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Undid revision 1008045060 by 117.220.100.241 (talk)

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{{More footnotes|date=August 2009}}
[[Image:Assam Valley.JPG|thumb|right|300px|Assam Valley and Environs]]
This article discusses the [[Geology|geological]] origin, [[Geomorphology|geomorphic]] characteristics, and climate of the [[North-East India|northeastern Indian state]] of [[Assam]]. Extending from 89° 42′ E to 96° E longitude and 24° 8′ N to 28° 2′ N latitude, it has an area of 78,438 km<sup>2</sup>, similar to that of [[Ireland]] or [[Austria]].

==Geology==
[[Image:Continental-continental convergence Fig21contcont.gif|thumb|right|300px|Plate Movements and Rise of the Himalayas]]
[[Geology|Geologically]], as per the [[plate tectonics]], [[Assam]] is in the easternmost projection of the [[Indian Plate]], where it thrusts underneath the [[Eurasian Plate]] creating a [[subduction zone]]. It is postulated that due to the northeasterly movement of the Indian plate, the sedimentary layers of an ancient geosyncline called the [[Tethys Ocean|Tethys]] (in between Indian and Eurasian Plates) were pushed upward to form the [[Himalayas]]. It is estimated that the height of the Himalayas is increasing by 4  cm each year. Therefore, Assam possesses a special [[geomorphology|geomorphic]] environment, with large plains and dissected hills of the South Indian Plateau system abutting the Himalayas to the north, north-east and east.

Geomorphic studies also conclude that the [[Brahmaputra]] is an [[antecedent drainage stream|antecedent river]], older than the Himalayas, which often crosses higher altitudes in the Himalayas eroding at a greater pace than the increase in the height of the mountain range to sustain its flow. The height of the surrounding regions still increasing forming steep [[Canyon|gorges]] in Arunachal.

Some say that the "flow" is usually neutral. The flow includes water, land, air, and other resources too. Entering the Assam region, the Brahmaputra becomes a [[braided river]], and, along with its tributaries, creates the flood plain of the Brahmaputra Valley.

==Physiography==
[[Image:STS065-96-048.jpg|thumb|left|300px|The Braided River Brahmaputra]]
The state of Assam comprises three physiographical divisions, namely, the Brahmaputra Valley, the Barak Valley and the Karbi-Anglong and the North-Cachar hills.<ref>{{Cite web|last=Saikia|first=Partha|title=Physiography of Assam and Assam Physiographical Divisions|url=https://www.northeastindiainfo.com/2020/10/assam-physiography.html|access-date=2020-10-12|website=North East India Info}}</ref>

The Brahmaputra Valley in Assam is approximately 80 to 100  km wide and almost 1000  km long. The width of the river itself is 16  km at many places within the valley.

The hills of [[Karbi Anglong]] and [[Dima Hasao district]] and those in and around Guwahati and North Guwahati (along with the Khasi and Garo Hills) are originally parts of the South Indian Plateau system. These are eroded and dissected by the numerous rivers in the region. The average height of these hills in Assam varies from 300m to 400m to a maximum of about 2000m almost. There are also hills in the North Bank bordering Bhutan and Arunachal Pradesh as well as those near Burma.

The southern [[Barak Valley]] is separated by the Karbi Anglong and North Cachar Hills from the Brahmaputra Valley in Assam. The Barak originates from the Barail Range in the border areas of Assam, Nagaland, and Manipur and flowing through the district of Cachar, it confluences with the Brahmaputra in Bangladesh. Barak Valley in Assam is a small valley with an average width and length of approximately 40 to 50  km.

==Mineral resources==
Assam is endowed with [[petroleum]], [[natural gas]], [[coal]], [[limestone]] and many other minor minerals such as [[Quartzite|magnetic quartzite]], [[kaolin]], [[sillimanite]]s, [[clay]] and [[feldspar]]. A small quantity of iron ore is also available in western parts of Assam.

The Upper Assam districts are major reserves of oil and gas. Petroleum was discovered in Assam in 1889. It is estimated that Assam and surrounding region possess around 150 million tonnes of petroleum reserves. Presently, Assam is the 3rd largest producer of petroleum (crude) and natural gas in the country accounting for 16% and 8% respectively of the total production of this mineral in the country.

A Tertiary coal belt is located in [[Tinsukia]], [[Dibrugarh]], [[Sivasagar]], [[Karbi Anglong]] and [[Dima Hasao]] districts with an estimated reserve of 370 million tonnes. Assam coal is friable in nature and has high sulfur content. It is mainly utilized by local railways, steamers, and hydro power stations. Low moisture, low volatile cooking coal has been discovered in the [[Hallidayga Singamari]] area.

Assam has rich limestone reserves. The major reserves of limestone are in Dima Hasao and Karbi Anglong districts. A total reserve of 97 million tonnes of limestone has been found in these two districts and almost half of the reserve is of cement grade. Moreover, there is an estimated reserve of 365 million tonnes of limestone near Umrangshu in Dima Hasao district. Among the minor minerals, there are quartzite reserves in the [[Nagaon]] district, kaolin reserves in [[Karbi Anglong]] and the Lakhimpur districts and [[sillimanite]]-bearing rocks in Karbi Anglong district.

==Climatic characteristics==
With the 'Tropical Monsoon Rainforest Climate', Assam is a temperate region and experiences heavy rainfall and humidity. Winter lasts from late October to late February. The minimum temperature is 6 to 8 degrees Celsius. Nights and early mornings are foggy, and rain is scanty. Summer starts in mid May, accompanied by high humidity and rainfall. The maximum temperature is 35 to 38 degrees Celsius, but the frequent rain reduces this. The peak of the [[monsoon]]s is during June. [[Thunderstorm]]s and frequent storms known as ''Bordoisila'' are frequent during the afternoons during the Bihu season.

==Biogeography and biodiversity==
[[Image:white-winged.wood.duck.arp.jpg|thumb|right|200px|A white-winged wood duck or deuhnah]]
[[Image:Golden Langur.jpg|thumb|right|200px|A golden langur]]
{{Main|Biodiversity of Assam}}

Assam is a part of the Biodiversity Hotspot area. There are a number of tropical [[tropical and subtropical moist broadleaf forests|rainforests]] in Assam, including the [[Dehing Patkai rainforest]]. Moreover, there are riverine grass lands, [[bamboo]] orchards and numerous [[wetland]] ecosystems. Many of these areas have been protected by developing national parks and reserved forests. The [[Kaziranga National Park|Kaziranga]] and [[Manas National Park|Manas]] are the two [[World Heritage Sites]] in the region. The Kaziranga is the home for the rare [[Indian rhinoceros]], while Manas is a tiger sanctuary.

Apart from the rhinoceros and the tiger, the spotted deer or [[chital]] / ''futukihorina'' (''Axis axis''), the [[swamp deer]] or ''dolharina'' (''Cervus duvauceli duvauceli''), the [[clouded leopard]] (''Neofelis nebulosa''), the [[hoolock gibbon]] or ''holoubandor'', [[pygmy hog]] or ''nol-gahori'' (''Sus salvanis''), the [[Water buffalo|wild buffalo]], the [[hispid hare]], the [[golden langur]] (''Chloropsis cochinchinensis''), the [[Asian golden cat|golden cat]], the [[giant civet]], the [[binturong]], the [[hog badger]], the [[civet|civet cat]] and the [[porcupine]] are all found in the state. Moreover, there are abundant numbers of [[Gangetic dolphins]], [[mongooses]], [[giant squirrels]] and [[pythons]].

A few of the major birds in Assam are: the [[blue-throated barbet]] or ''hetuluka'' (''Megalaima asiatica''), the [[white-winged wood duck]] or ''deuhnah'' (''Cairina scultulata''), the [[Pallas's fish eagle]] or ''kuruwa'' (''Haliaeetus leucoryphus''), the [[great pied hornbill]] or ''rajdhonesh'' (''Buceros bicornis homrai''), the [[Himalayan golden-backed three-toed woodpecker]] or ''barhoituka'' (''Dinopium shorii shorii''), and the migratory [[pelican]].

Assam is also known for [[Orchidaceae|orchids]] and also for valuable plant species and forest products.

==Natural disasters==
The region is also prone to natural disasters. High rainfall, deforestation, and other factors which have resulted in annual floods. These often cause widespread loss of life, livelihood and property. The region is also prone to earthquake, mild tremors are common, but strong earthquakes are rare. There have been three strong earthquakes: in 1869 the bank of the Barak sank by 15 ft. In [[1897 Assam earthquake|1897]] there was a tremor which measured 8.3 on the [[moment magnitude scale]], and another in [[1950 Assam–Tibet earthquake|1950]] which measured 8.6.

==References==
{{Reflist}}

==External links==
* [http://www.gauhati.ac.in/geography/ Department of Geography, Gauhati University]
* [https://web.archive.org/web/20070223165557/http://gu.nic.in/html/faculty/geology.htm Department of Geological Sciences, Gauhati University - Profile and Contacts]
* {{WWF ecoregion|name=Brahmaputra Valley Semi-evergreen Forests|id=im0105}}

{{Assam}}

{{DEFAULTSORT:Physical Geography Of Assam}}
[[Category:Geography of Assam]]
[[Category:Physical geography]]
[[Category:Environment of Assam]]

Physical geography of Assam - Revision history

imported>OhioanRCS: Undid revision 1008045060 by 117.220.100.241 (talk)