2. What are they?
• a ridge of sand created by the wind; found in
deserts or near lakes and oceans.
3. 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.
4. How is it formed?
• Where these three variables merge, a sand dune
• 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.
5. Image example
6. 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.
7. Famous Sand Dunes
• Great Sand Dunes National park:
Established: September 13, 2004
Size: 149,137 acres
contains the highest sand dunes at 750 feet tall
Wind often tops 40 an hour
• 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