Classification of Volcanoes

Volcanic eruptions occur mostly in two ways viz.

i) violent and explosive type of eruption of lavas, volcanic dust, volcanic ashes and fragmental materials through a narrow pipe and small opening under the impact of violent gases and

ii) quiet type or fissure eruption along a long fracture or fissure or fault due to weak gases and huge volume of lavas.

Thus on the basis of nature and intensity of eruptions volcanoes are divided into tow types

a) Central eruption type or explosive eruption type

b) Fissure eruption type or quiet eruption type

Volcanoes of Central Eruption type:

Central eruption type or explosive eruption type of volcanoes occur through a central pipe and small opening by breaking and blowing off crustal surface due to violent and explosive gases accumulated deep within the earth. The eruption is so rapid and violent that huge quantity of volcanic materials consisting of lavas, volcanic ashes and dust fragtmental materials etc. are ejected up to thousands of meters in the sky. These materials after falling down accumulate around the volcanic vent and form volcanic cone of various sorts. Such volcanoes are very destructive and are disastrous natural hazards. Explosive volcanoes are further divided into five sub-types on the basis of difference in the intensity of eruption, variations in the ejected volcanic material and the period of the action of volcanic events as given below:

i. Hawaiin type of volcanoes: Such volcanoes erupt quietly due to less viscus lava and non-violent nature of gases. Rounded blisters of hot and glowing mass / ball of lavas (blebs of molten lava) when caught by a strong wind glide in the air like red and glowing hairs. The hawaiin people consider these long and glassy threads of red molten lava as Pele's hair (pele is the Hawaiin goddess of fire). Such volcanoes have been named as Hawaiin type because of the fact that such eruptions are very common occurance on Hawaii island. The eruption of Kilavera volcano of the southern Hawaii island in 1959-60 continued for 7 days (from Nov 14-20, 1959) when about 30 million cubic meter of lava poured out. The intermittent eruptions continued up to Dec 21, 1959, when the volcano became dormant. It again erupted on Jan 13, 1960 and about 100 million cubic meters of lavas were poured out of one km long fissure.

ii. Strombolian type of volcanoes: Such volcanoes, named after Stromboli volcano of Lipari island in the Mediterranean Sea, with moderate intensity. Besides lava, other volcanic materials like pumice, scoria, bombs etc. are also ejected up to grated hight in the sky. These materials again fall down in the volcanic craters. The eruptions are almost rhythmic or nearly continuous in nature but sometime they are interrupted by long intervals.

iii. Vulcanian type of volcanoes: These are named after Vulcano of Lipari island in the Mediterranean Sea. Such volcanoes erupt with great force and intensity. The lavas are so viscous and pasty that these are quickly solidified and hardened between two eruptions and thus they crust over (plug) the volcanic vents. These lava crusts obstructs the escape of violent gases break and shatter the lava crusts into angular fragments and appear in the sky as ash-laden volcanic clouds of dark and often black colour assuming a Convoluted or cauliflower shape.

Types of Volcanoes

There is a wide range of variations in the mode of volcanic eruptions and their periodicity. Thus volcanoes are classified on the basis of

(i) the mode of eruption and

(ii) the period of eruption and the nature of their activities.

1. Classification on the Basis of Mode of Eruption

I. Central eruption type or explosive eruption type

a. Hawaiin type

b. Strombolian type

c. Vulcanian type

d. Peleean type

e. Visuvius type

II. Fissure eruption type or quiet eruption type

a. Lava flood or lava flow

b. Mud flow

c. Fumaroles

2. Classification on the Basis of Periodicity of Eruption

a. Active volcanoes

b. Dormant volcanoes

c. Extinct volcanoes

Components of Volcanoes

Volcanoes of explosive type or central eruption type are associated with the accumulated volcanic materials in the form of cones which are called volcanic cones or simply volcanic mountains. There is a vent or opening, of circular or nearly circular shape, almost in the center of the summital part of the cone. This vent is called volcanic vent or volcanic mouth which is connected with the interior part of the earth by a narrow pipe, which is called as volcanic pipe. Volcanic materials of various sorts are ejected through this pipe and the vent situated at the top of this pipe. The enlarged form of volcanic vent is known as volcanic crater and caldera. Volcanic material include lavas, volcanic dusts, and ashes, fragmental materials etc.

Concept of Vulcanicity

"A volcano is a vent, or opening usually circular or nearly circular in form, through which heated material consisting of gases, water, liquid lava and fragments of rocks are ejected from the highly heated interior to the surface of the earth".

According to A. Holmes, a volcano is essentially a fissure or vent, communicating with the interior, from which flows of lava, fountain of incandescent spray or explosive bursts of gases and volcanic ashes are erupted at the surface. On the other hand, "the term vulcanicity covers all those processes in which molten rocks material or magma rises into the crust or is poured out on its surface there to solidify as a crystalline or semi-crystalline rock". Some scientists have also used the term of vulcanicity. For example, P. G. Worcester has maintained that "vulcanism includes all the phenomena connected with the movement of heated material from the interior to or towards the surface of the earth".

It is apparent from the above definitions of volcano and vulcanicity that the later is a broader mechanism which is related to both the environments - endogenetic and exogenetic. In other words, vulcanicity includes all those processes and mechanisms which are related to the origin of magma, gases and vapour, their ascent and appearance on the earth's surface in various forms. It is evident that the vulcanicity has two components which operate below the crustal surface and above the crust. The endogenetic mechanism of vulcanicity includes creation of hot and liquid magma and gases, in the mantle and the crust, their expansion and upward ascent, their intrusion, cooling and solidification in various forms below the crustal surface (e.g. batholiths, loccoliths, sills, dykes, lopoliths, phacoliths etc.) while the exogenous mechanism includes the process of appearance of lava, fragmental material, mud, smoke etc. in different forms e.g. fissure flow or lava flood (fissure or quiet type of volcanic eruption), violent explosion (central type of volcanic eruption), hot springs, geysers, fumaroles, solfatara, mud volcanoes etc. It may be, thus concluded that the vulcanicity is a broader mechanism which includes several events and processes which work below the crust as well as above the crust where as volcano is a part of vulcanicity.

Distributional Patterns of the Continents and Ocean Basins

Characteristic features of the distributional patterns of the Continents and Ocean Basins

1. There is overwhelming dominance of land area in the northern hemisphere. More than 75% of the total land area of the globe is situated to the north of the equator. Contrary to this, water bodies dominate in the southern hemisphere. If we divide the globe in two such hemispheres where the North Pole stands located in the English Channel and the South Pole near New Zealand, then the northern hemisphere will be "land hemisphere" while the southern hemisphere a "water hemisphere". Thus the land hemisphere would represent 83% of the total land area of the globe while the water hemisphere would carry 90.6% of total oceanic areas of the globe.

2. Continents are arranged roughly in triangular shape. Most of the continents have their bases (of triangle) in the north while their apices are located in south. If we take North and South America together, they form equilateral triangle whose base would be along the arctic sea where as its apex is at Cape Horn. If we take them separately, again they form two separate triangles. Similarly Eurasia also assumes the form of a triangle the base of which is along the arctic sea and apex near East Indies. The base of African triangle is towards north while its apex is the Cape of Good Hope. Australia and Antarctica are the exceptions to this rule.

3. Roughly, the oceans are also triangular in shape. Contrary to the continents, the bases of the oceans are in south and their apices are in the north. The base of Atlantic ocean extends between the Cape Horn and Cape of Good Hope while its apex located near east of Green Land. The base of Indian Ocean is in the south where as it s two apices are in the Bay of Bengal and the Arabian Sea. The apex of Pacific Ocean is near Aleutian Islands while its base lies in the south.

4. The north pole is surrounded by oceanic water while south pole is surrounded by land area (of the Antarctica continent).

5. There is antipodal arrangement (situation) of the continents and oceans. Only 44.6% of oceans are situated opposite to ocean and 1.4% of the total land are opposite to land area. More tan 95% of total land area is situated diametrically opposite to water bodies. There are only two cases of exception to this rule - a) Patagonia is situated diametrically opposite to a part of North China, b) New Zealand is situated opposite to Portugal and Spain (the Iberian peninsula).

6. The great Pacific Ocean basin occupies almost one third of the entire surface area of the globe.

UPSC Geography Mains Syllabus

Paper- I

Principles of Geography

Section-A

Physical Geography

i) Geomorphology : Factors controlling landform development; endogenetic and exogenetic forces; origin and evolution of the earth’s crust; physical conditions of the earth’s interior; geosynclines; continental drift; isostasy; sea-floor spreading; plate tectonics; mountain building; volcanicity; earthquakes; concepts of geomorphic cycles; landforms associated with fluvial, arid, glacial, coastal and karst cycle; groundwater; Applied Geomorphology.

ii) Climatology : Temperature and pressure belts of the world; heat budget of the earth; atmospheric circulation; planetary and local winds; monsoons and jet streams; air masses and fronts; temperate and tropical cyclones; types and distribution of precipitation; Koppen’s and Thornthwaite’s classification of world climate; hydrological cycle; climatic change.

iii) Oceanography : Bottom topography of the Atlantic, Indian and Pacific Oceans; temperature and salinity of the oceans; ocean deposits; ocean currents and tides; marine resources–biotic, mineral and energy resources; coral reefs; sea-level changes.

iv) Biogeography : Genesis of soils; classification and distribution of soils; soil profile; soil erosion and conservation; factors influencing world distribution of plants and animals; problems of deforestation and conservation measures; social forestry, agro-forestry.

v) Environmental Geography : Human ecological adaptations; transformation of nature by man; environmental degradation and conservawtin; ecosystems and their management; global ecological imbalances–problems of pollution, global warming, reduction in bio-diversity and depletion of forests.

Section-B

Human Geography

i) Perspectives in Human Geography : A real differentiation; regional synthesis; dichotomy and dualism; environmentalism; quantitative revolution and locational analysis; radical, behavioural, human and welfare approaches; cultural regions of the world human and welfare approaches; cultural regions of the world; human development indicators.

ii) Economic Geography : World economic develpment–measurement and problems; world resources and their distribution; energy crisis; the limits to growth; world agriculture–typology of agricultural regions; agricultural inputs and productivity; food and nutrition problems; famine–causes, effects and remedies; world industries–location patterns and problems; patterns of world trade.

iii) Population and Settlement Geography : Growth and distribution of world population; demographic atrributes; causes and consequencies of migration; concepts of over–, under– and optimum population; world population problems.

Types and patterns of rural settlements; hierarchy of urban settlements; concept of primate city and rank-size rule; functional classificatipn of towns; sphere of urban influence; rural-urban fringe; satellite town; problems of urbanisation.

iv) Regional Planning : Concept of a region; types of regions and methods of regionalisation; growth centres and growth poles; regional imbalances; environmental issues in regional planning; planning for sustainable development.

v) Models, Theories and Laws in Human Geography : System analysis in Human Geography; Malthusian, Marxian and Demographic Transition models; Central Place theories of Christaller and Losch; Von Thunen’s model of agricultural location; Weber’s model of industrial location; Rostov’s model of stages of growth. Heart-land and Rimland theories; laws of international boundaries and frontiers.

Note : Candidates will be required to answer one compulsory map question pertinent to subjects covered by this paper.

Paper-II

Geography of India

Section-A

i) Physical Setting : Space relationship of India with neighbouring countries; structure and relief; drainage system and watersheds; physiographic regions; mechanism of Indian monsoons; tropical cyclones and western distrubances; floods and droughts; climatic regions; natural vegetation, soil types and their distributions.

ii) Resources : Land, surface and groundwater, energy, minerals, and biotic resources, their distribution, utilisation and conservation; energy crisis.

iii) Agriculture : Infrastructure–irrigation, seeds, fertilizers, power; institutional factors–land holdings, land tenure and land reforms; agricultural productivity, agricultural intensity, crop combination, land capability; agro-and social forestry; green revolution and its socio-economic and ecological implications; significance of dry farming; livestock resources and white revolution; blue revolution; agricultural regionalisation; agro-climatic zones.

iv) Industry : Evolution of industries; locational factors of cotton, jute, iron and steel, fertiliser, paper, drugs and pharmaceutical, automobile and cottage indusries; industrial complexes and industrial regionalisaiton; new industrial policy; multinationals and liberalisation.

v) Transport, Communication and Trade : Road, railway, waterway, airway and pipeline networks and their complementary roles in regional development; growing importance of ports on national and foreign trade, trade balance; free trade and export promotion zones; developments in communication technology and its impact on economy and society.

Section-B

i) Cultural Setting : Racial and ethnic diversities; major tribes, tribal areas and their problems; role of langague, religion and tradition in the formation of cultural regions; growth, distribution and density of population; demographic attributes–sex-ratio, age structure, literacy rate, work-force, dependency ratio and longevity; migration (inter-regional, intra-regional and international) and associated problems, population problems and policies.

ii) Settlements : Types, patterns and morphology of rural settlements; urban development; census definition of urban areas; morphology of Indian cities; functional classification of Indian cities; conurbations and metropolitan regions; urban sprawl; slums and associated problems; town planning; problems of urbanisaiton.

iii) Regional Development and Planning: Experience of regional planning in India; Five Year Plans; integrated rural development programmes; panchayati raj and decentralised planning; command area development; watershed management; planning for backward area, desert drought-prone, hill and tribal area development; multi-level planning; geography and regional planning.

iv) Political Aspects : Geographical basis of Indian federalism; state reorganisation; regional consciousness and national integration; international boundary of India and related issues; disputes on sharing of water resources; India and geopolitics of the Indian Ocean.

v) Contemporary Issues : Environmental hazards–landslides, earthquakes, floods and droughts, epidemics; issues related to environmental pollution; changes in patterns of land use; principles of environmental impact assessment and environmental management; population explosion and food security; environmental degradation; problems of agrarian and industrial unrest; regional disparities in economic development; concept of sustainable growth and development.

Note : Candidates will be required to answer one compulsory map question pertinent to subjects covered by this paper.

UPSC Geography Prelim Syllabus

Section-A

Physical Geography

i) Geomorphology : Origin of the earth; Geological Time Scale; Interior of the earth; Types and characteristics of rocks; Folding and Faulting; Volcanoes; Earthquakes; Weathering; Landforms caused by fluvial, aeolian and glacial actions.

ii) Climatology : Structure and composition of atmosphere; Temperature; Pressure belts and Wind systems; Clouds and rainfall types; Cyclones and anti-cyclones; Major climatic types.

iii) Oceanography : Ocean relief; Temperature; Salinity; Ocean deposits; Ocean currents, El Nino and La Nino; Waves and tides.

iv) Biogeography : Origin and types of soils; Major biomes of the world; Ecosystem and food chain; Environmental degradation and conservation.

Section-B

Human Geography

i) Man and Environment Relationship : Growth and development of Human Geography; Concepts of Determinism and Possibilism.

ii) Population : Races of mankind and tribes; growth and distribution of world population; migration; population problems of developed and developing countries.

iii) Economic Activities : Food gathering and hunting; pastoral herding; fishing and forestry; Types of agriculture-shifting, subsistence, commercial and plantation; Mining, Power; Manufacturing -locational factors of textile, iron and steel, sugar and fertilizer industries; Tertiary activities-trade, transport, communication and services.

iv) Settlements : Origin, types and patterns of rural settlements; Processes of urbanisation; morphology and functional classification of towns; million-cities and mega-cities.

Section-C

Geography of the World

i) Major Natural Regions : Characteristics, economic base and human adaptation.

ii) Regional Geography of Developed Countries : Canada, U.S.A., Western Europe, Russia, Japan, Australia and New Zealand.

iii) Regional Geography of Developing Countries : S.E. Asia, S.W. Asia, China, Southern Africa and Brazil.

iv) Regional Geography of South Asia

Section-D

Geography of India

i) Physical Setting : Landforms, drainage, climate, soils and natural vegetation.

ii) Economic Base : Minerals & energy resources, aquatic resources, forest resources; irrigation, agriculture and industries; trade and commerce.

iii) Population : Growth, distribution and density; demographic characteristics.

iv) Environmental problems, developmental issues and regional planning.

Section-E

Geographical Thought

i) Ancient Period : Contributions of Indians, Greeks, Romans and Arabs.

ii) Pre-Modern Period : Contribution of Verenius, Kant, Humboldt and Ritter.

iii) Modern Period : Dichotomy of determinism and possibilism; contributions of Ratzel, Semple, Huntington and La Blache.

iv) Recent Period : Quantitive Revolution; Radicalism, Behaviouralism and Humanism.

Section-F

Techniques of Geographical Analysis

i) Maps : Scale and types, uses.

ii) Diagrams : Types and uses

iii) Projections : Types, characteristics and uses.

iv) Remote sensing and geographical information system (GIS) : Aerial photographs and imagery, GIS.