Coastal beaches and dunes have a worldwide distribution. They are common in both temperate and humid tropical areas, in arid climates, and in regions covered by snow during the winter. Beaches and dunes are considered two of the most dynamic systems. They are not permanent structures, but rather huge sand deposits that move and have an episodic supply of sand.
They can be found in deserts as well as on dissipative coasts with a plentiful supply of sediments and where there are strong onshore winds or winds that are parallel to the coastline. Sand dunes are eolian bedforms and beaches are marine geomorphic structures. Dunes form from marine sand delivered to the beach from the near-shore by waves. The exposed sediment is dried by the sun and the wind then transports sand inland to form incipient dunes and foredunes. Tidal range is important in this process since a high range exposes a large intertidal area that often dries out between the tides. These sediments constitute a major source of wind-blown sand given that sand-sized sediments are more easily transported by wind.
Dune size varies considerably. Some of the biggest dunes are found in deserts such as Badain Jaran Desert in the Gobi Desert in China (approximately 500 m), the Sossuvlei Dunes, Namib Desert (380 m), and the Great Sand Dunes National Park Preserve in Colorado, USA (230 m). Along the coast, on the Bassin d'Arcachon, France, is Europe's largest sand dune, the Dune du Pyla, nearly 3 km long, reaching 107 m in height, and moving inland at a rate of 5 m yr~ .
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