S TRUCTURE AND P HYSIOGRAPHY C H A P T E R Palkonda range and the Mahendragiri hills, etc. The river valleys here are shallow with low gradients. You are aware of the method of calculating the gradient as a part of your study of the book Practical Work in Geography– Part I (NCERT, ). Can you calculate the gradient of the Himalayan and the Peninsular rivers and draw the comparisons?
Most of the east flowing rivers form deltas before entering into the Bay of Bengal. The deltas formed by the Mahanadi, the Krishna, the Kaveri and the Godavari are important examples. T HE H IMALAYAS AND OTHER P ENINSULAR M OUNTAINS 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, 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. I NDO -G ANGA -B RAHMAPUTRA P LAIN The third geological division of India comprises the plains formed by the river Indus, the Ganga and the Brahmaputra.
Originally, it was a geo-synclinal depression which attained its maximum development during the third phase of the Himalayan mountain formation approximately about 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 , - , m. It is evident from the above discussion that there are significant variations among the different regions of India in terms of their geological structure, which has far-reaching impact upon other related aspects.
Variations in the physiography and relief are important among these. The relief and physiography of India has been greatly influenced by the geological and geomorphological processes active in the Indian subcontinent. P HYSIOGRAPHY ‘Physiography’ of an area is the outcome of structure, process and the stage of development. The land of India is characterised by great diversity in its physical features.
The north has a vast expanse of rugged topography consisting of a series of mountain ranges with varied peaks, beautiful valleys and deep gorges. The south consists of stable table land with highly dissected plateaus, denuded rocks and developed series of scarps. In between these two lies the vast north Indian plain. Based on these macro variations, India can be divided into the following physiographic divisions: