“When rocks impregnable are not so stout,
Nor gates of steel so strong, but Time decays?”
― William Shakespeare, Shakespeare’s Sonnets
Here are some amazing pictures of Sam Dune Field in Rajasthan. Enjoy.Dunes are the accumulation of sand or loose sediments that are formed due to aeolian processes.
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A Duricrust means Hard crust (Latin, Duri= Hard ). Duricrusts are surface or near-surface of the Earth consisting of a hardened accumulation of silica (SiO2), alumina (Al2O3), and iron oxide (Fe2O3), in varying proportions. The area named as kala-dungar in Rajasthan consists of iron duricrusts.
In desserts there are two things that are common
(1) Temperature Variation (Daily and annual)
(2) Lack of Humidity
Here on top we have a Duricrust. A Duricrust can be, Iron rich – Ferric Duricrust. Calcium rich – Calcritic Duricrust. Silica rich – Silicritic Duricrust
Here we have,
Iron rich clay
Olive green clay
This phenomenon is due to residual weathering. Due to intense heat the iron ions move up and form a crust. Actually the water from the rocks is evaporated making these structures on top. In Gujarat bauxite deposits are formed in this way.
Lateritic clay gives red soil. Here we can see lisangang structures. First we had an iron sandstone. Due to residual weathering the iron (Fe2+ and Fe3+) moved up and formed a crust known as Duricrust. Lisangang structures are those structures which are formed due to ionic mobility of iron.
Photos of lisangang structures are as follows,
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