SEBA Class 9 Geography: Geography of Assam
EXERCISE QUESTION
1. What are the physiographic divisions of Assam?
Answer: Physiographically, Assam can be divided into four main divisions. These divisions have developed on the basis of geological structure and natural features such as plains, hills, and valleys.
The four physiographic divisions of Assam are:
1. The Brahmaputra Valley
2. The Barak Valley
3. The Karbi Plateau
4. The Barail Range and Southern Hills
2. What are the physiographic regions of the Brahmaputra Valley?
Answer: The Brahmaputra Valley is divided into four distinct physiographic units from north to south. These are:
1. The Northern Foothills.
2. The North and South Bank Plains.
3. The Floodplain and Charlands.
4. The Southern Foothills.
3. Write four names, each of the north-bank and south-bank tributaries of the Brahmaputra River.
Answer: The Brahmaputra River has many tributaries joining it from both the north and south banks.
North-bank tributaries:
1. Subansiri
2. Jia Bharali
3. Manas
4. Puthimari
South-bank tributaries:
1. Burhi Dihing
2. Disang
3. Dhansiri
4. Kopili
4. Give a brief description of the Brahmaputra plain region.
Answer: The Brahmaputra plain includes both the north bank plain and the south bank plain. The north bank plain extends from the northern foothills to the Brahmaputra River, while the south bank plain extends from the southern foothills to the river. These plains have been formed by the deposition of alluvial sediments brought down by the Brahmaputra and its numerous tributaries. The alluvial soils here are very fertile and suitable for agriculture. The plains are thickly populated and have a well-developed transport system. The north bank plain is wider in the lower parts, while the south bank plain is narrow in Kamrup, Goalpara, and Dhubri but becomes wider near the Kopili plain and eastern districts like Jorhat and Dibrugarh.
5. Give a brief description of the floodplain region of the Brahmaputra.
Answer: The floodplain region of the Brahmaputra lies between the north bank and south bank plains. It is formed by the frequent floods and depositional activities of the Brahmaputra River. This floodplain includes the charlands or sandbars developed on the riverbed. The width of the floodplain is not uniform everywhere because of hillocks and the formation of levees along the riverbanks. The north bank floodplain, especially in Dhemaji and Barpeta districts, has many wetlands and swamps, while the south bank floodplain is comparatively narrow but wider near the confluence of rivers like Burhi Dihing, Disang, Dhansiri, Kolang-Kopili, and Kulshi.
6. Write about the geographic location and origin of Majuli.
Answer: Majuli is a large river island located in the middle of the Brahmaputra River in Assam. It is one of the biggest river islands in the world. At present, it covers an area of about 422 square kilometres with a population of 1.68 lakh (2011 Census). Majuli became a district of Assam in 2016. The island was formed by the continuous depositional and erosional activities of the Brahmaputra and its tributaries. However, floods and bank erosion have become major problems for the people of Majuli. The land area of the island is gradually decreasing every year due to erosion caused by the changing course of the river.
7. Write briefly about the boundaries and characteristics of the Barak Valley.
Answer: The Barak Valley is an important physiographic region of Assam, made up of the Barak Plain and its northern and southern foothills. It is bounded by the Meghalaya Plateau and Barail Range on the north, the Manipur Hills on the east, and the Mizo Hills on the south, while it opens westward into the Sylhet Plain of Bangladesh. The Barak River flows about 225 km through Cachar, Hailakandi, and Karimganj districts. Its north-bank tributaries are Chiri, Jiri, Madhura, and Jatinga, and south-bank tributaries are Sonai, Dhaleswari, Singla, and Langai. The valley, also called the Cachar Plain, is formed by alluvial deposits and is fertile and densely populated.
8. Write briefly about the boundaries and characteristics of the Karbi Plateau.
Answer: The Karbi Plateau is a part of the Meghalaya Plateau based on its origin and geological formation. It is divided by the Kopili Valley into two parts — eastern and western. The eastern part, covered by the Rengma Hills, includes the Diphu and Bokajan sub-divisions and is about twice the size of the western part. The western part lies in the Hamren sub-division with an average height of about 900 metres, sloping from south-west to north-east. The physiography of this plateau has developed mainly due to the work of the Kopili and Barapani rivers and their tributaries.
9. Write briefly the characteristics of the Barail Range and Southern Hills.
Answer: The Barail Range and Southern Hills extend westward from Thensang across Nagaland into the North Cachar Hills district. It connects the Naga Hills in the east with the Meghalaya Plateau in the west and divides the area into two parts — the north-sloping part towards the Brahmaputra Valley and the south-sloping part towards the Barak Valley. The north-sloping side is lower, while the south-sloping side is higher.
10.What is the type of Assam's climate? Write briefly about its characteristics.
Answer: Assam has a sub-tropical monsoon climate with heavy rainfall in summer, dry winter, high humidity, and moderate temperature. Though mainly influenced by monsoon winds, variations in location, topography, and water bodies make it diverse. The Himalayan ranges block the moist south-west monsoon winds, causing rainfall, and protect the state from cold Tibetan winds in winter. The average temperature ranges from 7°C in winter to 35°C in summer, and the annual rainfall is about 200 cm.
11.What is the main reason behind occurrence of rainfall in Assam during summer season?
Answer: The main reason behind the occurrence of rainfall in Assam during the summer season is the orographic and cyclonic processes of the moist south-west monsoon wind. When the monsoon winds blow from the Bay of Bengal, they carry warm, moist air towards Assam. The Himalayan mountain range and its branches on the north and east obstruct these winds, causing them to rise and cool, which leads to heavy rainfall. The Meghalaya Plateau and other southern hills also help in this process. Therefore, due to the combined effect of these geographical features, Assam receives heavy summer rainfall.
12.Discuss briefly about the geographical factors influencing the climate of Assam.
Answer: The climate of Assam is influenced by several geographical factors. Its sub-tropical location and monsoon winds mainly determine the climatic conditions. The Himalayan ranges on the north and east block the cold winter winds from Tibet and also obstruct the south-west monsoon, causing heavy rainfall in summer. The Meghalaya Plateau and other southern hills also play a role by forcing moist winds to rise and cool, resulting in rainfall. The valley and hilly topography, presence of rivers and wetlands, and local winds like mountain and valley winds affect temperature and humidity. Due to these factors, Assam experiences high rainfall, moderate temperatures, and high humidity throughout the year.
13.What are the main seasons of Assam? Write in brief about the seasonal variation in the distribution of temperature and rainfall in Assam.
Answer: Assam experiences four main seasons — Pre-Monsoon, Monsoon, Retreating Monsoon, and Dry Winter.
1. Pre-Monsoon Season (March–May):
Temperature rises after winter. Mornings are pleasant, afternoons hot, and evenings often have rain with thunder and lightning. This rainfall helps in growing paddy, tea, and jute. The season also marks spring, and Bohag Bihu is celebrated in April.
2. Monsoon Season (June–September):
Caused by the south-west monsoon, this is the rainy season. Assam receives about 70% of its annual rainfall (around 200 cm) during this time. The temperature reaches about 35°C, and heavy rain often causes floods. The Sali paddy is transplanted in this season.
3. Retreating Monsoon (October–November):
The south-west monsoon withdraws, leading to decrease in temperature and rainfall. Wind direction reverses to north-east, and fog appears at night and in the morning.
4. Dry Winter (End of November/December to February):
This is the coldest season in Assam, marked by low temperature (below 10°C) and dry weather. Thick fog occurs in the morning, and the air remains cool and clear due to very little rainfall. During this time, Sali paddy is harvested, and Bhogali or Magh Bihu is celebrated.
14.Write the names of places in Assam witnessing the highest and lowest rainfall along with their amount of rainfall.
Answer: In Assam, the highest rainfall occurs in Tinsukia, Dibrugarh, Dhemaji, Lakhimpur, and Sivasagar districts of Upper Assam, and in Kokrajhar, Dhubri, Cachar, Karimganj, and Hailakandi, each receiving over 250 cm of rainfall annually. The lowest rainfall is recorded in Central Assam, especially in the Lanka–Lumding region of Nagaon district, which gets only 129 cm per year.
15.Why does the amount of rainfall not uniform in all places of Assam?
Answer: The amount of rainfall is not uniform in all parts of Assam because of differences in location and topography. The Himalayan ranges, Meghalaya Plateau, and other hills obstruct the south-west monsoon winds differently in various areas, causing variation in rainfall. The foothill regions of the Himalayas receive more rainfall, while the leeward sides of the hills, such as east of Karbi Anglong and north and east of Dima Hasao, get less rainfall. Similarly, the southern part of Nagaon district also receives low rainfall. Thus, the uneven topography and direction of monsoon winds cause unequal rainfall distribution across the state.
16.Write in brief about the spatial distribution of rainfall in Assam.
Answer: The rainfall in Assam shows a marked spatial variation due to its topography and location. The annual average rainfall of the state is about 200 cm, but it is not the same everywhere. The hills and foothill areas receive more rainfall than the plains. The upper Assam districts such as Tinsukia, Dibrugarh, Dhemaji, Lakhimpur, and Sivasagar, and the lower Assam districts like Kokrajhar and Dhubri, along with Cachar, Karimganj, and Hailakandi in southern Assam, get over 250 cm of rainfall annually. On the other hand, central Assam, especially Nagaon and Karbi Anglong, receives much less rainfall — the Lanka–Lumding region gets only 129 cm per year.
17.Give a short account of different types of soil found in Assam.
Answer: The soils of Assam are formed due to the combined effects of parent material, climate, organic processes, physiography, and time. Based on their characteristics and formation, the soils of Assam are divided into four main types:
1. Alluvial Soil: Found widely in the Brahmaputra and Barak Valleys, formed by the deposition of silt and clay by rivers. It is fertile and suitable for agriculture.
2. Piedmont Soil: Found in the northern foothill zone along the Himalayas. It includes the Bhabar and Tarai belts. The Bhabar belt has boulders and pebbles, while the Tarai belt remains water-saturated and supports tall grasses.
3. Hill Soil: Found in the southern hill areas like the Karbi Plateau and Barail Range. These soils are red sandy or red loamy, acidic, and rich in organic matter.
4. Laterite Soil: Found in the North Cachar Hills and southern Karbi Plateau. These are black, sandy soils with low nitrogen, potash, phosphoric acid, and lime.
18.What are the reasons behind soil erosion in Assam?
Answer: In Assam, soil erosion has become a major problem caused by both natural processes and human activities. It damages soil fertility and affects agriculture. The main reasons are:
1. Natural Causes:
o Heavy rainfall and surface runoff wash away soil from hill slopes.
o Water logging in plains and low-lying areas spoils soil properties.
2. Human Causes:
o Cutting of trees increases surface water flow, leading to erosion.
o Unscientific farming on hill slopes loosens topsoil.
o Jhum (shifting) cultivation removes the fertile upper layer of soil.
o Water logging caused by human settlements and construction.
o Excessive use of chemical fertilizers reduces soil quality.
19.What are the different types of forest in Assam? Explin.
Answer: The forests of Assam are classified into five main types based on rainfall, altitude, and soil conditions. These are:
a) Tropical Evergreen Forest: Found in areas with over 300 cm rainfall, mainly in the foothills near Arunachal Pradesh and southern Tinsukia and Dibrugarh. These forests have three vegetation layers and trees like Hollong and Mekai.
b) Tropical Semi-Evergreen Forest: Located in the northern Bhabar zone, Karbi Anglong, and Dima Hasao areas. These forests contain trees like Nahar, Bonchom, Cham, and Sirish, along with bamboos and canes.
c) Tropical Moist Deciduous Forest: Found in lower Brahmaputra Valley, Karbi Anglong, and Barak Valley, receiving 200–250 cm rainfall. Dominant trees are Sal, Makori Sal, Gomari, Amlokhi, and Simul.
d) Riverine Forest: Occurs along the rivers and wetlands of Assam. These forests have tall trees and grasses such as Chom, Showalu, Nal, Khagori, and Kohua.
e) Tropical Dry Deciduous Forest: Seen in dry floodplains slightly away from rivers. It has tall trees and grasses like Sisoo, Bhelkor, Khair, Birina, and Ulu.
20.What is rain forest? Describe the characteristics of rain forest in Assam.
Answer: A rain forest is a type of forest found in areas with very high rainfall (300 cm or more annually). In Assam, such forests are known as Tropical Evergreen Forests.
These forests are mainly found in the foothills near Arunachal Pradesh, the southern parts of Tinsukia and Dibrugarh districts, and in some hilly areas of the Barak Valley. They usually have three layers of vegetation — the first layer has very tall trees like Hollong and Mekai, the second layer includes medium-sized trees like Nahar, Chiya Nahar, and Amari, and the third layer has short trees and grasses. These forests also contain bamboos, canes, climbers, and orchids.
21.Write in brief about the importance and characteristics of riverine vegetation.
Answer: The riverine vegetation of Assam grows along the wet peripheries of rivers and wetlands. These areas are called riverine forests, and they once covered a large part of Assam.
The main characteristics of this vegetation are the presence of tall trees and grasses. Common trees include Chom, Showalu, Uriam, Moz, Ou, and Ajar, while the main grasses and bushy plants are Nal, Khagori, Tora, Koupat, Cane, Jao, and Kohua.
The importance of riverine vegetation lies in protecting riverbanks from erosion, providing habitats for wildlife, and maintaining the ecological balance. However, these forests are now declining rapidly due to the expansion of human settlements along the riverbanks.
22.State the location and land area of Kaziranga National Park.
Answer: Kaziranga National Park is located in the districts of Golaghat, Nagaon and Sonitpur. Its
Land area is 858.98 sq.km.
23.Write the names and location of the national parks of Assam.
Answer: The names and locations of the national parks of Assam are;
a) Kaziranga National Park: Golaghat, Nagaon and Sonitpur.
b) Manas National Park: Chirang and Baksa.
c) Orang National Park: Odalguri and Sonitpur.
d) Nameri National Park: Sonitpur.
e) Dibru-Saikhowa National Park: Dibrugarh and Tinsukia.
24.Write how the wildlife sanctuaries maintain the ecological balance.
Answer: The wildlife sanctuaries and national parks play a far-reaching role in nature conservation. These areas are protected from the destructive impact of human beings and serve as the home of wild elephants, tigers, rhinoceroses, buffaloes, deer, monkeys, and other wild animals. The presence of grasslands, trees, and wetlands in these protected areas attracts a large number of domestic and foreign tourists. The future of biodiversity of our state largely depends on the ability to protect these areas, which help in maintaining the ecological balance.
25.Write about the changes in administrative boundaries in Assam during the post-independence period.
Answer: After independence, the administrative boundaries of Assam changed several times. During the British rule, Meghalaya, Nagaland, and Sylhet (now in Bangladesh) were part of Assam. In 1947, after India’s partition, Sylhet was separated and joined East Pakistan (present-day Bangladesh). Later, Nagaland (1963), Meghalaya (1970), and Mizoram (1971) were created as separate states. The capital of Assam was shifted from Shillong to Dispur (Guwahati) in 1973.
Since 1971, Assam’s boundary has remained the same, but several new districts have been formed for better administration. At present, there are 33 districts, including six new ones formed in 2015–16 — Biswanath, Charaideo, Hojai, South Salmara–Mankachar, West Karbi Anglong, and Majuli.
The BTAD (Bodoland Territorial Area Districts) was created in 2003 to fulfil the aspirations of the Bodo tribal groups. It includes Kokrajhar, Chirang, Baksa, and Udalguri districts and aims to promote peace, development, and self-administration in the Bodoland region.
26. Write the names of the present districts of Assam and their headquarters.
Answer: The names of the present districts of Assam and their headquarters are-
Name of District:-District Headquarters
1. Dhubri:-Dhubri
2. Kokrajhar:-Kokrajhar
3. Goalpara:-Goalpara
4. Bongaigaon:-Bongaigaon
5. Chirang:-Kajalgaon
6. Barpeta:-Barpeta
7. Nalbari:-Nalbari
8. Baksa:-Masalpur
9. Kamrup:-Amingaon
10. Kamrup Metro:-Guwahati
11. Darrang:-Mangaldoi
12. Udalguri:-Udalguri
13. Sonitpur:-Tezpur
14. Lakhimpur:-North Lakhimpur
15. Dhemaji:-Dhemaji
16. Nagaon:-Nagaon
17. Morigao:-Morigaon
18. Golaghat:-Golaghat
19. Jorhat:-Jorhat
20. Sivasagar:-Sivasagar
21. Dibrugarh:-Dibrugarh
22. Tinsukia:-Tinsukia
23. Karbi Anglong:-Diphu
24. Dima Hasao:-Halflong
25. Karimganj:-Karimganj
26. Cachar:-Silchar
27. Hailakandi:-Hailakandi
28. Biswanath:-Biswanath Chariali
29. Charaideo:-Sonari
30. Hojai:-Sankardev Nagar
31. Majuli:-Garamur
32. South Salmara- Mankachar:-Hatsingimari
33. West Karbi Anglong:-Hamren
27. What is the land area of Assam? Where is the state's capital located? Write the names of the largest and smallest districts of Assam in respect of land area.
Answer: The land area of Assam is 78,438 square kilometres. The capital of Assam is located at Dispur (Guwahati). In respect of land area, Karbi Anglong district is the largest, covering 10,434 square kilometres, while the Kamrup Metropolitan district is the smallest, covering only 955 square kilometres.
28. What is the population of Assam according to 2011 Census? Write the names of the largest and smallest districts of Assam in terms of population size.
Answer: According to the 2011 Census, the population of Assam is 31.16 million. In terms of population size, Nagaon district is the most populous, with about 2.82 million people, while Dima Hasao district is the least populous, with a population of only 2.14 lakh.
29. Write Short Notes:
(a) Assam and Monsoon Climate
Answer: Assam has a sub-tropical monsoon climate mainly influenced by the south-west and north-east monsoon winds. The south-west monsoon brings heavy rainfall from June to September, while the north-east monsoon causes dry and cool weather in winter. The Himalayas obstruct the moist monsoon winds, leading to orographic rainfall, and also protect the state from cold Tibetan winds. Assam receives an average annual rainfall of about 200 cm, with high humidity and a temperature range of about 7°C in winter to 35°C in summer.
(b) South-West Monsoon Wind
Answer: The South-West Monsoon Wind is the main cause of rainfall in Assam during summer. It blows from the Bay of Bengal carrying warm and moist air. When these winds reach Assam, they are obstructed by the Himalayan ranges, Meghalaya Plateau, and other southern hills, causing orographic and cyclonic rainfall. This monsoon lasts from early June to the end of September and brings about 70% of Assam’s annual rainfall, averaging nearly 200 cm per year. The heavy rain during this season helps in the growth of crops like Sali paddy, but also causes floods in many areas.
(c) North-East Monsoon Wind
Answer: The North-East Monsoon Wind, also called the Retreating Monsoon, blows in Assam during October and November. It develops when high pressure forms over the Brahmaputra Valley due to a fall in temperature, while low pressure exists over the Bay of Bengal. This wind flows from the north-east to the south-west, opposite to the direction of the summer monsoon. Though generally dry, it sometimes absorbs moisture from the Brahmaputra and its tributaries and causes light rainfall in the south-western parts of Assam. During this season, humidity remains low and fog often forms in the mornings.
(d) Summer Season of Assam
Answer: The Summer Season in Assam generally lasts from early June to the end of September. During this time, the state comes under the influence of the south-west monsoon wind, which brings moderate to heavy rainfall almost continuously. The months of June, July, and August receive the maximum rainfall, nearly 70% of Assam’s total annual rainfall (about 200 cm). The temperature during summer rises to about 35°C. This season is very important for agriculture as the Sali paddy is transplanted. However, heavy rainfall often causes floods in the Brahmaputra and Barak valleys.
(e) Pre-Monsoon Season of Assam
Answer: The Pre-Monsoon Season in Assam lasts from early March to the end of May. During this period, the temperature gradually increases after winter. The mornings are pleasant, while afternoons become hot, often followed by rain with thunder and lightning in the evening or night. The weather remains unstable, and sometimes dust storms occur. Gradually, rainfall becomes more frequent, which helps in the cultivation of paddy, tea, and jute. This period also marks the spring season in Assam, when Bohag or Rongali Bihu, the festival of joy, is celebrated in mid-April.
(f) Spatial Distribution of Rainfall in Assam
Answer: Rainfall in Assam is unevenly distributed due to differences in topography and location. The state receives about 200 cm of rainfall annually, but the hills and foothills get much more. Upper Assam districts like Tinsukia, Dibrugarh, Dhemaji, Lakhimpur, and Sivasagar, and southern Assam districts like Cachar, Karimganj, and Hailakandi receive over 250 cm of rainfall, while central Assam areas such as Nagaon and Karbi Anglong get less — the Lanka–Lumding region gets only 129 cm a year.
(g) Administrative Divisions of Assam
Answer: The administrative divisions of Assam have undergone major changes since independence. Earlier, Assam included Meghalaya, Nagaland, and Sylhet (now in Bangladesh). After 1947, Sylhet was separated, and later Nagaland (1963), Meghalaya (1970), and Mizoram (1971) became separate states. The capital was shifted from Shillong to Dispur (Guwahati) in 1973.
At present, Assam has an area of 78,438 sq. km and a population of 31.16 million (2011 Census). The state now has 33 districts, including six new districts formed in 2015–16. Among them, Kokrajhar, Chirang, Baksa, and Udalguri are part of the BTAD (Bodoland Territorial Area Districts), formed in 2003 to meet the aspirations of the Bodo people.
(h) District Level Population of Assam
Answer: According to the 2011 Census, the total population of Assam is 31.16 million. Among all districts, Nagaon district has the highest population with about 2.82 million people, while Dima Hasao district has the lowest population with only 2.14 lakh people. The distribution of population in Assam is uneven due to geographical and economic factors. The fertile plains of the Brahmaputra and Barak valleys are densely populated, whereas the hilly areas have sparse population.
(i) BTAD
Answer: The BTAD (Bodoland Territorial Area Districts) was formed in 2003 to fulfil the hopes and aspirations of the Bodo tribal groups of Assam. It includes four districts — Kokrajhar, Chirang, Baksa, and Udalguri. These districts were created within the existing boundary of Assam to provide self-administration and promote the social, economic, and cultural development of the Bodo people. The BTAD plays an important role in maintaining peace, unity, and development in the Bodoland region.