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Physiography


Physiography is the description including form, substance, arrangement and changes of especially, natural features. The term was introduced in geography in 1869 by Huxley for the study or description of 'natural phenomena in general', but later came to mean, 'a description of the surface features of the earth, as bodies of air, water and land', with an emphasis on mode of origin; ie it became synonymous with physical geography, and embraced geology, pedology, meteorology and oceanography. Still later, the term was restricted to the part of physical geography that is involved with the description and origin of landforms. Physiographic region/unit refers to a region of which all parts are similar in terms of physical characteristics and which consequently had a uniform geomorphic history, and whose pattern of topographical features or landforms differs significantly from that of adjacent regions.

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With about half of its surface below the 10m contour line, Bangladesh is located at the lowermost reaches of three mighty river systems - the ganges-padma river system, brahmaputra-jamuna river system and surma-meghna river system. Coinciding with the division of the country based on altitude and relief, the land can be divided into three major categories of physical units: Tertiary hills, Pleistocene uplands and Recent plains (formed in recent epoch). The heavy monsoon rainfall coupled with the low altitude of major parts of the country make floods an annual phenomenon in Bangladesh.

Quaternary (began about 2 million years ago and extends to the present) sediments, deposited mainly by the ganges, brahmaputra (jamuna) and meghna rivers and their numerous distributaries, cover about three-quarters of Bangladesh. The physiography and the drainage pattern of the vast alluvial plains in the central, northern and western regions have gone under considerable alterations in Recent times. The deposition of Quaternary sediments was influenced and controlled by structural activities. The eastward shift of the Ganges and tista as well as the significant westward shift of the Brahmaputra during the last 200 years gives evidence of epeirogenic movements even in recent days. Hillocks and hills are confined to a narrow strip along the southern spur of the shillong plateau, to the eastern and southern portions of the Sylhet district, and to the chittagong hill tracts (CHT) in the southeast of the country bordering upon the Indian states of Tripura and Mizoram and Myanmar.

In the context of physiography, Bangladesh may be classified into three distinct regions (a) floodplains, (b) terraces, and (c) hills each having distinguishing characteristics of its own. The physiography of the country has been divided into 24 sub-regions and 54 units. Major sub-regions and units are as below:

i) Old Himalayan Piedmont Plain; ii) Tista Floodplain; iii) Old Brahmaputra Floodplain; iv) Jamuna (Young Brahmaputra) Floodplain; v) Haor Basin; vi) Surma-Kushiyara Floodplain; vii) Meghna Floodplain - a. Middle Meghna Floodplain, b. Lower Meghna Floodplain, c. Old Meghna Estuarine Floodplain, d. Young Meghna Estuarine Floodplain; viii) Ganges River Floodplain; ix) Ganges Tidal Floodplain; x) Sundarbans; xi) Lower Atrai Basin; xii) Arial Beel; xiii) Gopalganj-Khulna Peat Basin; xiv) Chittagong Coastal Plain; xv) Northern and Eastern Piedmont Plain; xvi) Pleistocene Uplands: a. Barind Tract, b. madhupur tract and c. Tippera Surface; xvii) Northern and Eastern Hills a. Low Hill Ranges (Dupi Tila and Dihing Formations), b. High Hill or Mountain Ranges (Surma and Tipam Formations).

Old Himalayan piedmont plain the gently sloping land at the foot of hills formed with colluvial and alluvial sediments deposited by rivers or streams. A portion of the Old Himalayan Piedmont plain stretches into Bangladesh at the northwestern corner of the country. This occupies most of the Dinajpur region. This region is covered by Piedmont sands and gravels which were deposited as alluvial fans of the mahananda and karatoya rivers and their distributaries issuing from the Terai area at the foot of the himalayas. The piedmont deposits may possibly be as old as late Pleistocene or early Holocene, but they are younger than madhupur clay. The drainage pattern is braided, with broad, smooth, but irregular-shaped ridges crossed by numerous, broad shallow channels which frequently branch out and reconnect. The Tista abandoned this landscape a long time ago, since when the area appears to have uplifted so that the small rivers crossing the plain are now entrenched up to about 6m deep (in the north; less in the south) below the main level of the plain. This plain gently slopes south from about 96m down to 33m above MSL (Mean sea level). This physiographic unit underlies most of the northwestern corner of the country, ie, entire Thakurgaon and the major parts of the Panchagarh and Dinajpur districts.

Tista floodplain A big sub-region stretches between the Old Himalayan Piedmont Plain in the west and the right bank of the N-S flowing Brahmaputra in the east. An elongated outlier representing the floodplain of the ancient Tista extends up to Sherpur (Bogra district) in the south. Most of the land is shallowly flooded during monsoons. There is a shallow depression along the ghaghat river, where flooding is of medium depth. The big river courses of Tista, dharla and dudhkumar cut through the plain. The active floodplain of these rivers, with their sandbanks and diyaras, is usually less than six kilometres wide.

Old Brahmaputra floodplain In 1787, a remarkable change in the course of the Brahmaputra took place. In that year, the river shifted from a course around the eastern edge to the western side of the Madhupur Tract. This new portion of the Brahmaputra is named Jamuna. The old course (old brahmaputra) between Bahadurabad and Bhairab shrank through silting into a small seasonal channel only two kilometre wide. The old river had already built up fairly high levees on either side over which the present river rarely spills. The Old Brahmaputra floodplain stretching from the southwestern corner of the Garo Hills along the eastern rim of the Madhupur Tract down to the Meghna exhibits a gentle morphology composed of broad ridges and depressions. The latter are usually flooded to a depth of more than one metre, whereas the ridges are subject to shallow flooding only in the monsoon season.

Jamuna (Young Brahmaputra) floodplain A dual name is used for the mighty Brahmaputra, because the Jamuna channel is comparatively new and this course must be clearly distinguished from that of the older Brahmaputra. Before 1787, the Brahmaputra's course swung east to follow the course of the present Old Brahmaputra. In that year, apparently, a severe flood had the effect of turning the course southwards along the Jenai and Konai rivers to form the broad, braided Jamuna channel. The change in course seems to have been completed by 1830. Due to the upliftment of the two large Pleistocene blocks of Barind and Madhupur, the zone of subsidence between those turned to a rift valley and became the new course of the Brahmaputra and came to be known as the great Jamuna. Both the left and right banks of the river are included in this sub-region. The Brahmaputra-Jamuna floodplain can again be subdivided into the Bangali-Karatoya floodplain, Jamuna-Dhaleshwari floodplain, and diyaras and chars.

The right-bank of the Jamuna - once a part of the Tista floodplain is part of the bigger floodplain. Several distributaries of the Jamuna flow through the left-bank floodplain, of which the dhaleshwari is by far the largest and sub-classed, namely, the Jamuna-Dhaleshwari floodplain. The southern part of this sub-region was once a part of the Ganges floodplain. Along the Brahmaputra-Jamuna, as along the Ganges, there are many diyaras and chars. In fact, there are more of them along this channel than in any other river in Bangladesh. There is a continuous line of chars from where this river enters Bangladesh to the off-take point of Dhaleshwari river. Both banks are punctuated by a profusion of diyaras. The soil and topography of chars and diyaras vary considerably. Some of the largest ones have point bars and swales. The elevation between the lowest and highest points of these accretions may be as much as 5m. The difference between them and the higher levees on either bank can be up to 6m. Some of the ridges are shallowly flooded but most of the ridges and all the basins of this floodplain region are flooded more than 0.91 m deep for about four months (mid-June to mid-October) during the monsoon.

Haor basin a large, gentle depressional feature, is bounded by the Old Brahmaputra floodplain in the west, the Meghalaya Plateau's foothills in the north, Sylhet High Plain in the east and Old Meghna Estuarine floodplain on the south. Its greatest length, both E-W and N-S, is just over 113 km. Numerous lakes (beels), large swamps and haors cover this saucer-shaped area of about 7,250 sq km. The sinking of this large area into its present saucer-shape seems to be intimately connected with the uplift of Madhupur Tract. Local tradition has it that the land sank 9 to 12m in the last 200 years. This area is still undergoing persistent subsidence. In addition to the hills located along the southern spur of the Shillong Massif, a number of hillocks, locally known as tila, form minor but morphologically distinct, ranges around Sylhet in northeastern Bangladesh. These elevations, as for instance Kailas Tila, Dupi Tila and the tilas at Beanibazar, east of Sylhet, are generally built up of Plio-Pleistocene clastic sediments and reach maximum elevations of about 60m above MSL. It is regularly flooded during the monsoon.

Surma-Kushiyara floodplain comprises the floodplain of rivers draining from the eastern border towards the Sylhet Basin (Haor Basin). Some small hill and piedmont areas near Sylhet are included within the boundaries. Elsewhere, the relief generally is smooth, comprising broad ridges and basins, but it is locally irregular alongside river channels. The soils are mainly heavy silts on the ridges and clays in the basins. This area is subject to flash floods in the pre-monsoon, monsoon and post-monsoon seasons, so the extent and depth of flooding can vary greatly within a few days. Normal flooding is mainly shallow on the ridges and deep in the basins.

Meghna floodplain is divided into four sub-regions: a) Middle Meghna floodplain, b) Lower Meghna floodplain, c) Old Meghna estuarine floodplain, and d) Young Meghna Estuarine floodplain.

Middle Meghna Floodplain The main channel of the Meghna upstream from its junction with the Dhaleshwari and Ganges as far as Bhairab Bazar is known as the middle Meghna. The floodplain of this river occupies a low-lying landscape of broad islands and many broad meandering channels which formed part of the Brahmaputra before it abandoned this channel when it changed course into the Jamuna two centuries ago. The Meghna sediments are mainly silty and clays and sandy Brahmaputra sediments occur at the surface on some ridges in the north. Seasonal flooding from the Meghna is mainly deep. Basin sites are submerged early and drain late.

Lower Meghna floodplain Southward from the junction of the Meghna and Ganges, the sediments on the left bank of the lower Meghna comprise mixed alluvium from the Ganges, Jamuna and Meghna. These deposits are predominantly silty. Close to the riverbank the deposits are slightly calcareous because of the inclusion of Gangetic material. Further inland, the sediments are not calcareous and many have been deposited before the Ganges shifted from the arial khan channel into the present Lower Meghna in around 1840 AD. This floodplain area has a slightly irregular ridge and basin relief, but also has large mounds used for settlement and cultivation. Seasonal flooding was formerly moderately deep, fluctuating in depth twice daily with the tides in the south, but flooding is mainly shallow and by rainwater within the area protected and drained by the Chandpur irrigation project.

Old Meghna Estuarine floodplain The landscape in this extensive unit is quite different from that on river and tidal floodplains. The relief is almost level, with little difference in elevation between ridges and basins. Natural rivers and streams are far apart in the southern part and drainage is provided by a network of man-made canals (khal). The sediments are predominantly deep and silty, but a shallow clay layer in some basin centres overlies them. Seasonal flooding is mainly deep, but it is shallow in the southeast. Some basin centres stay wet throughout the dry season. Virtually everywhere, this flooding is by rainwater ponded on the land when external rivers flow at high levels; the exceptions are the narrow floodplains alongside small rivers (such as the gumti) which cross the unit from adjoining hill and piedmont areas.

Young Meghna Estuarine Floodplain This sub-unit occupies almost the level land within and adjoining the Meghna estuary. It includes both island and mainland areas. New deposition and erosion are constantly taking place on the margins, continuously altering the shape of the land areas. The sediments are deep silts, which are finally stratified and are slightly calcareous. In many, but not all parts, the soil surface becomes saline to varying degrees in the dry season. Seasonal flooding is mainly shallow, but fluctuates tidally, and is caused mainly by rainwater or non-saline river water. Flooding by salt water occurs mainly on the lamed margins and during exceptional high tides during the monsoon; also when storm surges associated with tropical cyclones occur.

Ganges river floodplain comprises the active floodplain of the Ganges and the adjoining meander floodplain. The latter mainly comprises a smooth landscape of ridges, basins and old channels. The relief is locally irregular alongside the present and former river courses, especially in the west, comprising a rapidly alternating series of linear low ridges and depressions. The Ganges channel is constantly shifting within its active floodplain, eroding and depositing large areas of new char land each flood season, but it is less braided than that of the Brahmaputra-Jamuna. Ganges alluvium is calcareous when deposited, but most basin clays and some older ridge soils have been decalcified and acidified in their upper layers; lime is found only in the subsoil or substratum of such soils. Clay soils predominate in basins and on the middle parts of most ridges, with loamy soils (and occasionally sands) occurring mainly on ridge crests.

Seasonal flooding is mainly shallow in the west and north, with the highest ridge crests remaining above normal flood levels, but flood depths increase towards the east and the south. Flooding is mainly by accumulated rainwater and the raised groundwater table, except on the active Ganges floodplain and close to distributary channels which cross the meander floodplain. In time of small-scale mapping, Mahananda floodplain in the northwest and some detached areas of the Old Meghna estuarine floodplain in the southeast used to be included within this unit. The Mahananda floodplain comprises all irregular landscapes of mixed Tista and Ganges sediments. The cut-off parts of the Meghna floodplain have a smooth relief and predominantly silty soils, which are deeply flooded (by rainwater) in the monsoon season. The unit covers most of the districts of Rajshahi, Natore, Pabna, entire Kushtia, Rajbari, Faridpur, Meherpur, Chuadanga, Jhenaidaha, Magura, parts of Manikganj, Narayanganj, Munshiganj, Shariatpur, Madaripur, Barisal, Gopalganj, Narail, Khulna, Bagerhat, Satkhira, and most of Jessore. This physiographic unit is almost triangular in shape and bounded by the Ganges tidal floodplain on the south. On its southern end it traps the Gopalganj-Khulna Beels.

Ganges tidal floodplain The boundary between this unit and the Ganges floodplain is traditional. The tidal landscape has a low ridge and a basin relief crossed by innumerable tidal rivers and creeks. Local differences in elevation generally are less than 1m compared with 2-3m on the Ganges floodplain. The sediments are mainly non-calcareous clays, but they are silty and slightly calcareous on riverbanks and in a transitional zone in the east adjoining the lower Meghna. This unit covers most of Satkhira, Khulna, Bagerhat, Pirojpur, Barisal, Patuakhali, Bhola and the entire Jhalokati and Barguna districts but excludes the sundarbans in the southwest.

The river carries fresh water throughout the year in the northeast and east, but saltwater penetrates increasingly further inland towards the west, mainly in the dry season, but for most or all of the monsoon in the southwest. In the northeast, there is moderately deep flooding in the monsoon season, mainly by rainwater ponded on the land when the Ganges distributaries and the lower Meghna are at high flood levels. Elsewhere, there is mainly shallow flooding at high tides, either throughout the year, or only in the monsoon, except in the extensive areas where tidal flooding is prevented by embankments. Within embankments, there is seasonal flooding with accumulated rainwater. The soils are non-saline throughout the year over substantial areas in the north and the east, but they become saline to varying degrees in the dry season in the southwest.

Sundarbans South and southwest of the Ganges tidal floodplain, there is a broad belt of land, barely above sea level with an elevation of only 0.91m. This very low land of some 4,827 sq km area contains the Sundarbans forest and the reclaimed estates (cultivated land) - classified as the Sundarbans unit. There are two possible causes for the existence of such a large very low estuarine area - insufficient deposition by the Ganges distributaries or subsidence. The main distributaries of the Ganges never flowed through this region, and the small ones that did last a few centuries at most. The building up of this estuarine area is consequently not complete. On the other hand, it is possible that subsidence has played a major part in depressing this area. There are many evidences of this, such as large ruins in the heart of the swampy estuarine areas such as at Shekertek and Bedkashi, and the presence of human artefacts and tree stumps, buried in the alluvium many feet below the sea level. There is also an isolated part of Sundarbans (Chakaria Sundarbans) at the mouth of the matamuhuri river near Cox's Bazar.

Lower Atrai basin A small physiographic unit occupies a low-lying area where mixed sediments from the atrai and Ganges and from the barind tract overlie the down-warped southern edge of the Barind Tract. The landscape north of the Atrai is mainly smooth, but floodplain ridges and extensive basins occur south of the river. Heavy clay soils predominate, but loamy soils occur on ridges in the south and the west. Drainage from this unit is blocked when high river levels in the Jamuna obstruct the exit through the hurasagar. Seasonal flooding was formerly deep and extensive areas in chalan beel used to remain wet throughout the year. The construction of polder projects since the 1960s has improved drainage to some extent. However, deep flooding can still occur within polders as well as outside when there is heavy rainfall locally and when flash floods flow down the Atrai or off the adjoining Barind Tract, causing natural or manmade breaches of embankments.

Arial Beel a large depression of about 723 sq km lying between the Ganges and the Dhaleshwari south of Dhaka. Heavy clays occupy almost the whole landscape. Despite the proximity to the two major river channels, the deep seasonal flooding is predominantly by accumulated rainwater which is unable to drain into rivers when they are running at high levels. Much of this unit remains wet in the dry season.

Gopalganj-Khulna peat basin occupies a number of low-lying areas between the Ganges river Floodplain and the Ganges tidal floodplain. The major two beels of the area are Baghia Beel and Chanda Beel. Thick deposits of peat occupy perennially wet basins, but they are covered by clay around the edges and by calcareous silty sediments alongside the Ganges distributaries crossing the area. This is the largest peat stock basin of Bangladesh. The basins are deeply flooded by clear rainwater during the monsoon. In the basin close to Khulna, the floodwater is somewhat brackish. Subsiding process is still active in this physiographic unit.

Chittagong coastal plain the plain along the coast extends from the feni river to the mouth of the Matamuhuri delta, a distance of 121 km. It comprises gently sloping piedmont plains near the hills, river floodplains alongside the Feni, karnafuli, halda and other rivers, tidal floodplains along the lower courses of these rivers, a small area of a young estuarine floodplain in the north, adjoining sub-regional young Meghna estuarine floodplain, and sandy beach ridges adjoining the coast in the south. Sediments near the hills are mainly silty, locally sandy, with clays more extensive in floodplain basins. The whole of the mainland area is subjected to flash floods. Flooding is mainly shallow and fluctuates in depth with the tide (except where this is prevented by river or coastal embankments). The average daily rise in the tide is about two metres. Some soils on tidal and estuarine floodplains become saline in the dry season.

Northern and eastern piedmont plains generally sloping piedmont plains border the northern and eastern hills; (similar piedmont plains adjoining the hills in Chittagong region have been included in the Chittagong coastal plain). These plains, which comprise coalesced alluvial fans, mainly have silty or sandy deposits near to the hills, grading into clays in the basin adjoining the neighbouring floodplains. The whole area is subject to flash floods during the rainy season. On the higher parts, flooding is mainly intermittent and shallow; but it is moderately deep or deep in the basin. The sub-region covers most or parts of the upazilas of Nalitabari (Sherpur), Tahirpur, Bishwamvarpur, Dowarabazar, Companiganj (Sylhet), Gowainghat, Madhabpur, Habiganj Sadar, Chunarughat, Sreemangal, Kamalganj and Kulaura.

Pleistocene uplands comprising the lalmai hills of Comilla district together with the low hills in the east through Dhaka and Rajshahi divisions to West Bengal of India. The river systems of the Meghna and the Jamuna trisect the Pleistocene upland giving rise to three blocks of high lands that exhibit smooth rolling topography. The Barind Tract, the Madhupur Tract, and the Tippera Surface form three individual blocks. The Ganges limits the western, and the buriganga and Dhaleshwari, the two distributaries of the Jamuna, limit the southern extremities of the Pleistocene uplands. In the northernmost strip of Rajshahi division, Pleistocene upland merges with the piedmont of Himalayas and in the district of Mymensingh slopes down to the alluvial plains. Pleistocene uplands cover an area of about 10% of Bangladesh with an average elevation of more than 15m above MSL.

Barind Tract It comprises mid and lower western part of Rajshahi division, between the Ganges and Brahmaputra. The largest one of the three Pleistocene upland blocks, the Barind Tract spreads over an area of about 7,770 sq km. In the south, the Barind Tract is an older pleistocene terrace forming a small plateau with a flat or - in some sectors - a slightly undulating surface. This terrace consists of reddish and yellowish and partially mottled clays and is characterised morphologically by a dendritic drainage pattern, which is typical of all older Pleistocene terraces in Bangladesh. The Barind unit is comparatively at higher elevation than the adjoining floodplains. The contours of the tract suggest that there are two terrace levels - one at 40m and the other between 19.8 and 22.9m. Therefore, when the floodplains go under water during monsoon the Barind Tract stands free from flooding and is drained by a few small streams. About 47% of the Barind region is classified as highland, about 41% as medium-high land, and the rest are lowland. The depression at the southeast of the Barind Tract is called the bhar basin. It includes parts of Rajshahi and Pabna districts, with its centre in the vast marshy area called the Chalan Beel.

Madhupur Tract Another Pleistocene upland block in the Bengal Basin is located in the central part of Bangladesh comprising greater Dhaka and Mymensingh districts, between the courses of the Old Brahmaputra and the Jamuna rivers. Towards the south, this physiographic sub-region extends to as far as Dhaka, the capital of the country. Madhupur Tract measures about 4,105 sq km. Comparable to the Barind Tract, the area belongs to a Pleistocene terrace consisting mainly of red coloured and mottled clays. It is characterised by plateau-like hillocks varying in height from 9 to 18.5m, and a dendritic drainage pattern, typical of all Pleistocene terraces in Bangladesh. The valleys, mostly flat, are cultivated. The Madhupur jungle contains Shal trees (Shorea robusta), the hardwood which is second to teak in value.

Tippera Surface The area between the Meghna floodplain in the west and the tripura hills in the east was uplifted in Early Recent times. This physiographic unit consists of a Pleistocene terrace in the east, ie the Lalmai terrace, and the post-Pleistocene deltaic plain of the Tippera surface. The latter is made up of estuarine sediments of Early Recent age. The present-day rectangular drainage pattern of this flat area was artificially developed for irrigation purposes. The western edge of the Tippera surface grades transitionally into the Meghna floodplain. The Lalmai terrace, skirting the western slopes of the Tripura hills, consists of red, mottled clay, of the Pleistocene Madhupur clay type. Comparable to the Barind and Madhupur tracts, the Lalmai terrace displays the typical dendritic drainage pattern of all Pleistocene terraces. The surface is slightly undulating, except the Lalmai hills, with elevations ranging from 6 to 50m above MSL. It has been uplifted 1.22m to 1.83m in relation to the adjacent floodplains during the Holocene time (from 0.1 million years to the present).

Northern and eastern hills Hilly areas of Bangladesh comprise two main kinds of topography - a) Low Hill Ranges (Dupi Tila and Dihing Formations), b) High Hill or Mountain Ranges (Surma and Tipam Formations).

Low Hill Ranges comparatively low hill ranges occur between and outside the high hill ranges. They are mainly formed over unconsolidated sandstone and shale. Their summits generally are <300m above MSL. Most areas are strongly dissected, with short steep slopes, but there are some areas with rolling to early-level relief (eg in the best tea-growing areas of Sylhet region). In the Sylhet region, there are four main hillocks in the northern zone and six hill ranges project into the south of Sylhet district from the Indian state of Tripura. These six ranges, which project into the plains from the south, are, from east to west, Patharia, Harargaj, Rajkandi-Ita, Bhanugach, Tarap and Raghunandan.

In the Chittagong region, this unit includes the Sitakunda and Mara Tong ranges and the complex of hills to the south and east of Ramgarh, including the eastern part of the Middle Feni river valley. The Sitakunda range has 32-km long ridge in the middle, which reaches 352m at Sitakunda peak. To the north, the high peaks on this range are Rajbari Tila (274m) and Sajidhala (244m). To the south, there is an abrupt fall and Chittagong city heights are less than 92m. In the Mara Tong range a height of only 113m is reached. Further northeast the hills are higher. The topography is deeply eroded and rounded; the valleys are curved and almost isolated hillocks are common. At the Sitakunda peak, there are several hot springs. There are five broken ranges of hills between Karnafuli river and the southern tip of Bangladesh. South of bakkhali river the hills reach the sea at Cox's Bazar. Thereafter the main mass of hills goes down the Teknaf peninsula as the Teknaf range. There is a slight break in the west along the Rejukhal valley. In its northern part, the Teknaf range is comparatively low (61 to 91m). From Whykong a high ridge runs south; its main peaks are Baragong (119m), Taunganga (268m), and Nytong (168m). The southwestern end of this range ends at a village called Noakhali where there are a series of impressive cliffs, some 30m in height. The range ends at Teknaf Bazar. South of Gorjania (northeast of Teknaf peninsula) these hills continue into Myanmar. The Rejukhal valley is an important component of this broken-up landscape.

High hill or mountain ranges This sub-unit comprise an almost parallel ridge running approximately north-south and with summits reaching 300-1000 m. They have very steep slopes - generally >40%, often 100% and are subject to landslide erosion. They are mainly underlain by consolidated shales, siltstones and sandstones. This unit covers most of Chittagong Hill Tracts, some small parts of southern Habiganj, and the south and eastern borders of Maulvi Bazar. All the mountain ranges of the Hill Tracts are almost hogback ridges. They rise steeply, thus looking far more impressive than their height would imply, and extend in long narrow ridges, whose tops are barely 30m wide. Most of the ranges have scarps in the west, with cliffs and waterfalls.

These are different from the low rounded foothills to the west. There are extensive stretches of low hills and hillocks in between the ranges. Four ranges, with an elevation of over 300m, strike in N-S direction in the northern part of the region. The western-most, the Phoromani range, reaches 463m at Phoromani, 436m at Rampahar, and 417m at Bhangamura. The next range eastwards is the Dolajeri; its highest peak is Langtrai (429m). On the eastern side of this range are several high waterfalls: two of the highest have falls of 60 and 40m. Further east, across the Maini valley is the Bhuachari range, which rises to 611m at Changpai peak. The eastern-most, within Bangladesh, is the Chipui-Lungsir range (also known as the Barkal range). Its highest peaks, from north to south, are Khantlang (683m), Thangnang (735m), Lungtian (679m), Chipui (480m), Bara Toung (447m), and Barkal (572m).

South of the Karnafuli there are seven main mountain ranges within Bangladesh. The Muranja range rises out of the Chunoti hills 5 km east of Harbang, and strikes in a southeasterly direction. Its well-known peaks are Muranja (502m), Nashpo Taung (586m), and Basitaung (664m). East of the Muranja range and also roughly parallel to it are the Tyanbang, Batimain and Politali ranges. The Tyanbang or Chimbuk range rises south of Sangu river and continues into Myanmar. Its main peaks are Lulaing (720m), Thainkhiang (894m), Kro (868m), Rungrang (849m), and Tindu (898m). On a branch of the Lulaingkhal, near Lulaing peak, there is a waterfall of 107m height. The high peaks within Bangladesh are Waibung (808m), Mowdok Tlang (905m), Rang Tlang (958m), Mowdok Mual (1,004m) and Tajingdong, which is the highest peak of Bangladesh, officially called as Bijoy (1,280m). [Masud Hasan Chowdhury]

Bibliography FH Khan, Geology of Bangladesh, University Press Limited, Dhaka, 1991; Haroun Er Rashid, Geography of Bangladesh, University Press Limited, Dhaka, 1991; Klaus-Ulrich Reimann, Geology of Bangladesh, GebrFCder Borntraeger, Berlin-Stuttgart, 1993; Hugh Brammer, The Geography of the Soils of Bangladesh, University Press Limited, Dhaka, 1996.