Northeast India located in the extreme northeast corner of the Indian subcontinent with diverse physiography and relief features. In general, the region may be divided into three physiographical regions that are Plateau region, Plain regions and Mountain region.
Because of its diversity of physiography the region endowed with rich and varied biophysical environments bounded by hills and mountains on its three sides except a narrow gap in the west.
The region extends between 22° to 29°30' N latitude and 80° 41' to 97°25' E longitude and covers an area of 2,62,379 sq. km.
Thus, it is placed in the tropical and subtropical
belt in the world. Its spatial distance from the mainland, poor communication,
infrastructure facilities, vast mountainous terrain, dense forests, heavy
rainfall, wetlands, frequent floods and cold climate of high altitude region
have conveyed a sense of remoteness and isolation of Northeast India.
Hence, a considerable part of North East India has been perceived to have remained in a relatively pristine state i.e., untouched, unharnessed, unaltered, unmodified, and unpolluted by man and his activities.
Most of the Northeast region is mountainous in terrain with many peaks soaring to great heights. These are young mountains that are susceptible to frequent earthquakes and subsequent destructions. The region has abundant forests, with flora and fauna that is extremely diverse and unique in nature.
The mighty Brahmaputra, one of the major rivers in Asia, with its innumerable tributaries, flows through the region. Majuli, one of the most populous river islands in the world, formed by the Brahmaputra lies in Assam.
Physiographic Division of Northeast India
1. The Plateau Region
1.1 Meghalaya plateau
1.2 Karbi Plateau
2. Mountains and Hill region
2.1 The Arunachal Himalaya
2.2 Patkai-Purvanchal Hill
3. The Plains
3.1 The Brahmaputra Plain
3.2 The Barak Plain
3.3 The Manipur Plain
3.4 The Tripura Plain
1. The Plateau Region
The hard crystalline massif forming the core of the region is, in fact, an extension of the Deccan plateau. The latter extends underground to form the Rajmahal Hills of Chotanagpur Plateau below Malda Districts of West Bengal and Rajshahi, Dinajpur and Rangpur Districts of Bangladesh and appears in the Northeast above the surface as Meghalaya Plateau and Karbi Hills.
1.1 Meghalaya plateau
The Meghalaya plateau faces the Sylhet plain of Bangladesh to the south and the Brahmaputra valley to the north. It rises abruptly from the Sylhet plain for about 1000 miles and maintains a more or less uniform outline throughout southern front-facing Bangladesh, except in places where it is dissected by South flowing streams through gorges and waterfalls.
From this margin, the plateau continues to rise slowly northward till it reaches the central parts, where there is east-west alignment like Tura-Kylas Range and Shillong Range.
The Tura-Kylas range reaches its highest elevation at Nokrek (1,412 meters) in Garo Hills, while in the Khasi Hills the highest elevation is at Shillong Peak (1,961 meters).
The plateau then begins to lose its height in successive ranges in all directions. However, western and eastern parts of the plateau i.e. Garo and Jaintia Hills present a deeply dissected and denuded profile that merge with the Brahmaputra plain through gentle gradients and isolated hills and hillocks.
1.2 Karbi Plateau
The Karbi plateau easternmost part of the north-eastward projection of Gondwanaland lies almost detached from the Meghalaya Plateau due to headward erosion of Kapili and Dhansiri river. On the south-eastern side, it is separated from the Naga Hills.
It is only in the central portion the plateau attains a height of 1,359 meters at Chengheheson peak and 1,363 meters at Dambukso is the highest peak.
The Karbi plateau has assumed pear-shape, giving out numerous streams radially to Dhansiri, Kalang, and Kopili that surround it.
These streams often extend plain embayments into the plateau, which otherwise descends to the plain through terraces. Such terraces made of older alluvium and residual soils and support rich tea gardens in Golaghat and Nagaon districts.
2. Mountains and Hill Region
The second major physiographic unit of Northeast India consists of hills and mountains. This unit stretches from the Bhutan Himalaya, covering the northern part of the region and then turning southward, covers its eastern and southern parts.
2.1 The Arunachal Himalaya
The portion is an integral part of the eastern Himalaya. It stretched from the Bhutan-Arunachal border, demarcated by Jia Dhansiri river and the Arkhata Range in the west to Siang River in the east.
Structurally it continues north-eastward to Namcha Barwa Peak (7755 m) in Tibet and eastward beyond Siang-Dihang River to Mismi Hills and then takes a southward turn through a syntaxial bend to form the Purvanchal ranges.
Namcha Barwa is the highest peak in eastern Himalaya, Within Arunachal Himalaya, one of the highest peaks is Kangto (7590 m).
2.1.1 The Lesser Himalayan Region
The Lesser Himalayan Region rises from a mere 300 miles along the margin of the Brahmaputra Valley to about 5,000 matres through a confusing labyrinth of hills and ranges intervened by deep gorges.
This region receives heavy rainfall and hence clothed with thick vegetation. Bomdila in West Kameng and Apatani plateau in lower Subansiri are two important, although restricted, tablelands and of immense human significance.
Towards the north of this region, there appear peri-glacial features made of fluvioglacial deposits with thick layers of transported boulders, rocks, and soil.
2.1.2 Great Himalayan Zone
This region lies beyond the transitional peri-glacial region and is characterized by increasing height, devoid of significant vegetation cover roundish topographic features, rocky surface, and snow-capped high peak.
This great Himalayan range running along the Indo-Chinese border has an average height of 6,500 m in Tawang, west Siang districts o an average of 5,200m.
2.2 Patkai-Purvanchal Hill
The portion of Arunachal Pradesh, east of Siang river is like a mountain knot, extensive and high, giving out the range to the west, south, and north-east. The great Himalayan here continues north-eastward at a highest of about 4000m lengthen the bar 5000 m through Yonggyap (3962 m) and runs up to Trakge La (5800 m) in China.
The extensive hills of the Sikang-Lohit knot corresponding to the Lesser Himalayas are generally steep and high. Noi Aisong (4130 m), Diphu (4500 m), Dapha Bum (4578 m), Kumjawng (2930 m) are some of the important ranges and passes here.
The region also holds a relatively wide intermontane basin called Tarwan Valley with several glaciers and lakes named Yegrong Tso.
From the Sikang-Lohit knot, the range moves parallelly towards southwest through Changlang and Tirap districts of Arunachal Pradesh and enter Nagaland. These parallel ranges are higher eastward attaining maximum height at the Patkai bum bordering Myanmar.
In Nagaland, the ranges fan out to the west while continuing southward to Manipur and Tripura. While fanning out the Nagaland, the hills extend up to North Cachar Hills of Assam and the relatively high Barail Range and then runs north-east and south-west to reach as far south-west as Jaintia hills, acting as the divide of the Brahmaputra and Barak catchment areas.
3. The Plains
There are four important plains in North-East India, viz. the Brahmaputra Plain (54315 square kilometers), the Barak Plain (6962 square kilometers), the Manipur Basin (1843 square kilometers), and the Tripura Piedmont Plain (3500 square kilometers)
3.1 Brahmaputra Plain
This plain is surrounded by the Bhutan and the Arunachal Himalayan in the north, Patkai Bum and Arunachal hills in east and Naga Hills, Karbi plateau and Meghalaya plateau in the south. It is open to and joined with the Ganga Plain in the west.
It is, therefore, often referred to as the easternmost part of Indus-Ganga-Brahmaputra Plain. From the north-east to the west it is about 720 km long and from the north to the south it is on the average 90 km wide.
3.2 Barak Plain
The Barak plain is located in the southern part of Assam encircled on the north by the North Cachar Hills, on the east by the Manipur Hills and on the south by the Mizoram Hills. To the west, the plain merges with the Sylhet Plains of Bangladesh.
The plain is, in fact, the headword piedmont part of the Sylhet Plain. The plain is horse-shoe Shaped with 85 km of east-west extension and 70 km north-south extension near Bangladesh Border.
3.3 The Manipur Plain
It is of lacustrine origin like the Kashmir valley. The present basin area is 1,843 square kilometers and is roughly oval in outline with a maximum breadth of about 32 km. This intermontane basin slopes from an altitude of 838 meters in the north to 792.5 meters in the south, with an average gradient of 75 centimeters per kilometer.
There are local depressions, marshes, and lakes in the south-central part. The rivers Nambul, Imphal, Iril, Thoubal, and Khuga, along with their numerous tributaries drain this basin.
3.4 The Tripura Plain
The Tripura plain is a piedmont plain, representing part of the Bangladesh Plain. The north-south alignment of hills in Mizoram extended parallel in Tripura with less height and situated wide apart. In the western part of Tripura, there are only low is Gumti which have created this piedmont plain.