Wave Erosion and Marine Geology by pengxuebo

VIEWS: 0 PAGES: 62

									Wave Erosion and Marine
       Geology
      How waves behave
 How the sea modifies coastlines
Waves
           Essential Points
1. Waves are created by the wind
2. Water in waves oscillates but does not
   move with the wave
3. What happens when waves hit the shore
4. Storm surges can be catastrophic




              How Waves Behave
Wave Fetch
Wave Fetch
The Highest Recorded Ocean Wave




       1. Waves are created by the wind
Global Wave Heights




 1. Waves are created by the wind
Freak Waves               • Addition of waves
                            of different
                            frequencies
                          • Theoretically
                            could reach 200
                            feet in Gulf of
                            Alaska
                          • One nearly sank
                            the Queen Mary in
                            WWII, with 15,000
                            troops aboard.

     1. Waves are created by the wind
                 Wave Motions




• Particles in a wave travel circular paths
• The water in a deep-water wave does not
  move forward
• Below wave base, wave effects are negligible
2. Water in a wave oscillates but does not move with the wave
                 Wave Motions




2. Water in a wave oscillates but does not move with the wave
         When Waves Meet the Shore




When the bottom interferes with wave motion, the
 wave steepens and the top overtakes the bottom.
          3. What happens when waves hit the shore
             Wave Refraction




• Waves change path when they reach shallow
  water
• Wave energy is concentrated on headlands and
  spread out in bays
        3. What happens when waves hit the shore
Wave Refraction off Cape Cod




   3. What happens when waves hit the shore
  Rips




• When waves break parallel to a beach, rips
  occur
      3. What happens when waves hit the shore
Rips, Lake Superior
         Oblique Rips




3. What happens when waves hit the shore
Storm Waves: Galveston, Texas, September 8, 1900:




   • 6000-8000 dead
   • 3600 houses destroyed
            4. Storm surges can be catastrophic
Raising Galveston – 6 in. to 17 ft.
“A rickety maze such as Dr. Seuss might have drawn”
The Lift in Progress
 Pumping in
  the Sand




4. Storm surges can be
      catastrophic
The Galveston Seawall




4. Storm surges can be catastrophic
           Essential Points
1. Waves are created by the wind
2. Water in waves oscillates but does not
   move with the wave
3. What happens when waves hit the shore
4. Storm surges can be catastrophic




              How Waves Behave
How the sea modifies coastlines
            Essential Points
1. Wave Action erodes or deposits material
   along coastlines
2. Types of coastline
3. Deltas are governed by deposition, waves,
   and tides
4. Reefs are a special type of coastline in
   tropical regions
5. Global sea level is affected by ice ages and
   plate tectonics
           How the sea modifies coastlines
  In the long run, nothing is as
futile as trying to resist shoreline
              change.

     Change can be resisted for a while,
        but when the water wants
      something badly enough, it will
           come in and take it.

1. Wave Action erodes or deposits material along coastlines
    Property
   Values and
    Shoreline
     Erosion

• If more than half the original lot is left, it’s
  Location, Location, Location
• After that, it becomes obvious there soon
  won’t be any location left
1. Wave Action erodes or deposits material along coastlines
               Marine Erosion
                 •   Chemical Attack
                 •   Abrasion
                 •   Wave Impact
                 •   Compressed Air
                 •   Backwash



1. Wave Action erodes or deposits material along coastlines
    Water Velocity and Erosion




1. Wave Action erodes or deposits material along coastlines
Longshore
and Beach
  Drift


• Most Beach Sand Is Created by Weathering and
  Carried to Coasts by Rivers
• Beach Sand Moves along the Coast by Longshore
  and Beach Drift
 1. Wave Action erodes or deposits material along coastlines
Beach Drift, New Jersey
              Types of Coast
Degree of Modification
• Primary - Not Modified Much by Wave Action
• Secondary - Highly Modified by Wave Action
History
• Emergent - Land Rises or Water Level Falls
• Submergent - Land Sinks or Water Level Rises
Dominant Process
• Erosional
• Depositional

                2. Types of coastline
     Effects of the Pleistocene
• Sea level has risen at least 100 meters in
  the last 18,000 years
• Most coastlines globally are submergent
• Primary coastlines are very common




               2. Types of coastline
Secondary Coasts Are Modified
by Marine Erosion or Deposition
           Secondary Coasts
Erosion                        Deposition
• Stack                        • Spit
• Terraces                     • Lagoon
• Tombolo                      • Baymouth Bar
• Erosion rate becomes very    • Barrier Bar
  slow
  – wave energy dissipated
    crossing the wave-cut
    terrace.
  – Cliffs become higher,
    meaning more material to
    move.                        2. Types of coastline
Primary Coastlines Are Very Common

                                  • Drowned
                                    River
                                    Valleys
                                    (Estuaries)
                                  • Drowned
                                    Glacial
                                    Valleys
                                    (Fiords)


          2. Types of coastline
Estuaries, Chesapeake Bay
   Tidal
 Marshes,
Chesapeake
   Bay




2. Types of coastline
Fiord Coast, Labrador
Other Ways Primary Coasts Can
            Form
   • Deltas
   • Volcanic Activity
   • Uplift




           2. Types of coastline
Primary and
 Secondary
 Coastlines



  2. Types of coastline
Baymouth Bar, Michigan
Wave-Cut Platform, California




            Footer
Coastal Terraces, California
Sea Stacks, Washington
Former Stack, Michigan
Sea Caves, Apostle Islands
Wave-Cut Arch, Lake Superior
               Delta Coasts
         • Deposition-Dominated
         • Wave Dominated
         • Tide-Dominated




3. Deltas are governed by deposition, waves, and tides
The Mississippi – A Deposition-
      Dominated Delta




3. Deltas are governed by deposition, waves, and tides
Yukon and Nile Deltas – Balance
of Deposition and Wave Action




 3. Deltas are governed by deposition, waves, and tides
Sao Francisco, Brazil – A Wave-
       Dominated Delta
Ganges, Bangladesh – A Tide-
     Dominated Delta
Reefs Are a Major Type of Coast
       in Tropical Areas




4. Reefs are a special type of coastline in tropical regions
Fringing Reef, Tahiti
      Tarawa – A Typical Atoll




4. Reefs are a special type of coastline in tropical regions
Reefs Also Form along the Edges
of Large Islands and Continents

        These Are Barrier Reefs
        • Australia
        • Yucatan
        • Belize
        • West Florida and the Keys

 4. Reefs are a special type of coastline in tropical regions
 Sea Level and Tectonic Activity




5. Global sea level is affected by ice ages and plate tectonics
          Depth of Ocean Crust




5. Global sea level is affected by ice ages and plate tectonics
Sea-Floor Spreading and Sea Level




5. Global sea level is affected by ice ages and plate tectonics
 Sea Level and Tectonic Activity




5. Global sea level is affected by ice ages and plate tectonics
            Essential Points
1. Wave Action erodes or deposits material
   along coastlines
2. Types of coastline
3. Deltas are governed by deposition, waves,
   and tides
4. Reefs are a special type of coastline in
   tropical regions
5. Global sea level is affected by ice ages and
   plate tectonics
           How the sea modifies coastlines

								
To top