Landform Geography

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Landform Geography
Coastal Processes and Landforms
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Coastal Processes and Landforms

• Oceans and Seas
• Nature of Coastlines Intersection of Earths
  Spheres
• Coastal Landforms
• Human Impacts on Coastlines

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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.

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Oceans and Seas
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Water as Solvent

• Salinity concentration of dissolved solids in
  seawater global seawater salinity 34-37 parts
  per thousand ()
• Brine water with gt35 salinity
• Brackish water - lt35 salinity

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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

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Eustatic Sea Level Changes
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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)
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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 usually have highest tides up
  to 16 meters in Bay of Fundy in eastern Canada

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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

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Wave Compression
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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
• March 2011 Pacific plate subducts under North
  American plate which snaps upward massive
  tsunami hits Indian Ocean

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2011 Japan Earthquake
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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

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Littoral Drift
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Coastal LandformsErosional 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 waters edge

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Coastal Erosional Landforms
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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

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Beach Cross Section
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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

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Depositional Landforms
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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

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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

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Development of Atoll
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Global Distribution of Coral Reefs
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Human Impacts on Coastlines

• 37 of world pop. live lt60 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

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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

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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

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Sea Wall
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Groins and Jetties