Diagram of a Beach

 
Peralta Colleges, Physical Geography
Rita D. Haberlin, Instructor
COASTAL LANDFORMS STUDY GUIDE

CHIEF IDEAS:

  1. Many factors combine to create the variety of coastal landscapes. These factors include: erosion, transport, and deposition by waves, tides, currents, the landscape adjoining the coast, relative changes of sea and land, the influence of people’s engineering works, and special effects such as coral, volcanoes, ice, and deltas.

  2.  
  3. Waves are the force that shapes the coastline. Wind blowing over the surface of the ocean forms waves which transfer some of the wind's energy to the coastline. Orbital water motion extends to a depth of half a wavelength.

  4.  
  5. When a wave reaches shallow water, friction with the bottom flattens the wave orbits and causes the wave to slow down and peak up forming a crest. Eventually the crest collapses forward onto the beach.

  6.  
  7. Waves that approach the coast at an angle cause beach drifting (swash and backwash) and longshore currents in the surf zone. Longshore transport and progradation (forward building) create a variety of depositional features such as spits, baymouth bars, and beaches. Drifting sand may be deposited inside breakwaters or against jetties or groins.

  8.  
  9. Local erosion may supply some sediment but rivers supply most of the sand for beaches. If the rivers are dammed, the sand supply is cut off and beaches become narrower. Coastal property is threatened by wave erosion when beaches are narrow.

  10.  
  11. Waves erode landscapes by hydraulic action, abrasion, solution, and attrition. Slow (5-8 per minute) spilling waves build up the beach in calm weather. Faster (13-15 per minute) plunging waves erode the beach during storms.

  12.  
  13. The most common coastal landscapes are cliffed coastlines of headlands and bays and barrier island coasts. Most of the cliffed coastlines were formed due to submergence by rising sea level. Former river valleys drowned by the sea form ria coasts, drowned glacial valleys form fiord coasts.

  14.  
  15. Over time, coastlines of headlands and bays are straightened by erosion of headlands and deposition in the bays. Wave refraction concentrates wave energy on the headlands and disperses it in bays.

  16.  
  17. As waves erode the softer rock in cliffs, they form caves and arches. Stacks and stumps form when arches collapse. As the cliffs erode backward, they leave a wave-cut abrasion platform at the base. In deeper water, a wave-built depositional terrace forms.

  18.  
  19. Barrier island coasts develop where there is a gentle offshore gradient, slight tidal range, and a low-lying landscape bordering the coast. This is the most common coastline in the Eastern and Southern United States. Submarine bars that form parallel to the coastline grow into barrier islands which are gradually driven landward by wind and waves.

  20.  
  21. A rise of land relative to the sea produces wave-cut marine terraces.

  22.  
  23. Coral coasts form from biological organisms growing in warm, clear water. Coral may take the form of fringing reefs, barrier reefs, or atolls.

  24.  

STUDY OBJECTIVES:

  1. Describe the factors that combine to create the variety of coastal landscapes.
  2. Explain how waves form.
  3. What happens to waves when they reach the shoreline?
  4. Describe longshore transport. Draw a diagram to show how sand moves along a beach face when the waves approach a beach at an angle. Describe how longshore drift forms spits and baymouth bars. How can longshore drift be stopped or altered by people’s activities?
  5. What is the source of sand for beaches? What would happen to beaches if all the rivers were dammed?
  6. Explain how waves erode. How do summer beaches differ from winter beaches?
  7. What are the most common coastal landscapes? How do they differ?
  8. Describe how waves can straighten an irregular coastline of headlands and bays.
  9. Describe how waves affect coastlines with varying resistance to erosion to produce cliffs, caves, arches, stacks, and wave-cut abrasion platforms.
  10. Describe the development of a barrier island coast.
  11. Draw a diagram to show the formation of a marine terrace by a rise of land relative to the sea.
  12. Describe the circumstances in which coral may form.

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