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• The earth is approximately 460 million years old.
• The Islands of this archipelago have storm beaches consisting of unconsolidated pebbles, shingles, cobbles and boulders on the eastern seaboar.
• Over these long years, the earth has undergone many changes brought about primarily by the endogenic and exogenic forces.
• These forces have played a significant role in giving shape to various surface and subsurface features of the earth.
• The Indian plate which was to the south of the equator millions of years ago was much larger in size and the Australian plate was a part of it.
• Over millions of years, this plate broke into many parts and the Australian plate moved towards the south eastern direction and the Indian plate to the north.
• The northward movement of the Indian plate is still continuing and it has significant consequences on the physical environment of the Indian subcontinent.
• The present geological structure and geomorphologic processes active in the Indian subcontinent came into existence through the interplay of these endogenic and exogenic forces and lateral movements of the plates.
• Based on the variations in its geological structure and formations, India can be divided into three geological divisions: The Peninsular Block, The Himalayas and other Peninsular Mountains, and the Indo-Ganga-Brahmaputra Plain.
• The northern boundary of the Peninsular Block is a line running from Kachchh along the western flank of the Aravali Range near Delhi and then roughly parallel to the Yamuna and the Ganga as far as the Rajmahal Hills and the Ganga delta.
• Karbi Anglong and the Meghalaya Plateau in the northeast and Rajasthan in the west are also extensions of the Peninsular Block.
• The northeastern parts of the Peninsular Block are separated by the Malda fault in West Bengal from the Chotanagpur plateau.
• In Rajasthan, the desert and other desert-like features overlay the Peninsular Block.
• The Peninsula is formed by a great complex of very ancient gneisses and granites, which constitutes a major part of it.
• As a part of the Indo-Australian Plate, the Peninsular Block has been subjected to various vertical movements and block faulting.
• The rift valleys of the Narmada, the Tapi and the Mahanadi and the Satpura block mountains are examples of these movements.
• The physiography of Manipur is unique by the presence of a large lake known as ‘Loktak’ lake at the centre, surrounded by mountains from all sides.
• The Peninsular Plateau is a triangle in shape, rising from the height of 150 m above the river plains up to an elevation of 600-900 m.
• South of the Bhabar is the Tarai belt, with an approximate width of 10-20 km where most of the streams and rivers re-emerge without having any properly demarcated channel.
• The general elevation of the plateau is from the west to the east.
• The Peninsular India is made up of a series of plateau regions such as the Hazaribagh plateau, the Palamu plateau, the Ranchi plateau, the Malwa plateau, the Coimbatore plateau and the Karnataka plateau, etc.
• The Barak is an important river in Manipur and Mizoram.
• The south of Tarai is a belt consisting of old and new alluvial deposits known as the Bhangar and Khadar respectively.
• The maximum depth of alluvium deposits varies between 1,000-2,000 m.
• The northwestern part of the plateau has a complex relief of ravines and gorges.
• The Northern Plains are formed by the alluvial deposits brought by the rivers - the Indus, the Ganga and the Brahmaputra.
• The streams and rivers coming from the mountains deposit heavy materials of rocks and boulders, and at times, disappear in this zone.
• Delhi ridge in the northwest, Rajmahal hills in the east, Gir range in the west and the Cardamom hills in the south constitute the outer extent of the Peninsular plateau.
• Some of the important physiographic features of this region are tors, block mountains, rift valleys, spurs, bare rocky structures, series of hummocky hills and wall-like quartzite dykes offering natural sites for water storage.
• The average width of these plains varies between 150-300 km.
• The western and northwestern part of the plateau has an emphatic presence of black soil.
• The Bhabar is a narrow belt ranging between 8-10 km parallel to the Shiwalik foothills at the break-up of the slope.
• These plains extend approximately 3,200 km from the east to the west.
• The Tarai has a luxurious growth of natural vegetation and houses a varied wild life.
• Mizoram, also known as the ‘Molassis basin’, is made up of soft unconsolidated rocks.
• The Deccan Plateau is bordered by the Western Ghats in the west, Eastern Ghats in the east and the Satpura, Maikal range and Mahadeo hills in the north.
• Narmada, tapti, Mahanadi, Godavari, Krishna, and cauvery are some of the important rivers.
• The Satpura range is formed by a series of scarped plateaus on the south, generally at an elevation varying between 600-900 m above the mean sea level.
• The Satpura range forms the northernmost boundary of the Deccan plateau.
• The Northeastern Plateau is an extension of the main Peninsular plateau.