Plate tectonics exained

Plate tectonics is a theory which gave a new dimension to the knowledge of continental drift, ocean floor spreading, volcanic activity, seismic waves, structural features etc. This idea came out of the work of Harry Hess, who propounded the theory of ocean floor spreading. This theory gave some basic points over which the concept of plate tectonics was first given by WJ Moran (1967). The theory was further supported by McKenzie by and Parker by their individual works.

This theory is based on the assumption that the crustal structure of the earth is divided into a number of plates, and these plates are continuously in motion both with respect to each other and to the earth’s axis of rotation. Every plate is supported by plate boundary which is the surface zone of motion between two plates. The general theory of lithospheic plates with their relative motions and boundary interactions is plate tectonics. Tectonic is a noun mean the study of tectonic activity. Tectonic activity, in turn, refers to all forms of breaking and bending of the entire lithosphere.

The global system of lithospheric plates

The global system of lithospheric plates consists of seven major and six important minor plates. The major plates are named as the Pacific plate, the Indian plate, the North American plate, the South American plate, the African plate, the Eurasian plate, and the Antarctic plate. The minor plates are the Arabian plate, the Philippines plate, the Cocos plate, the Caribbean plate, the Nasca plate and the Scotia plate.

Geologists have identified and named several other smaller plates within the above-mentioned plates. The average thickness of the continental plate is 60-70 kms. However, some oceanic plates are only 5-11 km deep and the fold mountains is about 100 km thick.

Plates may be continental, oceanic and continental-cum-oceanic. The all plates rest over a viscous and plastic asthenosphere, also called the low velocity zone (LVZ). They not only rest but also make relative movement over this slippery upper mantle (asthenosphere).

As all the plates form part of the crust of a spherical earth and all the plate boundaries adjoin one another without leaving gap on any scale, it follows that tall plate motions are relative and depend upon one another.

All such movements, and construction and destruction of plates must be within the limiting factor so that the surface of the earth remains practically unchanged. It is proven by the fact that the radius of the earth has increased only about 5% during the last 600 million years.

Plate boundaries and margins, and the nature of movement

The edges of the plates are designated as boundaries and margins. When movement occurs, the edges are called boundaries. Margins refer only to the peripheries of the plates. Generally, plates spread away from the mid-oceanic ridges and is consumed along thee oceanic trench. Three types of movement occur along the plate margins. They are known as:

i.                 Constructive movement

ii.               Destructive movement

iii.             Conservative movement

Constructive movement occurs along the upwelling zone. Here, mid-oceanic ridges are formed and plates move apart. Destructive movement occurs along the oceanic trench where the moving plate bends down and plunges into the soft asthenosphere. The process of down-plunging of one plate beneath another is called subduction.

The leading edge of the descending plate is cooler than the surrounding asthenosphere. Its rocks are also more brittle and denser than the surrounding asthenosphere. Consequently, once subduction has begun, the slab sinks under its own weight. Gradually, however, the slab is heated by the surrounding asthenosphere and is ultimately converted into magma at a depth called the Benioff Zone.

This magma ascends like hot air balloons through the overlying continental lithosphere. By the time this magma reaches the earth’s surface, its quantity is huge enough to build a distinct structure called volcanoes, which tend to form a volcano chain parallel to the deep oceanic trench that marks the line of oceanic plate. That is, the meeting lines of the two plates beneath the ocean are littered with volcanoes.

It is clear that a single lithospheric plate is simultaneously undergoing accretion (growth by addition) and consumption (by softing and molting) so that the plate might conceivably maintain its size. A third type of movement is known as conservative or passive movement. Here, plate margins make just shearing or friction. One plate merely slides past the other with no head-on motion. The plane along which motion occurs is a nearly vertical fracture extending down the entire lithosphere. It is called a transform fault.

A fault is a plane of rock fracture along which there is motion of the rock mass on one side with respect to that on the other. Drawing below shows the top view of a single rectangular lithospheric plate with two transform boundaries. The rectangular plate, as assumed, is surrounded by a stationary plate.

Mechanics of plate movement

Plate movement is now a hundred per cent reality but not a single plate tectonic theory is able to explain satisfactorily the mechanism of plate movement. It is, however, believed that the low velocity zone keeps the basic clue of the movement of plates. Its low velocity and high temperature make rocks of shear strength. It becomes a plastic and slippery layer, and plates move over it withous resistance.

There are also other views. It is believed that plates may be pushed apart by mantle upwelling, pulled apart by sinkers, asthenosphere or simply slide under the influence of gravity. Moreover, stresses set up between and within plates may in part determine their motions. This may be particularly relevant in the case of smaller plates. It seems probable that plate movements are not solely attributable to any one of these effects, but result from a combination of all acting in varying degrees on individual plates.

Objections

Though this theory has received global appreciation but it is criticised on the following points:

i.                 Spreading boundaries are longer than the converging boundaries. Then how the balance is maintained.

ii.               Subduction zone is not found in all the oceans. It is limited to pacific coasts.

iii.             Some studies have revealed that same plates record constrasting movements which should not take place.

iv.             Actual number of plates is not known.

v.               Benioff Zone is also not found in the lower parts of all subduction zones.

vi.             This theory does not explain the origin of some old mountains. Eastern Highlands of Australia, Drakensberg of South Africa and Siena De la mar of Brazil are not explained.

The theory, however, is able to answer the following structural aspects:

i.                 It explains the causes of the occurrence of the Pacific trenches, the Andes Mountains, and volcanic intrusions.

ii.               It explains the causes of the origin of all tertiary mountains.

iii.             This theory explains the causes of the origin of transform fault and mid-oceanic ridges.

iv.             It gives more scientific explanation of the causes and the extent of volcanic and earthquake zones of the world.

v.               It gives a completely new dimension to the idea of continental drift. It is this theory which put forward the idea of the movement of plates and not of continents. It further gave more specified explanation of the nature continental drift.

vi.             This theory explains the symmetrical geology of the formation of mid-oceanic ridge, ocean floor, ocean deeps, coastal ranges and volcanic intrusion. No other theory is so much unifying than the plate tectonics theory. It is like a geological wizard explaining most of the complicated structures.

Though there are some objections to this theory, it is a revolutionary and comprehensive approach towards the complex systems of the geology of the earth. It is now almost accepted as the most powerful and fundamental theory explaining and correlating so many major geological features of the earth. To many, limited objections might be due to our limited knowledge about the mantle and the core of the earth. The theory has to its credit to give a new dimension to the geological and geographical investigations, and the apprehensions raised by some critics may disappear in due course.

(Based on RB Singh's lecture)

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.

Heritage Day, I chose to visit the Rance tidal power plant, a source of green energy commissioned in 1966!!! pic.twitter.com/LmI5uqxXEh

— Alain (@Jadorelesfemme1) September 17, 2022

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. 

Fisheries Minister Dr Hussain Rasheed Hassan has warned that unless action is taken now, the Maldivian people will become #ClimateRefugees, forced to leave their homeland because of the effects of global warming. @MMRI_Maldives @MoFMRAmv @ashadevos pic.twitter.com/wgXXgA0PDn

— Nekton (@nektonmission) September 15, 2022

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)

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)

If nuke does not kill you, famine will... a total of 5 bn

If the US and Russia go for a nuke war, it could kill 5 billion people, a new study has claimed. But this wiping out of more than two-thirds of the world would not be done by the nuclear bombs directly. Many would starve to death.

The study

Scientists at Rutgers University have mapped potential effects of six possible nuclear conflict scenarios. A full-scale war between the US and Russia has been treated as the worst possible case, which, they estimated, would wipe out more than half of humanity.

They said a modern nuclear war would release so much of soot in the atmosphere that it would block the sunlight from reaching the earth for a long time. In the absence of the sunlight, the planet would face massive famines. They estimated that five billion people would die. The study was published in Nature Food journal. 

The model

The scientists based their calculations of how much soot would enter the atmosphere from firestorms ignited by the detonation of nuclear weapons. Researchers used a climate forecasting tool, which allowed them to estimate productivity of major crops on a country-by-country basis. 

What if India, Pak…

The study suggested that even a relatively small-scale conflict would have devastating consequences for global food production. A localised battle between India and Pakistan would see crop yields decline by an estimated 7% within five years, while a US-Russia war would see production fall by 90% within three to four years. 

This comes after the spectre of conflict between the US and Russia was raised following Vladimir Putin's invasion of Ukraine. Russian Foreign Minister Sergei Lavrov warned in April that there was a "serious" risk of nuclear war breaking out.

I read this news report on Reuters.

Ashoka's Dhamma and his rock edicts: A recap

 

Maurya emperor Ashoka riding a chariot in a Sanchi Stupa relief (Photo: Twitter)

Ashokan policy of Dhamma has been a topic of lively discussion and the best source to know about his Dhamma is his edicts. The edicts were primarily written to explain to the people the principles of Dhamma. What comes out from his edicts is that the Dhamma was not any particular religious faith or practice. It was also not an arbitrarily formulated royal policy. Dhamma related to the norms of social behaviour and activities in a very general sense and in his Dhamma, Ashoka attempted a very careful synthesis of various norms which were current in his times.

The Dhamma had a historical background that served as a set of causes effecting in an official policy of one of the most powerful kings the world has seen.

SOCIOECONOMIC BACKGROUND

The Mauryan period witnessed a change in the economic structure of society largely due to the increasing use of iron. It has generally been argued that the use of the Northern Black Polished Ware (NBPW) pottery is an indicator of material prosperity of the period.

The use of punch-marked coins of silver and some other varieties of coins, the conscious intervention of the state to safeguard trade routes and the rise of urban centres point to a structured change in the economy. It required necessary adjustments in society.

The commercial classes had also come to the forefront. The emergence of urban culture by its very logic demanded a more flexible social organisation.

The incorporation of tribes and peoples from the outlying areas into the social fabric also presented a problem. The rigidity of the Brahmanical class sharpened the division within society. The lower orders turned to various heterodox sects and this created social tensions.

It was this socioeconomic situation which emperor Ashoka inherited when he ascended the Mauryan throne.

RELIGIOUS BACKGROUND

The Brahmanical hold over society was increasingly coming under severe attack. The privileges of the priests, the rigidity of the caste system and elaborate rituals were being questioned. The lower orders among the four caste-classes began to favour new sects. The opposition to the Brahmanism by the commercial class was to give a fillip to the other sects of society.

On the other hand, Buddhism opposed the dominance of the Brahmanas and the concept of sacrifice and rituals. Buddhism had begun as a schismatic movement from the more orthodox Brahmanism. Its fundamentals were based on an emphasis on misery and advocacy of the middle path. It appealed to the lower orders and to the emerging social classes. The humane approach to relations in society preached by Buddhism further attracted different sections to Buddhism. Ashoka’s Dhamma bore deep influence of Buddhism.

POLITICAL BACKGROUND

By the time Ashoka ascended the throne, the state system of Mahajanapadas had grown very elaborate and complex from where it had started during the Mahajanapada era.

Now, there was political supremacy of one region (Magadha) over a vast territory which comprised many previous kingdoms, gana-sanghas and areas where no organised states had existed before.

Within this vast territory, there was existence of various geographical regions, cultural areas and different beliefs, faiths and practices.

There was monopoly of fore by a ruling class of which the emperor was the supreme head.

The state appropriated a very substantial quantity of surplus from agriculture, commerce and other sources.

A large administrative apparatus was developed for governing the people and territories.

The complexity of the state system demanded an imaginative policy from the emperor based on minimal use of force in such a large empire having diverse forms of economy and religions. It could not have been controlled by an army alone. A more feasible alternative was the propagation of a policy that would work at an ideological level and reach out to all sections of society.

The policy of Dhamma was such an endeavour. Obviously, the policy of Dhamma was an earnest attempt at solving some of the problems a complex society faced. However, it is also true that Ashoka’s personal beliefs and his own perception of how he should respond to the problems of his empire were responsible for the formulation of the policy of Dhamma.

CONTENTS OF DHAMMA

The principles of Dhamma were so formulated as to be acceptable to people belonging to different communities and following any religious sect. Dhamma was not given any formal definition or structure. It emphasised on toleration and general behaviour of people. Its emphasis in particular was on dual toleration – of people themselves and also their various beliefs and ideas.

There is stress on showing consideration towards slaves and servants, obedience to elders, and generosity towards the needy, Brahmanas and Shramanas. Ashoka prescribed tolerance of different religious sects in an attempt to create a sense of harmony.

The policy of Dhamma also laid emphasis on non-violence, which was to be pracised by giving up war and conquests, and also as a restraint on killing of animals. However, Ashoka was conscious that display of his political and military might up to a certain degree could be necessary to keep his empire intact and certain sections of people, especially some primitive forest tribes in check.

The policy of Dhamma included certain welfare measures such as planting of trees, digging up of wells etc. Ashoka denounced certain ceremonies and sacrifices practised regularly on various occasions as meaningless.

A group of officers known as the Dhamma Mahamattas were instituted to implement and publicise various aspects of Dhamma. Ashoka thrust a very special responsibility on them to carry his messages to various sections of society. However, they seem to have developed into a type of priesthood of Dhamma with great powers and soon began to interfere in politics as well.

DHAMMA AS PER MAJOR ROCK EDICTS

Major Rock Edict-I

It declared prohibition of animal sacrifice and holiday festive gatherings.

Major Rock Edict-II

It related to certain measures of social welfare which were included in the working of Dhamma. It mentioned medical treatment for men and animals, construction of roads, wells and planting of fruit-bearing trees and medicinal herbs.

Also talked about states outside the boundaries of Magadh empire: Pandyas, Satyapuras and Keralaputras of South India.

Major Rock Edict-III

It declared that liberality towards Brahmanans and Shramanas is a virtue. Respect to mother and father is a good quality to have. Empire officials Yuktas, Pradeshikas and Rajukas would go every five years to different parts of his empire to spread Dhamma.

Major Rock Edict-IV

Dhammaghosha (bugle of righteousness or Dhamma) over Bherighosha (bugle of war). It said that due to the policy of Dghamma, the lack of morality and disrespect towards Brahmanas and Shramanas, violence, unseemly behavior towards friends, relatives and others, and evils of this kind have been checked. The killing of animals to a large extent was also stopped.

Major Rock Edict-V

It referred to the appointment of Dhamma Mahamattas for the first time in the twelfth year of his reign. These special officers were by the emperor to look after the interests of all sects and religions and spread the message of Dhamma in each nook and cranny of the state. The implementation of the plicy of Dhamma was entrusted in their hands.

It talked about treating slaves right and humane.

Major Rock Edict-VI

It was an instruction to Dhamma Mahamattas. They were told that they could bring their reports to the emperor at any time, irrespective of whatever activity he may be engaged in. the second part of the edict dealt with speedy administration and smooth transaction of business.

Major Rock Edict-VII

It talked the necessity of tolerance towards different religions among all sects, and welfare measures being undertaken by the emperor/empire for the public not only within the Magadhan territories but in his neighbouring kingdoms as well.

Major Rock Edict-VIII

It talked about Dhammayatras saying that the emperor would undertake these tours instead of traditional hunting expedition to improve and deepen his contact with various sections of people of the empire.

It mentioned about Ashoka’s first visit to Bodh Gaya and Bodhi Tree, giving importance to Dhamma Yatra.

Major Rock Edict-IX

It attacked ceremonies performed at birth, illness, marriage and before setting out for a journey. A censure was passed against ceremonies observed by wives and mothers. Ashoka instead laid stress on the practice of Dhamma and usefulness of ceremonies.

Major Rock Edict-X

It denounced fame and glory, and reasserted the merit of following the policy of Dhamma.

Major Rock Edict-XI

It is a further explanation of Dhamma with emphasis on showing respect to elders, abstaining from killing animals, liberality towards friends and being humane towards slaves and servants.

Major Rock Edict-XII

Similar to MRE-VIII, it reflected the anxiety of Emperor Ashoka that he fled owing to conflict between competing sects and carried instructions for maintaining harmony.

It mentioned about Ithijika Mahamatta, the high-ranking official in charge of women’s welfare.

Major Rock Edict-XIII

It is of paramount importance in understanding the Ashokan policy of Dhamma. It prescribed conquests by Dhamma instead of war. This was a logical culmination of the thought process which began with the first MRE. This is Ashoka’s testament against war. It graphically depicted the tragedy of war.

This MRE was issued at the end of the Kalinga War bearing testimony to how Ashoka underwent a change in heart from an being aggressive and violent warrior to a preacher of peace and Dhamma.

It gave details of Magadha’s victory over Kalinga and mentioned Ashoka’s Dhamma Vijay over Greek kings Antiochus of Syria (Amtiyoko), Ptolemy of Egypt (Turamaye), Magas of Cyrene (Maka), Antigonus of Macedon (Amtikini), Alexander of Epirus (Alikasudaro). It also mentioned about Pandyas and Cholas in South India.

There is another MRE, the fourteenth. It entailed the purpose of rock edicts – to spread Dhamma and policies of the emperor.

PS: Ashoka put out his instructions through a series of edicts inscribed on rocks installed across his empire. These edicts are categorized by historians into five simpler groups:

-        Major Rock Edicts

-        Minor Rock Edicts

-        Separate Rock Edicts

-        Major Pillar Edicts

-        Minor Pillar Edicts

There are altogether 33 inscriptions that have been found in the edicts recovered/survived so far.

ASHOKA’S DHAMMA AND HIS STATE

Ashoka’s Dhamma was not simply a collection of lofty and feel-good phrases. He consciously adopted Dhamma as a matter of state policy.

It was a major departure from Arthashastra, the political treatise that formed the basis of kingship during Chandragupta Maurya, the founder of the dynasty. In the Arthashastra, the king owed nothing to anyone. His only job was to rule the state efficiently.

But Ashoka’s Dhamma was a state policy. He declared that “all men are my children” and “whatever exertion I make, I strive only to discharge the debt that I owe to all living creatures”. It was totally a new and inspiring ideal of kingship.

Ashoka wanted to conquer the world through love and faith and hence he sent many missions to propagate Dhamma to even far flung places such as Egypt and Greece besides relatively nearby Sri Lanka.

The preparation of Dhamma included several measures for people’s welfare. Centres for medical treatment of men and animals/beasts were founded inside and outside the empire. Shady groves, wells fruit orchards and rest houses were laid out. This kind of charity work was a radically different attitude from the king of Arthashastra, who would not incur any expenses unless they brought more revenues in return.

Ashoka prohibited useless sacrifices and certain forms of gatherings which led to waste, and indiscipline and superstition. He recruited Dhamma Mahamattas for that purpose. They were to see to it that people of different sects were treated equally and fairly. Moreover, they were also asked to look after the welfare of prisoners. Many of the convicts who were kept in fetters after their sentence had expired were to be released. Those sentenced to death were to be given a grace for three days.

Ashoka launched Dhamma Yatra, righteous tours. He and his high-ranking officials were to tour the country in order to propagate Dhamma and establish direct contact with his subjects.

Ashoka renounced war and conquest by violence, and forbade killing of many animals. Ashoka himself set an example of vegetarianism by almost stopping consumption of meat in his royal household.

It was because of such attitudes and policies that modern writers like Kem called him “monk in a king’s garb”.

DHAMMA: INTERPRETATION

It has been suggested that it was the original Buddhist thought that was being preached by Ashoka as Dhamma, and later on, certain theological additions were made to Buddhism. This kind of thinking is based on Buddhist chronicles. But definitely, Ashoka did not favour Buddhism at the expense of other religious beliefs.

Ashoka’s creation of the institution of Dhamma Mahamatta indicates that Ashoka’s Dhamma was not to favour any particular religious doctrine. Had that been the case, there would not have been any need for such an official as Ashoka could have utilised the organisation of Sangha to propagate Dhamma.

Further, Ashoka wanted to promote tolerance and respect for all religious sects, and duty of the Dhamma Mahamattas included working for Brahmanas and Shramanas.

Some historians have suggested that Ashoka’s banning of sacrifices and the favour that he showed to Buddhists led to Brahmanical reaction, which, in turn, led to the decline of the Mauryan empire. Others believe that the stopping of wars and emphasis on non-violence crippled the military might of the empire. This led to the collapse of the empire, after the death of Ashoka.

However, Romila Thapar has shown that Ashoka’s Dhamma, apart from being a document of his humanness, was also an answer to the socio-political needs of the contemporary situation.

That it was not anti-Brahmanical is proven by the fact that respect for Brahmanas and Shramanas was an integral part of Ashoka’s Dhamma. His emphasis on non-violence did not blind him to the needs of the state. He warned the Atavikas (forest tribes) of using the military force of the empire if they did not mend their ways.

Ashoka’s ‘no to war’ policy came at a time when his empire had almost reached its natural boundaries. In the deep south, he had friendly ties with the Cholas and the Pandyas. Sri Lanka was an admiring ally. The policy of tolerance was a wise course of action in an ethnically diverse, religiously varied and class-divided society.

Ashoka’s empire was a conglomerate of diverse groups. There were farmers, pastoral nomads and hunter gatherers besides a burgeoning urban population. There were Greeks, Kamobjas and Bhojas, and hundreds of groups following divergent traditions.

In such a society and political composition, the policy of tolerance was the need of the hour. Ashoka tried to transcend the parochial cultural traditions by a broad set of ethical principles. It is, therefore, obvious that he was not establishing a new religion. He was simply trying to impress upon his society to guide along ethical and moral principles that suited his politics quite well.

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.