The area shown here (10 km across) is a small part of the dune field which is now protected as the Lençóis Maranhenses National Park, on Brazil's north coast, about 700 km east of the Amazon River mouth. Persistent winds blow off the equatorial Atlantic Ocean onto Brazil from the east, driving white sand inland from the 100 km stretch of coast (upper margin of the image), to form a large field of dunes. The strongly regular pattern of these dunes is a common characteristic of dune fields. The basic shape of each sand mass, repeated throughout the view, is a crescent-shaped dune. In an area with a rich supply of sand such as coastal Brazil, individual crescents coalesce to form entire chains many miles long. The wind strength and supply of sand are sufficient to keep the dunes active, and thus free of vegetation, despite 1500 mm (60 inches) of rainfall annually. The dark areas between the white dunes are fresh water ponds that draw fisherman to this newly established park. The characteristic regularity of the dune landscape can be detected downwind (west) for more than 100 km, beyond the present dune field. Now covered by dense forest, the greater extent of this dune field indicates that climates have been substantially drier at the Equator in the recent geological past.
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