Thar Desert
The Thar Desert, 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. Spread across an area of, it is one of the largest subtropical deserts in Asia by area. About two-thirds of the desert area lies in India, with the remaining in Pakistan. It forms about six percent of the geographical area of India, with 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 Aravali 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 obtained from the southwest monsoon, which on average is less than 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 eco tourism 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, with 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 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, 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, and early Pleistocene periods. As the Himalayas arose during the mid-Miocene period, it gave rise to the monsoon.During the Last Glacial Maximum, an estimated 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. 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 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
The eastern part of the Thar Desert, that lies in the western foothills of the Aravallis, consists of sandy plains intercepted by eroded hills of low elevation. It rises to about in elevations as it reaches the Aravallis, which continue as the plateau of the central India beyond the range. The sandy plains extend across to the west, with the altitude dropping to at the India-Pakistan border. Much of the desert area is covered by sand dunes that are formed due to accumulation of wind blown sand deposited over the sediments from the alluvial plains. The sand is highly mobile due to the strong winds that rise each year before the onset of the monsoon. Much of the bedrock is composed of igneous and metamorphic rocks.The geology of the region varies across its area. The oldest rocks are found in the Barmer region in the south, which are volcanic rocks composed of felsite. In the Pokhran area, there are various colored shales, with varying hardness. Pale colored sandstones composed primarily of quartz are found south of Jodhpur. Sandstones with fossils belonging to the Jurassic period are found to the east of Balmer, and to the east and north of Jaisalmer. In the Jaisalmer region, the underlying sandstone beds are covered with layers of sandstone and limestone, which also consist of numerous fossils, and are used extensively as building materials. Towards the west and north west of Jaisalmer, a tract of dark coloured sandstone rocks with calcium, capped by red coloured red sandstone layer, and interspersed with yellow ammonite rocks.
Climate and hydrography
The region has a desert climate. In the summer months of April to June, average maximum temperature ranges with average minimum of. The maximum temperature often reaches above during the peak summer. In the winter months of December to February, the minimum temperature reaches, with average maximum of with average minimum of. The region receives most of the rainfall during the southwest monsoon from June to September. Average annual rainfall ranges from, and occurs during the short July-to-September southwest monsoon. The distribution of rainfall also varies significantly across years. The semi arid parts in the east have fewer sand dunes and receive slightly more precipitation.The depth of the water table in the region varies between, and the water is mostly brackish. The region is drained by a minor inland river system. Luni River is the longest and major river in the desert. Other minor rivers that form part of the Luni river system include Bandi, Ghaggar, Guhiya, Jawai, Jojari, Liladi, and Sukri rivers. There are numerous endorheic salt water lakes-Sambhar, Kharaghoda, Didwana, Pachpadra, and Phalodi. These lakes accumulate water during the monsoon rains and often evaporate slowly during the dry season. The salt content of these lakes comes from the weathering of the surounding rocks in the region. The -long Indira Gandhi Canal, which channels water from the Indus River system, is a major source for irrigation and drinking water. Water reservoirs known as tobas, johads and taankas are used to store rain water.
History
Lithic tools belonging to the prehistoric Aterian culture of the Maghreb from the Middle Paleolithic era have been found in the Thar Desert. The Indus Valley Civilization flourished along the vicinity of the Ghaggar-Hakra River between 3300 BCE to 1300 BCE. After the collapse of the Indus Valley Civilisation, which occurred around 1900 BCE, groups of Indo-Aryan peoples migrated into north-western India and started to inhabit the region. During the Vedic period, various tribes inhabited the region, and the Kuru kingdom, the earliest Vedic state was formed by a super-tribe which joined several tribes in a new unit. Prior to the "second urbanisation" that occurred in the Indo-Gangetic Plains, small settlements of the Painted Grey Ware culture arose in the Ghaggar-Hakra valley.By the third century BCE, a large part of the Indian subcontinent was under the control of the Mauryan Empire, including portions of the desert. The Kushan Empire expanded out of what is now Afghanistan into the northwest of the Indian subcontinent in the middle of the 1st century CE. The Gupta Empire flourished between the 2nd and 6th centuries CE, reaching its peak in the 5th century CE, when its territory incorporated the present Thar Desert region. In the eastern part of the region, the Brahmin dynasty ruled in the 7th to 8th centuries CE, which was later annexed to the Umayyad Caliphate in early 8th century CE, and the Abbasid Caliphate later. The Pratihara dynasty ruled the eastern part of the region between the 8th and 11th centuries CE. Mahmud of Ghazni annexed the region to the Ghaznavid Empire in the 11th century CE.
In the later Middle Ages, the western part of the region was ruled by several Rajput states. These states started forming in the late 7th century CE, and rose to political prominence later. The eastern part of the region was ruled by the Soomras, and the Sammas from later 11th to early 16th century CE. The period was marked by the conflict between the Mughal Empire and the other dynasties that ruled the region. The conflict originated with the invasion by Timurid king Babur, which was resisted by the Rajput states under Rana Sanga. The conflicts continued for over 200 years, with the initial phase remaining indecisive. The Mughals gained an upper hand between the mid 15th and late 16th centuries, while the Rajputs retook control later after the Mughal empire began to collapse in the late 16th century. The Marathas took control over most of the region in the 18th century CE. In 19th century CE, the region came under the suzerainty of the British Raj, wherein it was composed of a large number of princely states, with powers divided amongst the local rulers and the British.
The partition of India resulted in the formation of the independent states of India and Pakistan, and the Thar Desert region was split between the two countries. It resulted in large scale conflicts, and mass migration of people across the borders. After the Political integration of India, and reorganisation of Indian states, majority of the eastern part of the desert became part of the Rajasthan state, with minor portions in Haryana, Punjab, and Gujarat. The western third became part of the Sindh and Punjab provinces in Pakistan. In 1965 and 1971, further population exchanges took place in the Thar region between India and Pakistan; 3,500 people, mostly Muslims, moved from India to Pakistan, while thousands of Hindu families migrated from Pakistani to the Indian section.