Geological Divisions of India

The earth is approximately 460 million years old. Over these long years, it has undergone many changes brought about primarily by the endogenic and exogenic forces. We already know about the Plate Tectonics and the movement of the Earth’s plates. According to the Tectonic theory, Indian plate was a part of greater plate south of the equator millions of years ago. Since the breakage of that plate, Indian plate is undergoing continuous movement northward, even today. This northward movement has significant consequences on the physical environment of the Indian subcontinent.

So basically, present geological structure and geomorphologic processes came through:

  1. the interplay of these endogenic and exogenic forces and
  2. lateral movements of the plates

Based on the variations in its geological structure and formations, India can be divided into three geological divisions:

  1. The Penisular Block 
  2. The Himalayas and other Peninuslar Mountains 
  3. Indo-Ganga-Brahmaputra Plain

Physiography verses Geology

Physiography (or physical geography) is that branch of natural science which deals with the study of processes and patterns in the natural environment like the atmosphere, hydrosphere, biosphere, and geosphere.

Geology is an earth science concerned with the solid Earth, the rocks of which it is composed, and the processes by which they change over time. Geology can also refer generally to the study of the solid features of any terrestrial planet.

Three Geological Divisions of India

The Penisular Block

Extent

  • Northern boundary: Kachchh -- western flank of Aravali Range -- Yamuna and Ganga -- Rajmahal Hills -- Ganga delta.
  • Karbi Anglong and Meghalaya Plateau in the northeast and Rajasthan in the west are also extensions of this block.
  • The northeastern parts are separated by the Malda fault in West Bengal from the Chotanagpur plateau.
  • In Rajasthan, the desert and other desert–like features overlay this block.

Composition

  • Peninsula is formed by a complex of very ancient gneisses and granites, which constitutes a major part of it. 
  • Since the Cambrian period, the Peninsula has been standing like a rigid block with the exception of some of its western coast which is submerged beneath the sea and some other parts changed due to tectonic activity without affecting the original basement. 
  • As a part of the Indo-Australian Plate, it has been subjected to various vertical movements and block faulting. The rift valleys of Narmada, Tapi and Mahanadi and Satpura block mountains are some examples of it. 
  • The Peninsula mostly consists of relict and residual mountains like Aravali hills, Nallamala hills, Javadi hills, Veliconda hills, Palkonda range and Mahendragiri hills, etc. 
  • The river valleys are shallow with low gradients.
  • Most of the east flowing rivers form deltas before entering into the Bay of Bengal. The deltas formed by Mahanadi, Krishna, Kaveri and Godavari are important examples.

The Himalayas and other Peninuslar Mountains

Composition

  • The Himalayas along with other Peninsular mountains are young, weak and flexible in their geological structure unlike the rigid and stable Peninsular Block. Consequently, they are still subjected to the interplay of exogenic and endogenic forces, resulting in the development of faults, folds and thrust plains
  • These mountains are tectonic in origin.
  • These are dissected by fast-flowing rivers which are in their youthful stage. Various landforms like gorges, V-shaped valleys, rapids, waterfalls, etc. are indicative of this stage.

Indo-Ganga-Brahmaputra Plain

Composition

  • The plains formed by the rivers Indus, Ganga and Brahmaputra were geo-synclinal depressions. They attained maximum development during the third phase of Himalayan mountain formation approximately about 64 million years ago.
  • Since then, it has been gradually filled by the sediments brought by the Himalayan and Peninsular rivers. Average depth of alluvial deposits in these plains ranges from 1,000-2,000 m.