After reading this article you will learn about Physiography of Arid Zone:- 1. General Physiography of Arid Zone 2. Physiographic Divisions of Arid Zone.
General Physiography of Arid Zone:
The whole region is dry and bears a desolate appearance with blown sand as its main feature.
Generally, three types of sand dunes are present, namely:
(a) Longitudinal dunes,
(b) Barchans, and
(c) Transverse dunes.
The longitudinal dunes, lying parallel to the prevailing winds, occur mostly in the south and west; barchans, with their concave side facing the wind, occur in the interior; and the transverse dunes aligned to the wind direction arc to the north and east where the dunes are stabilized due to vegetation.
In the Indian arid zone there are old river courses namely the Saraswati, the Ghaggar, the Luni etc. Most of these had dried up during historic times. Luni is the only river of any consequences in this area. It rises in the Aravalli hills near Ajmer and flows west by south west into the Runn of Kutch. Its chief tributaries are the Lilri, the Sukri, the Jawai, the Guhiya, the Bandi.
The region has two slopes—westwards to the Indus valley and southwards to the Runn of Kutch. More than half of the surface is between ISO UK) in in height and almost one-third (east of Bikaner) is between 300-500 metres. West of Jaisalmer the ground level falls to below 100 metres and the lower Luni valley is the most low-lying part of the region, rarely exceeding 20 metres.
In general, the eastern part of the zone is of an undulating nature, while further west it becomes almost a level plain containing a few or rare hills especially in western Jaisalmer. The main features to the north of Jaisalmer plain are a number of Playa lakes (Runns) which remain dry for the greater part of the year.
The main agents of denudation working in western Rajasthan are the diurnal changes in temperature and the impact of sand-laden winds. The former causes cracks in the rocks by the process of exfoliation, and the latter produces sculpturing and polishing effects on projecting rocks. In the neighbourhood of Jaisalmer, where the rocks are exposed above the ground, they reveal a characteristic erosional topography of the desert region.
Physiographic Divisions of Arid Zone:
Physiographically the whole of western Indian arid zone could be divided in to eight divisions, each of which has its own distinctive topography. However, the boundaries of these divisions could not be taken as rigid because of the dynamic nature of the sand.
This region, covered with a thick layer of sand with occasional rock projections, lies in the south-west. To the north it extends up to the dune free region of Jaisalmer, while the eastern boundary is marked by the Luni and the Little Desert.
The sand dunes resemble sea waves and are arranged at first NE-SW and then ENE-WSW. In the west (N. Barmer and S. Jaisalmer) the sand hills are quite conspicuous and attain a height of even 150 metres.
These sand hills, though running in a line, are mostly unconnected. In the western part of the region, in the neighbourhood of Jaisalmer town the soil is very stony and several low rocky ridges and undulating plains occur.
Dune-Free Region of Barmer-Jaisalmer:
Surrounded by the Great Desert from three sides (north, west and south) and embracing the little desert in the east lies a region of peculiar topography. This region (covering eastern Jaisalmer and western Jodhpur, in the form of a saddle and surrounded by sand dunes from all sides) is conspicuous by its dune-free topography and few isolated rocky projections.
North-east of the dune-free region of Bikaner lies the Little Desert, the eastern boundary of which is marked by the steppe desert. The region covers parts of Jodhpur, Bikaner, western Nagpur and south-western Churu.
The topography consists of undulating sand hills from 6 to 30 metres high and their slopes are furrowed by the action of-the winds. Seventy kilometers north-west of Bikaner is a small outcrop of the Vindhyan Sandstone which is largely queried for building purposes.
Between the southern limit of Little Desert and the dune-free region of jaisalmer lies the Bap-Phalodi region. In this region sand dunes attain a considerable height (100-130 metres), giving it a distinctive physiography. A large part of the area is covered by sand dunes of the transverse type and isolated hills of solid rock.
In the extreme north is a region which still bears the testimony of more humid conditions in the past as there are large numbers of dry river beds and ancient channels, now waterless and abandoned. These ancient abandoned river beds are flanked by continuous sand ridges.
In Bikaner the dried up bed of the Ghaggar is traced clearly in a westerly direction till it reaches the town of Hanumangarh. South-east of Hanumangarh the river bed is marked by sand ridges on both the sides.
North-Faster n Sand Hills Region:
Sand-witched between the Aravalli foreland and the Little Desert and extending 250 kins up to the Luni is a narrow zone of sand hills. The region on is studded with longitudinal sand hills along with basins of inland drainage associated with high temperatures and the consequence is the local deposits.
This region is dominated by the Aravalli mountain system. The Aravalli range runs diagonally due north, east, south west form south east of Sirohi district to near Delhi extending over a length of about 700 km. North of the Luni and west of Aravllis a belt of steppe country extends westwards and mergers imperceptibly into desert.
This is more or less a rocky plateau turned into a peneplain of arid wasteland due to denudation. The finer material is carried away by winds and spreads over large areas of barren country Occasional exposers of bed rock in this region are present.
Between the Great Desert and the sub-mountain zone lies the Luni basin. The Luni and its half a dozen tributaries have dissected the region to a plain. The eastern bank of the Luni is comparatively flat and has less dunes than the western bank.