© 2007, John Wiley and Sons, Inc. Physical Geography by Alan Arbogast Chapter 19 Coastal Processes and Landforms Lawrence McGlinn Department of Geography State University of New York - New Paltz

© 2007, John Wiley and Sons, Inc. Coastal Processes and Landforms Oceans and Seas Nature of Coastlines: Intersection of Earth’s Spheres Coastal Landforms Human Impacts on Coastlines

© 2007, John Wiley and Sons, Inc. Oceans and Seas Oceans – largest bodies of water: Pacific, Atlantic, Indian, Southern, and Arctic Seas – next largest water bodies: Black, Mediterranean, Barents, etc. Gulf – next largest, usu. opens to larger water body: Mexico, Alaska, Guinea, etc. Bay – smaller still: Fundy, Biscay, etc.

© 2007, John Wiley and Sons, Inc. Oceans and Seas

© 2007, John Wiley and Sons, Inc. Water as Solvent Salinity – concentration of dissolved solids in seawater – global seawater salinity parts per thousand (‰) Brine – water with >35‰ salinity Brackish water - <35‰ salinity

© 2007, John Wiley and Sons, Inc. Shaping the Coastline Key to shaping coastline is movement of water Eustatic Change - changes in water level in ocean – due to tectonic uplift or hydro cycle variation Land above sea level forms river valleys that extend to sea level – when sea level rises, valley floods, as with Chesapeake Bay or Delaware Bay Ria – river valley flooded by rising sea level Fjord – glacial valley flooded by rising sea level

© 2007, John Wiley and Sons, Inc. Eustatic Sea Level Changes

© 2007, John Wiley and Sons, Inc. North American Coastline through Time Lowest sea levels occurred during glaciations when water was tied up in glaciers (130k & 19k bp) – highest sea levels in interglacial periods (120k bp) Chesapeake Bay and Delaware Bay - Rias

© 2007, John Wiley and Sons, Inc. Tides Regular, predictable oscillations of sea level – due to gravitation of moon (56%) & Sun (44%) High tide on side of Earth facing moon and on side away from moon – ellipsoid shape Long, narrow bays usu. have highest tides – up to 16 meters in Bay of Fundy in eastern Canada

© 2007, John Wiley and Sons, Inc. Waves Oscillations in water due to force of friction from wind blowing across its surface Waves travel horizontally, but most movement of water is vertical, up-and-down Near coast seafloor slopes upward – wave base intersects ocean floor – wave pushes water up as it slows – waves pile up from behind - wave height exceeds 7X wavelength, and forms a breaker Only horizontal movement of water from breaker to beach, called surf – erosional agent

© 2007, John Wiley and Sons, Inc. Wave Compression

© 2007, John Wiley and Sons, Inc.Tsunami Caused by undersea earthquakes with vertical displacement, volcanic eruptions, or landslides Vertical displacement of water causes fast wave with long wavelength – no harm at sea, but massive as it hits coastline Dec 2004 – India plate subducts under Burma plate which snaps upward along 1000 km stretch – massive tsunami hits Indian Ocean Prior to arrival, ocean recedes, giving warning

© 2007, John Wiley and Sons, Inc Indian Ocean Tsunami

© 2007, John Wiley and Sons, Inc Indian Ocean Tsunami Before After

© 2007, John Wiley and Sons, Inc. Littoral Processes Transport & deposition of sediment in shore zone Longshore current – forms when wave hits beach at oblique angle – water deflects downwind, parallel to beach Longshore drift – process of longshore current eroding & carrying sediment down shore Beach drift – zig-zag motion of sediment down beach due to swash & backwash Littoral Drift – longshore & beach drift together

© 2007, John Wiley and Sons, Inc. Littoral Drift

© 2007, John Wiley and Sons, Inc. Coastal Landforms Erosional Coastlines Breaking waves have great power to erode Headland – promontory that juts into ocean or sea – made of resistant rock Waves slow & pivot around headlands – erosive power of waves concentrated on headland Retrogradation – retreat of coastline due to erosion Wave-Cut Bluff – basic erosional landform of coastlines – near-vertical cliff at water’s edge

© 2007, John Wiley and Sons, Inc. Coastal Erosional Landforms Wave Refraction

© 2007, John Wiley and Sons, Inc. Coastal Erosional Landforms Wave Cut Bluff

© 2007, John Wiley and Sons, Inc. More Erosional Landforms Marine Terrace (Falling Sea Level) Sea Stacks (Remains of Headlands)

© 2007, John Wiley and Sons, Inc. Evolution of a Rocky Coastline Submerged Coastline – Headlands Eroded Away

© 2007, John Wiley and Sons, Inc. Depositional Coastlines Progradation – process of coastline extending outward into water through deposition Beach – dynamic transition from sea to land Offshore – under water, where waves break Foreshore – rise & fall of tides Offshore Bar – between offshore & foreshore Beach Ridge – at high water line Backshore – flat, only covered in storms

© 2007, John Wiley and Sons, Inc. Beach Cross Section

© 2007, John Wiley and Sons, Inc. Spits and Baymouth Bars Longshore current carries sediment down beach Current slows upon reaching bay – sand deposited as a Spit extending out into bay – current in bay turns spit toward land in hook shape Baymouth Bar – spit extends across bay, isolating it from ocean – bay now called Lagoon Tombolo – longshore currents from 2 directions meet – sand extends out to island or sea stack

© 2007, John Wiley and Sons, Inc. Depositional Landforms Common Depositional Landforms Longshore Processes and Depositional Coastlines

© 2007, John Wiley and Sons, Inc. Depositional Landforms

© 2007, John Wiley and Sons, Inc. Barrier Islands Elongated bars of sand that form parallel to shore Likely formed from sand deposited on cont. shelf during last glaciation – waves & wind shaped sand Lagoons w/mudflats form behind barrier islands Mudflats develop into vegetated salt marsh

© 2007, John Wiley and Sons, Inc. Coral Reefs Coral polyps excrete external skeletons of calcium carbonate (limestone) – Coral Reefs New reefs form on top of old, dead reefs 30º N - 25º S latitude, water warmer than 20º C 3 settings: Fringing reef – on shallows around island Barrier reef – line of coral parallel to shore Atoll – semicircular reef around degraded volcanic island

© 2007, John Wiley and Sons, Inc. Development of Atoll

© 2007, John Wiley and Sons, Inc. Global Distribution of Coral Reefs

© 2007, John Wiley and Sons, Inc. Human Impacts on Coastlines 37% of world pop. live <60 mi. from shore (2 billion) – 50% within 120 miles of shore In US, 53% of pop. live near coastline Coastal Engineering Purposes: Protecting shore & property from hazards Stabilizing & nourishing beaches Maintaining traffic & trade into ports

© 2007, John Wiley and Sons, Inc. Mitigating Coastal Hazards Raise buildings on stilts so waves roll underneath Sea wall – vertical, concrete wall to absorb energy of waves Revetment – slope covered with large rocks (rip- rap) to absorb energy of waves These work locally, but they aggravate erosion up and down shore from wall due to wave refraction

© 2007, John Wiley and Sons, Inc. Beach Nourishment Bringing sand to beaches that have eroded – over $336M spent in Florida since 1960s How? Trucking in sand from remote location Limit loss of sand through groins – low walls built at right angles to beach – intercept longshore drift Jetties – stone or concrete structures to keep channel open, keep sand to side

© 2007, John Wiley and Sons, Inc. Sea Wall

© 2007, John Wiley and Sons, Inc. Groins and Jetties Groins Jetties

© 2007, John Wiley and Sons, Inc. Impact of Global Climate Change on Coastlines Melting ice sheets will lead to sea level rise – estimates of 5-35 inches – areas <5 ft elevation at greatest risk Pacific Islands & low-lying coastal areas will suffer greater erosion & flooding potential Coral bleaching by unusually warm water has also become a problem – ultimately kills coral

© 2007, John Wiley and Sons, Inc. Warming Threat on North Carolina Coast