Major Deserts of the World

Thar Desert

The Thar Desert , also known as the Great Indian Desert, is a desert located in western India and southeastern Pakistan. It lies mostly in the Indian state of Rajasthan, and extends into the southern portion of Haryana and Punjab states and into northern Gujarat state. In Pakistan, the desert covers eastern Sind province and the southeastern portion of Pakistan's Punjab province. In Pakistan's Punjab province it is known as the Cholistan Desert. Tharparker District of province Sindh Pakistan is also a part of Thar desert. Thar Desert's Total area is about 200,000 sq km. The Thar Desert is bounded on the northwest by the Sutlej River, on the east by the Aravalli Range, on the south by the salt marsh known as the Rann of Kutch (parts of which are sometimes included in the Thar), and on the west by the Indus River. Its boundary to the large thorny steppe to the north is ill-defined. Depending on what areas are included or excluded, the nominal size of the Thar can vary significantly.

According to the WWF definition, the desert proper has 92,200 square miles (238,700 km²). Another source gives the area of the Thar Desert as 446,000 km² extending 805 km (about 500 mi) long and about 485 km (about 300 mi) wide, with 208,110 square kilometres in India. Of the Indian portion, 61% falls in Rajasthan, 20% in Gujarat and 9% in Punjab and Haryana combined. The greater portion lies in Rajasthan, covering about three-fifths of the total geographical area.

Physiography and geology
It is a desolate country where sand is piled up into huge wind blown dunes (technically this is known as an erg). The sand dunes are of three types viz., longitudinal parabolic, transverse and barchans. The first type, running NNE-SSW, i.e. parallel to the prevailing winds, occurs to the south and west of the Thar. The transverse dunes, aligned across the wind direction, to the east and south of Thar and barchans, with the conclave sides facing the wind in the interior, predominant in Central Thar. On the whole the Thar Desert slopes imperceptibly towards the Indus Plain and surface unevenness is mainly due to sand dunes. The dunes in the south are higher, rising sometimes to 152 m whereas in the north they are lower and rise to 16 m above the ground level.
The Aravalli Range forms the main landmark to the south-east of Thar Desert. The more humid conditions that prevail near the Aravallis prevent the extension of Thar Desert towards the east and the Ganges Valley. In the heart of the sand covered area, the bare, dune free country of Barmer, Jaisalmer and Bikaner present an anomaly.

Desert soils
The soils of the Arid Zone are generally sandy to sandy-loam in texture. The consistency and depth vary according to the topographical features. The low-lying loams are heavier and may have a hard pan of clay, calcium carbonate (CaCO3) or gypsum. The pH varies between 7 and 9.5. The soils improve in fertility from west and northwest to east and northeast. Desert soils are Regosols of wind blown sand and sandy fluiratile deposits, derived from the disintegration of rock in the subjacent areas and blown in from the coastal region and the Indus Valley. The desert soils occupy the districts of Jodhpur, Bikaner, Churu, Ganganagar, Barmer, Jaisalmer, and Jalore. The Thar consists mainly of the wind-blown sand. The area is covered not only by sheet of sand but also of rocky projections of low elevations which constitute the older rocks of the country. Water is scarce and occurs at great depths, from 30 to 120 m below the ground level.
Some of these soils contain a high percentage of soluble salts in the lower horizons, turning water in the wells poisonous. Being poor in organic matter they show a low loss on ignition. They contain varying amount of calcium carbonate.