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Structure and tectonics of Kachchh region of western India: An appraisal

Physiographic Divisions
Taking into consideration the factors of altitude, slope and ruggedness of relief, Kachchh can be divided into four main physiographic units from north to south (Fig.2), viz; (1) The Ranns, (2) The Low Lying Banni Plain, (3) The Hilly Region, and (4) The Southern Coastal Plains.

The above four units show considerable diversity within each of them, depending on the rock types, their mode of occurrences and fault patterns.

The Rann is the most remarkable and unique feature of the Kachchh region occupying its northern and eastern parts, forming more than half of the areal extent of the Kachchh. It comprises a flat geomorphic terrain rising hardly upto 3 to 4 m above M.S.L, and is divisible into two parts, viz. the Great Rann occupying the northern part and the Little Rann forming the eastern and southeastern parts of the Kachchh. Within the Great Rann occur a chain of islands comprising Pachham, Khadir, Bela and Chorar, rising above the saline wasteland. The Rann area mostly remains dry except for the rainy season when it is covered by saline water. During summer and winter seasons, practically the whole region is covered with a fairly hard salt encrustation. Different aspects of the Rann have been described by a number of workers (Frere, 1879; Ghosh, 1981; Glennie and Evans, 1976 ; Roy and Merh, 1977 and Gupta, 1975).

The Plains of Banni represent an embayment between the Kachchh Mainland in the south, the uplifts of Pachham in the north, and the Wagad and the Bela uplifts in the east, and cover a wide area. These rise a little higher than the surrounding Rann and are covered with green grass and other shrubs. No outcrop is seen within these featureless plains. These receive water from the Mainland and the islands from the north and east respectively during rainy seasons.

The Hilly Region of the Kachchh consists of following three components:

1. Island Belt: It consists of four islands, viz. Pachham, Khadir, Bela and Chorar from west to east.
2. Mainland: The area lying to the south of Banni plains and extending upto the Gulf of Kachchh in south is called Mainland.
3. Wagad: This region lies to the NE of the Mainland and forms an isolated landmass.

The Mainland comprises a rocky terrain and broadly consists of two subparallel E-W trending hill ranges; viz the central highland and the northern hill range with an intervening low ground, and a southern coastal plain. Lithologically, the central highland is made up of Mesozoic rocks which southward have been separated from the Tertiary rocks and southern coastal plains by the Deccan trap basaltic rocks. Lithology and tectonics have played a very important role in the formation of present geomorphic features of the Kachchh Mainland. The northern hill range is bordered by the Banni plains and the Rann in the north and by the 80-140 m high upland areas in the south (Fig. 2). This hill range forms a chain of domes of Jurassic and Cretaceous rocks, and is flanked to the north by E-W trending Kachchh Mainland Fault (KMF). From west to east, it is marked by a series of domes like Jura, Jumara, Panjal, Keera, Lyari, Chari and Dhar Dongar and anticlines like Jhurio, Habo and Kas. The KMF has significantly controlled the physiography of this part of the terrain. On account of this fault, the northern slopes are steeper whereas the southern slopes coinciding with the dip of the strata are gentler. The southern coastal plains that border the Mainland and overlook the Gulf of Kachchh in the south and the Arabian sea in the west are made up of Tertiary and Quaternary sediments and form a 25-30 km wide belt showing very low gradient. These plains rise gradually from the high waterline to altitude of 80 m beyond which the ground tends to show a rather more conspicuous rise, merging into the central highland with a steeper gradient.

Drainage
The drainage of Kachchh provides an interesting example of a combination of lithologic and tectonic controls along with the influence of sea level fluctuations during Quaternary period. The Central highland forms the main watershed with numerous consequent streams draining the slopes with a radial pattern and pouring their water and sediment load into the Arabian sea, the Gulf of Kachchh and the plains of Banni and the Rann in west, south and north respectively (Fig. 3). The southward flowing streams include Naira, Kankawati, Chok, Sai, Vengdi, Kharod, Rukmawati, Khari, Nagavanti, Phot, Bhuki, Mitti, Sakra and Larekh streams which empty their water into the Gulf of Kachchh and the Arabian sea. The streams originating from the northern slopes of the Central highland, join the streams originated from the Northern hill rang e and pour their water into the Chhari, Bhukhi, Trambo, Kaila, Pur and Kaswali streams which, in turn, debouch into the Rann. In general, the streams are ephemeral (seasonal) and carry water only during good monsoon. Many streams like Kankawati, Kaswali, Kharod, Rukmawati and Bhukhi etc. show very broad channels and vertical cliffy banks in their lower reaches.

The drainage characteristics of the Kachchh Mainland and the relatively well carved valleys which now have only very little flowing water clearly point to the fact that the area had experienced a more wet climatic phase in the past during which the streams carried more water and sediment load and the stream dissection was more effective.


Fig 3. Drainage Map of Kachchh

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