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Erosion

Erosion. By Wind and Waves. Review Any natural process that removes sediments and carries them away from one place to another is called erosion . Gravity is the driving force behind all erosion. Everything on earth is constantly being pulled toward the earth’s center by gravity.

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Erosion

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  1. Erosion By Wind and Waves

  2. Review • Any natural process that removes sediments and carries them away from one place to another is called erosion. • Gravity is the driving force behind all erosion. • Everything on earth is constantly being pulled toward the earth’s center by gravity. • Any particle of matter that is free to move is going to move downward due to gravity unless some other force interferes.

  3. Wind Erosion • Wind erodes dry land much more effectively than it does moist land (more plants with roots to hold the soil). • As the wind erodes land it carries rock particles along with it, mostly sand, silt, and clay. • Sand material is moved along by a number of jumps and bounces, much how a pebble is moved along the bottom of a stream bed.

  4. The wind causes friction on sand grains to lift them into the air. Gravity pulls them down to the surface. • Sand grains, which cause most of the abrasion, do not rise higher than about 1 meter, and they move in the same direction the wind is blowing. • Dust particles (silt and clay) can be carried along great distances and at greater heights than sand particles.

  5. Effects of wind erosion • Abrasion is the weathering of rock particles by the impact of other rock particles. • In areas where there are strong, steady winds, large amounts of loose sand, and relatively soft rocks, abrasion causes a great amount of erosion.

  6. Pebbles and small stones exposed to wind abrasion show surfaces that are flattened and polished on two or three sides. • Rocks smoothed this way are called ventifacts.

  7. Particles that have been moved by the wind are well rounded by the repeated impact of grain against grain, and when examined with a magnifier, their surfaces have a frosted appearance.

  8. Outcrops of rocks in arid regions undergo the greatest amount of erosion close to their base, because particles transported by the wind remain close to the ground.

  9. DEFLATION Removal of fine particles by wind leaves hollows behind (Deflation Hollows) Also leaves a surface of closely packed stones (DESERT PAVEMENT)

  10. SAND DUNES are ridges of wind deposited sand - Usually 3 to 15 metres high, but can reach 180 metres - A continuously changing dune is ACTIVE Corbis Digital Stock

  11. The formation of dunes depends on: - amount of sand - speed and direction of wind - occurrence of vegetation Corbis Digital Stock

  12. wind direction BACKSLOPE SLIPFACE crest angle of repose movement of sand

  13. TYPES OF SAND DUNE 1.) BARCHAN - most common type - crescent-shaped backslope slip face Wind direction

  14. 2.) TRANSVERSE DUNES • low sand ridge at right angles to the wind direction • may form because of large amounts of sand wind

  15. 3.) LONGITUDINAL DUNES • low sand ridges parallel to the wind direction • may form because of a limited amount of sand • also known as seif dunes wind

  16. LOESS • Finely textured sediment (silt) wind-blown long distances • Wind-blown glacial debris formed large deposits

  17. Wave Erosion and Deposition • Energy from waves transfers to land and causes erosion to form erosional features such as cliffs. • Sand is the product of this erosion. The type of sand depends on the material being eroded (typically quartz and coral—white sand, or basalt—black sand). • Sand material is transported by waves and currents to form beaches and other transient coastal landforms.

  18. WAVES wave length crest trough wave height particles in waves follow a circular pattern

  19. At the shoreline • Water becomes shallow, wave height increases because wave length decreases • Waves become steeper, then collapse (breakers)

  20. Surf - sequence of breaking waves • Swash - water sliding up beach • Backwash - water flowing back down beach to sea

  21. Headland Wave refraction Bay

  22. Waves arriving at bays are slow (deposition) • At headlands, faster (erosion)

  23. A sequence of features is produced as headlands are degraded • Sea cliffs • Waves erode base -undercutting the cliff retreats

  24. Also produces sea caves • As cliffs retreat produces a wave-cut platform

  25. Headlands may be eroded back leaving a remnant (stack) stack

  26. Longshore drift • Waves arrive at a coast at an angle (swash) • Backwash returns at 90degrees Sand is moved along the beach = longshore drift or longshore current

  27. Coastal deposition • Result of longshore drift and a lot of sediment • produces extensions of deposit from the shoreline

  28. spit = curved extension • May grow across a bay (baymouth bar or barrier beach) • May link an island to the main land (tombolo)

  29. Sandbar • Off-shore sand deposit that lies just below the water surface

  30. Barrier Island Coasts • Occur on low lying coasts with gentle gradients • BARRIER ISLANDS - low ridges of sand built by waves • behind the islands are lagoons • shallow water with tidal deposits • TIDAL INLETS - gaps between the islands

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