Coastal Processes

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20 Coastal Processes and Terrain
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The Impact of Waves and Currents on the Landscape

• Coastal Processes
• Erosion Waves, mainly
• Deposition Currents, mainly
• Rocky cliffs and headlands
• Main erosional features
• Beaches and sandbars
• Main depositional features

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Coastal Processes

• Erosion and Deposition
• Involve the transfer of energy from the
  atmosphere to the hydrosphere (ocean) and then to
  the lithosphere (land).

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• Geomorphic agents
• Waves
• Wind-generated waves
• Fetch
• Other agents
• Longshore (littoral) currents
• Tides and tidal currents
• Volcanic eruptions and earthquakes
• Tidal (storm) surges
• Long-term (tectonic and climatic) effects on sea
  level change
• Reef-building corals
• Sea ice and glacial ice

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Waves

• Wave Motion and Wave Refraction
• Tsunami

• Animation
• Definition A disturbance in water caused by
  energy passing through it.
• Wave terms wavelength, wave crest and trough,
  swash
• Swell, height, and period

• Fig. 20-2

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• Waves of Oscillation and Translation
• Wave of Oscillation energy and mass move
  differently

• Fig. 20-2

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• Wave of Translation energy and mass move in the
  same direction (horizontally)

• Fig. 20-3

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• Wave Refraction water changes direction because
  of ocean bottom and/or land mass

• Fig. 20-5

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• Headland erosion (idealized)

Wave Refraction (blue lines)
Headland
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• Fig. 20-6. Headland erosion in Australia along
  the southern coast of the state of Victoria.

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• Wave Erosion
• Hydraulic pounding
• Chemical action
• Sea cliff erosion

• Fig. 20-7

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• Tsunami (Seismic Sea Waves)
• Rapid, pronounced vertical displacement
• Main causes
• Earthquake (submarine)
• Landslide (submarine)
• Volcanic island eruption

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• Fig. 20-8. Formation of a Tsunami.

Ex. 2004 Sub-oceanic 9.0 Earthquake and
Resulting Indian Ocean Tsunami
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• Tides
• Animation (Tides)
• Significant erosion agents in narrow bays,
  margins of shallow seas, and straits.

• Fig. 20-9. Bay of Fundy has the highest tidal
  range in the world. Tidal action created these
  pedestal rocks on the edge of the bay.

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• Changes in Sea Level and Lake Level
• Causes
• Tectonic uplift or sinking of landmass
• Eustatic sea-level change increase or decrease
  in the volume of water in the oceans (ice age vs.
  interglacial)

• Fig. 20-10. Northern California coast is
  experiencing tectonic uplift.

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• Global Warming and Sea-Level Change
• Causes
• Glacial melting - more water
• Thermal expansion - water takes up more space
• Consequences by 2100
• Vertical Sea Level Rise Up to 0.5 m (20) rise
  globally
• Horizontal Retreat of Shorelines Up to 30 m
  (ca. 100 ft.) in some coastal areas
• Ice Push
• Annual freezing of sea ice causes near-shore ice
  to push against the land, causing minor erosion
• Arctic and Antarctic regions only

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• Organic Substances
• Aquatic organisms and calcium carbonate
  secretions
• Reef-building coral polyps
• Stream Outflow
• Source of sediment for beaches

• Fig 20-11. Sediment plume of the Betsiboka River,
  Madagascar.

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• Currents and Coastal Sediment Transport
• Longshore Currents
• Wave refraction

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• Beach Drifting
• Particle-by-particle transport of beach material

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• Fig. 20-13. Waves approaching the shore obliquely
  causes longshore currents and beach drifting.

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• Coastal Deposition
• Sediment budget of a shore
• Input from longshore current and wave action
• Output from storm wave action, mainly.
• Large beaches and sand dunes
• Inputs exceed outputs.
• Sediment budget

Fig. 20-14

• Fig. 20-14. One of the largest coastal dune
  complexes is on the Oregon coast.

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Coastal Landforms

• Depositional Landforms
• Animation (Coastal Stabilization
  Structures)
• Beaches
• Most widespread marine dispositional feature on
  land
• Mostly sand deposits
• Extent
• Inland margin (storm wave deposits)
• Seaward margin (neap tide line)

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• Components of the beach environment

• Fig. 20-15

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• Spit and related features
• Spit - linear strand of marine sediments attached
  to shore
• Formation usually involves longshore current
  transport
• Related features
• Lagoon
• Estuary
• Delta

• Fig. 20-16. Types of spits and the longshore
  current.

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• Idealized drawings of formation of spit and
  related features

Bay
Land
Ocean
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• Tombolo formation

Land
Ocean
Small island, sea stack
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• Photographs of spits and related features

• Fig. 20-17. Spit at Cape Henlopen, Delaware

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• Fig. 20-18. Tombolo and Mont Saint Michel on the
  northwest coast of France.

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• Barrier Islands
• Coastal islands
• Parallel to the shoreline
• Sand and other materials
• Complex origins
• Pleistocene sediments washed toward mainland
• Longshore transport and spit segmentation

Barrier Island
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• Lagoon formation
• Landward side of barrier island, protected from
  large waves
• Low energy environment, fine mud deposits (tidal
  flats)

• Fig. 20-19

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• Human Alteration of Coastal Sediment Budgets
• Beach starvation (unintentionally shrinking
  beaches)
• Dam construction on rivers reduces sediment
  discharge into oceans, starving nearby beaches of
  sand

• Old debris dam in Santa Ynez Mountains, near
  Santa Barbara, CA (Richard A. Crooker photo)

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• Beach nourishment (re-building beaches)
• Adding sand to beaches by dredging and pumping
  sand from off-shore

• A slurry of sand and water is pumped on shore and
  the sand is spread onto the beach of Rehoboth
  Beach, DE (Richard A. Crooker photos) (overlay,
  dissolve)

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• Beach preservation (maintaining beaches)
• Build structures that modify longshore transport
  and wave action in order to keep sand on beaches
• Jetty, groin, breakwater

• Fig. 20-22

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• Shorelines of Submergence
• Ria Shorelines
• Hilly or mountainous areas
• flooded valleys become estuaries

• - Fig. 20-23. Chesapeake Bay.

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• Fjorded Coasts
• Fjord glacial trough that is inundated by the
  sea

• Fig. 20-24

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• Shorelines of Emergence and Erosion
• Wave-cut Cliffs and Platforms
• Marine Terraces

• - Fig. 20-27. Near Fort Ross, CA

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• Coral Coasts
• Coral Polyps
• Reef-building varieties, warm tropical waters

• Fig. 20-28

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• Shallow-water Platforms
• Australias Great Barrier Reef

A Major Problem Coral Bleaching death of the
entire ecosystem Why?

• Fig. 20-30

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• Sinking Islands
• Three types of reefs

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• Fig. 20-31

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• Fig. 20-32. Part of the fringing reef on the
  island of Moorea, French Polynesia.

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Homework

• Read Ch. 20
• Create a study guide including material from Ch.
  20.
• Summary, list, notes, review slides

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Coastal Processes and Terrain Ventura County
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Activity

• Read Ch. 20
• BEACH FIELDTRIP! (tba)
• Review next time
• Start preparing for the final, covering all
  lectures, activities, and homework throughout
  chapters 11 to 20.
• Suggestion Write a study guide and resolve
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