At dunes they are ecosystems made up of very fine sand grains that are developed mainly by the action of the winds, forming hills or mountains of different shapes and sizes.
They are extensive dynamic natural barriers that prevent the advance of the sea and also the entry of salt water into the groundwater. Furthermore, the dunes protect the adjacent areas against the erosion process.
We find dunes in deserts and close to coastal areas, however, they can be formed by rock erosion processes within continents and generally near river beds.
How are Dunes Formed?
Dunes are formed through a complex process resulting from the action of winds (wind dunes) and the sea. They usually appear in places with low rainfall (rain) and their expansion occurs slowly and gradually. The main elements of dune sands are silica, magnetite and quartz. For this reason, it is possible to find the dunes of varied colors.
This excessive accumulation of sand comes with strong and constant winds in a certain direction and also by the action of high tides which bring a lot of sand and cannot take everything back. For them to occur it is necessary a place of low vegetation with the presence of some barrier, which gradually form piles of sand.
Depending on the variation of the winds, the landscape can change over time. Therefore, we conclude that the dunes are ecosystems that are in constant transformation and can change their shape, move, decrease or increase. After this formation process, they form peaks (or an immense crest), where the direction of the winds that formed them is evident.
Fauna and Flora
Due to their environmental conditions, the Dunes are home to a restricted fauna and flora within an environment that has low humidity and salinity. In the development sites of the dunes it is possible to find insects and rodents.
As for vegetation, grasses, low and low sized plants are the most commonly found. Note that the sparse vegetation present, if removed, can alter the space, leading to the process of erosion and consequently, to the environmental imbalance.
Dunes of Brazil
Maranhenses Sheets
In Brazil there are several coastal dunes (mostly on the coast) and according to the legislation they are called environmental preservation areas.
Thus, in several places in the country it is possible to find these magnificent natural landscapes, for example: Lençóis Maranhenses, Jericoacoara, Natal, Areia Branca, Itaúnas, Genipabu, Jalapão, Florianópolis, Garopaba, Cano Frio, among others.
Dunes of the World
Many dunes are part of the landscape of other countries. The highest dune in the world is Cerro Branco (Cerro Blanco, in Spanish) which is located in the Nazca Valley in Peru. It has a height of 2,078 meters above sea level. In addition to the coastal dunes, there are desert dunes, which are formed in the region of deserts.
Types of Dunes
According to the movement, the dunes are classified into three types:
- stationary dunes: also called fixed or stable dunes, in this case, the dunes do not change their place of origin due to the vegetation present that prevents them from migrating.
- Migratory Dunes: also called mobile dunes, these types of dunes change location due to the strong action of the winds and the absence of vegetation or natural barrier that would stabilize them.
- Fossil Dunes: also called paleodunes, this type of formation is older and usually has a more reddish color. They receive this name since they bring together several fragments of prehistoric civilizations.
As for the shape they have, the dunes are classified into five types:
- Linear Dune: are straighter dunes that form long continuous lines.
- crescent dune: also called barchan dune, are the most common characterized by the shape of a half moon they have and also for being wider.
- Parabolic Dune: has a “u” shape and differs from crescent dunes in that the crest points upwards in parabolic dunes.
- Dune Estrela: grow more vertically and are named for the pyramidal shape they have.
- Dune Dome: These are the rarest dunes, characterized by their oval shape and low height.
Fun Facts: Did You Know?
The so-called underwater dunes (or sand waves) occur below the seas and rivers and are formed by the action of water currents, sedimentation and erosion.