The Face of the Land
Pakistan covers an area of 310,403 sq. miles of which 183,840 sq. miles in the north and west form mountainous terrain and tableland. The remaining 126,563 sq. miles comprise a flat gradational surface.
The lofty Himalayan mountains in the north of Pakistan, which extend eastward to form the northern rampart of India, are the “girders of Asia’s structure.” Their formation is explained as follows. In pre-Himalayan days, the area was occupied by a long, narrow, shallow sea, the Sea of Tethys, lying between two continents of ancient hard rocks, Angaraland to the north, and Gondwanaland to the south. (The plateau of Central Siberia and parts of the great plain of western Siberia are remnants of the northern block, and the Deccan and Arabian Plateaux remnants of the southern.) Sedimentary materials were deposited layer upon layer in the Sea of Tethys, the sandy materials forming sandstone, while organic remains, such as shells and the bones of sea animals, became limestone. As the northern and southern continental blocks were drawn toward each other by movements of the earth’s crust, the rocks in the sea of Tethys were compressed and contorted into fold mountains.
The uplift of the mountains continued in several intermittent phases, separated by long periods of time. Some of the upheavals were more pronounced than others. In the first major upheaval, the central axis of ancient sedimentary and crystalline rocks of the Himalayas was formed. The Murree sediments of the Potwar Plateau were formed in the second. In the third phase, the central part of the Himalayan system was further elevated and the outlying zone of the Siwaliks created.
The mountain-building movements were associated with subsidence of the northern part of the Deccan block, creating a deep trough. This trough began to be filled rapidly with sediments as a result of the increased erosive and carrying power of streams descending from the newly elevated mountains. The fracturing of the fold mountains still in the process of formation, may also have added to the amount of material to be transported. The weight of the sediments themselves may have depressed the earth’s crust, creating the trough. In any case the deposition formed the second great feature of the sub-continent, the Indo-Gangetic Plain. The thickness of the sediments beneath the Plain has been variously estimated to be between 6,500 and 15,000 feet.
Major Physical Divisions
The present study divides the country into five major physical divisions: the Himalayas; the Hindu Kush and the western bordering mountains; the Baluchistan Plateau; the Potwar Plateau and the Salt Range; and the Indus Plain. Within each of these there are a number of sub-divisions. For example, the Indus Plain includes the Upper Indus Plain, the Lower Indus Plain, and the Eastern Desert. Similarly, these divisions may be further sub-divided. Thus the Upper Indus Plain comprises: the Interfluves (doabs); the Himalayan Piedmont; and the Derajat or Sulaiman Piedmont. Still lower in the hierarchy, for example, are the individual doabs: Sind Sagar, Chaj, Rechna, Bari doabs, and the Bahawalpur plain.
The Himalayas comprises a series of ranges: (1) The Sub-Himalayas; 2,000-3,000 feet; (2) The Lesser Himalayas, 12,000-15,000 feet; (3) The Central or Great Himalayas, average altitude, 20,000 feet; (4) The Inner Himalayas or Ladakh Range; and (5) The Trans-Himalayan or Karakoram Ranges. Most of the zones 3,4 and 5 lie in the state of Jammu and Kashmir, large parts of which are occupied by India and are therefore excluded from the present discussion. The Sub-Himalayas or Siwaliks extend over the southern part Hazara and Murree and include the hills of Rawalpindi and the Pabbi Hills. Subjected to great strain and stress during the mountain-building period, the Siwalik rocks are much faulted, with many inverted or reverse folds and a high degree of dissection in the Pabbi Hills, where the material is unconsolidated.
The Lesser Himalayas occur in northern Hazara and Murree, where the main range, Dunga Gali, attains a height of over 15,000 feet in the north. The Dunga Gali descend into a number of spurs in the Murree Hills. The hill-station of Murree (7,445 feet) is a spectacular one hour drive from the Capital, Islamabad.
The Hindu Kush and the Western Mountains
The Hindu Kush branch off from the Himalayas at the Pamir Knot, where the borders of Pakistan, Afghanistan, U.S.S.R., and China meet. Whereas the strike of the Himalayas is northwest-southeast, that of the Hindu Kush is north-south. Peaks like Sad Istragh (24,170 feet) and Tirich Mir (25,263 feet) are capped with perpetual snow and ice. Several rangers branch south through Chitral, Swat and Dir, with deep, narrow valleys along the Chitral-Kunar, Panjkora and Swat rivers. Some passes permit communication. Abbottabad is connected with Gilgit through the Babusar Pass, the Lowari Pass connects Peshawar and Chitral, and the route from Chitral to Gilgit lies through Shandur Pass. Southward the altitude decreases to 5,000-6,000 feet in Mohmand Territory and the Malakand Hills.
South of the Kabul River, the strike of the ranges changes from north-south to west-east. The west-east strike is strongly represented by the Koh-i-Sofed Range. The general height of this range is 12,000 feet, with the highest peak, Sakaram, rising to 15,620 feet. Outliers in Kohat District have a height of 3,000-5,000 feet. South of the Koh-i-Sofed are the Waziristan Hills, with the same east-west alignment. The hills are traversed by the Kurram and Tochi rivers, and bounded on the south by the Gomal river.
South of the Gomal river, the Sulaiman Mountains run for a distance of about 300 miles in a north-south by direction. Takht-i-Sulaiman (11,295 feet) is the highest peak. At the southern end are the Bugti and Marri Hills, draining westward to the Bolan River.
The low Kirthar Hills run north-south and form the western boundary of the lower Indus Plain. The Hab and Lyari rivers drain into the Arabian Sea.
Pass through the western bordering mountains are of special geographical and historical interest. Comparatively broad passes, which are not difficult to traverse, occur south of the Kabul River. From north to south these are: Khyber, Kurram, Tochi, Gomal, and Bolan. The Khyber is sufficiently wide for the passage of troops, only 3,500 feet high at Landi Kotal, its highest point, and leads to the fertile Vale of Peshawar at the head of the Indo-Gangetic Plain. The total length of the Pass is 35 miles of which 25 (Jamrud-Torkham) are in Pakistan, and the remainder in Afghanistan. The Tochi pass connects Ghazni in Afghanistan with Bannu in Pakistan via northern Waziristan. The Gomal Valley provides a route from Afghanistan to Dera Ismail Khan. The Bolan Pass follows the river of the same name and connects the Kachhi-Sibbi Plain with Quetta. From Quetta a route goes to Chaman on the Pak-Afghan border, and thence to Kandahar. The route from Kandahar to Central Asia avoids the Hindu Kush which, after travelling northern Pakistan, continue into Afghanistan.
The Plateau of Baluchistan
The extensive plateau of Baluchistan has an average altitude of over 2,000 feet and is sharply divided from the Indus Plains by the Sulaiman, Kirthar, and Pak Ranges. It includes a great variety of physical features.
In the north-east, the Zhob-Loralai Basin forms a lobe surrounded on all sides by mountains. To the east and south lie the Sulaimans, which join the central Brahui Range near Quetta. The small Quetta Basin is surrounded on all sides by mountains, namely Zarghun, Takatu, Khalifat, Chiltan, and Murdar Ghar. In the north and north-west, the lobe is bordered by the Toba Kakar Range, the western extension of which is known as the Khwaja Amran Range.
The general terrain of north-western Baluchistan comprises a series of low-lying plateaux, some of which are separated from one another by mountain ranges. The Ras Koh Range in the east runs northeast-southwest. The Chagai Hills form the border with Afghanistan for some distance. This region is a true desert an area of inland drainage and dry lakes (hamuns), the largest of which is Hamun-i-Mashkel, some 54 miles long and 22 miles wide.
Southern Baluchistan includes the Sarawan area in the north and a vast wilderness of ranges in the south. The backbone of the mountain system of Baluchistan is the Central Brahui Range, which runs in a northeast-southeast direction for a distance of about 225 miles between the Zhob River in the north and the Mula River in the south. The Central and Coastal Makran Ranges lie to the south.
Along the coast are large areas of level mud flats forming the coastal plain or enclosed plains bordered by sandstone ridges. This arid coastal tract provides another route into the sub-continent, connecting the Lower Indus Plain with southern Iran.
The Potwar Plateau and the Salt Range
The Potwar Plateau is an area of about 7,00 sq. miles an elevation of 1,000-2,000 feet. It is bounded on the east by the Jhelum, on the west by the Indus, on the north by the Kala Chitta Range and the Margalla Hills, and on the south by the Salt Range. The gradual northern slope of the Salt Range makes the southern boundary of the Potwar ill-defined. The Plateau slopes from north-east to south-west and, with the exception of the south-eastern portion draining to the Jhelum, belongs to the Soan Basin. It is a typical “bad-land” cut up by deep-set ravines, known locally as Khaderas. Above the broken surface of the Soan Basin rise the limestone and sandstone hills of Khairi Murat, Kheri Mar and Kala Chitta.
The Salt Range is a feature of great geological interest since it presents a complete geological sequence from earliest times. The steep southern face, rising to about 2,000 feet, also evokes interest. It is an example of a “dislocation mountain”. Its orthoclinal outline suggests that these mountains are the result of a monoclinal uplift combined with vertical dislocation along their southern border which has depressed the other half underneath the plains.
The range begins in the east near the Jhelum in the Jogi Tilla and Bakralla Rides, and comprises parallel ranges of low, flat-topped hills enclosing small intermontane valleys, basin plains, or plateaux, and a number of saline lakes. Two of the larger lakes are Khabeki and Kallar Kahar. At Kalabagh the range crosses the Indus and then continues south-west into Bannu district.
Between the Indus and the western bordering ranges lie the Trans Indus Basins, including the Vale of Peshawar, the Kohat Valley, and the Bannu Plain. The Vale of Peshawar is hill-girt on all sides, except in the south-east where the Kabul River makes its way to the Indus. It spreads over the Peshawar and Mardan Districts. The Kohat Valley includes most of the district of Kohat, but is bordered by rugged hills. The Bannu Plain is 800-1,500 feet in elevation and is surrounded by hills, except in the south-east, where the combined Kurram and Tochi stream provides an opening toward the Indus. A narrow opening also exists towards D. I. Khan, through the Pezu Gap between the Bhittani and Marwat hills.
The Indus Plain
The Indus Plain forms the western part of the Indo-Gangetic plain of the northern part of the sub-continent. The general slope of the plain towards the sea is gentle, with an average gradient of one foot to the mile. The plain is featureless, but elements of microrelief assume great importance because of their relationship to flooding and irrigation.
Five distinct micro-relief landforms have been recognised. These are : active flood plain; meander flood plain; cover flood plain; scalloped interfluves; and tidal delta and deltaic plain.
Active flood plain is variously known as bet or khaddar land. It lies adjacent to a river, and is inundated almost every rainy season. It is often called ‘the summer bed of rivers”. The area is the scene of changing river channels, where erosion and deposition go on simultaneously. During the low-water season, the surface of the land can be seen scarred by numerous active or abandoned channels. Embankments or bunds have been built in many places along its outer margins to protect neighbouring areas from floods. The soils of the active flood plain are coarse-textured sand and silt. Active flood plain is found along all the rivers, except the lower half of the Ravi. Along the Indus this belt is quite wide from Kalabagh to the Delta.
Meander flood plain usually adjoins the active flood plain and is somewhat higher. It also occurs away from the present course of the river on the site of old channels. Identifying features are bars, meanders, levees, and ox-bow lakes. Relief is only a few feet, and soils differ because of diversity in materials deposited. The meander flood plain is widespread along the Jhelum, Chenab, and the upper reaches of the Ravi. Along the Indus, it is absent above Muzaffargarh, but widespread in Sind.
Cover flood plain consists of recent alluvium spread over former riverine features. The alluvial deposits have resulted from sheet floodings. The boundary between the meander flood plain and the cover flood plain is not sharp; the two often merge together. Because of the varying speeds of the flood waters at different locations and differences in the time of deposition, frequent changes of soil texture are noticeable. The cover flood plain is the most extensive of the plain areas in Sind, Bahawalpur, Ganji bar Rechna doab.
Scalloped interfluves or bars are found in the central, higher parts of the Chaj, Rechna and Bari doabs, but the Sind Sagar doab appear to have been covered by sand. Their boundaries are mostly formed by river-cut scarps, often over 20 feet high. Low sand or earth dunes appear on their southern ends. The soils of the scalloped interfluves are relatively uniform in texture over considerable distances, and the material is old alluvium or aeolian in origin.
Tidal Delta and Deltaic plain. The lower delta area is frequently inundated by tidal floods, creating saline waste-lands and tidal mud-flats. The Deltaic plain extends north to Thatta in an intricate pattern of low features formed by the many distributaries of the Indus. Its soils vary in texture from place to place.
The Upper Indus Plain
The Upper Indus Plain differs from the Lower Indus Plain in that major tributaries (Jhelum, Chenab, Ravi and Sutlej) divide the land surface into several interfluves or doabs. In the Lower Indus Plain there is but on large river, the Indus itself. The two plains are separated by a narrow corridor near Mithankot where the Sulaiman Ranges approach the river. The Upper Indus Plain is subdivided into four large doabs, plus the Bahawalpur Plain, and the Derajat or Sulaiman Piedmont.
The Sind Sagar Doab or Thal Desert (7.9 million acres) lies between the Indus and the Jhelum-Chenab, south of the Salt Range. About 80 per cent of the area is a gently undulating sand plain, with some tibbas or sand-dunes, the number and size of which increases from west to east. Here and there are narrow belts of level land (patti) between the sand hills.
The Chaj Doab (3.2 million acres) has as its central part the Kirana bar, above which rise some low bedrock hills known as the Kirana Hills. These outcrops are composed of old rocks similar to those of the Aravalli Hills in India. Narrow flood plains along the Chenab and Jhelum constitute 25 per cent of the area.
Rechna Doab (7.0 million acres) differs from the Chaj and Bari Doabs in that its northern and central parts are devoid of scalloped interfluves. This occurs only in the south in the Sandal bar. The bedrock hills near Chiniot, Sangla and Shah Kot in central Rechna Doab are similar to those of Chaj Doab.
Bari Doab (7.2 million acres) has extensive areas of cover flood plain and scalloped interfluve. The interfluve between the Ravi and the old course of the Beas is called Ganji Bar, while the high land between the old course of the Beas and the Sutlej is known as Nili Bar. These bars are long and narrow, and have some highly impermeable alkaline soils, locally known as Bara soils. The Sutlej cover flood plain has a number of channelways, the longest and deepest of which is the old abandoned course of the Beas.
The Bahawalpur Plain is grouped with the doabs because the riverine tract, known locally as Sind, is followed by an upland identical with the bars of the doabs. The north-eastern part is a cover and meander flood plain, the central part is a sand hill plain which has been largely levelled and irrigated, and the south-western portion is the cover flood plain of Dera Nawab. The area is a reclaimed part of the Thar Desert. Along its southern border is the Ghaggar channelway, a depression 3 miles in width.
The Derajat or Sulaiman Piedmont is seamed with numerous streams and torrents, as is also the Himalayan Piedmont on the northern border of the Indus Plain. The land here varies between flat and gently undulating, and the rivers have a comparatively steep gradient. The riverine tract, known locally as Sindhu, is narrow.
The Lower Indus Plain
The Lower Indus Plain is very flat, sloping to the south with an average gradient of only six inches per mile. Excluding the deltaic area, the predominant landforms are meander and cover flood plains. Meander flood plain is more extensive in the north-east sector of the upper Sind Plain, cover and meander plains are equally extensive in the upper and central Sind plains, and more than two-thirds of the lower Sind plain is cover flood plain.
The Kacchi-Sibi Plain is bounded on the north by the Marri-Bugti Ranges and on the west by the Kalat Ranges. Surrounded on three sides by arid mountains, it is a barren, desolate area, in which heat and aridity combined with uniformly textured soils, create ideal conditions for mirages. Its southern edge is its contact line with the Indus alluvium.
The Sind Plain forms the major part of the Lower Indus Plain. The upper Sind plain is agriculturally less developed, and more waterlogged and saline, than areas further south. Lake Manchhar is alternately full or dry according to the level of the Indus. The central part of the plain has a uniform landscape, but one outstanding feature is the Rohri cuesta, a ridge of nummulitic limestone, attaining a height of 250 feet and extending 30 miles south from Sukkur. The lower Sind plain, which starts from Hyderabad, is predominantly a cover flood plain. The Ganjo Takkar ridge, a cuesta of Kirthar limestone and an outlier of the Kohistan Rangers, stretches southward from Hyderabad for a distance of about 15 miles.
The Indus Delta has its apex some distance north-east of Thatta, where distributaries fan out to form the deltaic plain. Two of the larger distributaries are the Ochito and the Gungro. Many of the channels perform the dual function of distributaries and estuaries. The channel beds and their levees are higher than the adjacent lands, and the shallow troughs between them are often filled with water, resulting in swamps. The tidal delta is submerged at high tide, and has mangrove swamps and tamarisk groves in its western section. The eastern section is the Rann of Kutch, a saline marshy land. The coast is low and flat except between Karachi and Cape Monze, where the Pab Hills approach the shore.
The Karachi Plain has a thin mantle of soil over weathered bedrock. A few low hills rise to 50 feet. Shallow depressions are known as dhand. One of these, Haleji Dhand, is used as a reservoir for Karachi city.
The South-Eastern Desert spreads over eastern Bahawalpur, the eastern half of Khairpur, and the greater part of Tharparkar Districts. In Bahawalpur it is known as Cholistan or Rohi. The desert is separated from the central irrigated zone of the plain by the dry bed of the Ghaggar in Bahawalpur, and the Eastern Nara in Sind. The surface of the desert is a wild maze of sand-dunes and sand-ridges, occasionally rising 500 feet above the general surface. Generally speaking the alignment of the dunes is longitudinal in the south, where southerly winds are strong, becoming more and more transverse toward the north, where the winds are less strong and less constant in direction. With little rainfall and a low water table, the desert is a barren land of scattered, stunted, thorny bushes, mostly acacia.