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    Ch20 Ch20 Presentation Transcript

    • Chapter 20: CoastalProcesses and TerrainMcKnight’s Physical Geography:A Landscape Appreciation,Tenth Edition, Hess
    • Coastal Processes and Terrain• The Impact of Waves and Currents on theLandscape• Coastal Processes• Coastal Landforms2© 2011 Pearson Education, Inc.
    • The Impact of Waves andCurrents on the Landscape• Coastal processes affecta tiny portion of Earth’slandscape• Waves agents of erosion• Currents agents oftransportation anddeposition• Beaches mark transitionbetween land and waterand are highly variable3© 2011 Pearson Education, Inc.Figure 20-4
    • Coastal Processes• Interface of three majorcomponents of Earth’senvironment• Highly energetic due toconstant motion of waters• Importance of wind• Ocean and lake formationssimilar except for:– Tidal range smaller for lakes– Water level change differences– Reefs only in oceanic water4© 2011 Pearson Education, Inc.Figure 20-1
    • Coastal Processes• Waves—transfer of energy through cyclical rising andfalling of a substance• Most are wind generated over oceans• Wind stress generated waves, forced waves• Swells5© 2011 Pearson Education, Inc.
    • Coastal Processes• Waves of oscillation andtranslation– Waves that move in a circularor oscillatory fashion with littleforward movement, waves ofoscillation– Wave crests and troughs– Wavelengths and wave heights– Wave amplitudes– Shallow water waves influencedby ocean floor, gain forwardprogress, called waves oftranslation; wave breaks6© 2011 Pearson Education, Inc.Figure 20-2
    • Coastal Processes• Wave refraction– Change in wave direction asthey approach shore– Uneven coastline and irregularwater depth– Waves bent due to unevenslowing of waves from irregularwater depth– Wave action focused onheadlands, much gentler inadjacent bay areas7© 2011 Pearson Education, Inc.Figure 20-5
    • Coastal Processes• Wave erosion– Consistent pounding of smallwaves results in erosion– Large storms significantlyenhance coastal erosion– Air forced into cracks incoastal rocks when watermoves inland; air released aswater recedes and enhanceserosion– Chemical action of seawater– Notches cut in the bases ofcliffs8© 2011 Pearson Education, Inc.Figure 20-6
    • Coastal Processes• Tsunamis– Waves triggered by disruptionsin ocean floor– When fault rupture on oceanfloor generates tsunami, entiredepth of ocean above ruptureis displaced– Inconspicuous in open oceanwith long wavelengths and lowheights– Can travel over 400 mph– Significant withdrawal of up to 40meters before a significant surgeof water 9© 2011 Pearson Education, Inc.Figure 20-8
    • Coastal Processes• Tides– Alterations of ocean levelfrom gravitational pull of Sunand Moon– Two high tides and two lowtides per day– Topographic effectsgenerally small– Significant agents of erosiononly in narrow bays, aroundshallow seas, and inpassages between islands10© 2011 Pearson Education, Inc.Figure 20-9
    • Coastal Processes• Changes in sea level and lake level• Two primary causes of sea level changes– Rising or sinking of landmass (tectonic change)– Increase or decrease in amount of ocean water (eustaticsea-level change)– Emergent versus submergence land characteristics• Global warming and sea-level change– Thermal expansion of water and melting of ice caps increasingwater volume (eustatic)– Sea level rise of up to 0.5 m by the end of the century11© 2011 Pearson Education, Inc.
    • Coastal Processes• Ice push– Bodies of water that freeze in winter, resulting in expansionand subsequent contraction– Ice pushes onto land, significantly modifying land surface,similar to small glacial advance– Most common in Arctic and Antarctic regions12© 2011 Pearson Education, Inc.
    • Coastal Processes• Organic secretions– Many aquatic animals formcalcium carbonate shells– Animals cluster together andform enormous masses ofreefs, platforms, and atolls• Stream outflow– Streams important sourcesof sediment to oceans andlakes13© 2011 Pearson Education, Inc.Figure 20-11
    • Coastal Processes• Currents and coastalsediment transport• Longshore currents– Water moves parallel toshoreline (“along” shore)– Develop just offshore andset up by waves strikingcoast at an angle– Wind direction reflected inlongshore currents14© 2011 Pearson Education, Inc.Figure 20-12
    • Coastal Processes• Currents and coastalsediment transport (cont.)• Beach drifting– Short distance shifting ofsand by breaking waves andretreating water– Zigzag pattern of particlemovement downwind andparallel to coast– Affects of tides on debrismovement– Dune formation on coasts15© 2011 Pearson Education, Inc.Figure 20-13
    • Coastal Processes• Coastal deposition– Results when energy ofmoving water is diminished– Maritime deposits moreephemeral than noncoastaldeposits due to compositionand lack of vegetative cover– Sediment budget must be inbalance to allow for depositto persist16© 2011 Pearson Education, Inc.Figure 20-14
    • Coastal Landforms• Depositional landforms• Beaches– Beaches relativelyhomogeneous– Mark transition betweenland and ocean– Backshore contains berms;foreshore regularly coveredand uncovered by tides– Offshore is zone that ispermanently submerged17© 2011 Pearson Education, Inc.Figure 20-15
    • Coastal Landforms• Spits– At mouth of a bay, sedimentmoved into deeper water– Deposit attached to land atone end and extends toopen ocean in downcurrentdirection is a spit– Spits that extend across abay, bay barriers orbaymouth bars– Tombolos: waves convergeon each side and depositsand so the bar connectsto land 18© 2011 Pearson Education, Inc.Figure 20-16
    • Coastal Landforms• Barrier islands– Long, narrow sand bar built upin shallow offshore waters– Oriented approximately parallelto shore– Only rise a few meters abovesea level, but some extend togreat lengths– Lagoon formation; mudflats– Life cycle of a lagoon19© 2011 Pearson Education, Inc.Figure 20-20
    • Coastal Landforms• Human modification ofcoastal sediment budgets– Dams act as sediment traps,allowing less sediment toreach oceans and resultingin shrinking beaches– Use of groins to help impedethe downcurrent flow ofsediment– Jetties used to keep watermoving and reducesediment deposits innavigation channels20© 2011 Pearson Education, Inc.Figure 20-23
    • Coastal Landforms• Shorelines of submergence– Most oceanic coastline showsevidence of submergence atsome time within last 15,000years– Ria shorelines• Submergence results indrowning of previous rivervalleys, producing estuaries• Coast with numerous estuariesis called a ria shoreline21© 2011 Pearson Education, Inc.Figure 20-25
    • Coastal Landforms• Shorelines ofsubmergence (cont.)– Fjorded coasts• Extensive glaciation gougesout troughs by glaciers or icesheets• Troughs far below sea level,eventually fill with sea water• Deep coastal indentations arecalled fjords• Create extraordinarilyirregular coastlines22© 2011 Pearson Education, Inc.Figure 20-26
    • Coastal Landforms• Shorelines of emergence anderosion– Shoreline features raised well abovecurrent sea level• Wave-cut cliffs and platforms– Constant pounding of waves at baseof landforms cuts a notch at the highwater level– Broad erosional pattern called awave-cut bench or wave-cutplatform– Most cut debris shifted just beyondwave-cut bench to wave-built terrace23© 2011 Pearson Education, Inc.Figure 20-27
    • Coastal Landforms• Marine terraces– Wave-cut platforms upliftedalong tectonically risingcoasts– Several instances of marineterraces indicate severalepisodes of marine terraceformation– Can be used to deducehistory of the water levels ina region24© 2011 Pearson Education, Inc.Figure 20-28
    • Coastal Landforms• Coral coasts– Most continents and islands fringed with coral reefs oranother coralline structure– Critical element is a group of anthozoan animals– Calcium carbonate skeletons from coral polyps– Have a blossomlike appearance similar to plants– Have strict requirements for their survival– Fringing reefs: those built right onto a volcano– Barrier reefs: coral that appears to float around a volcano– Atolls25© 2011 Pearson Education, Inc.
    • Coastal Landforms• Distribution of coral coasts worldwide26© 2011 Pearson Education, Inc.Figure 20-29
    • Summary• Coastal regions make up a very small percentage ofthe Earth’s landscape, but have unique structure andprocesses• The coasts are the interface between three of thefour primary spheres of the Earth• The most energetic coastal processes are observedby wave motions• Tsunamis are significant dangerous waves that resultfrom underwater earthquakes, not from winds• Tides play a small role in the sculpting of landformsof coasts27© 2011 Pearson Education, Inc.
    • Summary• Numerous processes are involved that modify thelake level and sea level of bodies of water• Many other coastal processes, including ice push,organic secretions, and stream outflow, helpstructure coastal landforms• Currents are primarily responsible for the transport ofcoastal sediment• Coastal deposition takes place in areas where oceanwater moves more slowly, and is typically ephemeral• The most widespread coastal landform is called abeach28© 2011 Pearson Education, Inc.
    • Summary• Spits and barrier islands result from deposition ofsedimentary material by the longshore currents• Lagoons result when barrier islands cut off one smallregion of ocean water from the remaining ocean• Humans have modified the structure of shorelinesthrough damming and the building of groins andjetties• Shorelines can be divided into two categories,emergence or submergence• Coral coasts consist of organic material and typicallysurround volcanoes29© 2011 Pearson Education, Inc.