PHYSIOGRAPHY OF NORTH EAST INDIA

PHYSIOGRAPHY OF NORTH EAST INDIA

The North East India region is physiographically not a homogenous unit and the present coniguration of this region has taken shape during geologically recent time. But the ultimate result of vaious geological events took place through the geological past. North East India consists of very ancient Archaean and Shillong series rocks exposed in several parts of the Garo, Khasi, Jaintia and Karbi Hills. These rocks are similar to rocks exposed in the rest of the peninsular in Bengal and Bihar of which this was a part at one geological time. All these old rocks form the basement for very much younger Tertiary sediments in upper Assam.

A large part of this region was a landmass upto the formation of the Himalayas about 2,000 million years ago. Then the easten part of the Khasi Hills, the Jaintia Hills and the Westen pat of the Karbi Hills became a basin of sedimentation in which sandstones and shales of the Shillong series were deposited. Due to tectonic reasons these were later uplifted and became a landmass.

Thus the geomorphological evolution of the Noth-eastern region of India is one of uplift and sinking in various parts during the past 100 million years.

Richard E Murphy has divided the landforms of North East India on the basis of both genetic and empirical factors and his physiographic divisions and sub-divisions are given below:

1. The Plateaus: Meghalaya plateau, Karbi Plateau

2. The Hill and Mountains   Region: Himalayan Mountains Region, Inner Himalayan (Glacial and Periglacial) Lesser Himalayan Region, Easern Hills, Dibong-Lohit Knot, Patkai-Hrap-Nagaland-NothCadmr and Manipur Hills, Mizoram-Tripura Range and Valley country

3. The Plains :  Brahmaputra Plain, Bhabar-Tarai/Belt, Northern Built-Up strip, Brahmaputra Flood Plain, Southern Built-up Strip, Southern Foot-hill zone, Intermontane and Piedmont plains, Manipur Basin, Barak Plain, Tripura Plain.

But recent scholars have divided North East India into five physiographic units on the basis of lithology, age and mode of evolution. The physiographic divisions of the region are:

(1) Karbi-Meghalaya Plateau

(2) North-Eastem frontier mountain ranges or Arunachal Himalaya

(3) Brahamputra Valley

(4) Barak Plain or Cachar Plain

(5) South-Eastem Hill Ranges

 

The Plateaus: Meghalaya plateau, Karbi Plateau

l  Geologically the whole Meghalaya Plateau including the Karbi Anglong region of Assam is a detached part of the peninsular India. It is separated by the Malda gap which resulted of river erosion of the Ganga and the Brahamaputra.

l Thus the landscape evolution of the plateau is closely linked with the Indian peninsula and its landscape story consists of different types of erosion, sedimentation, folding, intrusions, movements of land and sea and emissions.

l The core of the plateau is an ancient mass of gneiss, schists and granite.

l The length of the plateau from the river Dhansiri in the east and Singimai river in the west is about 420 km and the width in 40 km on the average. The whole Meghalaya plateau is almost surrouded by the plain of Brahamaputra, Surma and the Kopili rivers.

l The plateau may be divided into four parts: (a) Western Meghalaya or the Garo Hills, (b) Central Meghalaya or the Khasi Hills, (c) Eastern Meghalaya or the Jaintia Hills and (d) the Karbi plateau or the detached part of the Meghalaya.

(a) The Garo Hills extends over the area of 7770 sq. km. The Moheskhola Adagui range is the demarcating line of the Garo and the Khasi hills. The most important physical features of this part are the Tura range and the Simsang valley. The general elevation of the Garo Hills is comparatively low. The highest elevation is being recorded at Nokrek peak (1418 m) on the Tura range.

(b) The Khasi Hills consists of several micro-physiographic units like the undulating hills in the north, central upland southern face of the upland, the valley in the south and the southern belt of low hills. The central upland is the most important physiographic unit of the entire plateau. The southern part is very much affected by fluvial erosion (of rivers like Uni-Reas, Umngriand and Um-Rilang at different times)and has given rise to three plateaus , namely Langkydrem plateau, the Cherrapunjee platform and the Mawsynram platform.

(c) The Jaintia Hills forms a contiguous part of the Khasi Hills consisting of northern undulating hills, Jowai upland and the southern escarpment. The general height of this part of the plateau is in between 1250 and 1750 metres. The Jowai upland acts as a watershed between the Brahmaputra valley and the Surma valley.

(d) Karbi plateau is the detached part of the Meghalaya plateau. It is mostly separated from the Meghalaya plateau by the degradation of the Kopili and its headstreams and from the Naga Hills by the Dhansiri and its headstreams. The central part of this dissected Karbi plateau is higher with an elevation of about 1360 metres.