Understand how the dunes and lagoons in Lençois Maranhenses are formed, resulting in a unique and surprising landscape!
Lençóis Maranhenses National Park is a unique natural wonder where dunes and lagoons are formed by a fascinating combination of wind and rain. Located in the northeast of Brazil, this curious combination is considered a unique landscape, found nowhere else in the world.
This destination combines giant sand dunes and crystal-clear lagoons linked to a few rivers. Although it looks like a desert terrain, the Lençóis Maranhenses surprises with freshwater lagoons that form during the rainy season, creating a paradise for ecotourists and adventurers, as well as a living laboratory for scientists.
Photo: Julius Dadalti
What makes Lençóis Maranhenses truly unique is how its landscape changes with the seasons. Around two-thirds of the park is covered in flowing sand dunes that, from above, resemble bedsheets, hence the name in Portuguese “Lençóis”. This rare combination of sand and seasonal lagoons earned the park its status as a UNESCO World Heritage Site.
But how exactly are the dunes and lagoons in Lençóis Maranhenses formed? And what makes this environment so unique? These are some of the questions we at PlanetaEXO, specialists in ecotourism in Brazil, will explore in this article. If you’re ready to begin your journey into this natural wonder, take a look at our Lençóis Maranhenses tours.
How are the dunes in Lençóis Maranhenses formed?
The formation of the dunes is the result of a natural process known as eolian erosion, the action of wind. Powerful coastal winds from the Atlantic Ocean blow fine sand particles inland, where the region’s topography traps and accumulates them. Over time, this sand builds up into massive dunes that can reach up to 40 meters in height. Shaped by the constant movement of the wind, these dunes take on smooth, crescent-like forms and are in a state of perpetual motion, giving the landscape a dynamic and ever-changing character.
Researchers believe that around 10,000 years ago, the area now known as Lençóis Maranhenses National Park was covered by the sea. As the ocean gradually receded, it first gave way to mangrove forests and eventually transformed into the vast dune fields we see today.
A significant portion of the sand in the park was brought by the Parnaíba River. The river carries sediment toward the sea, while ocean currents push it back toward the shore. This ongoing interaction between river flow, tides, and ocean currents allowed the sand to accumulate, forming the unique ecosystem of Lençóis Maranhenses.
Far from being static, the dunes are in constant motion. With the wind reshaping them regularly, they perform what locals poetically call the “dance of the dunes.” This phenomenon is especially visible during the dry season (July to December) when stronger winds and lower water levels in the lagoons make the movement even more noticeable.
👉 Discover 10 facts about the Lençóis Maranhenses
Understand the difference between active and inactive dunes
In Lençóis Maranhenses, not all dunes behave in the same way. The presence or absence of vegetation is what determines whether a dune is active or inactive.
Some dunes are considered inactive, meaning they stay in place thanks to the surrounding vegetation. Thus, the native plants help to fix the sand, forming a natural cover that prevents the wind from moving the dune, making it more stable and fixed in place.
On the other hand, active dunes are those that are in constant movement due to the force of the wind, rain and the absence of nearby vegetation, allowing the sand to do the dune dance.
Can the dunes disappear?
Researchers believe that the complete disappearance of the Lençóis Maranhenses dunes is unlikely. However, some factors could significantly alter their formation and have serious environmental and social consequences.
One of the main concerns is the unplanned installation of wind farms, as these structures can alter the wind patterns in the region, directly affecting the formation of the dunes. In addition, climate change plays a fundamental role, as it can cause alterations in the behavior of rainfall and winds.
How are the lagoons in Lençóis Maranhenses formed?
The beautiful, crystal-clear lagoons of Lençóis Maranhenses are formed by the significant amount of rainfall the region receives, which can reach 2,000 millimeters a year, mainly between January and June. During this rainy season, the rain is quickly absorbed by the sand, which raises the water table above the ground and fills the temporary lagoons that lie between the dunes.
But, the real secret behind the formation and maintenance of these lagoons lies in the soil, a mixture of sand and clay. Over time, this combination has developed characteristics similar to a sponge-like rock, allowing water to seep out slowly and thus prolonging the lifespan of the lagoons.
Photo: @gabrielachagas7
Rainwater accumulates in the low areas between the dunes, forming thousands of crystalline pools that can reach depths of around one meter and are most vibrant during the peak of the rainy season. Famous lagoons such as Lagoa Azul and Lagoa Bonita offer a breathtaking view of this unique phenomenon, while the humidity in the air also prevents the dunes from shifting during this period.
Dry season in Lençóis Maranhenses: do the lagoons dry up?
Many Lençóis Maranhenses lagoons begin to dry out during the dry season, which usually runs from July to December, intensifying from September onwards. In other words, as the rain stops and the sun prevails, the water in the smaller lagoons evaporates completely, while the larger, deeper ones can retain water for longer.
This seasonal change not only alters the visual landscape, but also affects the climate in the area. During the end of the second semester, the strongest winds return, causing the dunes to grow and move more quickly.
Photo: Glauco de Souza Santos
Everyone would love for the lagoons to be full all year round, it’s a breathtaking sight. However, it is essential for the ecosystem, and even for tourism, that the lagoons dry out periodically. Continuous water accumulation, combined with local vegetation and organic matter, would otherwise lead to excessive algae growth, making the water slimy and the lagoons unsuitable for swimming.
👉 Find all the information you need to plan your trip to Lençóis Maranhenses in our travel guide
Weather and Seasonality: Best time to visit Lençóis Maranhenses
The best time to visit Lençóis Maranhenses is from May to September, when the rainy season has just ended and the lagoons are at their peak, full of crystal-clear water.
The weather during this period is dry, with sunny skies and pleasant temperatures, ideal for hiking through the dunes and taking a refreshing dip in the lagoons.
Photo: Paraíso do Caju
Although the beginning of the dry season is considered the ideal time, each time of year offers a different kind of beauty. Whether it’s the vibrant lagoons of the rainy season or the giant dune formations of the dry months, Lençóis Maranhenses has unique experiences to offer all year round.
👉 Read the complete guide with more details about this
Discover Lençóis Maranhenses: Natural wonder that changes every season
Now that you know how the dunes and lagoons in Lençóis Maranhenses are formed, you can fully appreciate this breathtaking destination, where nature reinvents itself each season to offer a truly unique experience.
Photo: Drone Lencois Maranhenses
With PlanetaEXO tours in Lençóis Maranhenses, visitors are invited to take a closer look at this living landscape in search of adventure, connection with nature, and stunning views, all while respecting the ecosystem and supporting local culture and economy. We take care of every detail for you!
