Geography · Ch 2 — Structure and Physiography
The Indian Desert
The Indian Desert
The photograph shows three camels with riders moving in a line across a field of rippled sand dunes in the Thar desert. The dunes are the real subject — their smooth, wave-like crests and the dark shadows between them make the undulating surface of the desert immediately visible. The camels give a sense of scale: without them, the height and sweep of the dunes would be hard to judge.
What the image captures is exactly what the text describes as "undulating topography dotted with longitudinal dunes and barchans." The ripples on the sand surface are the work of wind, which is the dominant geomorphic agent here. The crescent-shaped barchan dunes, with their horns pointing downwind, and the long, straight longitudinal dunes aligned with the prevailing wind, are both products of wind deposition. The photograph makes the point that this is not a flat, lifeless expanse but a landscape with its own relief, shaped by aeolian processes. …
To the northwest of the Aravali hills lies the Great Indian desert, a region defined by its extreme aridity. Its very character — the landforms, the drainage, even its name — flows from one central fact: it receives less than 150 mm of rainfall a year. That single number shapes everything else about this landscape.
The desert is a land of undulating topography, its surface never flat but rolling, dotted with longitudinal dunes and barchans (crescent-shaped dunes). Because rainfall is so scarce, the climate is arid and vegetation cover is thin. These characteristic features — the dunes, the dryness, the sparse plant life — are why this region is also known as Marusthali, literally the land of the dead.
Geologically, this desert has a remarkable history. It is believed that during the Mesozoic era, this region lay under the sea. The evidence for this comes from two locations: the wood fossils park at Aakal, and marine deposits found around Brahmsar, near Jaisalmer. The wood fossils there are estimated to be about 180 million years old, a striking reminder that this parched land was once underwater.
The underlying rock structure of the desert is actually an extension of the Peninsular plateau. Yet the surface looks nothing like it, because the extreme arid conditions have carved the landscape through physical weathering and wind action. These processes have produced some of the desert's most well-pronounced land features: mushroom rocks, shifting dunes, and oases, the last of these found mostly in the southern part of the desert.
On the basis of orientation, the desert divides into two parts. The northern part slopes towards Sindh, while the southern part slopes towards the Rann of Kachchh. This slope direction matters because it controls where the scant drainage goes. …