Showing posts with label geography. Show all posts
Showing posts with label geography. Show all posts

Sunday, September 25, 2022

Marine Environment as Resource

Photo: Twitter/@cmlr_Kochi

The marine environment has emerged as a field of diversified resources in recent decades. Its importance is described in Indian mythological books but the functional effectiveness is established during recent years. It covers about 71% of the geographical area of the globe and its proper development for humankind would solve problems of the exhaustion of several resources. 

Continental resources occupying 29% of the geographical area have been the basis of the development of human civilisation. The present development level of society is at the cost of ruthless exploitation of the continental resources and the resultant scenario is the depletion of some valuable resources such as coal petroleum, natural gas and several others. 

This exhaustion tendency has threatened the very culture and civilisation of humankind. The marine environment has shown definite signals of its ability to meet the diversified demands of the world for a long time. Consequently, a new ray of hope has emerged in the world.

Schmidt (1937) estimated that the marine environment might be able to accommodate about 300 times more life cycles in comparison to the continental system. It gives an impression that the ocean environment may be able to provide enormous food and other resources to humankind. 

Fishing by coastal people has been a traditional subsistence occupation. Its commercial utilisation is a relatively recent phenomenon. In fact, the commercial utilisation of the marine environment began with the basic objectives, (a) to make use of newly discovered natural resources, (b) to conserve continental resources, and (c) to protect the continental environment from pollution and resource depletion. 

This commercial utilisation process was first started by the developed countries and several small island and littoral countries began to face the challenge of the utilisation of their marine resources by nearby developed countries. The problem was therefore raised by Malta representatives in the UN General Assembly in 1967 through a resolution. The resolution was supported by several countries and ultimately the way was cleared for the formulation of the international law of the seas. 

Finally in 1982, the Declaration of United Nations Conference on Law of Seas (UNCLOS) was adopted through which all littoral states received exclusive right to make economic utilisation of the adjacent ocean environment up to 320 km from the coastline. This is defined as the Exclusive Economic Zone (EEZ). The marine environment lying beyond EEZ is defined as the High Sea and is considered a treasure for all. No country has the right to exploit it. It can only be used for research and investigation purposes.

Exclusive Economic Zone provides vast off-shore area to the littoral states for economic usage. Several countries have begun exclusive utilisation of it. The reserved resources can simply be divided into four major types: 

a. Food resources

b. Chemical resources

c. Mineral resources

d. Energy resources

Food resources

Ocean environment has huge reserves of various types of fishes, which can provide nutritious diet to all sections of societies. It provides about 9% food requirements of Japan (around 2000). The Japanese have begun to take more interest in poultry products in recent decades but that has not reduced the significance of fisheries in the economy of Japan. According to a 2012 report, Japan consumes 6% of the world’s fish harvest – 81% of its fresh tuna – and imports more seafood than any other country.  Eating seafood is a central part of Japan’s national food culture. 

Top fish producing countries are China, Indonesia, Peru, India, Russia, the US and Viet Nam (FAO, 2020). There has been a phenomenal increase in fish production since the Second World War. It was only 10 million tonnes in 1946, increasing to 68 million tonnes in 1992, and now to 175 million tonnes (2020). The Food and Agriculture Organisation (FAO) estimates that more than 80% of the world’s fish stocks are fully exploited, overexploited or recovering. 

Though fishing is performed in all regions of the world but six oceanic regions have tremendous concentration of fishing occupations. They are, 

a. Southeast Pacific – stretching from South America’s Panama to Cape Horn; the Peru Current provides an ideal environment for fishing;

b. West-central Pacific – stretching from the Philippines and southern Indonesia to Australia, the region is famous for redfish, sea bass, mackerel, oyster, crab and tuna;

c. Northwest Pacific – stretching from Taiwan to the Bering Strait; principal producers here are Japan, China, Taiwan, South Korea and Russia;

d. Northeast Pacific – stretching from the western coast of Mexico to the Bering Strait; the beneficiary countries are the US, Canada and Mexico; this region has been famous for halibut fishing;

e. Northwest Atlantic – stretching from the Sparrow Point to the Davis Strait, the region is famous for fishing as coastal conditions have a lot of favourable conditions; New Foundland’s coastal areas and Grand Bank have been famous for fishing; Grand Bank occupies about 96 sq km area and is very rich in planktons which support fish habitat; principal producers are the US and Canada;

f. Northeast Atlantic – stretching from the coastal areas of Spain to the White Sea in the north of Scandinavian Plateau, it provides benefits to several European countries; the region has been famous for cod fishing; Norway was the largest producer of cod for long in the world, now China leads cod production followed by Iceland, Russia, the Netherlands and Germany.

Oceanic regions near India, Peru, Argentina and Brazil have emerged as new major fishing regions. Besides fish, ocean environment is taken as a food supplier from sea weeds. In the 1980s and 1990s, Japan was the heavy producer of sea weeds. It even began mushroom farming with the help of helicopters in the motionless oceanic environment areas. Now, China, Indonesia and the Philippines are the top sea weed producers.

Both fish and sea weeds have bright prospects as future food resources. There are about 5,000 species of fish but only about 50 species are in commercial utilisation. Fish farming has three important areas of future expansion. They are, deep sea environment, which is principally used by the developed countries and developing countries are yet to make significant inroads into this region. Secondly, the South Sea has been rich in whale and krill fish. Whale is the largest mammal having tremendous economic importance. Japan is the largest producer/catcher of whales. 

Commercial capture of whales was banned in 1986. There is – the International Whaling Commission (IWC) – a body dedicated to the conservation of whales. Currently, there are 88 members of the IWC. Japan pulled out of the IWC in 2018 to resume its commercial hunting for whales after 30 years. Other countries commercially hunting whales are Norway and Iceland. However, even when Japan was a member of the IWC, it had not completely stopped whaling. In 1992, for instance, Japan caught 40,000 whales. 

Photo: Twitter/@WHOI

Thirdly, the tropical ocean waters are comparatively untapped. They have different species and may be of tremendous use in future. India’s emergence as a major marine fish producing state has been due to the production of shrimp and prawn. India has been the largest producer of shrimp and prawn for years now. Similar fishery development policies of countries like South Africa, Australia, Brazil and Argentina have promoted tropical water fisheries in recent years but it still has much more potential, with a focus on sustainable resource management. 

The collection of food resources from the oceanic environment is still in a pre-mature stage, and keeps a bright prospect for the future. Molluscans and crustaceans, desalination of brackish water and the use of icebergs for drinking purposes would further enhance the importance of the ocean as a food resource reservoir. 

Chemical resources

The marine environment is full of chemical resources. It has more than 40 chemical elements and numerous compounds. Of all these, sodium sulphate, magnesium compounds and common salt have greater importance. Sodium sulphate is used in paper and pulp, pharmaceuticals, soap and gun powder industries. Magnesium is mainly used in aircraft industries. Common salt is used by tropical people as an eatable item. 

The availability of sodium sulphate and magnesium compounds has solved the problem of the shortage of these minerals in the continental environment. The availability of these two has reduced the prices to about 50% in the world market compared to what was seen in the second half of the 20th century. Sodium sulphate and magnesium compounds are mainly produced by Mexico, Spain, the US, France and Japan. Common salt is produced in a large number of countries including Nigeria, South Africa, Ghana, India, the Philippines and Mexico. Overall, the US, China and India are the top salt producers.

Mineral resources

Mineral resources of the oceanic environment may broadly be divided into two categories on the basis of their geographical locations. These are (a) deep sea minerals and shallow sea minerals, produced from the continental shelf. The shallow sea zone has a depth of up to 200 metres and is within easy reach of known technology. 

Petroleum and natural gas are the principal minerals produced from the shallow sea regions. It is estimated that about 14% of the geographical area of the oceans possesses mineral oil-bearing structures. Natural gas reserve is estimated to be about 90,235 thousand million cubic metres (around 2000). About 30% petroleum and 27% of natural gas are annually drilled from the ocean beds. Their shares have remained almost constant since the early 2000s. 

Ocean drilling is a post-Second World War phenomenon. It was strengthened after energy crisis that emerged due to the Arab-Israel War of 1973. Abnormal hike of oil prices by the OPEC countries compelled the development of off-shore drilling in different parts of the world. 

Consequently, the North Sea, the Red Sea, the California Sea, the Sea of Japan, the Caspian Sea, the Persian Gulf, the Arabian Sea, the South China Sea, the East China Sea and several other off-shore zones have become principal producers of oil and gas. Off-shore drilling has improved the petroleum production of the countries such as the UK, Ireland, Iceland, Norway, Sweden, Japan, India and several others. 

Shallow seas are also being exploited for other minerals. For example, Malaysia produces tin-ore, Japan iron ore, and the US gold off the California coast. Several countries collect sea shells to make their use as a substitute for limestone in cement industry.

Deep sea mining, on the other hand, is still in the early stages of development for commercial purposes. Poly-metallic nodules have been derived and are found to be a highly suitable substitute for traditional metallic minerals, which are in the course of depletion. Ocean bed is carpeted by thick layers of poly-metallic nodules in the oceanic zone of 3,500-6,000 metres. 

Continental metallic ores are exhaustible but ocean nodules are practically inexhaustible as they increase at the rate of 10 million tonnes per year due to some complex chemical processes taking place in the marine environment. The Pacific Ocean has the largest reserves of nodules. Its reserve is supposed to be about 105x10 12 tonnes of nodules. The poly-metallic reserves near Galapagos Series (valley) consists of 48% sulphur, 43% iron, 11% copper and vast amounts of zinc, tin, lead and silver in the oceanic environment. Further, more oceanic areas lying in between 700-6,000 metre depth is characterised by calcium-dominated sea, with an average thickness of 400 metres. In fact, the ooze deposits lie over this calcium shell. This layer is completely untouched and is a treasure for the future.

Deep sea mineral reserves are yet to be properly assessed because there is a lack of adequate deep sea mining technology. Only a few countries have acquired this technology and the technology flow is completely guarded. The next few decades may witness a politics of deep-sea mineral exploitation and technologically advanced countries would certainly be in an advantageous position.

Energy resources

The ocean environment may be considered as a storehouse of energy resources. Its energy resources can be divided into bed resources and water resources. Bed resources consist of mainly petroleum and natural gas which have been described under mineral head. Water resources may broadly be taken as tidal energy and geothermal energy. Coastal regions with tidal rising of six metres and above are ideal for tidal energy generation. Wave-activated Turbine Generators (WATG), the gyros are used to generate electricity. 

Tidal wave energy reserves are supposed to be about 3x106 mg watt and the world can generate 68-80 mg watt per minute. This technology was first used in France in the 1960s and since then it has become an important source of coastal electricity near the mouth of the Rive Rance.  

The mouth of this river has the world’s first and France’s largest tidal power generation centre with an installed capacity of 800 million kilo watt per year. It was the world’s largest tidal power generator for 45 years from 1966 until 2011, when South Korea built the world’s largest at Sihwa Lake. Kislaya Guba centre, installed in 1968, in Russia has an installed capacity of 440 million kilo watts. Both France and Russia have made rapid stride in tidal energy generation. Other important generators are Norway, the US, Australia and Sweden. India has also started commercial production near Okha on the Gujarat coast.


Geothermal energy is based upon Off-shore Thermal Energy Conversion (OTSC) technology. This technology harnesses temperature differences of ocean water. It is found that the ideal condition is one in which the ocean surface temperature is 28-29 °C and the temperature at the depth of 800-1,000 metres is 6-7 °C. It is estimated that geothermal sources alone can provide about 1 crore mg watt of electricity which would be 10 times of the present production level of the world. 

India’s coastal environment, too, has favourable conditions for its generation and its production may be about 50,000 mg watt per year. Cuba and France have made major breakthrough in this regard. India has also started production near Vishakhapatnam and Trivandrum. The world’s total reserve of geothermal energy is supposed to be about 300 quads while the present demand is only about 250 quads. A quad is a unit of energy equal to 10 (a short-scale quadrillion) BTU, or 1.055×10 joule (1.055 exajoules or EJ) in SI units. 

Some other probable energy sources have also been identified. They are salinity gradients, sea breeze and ocean currents. These alternatives need international cooperation on the front of required technology. Commercial generation is performed on the basis of sea breeze but salinity gradients and currents are yet to be used.

Utilisation and environment

There has been a rapid increase in the utilisation of marine resources in recent decades due to certain factors. First factor was food shortage in Japan and protein consciousness in various parts of the world. It has promoted marine fisheries on a large scale. Secondly, the Arab-Israel War compelled developed countries to develop alternative and substitute energy sources leading to massive assault on the ocean environment. 

Ocean environment provides global trade routes and increased trading operations and naval activities have brought humanity much closer to the mysteries of the oceans. Several expeditions to Antarctica and the Arctic regions, killing of whales and the netting of krill in high latitudes of the South Sea have practically made the entire ocean environment traversable, accessible and usable. High sea concept has been promoted to prevent the vast ocean environment from the ugly utilisation by humans.

The law of seas was meant for that but its helplessness has been exposed. The UN has no organ to watch over the violations of the high seas. Technologically advanced countries and countries having strong naval bases to whatever they want and exploit high seas in the name of research and experiments. Consequently, the marine environment has begun to show the symptoms of disaster. Continents are detached and solid crust prevents easy spreading of pollutants on continents. 

Oceans have different properties than continents. This vast body of liquid has mixing and oscillation properties due to which pollutants would spread over 71% of the globe. Removal of pollutants from this vast water body would be almost impossible and the biosphere may be under tremendous pressure of instability. 

Pollutant spreading has become alarming in some specific oceanic zones. They are the north Atlantic trade route, which carries about 27% world trade, drilling platforms in the North Sea and other drilling zones. Several mega cities of the world are situated on the coast and tonnes of residuals are released every day in the ocean causing instability of the estuarine environment. 

Larges fishes like whales are being killed and the vast residuals are left in the ocean along with oil and other pollutants. Consequently, this species is facing a serious danger of extinction. Species such as krill, cod and halibut are also exploited enormously creating a probable danger of extinction. The UN created the ICW for controlled whaling and a quota was fixed for the killing of whales but there have been reports that countries like Japan killed much more than the allotted number.

Over the past several decades, Russia has been accused of dumping nuclear wastes (rods) in the North Pacific after their utilisation of submarines. They may not produce radiation right now but recycling after some years would certainly pose health hazards and may eliminate some of the marine species. Increased naval exercises and geopolitics of marine environment have also begun to threaten the peace of ocean environment. 

The Gulf War sent a serious threat signal to the environmentalists who said that the war caused irreparable damage to the marine environment in the gulf region. Growing tensions for Spartly Island in the South China Sea, Kurile Islands (northwest Pacific) and islands of disputes in the Persian Gulf may aggravate the marine threat situation any time, and the real loser will be the oceanic environment. 


It is, therefore, understood that the danger bell has begun to ring even before the proper utilisation of ocean resources. The human race may be divided on the lines of territorial commitments but has to display eagerness and genuine sincerity towards the proper planning and integrated development strategies for ocean environment. The utilisation of this resource needs cooperation and not confrontation. Cooperation would bring resource substitutes and would continue the sojourn of development and prosperity of humankind but confrontation in the name of territorial sovereignty may trigger irreparable disaster. 

Practically, there is no need to advocate the supremacy of the sovereignty of nature. What is needed is to display genuine sincerity maintaining the interest of respective territorial sovereignty. The 'sovereignty of nature' concept was floated by some developed countries at the Rio de Janeiro conference in 1992, and developing countries tasted the flavour of politics in the name of global cooperation. Such politics continue to create problems as seen in global conferences year after year. 

Therefore, the countries must take the ocean as a common heritage of humankind. Its acceptance as a common heritage of humankind would promote its exploration and utilisation in the common interest and the gains would be accessible to all the countries irrespective of their geographical locations.

(Based on my notes of Prof RB Singh's lecture)

Saturday, September 24, 2022

Geographical Instruments

Instruments and their salient characteristics

1.    Theodolite: Angular measurement with the help of vernier scale; both horizontal and vertical angles are taken; helps in the measurement of the height of high-altitude mountains.

2.    Clinometers: A handy instrument used for the measurement of the height of the buildings and similar low altitude heights.

3.    Dumphy level: Helpful in the determination of spot height

4.    Pantograph, Echograph (for smaller area) and Camera Lucida: Used for enlargement and the reduction of the area.

5.    Planimeter: Area determination

6.    Barometer: Air pressure measurement

7.    Aneroid meter: Air pressure measurement; this instrument does not contain mercury

8.    Barograph: Air pressure measurement

9.    Anemometer: Wind velocity measurement

10. Dry and wet bulb thermometer: Relative humidity

11. Ran gauge: Rainfall measurement

12. Chain: Used for horizontal measurement

13. Tape: Used for short distance measurement

14.Ranging rod: Helps in locating objects

15. Optical square: Used for setting right angles for the measurement of short distance from the chain

16.Spirit level: Used for levelling of instruments

17. Trough compass: Magnetic north is directed

18. Guntur’s chain: A chain having length of 66 feet or 20 metres

19. Engineer’s chain: A chain having length of 100 feet or 30 metres

20. Steel tape or Invar tape: Used for the measurement of base line in geodetic survey or a survey considering the curvature of the earth

21. Prismatic compass: Used for closed traverse survey; angular recording is taken from magnetic north

22.Plane table: An instrument used for detailed survey; entire work is completed in the field

23. Alidade: A sighting rule used with plain table for the alignment of the objects

24. Pluviograph: Rainfall measurement instrument, better than rain gauge

25. Wind vane: Wind direction is indicated

26. Anemograph: Wind velocity measurement

27. Hygrograph: Relative humidity measurement; better than dry and wet bulb thermometer

28. Levelling staff: Used with Dumphy Level, gives reading up to 100th part of a metre or foot for showing ups and downs

29. Plumb bob: Used for the centering of the instrument

30. Opisometer: Measurement of distance on a map

31. Nanometer: Pressure measurement

32. Pyrometer: Measurement of invisible as well as indirect radiation

33. Sextant: Measurement of altitude, mostly used in navigation

34. Cyanometer: Measurement of blueness of the sky

35. Actinometer: Measurement of radiation


Lines in geographical map

1.    Isohypes: Lines of equal elevation or contours

2.    Isogons: Lines of equal magnetic declinations

3.    Isohyets: Lines joining points of equal rainfall

4.    Isobath: Lines of equal depth below the sea level

5.    Isoneph: Lines of equal cloudiness

6.    Isoniph: Lines of equal snow

7.    Isorymes: Lines of equal frost

8.    Isophene: Lines of equal seasonal phenomenon, like flowering dates of plants

9.    Isodapan: Lines of equal transportation cost distance

10. Isleabars: Lines of equal pressure difference

11. Isocline: Lines of equal slop

12. Isobronts: Lines showing places having thunderstorms at the same time

13. Isochromes: Lines of equal wind factor

14. Isochrones: Lines showing places located at equal travel time from a point

Graphs of geography

1.    Climograph: It shows variation of mean monthly temperature and relative humidity of over a period of a year for any weather station

2.    Hydrograph: It shows the relationship between stream discharge and precipitation at a place

3.    Ergograph: It shows the relationship between climate and the growing season of crops

4.    Hythergraph: It shows temperature and rainfall at a particular station

5.    Windrose: It shows the frequency and directions of winds at a particular place.

(Based on my notes of Prof RB Singh's lecture)

Saturday, July 30, 2022

Factors Affecting Ocean Currents

Ocean currents across seas (Photo: Windows to the Universe)

Ocean currents are large masses of surface water that circulate in regular patterns around the oceans. Those flowing from lower latitudes to higher latitudes have a higher surface temperature and are warm currents. Those flowing from higher to lower latitudes are cold currents.

Ocean currents follow a fixed pattern of movement, which is controlled or influenced by the following set of factors.

I. Factors in relation to the earth’s nature

a. Gravitational force

b. Deflective force by the earth’s rotation

II. Ex-oceanic factors

a. Atmospheric pressure and its variation

b. Wind and frictional force or planetary winds

c. Precipitation

d. Nature of evaporation and insolation [amount of solar radiation falling onto a particular area of the earth]

III. Sub-oceanic factors

a. Pressure gradient

b. Temperature differences

c. Salinity

d. Density

e. Melting of ice

IV. Other factors modifying the ocean currents

a. Direction and shape of the coastlines

b. Seasonal variation

c. Bottom topography or configuration

The gravitational pull increases towards the poles. This pull has two effects on the flow of ocean water. First, it compresses water body a bit more towards the poles making a level-gradient fro ocean water and as a result water moves towards the poles.

Secondly, the pull creates a centripetal force towards the earth’s centre but as the ocean floor obstructs water to reach destination, the ocean water starts moving horizontally in its attempt to reach the destination [the vector resolution rule].

The earth’s rotation deflects freely moving objects including ocean currents to the right. In the northern hemisphere, this is a clockwise direction, e.g. the circulation of the Gulf Steam and Canary current. In the southern hemisphere, this is anti-clockwise direction, e.g. Brazilian current, and the West Wind Drift.

Over the regions of greater atmospheric pressure, the level of the sea is found to be lowered and vice versa due to compressional phenomenon. Therefore, ocean water flows from higher level to lower level, that is, from low air pressure region to high air pressure zone. For example, Canary current flows from sub-polar low air pressure zone to sub-tropical high air pressure region.

Prevailing winds are perhaps the most influential factors of the flow of the ocean water. Trade Winds move equatorial waters westward and warm the eastern coasts of the continents and resultantly force equatorial waters to move towards the poles when obstructed by continental masses. For example, the NE Trade Winds move the North Equatorial Current and its derivatives, the Florida Current and the Gulf Stream Drift to warm the southern and eastern coasts of the US.

Similarly, the SE Trade Winds drive the South Equatorial Current which warms the eastern coast of Brazil as the warm Brazilian Current. The westerlies of of the temperate latitude result in a north-easterly flow of water in the northern hemisphere, e.g. the movement of North Atlantic Drift.

In the southern hemisphere, westerlies drive the West Wind Drift all around the globe and where obstructed by continental mass give rise to distinct ocean currents — the Peruvian Current towards equator off South America, Benguela Current off South Africa and West Australian Cold Current off Australia.

The strongest evidence of prevailing winds impacting the ocean current flow is seen in the North Indian Ocean. Here, the direction of currents changes completely with the direction of the monsoon winds.

Main ocean currents and the relevant prevailing are as follows:

Ocean Currents

Prevailing Winds

North Equatorial Warm Current

NE Trade Winds

South Equatorial Warm Current

SE Trade Winds

Counter-equatorial Warm Current

Counter-equatorial Westerlies

North Atlantic Drift

Westerlies

North Pacific Current

Westerlies

West Wind Drift

Westerlies

NB. When a current runs across a ocean, it is called drift.

Ocean regions receiving excessive additional water on account of greater amount of precipitation serve as the source regions of ocean currents, for example, the movement of equatorial warm currents to higher latitudes. The Gulf Stream, the Brazilian Current, East Australian Current, Kuro Siwo Current have their source in the equatorial ocean water due to excessive rains.

Differences in the distribution patterns of insolation and amount of evaporation over oceans lead to formation of a current. Insolation and evaporation at an oceanic place work in tandem and where its combined effect is less than the supply of water/precipitation, the current flow starts from there. Thus, current flows from equatorial zone to the temperate zone which also receives current from the polar zone due to the same reason.

Sub-oceanic pressure gradient also causes the flow of ocean water. But it is more important for vertical movement than the horizontal movement. However, temperature difference does play a major role. As warm air is lighter and rises higher than cooler air, ocean water gathers more along equatorial zone and as a consequence, the warm equatorial current/water moves along the surface slowly towards the poles. The heavier cold water of the polar region creeps slowly along the bottom of the sea towards the equator.

Salinity of ocean water varies from place to place. Waters of high salinity are denser than waters of low salinity. Hence, waters of low salinity flow on the surface of waters of high salinity or towards the regions of high salinity. At the bottom of the ocean, the flow is reversed. Hence, the Atlantic waters enter the Mediterranean Sea at surface and return at the bottom.

Density being the sum total of temperature, pressure and salinity directly controls an ocean current. Low density waters flow towards high density waters’ zone. Hence, waters from mid and low latitudes flow towards high latitudes. Similarly, warm waters flow towards cold waters.

Melting of ice adds fresh volume of water to the ocean in higher latitudes and as a result, it flows towards low latitudes, e.g. cold currents emerging from the Artic region — Labrador and Oya Siwo are cold currents.

Costal form modifies the direction of a current to some extent. The westward movement of the South Equatorial Current is obstructed by the Cape San Roque of South America bifurcating it into the Caribbean Stream and the Brazilian Current.

Changing seasons also bring some impact of current flow worldwide in terms of latitudinal shift of ocean currents. But the most remarkable impact is seen in the Indian Ocean where there is complete reversal of ocean current under the impact of the monsoonal winds of different seasons.

Bottom topography of ocean also determines the direction of ocean currents, especially the impact of mid-oceanic ridge is more pronounced. It is very apparent in the Atlantic Ocean where North Equatorial Current, whose normal range of flow is 0-12-degree latitude, is deflected northward even up to 25-degree latitude due to the presence of the mid-oceanic ridge.

It is therefore obvious that the origin and maintenance of ocean currents are influenced by a large number of factors but the most interesting part of this phenomenon is that none of the factors can be studied or taken alone as far as ocean currents’ flow is concerned.

Friday, December 31, 2021

Divisions of Himalayas, The Northern Mountains


Snow-capped Great Himalaya (Photo: Himachal Pradesh government tourism department)

Prabhash K Dutta

Geographically, the entire Himalayan region can be divided into three:

i.        The Himalayan ranges

ii.        The trans-Himalayan ranges

iii.       The Eastern hill

The Himalayan ranges

The Himalayan ranges are not a single chain but a series of more or less parallel or converging ranges. The ranges are separated by deep-cut valleys. As in all young fold mountains, the Himalayas are a densely dissected ridge-and-valley topography. Normally, the Himalayas are divided into three chains

a.  The Great Himalaya — Himadri

b.  The Middle Himalaya — Himachal

c.  The Siwalik

The Great Himalaya is the northern-most and loftiest range. It is about 2,400 km-long running from the Nanga Parvat in the west to the Namcha Barwa in the east, where it bends abruptly. It is made up of central crystalline rocks — granite and gneiss. The folds in this range are asymmetrical having steep slope southwards and obscurantly merges with the edges of the Tibetan Plateau.

The Great Himalaya boasts of the tallest peaks of the world such as the Mt Everest (and its ancillary peaks), Kanchenjunga, Makalu, Dhaulagiri, Annapurna Devi etc. Even the passes available in the Great Himalaya range are at such great heights that they are very difficult to cross.

 

A pass in Great Himalaya (Photo: Ministry of Culture, GOI)

Some of the famous passes are Burzil and Zoji La in Jammu and Kashmir, Bara Lach La and Shipki La in Himachal Pradesh, Lipu Lekh, Niti Lal and Thaga La in Uttarakhand, Jelep La and Nathu La in Sikkim. Shipki La and Jelep La provide good connectivity between India and Tibet.

The Lesser Himalaya

The Lesser Himalaya range or the Middle Himalaya runs almost parallel to the Greater Himalaya. It is more amicable and attracts more people.. It consists of a few individual mountain ranges such as the Pir Panjal, the Dhaulaldhar, the Mussoorie, the Naga Tibba and the Mahabharata Lekh. Of these, the Pir Panjal is the longest range running from River Jhelum to upper Beas for a distance of 300-400 km.

Pir Panjal range is separated from the Zaskar range by the Valley of Kashmir. Its elevation is 5,000 metres and more, and contains mostly volcanic peaks. Pir Panjal, Bidil, Gopalghar and Banihal passes are important gaps in the range. The Jammu-Srinagar highway passes through the Banihal pass.

South-east of Ravi, the Pir Panjal range is continued by the Dhauladhar range passing through Dalhousie, Dharamshala and Shimla. This range attains elevation higher than 4,000 metres.

Further east are situated the Mussoorie and the Nag Tibba ranges. The Mussoourie range has an average elevation of less than 3,000 metres, and runs from Mussoorie to Lansdowne for about 120 km. Mussoorie, Nainital, Chakrata and Ranikhet are important hill stations on the Mussoorie range.

Great Himalaya (Photo: HP Tourism)
The Mahabharata Lekh range is in Nepal. Crossing Nepal, Sikkim and Bhutan, the Lesser Himalaya marks its presence in Arunachal Pradesh. The Lesser Himalayan topography has some beautiful valleys such as the Kashmir Valley, Kangra Valley and Kulu Valley. 

The Kashmir Valley is supposed to have been occupied by a lake during Pleistocene but later an uplift and sedimentation did away with the lakh. It is generally believed to be a synclinal valley which is floor3ed with a variety of alluvial deposits, lacustrine [relating to or associated with lakes] fluvial and fluvo-glacial depositis. River Jhelum meanders through it majestically.

The Kangra Valley is a strike valley, and runs from the foot of the Dhauladhar range to the south of the Beas. Kulu Valley, on the other hand, in the upper course of river Ravi, is a transverse valley.

The Trans-Himalayan ranges

The trans-Himalayan mountain consists of the Zaskar, Ladakh, Kailash and Karakoram ranges. The Zaskar range separates at 80-degree East longitude from the Greater Himalaya and runs eastward. North of it is situated the Ladakh range which continues eastward to give off the Kailash range as an offshoot. River Indus originates from the northern slope of the Kailash range.

The Karakoram Range is the northernmost mountain range of India, and it has the highest peak of India as K-2 at 8,611 metres. It serves as the watershed between India and Tajikistan, and forms India’s boundary with Afghanistan and China.

(Photo: Niti Aayog)
To the northeast of the Karakoram range is situated the Ladakh Plateau which is the driest place of India — it is a cold desert. It is highly dissected and divided into several plains, for example, Soda Plains, Aksai Chin, Lingzi Tanga, Depsang Plans and Chang Chenmo.

The Eastern Hills

Beyond the Namcha Barwa-Brahmaputra Gorge, the Himalayas make a sharp southward turn and goes into the Arakan Yoma mountain of Myanmar. In between several small mountain ranges are situated. These are Patkai Bum, Naga Hills, Manipur Hills, Mizo Hills, Barail Hills, Kohima Hills, and Garo-Khasi-Jaintia Hills.

Patkai Bum is the northernmost among them and forms the boundary between India and Myanmar. It is made up of strong sandstone. Towards south, it merges with the Naga Hills. Patkai Bum and Naga Hills together form the watershed between India and Myanmar. In the Naga Hills is situated the highest peak of the Northeast India called the Saramati at 3,826 metres.

Further south is situated Manipur Hills forming border with Myanmar. In the extreme south is situated Mizo Hills having the highest peak in the southern NE India. It is called the Blue Mountain which reaches up to 2,157 metres.

There are also some outcrop hills such as Barail Range, which separates the Naga and the Manipur hills. Between the Barail Range and the Manipur Hills is situated the Loktak basin.

Another range is the Kohima Hills situated west of the Naga Hills made up of sandstone and slate, and are very rough topography. Besides, there are three hills, ranges or plateaus in Meghalaya called Garo, Khasi and Jaintia. They are rather considered as a portion of the Peninsular Plateau detached by the Bengal Basin.

Wednesday, September 15, 2021

Let's understand flood, in Indian context



A flooded area in Bihar. (Photo credit: Facebook/WHO Bihar Region)

According to the Indian Meteorological Department (IMD), flood is a meteorological situation when water of a river begins to flow above the danger mark. The danger mark is fixed on the basis of average flow of the river over 25 to 50 years during monsoon period.

Drought is the situation, according to the IMD, having less than 5 cm rainfall for four continuous week any time between mid-May and mid-October. If the rainfall is less than 5 cm for any month (four continuous weeks), it is meteorological drought situation.

Flood prone areas are located practically in all parts of the country excluding the internal plateau regions. However, there has been varying tenure of flood and from that point of view, eastern India, northeastern India and eastern coastal plains are the worst affected areas as far as flood is concerned.

The IMD has divided flood into four tenures of flood and affected geographical regions:

Six-week flood region: Assam valley

4-6-week flood region: Eastern Uttar Pradesh, Bihar plain, West Bengal and isolated plain areas of the Northeast – Loktak basin and Tripura basin.

1-4-week flood region: Eastern coastal plain, Punjab, western Uttar Pradesh, Delhi Union Territory, South Gujarat especially Narmada and Tapi basins, and Kashmir Valley.

Less than one-week flood region: Central and northern Gujarat, Rajasthan, Haryana and peripheral parts of peninsular plateau.

There are some rivers, which are highly flood prone. Brahmaputra and Ganga cover about 60 per cent of flood prone areas of the country. Some flood prone rivers are Teesta, Kapoli (a tributary of Brahmaputra), Dihang and Burhi Dihang (known for flash floods).

In the Ganga system of the Himalayan rivers, the main flood causing rivers are, Mahananda, Kosi, Gandak, Burhi Gandak, Kamla Balan, Saryu, Ghaghra, Gomati, Ramganga and Yamuna. Kosi was once called the sorrow of Bihar.

In the peninsular India, the main flood causing rivers are, Son, Punpun, Ajay and Damodar, which was known as the sorrow of West Bengal once. At present, both Kosi and Damodar rivers have been managed and controlled to some extent but others continue to play the same role.

Among the East Coast river, Mahanadi, Godawari, Krishna, Cauvery and Brahmi are highly flood prone. Among west flowing peninsular rivers, Tapi and Sabarmati are highly flood prone.

In the Punjab plains, Sutlej and Beas are highly flood prone while in Haryana Ghaggar and Yamuna bring floods. The Jhelum is flood prone in the Kashmir Valley.

Besides these rivers, there are several short-distance rives, which flow on high slope and create flash flood during monsoon season.

Total area under flood-prone category, according to the Seventh Five-Year Plan papers is 320 lakh hectares where flood happens every year. Total flood-affected area is 2.42 crore hectares where flood occurs but not every year.

Causes of flood:

Flood is the manifestation of many geographical factors and, to many geographers and geologists it has become an ecological factor. This does mean that flood is bound to come in this part of the world every year. It is a flood-ecology region.

Factors:

1. Erratic behaviour of monsoon -- Sometimes the catchment area receives very high rainfall and then flood arrives. In the western India – Rajasthan, Gujarat and Haryana –torrential rain brings sudden outburst of rain which leads to flashfloods. In contrast, in the North-East, even the regular rainfall brings heavy rainfall and that is responsible for flood situation in the region.

2. Geomorphology -- Flood occurs due to geomorphological profile of central plain of India. Brahmaputra Valley is a narrow ramp valley. Similarly, the Ganga basin is sandwiched between the Himalayas and the peninsular plateaus. Both river valleys are bordered by steep rising slopes while the plains are among the flattest ones in the world.

This topographical feature brings rapid run-off from the catchment areas while the run-off in the plain moves at a slow speed. Consequently, these river basins overflow bringing flood over large areas during monsoon season.

3. Deforestation -- Deforestation in the Siwalik Himalaya has increased the volume of the run-off and therefore frequency and tenure of floods in many of Himalayan rivers.

Several peninsular rivers including small ones have become flood prone in recent years due to loss of trees in the past few decades, e.g. Ajay river has become flood-prone due to deforestation in the catchment area. Jhelum was not flood-prone earlier.

Mahananda was not so acute in bring floods. But at present all these rivers bring flood almost every year and that is related to deforestation. Several plateau districts of Jharkhand and Madhya Pradesh have fallen under flood due to deforestation and rapid run-off in these areas.

4. Soil Erosion and Siltation -- These are responsible for increased flood-frequency mainly in the central plain of the country. According to the UNEP, River Kosi is the second-most affected siltation affected river in the world, only after Hwang-ho of China.

Bed siltation occurs due to soil erosion in the catchment area and the deposition of silt in the plains owing to rivers’ inability to carry the load any further. It makes the valley shallow and whenever there is voluminous flow of water, it brings flood and water spreads in the surrounding areas.

5. Drainage Pattern -- It is responsible for the flood in the central plain. Most of the rivers make meandering courses. So, overflow brings waters of different rivers close and vast areas, thus, get inundated.

Punjab does not witness spread of water because of parallel, man-made, drainage of rivers. Although, the rivers often flow over danger mark during flood season but water does not spread. In Punjab, the doab line is always free from flood due to parallel pattern of drainage but the meandering courses of rivers in Bihar and Uttar Pradesh, and braided courses in all delta regions create floods.

Most of the rivers have wide V-shaped valleys. So, the depth of the valley is not great and any increase in the volume of water leads to overflowing and inundation of the neighbouring areas.

Again some of the rivers have created natural levee which protects one side of the valley from flooding but the other bank is flooded and cause flood over low lying areas adjacent to that bank. Bihar plain is noted for this type of flood. Western banks of rivers in Darbhanga have natural levee.

In the central Bihar, there is also flood due to overflow of the main consequent river. Its overflow prevents the inflow of tributary water channels. In fact, the water of the main river, Ganga, begins to enter the course of the tributaries and the tributaries’ water is pushed back and water spreads over vast areas, e.g. Tal area flood in South Bihar and Jharkhand, Chaur area flood in West Bihar and West Bengal. Chaurs are the floodplains situated in the abandoned courses of rivers. They form ox-bow lakes during floods.

6. Shifting Course of Rivers -- Such flooding is mainly important in regions where river have a history of shifting their course. Rivers like Kosi, Teesta, Gomati and Mahananda are facing this problem.

Kosi is now believed to have settled in its course but others are still active. All these rivers have westward shifting courses. These rivers have a tendency to migrate to west. Hence, the west banks of these rivers are constantly being eroded and the east bank extends to a huge low lying floodplain. These rivers cause phenomenal spread of water beyond eastern banks onto the vast plain.

Rotation of the earth is held indirectly responsible for the westward shifting of these rivers and the associated floodplains. Rotational impact brings westward shift of rivers. The eastern banks become low lying and vulnerable to floods.

Eastern coastal plains receive floods not simply due to deforestation and rapid run-off but also because of cyclonic rainfall and greater havoc is caused by the combination of these factors. If there is high tide situation along with cyclone, rainfall causes great damage.

Cyclone brings rainfall and high tide water on the coastal plains as well as increases the velocity of the sea waves. Tidal water enters the mouth of the rivers pushing back the river water. The water level of the river increases. The river goes in a spate. The flow of the river is reversed and low lying floodplain is taken over by the floodwater. Such tidal flooding is seen in the Mahanadi and the Godawari.

Western coastal rivers generally receive flash floods. The duration of such floods is about one week. The situation mainly occurs due to deforestation along the Western Ghats. Loss of vegetation means less obstruction to run-off.

Rapid run-off leads to greater water volume in the river valleys than the channel is capable of carrying off to the sea. This pushes the water level up in the river valleys leading overflow and inundation in the neighbouring areas.

7. Human Factors -- Floods are also caused by human factors. Ironically, flood control programmes and some other developmental programmes have indirectly contributed in greater spreading of flood. Although, multi-purpose vally projects and other power generation projects have controlled floods in the basins of some of the rivers and regions. But the problem has emerged in a different way.

Due to siltation on the beds, the reservoirs’ capacity has reduced and whenever excess water is released from that reservoir through canals and other outlets, flood is caused. Flood water even enters the areas where flood had never come previously.

The canals also face siltation problems, which get compounded by the seepage of river water from the sides of the canals into neighbouring agricultural lands. These agricultural fields become unproductive due to excess of water and behave like marshy land and are waterlogged at times even if water is not pulled from these canals. The excessive wet lands are not conducive for agriculture.

This type of flood brings greater loss as this is relatively new phenomenon and people dependent on such lands are neither prepared nor equipped to deal with such a situation. In 1995, Banka district of Bihar turned into a wasteland due to opening of two reservoirs – Chandan and Orhni.

Governmental approach to construct embankments for the protection of settlement and agricultural lands has also deteriorated the situation in many parts of the country. Now, the approach is being modified. Such programmes are now being called flood protection programmes instead of flood control programme.

Thus, several new regions, e.g. in northeastern towns of Bihar, many new settlements have fallen in the trap of flood. Flood control measures have brought new dimensions in floods in India.