The Thar Desert (Rajasthani pronunciation: [t̪ʰaːɾ]), also known as the Great Indian Desert, is an arid region in the north-western part of the Indian subcontinent stretching across India and Pakistan. Covering an area of 264,091 km2 (101,966 sq mi), it is one of the largest subtropical deserts in Asia by area. About two-thirds of the desert area lies in India, with the remainder in Pakistan. It forms about six percent of the geographical area of India, with the majority of the desert lying in the state of Rajasthan, with portions extending into Gujarat, Haryana, and Punjab. Towards the west, it extends into the provinces of Sindh and Punjab in Pakistan. It is bordered by the Indo-Gangetic Plain to the north, west and northeast, Rann of Kutch to the south, and the Aravalli Range to the east. During the Last Glacial Maximum, an ice sheet covered the Tibetan Plateau, which reflected more solar radiation into space, resulting in cooling the overlying atmosphere during that period. Without the thermal low pressure caused by the heating, there was no monsoon over the Indian subcontinent, which led to the deposition of dust and the desertification of the region. The upliftment of the Aravallis brought about changes in the hydrography of the region, and the Ghaggar-Hakra River system that fed the region dried up, and the region became increasingly arid. Over the years, wind blown sediments and sand from the alluvial plains and the coast accumulated in the region. The topography consists of sandy plains intercepted by eroded hills of low elevation. The region has a tropical desert climate with extremely hot summers and cooler winters. Majority of the rainfall is received from the southwest monsoon, which on average is less than 500 mm (20 in) annually. The rainfall varies over the years, often with large spells of drought. There are very few sources of water, with the inland Luni River system being the only major river system in the region. Rain water is often stored in natural and man-made reservoirs for use in the dry season. The natural vegetation of the region is composed of trees, thorny scrubs and scattered grasslands. The desert is home to several animal and bird species. The Thar Desert is one of the most widely populated deserts in the world, with the Thar people inhabiting the area. The population is clustered into small villages, with majority of them nomadic in nature. Limited agriculture, herding of animals, and ecotourism drive the economy of the region.
Geography The Thar Desert is located in the north-western part of the Indian subcontinent stretching across the border between India and Pakistan, and is the eastern most extension of the Sahara–Arabian desert formation. It is spread across an area of 264,091 km2 (101,966 sq mi), with 195,091 km2 (75,325 sq mi) of the desert area lying in India, with the remaining in Pakistan. The desert forms about six percent of the geographical area of India, with the majority of the desert lying in the state of Rajasthan, with portions extending into Gujarat, Haryana, and Punjab. Towards the west, it extends into the provinces of Sindh and Punjab in Pakistan. The northeastern part of the Thar Desert lies between the Aravalli Hills, which separates the same from the Central highlands and the Indo-Gangetic Plain to the east. The desert stretches from the alluvial plains of the Indus River in the west and northwest, to the Great Rann of Kutch in the south.
Origin and formation
In the Mesozoic era (252 to 66 mya), the area was a low lying peneplain, covered by shallow waters. Erosion resulted in the formation of three layers of planation surfaces during the post-Mesozoic (66 to 2.6 mya), and early Pleistocene (2.6 mya to 11,000 years ago) periods. As the Himalayas arose during the mid-Miocene period (23.4 to 5.3 mya), it gave rise to the monsoon. During the Last Glacial Maximum (26,000–20,000 years ago), an estimated 2,400,000 km2 (930,000 sq mi) ice sheet covered the Tibetan Plateau. The low latitude ice sheet significantly affected radiative forcing, and reflected at least four times more solar radiation per unit area into space than ice at higher latitudes, resulting in further cooling of the overlying atmosphere during that period. Without the thermal low pressure caused by the heating, there was no monsoon over the Indian subcontinent. This lack of monsoon caused extensive rainfall over the Sahara region, while resulted in more dust deposited towards the Arabian Sea in the east. It also resulted in changes to the biotic life zones on the Indian subcontinent, as fauna responded to this shift in climate with species like Javan rusa deer migrating into India. The Aravalli Range formed rapidly, and reached significant altitude during the early Holocene period (11,700 years ago). Between 10,000 and 8,000 years ago, a channel of the Ghaggar-Hakra River, identified with the paleo Sarasvati River, after its confluence with the Sutlej River flowed into the Nara River, a delta channel of the Indus River, but then changed its course. The upliftment of the Aravallis brought about changes in the hydrography of the region, with an increase in waters flowing through the Yamuna River, while depriving the headwaters of the Ghaggar-Hakra system. This left the Ghaggar-Hakra as a system of monsoon-fed rivers that no longer reached the sea, which ended up in the Thar desert. Starting from around 4,500 to 5,000 years ago, when the monsoons that fed the river system diminished further, as the Aravallis blocked the monsoon winds from the east, the region became increasingly arid. The Indus Valley Civilisation had prospered in the area, with several settlements along the course of the river system. When monsoons diminished even further, the dried-up Hakra became an intermittent river, and the urban Harappan civilisation declined, becoming localized in smaller agricultural communities. Over the years, sand accumulated due to wind-blown sediments from the alluvial plains and the coast.
Topography and geology
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