Arrange the stages of barchan dune formation in an arid environment in sequential order from initial sand accumulation to the fully developed landform.
- 1Sand grains moving by saltation encounter an obstacle on a flat desert floor and begin to deposit.
- 2Sand accumulates into a mound featuring a gentle windward slope and a steep leeward slip face.
- 3Wind eddies around the edges of the mound advance sand faster at the margins, creating two horns pointing downwind.
- 4A mature crescent-shaped dune migrates continuously across the desert in the direction of the prevailing wind.
Answer
The correct sequence begins with sand encountering an obstacle and depositing, followed by the formation of a sand mound with a leeward slip face, the extension of lateral horns downwind by wind eddies, and finally the migration of a mature crescent-shaped barchan dune.
The correct sequence follows the physical progression of aeolian deposition: wind-blown sand first accumulates around an obstacle, forms an asymmetrical sand mound with a leeward slip face, develops two downwind-pointing horns as marginal sand moves faster than the center, and ultimately becomes a mobile crescent barchan dune.
Step-by-Step Solution
Key Concept
Barchan Dune Formation and Aeolian Deposition Processes