Physical Geography of Assam
Encyclopedia
Geology
Geology is the science comprising the study of solid Earth, the rocks of which it is composed, and the processes by which it evolves. Geology gives insight into the history of the Earth, as it provides the primary evidence for plate tectonics, the evolutionary history of life, and past climates...
origin, geomorphic
Geomorphology
Geomorphology is the scientific study of landforms and the processes that shape them...
characteristics, and climate of the northeastern Indian state
North-East India
Northeast India refers to the easternmost region of India consisting of the contiguous Seven Sister States, Sikkim, and parts of North Bengal...
of Assam
Assam
Assam , also, rarely, Assam Valley and formerly the Assam Province , is a northeastern state of India and is one of the most culturally and geographically distinct regions of the country...
.
Assam
Assam
Assam , also, rarely, Assam Valley and formerly the Assam Province , is a northeastern state of India and is one of the most culturally and geographically distinct regions of the country...
, extending from 89° 42′ E to 96° E longitude and 24° 8′ N to 28° 2′ N latitude, has an area of 78,438 km², similar to that of Ireland
Ireland
Ireland is an island to the northwest of continental Europe. It is the third-largest island in Europe and the twentieth-largest island on Earth...
or Austria
Austria
Austria , officially the Republic of Austria , is a landlocked country of roughly 8.4 million people in Central Europe. It is bordered by the Czech Republic and Germany to the north, Slovakia and Hungary to the east, Slovenia and Italy to the south, and Switzerland and Liechtenstein to the...
.
Geologic and geomorphic origin
Geology
Geology is the science comprising the study of solid Earth, the rocks of which it is composed, and the processes by which it evolves. Geology gives insight into the history of the Earth, as it provides the primary evidence for plate tectonics, the evolutionary history of life, and past climates...
, as per the plate techtonics
Plate tectonics
Plate tectonics is a scientific theory that describes the large scale motions of Earth's lithosphere...
, Assam
Assam
Assam , also, rarely, Assam Valley and formerly the Assam Province , is a northeastern state of India and is one of the most culturally and geographically distinct regions of the country...
is in the eastern most projection of the Indian Plate, where it thrusts underneath the Eurasian Plate
Eurasian Plate
The Eurasian Plate is a tectonic plate which includes most of the continent of Eurasia , with the notable exceptions of the Indian subcontinent, the Arabian subcontinent, and the area east of the Chersky Range in East Siberia...
creating a subduction zone. It is postulated that due to the northeasterly movement of the Indian plate, the sedimentary layers of an ancient geocyncline called the Tethys
Tethys Ocean
The Tethys Ocean was an ocean that existed between the continents of Gondwana and Laurasia during the Mesozoic era before the opening of the Indian Ocean.-Modern theory:...
(in between Indian and Eurasian Plates) were pushed upward to form the Himalayas
Himalayas
The Himalaya Range or Himalaya Mountains Sanskrit: Devanagari: हिमालय, literally "abode of snow"), usually called the Himalayas or Himalaya for short, is a mountain range in Asia, separating the Indian subcontinent from the Tibetan Plateau...
. It is estimated that the height of the Himalayas is increasing by 4 cm each year. Therefore, Assam possesses a special geomorphic
Geomorphology
Geomorphology is the scientific study of landforms and the processes that shape them...
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 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
Canyon
A canyon or gorge is a deep ravine between cliffs often carved from the landscape by a river. Rivers have a natural tendency to reach a baseline elevation, which is the same elevation as the body of water it will eventually drain into. This forms a canyon. Most canyons were formed by a process of...
in Arunachal.
Physiography
Braided river
A braided river is one of a number of channel types and has a channel that consists of a network of small channels separated by small and often temporary islands called braid bars or, in British usage, aits or eyots. Braided streams occur in rivers with high slope and/or large sediment load...
, 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. The width of the river itself is 16 km at many places within the valley.
The hills of Karbi Anglong and Dima Hasao district
Dima Hasao district
Dima Hasao district is an administrative district in the state of Assam in north-eastern India. As of 2011 it is the least populous district of Assam .-History:...
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 400m.
The southern Barak
Barak River
The Barak River is one of the major rivers of southern Assam and is a part of the Surma-Meghna River System. It is the biggest and the most important of all the rivers in the Manipur hill territory, from where it originates....
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 petroleumPetroleum
Petroleum or crude oil is a naturally occurring, flammable liquid consisting of a complex mixture of hydrocarbons of various molecular weights and other liquid organic compounds, that are found in geologic formations beneath the Earth's surface. Petroleum is recovered mostly through oil drilling...
, natural gas
Natural gas
Natural gas is a naturally occurring gas mixture consisting primarily of methane, typically with 0–20% higher hydrocarbons . It is found associated with other hydrocarbon fuel, in coal beds, as methane clathrates, and is an important fuel source and a major feedstock for fertilizers.Most natural...
, coal
Coal
Coal is a combustible black or brownish-black sedimentary rock usually occurring in rock strata in layers or veins called coal beds or coal seams. The harder forms, such as anthracite coal, can be regarded as metamorphic rock because of later exposure to elevated temperature and pressure...
, limestone
Limestone
Limestone is a sedimentary rock composed largely of the minerals calcite and aragonite, which are different crystal forms of calcium carbonate . Many limestones are composed from skeletal fragments of marine organisms such as coral or foraminifera....
and many other minor minerals such as magnetic quartzite
Quartzite
Quartzite is a hard metamorphic rock which was originally sandstone. Sandstone is converted into quartzite through heating and pressure usually related to tectonic compression within orogenic belts. Pure quartzite is usually white to gray, though quartzites often occur in various shades of pink...
, kaolin, sillimanite
Sillimanite
Sillimanite is an alumino-silicate mineral with the chemical formula Al2SiO5. Sillimanite is named after the American chemist Benjamin Silliman . It was first described in 1824 for an occurrence in Chester, Middlesex County, Connecticut, USA....
s, clay
Clay
Clay is a general term including many combinations of one or more clay minerals with traces of metal oxides and organic matter. Geologic clay deposits are mostly composed of phyllosilicate minerals containing variable amounts of water trapped in the mineral structure.- Formation :Clay minerals...
and feldspar
Feldspar
Feldspars are a group of rock-forming tectosilicate minerals which make up as much as 60% of the Earth's crust....
. 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
Tinsukia
Tinsukia is a city and a municipal board in Tinsukia district, Assam, India.Tinsukia is a business city in the Indian state of Assam. It is situated north east of Guwahati and kilometres away from the border with Arunachal Pradesh. It is the administrative headquarters of Tinsukia District of...
, Dibrugarh
Dibrugarh
Dibrugarh is the headquarters of Dibrugarh district, Assam, India, and is the second largest city in Assam after Guwahati. It is situated on the banks of the Brahmaputra River, about north-east of Guwahati. It is the gateway to the three tea-producing districts of Tinsukia, Dibrugarh, and Sibsagar...
, Sivasagar, Karbi Anglong and Dima Hasao 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 the Hallidayganj Singrimari 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
Nagaon
Nagaon , is a medium sized city and a municipal board in Nagaon district in the Indian state of Assam. It is situated east of Guwahati. An older spelling of the name is Nowgong.It is one of the fastest growing cities of the northeast.-History:...
district, kaolin reserves in Karbi Anglong and the Lakhimpur districts and sillimanite
Sillimanite
Sillimanite is an alumino-silicate mineral with the chemical formula Al2SiO5. Sillimanite is named after the American chemist Benjamin Silliman . It was first described in 1824 for an occurrence in Chester, Middlesex County, Connecticut, USA....
-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 monsoonMonsoon
Monsoon is traditionally defined as a seasonal reversing wind accompanied by corresponding changes in precipitation, but is now used to describe seasonal changes in atmospheric circulation and precipitation associated with the asymmetric heating of land and sea...
s is during June. Thunderstorm
Thunderstorm
A thunderstorm, also known as an electrical storm, a lightning storm, thundershower or simply a storm is a form of weather characterized by the presence of lightning and its acoustic effect on the Earth's atmosphere known as thunder. The meteorologically assigned cloud type associated with the...
s 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
Biodiversity of Assam
The Biodiversity of Assam, a state in North-East India, makes it a biological hotspot with many rare and endemic plant and animal species. The greatest success in recent years has been the conservation of the Indian rhinoceros at the Kaziranga National Park, but a rapid increase in human...
zones in the world. There are a number of tropical rainforests
Tropical and subtropical moist broadleaf forests
Tropical and subtropical moist broadleaf forests , also known as tropical moist forests, are a tropical and subtropical forest biome....
in Assam. Moreover, there are riverine grass lands, bamboo
Bamboo
Bamboo is a group of perennial evergreens in the true grass family Poaceae, subfamily Bambusoideae, tribe Bambuseae. Giant bamboos are the largest members of the grass family....
orchards and numerous wetland
Wetland
A wetland is an area of land whose soil is saturated with water either permanently or seasonally. Wetlands are categorised by their characteristic vegetation, which is adapted to these unique soil conditions....
ecosystems. Many of these areas have been protected by developing national parks and reserved forests. The Kaziranga
Kaziranga National Park
Kaziranga National Park is a national park in the Golaghat and Nagaon districts of the state of Assam, India. A World Heritage Site, the park hosts two-thirds of the world's Great One-horned Rhinoceroses. Kaziranga boasts the highest density of tigers among protected areas in the world and was...
and Manas
Manas National Park
Manas National Park or Manas Wildlife Sanctuary is a Wildlife Sanctuary, UNESCO Natural World Heritage site, a Project Tiger Reserve, an Elephant Reserve and a Biosphere Reserve in Assam, India. Located in the Himalayan foothills, it is contiguous with the Royal Manas National park in Bhutan...
are the two World Heritage Sites in the region. The Kaziranga is the home for the rare Indian Rhinoceros
Indian Rhinoceros
The Indian Rhinoceros is also called Greater One-horned Rhinoceros and Asian One-horned Rhinoceros and belongs to the Rhinocerotidae family...
, while Manas is a tiger sanctuary.
Apart from the rhinoceros and the tiger, the spotted deer or chital
Chital
The chital or cheetal , also known as chital deer, spotted deer or axis deer is a deer which commonly inhabits wooded regions of Sri Lanka, Nepal, Bangladesh, Bhutan, India, and in small numbers in Pakistan...
/ Futukihorina (Axix axix), the swamp deer or Dolharina (Cervus duvauceli duvauceli), the clouded leopard
Clouded Leopard
The clouded leopard is a felid found from the Himalayan foothills through mainland Southeast Asia into China, and has been classified as vulnerable in 2008 by IUCN...
(Neofelis nebulosa), the hoolock gibbon
Hoolock gibbon
The hoolock gibbons , also known as hoolocks, are two primate species from the family of the gibbons .Hoolocks are the second largest of the gibbons, after the Siamang. They reach a size of 60 to 90 cm and weigh 6 to 9 kg...
or Holoubandor, pygmy hog
Pygmy Hog
Pygmy hog is an endangered species of small wild pig, previously spread across India, Nepal, and Bhutan but now only found in Assam. The current world population is about 150 individuals or fewer...
or Nol-gahori (Sus salvanis), the wild buffalo, the hispid hare
Hispid Hare
The Hispid hare Caprolagus hispidus, also called Assam rabbit is a leporid native to South Asia, whose historic range extended along the southern foothills of the Himalayas. Today, the habitat of hispid hares is highly fragmented with an area of occupancy of less than extending over an estimated...
, the golden langur (Chloropsis cochinchinensis), the golden cat
Golden cat
A golden cat is a medium-sized wild cat belonging to either the genus Catopuma or Profelis. There are three species of golden cats:* African Golden Cat, Profelis aurata* Asian Golden Cat, Catopuma temminckii* Bay Cat, Catopuma badia...
, the giant civet
Giant Civet
The Sulawesi Palm Civet , also known as the Sulawesi Giant Civet, the Giant Civet and the Celebes Palm Civet, is a large and little known species of carnivore endemic to the Indonesian island of Sulawesi, where it is found particularly in the North and Central regions...
, the binturong
Binturong
The Binturong , also known as the Asian Bearcat, the Palawan Bearcat, or simply the Bearcat, is a species of the family Viverridae, which includes the civets and genets. It is the only member of its genus...
, the hog badger
Hog Badger
The hog badger is a terrestrial species of the mustelid family. It has medium-length brown hair, stocky body, white throat, two black stripes on an elongated white face and a pink pig-like snout. The head-and-body length is , the tail measures and the body weight is...
, the civet cat
Civet cat
Civet cat is an imprecise term that is used for a variety of cat-like creatures including:*Civets, of the families Viverridae and Nandiniidae*Ring-tailed Cat or North American Civet Cat , related to the raccoons...
and the porcupine
Porcupine
Porcupines are rodents with a coat of sharp spines, or quills, that defend or camouflage them from predators. They are indigenous to the Americas, southern Asia, and Africa. Porcupines are the third largest of the rodents, behind the capybara and the beaver. Most porcupines are about long, with...
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 bluthroated barbet or hetuluka (Megalaima asiatica), the white-winged wood duck
White-winged Wood Duck
The White-winged Duck or White-winged Wood Duck is a large species of duck, formerly placed in the genus Cairina and allied with the dabbling ducks...
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 woodpecker or barhoituka (Dinopium shorii shorii), and the migratory pelican.
Assam is also known for orchids
Orchidaceae
The Orchidaceae, commonly referred to as the orchid family, is a morphologically diverse and widespread family of monocots in the order Asparagales. Along with the Asteraceae, it is one of the two largest families of flowering plants, with between 21,950 and 26,049 currently accepted species,...
and also for valuable plant species and forest products.