Indian subcontinent can be divided into following Physiographic regions:-
1- The Northern Mountain Region
2- The Great Northern Plains
3- The Great Peninsular Plateau (Deccan Plateau)
4- The Coastal Plains
5- The Great Indian Desert
6- The Island Groups.
1- The Northern Mountain Region
The Great mountain region extends uninterrupted for 2500 km from Jammu and Kashmir to Arunachal Pradesh in the West. Its on an average wider in the west(500 km) than in the east (200 km) due to greater compressive force in the east and thus highest mountain peaks of the world are located in Eastern Himalayas.
The Northern Mountain belt can further be divided into :-
(a) The Himalayan Mountain Region
(b) The Trans- Himalayan Mountain Region
(c) The Eastern or Purvanchal Hills
Physiographic Divisions of the Himalayas:-For a systematic study of the physiography and relief, the Himalayas may be divided into the following four divisions from north to south:
The Greater Himalayas
The Lesser Himalayas
The Shiwaliks or the Outer Himalayas.
- The Trans-Himalayas:-about 40 km wide, contain the Tethys sediments.The rocks of this region contain fossils bearing marine sediments which are underlain by ‘Tertiary granite’.partly metamorphosed sediments and constitutes the core of the Himalayan axis. a great accumulation of debris in the valleys of defeated streams which could not maintain their southerly course across the rising barrier of the Himalayas.
- The Greater Himalayas:-rise abruptly like a wall north of the Lesser Himalayas.The Main Central Thrust separates the Greater Himalayas from the Lesser Himalayas.about 25 km wide with an average height above 5000 metres. Almost all the lofty peaks of the Himalayas lie in this zone. composed of crystalline, igneous or metamorphic rocks (granite, schists, and geneiss). The basal complex of the Himalayas is Archaean. At places, due to heavy thrust, older rocks are found overlying the newer rocks. almost a contiguous range. very few gaps mainly provided by the antecedent rivers. receive less rainfall as compared to the Lesser Himalayas and the Shiwaliks. Physical weathering is pronounced. Erosion is, however less effective over the Greater Himalayas as compared to the Lesser Himalayas. Being lofty, they have very little forest area.
- The Lesser Himalayas:-about 80 km with an average height of 1300-5000 m. consists, generally, of unfossiliferous sediments or metamorphosed crystalline. main rocks are slate, limestone and quartzites. Along the southern margin of the Lesser Himalayas lies the autochthonous belt of highly compressed Upper Palaeozoic to Eocene rocks, often containing volcanic material. Examples of autochthonous belts are found between Murree and Panjal thrust in Kashmir, Giri thrusts in the Shimla region and Karol and Main Boundary Thrust (MBT) in Garhwal region. extensive erosion due to heavy rainfall, deforestation and urbanisation.
- The Shiwaliks or Outer Himalayas/Sub-Himalayas:-extend from jammu Division of jammu and Kashmir State to Assam. In width, Shiwaliks vary from 8 km in the east to 45 km in the west with an average elevation of about1300 m above sea level. not a continuous range. broader in the west and narrows down in the east. Between the Shiwaliks and the Lesser Himalayas are longitudinal valleys called Doons/ Duns. important Duns are Dehra Dun, Potli, Kothri, Kathmandu, Chumbi and Kyarda.
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