Physical Geography of Assam

Physical geography

Main article: Physical Geography of Assam

See also: Biodiversity of Assam

Assam and its Environs: As per the plate tectonics, Assam is in the eastern-most projection of the Indian Plate, where the plate is thrusting underneath the Eurasian Plate creating a subduction zone and theHimalayas.^[6] Therefore, Assam possesses a unique geomorphic environment, with plains, dissected hills of the South Indian Plateau system and with the Himalayas all around its north, north-east and east.

Geomorphic studies conclude that the Brahmaputra, the life-line of Assam is an antecedent river, older than the Himalayas. The river with steep gorges and rapids in Arunachal Pradeshentering Assam, becomes a braided river (at times 10 mi/16 km wide) and with tributaries, creates a flood plain (Brahmaputra Valley: 50–60 mi/80–100 km wide, 600 mi/1000 km long).^[7] The hills of Karbi Anglong, North Cachar and those in and close to Guwahati (also Khasi-Garo Hills) now eroded and dissected are originally parts of the South Indian Plateau system.^[7] In the south, the Barak originating in the Barail Range (Assam-Nagaland border), flows through the Cachar district with a 25–30 miles (40–50 km) wide valley and enters Bangladesh with the name Surma.

Assam is endowed with petroleum, natural gas, coal, limestone and other minor minerals such as magnetic quartzite, kaolin, sillimanites, clay and feldspar.^[8] A small quantity of iron ore is available in western districts.^[8] Discovered in 1889, all the major petroleum-gas reserves are in Upper parts. A recent USGS estimate shows 399 million barrels (63,400,000 m³) of oil, 1,178 billion cubic feet (3.34×10¹⁰ m³) of gas and 67 million barrels (10,700,000 m³) of natural gas liquids in the Assam Geologic Province.^[9]

With the “Tropical Monsoon Rainforest Climate”, Assam is temperate (summer max. at 95–100 °F or 35–38 °C and winter min. at 43–46 °F or 6–8 °C) and experiences heavy rainfall and high humidity.^[7][10] The climate is characterized by heavy monsoon downpours reducing summer temperatures and affecting foggy nights and mornings in winters. Thunderstormsknown as Bordoicila are frequent during the afternoons. Spring (Mar–Apr) and Autumn (Sept–Oct) are usually pleasant with moderate rainfall and temperature.

Assam is one of the richest biodiversity zones in the world and consists of tropical rainforests,^[11] deciduous forests, riverinegrasslands,^[12] bamboo^[13] orchards and numerous wetland^[14] ecosystems; Many are now protected as national parks and reserved forests. The Kaziranga, home of the rare Indian Rhinoceros, and Manas are two UNESCO World Heritage Sites in Assam. The state is the last refuge for numerous other endangered species such as the Golden Langur (Presbetis geei), White-winged Wood Duck orDeohanh (Cairina scutulata), Bengal Florican, Black-breasted Parrotbill, Pygmy Hog, Greater Adjutant and so on. Some other endangered species with significant population in Assam are the tiger, elephant, Hoolock gibbon, Jerdon's Babbler and so on to name a few. Assam is also known for orchids.^[15]

The region is prone to natural disasters with annual floods and frequent mild earthquakes. Strong earthquakes are rare; three of which were recorded in 1869, 1897 (8.1 on the Richter scale); and in 1950 (8.6).

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  A view of the Brahmaputra river.
 
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  An Indian Rhinoceros at Kaziranga National Park.
 
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  Areca nut or Tamul; the seed of the Areca catechu is an important element of cultural symbolism.
 
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  A Golden Langur; endangered and found in the Chakrashila Wildlife Sanctuary in Dhubri district and in the pea-cock island of Guwahati.
 
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  A White-winged Wood Duck orDeohanh, endangered. Mostly found in the Upper Assam Tropical Forests.
 
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  A tea garden of Assam

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