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Waves and Coastlines

Waves and Coastlines. Geology Today Barbara W. Murck Brian J. Skinner. Chapter 13 Oceans, Winds, Waves, and Coastlines. N. Lindsley-Griffin, 1999. Sea arches, California. Ocean Waves. Wave Properties. Houghton Mifflin 1998; N. Lindsley-Griffin, 1999. Ocean Waves.

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Waves and Coastlines

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  1. Waves and Coastlines Geology Today Barbara W. Murck Brian J. Skinner Chapter 13 Oceans, Winds, Waves, and Coastlines N. Lindsley-Griffin, 1999 Sea arches, California

  2. Ocean Waves Wave Properties Houghton Mifflin 1998;N. Lindsley-Griffin, 1999

  3. Ocean Waves A single particle at the surface moves in a circular path as each wave passes. Motion decreases to nothing, at a depth equal to one-half the wavelength. N. Lindsley-Griffin, 1999

  4. Waves “feel” bottom Waves Near Shore As bottom shallows, waves are forced into smaller space. Their shape distorts as the front slows down.

  5. Waves Near Shore Breakers form as the wave oversteepens and topples N. Lindsley-Griffin, 1999

  6. Waves Change Near Shore Fig. 13.16, p. 387 N. Lindsley-Griffin, 1999

  7. Erosion by Waves The part of a wave that “feels” bottom first, slows down. The part still in deeper water moves faster, and the entire wave line curves, forcing wave energy towards headlands. Houghton Mifflin 1998; N. Lindsley-Griffin, 1999

  8. Erosion by Waves Headlands are eroded by waves refracted towards them. Less resistant rock (like shale) will erode faster. More resistant rock (like sandstone) will be left behind as sea stacks. N. Lindsley-Griffin, 1999

  9. Erosion by Waves Sea stacks Oregon coast Sea cliffs, sea stacks northern California coast N. Lindsley-Griffin, 1999

  10. Waves move away from the prevailing wind direction, approaching coastlines at an angle. N. Lindsley-Griffin, 1999

  11. Transport of Sediments As waves approach shore at an angle, they generate a current parallel to shore called the longshore current. Longshore Current Wind N. Lindsley-Griffin, 1999

  12. Transport of Sediments Waves run up shore at an angle Water runs straight back along steepest slope Sediment particles are transported along shore in a zigzag path Net motion = beach drift N. Lindsley-Griffin, 1999

  13. Transport of Sediments Longshore current and beach drift combine to transport large quantities of sediment parallel to the shore Fig. 13.18, p. 389 N. Lindsley-Griffin, 1999

  14. Sediment transport by longshore current N. Lindsley-Griffin, 1999

  15. Human Interference Groins - Sand is deposited by longshore current on the up-current side; eroded by wave action on the down-current side. J. Wiley, J.R. Griffin, N. Lindsley-Griffin, 1999

  16. Human Interference Erosive effect of wave action decreased by breakwater; beach builds out. Asymmetry of beach indicates longshore drift direction from bottom to top. J. Wiley, J.R. Griffin, 1999 N. Lindsley-Griffin, 1999

  17. Transport of Sediments Water carried onshore must find a path back to sea Rip currents flow out to sea along narrow channels and broad sheets J. Wiley; N. Lindsley-Griffin, 1999

  18. Rip currents transport sediments out to deeper water, can create dangerous undertows. J. Wiley; N. Lindsley-Griffin, 1999

  19. Wave-cut bench and sea cliffs, Oregon Waves Near Shore Breaking waves apply force in a narrow plane Erosion is greatest in a knife-edge right at water level Effects: wave-cut benches undermined sea cliffs sea arches and caves sea lion perches Sea lions, La Paz, Mexico N. Lindsley-Griffin, 1999

  20. Waves Near Shore Wave-cut notches and sea caves represent the early stage of undermining that eventually results in mass-wasting collapse of cliffs and sea stacks Sea Cave, California Wave-cut notch, New Brunswick N. Lindsley-Griffin, 1999

  21. Waves Near Shore J. Wiley; N. Lindsley-Griffin, 1999

  22. Coastal Landforms Wavecut bench at water level, uplifted wavecut bench - north of San Francisco, California N. Lindsley-Griffin, 1999

  23. Coastal Landforms Two wave-cut benches, with headlands and beaches (Tongue Point, New Zealand) Fig. 13.19, p. 390 N. Lindsley-Griffin, 1999

  24. Coastal Landforms Modern sea stack Fossil sea stack Tectonically uplifted wave-cut bench with fossil sea stacks (north of San Francisco, CA) N. Lindsley-Griffin, 1999

  25. Coastal Landforms Houghton-Mifflin, 1998; N. Lindsley-Griffin, 1999

  26. Coastal Landforms Sea arches form where waves cut through headlands. Eventually wave action and mass wasting will remove the top of the arch and leave sea stacks behind. N. Lindsley-Griffin, 1999

  27. Coastal Landforms Longshore drift deposits sand in a south-pointing spit at the mouth of the Russian River, northern California

  28. Coastal Landforms A tombolois a spit or bar that connects an island or sea stack to the mainland. Big Sur coast, California

  29. Coastal Landforms Tombolo seen from space J. Wiley, J.R. Griffin, 1999

  30. Coastal Landforms A baymouth bar blocks the mouth of a bay. (Oregon coast)

  31. Human Interference Beach houses attacked by hurricane, North Carolina Houghton Mifflin 1998 N. Lindsley-Griffin, 1999

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