The Peninsular Uplands are flanked by coastal plains of varied width extending from Kachchh to Orissa. But there is striking difference between the western and the eastern coastal plains. With the notable exception of Gujarat the west coast has a narrow alluvial margin interspersed by hilly terrain and characterised by wet climate.
It is a submerged coast and hence tilting has left no scope for depositional action of the rivers. The backwaters are the characteristic features of this coast. It has little indentations except in the south where the beautiful lagoons introduce an element of diversity and the plains are wider. From Kachchh t Cape Camorin it has a total length of 1,840 km and an average width of 10-15 km tin Gujarat 300 km).
The East Coast Plains, on the other hand, are broader, associated with depositional activity of rivers and witness comparatively drier climates. It stretches about 1,800 km from Mahanadi mouth to Cape Camorin with an average width of 60 km. It is acoast of emergence in which the deltas of Mahanadi, the Godavari, the Krishna, and the Kaveri etc. are characteristic features of the coast. Here the formation of the deltaic plain into the sea is still continuing.
According to some geologists the origin of the western and eastern coasts of India may be attributed to faulting and subsidence of the Arabian Sea and Bay of Bengal blocks towards the close of the Eocene period. Consequently alluvial deposits along these coasts are of very recent in origin, ranging in age from Pliocene to recent times.
An examination of coastlines along these coasts shows evidences of emergence and submergence. According to Krishnan (1982, p. 63) an important marine transgression took place during the Mid Cretaceous period, both along the southern part of Assam plateau and in the coastal region of southern Tamil Nadu.
The Anadaman Sea, i.e., the basin between Myanmar and the Andamans probably took shape at the end of the Cretaceous. The Andaman Sea was probably much shallower originally but was faulted down later to its present depth (2,000 fathoms) (Krishnan, 1982, p. 63). E. Ahmad has divided the coasts of India into ten sections on the basis of their characteristic features and mode of formation.
1. North Circar Coast between the Ganga and Krishna deltas is mainly a coast of emergence. It is full of beaches, sand dunes and spits. The entire area is dominated by deltaic deposits and there is hardly any cliff visible along the coast. The most important physiographic feature of this area is Chilka lake on the Ganjam coast which was formed during the Pleistocene period.
2. Coromandel Coast extending from the delta of Krishna to Cape Camorin is fairly straight. It is also an example of coast of emergence with deltaic deposits of Krishna, Kaveri, Penner etc. There is abundance of off-shore bars along the coast but absence of cliffs and lagoons. Recently there have been some archaeological evidences of suhmeij gence along the Tamil Nadu coast.
3. The Malabar Coast between Cape Camoi and Goa is a compound coast depicting mixed features of submergence and emergence. While goons (locally called Kayals), offshore bars spits indicate emergence, the back waters and cliff support submergence.
4. The Konkan Coast between Karwar and Bulsar is capped by the Deccan lava and is a typical example of submerged coast. Here sea cliffs, wattle cut platforms, sea caves, stacks; rocky islands, natural bridges etc. are characteristic features along the coast.
5. From Bulsar to Bhavnagar the coast 1 also presents evidence of submergence. Here Narmai and Tapi rivers have formed long estuaries and extensive swamps.
6. The Kathiawar Coast between Bhavnagai and Diu displays signs of submergence (entrench estuaries, estuary islands) and emergence (straight shoreline and off sore bars).
7. South-west of Kathiwar between Verval and Dwarka the coast shows straight shore, offshore bars, swamps and spits.
8. The coast along the Gulf of Kachchh is characterised by estuary and isolated islands. It also depicts swamps and cliffs formed by the lava flows.
9. The Lakshadweep coast is characterised by coral reefs. It is a neutral coast without any evidence of submergence and emergence.
10. The coast around the Andaman and Nicoh islands is a mixed coast exhibiting signs of summer gene and emergence. The coast presents features like cliffs, submerged river channels, coral deposits and mangrove forests.