Transition) andandWaves of TranslationWaves of Translation•Water molecules on the open ocean move in Water molecules on the open ocean move in

a circular motiona circular motion– The motion passes through the water, but the The motion passes through the water, but the

water doesn’t move forward (to oscillate is to water doesn’t move forward (to oscillate is to move up and down)move up and down)

– What moves the water forward is wind blowing What moves the water forward is wind blowing over the surface and the movement of currentsover the surface and the movement of currents

•Water molecules that reach the shore have Water molecules that reach the shore have their circular motion interruptedtheir circular motion interrupted– Their energy is translated into the shore face (it Their energy is translated into the shore face (it

passes from the water to the land, where it does passes from the water to the land, where it does work to move material—like sand—around)work to move material—like sand—around)

Wave BreakWave Break

Wave Refraction,Wave Refraction,Longshore Current and Beach Longshore Current and Beach DriftDrift

Wave Refraction andWave Refraction andLongshore CurrentLongshore Current

•As waves reach the shore and “feel” the As waves reach the shore and “feel” the bottom, they slow and breakbottom, they slow and break

•The direction of wave break follows the The direction of wave break follows the underwater topographyunderwater topography

•This causes the wave to “bend” and become This causes the wave to “bend” and become more parallel to the shorelinemore parallel to the shoreline– This bending is called This bending is called wave refractionwave refraction

•As it breaks from one side to the other, it As it breaks from one side to the other, it creates a currentcreates a current– This current, called the This current, called the longshore currentlongshore current picks picks

up and moves sediment (sand) down the shoreup and moves sediment (sand) down the shore

Erosional EnvironmentsErosional Environments

•If there is not enough sediment replacing If there is not enough sediment replacing what’s being lost through wave what’s being lost through wave erosion/longshore current, erosion will occur, erosion/longshore current, erosion will occur, creating a rocky coastlinecreating a rocky coastline– Dam or channelized streams and sediment can’t Dam or channelized streams and sediment can’t

get to the beachget to the beach

•Erosive environments create distinctive Erosive environments create distinctive landformslandforms– rocky headlands and pocket beaches, sea arches rocky headlands and pocket beaches, sea arches

and sea stacks, wave-cut cliffs, wave-cut and sea stacks, wave-cut cliffs, wave-cut platforms, wave-built terraces, etc.platforms, wave-built terraces, etc.

Wave Energy is Concentrated at Wave Energy is Concentrated at Headlands and Dissipated in Headlands and Dissipated in BaysBays

Wave Motion and Wave Wave Motion and Wave RefractionRefraction

Laguna Beach, CALaguna Beach, CAHeadlandsHeadlands

Headland ErosionHeadland Erosionand the Formation of Sea and the Formation of Sea ArchesArches

Stacks and CliffsStacks and CliffsVictoria, AustraliaVictoria, Australia

Depositional Environments:Depositional Environments:The Structure of a BeachThe Structure of a Beach