Aravalli Range and Thar Desert: Peaks, Passes and Dunes

Two landforms decide almost everything about Rajasthan: an old worn mountain chain running across the middle of the state and a sand desert spread to the west of it. The Aravalli Range is the oldest fold mountain system of India, and the Thar, the Great Indian Desert, is the largest desert in the country. Where the rain falls, where the rivers run, where canals had to be dug and where the towns grew all follow from the line the Aravalli draws. These notes give the range and the desert in the order the Rajasthan papers ask them, with the peaks, passes, dunes, rivers and lakes that are asked by name.

The Aravalli Range

The Aravalli is a Precambrian fold mountain system, worn down by erosion over hundreds of millions of years into a chain of residual hills. It runs from Palanpur in Gujarat through Rajasthan to the Delhi ridge near Raisina hill, a distance of about 692 kilometres, of which roughly 550 kilometres lie in Rajasthan. Its trend is from south-west to north-east. South of Ajmer the range is continuous and high; north of Ajmer it breaks into scattered, lower hills across Shekhawati and Alwar. Because the range runs parallel to the Arabian Sea branch of the south-west monsoon instead of standing across it, it cannot force those winds to rise, and the land to its west stays dry. That single fact explains the Thar.

The southern section around Mount Abu is the Abu block, and between Gogunda and Kumbhalgarh in Udaipur lies the Bhorat plateau, the highest plateau of the range. Mount Abu in Sirohi district is the only hill station of Rajasthan and holds Nakki Lake and the Dilwara temples. Passes cut the range at a few places, the best known being Haldighati between Rajsamand and Udaipur and Desuri Nal in Pali. The Aravalli is also a water divide: the Banas and the Chambal system drain east through the Yamuna to the Bay of Bengal, while the Luni and the Sabarmati drain west to the Arabian Sea. Mineral wealth follows its rocks, with zinc and lead at Zawar in Udaipur, copper at Khetri in Jhunjhunu and marble at Makrana in Nagaur.

The Thar Desert

The Thar, or Great Indian Desert, lies west and north-west of the Aravalli and extends into Gujarat, Punjab and Haryana, and beyond the border into Pakistan. It covers roughly three-fifths of the area of Rajasthan and is the most densely populated desert in the world, since its settlements grew around wells, canals and caravan routes rather than being empty sand. Jaisalmer, Barmer, Bikaner, Jodhpur, Churu, Nagaur, Sri Ganganagar, Hanumangarh and Jalore lie wholly or partly within it.

The desert is not one surface. The true desert, with less than twenty-five centimetres of rain, is called the Marusthali and lies in the far west; between it and the Aravalli lies the semi-arid Rajasthan Bagar, which gets more rain and carries dry stream beds. Sand dunes take several forms: barchans are the crescent-shaped dunes that move with the wind and are the most widespread, longitudinal or seif dunes lie parallel to the wind, transverse dunes lie across it and parabolic dunes are anchored by vegetation. Shifting dunes are called dhrian locally, and the flat tracts between dunes are used for the little cultivation there is.

Water in the desert

• Luni is the only large river of the desert. It rises in the Naga hills near Ajmer, flows south-west through Pali, Jodhpur, Barmer and Jalore and ends in the Rann of Kachchh; its water is sweet in the upper course and becomes saline below Balotra. Jojari, Sukri, Jawai, Bandi and Guhiya are its tributaries.
• Ghaggar is a dead river that disappears into the sands of Hanumangarh and Sri Ganganagar and is identified by many with the ancient Saraswati.
• Salt lakes are a feature of the inland drainage: Sambhar in Jaipur and Nagaur is the largest inland salt lake in India, and Pachpadra in Barmer, Didwana in Nagaur and Lunkaransar in Bikaner are the others asked by name.
• Indira Gandhi Canal, earlier the Rajasthan Canal, takes off from the Harike barrage in Punjab, below the meeting of the Sutlej and the Beas, and carries water about 649 kilometres into the north-western desert, turning parts of Sri Ganganagar, Hanumangarh, Bikaner and Jaisalmer into cropland.
• Traditional harvesting survives in the khadin of Jaisalmer, where run-off is held behind an earthen bund, and in tanka, nadi, johad, beri and toba structures.

Climate, wildlife and conservation

Rainfall falls away sharply from south-east to north-west: Mount Abu is the wettest place in the state while Jaisalmer receives the least rain, and summer brings the hot loo wind and the dust storms called andhi. The Desert National Park in Jaisalmer and Barmer districts, spread over about 3,162 square kilometres, protects this landscape and the great Indian bustard, the godawan, which is the state bird of Rajasthan. Khejri, the state tree, holds the sandy soil and feeds livestock, and the Bishnoi tradition of protecting it and the blackbuck is part of the same story. Shifting sand, overgrazing and falling groundwater remain the standing problems, and tree planting along the Aravalli is the main answer attempted against the eastward spread of the sand.