Wave Erosion and Marine Geology

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Wave Erosion and Marine Geology
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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

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The Highest Recorded Ocean Wave
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When Waves Meet the Shore

• When the bottom interferes with wave motion, the
  wave steepens and the top overtakes the bottom.

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Wave Refraction

• Waves change path when they reach shallow water
• Wave energy is concentrated on headlands and
  spread out in bays

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Rips

• When waves break parallel to a beach, rips occur

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Storm Waves Galveston, Texas, September 8, 1900

• 6000-8000 dead
• 3600 houses destroyed

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Raising Galveston 6 in. to 17 ft.
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A rickety maze such as Dr. Seuss might have
drawn
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The Lift in Progress
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Pumping in the Sand
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The Galveston Seawall
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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.

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Property Values and Shoreline Erosion

• If more than half the original lot is left, its
  Location, Location, Location
• After that, it becomes obvious there soon wont
  be any location left

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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.

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Marine Erosion

• Chemical Attack
• Abrasion
• Wave Impact
• Compressed Air
• Backwash

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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

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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

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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

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Secondary Coasts Are Modified by Marine Erosion
or Deposition
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Secondary Coasts

• Erosion
• Stack
• Terraces
• Tombolo
• Erosion rate becomes very slow
• wave energy dissipated crossing the wave-cut
  terrace.
• Cliffs become higher, meaning more material to
  move.

• Deposition
• Spit
• Lagoon
• Baymouth Bar
• Barrier Bar

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Primary Coastlines Are Very Common

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

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Other Ways Primary Coasts Can Form

• Deltas
• Volcanic Activity
• Uplift

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Primary and Secondary Coastlines
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Delta Coasts

• Deposition-Dominated
• Wave Dominated
• Tide-Dominated

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The Mississippi A Deposition-Dominated Delta
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Yukon and Nile Deltas Balance of Deposition and
Wave Action
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Sao Francisco, Brazil A Wave-Dominated Delta
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Ganges, Bangladesh A Tide-Dominated Delta
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Reefs Are a Major Type of Coast in Tropical Areas
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Tarawa A Typical Atoll
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Reefs Also Form along the Edges of Large Islands
and Continents

• These Are Barrier Reefs
• Australia
• Yucatan
• Belize
• West Florida

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Turbidity Flows Grand Banks, 1929