Physiographic divisions of Assam
Physiographic divisions are the classification of a region into different parts according to its physical features such as:
Mountains / Hills
Plateaus
Plains
Valleys
A region is divided physiographically based on:
Relief – height and slope of land
Geological structure – rocks and tectonic history
Geomorphic processes – river action, erosion, deposition
Drainage pattern
Soil type and landform
Assam is located in the north-eastern part of India and exhibits diverse physiographic features due to the interaction of the Himalayan system, Peninsular Plateau, and riverine processes of the Brahmaputra and Barak rivers.
The physiography of Assam can be broadly divided into four major divisions:
| Physiographic Divisions of Assam | Area covered |
|---|---|
|
Plateau |
9% |
|
Hills |
9% |
|
Plains (Brahmaputra plain , Barak plain) |
78% (69% , 9%) |
|
Riverine Islands |
4% |
Plateau of Assam
A plateau is an elevated, flat-topped landform raised sharply above surrounding terrain with low relief and often steep slopes.
Plateaus in Assam are mainly represented by – the Karbi (Mikir) Plateau, and the Hameran Plateau , forming the northeastern extension of the Indian Peninsular Plateau and linking with the Meghalaya Plateau.
| Assam Plateau | Area covered |
|---|---|
|
1. Karbi AnglongPlateau |
6.7% |
|
2. Hameran Plateau |
2.3% |
1. Karbi Anglong Plateau (Mikir Hills)
Location and Nature
Lies south of the central Brahmaputra Valley, mainly in Karbi Anglong district; often called Karbi or Mikir Plateau.
Pear‑shaped plateau, about 7,000 sq km in area (covering 6.7% area of Assam), almost detached from the Hameran Plateau(covering 2.3% area of Assam) by the Kopili river.
Seperated from :
1. Hameran Plateau (west) by Kopili River and Nagaon Plains
2. Naga Hills (east) by Dhansiri river and Golaghat Plains.
Relief and Geology
Elevation generally 300–400 m; central part rises to about 1,300–1,360 m at Dambuksu Peak (highest point) and Singhason peak (2nd highest point) in Karbi Anglong.
Composed predominantly of ancient crystalline (Archaean) rocks; structurally an extension of the Shillong Plateau.
Rengma Range (Rengma Hills) is a hilly tract within the Karbi Anglong Plateau . It is made of Hard crystalline resistant rocks ,which is fairly subdued and least erroded by age- old weathering and erosion underb hot and humid tropical monsoon condition of Assam.
Land Use and Ecology
Dominated by dense forests, shifting cultivation patches, and small valleys supporting paddy and horticulture.
Important tribal habitat (Karbi, Dimasa, etc.), rich in biodiversity and mineral resources but ecologically fragile.
2. Hameran Plateau
Location and Nature
- Lies in West Karbi Anglong district (Hamren sub-division); often called Hamren or Hameran Plateau.
- Roughly rectangular plateau, about 3,000 sq km in area (covering 2.3% area of Assam),
- Separated from Karbi Anglong by Kopili River and its tributaries.
Relief and Geology
- Elevation generally 300–600 m rising towards Jaintia Hills.
- Highest peak between Karbi Langpi and Umiam rivers (exact height not specified because several peaks still remains unnamed).
- Composed of ancient crystalline rocks; structurally contiguous with Jaintia Plateau (eastern Meghalaya extension).
Land Use and Ecology
- Features steep to moderately sloping hilly surfaces ( > 80% area of West Karbi Anglong District), undulating plains, dense forests, and river valleys with paddy/horticulture.
- Tribal habitat (Karbi communities), biodiversity-rich with radial drainage pattern (rivers: Umiam/Killing, Karbi Langpi, Barapani, Kapili), ecologically sensitive due to erosion.
Hills of Assam
Assam is dominated by Hills (not Mountains), because the elevations are lower. This physiographic feature covers roughly 9% of Assam’s geographic area.
Barail and Southern Hills (North Cachar / Dima Hasao & Adjoining Ranges)
Location and Components
Popularly known as Barail range covering Southern Dima Hasao district and northern Cachar belts.
Acts as a water divide (Watershed) between Brahmaputra Valley to the north and Barak Valley to the south.
Relief and Orientation
Barail range trends roughly east–west; elevations often 1,000–1,800 m, with some peaks above 2,000 m in neighbouring Nagaland and Manipur sections.
Steep slopes, deep river valleys, and a rugged dissected topography.
The Barail ranges support the highest peaks of Assam.
Laike Peak (highest peak in the Barail Range) (1,959 m)
Theipibung (1,866 m),
Mahadeo (1,739 m) and
Kaukaha (1,736 m).
Geology and Drainage Role
Made up of folded and faulted sedimentary rocks, linking the Patkai–Naga hill system with Meghalaya Plateau.
They are not denuded like the Karbi Plateau because these are made of young tertiary folds; the ranges are high and alternate with valleys
Acts as a watershed:
North‑flowing streams drain into Brahmaputra.
South‑flowing streams join Barak and its tributaries.
Human and Ecological Significance
Sparse population; dominated by tribal communities with jhum (shifting) cultivation and emerging terrace farming.
Acts as a cultural divide between Assamese speaking Assamese people (North) and Bengali speaking Assamese people (South)
High forest cover; important for biodiversity, headwater protection, and landslide–flood linkages in both valleys.
Plains of Assam
Plain region in Assam forms a vast alluvial lowlands south of eastern Himalayas, with elevations 40-130m above the Mean Sea Level. Covering a geographic area of around 78% of Assam,they are further subdivided into :
| Assam Plains | Area covered |
|---|---|
|
1. Brahmaputra Plains |
69% |
|
2. Barak Plains |
9% |
1. Brahmaputra Plains
Location and Extent
- Largest plain of North East India.
Forms the northern and central part of Assam, running east–west along the Brahmaputra River.
Avg. Length roughly 720 km; avg. width 80 km, covering about 69% of Assam’s area.
Relief and Landforms
Broad alluvial plain with very low relief; average elevation mostly 40–130 m above Mean sea level (MSL).
Sadiya region : 174 m above MSL
Guwahati : 58 m above MSL
Dhubri : 34 m above MSL
- Structurally Brahmaputra Valley is quite similar to the north Indian planes.
- Plains are formed by the deposition of thick alluvium due to rivers originating from the Himalayas, Naga hills & Manipur Hills and from the nearby Meghalaya and Karbi plateau.
Dominant landforms:
Active and older floodplains, natural levees.
River islands (Chars/Chaporis) like Majuli.
Meander scars, ox‑bow lakes, beels (wetlands).
Brahmaputra Plains being a matured alluvial system exibit standard classifications like the Indo-Gangetic plains:
Bhabar (foothill gravel zone near Arunachal/Bhutan).
Terai (marshy tracts with sal forests).
Bhangar (older alluvial terraces).
Khadar (active floodplains with fresh silt).
Boundaries and Structural Setting
- Boundaries:
North: Himalayan foothills of Arunachal Pradesh and Bhutan.
South: Meghalaya Plateau;
East: Naga–Patkai hills;
West: merges with plains of West Bengal.
Middle region : Karbi Anglong–Mikir Hills.
Geologically part of the tethys sea region, filled with thick alluvial sediments.
- Boundaries:
Drainage
Main river: Brahmaputra
Important tributaries:
North bank tributaries of Brahmaputra: Subansiri, Jia Bharali, Manas,Sankosh etc.
South bank tributaries of Brahmaputra: Kopili, Dhansiri
Socio‑Economic Importance
Most densely populated and agriculturally important region of Assam.
Supports extensive rice cultivation, tea in adjoining uplands, major towns (Guwahati, Jorhat, Dibrugarh), and transport corridors along the river and NH network.
- Brahmaputra Plains in Assam accounts for 6.2% of the culturable area of the country
Barak Plains
Location and Extent
Situated in southern Assam; mainly includes Cachar, Sribhumi(Karimganj) and Hailakandi districts.
Much smaller than the Brahmaputra Valley (covering 9% of area of Assam) ; length and width broadly 40–50 km each.
Relief and Landforms
Alluvial plain formed by the Barak River and its tributaries; often called the Cachar plain.
Barak Plains are 75 m above MSL
Structurally Barak Valley is similar to the Brahmaputra Valley.
Enclosed by:
North: Barail range (North Cachar Hills).
East: Manipur Hills.
South: Mizo Hills.
West: merges into Surma–Kushiyara plains of Sylhet (Bangladesh).
Barak plains do not have the standard Indo-Gangetic classifications of bhabar, terai, bhangar, and khadar. Rather Barak plains are much smaller, enclosed by Barail hills on all sides (no direct Himalayan piedmont), so they lack bhabar/terai gradients. Instead, they show uniform khadar-like active floodplains with beels (wetlands) and minimal elevation differentiation.
Hydrology and Climate
Barak river originates in Japvo Peak along Nagaland–Manipur border bringing lots of sediments from there forming Barak Plains, and then flows through Cachar, then splits into Surma and Kushiyara in Bangladesh.
High rainfall, frequent floods and water‑logging; supports lush tea gardens and paddy fields.
Drainage
Main river: Barak
Important tributaries:
North bank tributaries of Barak : Jiri, Chiri, Madhura, Jatinga, Marang
South bank tributaries of Barak: Sonai, Rukni, Dhaleswari, singla,Longai0
Socio‑Economic Importance
Acts as a secondary agricultural and industrial pocket (silk, tea, small industries).
Culturally distinct (Bengali‑speaking majority) but physically similar to a mini‑Brahmaputra valley.
- Barak Plains: Account for about 0.5% of India’s culturable area
Riverine islands in Assam
Deposition of huge volume of sediments along the braided channel of Brahmaputra results in the formation of these sandbars in the Brahmaputra,locally named as ;
- Chars (small in size, shifting sandbars)
- Chaporis (larger and attached to riverbanks, stable vegetated islands)
They cover 3,608 sq km (4% of state area) and house ~25 lakh people. They are dynamic fluvial features vital for ecology, culture, and flood management.
Chars: Temporary, low-lying sand/silt deposits in braided Brahmaputra channels; highly erosion-prone, reform seasonally.
Chaporis: Larger, elevated stable islands with grasslands/forests; support permanent settlements.
Formed by aggradation (sediment deposition) during floods; Brahmaputra carries ~1.5 billion tonnes silt annually, creating ~2,000 such features.
Distribution and Major Islands
Brahmaputra River Islands
Well distributed along the full length of River brahmaputra.
Majuli Island: World’s largest river island ; between Brahmaputra (south) and Kherkutia Xuti-Subansiri (north); India’s first island district (2016).
Others: Umananda (smallest, Guwahati), Neematighat chars, etc.
Barak Valley Islands
Fewer, smaller due to narrower single-channel flow; minor chars in Surma-Kushiyara system.
Physical Characteristics of Chars / Chaporis
Elevations: 1–10 m above riverbed; flood-prone annually.
Soils: Coarse sand/silt; fertile post-flood but infertile during dry seasons.
Vegetation: Tall elephant grass (Nara/Phumdi), grasslands.
Erosion shrinks ~10–15% area yearly.
Socio-Economic Significance
Population and Livelihood
Population of Chars/Chaporis; ~24.9 lakh people (5–6% of Assam).
Dominant communities : Mising, Nepalis, Bengali Muslims dominant.
Social conditions; high poverty, flood vulnerability.
Economy: Single-crop paddy, fishing, livestock; Directorate of Char Areas Development aids infrastructure.
Cultural Importance
Majuli: Vaishnavite Sattras (30+ monasteries), neo-Vaishnavite hub founded by Sankardev; Majuli is also under UNESCO tentative site.
Tribal festivals, mask-making, migratory bird roosts.
Ecological Role
Biodiversity hotspots: Grasslands for tigers (Brahmaputra tiger corridor), birds (IBA sites), Gangetic dolphins.
Flood buffers, silt traps; wetland nurseries (beels on chars).
Threats: Erosion (Majuli lost 70% area), encroachment, grassland burning, climate change.
Challenges and Government Initiatives
Erosion: ~4,000 ha lost yearly; chars shift 1–2 km annually.
Floods/Isolation: No bridges; ferry-dependent access.
Government Initiatives:
Char Areas Development Mission (reclamation from encroachers),
Embankment protection – Aimed at phased strengthening of embankments against Brahmaputra erosion/floods.
Majuli Master Plan – Assam’s integrated strategy for protecting the world’s largest river island (Majuli) from Brahmaputra erosion/floods while promoting sustainable development, culture, and carbon neutrality.
- Zero Erosion 2030 initiative – an ambitious vision by Assam government to completely eliminate riverbank erosion, particularly along the Brahmaputra and Barak rivers, by 2030.
Let us know any further suggestions ,we at sudurbhai.com will be happy to hear from you in our comment section below !