A coastal plain is an area of low, flat land near the coast. In South America, coastal plains are found on the northeastern coast of Brazil, on the Atlantic Ocean, on the Ecuadorian coast, and on the western Pacific coast of Peru and Chile. The coastal plains of northeastern Brazil are extremely dry. The Brazilian Planalto acts as a wedge that moves moisture from the sea winds away from the coastal plains. In the western coastal plains there are humid plains like those of Ecuador and dry plains like those of Peru and Chile so there is very little vegetation. These are trapped between the cold Humboldt Current to the west and the Andes Mountains to the east. This cold surface water causes a thermal inversion: cold air at sea level and warmer and stable air above it. The thermal inversion produces a thick layer of fog at low altitudes; these clouds descend over much of the Pacific coast in Peru and Chile and do not allow precipitation to form. The Atacama Desert, Chile is considered the driest region in the world. The average rainfall is about one millimeter per year and some parts of it have never received a drop of water in recorded history. Although the Atacama Desert lacks flora and fauna, it is a rich deposit of copper, a key resource of the Chilean economy