Explanation:

Correct Option: (b)

• Statement 2 is incorrect: Barchans are initiated probably by a chance accumulation of sand at an obstacle, such as a patch of grass or a heap of rocks.
• They occur transversely to the wind, so that their horns thin out and become lower in the direction of the wind due to the reduced frictional retardation of the winds around the edges.
• The windward side is convex and gently-sloping while the leeward side, being sheltered, is concave and steep.
• Barchans  A barchan dune is also sometimes referred to as a crescentic dune, is a U-shaped type of sand dune that consists of horns or tips that point downwind or against the wind.
• Sand supply is abundant where barchans occur along with a hard ground and a constant wind direction.
•  Barchans can usually be found around shrubs and larger rocks as these act as anchors to hold the central area of the dune in place whereas the tips are blown away by the wind.
• Some barchan dunes can be over 100 feet high.
• The word Barchan comes from Russian word “Barkhan”.
•  A barchan dune can form when a lot of sand is present in the desert.
• A steady wind from one direction is needed.
• The face of a barchan is very steep.
•  As sand escapes over the top of the dune, it forms a trailing wall that is not steep, extending further backward and meeting the desert fl oor.
•  The trailing wall has a rounded shape from the ends on either side toward the middle, like the form of a crescent moon when it is one quarter full.
• If there is a substantial change in wind direction, the crescent form can be destroyed.
•  Barchans dunes can be found in deserts around the world where sand dunes occur.
• The most famous of these are the Sahara desert in Egypt and the Gobi desert in Asia.
• Photos taken by orbiting spacecraft have revealed barchan dunes on the surface of Mars, created by strong winds.