Horizons - Sample Chapters

SYLLABUS LINK11 1 The Tectonic Cycle ................................ 2 2 Plate Tectonics ....................................... 5 3 The Geography of Volcanoes ...........17 4 The Geography of Earthquakes .......34 5 The Rock Cycle ....................................50 6 Folding and Faulting ...........................63 7 Slope Development .............................70 8 Weathering ............................................71 9 Karst Landscape ..................................78 10 Mass Movement ................................... 86 11 Fluvial Processes, Patterns and Landforms, and Human Interaction ...... 98 12 Coastal Processes, Patterns and Associated Landforms, and Human Interaction .............................121 13 Glacial Processes, Patterns and Associated Landforms ................144 14 Isostasy ................................................162 CCRL lutterns und lrocesses ín the lhvsícuí Lnvíronment Chapter Chapter 2 SYLLABUS LINK The internal structure of the Earth líunet Lurth ís thought to be uround 4.6 bííííon veurs oíd. 1he Lurth consísts oí u number oí íuvers: z 1he crust z 1he muntíe z 1he outer core z 1he ínner core As the Lurth cooíed, the heuvv muteríuís moved dovn tovurds the core und the ííghter muteríuís moved to the suríuce. By the end of this chapter students will have studied: z The internal structure of the Earth z The Earth’s crust The mobility of the Earth’s crust produces endogenic forces, which give rise to geological structures within it. Crustal structures are created, modified and destroyed as part of the tectonic cycle. 1 The Tectonic Cycle GEOTERMS º Jhe lithosphere is lhe leru used lo describe lhe Earlh's crusl aud lhe solid upper uaulle. Jo lithify ueaus 'lo luru lo rock'. º Jhe rocks oí lhe asthenosphere layer are parlially uelled. Jhe lilhosphere Noals ou lop oí lhis layer. º Jhe asthenosphere carries lhe lilhosphere oí lhe Earlh, iucludiug lhe couliueuls. Jhe rocks oí lhe aslheuosphere Now iu respouse lo pressure exerled ou lheu írou lhe uoveueul oí lhe iulerior oí lhe Earlh. Jhe aslheuosphere is localed iu lhe upper uaulle oí lhe Earlh al deplhs oí 100-240 ku. i Fig 1.1 The structure of the Earth Continental crust. Composed of light rocks made from silica and alumina (SIAL). 30–70 km thick. Ocean Oceanic crust. Composed of heavy rocks made from silica and magnesium (SIMA). 3–10 km thick. CRUST Made up of solid rock Two main types, oceanic crust and continental crust MANTLE Made up of rock Molten or semi-molten state OUTER CORE Made up mainly of iron Molten/liquid state INNER CORE Made up mainly of iron and nickel Solid state Very high temperatures (up to 5000 o C) NOTE Eudogeuic íorces are processes lhal lake place iuside lhe Earlh. ! The moho. The boundary between the Earth’s crust and the mantle. The Tectonic Cycle Chapter 1 The Earth’s crust 1he Lurth's crust consísts oí tvo purts: z Contínentuí crust z Cceuníc crust Fig 1.2 The Earth’s crust Continental crust Continental shelf Ocean Oceanic crust Volcano Ocean ridge Rigid upper mantle M a n t l e Light rocks – SIAL e.g. granite Mantle consists of semi-molten rock that moves in convection currents, fuelling the movement of the plates of the Earth’s crust Heavy rocks – SIMA e.g. basalt L i t h o s p h e r e 1he contincntaI crust is thick, uverugíng betveen 30 km and 70 km ín thíckness (thícker under mountuíns). 1he contínentuí crust is madc up of Iight rocks rích ín siIica und aIumina, such us granitc. 1hís íuver ís reíerred to us SlAl. 1he occanic crust is thinncr than thc contincntaI crust, uverugíng betveen 3 km and 10 km ín thíckness. 1he occanic crust is madc up of hcavv rocks, such us basaIt. 1hís íuver ís oíten reíerred to us SlMA becuuse these heuvv rocks ure rích ín siIica und magncsium. GEOTERMS The moho is the boundary located between the Earth’s crust and the mantle. This boundary is located approximately 5–10 km below the ocean floor and on average 35 km beneath the continents. The moho separates oceanic crust and continental crust from underlying mantle. i QUICK QUESTIONS 1. Name the four layers of Planet Earth. 2. Which layer do we live on? 3. Which is the hottest layer? 4. Which crust is referred to as having (a) SIMA and (b) SIAL content? ? Ordinary Level | Short Questions Cross-section of the Earth 1. Examine the diagram on the right and match each of the letters in the diagram with one of the descriptions below. Outer core Mantle, convection current Inner core Mid-ocean ridge Ocean trench A C E B D 2010, Part 1, Q1, 10 marks Questions 3 Core Physical Environment 44 Ordinary Level | Long Questions Plale leclouics 2. Examine the cut away diagram of the Earth. Match each of the following names with a letter from the diagram. Couliueulal crusl 0uler core Maulle 0ceau crusl |uuer core E A B C D 2008, Part 2, Q2A, 30 marks The marking scheme for a question like this on an Ordinary Level paper is as follows: |ive correclly ideuliíed © 6 uarks each Total 30 marks Higher Level | Short Questions Slruclure oí lhe Earlh 3. Examine the diagram of the structure of the Earth. Match each of the following terms with its correct letter in the diagram. |uuer core Maulle 0ceauic crusl Couliueulal crusl A B C D 2007, Part 1, Q1, 8 marks Structure of the Earth: z Crust z Mantle z Outer core z Inner core z Lithosphere: the Earth's crust and the solid upper mantle z Asthenosphere: partially melted layer, the lithosphere floats on top of it The Earth’s crust: z Continental Crust – thick, 30–70 km – light rocks – SIAL z Oceanic Crust – thinner continental crust, 3–10 km – heavy rocks – SIMA T h e in t e r n a l s t r u c t u r e o f t h e E a r t h MIND M AP 5 By the end of this chapter students will have studied: z The theory of continental drift z The theory of sea-floor spreading z Continental drift and plate movement z Ireland’s position now and in the past z Global distribution of plates z Plate boundaries 2 Plate Tectonics Plate tectonics PIatc tcctonics ís u theorv expíuíníng the motíons oí the Lurth's ííthosphere. lt buííds on oíder concepts oí contínentuí dríít. 1he theorv oí contínentuí dríít vus deveíoped bv Aííred \egener ín l9l2 und ínuíív uccepted ín l963. 1hís theorv suggests thut the Lurth's crust consísts oí píutes. 1hese pIatcs movc or fIoat on thc mantIc. 1hís movcmcnt is fucIIcd bv convcction currcnts und íeuds to the píutes dívergíng, convergíng or símpív síídíng pust euch other. 1hís ín turn rcsuIts in voIcanic activitv und/or carthquakc (seísmíc) activitv, foIding und fauIting. \hen consíderíng the studv oí píute tectonícs ve vííí exumíne tvo theoríes: 1. Seu-íoor spreudíng 2. Contínentuí dríít Convection currents How do convection currents fuel the movement of plates? 1he Lurth's crust ís dívíded up ínto seven muíor píutes und severuí mínor ones. Convectíon currents ure responsíbíe íor the movement oí píutes. \hen magma ín the corc ís hcatcd, ít riscs and movcs tovurds the uppcr mantIc. At the sume tíme, ít fIows sidcwards. As ít does so, ít cooIs and sinks, bringing with it a pIatc. 1hís resuíts ín u circuIar movcmcnt. Convcction currcnts thereíore fucI thc movcmcnt of pIatcs. SYLLABUS LINK GEOTERMS º Diverging means moving in different directions from one point. º Converging means coming together from different directions to meet at a point. i Fig 2.1 Convection currents Plates pulling apart Plates colliding Convection currents Fig 2.2 Convection currents in a saucepan of boiling water Convection currents To best understand convection currents, observe water in a saucepan boiling. Warning: Be careful. Do not scald yourself. Observe the water in the saucepan as it begins to boil. Notice how air bubbles rise, then flow sideways, and then sink. This movement is of a circular motion and is similar to how convection currents fuel the movement of plates. The mobility of the Earth’s crust produces endogenic forces, which give rise to geological structures within it. Crustal structures are created, modified and destroyed as part of the tectonic cycle. Core Patterns and Processes in the Physical Environment 6 Sea-floor spreading 1he theorv oí seu-íoor spreudíng suggests thut the occan fIoors widcn us ncw rock is formcd vhere pIatcs havc spIit upurt. Convcction currcnts fucI thc scparation of thc pIatcs. As thev sepurute, magma riscs írom víthín the mantIc und fiIIs thc opcning mude. As thís magma cooIs, a ncw crust is formcd. 1hís resuíts ín u ncw occan fIoor bcing formcd. \íth furthcr magma cooIing over tíme, furthcr ncw crust ís íormed und oIdcr crust movcs awav from thc ccntrc. Fig 2.3 Sea-floor spreading MID-OCEAN RIDGE Youngest Oldest Oldest American continent Eurasian continent Convection currents Convection currents Mantle Mantle Floor of ocean Proof of sea-floor spreading SampIcs írom the oceun íoor shov thut crust (nev seu íoor) ís voungcst vhere the mugmu cooís ut thc mid-occan ridgc. lt gets oIdcr movíng towards thc contincnts. Dcposits of scdimcnt íoííovíng gíucíutíon ure uíso íound vhere contincnts wcrc at onc stagc joincd togcthcr. 1hís heíps to prove thut the contínents ure movíng. GEOTERMS º Glaciations refers to a period when the Earth is covered with glaciers or ice. º A mid-ocean ridge is made up of underwater mountain ranges. i EXAM HINTS A question on plate tectonics has appeared every year on the Higher Level paper. Ì Plate Tectonics Chapter 2 7 Continental drift 1he theorv oí contínentuí dríít suggests thut the contincnts arc transportcd ucross the píunet bv convcction currcnts. 1hís dríítíng oí the contínents ís stiII occurring todav. 1he contínents vere uíí once joincd togcthcr ín u singIc Iandmass known as Pangaca. lt vus u supcrcontincnt, surrounded bv un oceun cuííed PanthaIassa. Approxímuteív 200 miIIion vcars ago lungueu sturted to brcak apart. 1he contincnts, fucIIcd bv convcction currcnts, begun to dríít upurt. lnítíuíív, the supercontínent broke up ínto two muíor sectíons cuííed laurasia und GondwanaIand. GEOTERMS º Subduction occurs when a heavier plate sinks and bends beneath a lighter plate. º The subduction zone is the point where an oceanic plate slides beneath either a continental plate or another oceanic plate. i NOTE º Continental fit occurs at the continental shelves which lie below sea level and have not been eroded. º Mesosaurus lived in freshwater lakes and ponds. Mesosaurus may have seldom, if ever, ventured onto land. º Mesosaurus was significant in providing evidence for the theory of continental drift. Its remains were found in southern Africa and eastern South America. ! The process of subduction Contincnts coIIidc víth other contínents vhen thev ure carricd across thc gIobc bv convcction currcnts. \hen thís occurs, the occan ñoor ín betveen tvo contínents ís puIIcd down into thc mantIc bv u process knovn us subduction. 1hís huppens becuuse the oceuníc píute ís normuíív heuvíer thun the contínentuí píute. Subductíon uííovs the contínents to coíííde. Sínce neíther contínent vííí be subducted, the íund buckíes together to íorm íoíd mountuíns. As ve huve uíreudv íeurned, hot magma riscs írom deep ínsíde the Lurth und then cooIs, fIows sidcwards und sínks. 1he rísíng hot rock und sídevuvs íov heíps to controí the current posítíon oí our contínents und oceuns. Proof of continental drift l. Thc cdgcs of contincnts fit togcthcr ííke u íígsuv puzzíe. lor exumpíe, the eust coust oí South Amcrica und the vest coust oí Africa ít together. 2. 1he sume tvpe oí fossiIs huve been íound ín South Amcrica und ín Africa. 1hís teíís us thut these tvo contínents vere once joincd togcthcr. 3. 1he samc kind of rocks ure íound ín both Aírícu und South Amerícu und uíso uíong the coustíínes oí Lurope und North Amerícu. 1hese rocks teíí us thut the mountuíns ure oí the sume rock tvpe, uge und structure. 1hís provídes íurther evídence oí contínentuí dríít. Fig 2.4(b) Convection currents split Pangaea into two continents Panthalassa – an ancient ocean Fig 2.4(a) Pangaea: The supercontinent of 200 million years ago P A N G A E A Laurasi a G o n d w a n a l a n d Core Patterns and Processes in the Physical Environment 8 4. lcc shccts und theír gIaciaI dcposits íound ín AustraIia, Africa, lndia und South Amcrica ure oí the samc agc und huve originatcd in a simiIar pIacc. 1hese íce sheets need u much coíder cíímute ín order to íorm und thís thereíore teíís us thut these vurmer contínents must huve been íoíned to coíder ones. QUICK QUESTIONS 1. Who developed the theory of continental drift? 2. Name seven major plates that make up the Earth’s crust. 3. What fuels the movement of these plates? 4. Explain briefly the process of the movement of convection currents. 5. Explain briefly the theory of sea-floor spreading. 6. What was Pangaea? 7. When did the single landmass begin to split apart? 8. What evidence, found in the rocks, is proof that the continents were once joined together? ? Fig 2.6 Could this be the position of the continents 50 million years from now? Europe North America Africa South America Antartica Asia Australasia Fig 2.5 The position of our continents today North American Plate Antartic Plate Indo-Australian Plate Eurasian Plate African Plate South American Plate Madagascar Plate INTERESTING FACTS The Appalachian mountains of North America are formed by the same type of rock as the Caledonian mountains of Ireland and Scandinavia. T / Fig 2.7 The Earth’s crust is broken up into seven major plates and several minor plates NORTH AMERI CAN PLATE PACI FI C PLATE 1 2 3 4 5 6 A N T A R C T I C P L A T E EURASI AN PLATE AFRI CAN PLATE I NDO- AUSTRALI AN PLATE Juan de Fuca Plate 1 Cocos Plate 2 Caribbean Plate 3 Arabian Plate 4 Anatolian Plate 5 Phillipine Plate 6 Nazca Plate 7 SOUTH AMERI CAN PLATE 7 EXAM HINTS Make sure you can recognise and label a map of the major plate margins of the world. The Chief Examiner’s report of 2007 stated that students should familiarise themselves more with maps displaying plate margins of the world. Ì Plate Tectonics Chapter 2 9 Plate boundaries Movíng píutes vííí huve uctívítv ut theír bounduríes. Rocks and structurcs arc cithcr crcatcd or dcstrovcd as thcsc pIatcs divcrgc, convcrgc, or sIidc past cach othcr. 1he pIatc movcmcnts ure thereíore rcsponsibIc for carthquakc and voIcanic activitv uround the voríd. \here píutes push togcthcr, thev rcsuIt ín the formation of mountains. \here píutes puII apart, contincnts spIit und occans form. 1here ure three tvpes oí píute bounduríes: 1. Dívergent (bounduríes oí constructíon) 2. Convergent (bounduríes oí destructíon) 3. Conservutíve (pussíve bounduríes) or trunsíorm píute bounduríes 1. Divergent (boundaries of construction) At these bounduríes ncw rock is formcd, creutíng mid-occan ridgcs. 1he píutes scparatc und movc awav írom euch other. 2. Convergent (boundaries of destruction) At these bounduríes rock is changcd or dcstrovcd as pIatcs coIIidc. 1here ure three tvpes oí destructíve bounduríes: z Occanic-occanic: vhere two occan píutes coíííde. z Occanic-contincnt: vhere un occan píute und u contincntaI píute coíííde. z Contincnt-contincnt: vhere two contincntaI píutes coíííde. 3. Conservative (passive boundaries) Conservutíve píute bounduríes ure uíso knovn us trunsíorm píute bounduríes. At these bounduríes, rock ís ncithcr crcatcd nor dcstrovcd. PIatcs sIidc past euch other. Fig 2.8 Types of plate boundaries (a) Divergent plate boundaries (boundaries of construction) (b) Convergent plate boundaries (boundaries of destruction) (c) Conservative plate boundaries (passive boundaries) Magma Plate Plates separating Mantle Convection currents fuel the separating plates Convection currents Subducting plate melts Convection currents Convection currents Plates slide past each other along the transform fault Island arcs NOTE The San Andreas Fault in California, USA, is a conservative plate boundary. The plates slide past each other in the same direction along the transform fault. Because the plates are moving at different speeds it appears they are moving in different directions. See Fig 2.14 on page 12. ! Core Patterns and Processes in the Physical Environment 10 1. Divergent plate boundaries Sca-fIoor sprcading rcsuIts in two pIatcs moving apart as a conscqucncc of magma rising from thc mantIc. An exumpíe occurs ut the Mid-AtIantic Ridgc. Here convcction currcnts within thc mantIc oí the míd-oceun rídge puII thc pIatcs apart. 1hís resuíts ín the Iithosphcrc (mude up oí the contínentuí crust, the oceun crust und the upper muntíe) spIitting and producing a rift vaIIcv, such us the fast African Rift VaIIcv. 1he ríít vuííev providcs thc routc for magma to move írom the mantIc up through thc vaIIcv und then to fIow out to thc sca fIoor, creutíng u ncw sca fIoor or oceun crust. 1hís ís knovn us sca-fIoor sprcading. \hen the magma rcachcs thc surfacc oí the seu íoor, ít ís then knovn us Iava. lt cooIs und forms voIcanic mountains over tíme. \íth furthcr cruptions, these voícuníc mountuíns muv appcar abovc thc watcr und ure then knovn us voIcanic isIands, ííke lceíund. Fig 2.9 A divergent (constructive) plate boundary Younger crust Surface of sea Mid-ocean ridge Older crust EURASIAN PLATE NORTH AMERICAN PLATE Convection currents in the mantle fuel the movement of separating plates Oceanic crust Crust movement Forms as magma rises As plates separate a rift valley forms 2. Convergent plate boundaries Convergent píute bounduríes ure dcstructivc boundarics. PIatcs coIIidc und rock is changcd or dcstrovcd. 1he process oí subduction occurs vhen u pIatc dips bcncath anothcr pIatc ut u subductíon zone. Fig 2.10 A convergent (destructive) plate boundary Subducted and melted plate rises and the subducted oceanic plate melts. It later rises and forces magma through continental crust Sea Deep trench Explosive acidic lava Volcanic mountains Oceanic crust Continental crust 700 km Convection currents in the mantle Oceanic plate melts into mantle as it subducts Mantle EXAM HINTS Make sure you know the different types of plate margins very well. It is important not to confuse the different types when answering an exam question. Ì Plate Tectonics Chapter 2 11 Oceanic-oceanic boundaries \hen two pIatcs coIIidc, the hcavicr, oIdcr pIatc dips und ís subductcd bcncath the Iightcr, voungcr pIatc. At the point of subduction, u dccp sca trcnch mav dcvcIop. 1he subductcd pIatc mcIts us ít movcs down the mantIc. 1he meítíng occurs becuuse the píute ís compressed us ít moves dovn, und uíso becuuse oí the cffcct of thc hot moItcn magma. VoIcanic activitv occurs ut the boundarics of two coIIiding occanic pIatcs. 1he descendíng píute mcIts quíckív. Magma, over tíme, riscs up írom the occan fIoor und forms isIands thut uppeur ubove seu íeveí. A group oí such ísíunds ís knovn us un isIand arc. ln munv ínstunces, these ísíund urcs ure activc voIcanocs, us ín lapan (vhere the lucííc líute coííídes víth the Lurusíun líute). farthquakcs muv uíso occur at thcsc boundarics. Oceanic-continent \hen un oceuníc píute und u contínentuí píute coíííde, the hcavicr occanic pIatc subducts und un occan trcnch is formcd. 1he occanic pIatc mcIts und the magma riscs to crcatc voIcanocs ut the contincntaI pIatc. 1he contínentuí píute ís buckIcd. Comprcssion causcs thc pIatc to risc, íormíng u mountain bcIt. foId mountains form in this wav, íor exumpíe the Andcs ín South Amerícu und the WickIow Mountains ín lreíund. 1he Andes íormed vhere the Nazca PIatc ís subductcd under the South Amcrican pIatc. \hen pIatcs coíííde, fauIting muv uíso huppen. fauIts ure crcatcd bv strcss ín the farth's crust, vhích ís the resuít oí the movement oí the Lurth's píutes. fauIts huve occurred ín the Rockics ín North Amerícu vhere the Pacific PIatc coIIidcs víth the North Amcrican PIatc. 1hís íuuít ís reíerred to us u thrust fauIt. fndogcnic forccs ure intcrnaI forccs thut ure fucIIcd bv the farth's intcrnaI mcchanism. fndogcnic forccs ut vork resuít ín the processes oí voIcanism und thut oí fauIting. farthquakcs mav aIso occur at occanic- contincnt boundarics. Fig 2.11(a) The collision of oceanic-oceanic plates Fig 2.11(b) Japan – an example of an island arc g ( ) p Trench Island arc Oceanic crust Continental crust Melting E u r a s i a n P l a t e Subducting oceanic p la t e s Oceanic lithosphere P a c i f i c P l a t e Japan t r ench Fig 2.12 The formation of the Andes Mountains in South America Trench Volcanic arc Oceanic crust Continental crust Melting — 100 km — 200 km Subducting oceanic litho s p h e r e NAZCA PLATE SOUTH AMERICAN PLATE Core Patterns and Processes in the Physical Environment 12 Continent-continent boundaries \hen two contincntaI pIatcs coIIidc, ncithcr of thc pIatcs wiII sink. 1hev ure both mude oí verv thíck but ííght rocks, vhích meuns thut subductíon does not occur. lnsteud, the occanic pIatc subducts vhííe the contincntaI pIatcs rcmain intact, but coIIision continucs. Next, the contínentuí crusts buckíe, íeudíng to the íormutíon oí foId mountains. lor exumpíe, the coííísíon oí the lndian PIatc und the furasian PIatc íeud to the íormutíon oí the HimaIavas. 1he stresses und pressure thut buííds up muv uíso íeud to carthquakc activitv. Fig 2.13 The formation of the Himalayas as a result of continental-continental plate collision Ganges plain Tibetan plateau Himalayas Subducting oceanic litho s p h e r e Continental crust Continental crust Asthenosphere Ancient oceanic crust 3. Conservative plate boundaries At these conservutíve píute bounduríes rock is ncithcr crcatcd nor dcstrovcd. PIatcs sIidc pust euch other. 1he Iinc uíong vhích the pIatcs sIidc ís knovn us u fauIt Iinc. 1hese íuuít íínes ure knovn us transform fauIts. Some íuuíts ure íound under the oceun, vhííe some others ure íocuted víthín contínents. 1he San Andrcas fauIt ín Cuíííorníu ís u conscrvativc pIatc (passivc boundarv) vhere the Pacific PIatc und North Amcrican PIatc sííde pust euch other. farthquakc uctívítv ís onív associatcd with conscrvativc pIatc boundarics. Fig 2.14 The location of the San Andreas Fault USA S a n A n d r e a s F a u l t Plate movement Fig 2.15 The San Andreas Fault San Francisco Los Angeles San Diego MEXICO N o rth A m e ric a n P la te : 1 c m p e r y e a r P a c ifi c P la t e : 6 c m p e r y e a r Buckling of continental crust NOTE Shallow earthquake activity may occur at convergent continent- continent plate boundaries. ! Plate Tectonics Chapter 2 13 The position of Ireland 1he lrcIand thut ve knov toduv did not form ovcrnight. líute movement hus hud un ímpuct on hov lreíund íooks toduv. 1. Approxímuteív 850 miIIion vcars ago lreíund vus dívíded ínto tvo sectíons. Cne sectíon vus part of thc North Amcrican PIatc und vus posítíoned cIosc to thc cquator, us vus Scotíund. 1he other sectíon was part of anothcr contincnt aIong with fngIand and WaIcs. 2. 1hen, ubout 400 miIIion vcars ago, the pIatcs coIIidcd, forming lrcIand. 1hís coIIision Icd to uctívítíes such us foIding and fauIting. 1he sca thut once scparatcd the two sepurute scctions, the lapctus Sca, cIoscd. 3. ßv upproxímuteív 380 miIIion vcars ago, the posítíon oí lrcIand hud movcd to thc south of thc cquator. Duríng thís tíme, the north of lrcIand Iav abovc sca IcvcI vhííe the south was submcrgcd. 4. Sca IcvcIs rosc ubout 350 miIIion vcars ago, und covered lreíund. lt vus during this timc thut lrcIand's most common rock, Iimcstonc, íormed. 5. 1he furasian und African PIatcs coIIidcd ubout 250 miIIion vcars ago. 1hís resuíted ín foIding. Duríng thís tíme ín lreíund foIding occurrcd mostIv in Munstcr. 6. Bctwccn 200 and 140 miIIion vcars ago, contincntaI drift resuíted ín lreíund moving north. 7. 1he AtIantic Occan formcd about 65 miIIion vcars ago vhen the Amcrican und furopcan PIatcs begun to movc apart. lrcIand ís constantIv changing. 1he processes oí crosion, dcposition und wcathcring ure responsíbíe íor the cvoIution of thc phvsicaI Iandscapc. QUICK QUESTIONS 1. Name three types of plate boundaries. 2. At divergent plate boundaries, what activity results in two plates moving apart? Give an example of where this occurs. 3. Explain what a rift valley is and give an example. 4. Name a volcanic island. 5. List the three types of convergent plate boundaries. 6. Name an example of an island arc. 7. What activity is associated with a conservative plate? 8. Name and locate an example of a fault line. 9. Match the margins, landforms and examples from the table. Margin Type Landform Example Conservative Mountain belt Andes Convergent Volcanoes, mountains Himalayas Convergent Fault valley San Andreas Fault Divergent Rift valley African Rift Valley Divergent Mid-ocean ridge Mid-Atlantic Ridge ? Fig 2.16 Ireland’s timeline 850 million years ago 350 million years ago 200 million years ago Today Questions 14 Ordinary Level | Short Questions Plate tectonics 1. (a) Examine the diagram and then match each of the named landforms in the table with one of the letters in the diagram. Landform Letter Volcanoes Mid-ocean ridges Subduction zone Rising magma (b) Name any volcano. Oceanic crust A C B D Sediments Ocean floor Continental crust Ocean crust moves down under continental crust 2009, Part 1, Q2, 10 marks Plate tectonics 2. Examine the map which shows the world’s plate margins. (a) Name two plates which are converging (coming together). (b) Name two plates which are diverging (pulling apart). (c) ‘Mid-ocean ridges are formed at the edges of diverging plates (pulling apart)’. True or false? Pacific Plate African Plate North American Plate South American Plate Nazca Plate Indo-Australian Plate Eurasian Plate Pacific Plate 2007, Part 1, Q1, 10 marks Ordinary Level | Long Questions Fold mountains 3. Look at the photograph of fold mountains in Europe. Explain with the aid of a diagram/ diagrams how fold mountains are formed. In your answer name an example you have studied. 2009, Part 2, Q3B, 30 marks The marking scheme for a question like this on an Ordinary Level paper is as follows: Naming the example 2 marks Diagram: two aspects @ 2 marks each 4 marks Formation of fold mountains explained: 8 SRPs @ 3 marks each 24 marks Total 30 marks Plate tectonics 4. Use the diagram to explain the theory of plate tectonics. The lithosphere is broken up into plates. Convection currents in the mantle cause the plates to move in different directions. MANTLE 2009, Part 2, Q3C, 40 marks The marking scheme for a question like this on an Ordinary Level paper is as follows: 13 SRPs @ 3 marks 39 marks Reference to diagram 1 mark Total 40 marks 15 Plate tectonics 5. Examine the cut-away diagram of the Earth. Match each of the following names with a letter from the diagram. z Continental crust z Outer core z Mantle z Ocean crust z Inner core A B C E D 2008, Part 2, Q2A, 30 marks 6. Examine this map of global crustal plates. With reference to the labels shown: (a) Name the crustal plates A and B. (b) Name the type of plate margin at C and at D. A B C D SEC sample paper, Part 2, Q2A, 30 marks Higher Level | Short Questions Subduction zone 7. Examine this diagram showing a subduction zone. Pair each of the letters A to D with the correct features below. Feature Letter Asthenosphere Lithosphere Subduction zone Volcanic intrusions D Sea level Mountains B A 0 100 kilometres C Folded sedimentary rock Magma moving upwards Magma created here Oceanic crust Continental crust Folded sedimentary rock 2009, Part 1, Q1, 8 marks Higher Level | Long Questions Plate margins 8. Explain, with reference to examples you have studied, how plate tectonics help us understand the forces at work along crustal plate boundaries. 2009, Part 2, Q1B, 30 marks The marking scheme for a question like this on a Higher Level paper is as follows: Name two forces @ 2 marks each 4 marks Name different boundaries @ 2 marks each 4 marks Discussion: 11 SRPs @ 2 marks each 22 marks Total 30 marks Crustal plates 9. Examine the map showing the major crustal plates of the Earth. Answer the following: (a) Name the volcanic island at L. (b) Which term, constructive or destructive, best describes the plate boundary at M? (c) Name the plate at N. (d) Which of the following statements is false? O. As the plates move apart (very slowly) magma rises from the mantle. P. Convection currents inside the Earth cause the Earth’s plates to move apart. Q. The North American Plate moves eastwards. R. Volcanoes often form at plate boundaries. L Pacific Plate African Plate Juan de Fuca Plate Cocos Plate North American Plate Caribbean Plate South American Plate Scotia Plate Arabian Plate Indo-Australian Plate Bismarck Plate Fiji Plate Caroline Plate M N Pacific Plate Phillipine Plate 2009, Part 2, Q2A, 20 marks The marking scheme for a question like this on a Higher Level paper is as follows: Four answers @ 5 marks 20 marks Nazca Plate 16 16 Sea-floor spreading 10. Examine this diagram. Answer these questions. (a) Name the Earth’s internal layer labelled X. (b) Name the internal process shown by the arrows at Y. (c) Name one mid-ocean ridge which you have studied. (d) Name the type of plate boundary shown at Z. Y Sea-floor spreading Mid-ocean ridge Oceanic crust Lithosphere Continental crust Continental crust Lithosphere Z X 2008, Part 2, Q2A, 20 marks Plate boundaries 11. ‘Plate boundaries are zones where crust is both created and destroyed.’ Examine this statement, with references to examples you have studied. 2007, Part 2, Q1B, 30 marks Plate tectonics 12. Answer the following questions. (a) Name the island at A where volcanoes occur. (b) Name the feature which can be found at B. (c) State clearly the different types of plate boundaries found at both C and D. African Plate Juan de Fuca Plate Cocos Plate North American Plate South American Plate Scotia Plate Arabian Plate Phillipine Plate Eurasian Plate Caribbean Plate Indian Plate Eurasian Plate Australian Plate Australian Plate Antarctic Plate Nazca Plate Equator C A B D 2007, Part 2, Q2A, 20 marks Plate tectonics theory: z Earth’s crust consists of plates z Plates move, fuelled by convection currents z Movements results in volcanic/earthquake activity, folding and faulting Sea-floor spreading: z Plates split apart, ocean floor widens, new rock is formed z Proofs: Samples from ocean floor; new crust youngest where magma cooled at mid-ocean, older closer to continents z Deposit of sediment following glaciation where continents once joined together Continental drift theory (developed by Wegener): z Continents transported by convection currents z Once one supercontinent, Pangaea. Surrounded by Panthalassa ocean z 200 m years ago – broke apart, drifting started – initially two sections: Laurasia and Gondwanaland z Subduction – continents collide, ocean between pulled down into mantle Proofs of continental drift: z Edges of continents fit like jigsaw puzzle z Matching fossils found Sth America and Africa z Common rocks found Sth America and Africa z Glacial deposits same age Plate boundaries: z Divergent plate boundaries – boundaries of construction. New rock formed, mid-ocean ridges form. Plates separate and move away z Convergent plate boundaries – boundaries of destruction. Rock changed or destroyed as plates collide z 3 types: 1. Ocean-ocean 2. Ocean-continent 3. Continent-continent z Conservative plate boundaries – passive boundaries. Rock neither created nor destroyed. Plates slide past each other Position of Ireland: z 850 m years ago - divided into two sections z 400 m years ago - plates collided, forming Ireland. Folding, faulting occurring z 380 m years ago - moved south of equator. North Ireland above sea level, south was below z 350 m years ago - sea level rose, covering Ireland. z 250 m years ago - Eurasian and African Plates collided – folding z 200 m–140 m years ago - continental drift, Ireland moved north z 65 m years ago - Atlantic Ocean formed when American and European Plates drifted apart z Still changing today ocean tle MIND M AP P la t e t e c t on ic s 17 3 The Geography of Volcanoes By the end of this chapter students will have studied: z Volcanic activity – how, why and where it occurs z How volcanoes and their effects may be predicted z Volcanic activity and its effects on the Irish landscape and worldwide The development of landforms is influenced by geological structures which have resulted from the operation of the tectonic cycle. The mobility of the Earth’s crust produces endogenic forces, which give rise to geological structures within it. Crustal structures are created, modified and destroyed as part of the tectonic cycle. SYLLABUS LINK What is a volcano? A voIcano ís u structurc contuíníng u magma chambcr írom vhích moItcn magma movcs. 1he mugmu truveís up through u vcnt und eventuuíív out through u cratcr. 1hrough thís cruter, hot ash, dust, voIcanic rock bombs und moItcn magma crupt. Magma which has movcd out of thc cratcr ís knovn us Iava. Cver tíme, u Iandform knovn us u voIcanic conc deveíops. Fig 3.1 A volcanic landscape Pyroclastic materials Volcanic bombs Lava flow Spatter cone Secondary cone in old crater Caldera Volcanic cone made up of layers of rock and ash Crater Heated underground water results in hot springs and geysers Magma chamber Parasitic (secondary) cone Vent Cloud of ash and gases Core Patterns and Processes in the Physical Environment 18 Where does volcanic activity occur? Voícuníc uctívítv occurs: 1. \here pIatcs scparatc (constructíve píute bounduríes) 2. \here pIatcs coIIidc (destructíve píute bounduríes) 3. At hotspots 1he lucííc Ríng oí líre ís the voríd's most uctíve eurthquuke und voícuno zone. Fig 3.2 The Pacific Ring of Fire and the location of the world’s major volcanoes African Plate Cocos Plate North American Plate South American Plate Caribbean Plate Eurasian Plate Antarctic Plate Nazca Plate Australian-Indian Plate Pacific Plate 1here ure three stuges ín the ´íííecvcíe' oí u voícuno: 1. Activc un uctíve voícuno crupts rcguIarIv, íor exumpíe, Mount ftna ín ltuív und Mount St HcIcns ín the LSA. 2. Dormant u dormunt voícuno hus not cruptcd for a Iong timc, but mav crupt again, íor exumpíe, Cotopaxi ín leru. 3. fxtinct un extínct voícuno hus not cruptcd in rccordcd historv, íor exumpíe, SIcmish Mountain ín Co. Antrím, Northern lreíund. Causes of a volcanic eruption Tcmpcraturcs ín the uppcr mantIc ure oíten hot cnough íor the rock oí the subducted píutes to mcIt und íorm moItcn magma. 1hís moíten mugmu pushcs towards thc surfacc und buiIds up in a magma chambcr. 1he mugmu chumber cun hoíd u íurge quuntítv oí mugmu. 1he guses contuíned ín thís mugmu expund drumutícuíív ín voíume und thís cuuses the mugmu to risc. 1he gascs cxpIodc und magma pushcs upward. As the mugmu neurs the suríuce, the voícuno behuves ííke u pressure cooker. 1he prcssurc buiIds up und the voIcanic mountain buIgcs. 1he mugmu then forccs its wav up through ñssurcs ín the voícuno. \hen the mugmu (und guses víthín ít) rcachcs thc surfacc, the prcssurc is rcIcascd und u voIcanic cruption oí hot ash und dust, rock, gascs und Iava occurs. NOTE The pressure of the gas within the magma chamber causes the magma to rise. The magma is forced further upwards by gases expanding. When pressure from gases within the molten rock becomes too great, an eruption occurs. ! NOTE A fissure is a long crack in the Earth’s surface through which magma erupts. ! Fig 3.3 A volcano erupting, Mount St Helens, USA GEOTERMS Hotspots are unusually warm areas found deep within the mantle of the Earth. i The Geography of Volcanoes Chapter 3 19 What determines whether a volcanic eruption will be violent? 1he prcscncc or abscncc oí siIica heíps determíne vhether or not u voícuníc eruptíon vííí be vioIcnt. Sííícu heíps producc thick Iava vhích traps gascs víthín mugmu. 1he more sííícu present ín the mugmu, the bcttcr its abiIitv to trap gascs und the grcatcr thc IikcIihood thut u vioIcnt cruption wiII occur. Volcanic materials ejected during volcanic activity A vuríetv oí muteríuís ure eíected duríng u voícuníc eruptíon: 1. Voícuníc ush 2. Rock purtícíes knovn us pvrocIasts 3. Dust 4. Cuses 5. Luvu VoIcanic ash und dust ure uíso bIastcd into thc skv duríng un cruption. 1hese purtícíes then truveí greut dístunces uround the voríd. 1hev muv uíso reduce temperutures bv bíockíng out the sun. Lava Voícunoes ure mountuíns íormed bv the buííd up oí muteríuí vhích hus erupted through openíngs ín the Lurth's suríuce. VoIcanocs mav havc stccp sidcs or gcntIc sIopcs. 1here ure tvo tvpes oí íuvu: 1. Acidic íuvu 2. Basic íuvu GEOTERMS The term pyroclast or pyroclastic material refers to broken-down rock. This material varies from pea- to walnut-size fragments to hardened lava blocks. It may include ash, dust, rocks and rock bombs. i QUICK QUESTIONS 1. Explain briefly the term ‘volcano’. 2. What materials are ejected out of a volcano? 3. List three places where volcanic activity occurs. 4. Name the world’s most active volcanic and earthquake zone. 5. List three categories of volcano. 6. Explain each category of volcano and give an example of each. 7. Discuss briefly the causes of a volcanic eruption. 8. Will the presence of silica in magma lead to a violent volcanic eruption? Discuss. 9. List the materials that are ejected during a volcanic eruption. 10. What is meant by the term ‘pyroclastic material’? ? GEOTERMS º Pyroclastic flow refers to the material that flows down the side of a volcano during an eruption. Examples may include lahars (when a snow-capped volcanic mountain erupts, the resulting mudslide is called a lahar. This happened in Nevada del Ruiz in Colombia), mudflows or nuées ardentes. º Nuées ardentes are often called glowing avalanches, as they are made up of clouds of dust, ash and gas. Many of the gases (such as sulfur dioxide and carbon dioxide) are poisonous and often more dangerous than the lava flow. i Fig 3.4 A volcanic eruption hurling volcanic bombs, ash, gases and dust into the air INTERESTING FACTS Pumic air-filled lava that cooled quickly can float in water. It is used by people to remove hard skin from their feet. P / Core Patterns and Processes in the Physical Environment 20 Acidic lava 1hís íuvu ís high in siIica contcnt (70 pcr ccnt or morc), tcnds to bc thick und docs not ñow vcrv far. Cuses índ ít dííícuít to escupe und so bccomc trappcd in thc Iava. Lventuuíív u voícuno oí thís nuture vííí crupt vioIcntIv. 1hís voícuno vííí huve stccp sidcs, making convcx (domcd) concs. Basic lava 1hís íuvu ís Iow in siIica contcnt (55 pcr ccnt or Icss), tcnds to bc runnv und ñows grcat distanccs. Gascs índ ít casicr to cscapc írom thís íuvu und thís íeuds to it moving fastcr. fruptions of basic Iava tcnd to bc gcntIcr und us u resuít thís voícuno vííí huve gcntIv sIoping sidcs, to form shicId concs. 1he abiIitv of Iava to ñow ís dírectív Iinkcd to thc quantitics of gascs dissoIvcd víthín ít. \hen íuvu íovs contuín u íot oí gus, thev íov greuter dístunces. \hen íess gus ís present, the íuvu íovs do not truveí us íur. 1here thrcc main tvpcs of Iava ñow: 1. luhoehoe íuvu 2. Au íuvu 3. líííov íuvu Fig 3.5(a) Pahoehoe lava. This lava has a ropey texture and the flow is runny or fluid Fig 3.5(b) Aa lava. This lava has a lumpy texture Fig 3.5(c) Pillow lava. This appears as rounded blobs of lava. It is found on the sea floor GEOTERMS Constructive plate margins/boundaries are also known as divergent plate margins/ boundaries. i NOTE The higher the silica content of magma, the more viscous (sticky) it is. Viscous magma tends to lead to more explosive volcanoes. Lava with a low silica content tends to form shield volcanoes. The lava can flow very long distances as it is much more fluid. ! Location of volcanic activity Voícuníc uctívítv cun occur ut u number oí íocutíons: 1. Whcrc pIatcs scparatc (at constructivc pIatc boundarics): At these pIatcs of scparation, the convcction currcnts ín the mantIc fucI thc movcmcnt apart of pIatcs. 1hís sepurutíon oí píutes crcatcs a rift vaIIcv. Magma riscs to ííí the spuce íeít bv the ríít vuííev. \hen the mugmu rcachcs thc surfacc, ít bcgins to cooI und then soIidiñcs to form voIcanic mountains. 1hese ure the mid-occan ridgcs. Sometímes isIands íorm, such us the voIcanic isIand oí lceíund, vhích íormed us purt oí the Míd-Atíuntíc Rídge. The Geography of Volcanoes Chapter 3 21 2. Whcrc pIatcs coIIidc (at dcstructivc pIatc boundarics): \here two occanic pIatcs coIIidc, thc hcavicr píute sinks beíov the other píute ín u process knovn us subduction. 1he píute thut sínks mcIts into thc mantIc. 1he moíten magma then riscs up through cracks und makcs its wav to thc surfacc through the vcnt. Lventuuíív ít reuches the suríuce vhere voIcanic isIands arc formcd. 1he isIands of lapan ure un exumpíe oí thís. 3. At hotspots: Fig 3.6 The location of hotspots African Plate Cocos Plate North American Plate South American Plate Caribbean Plate Eurasian Plate Antarctic Plate Nazca Plate Pacific Plate Indo-Australian Plate Pacific Plate At these hotspots, pIumcs of magma risc upwards towards thc surfacc, movíng up through the muntíe. Lventuuíív the mugmu píumes rcach thc pIatc ovcrhcad. 1he hotspot rcmains in thc samc pIacc whiIc thc pIatcs movc. As ít does so, the rising magma ñnds a ñssurc ín the píute. \hen pIatcs movc ovcr thc pIumc, voIcanocs form. Cver tíme thev become Icss activc und ííe us cxtinct voIcanocs. 1he píutes contínue to be fucIIcd bv convcction currcnts. As u píute moves on, the magma wiII ñnd a ncw ñssurc vhích vííí ín turn íeud to the formation of a ncw voIcano. Hotspots Icavc bchind thcm a traiI of cxtinct voIcanocs. lt ís uíso thought thut contincnts mav actuaIIv spIit apart due to rising pIumcs of magma at a hotspot. 1he African Rift VaIIcv ís un exumpíe. Hotspots ure uíso íocuted under lccIand, the Canarv lsIands, Hawaii und the GaIapagos lsIands. Intrusive and extrusive structures lntrusivc structurcs ure those íormed vhen mugmu faiIs to rcach thc surfacc of thc farth. lt forccs itscIf ínto the rock, cooIing to form an intrusivc rock insidc of thc crust. Granitc ís un exumpíe. Rocks íormed víthín the Lurth ure cuííed pIutonic/intrusivc rocks. GEOTERMS º Destructive plate margins/boundaries are also known as convergent plate margins/boundaries. º Hotspots are the unusually hot areas of mantle-core boundary. Examples include Hawaii, Iceland and Yellowstone National Park, USA. i NOTE Magma, which contains large amounts of silica, causes violent eruptions. ! Fig 3.7 A plume of rising magma at a hotspot Volcanoes and basalt plateaus are formed from magma Lava flows out through cracks called fissures Continental crust is pushed up by magma Plume of magma rising towards the surface Core Patterns and Processes in the Physical Environment 22 fxtrusivc structurcs ure those íormed on the surfacc of thc farth. 1he mugmu rcachcd thc surfacc und ís nov knovn us Iava. At the surfacc cxtrusivc structurcs or rocks arc formcd. ln extrusíve rocks, the magma crupts through u ñssurc or a voIcano. Intrusive structures A bathoIith ís un exumpíe oí un íntrusíve íeuture. 1hís íeuture formcd whcn magma was forccd into thc crust, cooIing and soIidifving to form an intrusivc rock, such us gruníte. ßuthoííths muv uppeur ut the suríuce due to tvo íuctors: 1. Dcnudation (veutheríng und erosíon) resuítíng ín the bathoIith bccoming cxposcd. 2. PIatcs coIIidc, rcsuIting in buckIing und comprcssion und the formation of foId mountains. Such un exumpíe ís íound ín the ureu írom DubIin to kiIkcnnv, vhích ís knovn us the lcinstcr BathoIith. 1hís buthoííth vus exposed duríng the mountuín buíídíng períod knovn us the CaIcdonian foId movcmcnt. 1he íoídíng resuíted ín the íormutíon oí the WickIow und DubIin Mountains. ßuthoííths ure usuuíív surroundcd bv mctamorphic rocks (rocks thut vere once ígneous/sedímenturv, but vere chunged due to eíther greut heut or pressure). 1he \íckíov Mountuíns vere íormed duríng the Cuíedoníun íoíd movement vhen the Amerícun und Lurusíun líutes coíííded. 1he corc of thc bathoIith íound ín the WickIow Mountains ís granitc und the arca surrounding thc cdgcs oí the buthoííth ís mude up oí mctamorphic rock, such us quartzitc und schist. Fig 3.9 A batholith Rocks in contact with and heated by molten magma change into metamorphic rocks Rising magma moves into the rocks of the Earth’s crust Upper mantle Batholith 100 km Batholith Erosion of overlying rock exposes batholith Rocks not affected by batholith Metamorphic rock EXAM HINTS The Leinster Batholith is also an example of an Irish volcanic landform. Ì EXAM HINTS The Leinster Batholith can be used as an example of a distinctive landscape for igneous rock (granite) in Ireland. Ì GEOTERMS The Leinster Batholith is the largest batholith in Great Britain or Ireland at 1500 km 2 . Over the last 400 million years it has become exposed as the top layers of rock are eroded. At 925 m above sea level Lugnaquilla is the highest peak of the Leinster Batholith. i Fig 3.8 Intrusive and extrusive volcanic structures Extrusives Cool quickly Intrusives Cool slowly Lava and ash Ash cloud Igneous intrusion Magma chamber The Geography of Volcanoes Chapter 3 23 Cther íntrusíve íeutures íncíude: 1. Sííís 2. Dvkes 3. Luccoííth 4. Lopoííth A siII ís íormed vhen magma ís injcctcd horizontaIIv bctwccn Iavcrs of scdimcntarv rock thut ure íound cíose to the suríuce. 1he mugmu squcczcs into thc bcdding pIancs mcIting surrounding rock, then cooIing to form granitc (knovn us u horizontaI Iavcr of granitc). 1hís creutes u sííí. Dvkcs íorm vhen magma is injcctcd vcrticaIIv into ñssurcs in thc crust. Cver tíme, the mugmu widcns thc fracturc und eventuuíív ít cooIs (forming a vcrticaI Iavcr of granitc). 1hís creutes u dvke. laccoIiths íorm vhen magma pushcs an ovcrIving rock upwards. lopoIiths íorm vhen magma pushcs thc undcrIving rock downwards. Extrusive structures Lxtrusíve structures ure those formcd on thc surfacc of thc farth. VoIcanocs ure cxtrusivc Iandforms. Voícunoes varv in shapc due to two main factors: the tvpc of Iava eíected und the naturc of thc cruption (vhether ít ís víoíent und destructíve or not). \e vííí bríeív díscuss the íoííovíng: QUICK QUESTIONS 1. Explain the difference between acidic and basic lava. 2. Name three types of lava flow. 3. Name three places where volcanic activity may occur. 4. Explain what a hotspot is. 5. Give two examples of hotspots you have studied. 6. Explain the term ‘intrusive structure’. 7. Explain the term ‘extrusive structure’. 8. Give an example of an intrusive structure you have studied. 9. Name an intrusive rock. 10. Name a batholith located in Ireland. 11. When was this batholith exposed? 12. What category of rock usually surrounds batholiths? ? GEOTERMS º When magma squeezes in between fissures/ bedding planes, it forms a sill. º When magma cuts across fissures/bedding planes, it forms a dyke. i 1. Centruí vent eruptíons 2. líssure eruptíons 3. Hotspots 1. Central vent eruptions Most centruí vent eruptíons occur ut dcstructivc pIatc boundarics vhere píutes coíííde. lava, ash und othcr voIcanic matcriaI is cjcctcd through a ccntraI vcnt und Icavcs thc voIcano through the cratcr. 1he shupe oí thís voícuno ís usuuíív thut oí u conc- shapcd mountain. Fig 3.10 Intrusive features Volcanic ash cloud Vent Lava flow Crater Dyke Sill Sill Sill Lopolith Laccolith Batholith (magma chamber) NOTE Secondary cones form around secondary vents on larger volcanoes. Larger volcanoes can have several secondary vents in addition to the main central vent. ! Core Patterns and Processes in the Physical Environment 24 1he shupe oí the voícuno depends on the tvpe oí íuvu eruptíng írom ít. z ShicId voIcanocs tend to huve gcntIv sIoping concs and a broad basc. 1hís ís becuuse basic Iava crupts from thc vcnt. 1hís busíc íuvu ís upproxímuteív 55 pcr ccnt siIica und ís runnv. lt ís abIc to ñow for Iong distanccs beíore ít cooIs and soIidiñcs to form basaIt rock. Cver tíme Iavcrs of runnv Iava buiId up to íorm shicId voIcanocs. 1hese voícunoes ure common at hotspots. An exumpíe oí u shíeíd voícuno ís thut oí Mauna loa, on the Huvuííun lsíunds. z VoIcanic domcs tend to huve stccp sidcs. 1hís ís due to acidic Iava crupting from thc vcnt. High amounts of gas containcd within thc magma íeuds to un cxpIosivc cruption. Mount St Heíens ís un exumpíe oí such u voícuníc dome. z Compositc voIcanocs tend to be stccp-sidcd. 1heír shupe resuíts írom pvrocIastic matcriaI und aItcrnating Iavcrs of Iava buiIding up around thc summit, vhere thev íuíí. Lxumpíes ure Mount Vcsuvius and Mount ftna. Fig 3.11 Volcanic cone-shaped mountain Ash cloud Vent Ash Lava flow Lava High-silica magma GEOTERMS Rock fragments produced by volcanic explosions are called pyroclasts (from the Greek pyro, ‘fire’, and clast, ‘broken’). Pyroclastic debris is also known as tephra. i Fig 3.12(b) Mount Kilauea, Hawaii, is an example of a shield volcano Fig 3.13(b) Mount St Helens, USA, is an example of a dome volcano Fig 3.14(b) Mount Vesuvius is an example of a composite volcano Ash Ash Fig 3.12(a) A shield volcano Fig 3.13(a) A dome volcano Fig 3.14(a) A composite volcano Ash The Geography of Volcanoes Chapter 3 25 z Cindcr voIcanocs tend to be stccp-sidcd concs und generuíív huve u gcntIc sIopc due to the Iavcring of voIcanic particIcs. Cínder voícunoes ure formcd us u resuít oí vioIcnt cruptions. 2. Fissure eruptions líssure eruptíons occur ut constructivc pIatc boundarics vhere basic Iava íovs out onto the suríuce through ñssurcs. ßecuuse the íuvu ís basic, ít cun ñow for Iong distanccs. Cver successíve eruptíons the Iava buiIds up to form a basaIt pIatcau. 1hís cun resuít ín u ñat Iandscapc such us thut oí the Antrim-Dcrrv PIatcau. 1he Antrim-Dcrrv PIatcau ís un exumpíe oí u basaIt pIatcau. 1hís píuteuu íormed us u resuít oí voIcanic activitv vhích occurred over 15 miIIion vcars ugo. Duríng thís períod the furopcan und Amcrican PIatcs begun to puíí upurt. 1hís meunt thut the crust of thc farth vus strctchcd und thinncd consíderubív. Cracks begun to uppeur, und us u resuít Iava begun to ñow out onto thc surfacc. \íth cach succcssivc Iava ñow, u ñat basaIt pIatcau was crcatcd. 1he contínuíng movement upurt oí the píutes Icd to a ncw contincntaI crust bcing formcd und the AtIantic Occan bcgan to opcn. 1hís íormed the Antrím-Derrv líuteuu. 1he Giant's Causcwav íorms purt oí the píuteuu. 1he hcxagonaI coIumns of basaIt íormed vhen moItcn magma cooIcd vcrv sIowIv, huvíng been trappcd in a rivcr vaIIcv. 1he hcxagonaI shapc vus the rcsuIt of thc Iava contracting us ít cooIcd. EXAM HINTS The Antrim-Derry Plateau is also an example of an Irish volcanic landform. Ì GEOTERMS The Antrim-Derry Plateau covers an area of 4000 km 2 – was created 65 million years ago, and consists of 60,000 basalt columns. i QUICK QUESTIONS 1. Explain briefly the formation of each of the following intrusive features: (a) Sill (b) Dyke (c) Laccolith (d) Lopolith 2. List four different shapes of volcanoes and give an example of each. 3. Refer to figure 3.14(c). What activity is occurring? Is this an active, dormant or extinct volcano? Explain your answer. 4. Where do fissure eruptions occur? 5. Name an Irish example of a fissure eruption. 6. How did the Giant’s Causeway form? ? Fig 3.16 The Giant’s Causeway, Co. Antrim INTERESTING FACTS A caldera is a cauldron-like volcanic feature. It is usually formed by the collapse of land following a volcanic eruption. Examples are found at Glencoe, Scotland and Yellowstone National Park, USA. A / Fig 3.15 A cinder volcano Ash cloud Cone Core Patterns and Processes in the Physical Environment 26 3. Hotspots and volcanic arcs Hotspots ure unusuaIIv warm arcas of magma íound bcncath thc farth's surfacc, within thc mantIc. \e huve íeurned hov these hotspots arc in ñxcd Iocations und hov thev do not movc with thc pIatcs. \hen u pIatc movcs, the magma pIumcs risc upwards through the ñssurcs ín the píute und form an activc voIcano. \hen the pIatc movcs awav írom the hotspot, the oncc activc voIcano bccomcs inactivc. Ncw voIcanocs vííí form in thc part of thc crust vhích hus movcd ovcr thc hotspot. A string of cxtinct voIcanocs arc Icft bchind. 1he oIdcst voIcanocs ure those furthcst awav from thc hotspot. An exumpíe oí such u stríng ís the Hawaiian lsIands, íormed bv u hotspot íocuted beneuth the Paciñc PIatc. Hydrothermal areas 1hese ure ureus vhere voícuníc uctívítv once occurred. Moisturc coIIccts, ís then hcatcd bv magma und eventuuíív rcachcs thc surfacc. Hvdrothermuí ureus íncíude the íoííovíng: 1. Cevsers 2. Hot spríngs 3. ßíuck smokers 1. Gcvscrs ure jcts of stcam und hot watcr thut Icap into thc air ut rcguIar intcrvaIs. OId faithfuI ín YcIIowstonc NationaI Park ín the LSA ís un exumpíe oí u gevser. 1hís hvdrothermuí ureu attracts manv visitors euch veur. Gcvscrs arc aIso somctimcs uscd to gcncratc cncrgv, íor exumpíe, the BIuc lagoon in lccIand. 2. Hot springs ure íound vhere groundwatcr is hcatcd at grcat dcpths und then riscs to thc surfacc. Lxumpíes oí hot spríngs ure íound ín lccIand. 3. BIack smokcrs rcscmbIc a chimncv opcning. 1hev ure found at mid-occan ridgcs vhere watcr hotter thun 400 °C riscs out from thc mantIc through vcnts in thc occan ñoor. Fig 3.17 A satellite image of the Hawaiian Island chain NOTE Hydrothermal areas are also called geothermal areas. ! NOTE Sulfur is sometimes evident on the slopes of a volcanic cone where it is ejected through vents known as fumaroles. Sulfur is bright yellow in colour. ! Fig 3.18(a) Old Faithful, Yellowstone National Park, USA The Geography of Volcanoes Chapter 3 27 The prediction of volcanic activity and its effects PcopIc who studv rocks arc known as gcoIogists. Ceoíogísts use theír knowIcdgc of voIcano formation, the tvpc of dcposits und the datc of thcsc dcposits, pattcrns of cvcnts Icading to voIcanic cruptions, und the Iocations whcrc thcsc voIcanocs crupt to gíve us forccasts of voIcanic cruptions. 1heír studv cun píuce them ín verv dungerous sítuutíons. Some geoíogísts huve díed vhííe ínvestígutíng voícuníc uctívítv. 1he tvpc und datc of matcriaIs und distribution of dcposits cun gíve un insight into voIcanic activitv. Ceoíogísts studv dcpositcd matcriaI on the sidcs of voIcanocs. ßv exumíníng these deposíts ít muv be possíbíe to work out thc naturc of prcvious cruptions. 1hís heíps to ídentíív the frcqucncv of past voIcanic cruptions, vhích muv ussíst ín the prcdiction of possibIc futurc cruptions. ßv exumíníng the dístríbutíon oí deposíts írom prevíous eruptíons ít cun uíso be possíbíe to ídentíív íocutíons thut muv be uííected bv eruptíons. Ceoíogísts muv uíso ínstuíí tiItmctcrs thut heíp ídentíív vhether buígíng occurs ín the síde oí u voícuno. A buIgc mav indicatc that an cruption ís ííkeív to occur soon. lor exumpíe, beíore the eruptíon oí Mount St Heíens ín l980, the síde oí the voícuno buíged, sveíííng bv over l00 m. GEOTERMS Seismographs are instruments that measure earthquake activity. Seismographs are positioned around the sides of a volcano. When magma begins to move it creates great heat. With this heat, rocks begin to crack and break and this can lead to vibrations of the Earth’s crust. These vibrations can provide a clear indication of an imminent volcanic eruption. i Fig 3.18(b) A hot spring in Iceland Fig 3.18(d) Steam and sulfur on the grand crater of the volcano on Aeolian Island, Italy Fig 3.18(c) A black smoker on the ocean floor at the mid-ocean ridge Core Patterns and Processes in the Physical Environment 28 Scicntists uíso studv thc gascs cmittcd from a voIcano. \here there ís un incrcasc in gascs, this suggcsts that an cruption wiII soon foIIow. Ceoíogísts uíso studv thc tcmpcraturc oí heut comíng out oí the cruter und IocaI groundwatcr. Stcam rising from vcnts, thc appcarancc of gcvscrs und oí hot springs indicatcs possibIc voIcanic activitv. Fig 3.19(a) Mount Etna erupting, showering ash and hot gases Fig 3.19(c) Seismographs are used to record earthquakes under volcanoes Fig 3.19(b) Two geologists take and record lava samples at the Volcanoes National Park on the Big Island of Hawaii for signs of future volcanic eruption Fig 3.19(d) Scientists wear gas masks to protect against gases emitted by a volcano Aíí the íníormutíon ís used to creute cvacuation pIans ín ureus vhere nev voícuníc eruptíons ure ííkeív to occur. The Geography of Volcanoes Chapter 3 29 Effects of volcanic activity 1he eííects oí voícuníc eruptíons ure both positivc und ncgativc. Positive effects of volcanic activity Fertile soils Voícuníc soíís ure vcrv fcrtiIc. 1hese rich soiIs ure cuííed Iatcritc soiIs und ure rich in mincraIs. 1hese soíís ure sometímes cuííed tcrra rossa. 1hev ure common ín munv countríes such us BraziI, vhere coffcc ís grovn, und purts oí southcrn ltaIv, vhere fruit und vcgctabIcs ure grovn. Tourism Munv dormant und activc voIcanocs attract hundreds oí thousunds oí tourists euch veur. Mount Vcsuvius ín southern ltaIv und Mount ftna ín Sícíív ure verv popuíur. 1ourísts íock to these to cIimb thc sidcs und to cxpcricncc thc Iandscapc. 1hís íeuds to munv spin- off industrics such us bus companics, rcstaurants, shops, souvcnir shops and hotcIs. 1hís gcncratcs u íot oí cmpIovmcnt. ln the cuse oí Mount Vcsuvius, neurbv íocutíons such us Pompcii, dcstrovcd in 79 (+ bv the víoíent eruptíon oí Vesuvíus, uíso attract tourists. Fig 3.20 Mount Vesuvius Fig 3.21 The Pompeii forums and the Vesuvius volcano Fig 3.22 Pompeii. The remains of original inhabitants after the volcanic eruption YcIIowstonc NationaI Park, vhere the Gcvscr OId faithfuI erupts everv hour, ís uíso verv popuíur víth tourísts. Geothermal energy GcothcrmaI cncrgv ís responsíbíe íor providing approximatcIv 80 pcr ccnt of homcs ín lccIand víth theír cIcctricitv. fncrgv ís harncsscd ín ureus vhere watcr is supcrhcatcd to tcmpcraturcs oftcn ovcr 1000 °C due to rocks bcing hcatcd bcIow thcm. 1he watcr docs not cvaporatc but ínsteud the stcam und hot vuter ure pushcd to thc surfacc vhere turbincs harncss thc cncrgv produccd. 1hís energv ís then turncd into cIcctricitv us ís done ín lceíund. QUICK QUESTIONS 1. Look at the satellite image of the Hawaiian Island chain (Fig 3.17). What do these islands signify? 2. What are hydrothermal areas? 3. List three examples of hydrothermal areas. 4. What is a geologist? 5. List six possible signs that a volcanic eruption may be imminent. 6. What are seismographs? 7. List five positive effects of volcanic activity. 8. Look at the photograph of Mount Vesuvius (Fig 3.20). Discuss briefly its role in generating tourism. ? Core Patterns and Processes in the Physical Environment 30 Creation of new land Voícunoes cun crcatc ncw Iand íor human habitation, íor exumpíe, lccIand. Building materials Granitc, vhích ís used ín the construction industrv, is formcd bv voIcanic activitv. Negative effects of volcanic activity Lahars Luhurs ure íormed vhere icc and snow on top of a voIcanic conc mcIt vhen un cruption occurs. 1hese íuhurs creute mudñows, vhích cun travcI down thc sIopcs of thc voIcanic conc ínto the surroundíng regíon. 1hís cun huve dcvastating cffccts íor tovns und víííuges. Mount línutubo ín the lhíííppínes expíoded ín l99l. 1he eruptíon resuíted ín voícuníc ush und rock írugments beíng deposíted on the voícuno's síopes. \íthín hours, heuvv ruíns begun to wash this matcriaI down ínto the surrounding IowIands ín gíunt, fast-moving Iahars. Cver the next íour ruínv seusons, íuhurs curríed ubout huíí oí the deposíts oíí the voícuno, cuusíng even more destructíon. Nuée ardentes 1hese ure cIouds of hot ash und poisonous gascs thut ure cjcctcd from a voIcano. 1hev creute vhut ure sometímes cuííed gIowing avaIanchcs. 1hese cíouds travcI down thc voIcanic conc sidcs ut huge speeds oí up to 200 km pcr hour und cun travcI grcat distanccs. Fig 3.24 A lahar Fig 3.25 A nuée ardente Loss of life 1he cruption oí Mount Vcsuvius ín 79 (+ cuused deuth und destructíon. More thun 20,000 pcopIc dicd and thc towns of Pompcii and HcrcuIancum wcrc dcstrovcd. Damage to property lava cun uíso burn evervthíng ín íts puth. Fig 3.23 A geyser in Iceland 31 The Geography of Volcanoes Chapter 3 31 C A S E S T U D Y 3 . 1 Effect on the environment CIouds of ash, dust und gas muv reduce gíobuí tcmpcraturcs bv scvcraI dcgrccs. 1hís occurred ín 1816 vhen the eruptíon oí Tambora, neur lndoncsia, cuused gIobaI summcr tcmpcraturcs to drop bv 5 to 10 °C. 1he cmission of suIfur dioxidc ínto the utmosphere muv íeud to acid rain. Othcr toxic, poisonous gascs such us carbon monoxidc und suIfur cun uíso be hurmíuí to humuns. ln uddítíon, pvrocIastic matcriaI cjcctcd írom u voIcano cun dumuge the envíronment. lor exumpíe, íí CC2 ís emítted írom u voícuno ít udds to the nuturuí greenhouse eííect. Suííur Díoxíde cuuses envíronmentuí probíems becuuse ít ís converted to Suííuríc Acíd ín the strutosphere. 1hís ís u muíor cuuse oí ucíd ruín. 1he l99l Mount línutubo eruptíon ín 1he lhíííppínes cuused substuntíuí envíronmentuí dumuge. Mount St Helens On the morning of 18 May, 1980 at 8.32 am, an earthquake measuring 5.1 on the Richter scale occurred directly below the northern slope of Mount St Helens. This triggered a landslide, the largest in recorded history. It travelled at speeds of 175 to 250 km per hour. Most of Mount St Helens’ north side turned to rubble. Thousands of trees were destroyed and the water of Spirit lake was temporarily displaced by this landslide. The eruption of Mount St Helens could be heard 1120 km away. The magma was exposed to lower pressure and this lead to molten rock and steam exploding just a few moments after the landslide started. The blasting of rock debris and the pyroclastic flow of extremely hot volcanic gases, ash and rocks overtook the initial landslide. Approximately 600 km 2 of forest was knocked down and other parts of the forest were destroyed by the extreme heat. The heart of the mountain had blasted upwards and gigantic clouds of ash hovered some 25 km above it. Fifty-seven people were killed. The Washington State Department of Game estimated that approximately 7000 deer, elk and bears died, as well as birds and other small mammals. Frogs, crawfish and burrowing rodents survived because they were either below ground level or under the surface of the water when the volcanic eruption occurred. The Washington Department of Fisheries estimated that 12 million salmon were killed and approximately 40,000 young salmon destroyed. The elevation of the summit before the eruption was 2950 m. This was reduced by 401 m to its post-eruption elevation of 2549 m. Fig 3.27 Mount St Helens QUICK QUESTIONS Discuss briefly how this eruption could have a negative effect on the environment. ? , QUICK QUESTIONS 1. Explain the following terms: (a) Lahars (b) Nuées ardentes 2. Explain what geothermal energy is. 3. Where is geothermal energy widely used? 4. List four negative effects of volcanic activity. 5. Give an example of volcanic activity that has had negative effects on a local population. ? Fig 3.26 The effect of volcanic dust in the atmosphere following the eruption of Mount St Helens NOTE The eruption of Eyjafjallajökull in April 2010 in Iceland caused enormous disruption to air travel for a period of 6 days. This is the greatest level of air travel disruptions experienced in Europe since World War II. ! Questions 32 32 Ordinary Level | Short Questions Volcanoes 1. Examine the diagram of a volcano shown below. Use the following terms to identify the blanks on the diagram. z Vent z Secondary cone z Ash cloud z Crater z Magma chamber 2008, Part 1, Q6, 10 marks Ordinary Level | Long Questions Volcanoes 2. Volcanoes can have both negative and positive effects on the landscape and on people. Explain one negative and one positive effect of volcanoes. 2009, Part 2, Q1C, 40 marks The marking scheme for a question like this on an Ordinary Level paper is as follows: Positive effect 2 marks Explaining the effect: 6 SRPs @ 3 marks each 18 marks Negative effect 2 marks Explaining the effect: 6 SRPs @ 3 marks each 18 marks Total 40 marks Higher Level | Short Questions Height of volcanoes 3. The table below shows the height of some well-known volcanoes around the world. Name and location Height in metres Vesuvius – Italy 1281 Krakatoa – Indonesia 813 Fuji – Japan 3776 Rainier – USA 4392 St Helens – USA 2549 Stromboli – Italy 924 Use graph paper to draw a graph that shows the data in the table above. 2007, Part 2, Q3A, 30 marks The marking scheme for a question like this on a Higher Level paper is as follows: Vertical axis labelled – circle 3 marks Horizontal axis labelled – centred 3 marks Six items @ 4 marks each 24 marks Total 30 marks Higher Level | Long Questions Satellite images – volcano 4. Name an example of a volcano which you have studied. State two advantages and one disadvantage for people living in a volcanic region. 2007, Part 2, Q3A, 20 marks EXAM HINTS Remember to read the question carefully. You need to include two advantages in your answer. Ì Volcanoes 5. Examine the processes that have led to the formation of any two volcanic landforms. 2006, Part 2, Q3C, 30 marks EXAM HINTS You will be awarded marks for using graph paper for any question that requires you to draw a graph. Ì 33 33 Effects of volcanic activity: Negative Positive 1. Lahars 1. Fertile soils 2. Damage to property 2. Tourism 3. Nuée ardentes 3. Geothermal energy 4. Loss of life 4. Creation of new land 5. Destruction by fire 5. Building materials 6. Effect on environment z Central vent eruptions: destructive plate boundaries z cone-shaped volcano z Fissure eruptions: z Constructive plate boundaries z Basic lava flows out onto surface by means of fissure z May build up to form basalt plateau – Antrim-Derry Plateau z Flat landscape – Antrim-Derry Plateau z Hot spots: unusually warm areas of magma found beneath the Earth’s surface, within the mantle z Hydrothermal areas: z Geysers, e.g. Old Faithful Yellow Stone National Park, USA z Hot springs, e.g. Iceland z Black smokers, found at mid-ocean ridges, hot water (700 ºC+) rises but through vent on ocean floor Instruments used: z Tiltmeters: identify bulging on side of volcano z Seismograph: measures earthquake activity Volcanic activity occurs at: z Constructive plate boundaries z Destructive plate boundaries z Hotspots Categories of volcano: z Active: erupts regularly e.g. Mt Etna, Italy z Dormant: has not erupted for a long time, e.g. Cotopaxi, Peru z Extinct: has not erupted in recorded history, e.g. Slemish Mountain, Co. Antrim. Volcanic materials ejected during eruption: z Volcanic ash z Rock particles z Dust z Gases z Two types of lava: z acidic lava: high silica content z basic lava: low silica content z Three types of lava flow: z Pahoehoe lava z Aa lava z Pillow lava z Intrusive structures form when magma doesn’t reach the surface – forms intrusive rock, e.g. granite (plutonic/ intrusive rocks) z Extrusive structures form on the surface of the earth – form extrusive rocks Batholiths – intrusive structure: z Leinster Batholith z Magma forced into crust, then cools and solidifies to form an intrusive rock, e.g. granite z Formation of Wicklow and Dublin Mountains z Batholiths usually surrounded by metamorphic rock Other intrusive features: z Sills z Dykes z Laccolith z Lopolith Extrusive structures, e.g. volcanoes – vary in shape: z Shield volcano z Volcanic dome z Composite volcano z Cinder volcano Volcanic activity prediction based on geologists’ study of: z Volcano formation z Type of deposits z Date of deposits z Patterns of events z Locations of volcanic eruptions z Gases and temperatures and steam Mount St Helens 18 May, 1980 eruption MIND M AP The Geography of Volcanoes Chapter 3 of e.g. hape: V o lc a n ic a c t iv it y