Question

What are barchans? Where are they found?

Answer 1

Hint: Desert is a dry region distinguished by extremely high or low temperatures and has scarce vegetation. Sand dunes are ridges of sand made by the wind, seen in deserts or near lakes and ocean. Sand dunes are the crescentic dune, the linear dune, the star dune, the dome dune, the parabolic dune.

Complete step by step solution
Sand dune forms where these three variables merge. As the wind picks up the sand, the sand travels, but generally only about an inch or two above ground. Wind moves sand in one of following three ways:
1. Saltation: the sand grains jounce along in the wind. About $95\% $ of sand grains move in this manner.
2. Creep: when sand grains crash with other grains- like clay or gravel. Creep accounts for about $4\% $ of sand movement.
3. Suspension: sand grains blow high in air and then will settle. About $1\% $ of sand travels this way.

Types of sand dunes
1. The crescentic dune: it is the most common dune. It forms as the shape of a crescent moon when the wind blows from one direction.
2. The linear dune: it is longer than its width and features a prominent ridge.
3. The star dune: it looks like arms extended out from the center mound, forming by multidirectional wind.
4. The dome dune: it looks like an oval shape.
5. The parabolic dune: it looks U- shaped like crescentic.
Barchans are a crescent shaped dune formed by wind blows mainly from one direction. It looks like a convex structure. It can be seen in Indian desert.

Note Measurement of barchans are $9 - 30$ m in height, $370$ m wide at the base measured perpendicular to wind. Migration rate of barchans ranges about meter to a hundred meters per annual year. Barchans dunes have been observed on mars. On Mars, a thin atmosphere forms winds strong enough to move sand and dust.