Reversing dunes are formed by variations in wind direction, specifically when winds from opposite directions blow during different seasons.
The Formation Process
Dune shapes are often determined by the predominant wind direction in an area. However, in some regions, the wind direction isn't constant throughout the year. When winds blow significantly from two opposed directions at different times, often on a seasonal cycle, a unique dune type called a reversing dune is created.
Key Characteristics
The defining feature of a reversing dune, directly resulting from this alternating wind pattern, is that its slip faces face first in one direction and then in the other. A slip face is the steeper, downwind side of a dune where sand slides down when the angle becomes too steep.
- Seasonal Wind Shifts: The formation hinges on a predictable change in the dominant wind direction, usually tied to the seasons.
- Opposed Directions: The winds must come from roughly opposite directions to build the dune in one direction and then erode and rebuild it in the reverse direction.
- Alternating Slip Faces: As one wind direction builds the dune and creates a slip face, the change in season brings wind from the opposite direction, which then begins to reverse the dune's structure, eventually forming a new slip face on the opposite side.
This continuous process of building and reversing based on seasonal wind cycles results in the characteristic form and behavior of reversing dunes.
