Brazil's Lençóis Maranhenses National Park looks like a desert, but it receives about 125 centimetres of rain each year. Its white quartz dunes can rise 30 metres above hundreds of freshwater lagoons. The lagoons form because rock and clay below the sand block wet-season water from draining away. Water levels usually peak around June. The park is on Brazil's Atlantic coast.
The landscape changes quickly after the rainy season. From August to November, rainfall decreases and many lagoons become smaller. Most are dry by December, although a few remain. Winds also move the dunes westward, reshaping the area over time. Satellite images help scientists follow changes across the park's 900-square-kilometre dune field. They reveal how rain, geology and wind create this unusual environment.