Sand dunes
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Sand dunes

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    Sand dunes Sand dunes Presentation Transcript

    • Sand Dunes
    • What are they? • a ridge of sand created by the wind; found in deserts or near lakes and oceans.
    • What is needed? • A large amount of loose sand in an area with little vegetation usually on the coast or in a dried-up river lake or sea bed. • A wind or breeze to move the grains of sand • An obstacle that causes the sand to lose momentum and settle. • This obstacle could be as small as a rock or as big as a tree.
    • How is it formed? • Where these three variables merge, a sand dune forms. • As the wind picks up the sand, the sand travels, but generally only about an inch or two above the ground. • Wind moves sand in one of three ways: • Saltation: The sand grains bounce along in the wind. About 95 % of sand grains move in this manner. • Creep: When sand grains collide with other grains -- like clay or gravel -- causing them to move. Creep accounts for about 4 % of sand movement. • Suspension: Sand grains blow high in the air and then settle. About 1 % of sand moves this way.
    • Image example
    • Types of Sand Dunes • The Crescentic Dune: This is the most common dune. It forms the shape of a crescent moon when the wind blows from one direction. • The Linear Dune: This dune is longer than it is wide and features a prominent ridge. • The Star Dune: This dune has arms that extend out from a centre mound. It's formed by multidirectional winds. • The Dome Dune: This is a rare dune that is shaped like an oval or circle. • The Parabolic Dune: This dune is U-shaped like the crescentic dune, but its crest points upward and has elongated arms that trail behind it.
    • Famous Sand Dunes • Great Sand Dunes National park: Location: Colorado Established: September 13, 2004 Size: 149,137 acres contains the highest sand dunes at 750 feet tall Wind often tops 40 an hour
    • Continued…. • The Great Dune of Pyla Location: Le Teste-De-Butch in the Arcachon Bay area, France 60 km from Bordeaux Tallest Sand Dune in Europe at 110 m above sea level