What types of sand dunes occur in the Sahara Desert?

The Sahara Desert features a diverse array of sand dunes shaped by wind patterns and local topography. These formations, along with sand sheets, cover approximately 25 percent of the desert's surface.1

The principal types of dunes found in the Sahara include:

• Barchans: Common crescent-shaped dunes that are convex toward the wind, with their horns pointing downwind.12
• Seifs: Long, narrow, longitudinal dunes or chains of dunes that are oriented parallel to the prevailing wind or formed by winds blowing at acute angles.13
• Transverse dunes: Ridges that form at right angles to the wind, often composed of alternating crescentic elements.14
• Tied dunes: Formed in the lee of hills or other topographic obstacles.1
• Parabolic blowout dunes: A type of dune characterized by a U-shaped or parabolic form.1
• Compound dunes (draa): Massive, complex mountainous sand ridges that dominate the ergs (sand seas). These can reach heights of up to 1,000 feet and are often covered by smaller, secondary dune patterns.14

Additionally, the desert contains "echo dunes," which are deposited on the upwind side of large hill massifs or scarps.4