3/26/15 COASTAL LANDFORMS (32) I Main topics A Why study coastal landforms? B Sediment budget and system response C Coastal landforms 3/26/15 GG454 1 II Why study coastal landforms? A Dynamic systems B Reflect geologic history and human influence 1  Tectonics 2  Sea level change 3  Sediment budget C Provide a basis for predicQng “long-­‐term” future behavior of a coastal system D Dense populaQons 3/26/15 GG454 2 1 3/26/15 III Sediment budget and system response Mississippi River Delta New Orleans, Louisiana A Where sediment input > sediment loss: accreQon B Where sediment loss > sediment input: erosion C Where subsidence rate > sedimentaQon rate: submergence hYp://en.wikipedia.org/wiki/Mississippi_River_Delta 3/26/15 GG454 3 IV Coastal landforms 3/26/15 GG454 4 2 3/26/15 A Beaches, berms, and bars 1 Beach: AccumulaQon of rock fragments that can be moved by ordinary wave acQon 2 Berm: The above water porQon of a beach 3 Bar: The below water porQon of a beach; bars typically extend to depths of ~10m below low Qde level 4 Sand commonly moves offshore in winter, onshore in summer (berm!" bar) hYp://en.wikipedia.org/wiki/LiYoral_zone hYp://w3.salemstate.edu/~lhanson/gls214/gls214_beach1.htm 3/26/15 GG454 5 B Wave-­‐cut bench 1  A narrow flat area created by wave erosion 2 Result from sea-­‐level fall and/or land rise Wave-­‐cut bench, Hanauma Bay Wave-­‐cut bench, Hanauma Bay hYp://sadtp.soest.hawaii.edu/space/hawaii/ves/oahu/oahu_se/se.ground.photographs3.html 3/26/15 GG454 6 3 3/26/15 C Wave-­‐cut terrace or pladorm 1  A broad flat area created by wave erosion 2 Result from sea-­‐level fall and/or land rise Wave-­‐cut terrace Wilder Ranch State Park, California Wave-­‐cut pladorm Aberystwyth, Wales hYp://maps.unomaha.edu/maher/GEOL1010/lecture14/waveterraceUSGS.jpg 3/26/15 hYp://en.wikipedia.org/wiki/Wave-­‐cut_pladorm GG454 7 D Deltas 1 Sedimentary bodies deposited at a river mouth a Sediment sources i Natural and arQficial ii Dynamic B Influences i Stream-­‐dominated: distributaries prominent: (“birdfoot” deltas) ii Wave-­‐dominated: delta shape asymmetric 3/26/15 Mississippi River Delta hYp://en.wikipedia.org/wiki/River_delta GG454 8 4 3/26/15 E Spits Dungeness Spit, Washington 1  AYached, shore-­‐
parallel ridges of sand 2  Require a supply of sand, a transporQng current, and a deposiQonal site Farewell Spit, South Island, New Zealand hYp://en.wikipedia.org/wiki/Spit_(landform) 3/26/15 GG454 9 F Barrier islands 1  Barrier islands: low, elongate, shore-­‐parallel islands 2  Emergence of offshore bars 3  Submergence of beaches and beach dunes 4  Help protect landward coast from erosion 3/26/15 Barrier islands, Mobile Bay, Alabama hYp://commons.wikimedia.org/wiki/File:Baie_de_Mobile.jpg GG454 10 5 3/26/15 G Lagoons 1  Lagoon: a shallow Lagoon, Bora Bora body of water separated from a larger body of water by a shallow or exposed shoal, coral reef, or similar feature 2  Commonly elongate, annular, or circular in hYp://en.wikipedia.org/wiki/Lagoon#/media/File:Boraboralue_gerade.jpg map view 3/26/15 GG454 11 H Reefs 1 Indicate approximate level of sea level at the Qme of reef formaQon 2  Elevated reefs indicate former sea level highstands and/or coastal emergence 3  Submerged reefs indicate former sea level lowstands or coastal subsidence Flat Island, Kailua Bay hYp://www.onlyinhawaii.org/wp-­‐content/uploads/2014/06/Popoia-­‐Island-­‐Oahu-­‐Hawaii.jpg 3/26/15 GG454 12 6 3/26/15 H Reefs Flat Island, Kailua Bay 1 Indicate approximate level of sea level at the Qme of reef formaQon 2  Elevated reefs indicate former sea level highstands and/or coastal emergence 3  Submerged reefs indicate former sea levels and/or coastal subsidence 3/26/15 hYp://www.soest.hawaii.edu/coasts/data/oahu/pictures/ oblique_photos/Windward/images/092_Kailua_Beach_Park.jpg GG454 13 I Estuaries I Inundated stream valleys 2  Typically reflect recent sea level rise 3  Sediment “traps” San Francisco Bay Chesapeake Bay hYp://en.wikipedia.org/wiki/San_Francisco_Bay hYp://en.wikipedia.org/wiki/Chesapeake_Bay#/media/File:Chesapeakelandsat.jpeg 3/26/15 GG454 14 7 3/26/15 J Fjords 1  Inundated glacial valleys 2  Commonly very deep 3  Rockfalls common Milford Sound, New Zealand 512 m deep Sognesord, Norway 1300 m deep hYp://en.wikipedia.org/wiki/Fjord 3/26/15 GG454 15 8