Chapter 2 The Geomorphology of Eroding and Accreting Coasts by hmv21438

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									 Chapter 2: The Geomorphology of Eroding and
               Accreting Coasts

     Examples
     Continental Margins
     Tectonic Classification of Coasts
     Tectonic effects on coastal sediment supply




Example Coastlines & Morphology




                                                   1
Terminal Moraine: Long Island




            Transgressive & Regressive Sequences




                                                   2
Natural vs Engineered
Barrier Island Profiles




Data: Westhampton Beach




                          3
               Sources of Sand For Littoral Transport

 Bluff Erosion
 Offshore Glacially Deposited Sand Ridges, Relict Ebb Shoals

                                               Cliff or Bluff
                                                   Coast
Tide Dominated
       &
   Riverine

                        2m                                Gravel

                                                       Wave Dominated




                                   Sand



  Barrier Island             Mixed Energy




                                                                        4
5
6
Spit Accretion Theory




            Spit Accretion   Fire Island Inlet




                                                 7
•Littoral Transport reaches a maximum rate of 463,015 to
601,657 yd3/yr at Democrat Point (Fire Island Inlet)




                                                           8
                 Continental Margins




Continental Shelves:
broad shallow extension of the continents (~75km wide)
Regions of deposition (rivers, glaciers, scrapped marine
deposits, calcium carbonate)
Large bedform features, reworked by tides, storms,
waves




                                                           9
Continental Slopes:
continental crust thins into oceanic crust
steep (~20km, 1-25 degrees), 5deg Pacific, 3deg Atlantic
extend to depths between 1500-4000 m




Continental Rise:
Fan like deposit where the continental slope intersects
the abyssal plains
Formed by turbidity currents




                                                           10
             Tectonic Evolution of Continental Margins




Atlantic Margin: passive margin, edge of the continent is in the
middle of a lithospheric plate, little seismic activity, no volcanism
Pacific Margin: active margin, edge of the continent coincides
with a plate boundary, rim of the Pacific Ocean, ring of fire,
seismic activity and volcanism




        Tectonic Coastline Classification (Inman & Nordstrom)
Tectonic Setting (Pacific-vs-Atlantic type margin)
Tectonic Setting of opposite side of the continent
Geologic Age of the coast
Exposure to open ocean conditions


1.   Collision Coasts
         Continental collision coasts
         Island arc collision coasts
2.   Trailing Edge Coasts
         Neo-trailing edge coasts
         Afro-trailing edge coasts
         Amero-trailing edgo coasts
3.   Marginal Sea Coasts




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Continental collision coasts
    continental – oceanic plate boundary
    narrow margin, deep trench
    seismic activity, coast backed by high
    mountains




Island Arc collision coasts
    oceanic – oceanic plate boundary
    narrow margin, deep trench
    moderate mountain ranges
Ex Japan, Philippines, Aleutian Islands




                                             12
Neo-Trailing Edge Coasts
    Atlantic type margins
    geologically young
Ex Red Sea, Gulf of Aden, Gulf of California




  East African Rift System




                                               13
Afro-Trailing Edge Coasts
   both sides of the continent are
   passive margins
   lack organized drainage pattern
Ex Africa, Greenland




Amero-Trailing Edge Coasts
   opposite side of the continent is
   an active margin
   organized drainage pattern
Ex Atlantic coast of N&S America
    and Europe, India




                                       14
                     Marginal Sea Coasts
                         direct exposure to the ocean is
                         reduced due to island arc system
                     Ex Gulf of Mexico, Bearing Sea, Sea
                        of Japan, East and South China
                        Seas




    Classification Based on Tidal Range




Microtidal:   <2m
Mesotidal:    2–4m
Macrotidal:   >2m




                                                            15
     Classification Based on Wave Energy
       correlation of morphology based on energy regime


                               Hs2T2


       Hs         = significant wave height
       T          = significant wave period


       Hs2T2      0 – 30               = mildly exposed coast
       Hs   2T2   30 – 300             = moderately exposed coast
       Hs2T2      > 300                = highly exposed coast



                                                         Walton and Adams, 1978




     Hydrodynamic Coastline Classification

Tide Dominated



Wave Dominated                                                      Shinnecock
                                                                       Inlet


 Mixed Energy




                                                         (Hayes, 1975)




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                        Long Island Classification
 Amero-Trailing Edge Coast
 South Shore Significant Wave Conditions: H ~= 1.5 m, T = 8 sec
 Micro-Tidal Environments

                                       Tide Dominated         Cliff or Bluff
                                                                  Coast
Tide Dominated
       &            Gravel, sand
   Riverine

                             2m                                          Gravel

                                                                      Wave Dominated




                                        Sand



  Barrier Island                  Mixed Energy




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