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INTRODUCTION TO PHYSICALGEOGRAPHY
INTRODUCTION TO PHYSICALGEOGRAPHY
GE:140
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INTRODUCTION• Physical geography is a discipline that is part of a
much larger area of understandingcalled geography.
• Most individuals define geography as a field ofstudy that deals with maps.
• This definition is only partially correct. A betterdefinition of geography may be the study ofnatural and human constructed phenomenarelative to a spatial dimension.
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• The discipline of geography has a history thatstretches over many centuries.
• Over this time period, the study of geographyhas evolved and developed into an importantform of human scholarship.
• Examining the historical evolution ofgeography as a discipline provides someimportant insights concerning its character andmethodology
• These insights are also helpful in gaining abetter understanding of the nature of physicalgeography.
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WHAT IS PHYSICAL GEOGRAPHY• Physical geography is “the spatial analysis of the
physical elements and processes that make up theenvironment: energy, air, water, weather, climate,landforms, soils, animals, plants, microorganisms,and Earth itself”
• Physical geography also examines theinterrelationships of these phenomena to humanactivities. This sub-field of geography isacademically known as the Human-LandTradition. This area of geography has seen verykeen interest and growth in the last few decadesbecause of the acceleration of human inducedenvironmental degradation.
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SCOPE OF PHYSICAL GEOGRAPHY• Physical geography encompasses elements of
many disciplines, including climatology,meteorology, oceanography, geomorphology(study of landforms), soil science, biogeographyand ecology (distribution and ecology of life),hydrology, and natural resources.
• Thus, physical geography's scope is much broaderthan the simple spatial study of nature. It alsoinvolves the investigation of how humans areinfluencing nature.
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• Geomorphology - studies the various landformson the Earth's surface.
• Pedology - is concerned with the study of soils.• Biogeography - is the science that investigates
the spatial relationships of plants and animals.• Hydrology - is interested in the study of water
in all its forms.• Meteorology - studies the circulation of the
atmosphere over short time spans.• Climatology - studies the effects of weather on
life and examines the circulation of theatmosphere over longer time spans.
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• Geology - studies the form of the Earth's surfaceand subsurface, and the processes that create andmodify it.
• Ecology - the scientific study of the interactionsbetween organisms and their environment.
• Oceanography - the science that examines thebiology, chemistry, physics, and geology ofoceans.
• Cartography - the technique of making maps.
• Astronomy - the science that examines celestialbodies and the cosmos.
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Topic 1: Earth Processes and Landforms
• 1.1 Internal processes and movements• 1.2 Rock forming processes• 1.3 Geomorphic processes and landforms• 1.4 Desert processes and landforms•
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1.1 Internal processes and movements
• Internal Processes• - a process that shapes the earth with
forces from the interior of the earth e.g.plate tectonics, volcanic formations,earthquakes,
. Note: Internal processes are known asendogenetic processes
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- Internal processes operate within Earth,drawing energy from heat
- In general, they are building forces,increasing relief of land surface
- The three forces are compressional force,tensional force and shear/lateral force.
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Forces in Earth’s Crust
• A force that acts on rock to change its shapeor volume is stress
• 3 types of stress acting on rock layers- Tension pulls on the crust- Compression squeezes rock- Shearing pushes a mass of rock in two
opposite directions
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Types of Stresses
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Tension Force• Tension pulls on the crust, stretching rock so
that it becomes thinner in the middle.(divergent boundaries)
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Compression Force
• Compression squeezes rock until it folds orbreaks. (convergent boundaries)
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Shearing Force• Shearing pushes a mass of rock in two
opposite directions. (transform boundaries)Rock breaks and slips apart or changes shape.
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Faulting• When enough stress builds up in rock, the rock
breaks, creating a fault.• A fracture is a break in the rock.• A joint is a fracture where rock movement
doesn’t occur.• A fault is a break in the rock of the crust where
rock surfaces slip past each other.• Most faults occur along plate boundaries, where
the forces of plate motion push or pull the crustso much that the crust breaks.
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Three main types of faults:• 1. normal faults-• Tension causes a normal fault. Divergent
boundary.• In a normal fault, the fault is at an angle, and
one block of rock lies above the fault while theother block lies below the fault.
• The block of rock that lies above is called thehanging wall. The rock that lies below is calledthe footwall.
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Normal Fault
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Example of a normal fault at Kilve Beach - Devon- UK
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Kanda Fault in Tanzania(West of the Rukwa Rift)
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View of the Kanda fault at NESumbawanga
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• 2. reverse faults- (Compressional fault)• Compression causes reverse faults. Convergent
boundary. (hanging wall slips upwards along the fault)• A reverse fault has the same structure as a normal fault,
but the blocks move in the opposite direction. Verticalrock motion. e.g. South Oregon USA
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A reverse Fault
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Reverse fault zone, Ketobe Knob, Utahat Colorado USA
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Areas with fault features in Tanzania
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• 3. strike-slip faults-• Shearing creates strike-slip faults. Transform
boundary.• In a strike-slip fault, the rocks on either side of
the fault slip past each sideways, with little up ordown motion. Horizontal rock motion. Ex. SanAndreas Fault.
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• The Shear fault is also known as a Wrench Fault• It is also formed when the two blocks slide
passed other instead of colliding.• It involves the horizontal displacement• Good examples of Wrench faults are the San
Andreas fault, Aswa valley in northern UgandaGreat Glen of Scotland, Great Alpine Fault ofNew Zealand
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This block diagram of a wrench-fault zone showsthat vertical movement is often very complex.Faults may appear to be normal or reverse alongthe fault zone, and fault reversals and scissoringare common; horizontal displacement is greaterthan these vertical complications 29Ngogo Mn. 2018/2019
San Andreas Fault (US)
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FAULTING AND LAND FORMS
• 1. Rift Valley- An elongated trough or depression which is
bordered by in-facing fault scarp.
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Theories supporting the formation ofrift valley
• 1. Tensional force theory- The theory holds that rift valley is formed due
to tensional force- The force act on the crust resulting into
development of parallel fault lines- As the forces pull away, the central block
become loose and then sinks or subside as atrough rift valley. E.g. Kenya (G.E.A.R.V), MiddleRhine between Vosges etc
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Kenyan section in the Great EastAfrican Rift Valley
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2. Compressional Force Theory
• Suggests that a rift valley resulted fromcompressional forces
• The side parts are up thrusted leaving atrough bordered by steep sides-rift valley
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Differential in uplift theory• Contends that r. valley might have formed from
a tilted block.• Followed by the uplifted of land whereby the
central block was lifted at a slower pacecompared to the side blocks.
• The central block remained as a depressionbordered by in-facing steep sides
• Hence, a rift valley is also called a step-faultedrift valley as it is characterized by the sideswhich are like steps formed due to differentialin uplift.
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Tilted block resulting into a Rift Valley
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Block Mountain or Horst• It is an upland which is bordered by a fault line
on one or more side.• It may be formed due to uplift or sinking of the
crust on either side of a pair of faults or thebodily uplift of a mass between them.
• E.g. Usambara, Uluguru in TZ, Ruwenzori inUganda Vosges in France and Black forestmountain in Germany are good examples
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Usamabara Mountains
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Uluguru Mountains
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Vosges Mountains in France
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Fault-Scarps and Fault-line Scarp
• It is an escapment or steep slope along a faultor rift valley or block mountain
• Forms due to vertical movement of blockalong a fault line.
• Development of faults may be followed byeither an upward or down ward movement
• E.g. Butiaba-Uganda, Elgeyo-Kenya, Chunyaand Manyara in TZ
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Formation of Fault-Scarps
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Chunya Mbeya
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Elgeyo Escarpment
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Fault-Guided River Valley
• Is a valley along a fault line cut by a river.• Sometimes rivers may leave their course and
flow along fault line to erode and widen thefault to become a valley where it flows. It maydevelop a trellis pattern
• E.g. Zambezi river at Batoka Gorge-below theVictoria falls, River Aswa in Uganda and KleinBerg River near Tlbagh in South Africa.
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Batoka Gorge-below the victoria falls inZambia/Zimbabwe
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Rift valley lake
• A lake found at the floor of a rift valley
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A crack in the G.E.A.R.V
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Earth Movements
• The powerful internal forces operating fromwithin the crust are called earth movements.Such movements may be slow and sudden.
• Our earth is unstable, every second somedisturbances are taking place in any part ofthe earth.
• Submergence, volcanic eruption, platetectonic and ocean floor spreading arecommonly cited as earth’s crust disturbances.
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Causes of the Earth Movements• The speculation of land forms on the earth
surface in different ages of geological timesand at different places enforce the geologistand geomorphologist to think over the geneticforces and processes responsible for theirorigin.
• The forces of the earth movement rest in thecrust
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How the forces of earth movementcame into being
• 1. From time to time certain sections belowthe earth surface become heated, probably,by heat given off by radioactive elements. Thiscaused expansion which brings about a seriesof events resulting in the folding of adjacentsections of the rock at the surface.
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2. The elevated parts of continental regions arecontinually denuded and the eroded materialsare transported and deposited in the sea.
• Consequently, the continents become lighterand the seas become heavier.
• Thus a slow adjustment takes place by thepushing down the oceanic segment andforcing up the land segment.
• Due to this isostatic adjustment, convectionalas well lateral forces are originated in theearth’s crust.
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Types of the Earth Movement
• The earth movements are determined bymagnitude and intensity.
• Their effects may appear in different durationof time
• They are differentiated on the basis of whetherthey are lifted or depressed parts of the surfaceor whether they are subjected to lateralstretching or compressions
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• On the basis of time, earth movements can beclassified as
• 1. Sudden Earth Movements• 2. Slow or Secular Earth Movements
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1. Sudden Earth Movements• When the effect of the earth-movemnet
appears on the surface suddenly orabruptly and they finish in short time
• E.g. Earthquakes and volcanoes• These movements cause heavy loss of
properties and life as due to their suddenoccurrence.
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2. Slow or Secular Earth Movements• This type of earth movement continues for
longer, more than span of our lives• The effect of these movements is felt very
slowly.• For example formation of Himalays from the
floor of Tythes.
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Classification of Secular earthMovements
1) Epirogenic Earth Movements2) Orogenic Earth Movements
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Epirogenic Earth Movements
• The vertical force which causes the upliftmentor subsidence of some segment of the earthsurface
• Uplifted land = up warping• Subsidence = down warping• Continents and oceans are formed from those
movements• Also known as continental building earth
movement
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2. Orogenic Earth Movements
• The Orogenic from Greek “Oro” meaningMountain.
• This movement is also known as mountainbuilding earth movement b’se the various typeof structural mountains are formed by thismovement.
• It is a lateral movement of force causesstretching and tension in the rocks
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For notes and personal studies
• Visit
• www.sautgeodept.wordpress.com
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2 kinds of Orogenesis on the basis ofmovement direction
i. Compressional Force
ii. Tensional Force
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Compressional Force• When the lateral force inside the crust move
from opposite direction to common point.
• The rocks are deformed and their area aresqueezed.
• Consequently, a wave like structure, calledfold is formed
• The up fold is described as crest or anticline
• The down fold as trough or syncline
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Up fold and down Fold
The nature of folds vary from region to region due tovariation in the amount of compression exerted on thesides of the folds
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An anticline in Alberta, Canada in theRocky Mountains
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Syncline sidling hill
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Kinds of Fold
i. Symmetrical folds
ii. Asymmetrical folds
iii. Isoclinal folds
iv. Monoclinal folds
v. Recumbent or over folds
vi. Overthrusts or Nappe folds
vii.Tensional Force
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Groups of Folds
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1. Symmetrical Folds• When the two limbs of the fold dip at equal
angle due to compression of same amount ofthem.
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2. Asymmetrical Folds• It is the type of folds in which the limbs of
folds dip at unequal angles. One Limb inclinesdeeply than the other limb
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3. Isoclinal Folds• The compression force is strong and the two
limbs of folds dip in the same direction andbecome parallel.
• Their axial plane is neither vertical norhorizontal
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Isoclinal folds
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4. Monoclinal Folds• It is a modified form of a symmetrical fold.
• One limb of the fold dips at right angle whilethe other at acute angle.
• Also formed by imposition of unequalcompression on the limbs of the folds
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Monoclined Fold
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5. Recumbent or Overfold• Sometime, two limbs of the folds become
parallel, one lies above the other, due to excessiveamount of compression exerted on them fromopposite sides.
• Limbs overturned and become horizontal in theiraxial plan.
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Recumbent fold
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6. Overthrust or Nappe folds• When the compression force exceeds the bearing
capacity of the rocks, the folds become veryacute and break up.
• One limb thrust over the other, thus a thrust faultdevelops in a recumbent fold
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Folding and Landforms
• 1. Fold Mountains
- Folding is responsible for wrinkling of thecrust into lofty upfolds and deep down folds.
- The loft landscapes becomes a fold mountainssuch as Atlas, Himalayas, Rockie
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A view of Himalayan Mountains in theNorth Eastern India
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• 2. Valleys- The wrinkled down folds may be in form of
narrow and deep valleys. Such valleys aretermed as synclinical valleys.
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Synclinical valley at Usambaramountain ranges
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3. Basins
• Sometimes the down folds associated tofolding are broad and shallow as well as gentlysloping.
• Such down folds are called synclinal basins• For example: London basin, Paris basin, upper
basin etc
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Sudden Earth Movements
• There are two kinds of sudden earthmovements
1. Volcanism2. Earthquake
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Volcanism or Volcanoes
• Volcanism is a process in which the hot rockseither in the form of liquid like magma or inthe form of solid small pieces are ejecting outon the earth surface through a vent orpassage of the crust
• Beside, streams gases and smokes are alsocoming out at the time of volcanic eruption
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• Thus, the ejecting out of these materials frombeneath the earth surface through the Vent isknown as Volcano
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Classification of Volcanoes
1. On the basis of nature of eruption2. On the basis of ejected materials into
different forms
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On the Basis of Nature of Eruption
• There of two kinds1. Central Type Volcanoes: when the volcanic
eruption takes place through a vent with agreat force and the ejected materials aredeposited around the vent to form volcaniccones .Such volcanoes are known as centrallytyped volcanoes
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2. Fissure Type Volcanic Eruption.- When the magma or hot materials from within
the crust are coming out on the surfacethrough the fractures or cracks in the crust
- The flow of ejection is slow and ejectedmaterials spread over the wide area like a thinsheet called as Volcanic Shields
- Deccan plateau of India formed by depositionof Magma through fissure eruption
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On the Basis of Ejected Materials
1. Pyroclastic or Cinder volcanoes2. Dome shaped volcanoes3. Shield type volcanoes4. Composite Volcanoes
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1. Pyroclastic or Cinder volcanoes
• The volcanic cones which are formed bydepositions of solid ejected materials likecinder lappili and ash through the vent ofvolcanoes, from beneath the earth surface.
• Such volcanoes are having rather moreheights and steep slopes
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Stromboli Mountain in Aeolian Islands
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Dome Shaped Volcanoes
• When very viscous magma comes out andpiles up in small area around the mouth ofvent.
• It has narrow base and rather more heightwith steep slope (Also known as acid lavavolcano)
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Dome Shaped Volcanoes
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Shield or Basalt Type Volcanoes• The fluid basis magma spreads over a large area
after the explosion through the volcanic vent dueto its low viscosity.
• High rate fluidity the ejected and accumulatedmagma does not pile up to the considerableheight.
• Base is broader and the height is rather low.• Are also know as shield or basaltic volcano• Usually plateau and those formed in oceans are of
the same type, rarely rise above sea levelNgogo Mn. 2018/2019 95 Ngogo Mn. 2018/2019 96
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Composite Volcanoes• When a volcanic cone is formed by alternate
accumulation of Pyroclastic (solid) materialsand magmas ejected out around centre of thevent.
• It is formed of roughly alternating layers of lavaand ash.
• Magma may penetrate the structure ofvolcanoes forming dykes radiating from thecentral vent.
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• Rare volcanic eruptions with an individualmaterial in isolation occur in the world butthey are the combination of different types ofejected materials
• Fujiyama (Japan) and Vesuvius (Italy) are theexamples of such volcanoes
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Composite Volcanoes
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Fuji Mountain (Japan)
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On the Basis of Duration of Activity ofVolcanic Eruption
1. Active Volcanoes: the volcanoes whichshow continuous eruption. There areabout 500 active volcanoes all over theworld.
2. Dormant Volcanoes: The eruptionactivities of some volcanoes are ceasedup due to some reasons for a long period.
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• 3. Extinct Volcanoes• Extinct volcanoes are such ones
which have stopped for ever.Possibility of reoccurrence is notfound there
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Materials Ejected from the Volcanoes
1. Pyroclastic Materials: Include all types ofsolid fragmented materials ejectedduring volcanic eruption: Bomb, Cinder,Lappili, Ash and volcanic dusts arecommon PM according to the size ofdiameters of particles in descendingorder
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2. Lava and Magma:- these are the main constituent of volcanic
eruption.- When the magma reaches on the earth surface
is called lava
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- Two kinds of magmai. Acidii. Basic
i. Acid Magma• Depending upon the content of silica. The
acid magma is more viscous with highpercentage of silica
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ii. Basic Magma
• It is non-viscous with low proportionof silica
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3. Vapours and Gases
• Steams and gases of different typesare ejecting out at the time ofvolcanic eruption.
• Carbon dioxide, hydrogen, Sulphurdioxide, carbon mono-oxide etc areimportant volcanic gases
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Vapours and Gases (from volcanoes)CAUSES OF VOLCANISM
• Formation of volcanoes takes placedue to the ejection of hot solid, liquidand gaseous materials from beneaththe earth surface.
• The most important matter, which isto be explored is the cause offormation of magma and its ejectionafter the breaking of overlying rocks.
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1. Percolation of Water• Water percolates down from the bottom of
water bodies like sea and oceans in largeproportions to underground
• Temperature in the interior of the earth ishigh as it increases at a rate of 1⁰C for 165Mt depth from the earth surface
• When the percolated water gets contactwith hot rocks, converts into steams andvapours.
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• The steams and vapours make Endeavourto come out and along the weak zone ofthe earth crust, wherever outlets areavailable.
• Due to great force of these steams, somemolten materials like magma begin toeject and form volcanoes on the earthsurface
• More than 90% volcanoes are foundalong the continents and ocean’s margins
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2. Tectonic Earth Movements
• The time of mountain buildingmovement, the crustal rocks aredeformed into form of folding andfaulting.
• Faulting leads to dislocation anddisplacement of rocks along the faultplanes causing the release of superincumbent pressure of overlying rocksinside the earth crust.Ngogo Mn. 2018/2019 113
• Beneath the earth surface relativelyat 100 km depth temperature is veryhigh due to disintegration ofradioactive elements.
• Under high temperature rocks arenot melted due to increasingpressure of overlying rocks.
• The pressure increases the meltingpoints of the underlying rocks.
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• Thus, when pressure of overlyingrocks is released by dislocation of therocks in tectonic movement, theunderlying rocks are melted andmagma is formed in the uppermantle.
• This magma ejects out through theweak zone of the earth crust to formthe volcanoes.
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Geographical distribution of Volcanoesin the World
1. Circum Pacific or Zone of Subduction Region- Large number of active volcanoes
concentrated along the margin of PacificOcean
- Volcanoes are found in chain here- Also known as the ring of fires- The main cause (subduction of plates in
oceanic trenches along the Asiatic andAmerican coasts
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Circum Pacific or Zone of SubductionRegion
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Mid Oceanic Ridge
• Along the mid-oceanic ridges especially inAtlantic ocean fissure type volcanic eruptionsare common due to moving away of plates.Magma is of basaltic type and volcanoes ofhigh elevation rarely occur
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Mid Oceanic Ridges
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Mid- Continental Regions
• includes the weak zone of Europe and Asiaalong the mountain chain of tertiary era.
• Starts from Alps fold mountains in Europe andreaches up to islands of S.E Asia throughAfghanistan, Baluchistan, India and Indo-Burma border.
• Crustal dislocation during mountainmovement is common cause of occurrence ofvolcanoes in this region
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Intrusive volcanic features
• Volcanic feature formed when magma doesn’treach the Earth’s surface.
• It solidifies below the surface.• Also known as plutonic features
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Processes
• Denudation exposes the features• Discordant Plutons: cut across the bedding or
foliation of the host rock (dykes, necks)• Concordant Plutons: injections of magma
parallel to the bedding or foliation of hostrocks (sills, laccoliths)
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Discordant Plutons: separated based onsize
- Volcanic Necks: solidification ofmagma in the main conduit, exposedthrough differential erosion
- Dikes (dykes): tabular plutons, cutacross bedding, usually associatedwith solidification in fissures
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Discordant Plutons
• Stocks: irregularly shaped, largerthan other intrusions < 100 km sq
• •Batholiths: irregularly shaped,larger than other intrusions > 100 kmsq e.g. High, Sierra
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Concordant Plutons:• Laccolith: mushroom-shaped plutons• injected parallel to the structure of
the host rock• domes up the overlying rocks• < 10:1 diameter vs thickness
(laccolith grades to sill)
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• Sills: tabular plutons intruded parallelto the structure of enclosing rocks
- Injected along bedding planes ofsedimentary rocks
- Mesas, buttes, cuestas, hogbacks- Order cm – 10s m thick, km in length
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Summarized volcanic features
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Earthquake
• Earthquakes represent the vibrationof Earth because of movements onfaults.
• The focus is the point on the faultsurface where motion begins.
• The epicenter is the point on Earth'ssurface directly above the focus
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• An earthquake occurs when Earth’ssurface shakes because of the releaseof seismic energy following the rapidmovement of large blocks of the crustalong a fault.
• Faults are breaks in the crust that maybe hundreds of kilometers long andextend downward 10 to 20 km (6-12miles) into the crust.
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• The point on the fault surface wheremovement begins, the earthquake source,is termed the focus.
• Seismic waves radiate outward from thefocus. Earthquake foci (plural of focus)occur at a range of depths.
• The majority of earthquakes occur atshallow depths that range from the surfacedown to 70 km (44 miles). Less frequentintermediate (70-300 km; 44-188 miles)and deep (300-700 km; 188-438 miles)
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• Earthquakes are generally associated withsubduction zones where plates descend intothe mantle.
• Damage is greatest from shallow earthquakesbecause the seismic waves travel a shorterdistance before reaching the surface.
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Origin of Earthquake
• Most natural earthquakes are caused bysudden slippage along a fault zone
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The elastic rebound theory
• The theory suggests that if slippage along afault is hindered such that elastic strain energybuilds up in the deforming rocks on either sideof the fault, when the slippage does occur, theenergy released causes an earthquake.
• This theory was discovered by makingmeasurements at a number of points across afault.
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• Prior to an earthquake it was noted that the rocksadjacent to the fault were bending. These bendsdisappeared after an earthquake suggesting thatthe energy stored in bending the rocks wassuddenly released during the earthquake.
• Friction between the blocks then keeps the faultfrom moving again until enough strain hasaccumulated to overcome the friction andgenerate another earthquake. Once a fault forms,it becomes a zone of weakness - so long as thetectonic stresses continue to be present moreearthquakes are likely to occur on the fault. Thusfaults move in spurts and this behavior is referredto as Stick Slip.
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• If there is large displacement during anearthquake, a large earthquake will begenerated. Smaller displacements generatesmaller earthquakes. Note that even for smalldisplacements of only a millimeter per year,after 1 million years, the fault will accumulate 1km of displacement.
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Fault Creep
• - Some faults or parts of faults movecontinuously without generating earthquakes.This could occur if there is little friction on thefault & tectonic stresses are large enough tomove the blocks in opposite directions. This iscalled fault creep.
• If creep is occurring on one part of a fault, it islikely causing strain to build on other parts ofthe fault.
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Seismology,The Study of Earthquakes
• When an earthquake occurs, the elasticenergy is released sending out vibrations thattravel throughout the Earth.
• These vibrations are called seismic waves. Thestudy of how seismic waves behave in theEarth is called seismology.
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Important terms
• Focus- The source of an earthquake which is an exact
location within the Earth where seismic wavesare generated by sudden release of storedelastic energy.
• The epicenter- the point on the surface of the Earth directly
above the focus. Sometimes the media getthese two terms confused.
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Types of Seismic waves
• Body Waves – emanate from the focus andtravel in all directions through the body of theEarth.
There are two types of body waves: P -waves S-waves
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P -waves
• Are Primary waves. They travel with a velocitythat depends on the elastic properties of therock through which they travel.
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Where, V is the velocity of the P-wave, K is theincompressibility of the material, µ is the rigidityof the material, and ρ is the density of thematerial.
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• P-waves are the same thing as sound waves.They move through the material by compressingit, but after it has been compressed it expands,so that the wave moves by compressing andexpanding the material as it travels.
• Thus the velocity of the P-wave depends on howeasily the material can be compressed (theincompressibility), how rigid the material is (therigidity), and the density of the material. P-waves have the highest velocity of all seismicwaves and thus will reach all seismographs first.
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S-Waves
• - Secondary waves, also called shear waves.They travel with a velocity that depends onlyon the rigidity and density of the materialthrough which they travel:
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• S-waves travel through material by shearing itor changing its shape in the directionperpendicular to the direction of travel.
• The resistance to shearing of a material is theproperty called the rigidity. It is notable thatliquids have no rigidity, so that the velocity ofan S-wave is zero in a liquid.
• that S-waves travel slower than P-waves, sothey will reach a seismograph after the P-wave
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Surface Waves• Surface waves differ from body waves in that they
do not travel through the Earth, but instead travelalong paths nearly parallel to the surface of theEarth.
• Surface waves behave like S-waves in that theycause up and down and side to side movement asthey pass, but they travel slower than S-waves anddo not travel through the body of the Earth.
• Surface waves are often the cause of the mostintense ground motion during an earthquake.
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Seismometers• Seismic waves travel through the Earth as
vibrations.
• A seismometer is an instrument used to recordthese vibrations
• Seismogram: the resulting graph that showsthe vibrations.
• Isoseismal: it is an imaginary line, drawn onthe map, connecting the places of uniformintensity of earthquakes.
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• Intensity of earthquakes are measured byseismography on Richtar Scale
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Effects of earthquakes• Deformation on the earth surface e.g. thrust
fault, upliftment and subsidence of part of theearth.
• Loss of lives and properties. E.g. Anearthquake of 5.9 magnitude hit North WestTanzania on Saturday 10/09/2016, about 44 kmfrom Bukoba town, 20 deaths reported (13adult, 7 children), 269 people injured, 905houses totally destroyed, 1124 houses heavily topartially damaged (deep cracks)
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• Land slides liquefaction and tsunamis
• Fires floods and diseases
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Area of Earthquakes
• Like volcanoes, the earthquakes are alsoconcentrated into three importantgeographical regions
Circum Pacific Region
Mid-Atlantic Region
Mid- Continental Region
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