notes on crustal movement

7/29/2019 Notes on Crustal Movement

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Geography

1. Describe, with the aid of diagram, the internal structure of the earth.a) The crust is formed when a molten mass of rock and metal cooled. It is the outer layerof the earth and it varies in thickness from 5 to 70km.i) Continental crust consist of granite and is less dense.ii) Oceanic crust consist of basaltic rocks and 'float'on the mantle.b) Mantle is the second layer of the earth's structure. It consist of hot and semi-liquidplastic rock .c) The outer core is liquid and the inner core consists of solid rock.

2. Explain the Continental Drift Theory (Alfred Wegner)a) all continents were part of one large land mass called 'Pangea". The continents brokeup and pieces drifted apart.b) Evidence of Theory:i) outline of S. America fit Africa like a jig-saw puzzle.ii) similar fossil animals in South America and Africaiii) similar minerals found in South America and Africa.iv) Mountain ranges in N.America and N.Europe similar.

3. Explain the Plate Tectonic Theorya) The crust is cracked into pieces called tectonic plates which float on the mantle.

b) Plates move due to convection currents in the mantle.c) Evidence: i) discoveries of mid-ocean ridges in the Atlantic Ocean and the spreadingof the sea floor.ii) volcanoes, earthquakes and young mountains all occur at the plate boundaries.

4. Identify the crustal plates on a world map.

5.Explain the types of plate movements and features formed at the boundaries.a) Divergent plate movement (constructive margin) : when crustal plates move apart,molten rock rises from mantle through a fault line. When it comes in contact with the cold

ocean water, the magma solidifies to form ridges. Layer upon layer of such solidifiedmagma is formed on top of each other until an oceanic moutain ridge is formed at thesides of the fault line, eg. mid-Atlantic ridge.

b) Convergent plate movement(destructive margin): when two plates meet head on, onewill dip below the other forming deep trenches. This is the result of subduction.E.g. The Australian plate dip below the Eurasian plate forming the Java Trench. As the


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oceanic crust is force downward, the molten material (magma) force its way up to thesurface through the layers of rocks . This results in the formation of the many volcanoesin Indonesia. When two continental plates converges, the sedimentary rocks in betweenare compressed and folded. Fold mountains are formed.

c) When two plates slide past each other, a transform fault is formed. e.g. San AndreasFault is formed when the Pacific Plate slides past the America Plate.

6. Explain the cause of earthquakeEarthquakes occur at the plate boundary because this is th most active part of the earths

crust. As plates converge, one plate is being pushed underneath another, and a zone ofsubduction is formed. As one plate moves over the other, the movement is not smoothbecause the surface of the crust is not smooth. There is friction and this friction causesthe movement to jerk.The crust is also under great stress when the plates move in opposite direction. Thestress in the rocks is so tremendous that it finally causes the rocks to jerk free. Therelease of tension in the form of seismic waves make the ground vibrate.

7. Explain what is the focus and epicentre of an earthquake.Focus is the place where the earthquake take place. Epicentre is the point on the surfaceabove the focus.

8. Name the instrument used for recording earthquake and state how the intensityofearthquake is measured.A seismograph is used for recording earthquake. The intensity of earthquake ismeasured on the Richter scale graded from 1 to 9. The higher the number, the greaterthe intensity.

9. Describe the effects of earthquakes.a) vertical and lateral rupture of the crustb) Tsunami - giant waves travelling up to 700 km/hc) collapse of buildings and bridgesd) deaths and injuriese) disruption to the transport and communication systemf) other hazards such as fire, floodingg) landslides on steep slopes.h) supply of water, gas and sewerage disposal disruptedi) diseases are rampant because of contaminated water and decomposed bodiesj) many are left homeless suffering from shortage of food, clothing, medicine

10. Explain why some earthquakes are more damaging than others.Some earthquake causes more damage because the intensity of the earthquake differ.Places located near to the epicentre will experience high intensity of the earthquake andthus suffer the greatest amount of damage.The extent of damage also depends on the amount of development in the areas whereearthquake takes place. An earthquake which struck a desert is less damaging than in acity. The foundations of the buildings and bridges are also important because if the

foundation is good, it will withstand the vibration. Developed areas suffer more damagesas water and gas pipes broke. Urban areas are heavily built up with dense populationdensities and heavy traffic movements. As residents in big urban areas usually live inhigh rise buildings because land is scarce in the cities, damage to properties and loss oflives can be phenomenal as the high rise building collapse when earthquakes occur. Asbuilding collapse, other related hazards usually occur such as fire from damaged powerlines. Destruction to highways, streets, flyover and bridges leads to widespread trafficcongestion and commuters may be killed and hurt. Telephone line and power supply willbe disrupted, and this will affect communication with outside world which in turn willhamper rescue work.The strength of the earthquake also depends on the depth of its origin and the geology ofthe epicentre. e.g. Mexico, built on layers of mud and sand, vibrates like jelly in the 1985

earthquake which killed 7000.

11. Identify and name earthquake zone on a world map.

12. Suggest ways to reduce damages from earthquake:a) early warning, e.g. detecting foreshocks by seismometers


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b) erection of reinforced bricks and concrete buildings, reinforced bridgesc) shutdown switches for major electricity generators activated by seismic waves.d) earthquakes drille) disaster plan and civil defence forcef) survival kits kept in homesg) supplies of food, blankets, drinking water stockpile for emergency

13. Define vulcanicity.The processes by which molten materials (magma) are forced from the earth's interiorinto the earth's crust or onto the earth's surface. The materials include gases, (e.g.

carbon dioxide, hydrogen), liquid and solids(dust and ash)

14. Draw a cross-section of a volcano and label the features: layers of lava andash,vent, pipe, crater, magma chamber.

15. Identify and explain the formation of volcano and lava plateau.a) Volcano: At the zone of subduction of two converging plates, the magma isdisplaced.The hot molten rock materials push their way onto the earth's surface uponpressure release along lines of weakness and escape through a vent in the crust. The

lava cools upon contact with the atmosphere and solidifies layer upon layer to form acone-shaped structure called a volcano.

b) lava plateau: It is formed by outflow of lava along fissures(cracks). It is often dissectedby rivers. It weathered to form deep, fertile black soil. e.g. Deccan Plateau

16. Identify and explain the formation of intrusive features such as sill, dyke,batholithWhen magma cools and solidifies within the earth's crust without reaching the earth'ssurface, it form intrusive volcanic features such as sill, dyke and batholith. A sill is formedalong bedding planes dyke is formed when magma cuts through layers of sedimentary

rock before it cools and solidifies. A batholith is formed when magma cools and solidifiesto form a large crystalline rock deep below the crust.


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17. Define the terms active, dormant and extinct volcano and to give an e.g. foreach.a) active volcano: shows sign of activities recently. e.g. Mt . Mayon in Philippinesb) dormant volcano: has not erupted recently but will erupt again e.g. Mt Fuji, Japanc) extinct volcano: will not erupt again e.g. Kilimanjaro (Tanzania)

18. Explain the formation of basic lava cone, acid lava cone, ash and cinder coneand composite volcano with labelled diagrams and an example for each.a) Acid lava cone is made up of viscous acid lava with high silica content. The acid lava

solidifies quickly and does not travel far forming steep convex slopes. It is associatedwith violent and sporadic eruption. e.g. Mt Mayon

b) basic lava cone is also called a volcanic shield. It is made up of fluid lava with lowsilica content.It is more mobile and spreads away from the vent before it solidifies forminggentle concave slopes. It is associated with quiet eruption e.g. Mauna Loa (Hawaii)

c) Ash and cinder cone is formed by the successive ejection and accumulation of solidpyroclastic materials. The periodic and violent eruptions cause alternate layers of ashand cinder. e.g. Vulcano (Italy)

d) Composite cone has a stratified structure. There is periodic violent eruptions with

alternate layers of lava and ash accumulated.It is high with steep slopes near the summitand gradient decreases toward the base. Parasitic cones develop due to thedevelopment of cracks during violent eruptions. e.g. Mt Fujiyama in Japan

19. Describe the formation of caldera, crater lake and volcanic plug and to give ane.g for each.When magma in the crater and vent solidifies, a cap of solid rock called a plug is formedabove the molten material. e.g. Mont Pelee on the island of Martinique.The plug may prevent magma from passing up the vent and massive pressure buildsup,swelling the volcano's base.This may eventually cause a very violent eruption whichshatters the top of the volcano into a huge depression called a caldera. Water may fill thecaldera to form crater lake such as Lake Toba in Sumatra, Indonesia.

20. Explain the associated features of vulcanicity: hotsprings, fumarole andgeysersa) Hotspring: As groundwater is heated by contact with magma, the superheatedgroundwater flows quietly in a volcanic region as hotspring.e.g. Tangkuban Prahu in Javab) a fumarole refers to the ejection of gases or steam only from the thermal heating ofmagma.c) geyser: It is a fountain of hot water and superheated steams which is ejected onto thesurface at Intervals. e.g. Old faithful in Yellowstone park,USA

21. Describe the benefits of vulcanicity to man.a) volcanic regions are often rich in sulphur deposits which can be mined for industrial

use.b) basic lava often produce fertile soil after weathering which is suitable for cultivation.e.g. fertile volcanic soils in Java and Deccan Plateau in Indiac) geothermal power may be utilised for making steam to generate electricity e.g. NewZealand gets 10% of her power supply from geothermal energy.d) Volcanic areas offer spectacularly beautiful attractions for tourists. e.g Mt Fuji in Japane) Volcanic ash can be used to surface roads and manufacture bricksf) In some parts of the world, valuable materials such as gold, iron and diamondshave been formed by volcanic activity, and large mining centres have developed.

22. Describe the problems of vulcanicity to man.a) volcanic eruptions claim many lives and destroy buildings and property,

b) Poisonous gases such as compounds of sulphur, carbon monoxide and carbondioxide are produced.c)ash and volcanic dust ejected by volcanoes may be blown away to pollute the aird) When snow-capped volcanoes erupt, a sudden flash flood will also result from themelting of snow and ice. Mudflow may also be produced.


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23. What are the dangers faced after an earthquake?There could still be aftershocks of lower magnitudes as there are adjustments to therepositioning of the fault. As many buildings are already weakened by the main shock,the aftershocks will cause more collapse and there will be more casualties. Dead animalsand corpse will start to rot and if not disposed quickly, there might be an outbreak ofepidemic such as Malaria.

23. Describe the cause of folding.When the layer of rocks are compressed, the layers of rocks may be folded in a variety of

ways. The upfold is called the anticline and the downfold is called the syncline.

24. Draw a simple fold and name the parts .

25. Draw and name the types of fold: symmetrical, assymetrical fold, overfold,recumbent fold and overthrust.

26. Describe the formation of fold mountains with the aid of a diagram.

Over a long period of time, deep deposits build up and the sea bed sinks under this greatweight. As plates move nearer, sediments are compressed to form an island in the sea.Further compression caused the layer of rocks to be folded. The anticlines form the foldmountains and the synclines became the sites of seas and valleys. e.g. The convergenceof the Indo-Australian plate and the Eurasian plate results in the formation of theHimalayas.

27. Name the young fold mountains on a world map: Himalayas, Andes, Rockies,Alpsand Andes.

28. Explain the cause of faulting.Where relatively rigid part of the crust moves along the lines of weakness, faults are

formed. The layers of rocks are displaced horizontally or vertically along the fault lines.It can be caused by either tensional or compressional forces which are applied to rockseither laterally or vertically.

29. Draw a diagram of a normal fault and label the following: fault line, upthrowdownthrow, scarp.


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30. Draw and expalin the types of faults: normal, reverse and tear.

31. Explain the formation of a horst, block mountain.A block mountain refers to a block of crust which is uplifted due to faulting,the smaller ofwhich are called horst. It is formed when a block of crust remains standing tall due to thesinking of the crust on either side of a pair of faults or the uplifting of a rock massbetween two faults. e.g. Black Forest in the Rhine Basin.

32. Explain the formation of a graben, rift valley with the aid of diagramsRift valleys are steep-sided trenches, the smaller of which are sometimes called graben.They are caused by either subsidence of a section of the crust between two faults whentensional forces are applied, or then the land on either side of two parallel faults areuplifted due to compression. e.g. East African rift valley

Horst Rift Valley fault scarp

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