Correct Option
The correct option is A dune similar to a barchan but with only one wing or point..
Explanation
Aeolian landforms are features produced by the wind's erosional or depositional action. Sand dunes are prominent depositional landforms classified based on their shape and alignment relative to the wind direction. A Seif dune is a specific type of linear dune.
Option Analysis
- A dune with two wings directed away from the wind. is incorrect: A dune with two wings directed away from the wind describes a Barchan. Barchans are crescent-shaped dunes formed in areas with constant wind direction and limited sand supply.
- A dune similar to a barchan but with only one wing or point. is correct: A Seif dune is similar to a Barchan but possesses only one wing or point. The term "Seif" is Arabic for "sword," referring to its shape. These form when there is a shift in wind conditions. If the wind direction changes, one wing of a Barchan may elongate while the other remains stunted or merges into the main body, resulting in a Seif dune. They are typically long, narrow ridges of sand.
- A dune formed perpendicular to the wind direction. is incorrect: Dunes formed perpendicular to the prevailing wind direction are known as Transverse dunes. These form where the wind is constant and the sand supply is abundant.
- A dune formed when vegetation covers the sand. is incorrect: Dunes formed when vegetation covers the sand are typically Parabolic dunes. In these dunes, the vegetation anchors the sand, causing the wings to point into the wind (upwind), opposite to the orientation of a Barchan.
Key Takeaway
Seif dunes are distinguished by their single-wing structure, evolving from Barchans due to shifting wind directions, whereas Barchans have two symmetrical wings pointing downwind.