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COASTAL  LANDFORMS  (32)    

I  Main  topics  A  Why  study  coastal  landforms?  

B  Sediment  budget  and  system  response  

C  Coastal  landforms  

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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    

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III  Sediment  budget  and  system  response    

A  Where  sediment  input  >  sediment  loss:  accreQon  

B  Where  sediment  loss  >  sediment  input:  erosion  

C  Where  subsidence  rate  >  sedimentaQon  rate:  submergence  

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Mississippi  River  Delta  New  Orleans,  Louisiana  

hYp://en.wikipedia.org/wiki/Mississippi_River_Delta  

IV  Coastal  landforms  

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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)  

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hYp://w3.salemstate.edu/~lhanson/gls214/gls214_beach1.htm  

hYp://en.wikipedia.org/wiki/LiYoral_zone  

B  Wave-­‐cut  bench    1  A  narrow  flat  area  

created  by  wave  erosion  2  Result  from  sea-­‐level  fall  

and/or  land  rise    

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hYp://sadtp.soest.hawaii.edu/space/hawaii/ves/oahu/oahu_se/se.ground.photographs3.html  

Wave-­‐cut  bench,  Hanauma  Bay  Wave-­‐cut  bench,  Hanauma  Bay  

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C  Wave-­‐cut  terrace  or  pladorm    

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hYp://en.wikipedia.org/wiki/Wave-­‐cut_pladorm  

Wave-­‐cut  pladorm  Aberystwyth,  Wales  

hYp://maps.unomaha.edu/maher/GEOL1010/lecture14/waveterraceUSGS.jpg  

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  

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  

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hYp://en.wikipedia.org/wiki/River_delta  

Mississippi  River  Delta  

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E  Spits  

1  AYached,  shore-­‐parallel  ridges  of  sand  

2  Require  a  supply  of  sand,  a  transporQng  current,  and  a  deposiQonal  site  

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hYp://en.wikipedia.org/wiki/Spit_(landform)  

Dungeness  Spit,  Washington  

Farewell  Spit,  South  Island,  New  Zealand  

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  

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hYp://commons.wikimedia.org/wiki/File:Baie_de_Mobile.jpg  

Barrier  islands,  Mobile  Bay,  Alabama  

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G  Lagoons  

1  Lagoon:  a  shallow  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  map  view  

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hYp://en.wikipedia.org/wiki/Lagoon#/media/File:Boraboralue_gerade.jpg  

Lagoon,  Bora  Bora  

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  

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hYp://www.onlyinhawaii.org/wp-­‐content/uploads/2014/06/Popoia-­‐Island-­‐Oahu-­‐Hawaii.jpg  

Flat  Island,  Kailua  Bay  

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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  levels  and/or  coastal  subsidence  

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hYp://www.soest.hawaii.edu/coasts/data/oahu/pictures/  oblique_photos/Windward/images/092_Kailua_Beach_Park.jpg  

Flat  Island,  Kailua  Bay  

I  Estuaries  I  Inundated  stream  valleys  

2  Typically  reflect  recent  sea  level  rise  

3  Sediment  “traps”  

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hYp://en.wikipedia.org/wiki/San_Francisco_Bay  hYp://en.wikipedia.org/wiki/Chesapeake_Bay#/media/File:Chesapeakelandsat.jpeg  

Chesapeake  Bay  San  Francisco  Bay  

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J  Fjords  

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hYp://en.wikipedia.org/wiki/Fjord  

1  Inundated  glacial  valleys  2  Commonly  very  deep  3  Rockfalls  common  

Sognesord,  Norway  1300  m  deep  

Milford  Sound,  New  Zealand  512  m  deep