Linear dunes
Overview
Linear dunes, also known as longitudinal dunes, are a specific type of aeolian landform that are elongated in the direction of the prevailing wind. These dunes are typically straight or slightly sinuous sand ridges typically much longer than they are wide. They may be more than 160 kilometers long, and vary in width from 0.3 to 3.0 kilometers and in height from 1 to 75 meters. Linear dunes may occur as isolated ridges, but they generally form sets of parallel ridges separated by miles of sand, gravel, or rocky interdune corridors.
Formation
Linear dunes form under conditions where sand supply is relatively abundant, the prevailing winds are steady, and the wind direction does not change significantly. The wind aligns the dune in a consistent direction, causing a build-up of sand where the wind strength decreases. The dune grows as long as the wind continues to deposit sand at the crest. The windward side of the dune is typically a gentle slope, while the leeward side is a steep slip face.
Characteristics
The primary characteristic of linear dunes is their long, straight, or slightly wavy ridges that are parallel to the dominant wind direction. These dunes are usually symmetrical, with the slip face and windward side being about the same length. The dune ridge is typically sharp and narrow at the crest, becoming broader and more diffuse towards the base. The interdune corridors between linear dunes are usually flat and often contain deflationary pans, playas, or desert pavements.
Distribution
Linear dunes are found in desert regions around the world, including the Sahara, the Namib, the Great Sandy Desert in Australia, and the Rub' al Khali in Saudi Arabia. They also occur in some coastal areas where onshore winds consistently blow sand inland.
Types of Linear Dunes
There are several types of linear dunes, including simple linear dunes, compound linear dunes, and complex linear dunes. Simple linear dunes are single, relatively small dunes with a straightforward form. Compound linear dunes consist of large linear dunes with smaller superimposed dunes. Complex linear dunes are large dunes with superimposed smaller dunes and with secondary dunes at their base.
Ecological Significance
Linear dunes play a crucial role in desert ecosystems. They provide habitats for a variety of desert-adapted plants and animals. The interdune corridors, in particular, can be important areas for plant growth, as they may receive more water from rain or dew than the dune crests. Some species of desert rodents and insects are adapted to live in the corridors between linear dunes, while others are adapted to live on the dunes themselves.
Human Interaction
Humans have interacted with linear dunes in various ways throughout history. In some desert regions, linear dunes have served as natural corridors for human travel and trade. However, they can also pose challenges for human activities. For example, the movement of linear dunes can bury human structures or block transportation routes. In some cases, efforts have been made to stabilize dunes through the planting of vegetation or the construction of fences or other barriers.