ପ୍ରାକୃତିକ ବିଭାଗ || class 9 geography chapter-1 in odia || part-2 || ପ୍ରାକୃତିକ ବିଭାଗ / ଭୌତିକ ବିଭାଗ

#prakrutika_bibhaga #class9geography #physiographic_unit India is divided into six physiographic divisions on basis of the varied physiographic features: units as follows: Northern and North-eastern Mountain; Northern Plain; Peninsular Plateau; Indian Desert; Coastal Plains; and Islands. Unit # 1. The Himalayas: The Himalayas consist of a series of parallel mountain ranges that stretch in a north-west to south-east direction. It has been recognised as a natural guard on the north of the sub-continent. The total length of the Himalayas is about 2415 kilometres and is considered to have consisted of four main sections separated by the gorges of different rivers. The Himalayas is the highest mountain range in the world. The Himalayan Mountain ranges were formed by the sediment collected on the bed of the Tethys Sea for millions of years. The sediments might have been derived from the two stable land masses—Angara land to the north and peninsular landmass to the south. Geologists believe that the lateral force came from the northern Angaraland, and the sedimentary strata resting on the Tethys floor were tightly squeezed against the southern rigid mass of peninsular India, commonly known as Gondwanaland. As a result, the Himalayas originated as folded mountains. The Himalayas follow a general west to east direction exactly in conformity with the alignment of the Tethys Sea. The other mountains like Aravalli, Rajmahal and Meghalaya originated from the Gondwanaland, and are situated approximately in the north-south direction. Geological studies reveal that the Himalayas came into the present stage as results of the development during three geological phases or epoch. During the first phase, the middle Himalayan range was raised during the Oligocene Epoch or era. This range is formed of the old crystalline and old sedimentary rocks. The squeezing of the Himalayas for the second epoch took place during Miocene era. During this period the sediments of the Potwar Basin (now in Pakistan) were raised. The squeezing of the Himalayas for the third time took place during the later part of the Pliocene era. The Siwaliks were formed during this time. An examination of the location and direction of the north-western part and the part located in the Indo-Myanmar border of the Himalayas, clearly indicates that the lateral pressures were exerted against the Gondwana landmass from the north-west and from the eastern side of the sub-continent. Again some other geologists and earth scientists offer an opposite view against the one mentioned above. They believe that the lateral pressures were exerted by the Gondwana landmass against the Angaraland. That is, the pressure came from south towards north. International debates are going on till now in support of and against the two schools of thought. However, the first hypothesis is found to be more acceptable. 1. The Punjab Himalayas extending over a distance of 560 km between the Indus and the Sutlej. 2. The Kumaon Himalayas between the Sutlej and the Kali stretching over a distance of 320 km. 3. The Nepal Himalayas between the Kali and the Tista stretching over a distance of 800 km. 4. The Assam Himalayas extending over a distance of 720 km between the Tista and the Tsangpo-Brahmaputra in the east. Similarly, the Himalayan mountain chain, when arranged in longitudinal direction, is found to consist of three main series of parallel ranges. They are separated by Longitudinal Valleys of tectonic origin. From the Indus-Ganga-Brahmaputra plain in the south towards the north, the three ranges are identified as: (a) The Siwalik or Sub or Outer Himalayas (b) The Mid or Lesser Himalayas (c) The Great or Inner Himalayas The existence of the undulating erosional plains of Aksai Chain, Deosai, Depsang and Lingzi Tang at high altitude within the Himalayas indicates that these plains were formed due to erosional activities much before the formation of the Himalayas. On the other hand, there are many small longitudinal valleys. They are of tectonic origin and they are known as Duns. Dehra Dun, Kothri Dun, Path Dun and the Vale of Kashmir are some of the famous examples. The physiographic complexity of the Himalayas is found to have increased in altitude from the outer towards the inner Himalayas. The average height of the great Himalayas is 6091 metres. Almost all the world famous peaks are located here. Of them, Everest (8848 metres), Kanchanjunga (8598 metres), Dhawalgiri (8126 metres), Nanga Parbat (8125 metres), Nanda Devi (7817 metres) and Namcha Barwa (7756 metres) are important. The average width of the middle or lower Himalayas is about 80 km, and average height is 4500 metres. The average width of the outer or sub-Himalayas is only 10-50 km and average height between 900-1200 metres.