The Paradox of Lençóis Maranhenses National Park

• Lençóis Maranhenses National Park in Brazil features a rare, surreal landscape of white quartz dunes interspersed with seasonal freshwater lagoons.
• Despite appearing like a desert, the region receives approximately 125 centimeters (50 inches) of rain annually, enabling the formation of these lagoons.
• The park spans roughly 900 square kilometers, with dunes reaching up to 30 meters in height.

Formation and Seasonal Dynamics

• The lagoons form during the wet season because a layer of impermeable bedrock and clay beneath the sand prevents water from draining.
• Water levels typically peak in June; as rains subside between August and November, the water table drops, and most lagoons dry up by December.
• The park's name, meaning "bedsheets" in Portuguese, describes the appearance of the dune field from afar.

Geographic and Geological Factors

• The dunes are formed by a convergence of environmental factors:
  • Quartz sand is deposited by regional rivers, such as the Mearim and Parnaíba.
  • Persistent easterly trade winds, which can reach 50 kilometers per hour in the dry season, shape and push the dunes westward.
  • Movement occurs at a rate of 4 to 25 meters per year.
• The park sits at the intersection of three major biomes: the Amazon rainforest, the Cerrado tropical wooded savannas, and the Caatinga dry shrublands.

Coloration and Optics

• The lagoons exhibit varying hues due to several factors:
  • Light blue/turquoise: Shallower water reflecting off the sand bottom.
  • Dark blue: Deeper water absorbing longer light wavelengths.
  • Green/Brown: Presence of suspended sediment, algae, or dissolved organic matter.