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ne pa  India as a
tropical country: The temperate part (north of Tropic of Cancer) is twice the
area of tropical part.But India has
always been treated as a tropical country for two different reasons – physical and cultural: Physical
Reasons: The country is separated from the rest of
Asia by Himalayas. Its climate is dominated by the tropical monsoons and the
temperate air masses are blocked by Himalayas. Entire area south of
Himalayas is essentially tropical from climatic point of view:
Although the night temperatures in winter at several places in North
India may come down to the level of those prevailing in temperate lands, yet
clear skies and intense insolation raise the day temperatures to a tropical
level. Cultural
Reasons: •
Settlements, diseases, agricultural and
primary economic activities are all tropical in nature. •
Hence, It is primarilybecause of Himalayas that India is a tropical country. STRUCTURE AND PHYSIOGRAPHY
OF INDIA •
Earth is approximately 4600 million years
old.Overtime it 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 earth.
Indian plate was south of equator, millions of years ago. It 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 Eurasianplate moved towards
south eastern direction and Indian plate to the north. This northward movement of the Indian plate
is still continuing and it has significant consequences on physical
environment of Indian subcontinent. It is primarily through the interplay of these endogenic and exogenic forces and lateral
movements of plates that present geological structure and geomorphologic
processes active in the Indian subcontinent came into existence. Based on the variations in its geological structure and
formations, India can be divided into three
geological divisions. These divisions follow the physical features: (i)
The
Peninsular Block (ii) The Himalayas and other Peninsular
Mountains (iii) Indo-Ganga-Brahmaputra Plain. |
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(i) The
Peninsular Block: Peninsular
Block Extension: •
The northern boundary of the Peninsular Block
- 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. •
KarbiAnglong and Meghalaya Plateau in the
northeast and Rajasthan in the west are also extensions of this block. •
The north-eastern parts are separated by Malda
fault in West Bengal from Chotanagpur plateau. (i)
Peninsular
block formation •
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, it 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 some examples of it. •
The Peninsula mostly consists of relict and
residual mountains like the Aravali hills, the Nallamala hills, the Javadi
hills, the Veliconda hills, the Palkonda range and the Mahendragiri hills,
etc. •
The river valleys here are shallow with low
gradients. 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. (ii) The Himalayas and other Peninsular Mountains •
The Himalayas 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 planes. •
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. (iii) Indo-Ganga-Brahmaputra
Plain •
The third geological division of India
comprises the plains formed by the river Indus, Ganga and Brahmaputra. •
Originally, it was a geo-synclinal depression
which attained its maximum development during the third phase of the
Himalayan mountain formation approximately 64 million years ago. •
Since then, it has been gradually filled by
the sediments brought by the Himalayan and Peninsular rivers. •
The relief and physiography of India has been
greatly influenced by the geological and geomorphological processes active in
Indian subcontinent. Physiography: •
Physiography of an area is the outcome of
structure, process and the stage of development. •
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 liesvast north Indian
plain. Based
on these macro variations, India can be divided into following physiographic
divisions: A)
The Northern and North-eastern Mountains B)
The Northern Plain C)
The Peninsular Plateau D)
The Indian Desert E) The Coastal Plains F) The
Islands. A. The North
and North-eastern Mountains • The North and North-eastern
Mountains consist of Himalayas and the North-eastern hills. |
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