Monday, 11 December 2017

Seismology:

The hills of the whole zone of the eastern frontier of Indian including Manipur were built up during the late Pleistocene period and hence isostatic and seismic balances are yet to be attained. Manipur falls in one of the most seismically active zones of the Trans-Asiatic Earthquake Belt. This is of tectonic origin associated with momentary relief of mechanical strain arising from mutual displacement (vertical and horizontal) of separate blocks of lithosphere, Khan et. al.(1985) believe that the ultramaphic belt along the Indo-Burma border may be a plate boundary between Indian and Burmeses plates.

Valley Formation:

Legends have it that Lord Shiva made Manipur valley which once underwater by draining the water through a tunnel drilled by his trident through the southern hills. A similar legend traces the earliest centres of human settlements on top of higher peaks like the Nongmaijing Hill (Longmaiching) and the Koubru Hill etc.when the valley at the lower reaches remained a vast sheet of water. Downward human migrations into the valley started as the water receded.

Some investigators are of the view that the valley was formed as a result of a lake being filled up by the riverborne sediments. The present Loktak and other lakes in the valley are said to be the remnants of the original lake.

But the lacustrine origin of Manipur valley has been questioned by various other theories. Dun(1996) was of the opinion that the Mnaipur Plain was formed by the depositions of a stream that was blocked by some convulsions at earth movements. Rajkumar (1982) also supports the theory of the riverine origin of the valley. In his words, the formations of Manipur valley may closely be connected with the upliftment of South Manipur Hills and subsequent downcutting of the area by the Manipur River and its tributaries, that at the same time drained the area of the valley.

Lithologically, the valley represents the axial region of an anticlinorium, the weak crest of which have been eroded. The erosional environments of the past in the valley have been studied in geomorphorlogical and geoarchaeological perspectives by several workers (Joshi et. al. 1979, Rajkumar), 1982, Thokchom, 1984). Fluvio-lacustral sediments are encountered in many parts of the valley to a depth of 152 m below the ground level (b.g.l). And, at the same time black clay of lake formation is exposed upto 40 m above the modern water level of the Loktak Lake. A few C14 data on Carbonised samples from Lamphel (at a depth of 0.35 to 0.40 m) and the Loktak Hydel Project area ( at a depth of 5.3 m to 12 m) indicates that the age of the central and southern parts of the valley ranges from 7980+ - 470 B.P. to 25,000 + - 600 B.P. The above observations drive us to infer that a considerable vertical change in the lake level has occurred in the valley. The lake levels were conspicuously higher around 25 K.B.P.-23 K.B.P. (Thokchom, 1984).

Thus, the origin and evolution of the valley may be ascribed to a tectonic theory and neo-tectonism remarkably influenced by a long history of fluvio-lacustral system. The valley remained free from Pleistocene glaciation. There was not a singular existence of lacustrine basin in the valley during the Quaternary. Low energy, fluvo-lacustral system anastomosing drainage with a number of disconnected lentic waterbodies on aggraded land dominated the landscape of this intermontane valley in the Quaternary.

Palaeoclimate:

From the marine environment under the Tethys sea, the land was raised slowly and exposed to the warm climate of the tertiary period. it appears that the land escaped the Pleistocene glaciation of the early Quaternary. But, it remained cool and dry. There is no geological evidence of Quaternary glacial or periglacial climate upto an elevation of about 1500 M. a.s.l. In fact, ferrugenous(oxidised) cement and matrix of gravel formations in the region suggest a sub-tropical Quarternary (Joshi et.al., 1979). The climate in the late Quaternary was warm and humid (Thokchom, 1984) and it has not changed drastically since then.

Modern Climate:

Besides the influence by its locations around the latitudes just north of the Tropic of Cancer, the climate of the state is governed by the relief of land and the rain bearing winds viz. the South-West Monsoon in summer and the North-East Monsoon and the Mediterranean winds in Winter. The eastern lowlands along the Indo-Burma border and the Western Assam Manipur border lowlands fall between the altitudes 30-100 m above M.S.L. and thus reigned by a tropical climate. The Manipur Valley at a height of 780-800 m. above M.S.L. has sub-tropical climate while the higher reaches of the mountains surrounding the valley have a temperate climate.

Referring to latitude of 240N, Manipur valley at an average height of 790 m. above M.S.L. receive direct and diffuse solar insolation as follows.

Total radiation=290.36- 780.86 cal/sq.m.day.
Visible radiation =113.37- 295.37 g.cal/sq.m./day.

The minimum values are recorded towards the winter months a peak in June. duration of bright sunshine has a variation of 3 hrs/day in July and 9 hrs/day of January. the surface level pressure ranges between 900 mb. and 930 mb.

Five seasons are distinct in the state viz; Summer ( May-June), Rainy (Monsoon) season (July-Sept), Autumn (Oct.-Nov), Cold winter (Dec.-Feb) and Spring (March-April). Since the onset, duration and amount of precipitation of the monsoon rain are erratic, this season classification may not hold good for a particular year and thus serves for general reference.

The temperature ranges between -20C to 360C. annual rainfall is sometimes as low as 975 mm and sometimes as high as 2646 mm. Average relative humidity is between 36% and 100%. Rate of evaporation at the level of Imphal valley between 1.8 mm. in January and 4 mm in May.

Population of Manipur according to the Provisional Results of 2001 Census:

State/Districts

Total Population

Sex ratio(females per 1000 males)

Density(per sq.km.) Decadal growth in P.C.
(1991-2001)
Persons

Males

Females

Manipur 2,388,634 1,297,338 1,181,296 978 107 30.02
Senapati 3,79,214 196,646 1,82,568 928 116 81.96
Tamenglong 1,11,496 57,994 53,499 922 25 29.23
Churachanpur 2,28,707 114,740 113,967 993 50 29.81
Bishnupur 2,05,907 102,772 103,135 1,004 415 13.90
Thoubal 3,66,341 183,338 183,003 998 713 24.62
Imphal West 4,39,532 218,947 220,585 1,007 847 15.42
Imphal east 3,93,780 197,710 196,070 992 555 19.16
Ukhrul 1,40,946 73,413 67,533 920 31 28.98
Chandel 1,22,714 61,778 60,936 986

37

72.80

Note: Population density at the District level is calculated on the basis of provisional area figures.
Source: Directorate of Census Operations, Manipur.