Physical Geography of Assam

Physical Geography of Assam

Physical Geography of Assam is extremely interesting with its geologic origin, geomorphic characteristics, climate, rich biodiversity, etc. Assam, extending from 89 degree 42 minutes E longitude to 96 degree E longitude and 24 degree 8 minutes N latitudes to 28 degree 2 minutes N latitudes in the graticule is a North Eastern state of India. Assam is located at the central part of the North-East India and with an area of 78,438 km² it is almost equivalent to the size of Ireland or Austria.

Geologic and geomorphic origin

Geologically, as per the plate techtonics, Assam is in the eastern most projection of the Indian Plate, where it is thrusting underneath the Eurasian Plate creating a subduction zone. It is postulated that due to the northeasterly movement of the Indian plate, the sediment layers of an ancient geocyncline called Tethys (in between Indian and Eurasian Plates) have been 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 unique geomorphic environment, with plain areas, dissected hills of the South Indian Plateau system and with the Himalayas all around its north, north-east and east.

Geomorphic studies also conclude that the Brahmaputra is a paleo-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 gorges in Arunachal.


Entering Assam, the Brahmaputra becomes a braided river and along with its tributaries, creates the flood plain of the Brahmaputra Valley. The Brahmaputra Valley in Assam is approximately 80 to 100 km wide and almost 1000 km long and the width of the river itself is 16 km at many places within the valley.

The hills of Karbi Anglong and North Cachar 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. Average height of these hills in Assam varies from 300 to 400mt.

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 magnetic quartzite, kaolin, sillimanites, clay and feldspar. A small quantity of iron ore is also available in western parts of Assam.

The Upper Assam districts are the 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 North Cachar Hills districts with an estimated reserve of 370 million tonnes. Assam coal is friable in nature and has a high sulphur content. It is mainly utilised by local railways, steamers, and hydro power stations. Low moisture, low volatile cooking coal has been discovered in Hallidayganj Singrimari area.

Assam has rich limestone reserves. The major reserves of limestone are in North Cachar Hills and Karbi Anglong districts. A total reserve of 97 million tonnes of limestone is already proved 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 the North Cachar Hills district.

Among the minor minerals, there are quartzite reserves in Nagaon district, kaolin reserves in Karbi Anglong and Lakhimpur district 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 monsoons is during June. Thunderstorms known as "Bordoicila" are frequent during the afternoons. Spring and Autumn with moderate temperatures and modest rainfall are the most comfortable seasons.

Biogeography and biodiversity

Assam is one of the richest biodiversity zones in the world. There are number of tropical rainforests in Assam. 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 and Manas are the two World Heritage Sites. 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" (Axix axix), the Swamp Deer or "Dolharina" (Cervus duvauceli duvauceli), the Clouded Leopard (Neofelis nebulosa), the Hoolock Gibbon or "Holoubandor", Pigmy Hog or "Nol-gahori" (Sus salvanis), the Wild Buffalo, the Hispid Hare, the Golden Langur (Chloropsis cochinchinensis), the Golden Cat, the peculiar Giant Civet, the Binturong, the Hog Badgers, the Porcupines, the Civet cats, etc are found in Assam. Moreover, there are abundant numbers of Gangetic Dolphins, Mongooses, Giant Squirrels and Pythons.

Few of the major birds in Assam are: Bluthroated Barbet or "Hetuluka" (Megalaima asiatica), the White-winged Wood Duck or "Deuhnah" (Cairina scultulata), the Ring-tailed Fishing Eagle or "Kuruwa" (Haliaeetus leucorythus), the Great Pied Hornbill or "Rajdhonesh" (Buceros bicornis homrai), the Himalayan Golden-backed Three-toed Wood-pecker or "Barhoituka" (Dinopium shorii shorii), and the Migratory Pelicans.

Assam is also known for 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 have resulted in annual floods that cause widespread loss of life, livelihood and property. The region is also prone to earthquakes. Mild tremors are familiar, and strong earthquakes are rare. There have been three strong earthquakes: in 1869 the bank of the Barak sank by 15 ft; 1897 (8.1 on the Richter scale); and 1950 (8.6).

External links

* [ Department of Geography, Gauhati University - Profile and Contacts]
* [ Department of Geological Sciences, Gauhati University - Profile and Contacts]
* [ Brahmaputra Valley Semi-evergreen Forests]

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