physical geography 1

7/29/2019 Physical Geography 1

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Physical geography: fundamentals

of the physical environment

V. Ettwein and M . M aslin

GY1147, 2790147

2011

Undergraduate study in

Economics, Management,

Finance and the Social Sciences

This is an extract from a subject guide for an undergraduate course offered as part of the

University of London International Programmes in Economics, M anagement, Finance and

the Social Sciences. M aterials for these programmes are developed by academics at the

London School of Economics and Political Science (LSE) .

For more information, see: www.londoninternational.ac.uk


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This guide was prepared for the University of London International Programmes by:

Dr Virginia Ettwein, Environmental Change Research Centre, Department of Geography,University College London.

Dr Mark Maslin, Environmental Change Research Centre, Department of Geography,University College London.

This is one of a series of subject gu ides published by t he University. We regret that due t o

pressure of w ork t he autho rs are unable to enter into any correspondence relat ing to, or aris-ing from, the guide. If you have any comments on this subject guide, favourable or unfavour-able, please use the form at the back of this guide.

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Published by: University of Lond on

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Reprinted w i th mino r revisions 201 1

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Contents

i

Contents

Introd uction ............................................................................................................ 1

Aim s and objective s ................................ ................................ ................................. ...... 1

Learnin g ou tco mes ................................. ................................ ................................. ...... 1

Syllabu s ................................ ................................. ................................ ........................ 2

How to use this subject guid e .... . . . .. . . . . . .. . . . . . .. . . . . . . .. . . . . . .. . . . . . .. . . . . . . .. . . . . . .. . . . . . . .. . . . . . .. . . . . . .. . . . . . . 2

Reading ............................... ................................. ................................ ........................ 2

Essentia l read ing .............................. ................................ ................................. ............ 3

Furth er read ing ................................ ................................. ................................ ............. 3

Onlin e stud y resou rces ............................ ................................ ................................. ...... 4

Examin atio n advice..... ................................ ................................. ................................ .. 6

Chapter 1: The structure of the Earth ..................................................................... 7

Essentia l read ing .............................. ................................ ................................. ............ 7

Furth er read ing ................................ ................................. ................................ ............. 7

Inter net resour ces ............................. ................................ ................................. ............ 7

Learnin g ou tco mes ................................. ................................ ................................. ...... 8

Intr od ucti on ............................... ................................. ................................ .................. 8

Stru ctur e of th e Earth ............................ ................................. ................................ ....... 8

Plate tecto nics ............................ ................................. ................................ ................ 10

Earthq uak es ............................... ................................ ................................. ................ 15

Tsunam is .............................. ................................. ................................ ...................... 19

Vulcan icity ............................. ................................ ................................. ..................... 20

Extrusive landfo rms: volcanoes..... . .. . . . . . .. . . . . . . .. . . . . . .. . . . . . .. . . . . . . .. . . . . . .. . . . . . .. . . . . . . .. . . . . . .. . . . . . .. . . . . 22Rock typ es ............................ ................................. ................................ ...................... 26

Reminder of learning out comes..... . .. . . . . . .. . . . . . . .. . . . . . .. . . . . . .. . . . . . . .. . . . . . .. . . . . . . .. . . . . . .. . . . . . .. . . . . . . .. . . 28

Samp le examinat ion question s .... . . . .. . . . . . .. . . . . . . .. . . . . . .. . . . . . .. . . . . . . .. . . . . . .. . . . . . .. . . . . . . .. . . . . . .. . . . . . .. . . . 28

Chapter 2: The at mosphere .................................................................................. 31

Essentia l read ing .............................. ................................ ................................. .......... 31

Furth er read ing ................................ ................................. ................................ ........... 31

Inter net resour ces ............................. ................................ ................................. .......... 31

Learning out comes .... . . .. . . . . . .. . . . . . .. . . . . . . .. . . . . . .. . . . . . .. . . . . . . .. . . . . . .. . . . . . . .. . . . . . .. . . . . . .. . . . . . . .. . . . . . .. . . . . . . 32

Intr od ucti on ............................... ................................. ................................ ................ 32

Atm ospheric comp osit ion .... . . .. . . . . . . .. . . . . . .. . . . . . . .. . . . . . .. . . . . . .. . . . . . . .. . . . . . .. . . . . . .. . . . . . . .. . . . . . .. . . . . . .. . . . 32Greenh ou se gases ............................ ................................ ................................. .......... 33

M ass of the atm osphere .... . . .. . . . . . . .. . . . . . .. . . . . . .. . . . . . . .. . . . . . .. . . . . . .. . . . . . . .. . . . . . .. . . . . . .. . . . . . . .. . . . . . .. . . . . . 34

Atm ospheric energy .... . . .. . . . . . .. . . . . . . .. . . . . . .. . . . . . .. . . . . . . .. . . . . . .. . . . . . .. . . . . . . .. . . . . . .. . . . . . . .. . . . . . .. . . . . . .. . . . . . 35

Vertical struct ure .............................. ................................ ................................. .......... 37

Atm ospheric mo tion .... . . .. . . . . . .. . . . . . . .. . . . . . .. . . . . . . .. . . . . . .. . . . . . .. . . . . . . .. . . . . . .. . . . . . .. . . . . . . .. . . . . . .. . . . . . .. . . . . 38

Wea th er ............................... ................................ ................................. ...................... 41

Sto rm s ................................. ................................ ................................. ...................... 43

Con clusion ............................ ................................ ................................. ..................... 46

Reminder of learning out comes..... . .. . . . . . .. . . . . . . .. . . . . . .. . . . . . .. . . . . . . .. . . . . . .. . . . . . . .. . . . . . .. . . . . . .. . . . . . . .. . . 46

Samp le examinat ion question s .... . . . .. . . . . . .. . . . . . . .. . . . . . .. . . . . . .. . . . . . . .. . . . . . .. . . . . . .. . . . . . . .. . . . . . .. . . . . . .. . . . 47


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147 Physical geography: fundament als of the physical environment

ii

Chapter 3: Climat e and tecto nics ......................................................................... 49

Essentia l read ing ............................. ................................ ................................. ........... 49

Furth er read ing ............................... ................................. ................................ ............ 49

Learning out comes .... . . .. . . . . . .. . . . . . . .. . . . . . .. . . . . . .. . . . . . . .. . . . . . .. . . . . . .. . . . . . . .. . . . . . .. . . . . . . .. . . . . . .. . . . . . .. . . . . . . 49

Intr od ucti on .............................. ................................ ................................. ................. 49

Direct effect s ............................. ................................ ................................. ................. 49

Indir ect effect s ................................ ................................. ................................ ............ 57Global cl imate and evolutio n .... . . . .. . . . . . .. . . . . . .. . . . . . . .. . . . . . .. . . . . . .. . . . . . . .. . . . . . .. . . . . . . .. . . . . . .. . . . . . .. . . . . . 57

Con clusion ................................ ................................ ................................. ................. 58

Reminder of learning out comes..... . .. . . . . . . .. . . . . . .. . . . . . .. . . . . . . .. . . . . . .. . . . . . .. . . . . . . .. . . . . . .. . . . . . . .. . . . . . .. . . 59

Samp le examinat ion question s .... . . . .. . . . . . .. . . . . . . .. . . . . . .. . . . . . .. . . . . . . .. . . . . . .. . . . . . . .. . . . . . .. . . . . . .. . . . . . . .. . . 59

Chapter 4: Hydrosphere ........................................................................................ 61


Furth er read ing ............................... ................................. ................................ ............ 61

Inter net resour ces ............................ ................................ ................................. ........... 61


Intr od ucti on .............................. ................................ ................................. ................. 62The hydr olo gical cycle ............................ ................................. ................................ ..... 62

River for m ................................. ................................ ................................. ................. 65

Fluvial erosion ................................. ................................ ................................ ............ 69

Fluvial tran sport .............................. ................................ ................................. ........... 70

Fluvial g eomo rpho logy o f erosional environm ents ... . . .. . . . . . .. . . . . . .. . . . . . . .. . . . . . .. . . . . . .. . . . . . . .. . . . . . 72

Fluvial dep ositio n ............................ ................................. ................................ ........... 72

Fluvial geomorpho logy of combined erosional and deposi t ional environments . .. . . .. . .. . . .. 75

Lakes ............................ ................................. ................................ ............................. 77



Chapter 5: Landfor m evolut ion ............................................................................ 79


Furth er read ing ............................... ................................. ................................ ............ 79

Inter net resour ces ................................ ................................. ................................ ...... 79


Intr od ucti on .............................. ................................ ................................. ................. 80

Wea th ering ............................... ................................ ................................. ................. 80

Hil lslope dynam ics an d mass mo vement ... . . . .. . . . . . . .. . . . . . .. . . . . . .. . . . . . . .. . . . . . .. . . . . . .. . . . . . . .. . . . . . .. . . . . 88

Slop e evolu tio n............... ................................. ................................ ............................ 92



Chapter 6: Biosphere ............................................................................................ 97


Furth er read ing ............................... ................................. ................................ ............ 97

Inter net resour ces ............................ ................................ ................................. ........... 97


Intr od ucti on .............................. ................................ ................................. ................. 98

Ecosystem concep ts ............................... ................................ ................................. ..... 98

Contro ls on biom e type .... . . .. . . . . . . .. . . . . . .. . . . . . .. . . . . . . .. . . . . . .. . . . . . .. . . . . . . .. . . . . . .. . . . . . .. . . . . . . .. . . . . . .. . . . . 10 0

Distributio n of w orld biom es .... . . .. . . . . . . .. . . . . . .. . . . . . . .. . . . . . .. . . . . . .. . . . . . . .. . . . . . .. . . . . . .. . . . . . . .. . . . . . .. . . . . 10 2

Energy f low s w ithin the ecosystem .... . . . . . . .. . . . . . .. . . . . . .. . . . . . . .. . . . . . .. . . . . . .. . . . . . . .. . . . . . .. . . . . . .. . . . . . . . 10 3

Ecologica l pro cesses: plan t successions ............................... ................................. ...... 10 8

Soils .............................. ................................. ................................ ........................... 11 0


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Contents

ii i

Vegetation soil climate interaction s .... . . .. . . . . . . .. . . . . . .. . . . . . .. . . . . . . .. . . . . . .. . . . . . . .. . . . . . .. . . . . . .. . . . . . . . 11 7

Case studies of biom es .... . . . . . . . .. . . . . . .. . . . . . . .. . . . . . .. . . . . . .. . . . . . . .. . . . . . .. . . . . . .. . . . . . . .. . . . . . .. . . . . . . .. . . . . . .. 11 8

Reminder of learning out comes..... . .. . . . . . . .. . . . . . .. . . . . . .. . . . . . . .. . . . . . .. . . . . . .. . . . . . . .. . . . . . .. . . . . . . .. . . . . . .. 12 3

Samp le examinat ion question s .... . .. . . . . . .. . . . . . .. . . . . . . .. . . . . . .. . . . . . .. . . . . . . .. . . . . . .. . . . . . .. . . . . . . .. . . . . . .. . . . 12 3

Chapter 7 : Global environm enta l change........................................................... 125

Essentia l read ing ............................. ................................ ................................. ......... 12 5

Furth er read ing ............................... ................................. ................................ .......... 12 5Inter net resour ces ............................ ................................ ................................. ......... 12 5

Learning out comes .... . . .. . . . . . .. . . . . . . .. . . . . . .. . . . . . .. . . . . . . .. . . . . . .. . . . . . .. . . . . . . .. . . . . . .. . . . . . . .. . . . . . .. . . . . . .. . . . . 12 6

Introd uction .... . . .. . . . . . . .. . . . . . .. . . . . . .. . . . . . . .. . . . . . .. . . . . . .. . . . . . . .. . . . . . .. . . . . . . .. . . . . . .. . . . . . .. . . . . . . .. . . . . . .. . . . . . . 12 7

Glacial/ int ergla cial cycles ............................. ................................. ............................. 12 7

Causes of glacial/ interg lacial cycles .... . . .. . . . . . .. . . . . . . .. . . . . . .. . . . . . .. . . . . . . .. . . . . . .. . . . . . .. . . . . . . .. . . . . . .. . . 12 8

Evidence for glacials a nd interglacials ... . . . .. . . . . . .. . . . . . .. . . . . . . .. . . . . . .. . . . . . .. . . . . . . .. . . . . . .. . . . . . . .. . . . . . 13 2

Short er-term climatic change .... . . . .. . . . . . .. . . . . . .. . . . . . . .. . . . . . .. . . . . . .. . . . . . . .. . . . . . .. . . . . . . .. . . . . . .. . . . . . .. . . . 13 8

Wh at does the futu re hold ? .... . . .. . . . . . . .. . . . . . .. . . . . . .. . . . . . . .. . . . . . .. . . . . . . .. . . . . . .. . . . . . .. . . . . . . .. . . . . . .. . . . . . 14 0

Reminder of learning out comes..... . .. . . . . . . .. . . . . . .. . . . . . .. . . . . . . .. . . . . . .. . . . . . .. . . . . . . .. . . . . . .. . . . . . . .. . . . . . .. 14 3

Samp le examinat ion question s .... . .. . . . . . .. . . . . . .. . . . . . . .. . . . . . .. . . . . . .. . . . . . . .. . . . . . .. . . . . . .. . . . . . . .. . . . . . .. . . . 14 4Appendix: Samp le exa minat ion pape r ............................................................... 145


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Notes


iv


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Int roduct ion

1

Introduction

Welcome to this 100 course, 1 4 7 P h y s ic a l ge o g ra p h y : fu n d a m e n t a l s

o f t h e p h y s i ca l e n v iro n m e n t , w hich most of you w ill be studying atthe start of your BSc Geography a nd Environment.

Understand ing the physical environment is fundamenta l to understanding

the planet on which we live. Everything we do from the energy resources

we use to the weather we experience is controlled by the Earths physical

environment. For the first time ever it seems that we are also influencing

the global physical environment by ad ding carbon d ioxide to the

atmosphere causing global w arming.

In this course we will investigate the structure of the Earth and how violent

movements of t he surface plates can ca use volcanoes, earthq uakes and

tsunamis, sometimes resulting in the loss is hundreds of t housand s of lives,

such as the 2004 Boxing Day S outhea st Asian tsuna mi. We w ill take a lookat how w eather is produced, w hich can result in massive hurricanes and

the destruction of w hole cities, such a s New Orleans in 2005. We then put

the tw o parts of the course together and see how changes in the position of

the continents have a ffected g lobal climate and even evolution.

The most important resource for life on the planet is water so we will

also take a look at how the w ater cycle works. This leads us to how the

landscape around us has been shaped over millennia by the a ction of w at er,

ice and w ind. We also investigate the biosphere, how and w hy plants a nd

animals differ in different environments and how life has ma intained a

habitable environment on the Earth for the last 500 million years. Finally,

w e look at how the global environment has changed, first a s a result of thecoming and going of the great ice ages, when there were ice sheets 3 km

thick over North America a nd Europe.

We investigat e how w e humans a re currently chan ging the physical

environment of the planet by w arming it up and w e look at w hat t he

consequences of global w arming w ill be if we do nothing about it.

Aims and object ives

This course provides a w ide-ran ging intro duction t o the principles of

physical geography. These are concerned with the form and functioning of

the na tural environment a nd how they change over various timescales.This course is the foundat ion for further an d more deta iled study in the

fields of geomorphology, climatology, biogeography, hyd rology a nd pa st

environmental change. It also provides valuable context for studying human

geography in areas such as environmental management and sustainability.

Learning outcomes

After completing th is course you should ha ve:

insight into the basic components of the natura l environment and a n

understanding of how these are shaped by natural and some human

processes knowledge of how these processes interact w ith one another and some

perspective of both the time a nd spatia l scales at w hich they operate.


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2

These skills w ill be developed by using idea s and informa tion a cquired

from reading to approach problems and a nswer questions about the

natura l environment.

Syllabus

There a re no prereq uisites for t his course. Topics covered in this course

are:

Composition of the Earth: plate tectonics, earthqua kes, volcanoes, rock

types, geohaza rds.

Tectonics and climat e: setting the scene for our unique modern climate

system.

Atmosphere: composition and circulat ion.

Hydrosphere and land scape evolution: precipitat ion, rivers, lakes,

erosion, weathering patterns, hillslope dynamics.

Oceans: surface and deep circulation, upw elling, productivity and

climate.

Biosphere: evolution, ecosystem concepts, ecological processes, soil

dynamics, vegetationgeologyclimate interactions.

Global environmental change: gla cial-interglacial cycles, sea-level

chan ges, Heinrich events, El Nio South ern Oscillation, North Atlantic

oscillat ion, global w arming.

How to use this subject guide

For some courses that you study, you are directed to read your essential

textbooks after you have worked through a chapter. For this course, the

best thing to do is skim-read through the chapter to give you an idea of

w hat the chapter is about, then familiarise yourself w ith the chapters in

your textbooks. Then w ork slow ly and carefully through t he chapters in

this guide, taking note of the learning outcomes.

We have provided yo u w ith activities through out. We suggest tha t you d o

these, a s they w ill bring together the topics and help you to understand

them. You are strong ly ad vised to ha ve access to the internet a s we w ill

direct you to the internet to so dome research for some of these activities.

When you have finished the chapter make sure that you can tick off all

of the points you should have covered. If you cant, go back and read

ag ain ca refully. You might find tha t visiting some of the w ebsites tha t w e

recommend may well help bring your studies together as they can providemany more interactive features and illustrations than w e can in this

subject g uide.

Reading

You w ill find advice on wha t books you need to buy or otherw ise have

access to a t the beginning o f each of t he chapters of this guide. You should

not continue to use an old edition of a textbook if a new edition has been

published. Always buy the latest edition of recommended textbooks; if the

latest edition is more recent than the edition to which the subject guide

refers, use the index and tables of contents to identify the relevant parts of

the new edition.

We have provided here for ea se of reference a listing of a ll the reading an d

resources in this course.


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Int roduct ion

3

Essent ial reading

Christ opherson , R.W. Geosystems: An Int roduction t o Physical Geography.

(Upper Sadd le River, NJ: Pearson Education, 2011) eighth edition [ISBN

9780321770769].

Maslin, M. Global Warm ing: A Very Short I nt roduction. (Oxford: Oxford

University Press, 2008) [ISBN 9780199548248].

Rudd ima n, W. Earths Climate: Past and Futur e. (New York: Freema n, 2007)

second edition [ISBN 9780716784906].

Smith son, P., K. Addison a nd K. Atkinson Fundamentals of the Physical

Environment.(London: Routledge, 2008) fourth edition

[ISBN 9780415395168].

Waugh, D. Geography: An Int egrat ed Approach. (Walton-on-Tha mes: Nelson

Thornes, 2009) fourth edition [ISBN 9781408504079].

Detailed reading references in this subject guide refer to the editions of the

set textbooks listed above. New editions of one or more of these textbooks

may ha ve been published by the t ime you study t his course. You can use

a more recent edition of any of t he books; use the detailed chapter and

section headings and the index to identify relevant readings. Also checkthe virtual learning environment (VLE) regularly for updated guidance on

readings.

Further reading

Please note that as long a s you read t he Essential read ing you are then free

to read a round the subject area in a ny text, pa per or online resource. You

w ill need to support your learning by reading a s w idely a s possible and by

thinking about how these principles apply in the real w orld. To help you

read extensively, you have free access to t he VLE and University of London

Online Library (see below) .

Other useful texts for t his course include:

Barry, R. a nd R. Chorley Atmosphere, Weather and Climat e. (London: Routledge,

2001) seventh edition [ISBN 0415077613].

Bell, M. and M.J .C. Walker Late Quaternary Envir onmental Change: Physical and

Human Perspectives. (London: Longma n, 1992) [ISBN 0582045142].

Benn, D.I. and D.J.A. Evans Glaciers and Glaciat ion. ( London: Arnold, 1997)

[ISBN 0340584319].

Bradley, R. Quaternar y Paleoclimatology. (London: Academic, 1999)

[ISBN 012124010X].

Bras, R.E. Hydrology: An Int roduction to Hydrologic Science. (Reading, MA:

Add ison-Wesley, 1990) [ ISBN 0201059223] .

Briggs, D. and P. Smithson The Fundamenta ls of Physical Geography. (London:

Routledge, 1993) [ISBN 0044458223].

Burroug hs, W. Climate Change: A Mult idi scipli nar y Approach. (Cambridge:

Cambridge University Press, 2001) [ISBN 0521567718].

Collard, R. The Physical Geography of Landscape. (London: Collins Educational,

1992) [ISBN 0003222853].

Cox, J. Weather for Dummies. (New York: Hung ry Minds, Inc., 2000)

[ISBN 0764552430].

Da vies, G .F. Dynamic Eart h. (Ca mbridge: Cambridge University Press, 1999)

[ISBN 0521590671].

Dickson, G. and K. Murphy Ecosystems. (London: Routledge, 1997)

[ISBN 0415145139].Ha y, W.W. Tectonics and clima te, Geologi sche Rundschau: Zeit schri ft fr

all gemein Geologie85 1996, pp.40937.


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4

Henderson-Sellers, A. a nd P.J . Robinson Contemporar y Climatology. (Harlow:

Longman, 1999) [ISBN 0582276314].

Imbrie, J . and K.P. Imbrie Ice Ages: Solvi ng the Mystery. (Ca mbridge, MA:

Harvard University Press, 1986) [ISBN 0674440757].

Keller, E. Acti ve Tectonics: Ear thquakes, Upl if t, and Landscape. (Upper Saddle

River, NJ: Prentice Hall, 1995) [ISBN 0023632615].

Knighton, D. Fluvi al Forms and Processes. ( London: Arnold, 1998)

[ISBN 0340663138].Lamb, S., a nd D. Sington Eart h Story. (London: BBC Consumer Publishing,

1998) [ISBN 0563387998].

Low e, J . a nd M. Walker Reconstr ucting Quaternar y Environments. (Harlow:

Longma n Higher Educat ion, 1997) second ed ition [ISBN: 0582101662].

Molnar, P. a nd P. England Lat e Cenozoic uplift of mounta in rang es and globa l

climat e change: chicken or egg?, Nature346 1990, pp.2934.

Morton, O. The storm in the machine, New Scienti st157 1998, pp.2227.

Newson, M.D. Hydrology and the River Envir onment. (Oxford: Bla ckwell, 1994)

[ISBN 019874157X].

OHare, G . Soils, Vegetat ion and The Ecosystem. (Harlow: Oliver &Boyd, 1988)

[ISBN 0050042378].

Open University Dynamic Eart h. (Milton Keynes: Open University, 1997) [ISBN

0749281839].

Open University Ocean Cir culat ion. (Oxford: Open University/Pergamon Press,

1989) [ISBN 0080363695].

Robinson, D.A. and R.G.B. Williamson Rock Weathering and Landform Evoluti on.

(Chichester: Jo hn Wiley and Sons, 1994) [ ISBN 0471951196].

Rowell, D.L. Soil Science: Methods and Appl icati ons. (Upper Sa ddle River, NJ:

Prentice Hall, 1994) [ISBN 0582087848].

Sha w, E.M. Hydrology in Practi ce. (London: Chapman a nd Ha ll, 1994)

[ISBN 0412482908].

Skinner, B. and S. Porter The Dynami c Eart h: An Int roduction t o Physical

Geology. (Chichester: J ohn Wiley and Sons, 2000) fourth edition[ISBN 0471161187].

Sla yma ker, O. a nd T. Spen cer Physical Geography and Global Environmental

Change. (Ha rlow: Longma n, 1998) [ISBN 0582298296].

Summerfield M.A. Global Geomorphology. (Ha rlow : Longman, 1991)

[ISBN 0582301564].

Van Andel, T.H. New Views on an Old Planet: A Histor y of Geological Change.

(Cambridg e: Cambridge University Press, 1994) [ISBN 0521447550].

Ward , R.C. a nd M. Robinson Prin ciples of Hydrology. (London: McGraw -Hill,

1999) [ISBN 0077095022].

Wat son, R. ( ed.) Climate Change 2001: Synt hesis Report IPCC Intergovernmental

Panel on Climate Change, The Intergovernmental Panel on Climat e.

(Cambridg e: Cambridge University Press, 2002) [ISBN 0521015073].Williams, M., D . Dunkerley, P. de D eckker, P. Kersha w an d J . Cha ppell (eds)

Quaternar y Envir onments. (London: Arnold, 1998) [ISBN 0340691514].

Wilson, R.C.L., S. A. Drury a nd J. L. Cha pman (eds) The Great Ice Age. (London:

Routledge, 1999) [ISBN 0415198429].

Online study resources

In addition to the subject guide and the Essential reading, it is crucial that

you ta ke advanta ge of the study resources that are a vailable online for this

course, including the VLE and the Online Library.

You ca n a ccess the VLE, the Online Libra ry a nd your University of London

email account via t he Student Portal at:

http://my.londoninternational.ac.uk

You should receive your login deta ils in your stud y pack. If you ha ve not,


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Int roduct ion

5

or you have forgotten your login details, please email uolia.support@

london.ac.uk quoting your student number.

The VLE

The VLE, w hich complements this subject g uide, ha s been d esigned to

enhance your learning experience, providing additional support and a

sense of community. It forms an important part of your study experience

with the University of London and you should access it regularly.

The VLE provides a range of resources for EMFSS courses:

Self-testing activities: Doing these allows you to test your own

understanding of subject mat erial.

Electronic study mat erials: The printed materials that you receive from

the University of London a re ava ilable to dow nload, including updated

reading lists and references.

Past examination papers and Examiners commentar ies: These provide

ad vice on how each examination question might best be answered.

A student discussion forum: This is an open space for you to discuss

interests and experiences, seek support from your peers, wo rk

collaboratively to solve problems and discuss subject material.

Videos: There are recorded aca demic introductions to the subject,

interviews and debates and, for some courses, audio-visual tutorials

and conclusions.

Recorded lectures: For some courses, w here appropriat e, the sessions

from previous years Study Weekends have been recorded and ma de

available.

Study skills: Expert advice on preparing for examinations and

developing your d igital literacy skills.

Feedback forms.

Some of these resources are available for certain courses only, but we

are expa nding our provision a ll the time a nd yo u should check the VLE

regularly for updates.

Making use of the Online Library

The Online Library cont ains a huge arra y of journal art icles and ot her

resources to help you read widely and extensively.

To a ccess the ma jority of resources via the Online Library you w ill either

need to use your University of London Student Portal login details, or you

will be required to register and use an Athens login:http://tinyurl.com/ollathens

The easiest wa y to locate relevant cont ent an d journal articles in the

Online Library is to use the Summon search engine.

If you are having trouble finding an article listed in a reading list, try

removing any punctuation from the title, such as single quotation marks,

question marks and colons.

For furth er advice, please see the online help pag es:

www.external.shl.lon.ac.uk/summon/about.php


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6

Examinat ion advice

I m p o r t a n t : the information and advice given here are based on the

examination structure used a t the time this guide wa s written. Please

note that subject guides may be used for several years. Because of this

w e strongly advise you to alw ays check both the current Regulationsfor

relevant information a bout the examina tion, and the VLE where you

should be ad vised of a ny forthcom ing chang es. You should a lso carefully

check the rubric/instructions on the paper you actually sit and follow

those instructions.

Remember, it is important to check the VLE for:

up-to-da te informat ion on examination and assessment arra ngements

for th is course

w here available, past examination papers and Examiners commentar ies

for the course which give advice on how each question might best be

answered.

This course is assessed by a three-hour unseen w ritten exa minat ion. There

is a Sample examination paper at the end of this subject guide on p.145.You w ill be required to a nsw er three questions from a choice of 10. The

Examiners may set questions on any part of the syllabus, or set questions

w hich draw together parts of the syllabus.


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Chapter 1 : The structure of the Earth

7

Chapt er 1: The st ructure of the Eart h

Essent ial reading

Christ opherson , R.W. Geosystems: An Intr oduction t o Physical Geography. (Upper

Sad dle River, NJ: Pearson Education, 2011) eighth edition

[ISBN 9780321770769] Chapters 11 a nd 12.

Smith son, P., K. Addison a nd K. Atkinson Fundamentals of the Physical

Environment.(London: Routledge, 2008) fourth edition

[ISBN 9780415395168] Chapter 10.

Waugh, D. Geography: An Int egrat ed Approach. (Walton-on-Tha mes: Nelson

Thornes, 2009) fourth edition [ISBN 9781408504079].

Further reading

Collard, R. The Physical Geography of Landscape. (London: Collins Educational,

1992) [ISBN 0003222853].

Keller, E. Acti ve Tectonics: Ear thquakes, Upl if t, and Landscape(Upper Saddle

River, NJ: Prentice Hall, 1995) [ISBN 0023632615].

Open University, Dynamic Eart h. (Milton Keynes: Open University, 1997)

[ISBN 0749281839].

Skinner, B. a nd S. Porter The Dynami c Eart h: An In tr oducti on t o Physical Geology.

(Chichester: J ohn Wiley and S ons, 2000) fourth edition

[ISBN 0471161187].

Summerfield, M.A. Global Geomorphology. (Harlow: Longman, 1991)

[ISBN 0582301564].

Internet resources

http://earthobservatory.nasa.gov/

If you are going to visit just one website out of the ones listed, visit this

one! An excellent site, containing information about practically everything

there is to know about planet Earth. Highly recommended. Pay particular

attention to http://earthobservatory.nasa.gov/Study/ which contains many

excellent links to useful snippets of informa tion.

http://earthobservatory.nasa.gov/Laboratory/

Interactive experiments w here you can learn how and w hy the Earth

changes throug h the use of intera ctive computer models. Although these

experiments are aimed at younger members of the population, they

contain useful background information. The Mission Biome experimentis part icularly informa tive: (htt p://earthob servatory.na sa.gov/Lab orat ory/

Biome/).

www3.cerritos.edu/earth-science/tutor/landform_identification.htm

Online landform identification, with virtual visits to field examples.

http://geothermal.marin.org/pwrheat.html

Informat ion about geothermal energy from the Geothermal Education

Office.

www.abag.ca.gov/bayarea/eqmaps/links.html

Maps of current earthquake activity.www.abag.ca.gov/bayarea/eqmaps/eqmaps.html

A site full of information pertaining to earthquakes, from maps of

earthquakes (principally California) to the effects of earthquakes.


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8

Learning outcomes

When you have studied this chapter and the recommended reading, you

should be able to:

describe the nature and composition of the Earths crust

outline the history and explain the theory of plate tectonics

discuss the types of land forms that occur at different plat e boundaries

describe the main features of an earthq uake

list the different landforms associated w ith vulcanicity, and describe the

different types of volcano

explain the three ma in rock types an d discuss their differences.

Introduction

This chapter introduces the fundamental aspects of the structure of the

Earth. We begin with the composition of the Eart h and w hy there are

different layers. For us the most important layer is the crust, which isconstantly moving. The theory of this constan t movement of the surface

of the Earth is called plate tectonics and influences every aspect of the

natura l environment, for example where the continents have a huge

impact on global climate (see Chapter 3). Plate tectonics also influence

the composition of the atmosphere (see Chapters 2 and 3). However,

w hat w e discuss in this chapter is how plate tectonics cause geohazards

such a s earthqua kes, volcanoes a nd tsuna mis. In a ddition, w e discuss the

landforms that are the results of our dynamic a nd restless planet.

Structure of the Eart h

We have found out ab out the Eart hs structure through ma ny subtle forms

of investigation, particularly by studying the pat hs of earthqua ke waves

as they travel through the Earths interior, and by studying evidence of

volcanic eruptions which bring material from deep within the Earths

interior to the surface.

You w ill see from Figure 1.1 that the Eart hs structure is divided into t hree

zones.

Figure 1.1: The str ucture of the Earth

Crust

Mant le

Outer Core(l iquid)

Inner Core(solid)

< 3 .0 3 .4 1 0 .5 16Density

2900 k m

2000 k m

Up to 40 km

1370 k m

Depth


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9

Crust

This is the solid out er layer of the Eart h, a nd in rela tive terms, this is

equivalent to the skin of an apple. Its depth is usually never more than

1 per cent of the Earths radius, or averaging 4050 km, but this varies

considerably a round the globe. There are tw o different types: oceanic and

continenta l and t hey a re compared in Table 1.1.

Oceanic crust Cont inental crust

Know n as sima (rich in si l ica, and

magnesium)

Know n as sial (rich in si l ica and

aluminium)

Co m po sed m a in ly o f b asa lt ic l ava s Co m po sed ma in ly o f g ra nit ic r ock s

A verage 6 1 0 km in th ickness A verage 3 5 40 km in th ickness, but can

be up to 7 0 km th ick under mounta in

ranges

Relatively denser than continental crust

(average densi ty = 3; NB water = 1)

Relatively less dense th an o ceanic crust

(average densi ty 2.72 .8; NB soi l = 2.75)

Can be subducted beneath cont inental

crust as it is denser. At i ts d eepest (in

subduction zones), has a temperature of

1200C

Cannot b e subducted, but instead f loats

above the denser oceanic crust

Occurs under the oceans and forms

60 70 per cent of the total crust

Occurs only under large lan d m asses or

continental shelves, or beneath certain

shal low seas, and forms 30 4 0 per cent

of the total crust

Relatively younger than continental crust

(is destroyed at subduction zones and isrecycled)

Relatively older th an oceanic crust

the worlds oldest rocks are the greatcontin ental shields, e.g. North Am erica,

Australia.

Table 1.1: The dif fere nces bet w een oceanic and contine nta l crust

The boundary betw een the crust and the mantle is know n a s the

Mohovor i i d i scon t inu i ty, or Moho. At t his point, shockwa ves (e.g.

from earthq uakes) begin to travel faster, indicating a change in structure.

Mantle

This is the zone w ithin the Eart hs interior ran ging from 25 t o 70 km

below the surface, to a depth of ~ 2,900 km. It is composed mainly of

silicate rocks, rich in iron and magnesium. Apart from the rigid top layer

(the l i t h o s p h e re , w hich also includes the crust), the low er mantle (the

a s t h e n o s p h e r e ) rema ins in a semi-molten1 state. At the base of the

mantle, temperatures may reach up to 5,000C. These high temperatures

may help to generate convection currents which drive plate tectonics.

The boundary betw een the mantle and the core is know n a s the

Gu t e n b e rg d i s co n t i n u i t y.

Core

This is the very centre of the Eart h and is composed of iron a nd n ickel.

It consists of a n out er core (semi-molten) a nd inner core (solid). The

temperature a t the very centre of the Earth (~ 6,300 km below surface)

may reach 5,500C.

1 Molten = melted, so it

becomes like liquid


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10

Activity

Study the above section carefully, and make sure that you understand the differences

betw een the each o f zones of t he Earths structu re. If i t w il l make it clearer, redraw

Figure 1.1, and make your own an notat ions f rom th e text , and the informat ion given in

Table 1 .1.

Plate t ectonics

History

Francis Bacon (in 1620) wa s the first to formally draw at tention to the fact

that the continents could be fitted together like a jigsaw puzzle.

In the ea rly tw entieth century, both Alfred Wegener (Germany ) a nd F.B.

Tay lor (USA) came independent ly to same idea , tha t continents w ere not

static, but were drifting. However, the concept of c o n t i n e n t a l d r i ft

usua lly at tribu ted t o Alfred Wegener.

Wegener suggested tha t there w as once one large supercontinent, w hich

he named Pangea . From the Carboniferous (250 million years ago) untilsome time in the Quaternary (from 2.5 million years ago), this broke up,

first splitting into Lauras ia in the north and G o n d w a n a l a n d in the

south, before forming the continental configurations that w e know tod ay.

You ca n see his theory in Figure 1.2.

Figure 1.2: The supercontinent cycle

Wegener d rew evidence from several sciences to support this theory.

Biology

Certain identical rare fossils have been found in different continents,

now separated by vast oceans.

Mesosaurus(a small Permian reptile), for example, has only been foundin South Africa and Brazil.

A plant w hich existed only during coal-forming times has only been

found in India a nd Antarctica.

Geology

Rocks of similar type, format ion and a ge have been found in South

Africa and Brazil.

Mounta in ranges and fold belts all become consistent if the modern-

da y continents are fitted back into the Pangea n landma ss (e.g. the

mountains of northwest Europe correspond geologically with theAppalachians of the USA). Look at Figure 1.2 and imagine where the

modern-da y mountain ra nges are found you will see that w hen the

continents are fitted together, the mountain ranges line up.


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1 1

Climatology

Evidence of glaciation has been found in tropical Brazil and central

India.

Coal (which forms under w arm, humid conditions) has been found

under Antarctica.

Limestone, sand stone and coal found in Britain could not have formed

under its current climat ic regime.

How ever, Wegeners theory w as rejected a t first, ma inly because he w as

unable to explain a driving mechanism that w ould force the continents to

drift apart.

Later evidence in support of sea floor spreading

In the 1950s, scientists began to study palaeomagnetism as molten lava

cools at the surface of the Earths crust, the minerals contained within

it (especially iron) align themselves with the magnetic pole. Although

the Earths magnetic pole w as already know n to vary on an a nnual

basis, it was discovered that periodically, the magnetic pole actually

reversed completely (during the past 76 million years, there are thoughtto have been 171 reversals). As new lava was being extruded from the

submarine volcanoes, the minerals contained w ithin it w ould therefore

align themselves according to the direction of the m a g n e t i c p o l e , and

would thus contain a record of the Earths magnetic polarity. This magnetic

striping was found to be virtually symmetrical either side of the Mid

Atlantic Ridge.

In 1962, w hile investiga ting island s in the mid -Atlantic, American

oceanographer Maurice Ewing discovered a continuous submarine

mountain range extending the entire longitudinal length of the Atlantic

sea floor. He also noted that the rocks were of volcanic origin, and

geologically young (not ancient, as previously assumed). What he hadactually discovered was in fact the Mid Atlantic Ridge.

Also in 1962, there was the discovery that the sea floor was spreading.

While studying the a ge of rocks from the edg e of the North American

coast to the middle of the Atlantic Ocean, American geologist Harry Hess

discovered that the rocks became progressively younger towards the Mid

Atlantic Ridge. He confirmed that the newest rocks were still being formed

in Iceland, and that the Atlantic could be widening by up to 5 cm per year.

However, if new crust was being formed at the Mid Atlantic Ridge, yet the

Earth w as not expanding in size, evidence wa s needed to suggest that the

crust must be being destroyed elsewhere. This was found to be so around

the margins of the Pacific, and thus the now virtually universally acceptedtheory of plate tectonics wa s born.

The t heory of plate tectonics

The Earth s lithosphere (crust and upper mant le) is divided into seven

large, a nd several smaller p l a t e s(see Figure 1.3). These plates are

consta ntly moving, and are d riven by convection currents in the ma ntle.

Plate bounda ries mark the sites of the worlds major landforms, a nd they

are a lso a reas w here mountain-building, volcanoes a nd ea rthqua kes can

be found.


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12

Figure 1.3: The w orld distribution of tectonic plate boundaries

However, in order to account for such activity at the plate boundaries,

several points should be noted (mod ified from Waug h, 2000):

Continenta l crust is less dense tha n oceanic crust so it does not sink.

Whereas oceanic crust is continuously being created and destroyed,

continental crust is permanent, and hosts the oldest rocks on the planet

(the shieldlands).

Continental plat es may be composed of both continental and oceanic

crust (e.g. Eurasia).

Continental crust may extend further than the margins of the land

masses (when continental crust is covered by an ocean, it is known a s

c o n t i n e n t a l s h e lf ).

It is not possible for plat es to overlap, so they may either crumple up toform mountain chains, or one plate must sink below the other.

If tw o plates are moving apa rt, new crust is formed in the intervening

space, as no gaps may occur in the Earths crust.

The earth is not expanding, so if newer crust is being creat ed in one

area, older crust must be being destroyed elsewhere.

Plate movements are geologically fast and continuous. Sudden

movements manifest themselves as earthquakes.

Very little structura l chang e ta kes place in the centre of the plates

(the shieldlands). Plate margins mark the sites of the most significant

landforms, including volcanoes, batholith intrusions, fold mountains,island arcs and deep-sea trenches (see later sections throughout this

chapter).

Plate boundaries

There are three types of plate bounda ry (or ma rgin): construct ive,

destructive and passive.

Constructive margins

These arise w here tw o plates move aw ay from ea ch other, and new crust

is creat ed at the bounda ry. They are ma inly found betw een oceanic plat es,

and are consequently underw ater fea tures. Rift valleys may initiallydevelop, but molten rock from the mantle (magma) rises to fill any

possible gaps. Constructive margins are often marked by ocean ridges

(e.g. the Mid Atlan tic Ridge, th e East Pacific Rise). The rising ma gma


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1 3

forms submarine volcanoes, which in time may grow above sea level (e.g.

Iceland , Tristan d a Cunha an d Ascension Island on the Mid Atlan tic Ridge,

and Easter Island on the East Pacific Rise). Different rates of latitudinal

movement a long the boundary ca uset r a n s fo rm fa u l t s to develop as

the magma cools these lie perpendicular (at a right angle) to the plate

boundary. Of the annual volume of lava 2 ejected onto the Earth s surface, 73

per cent is found on mid-ocean ridges, and approximately one-third of the

lava ejected onto the Earths surface during the past 500 years is found in

Iceland . The Atlan tic Ocean formed a s the continent of Laura sia split in tw o,

an d the Atlan tic is continuing to w iden by a pproxima tely 25 cm per year.

Very rarely, constructive marg ins can occur on land , and it is though t tha t

this is happening in Ea st Africa a t t he Grea t African Rift Valley System.

Extending for 4,000 km from the Red Sea to Mozambique, its width varies

from 10 to 50 km, and at points its sides reach over 600 m in height.

Where the land has dropped sufficiently, the sea has invaded it has been

suggested tha t the Red Sea is the beginnings of a newly forming ocean.

Associat ed volcan oes include Mount Kilimanja ro and Mount Kenya to t he

east and Ruwenzori to the west.

Destructive margins

These occur w here tw o plates move tow ard s each other, an d one is

forced below the other into the mantle. The Pacific Ocean is virtually

surrounded by d estructive plate ma rgins with their associat ed features, and

its perimeter ha s become known as t he Pacific Ring of Fire. The feat ures

present at destructive margins will depend upon w hat types of plat es are

converging.

When ocean ic crust meets cont inenta l crust:

The thinner, denser oceanic crust is forced to dip dow nw ards at a n angle

and sink into thes u b d u c t io n z o n e

beneath the thicker, lighter and

more buoyant continental crust.

A d e e p -s e a t r e n c h forms at the plate ma rgin as subduction ta kes

place. These form the deepest areas on the planet.

As the oceanic crust descends, the edge of the continental crust may

crumple to form fo l d m o u n t a i n s , w hich run in chains parallel to the

boundary (e.g. the Andes).

Sediments collecting in the deep-sea trench may also be pushed up to

form fold mounta ins.

As the oceanic crust descends into the hot mantle, ad ditional heat

generated by friction helps the plate to melt, usually a t a depth of

400600 km below the surface.

As it is less dense than the mantle, the newly formed magma w ill tend to

rise to the Earths surface, where it may form volcanoes.

However, as the rising magma a t destructive margins is very acidic, it

may solidify before it reaches the surface a nd form a batholith at the

base of the mounta in chain (see below).

As the oceanic plate descends, shallow earthqua kes occur w here the

crust is stretched as it dips beneath the surface. Deeper earthquakes

arise from increases in friction and pressure may be released as

earthquakes.

As the oceanic plate descends, increased stresses may trigger

earthqua kes: sha llow earthqua kes occur where the crust is stretched

as it dips beneath the surface, and deeper earthq uakes occur due to

increases in friction and pressure as the plate subducts.

2 Once magma reaches

the Earths surface, it is

known as lava.


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14

The area in the subduction zone where most earthq uakes ta ke place is

known as the Ben ioff zon e .

The depth of the deeper earthquakes may a lso provide an indication as to

the angle of subduction, where gentler angles of subduction give rise to

shallower earthq uakes.

If subduction occurs offshore, i s la n d a r c s may form (e.g. Ja pan, the

West Ind ies).

When ocea nic crust meets ocea nic crust:

Where tw o oceanic plates collide, either one may be subducted.

Similar features arise as those w here an oceanic plate meets a continental

plate.

When continental crust meets continental crust (note that this is very rare):

Because continenta l crust cannot sink, the edges of the tw o plates and

the intervening sediments are crumpled to form very deep-rooted fold

mountains.

The zone marking the boundary of the tw o colliding plat es is know n as

the s u t u r e l in e .

These bounda ries mark the site at w hich the Eart hs crust is at its thickest.

For example, the Indo-Australian Plate is moving northeastwards and is

crashing into t he rigid Eurasian Pla te, creating the Himalaya s.

Uplift is a continuous process (it is happening right now ); how ever,

w eathering and erosion of the mountain tops means that the actua l height

of the mounta ins is not a s great a s the rate of uplift w ould suggest.

Sediments w hich form part of the Himalaya s w ere once underlying the

Tethys Sea , w hich existed a t the time of the Pang ean supercontinent.

Passive marginsThese occur where two plates slide past each other and crust is neither

created nor destroyed. The bounda ry betw een the tw o plates is chara cterised

by pronounced t r a n s fo rm f a u l t s , which lie parallel to the plate boundary.

As the plat es slide past each other, friction builds up and causes the plat es to

stick, and release is in the form of earthquakes.

An excellent exa mple of a pa ssive marg in is the San Andrea s Fault (one of

several hundred known faults) in California, w hich marks a junction between

the North American and the Pacific Plates. Although both plates are moving

in a northw esterly direction, the Pacific Plate moves at a faster rate t han

the North American late (6 cm per year, compared with just 1 cm per year),

creating the illusion that the plates are moving in opposite directions.

Activity

M any good t extbooks have f igures i l lustrat ing the di f ferent plate margins you should b e

able to f ind go od examp les in th e recommended reading, for example. Using these f igures

as guides, sketch ou t your ow n diagram for each type of m argin, being sure to annotate t he

main features. Features to note include, for example:

Construct ive margins in the ocean

central ri f t valley

fractures and transform faults on the sea bed

r ising magm a from t he asthenosphere

arching oceanic crust creating a ridge along the sea f loor.


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1 5

Construct ive margins o n land

ri f t valley/rif t valley system

central plateau

r ising magm a forming volcanoes

Destructive margins oceanic meets continental crust

descending o ceanic crust oceanic t rench at t he subduct ion zone

Beniof f zone w here earthquakes occur

fold mou ntains at edge of cont inental plate

melting oceanic crust, which rises to the surface to form volcanoes

Destructive margins oceanic meets oceanic crust

descending o ceanic crust

oceanic t rench at t he subduct ion zone

Beniof f zone w here earthquakes occur

melting oceanic crust, which rises to the surface to form volcanoes

chain of volcanic islands (island arc)

Destructive margins continental meets continental crust

suture l ine (marking the point of col l ision)

coll ision zone

deep mounta in roots

Passive margins

tension faul ts that develop near to the margin

On each f igure, also m ark the d i rect ion in w hich the plates are moving this may helpyou to understand w hy some of th e features are occurring.

Earthquakes

General informat ion

Earthquakes result from the sudden release of pressure which has slowly

built up w ithin the rocks of the Earth s crust. Energy is released in the

form of shockwaves known a s se i smic waves , which lose energy as they

radia te outwa rds from the centre of the earthqua ke (the focus ). The po int

on the Earths surface that suffers the greatest intensity of seismic waves is

th e e p i c e n t r e , which lies directly above the focus.Earthquake i n t e n s i t y is measured on t he m odi f ied Merca l li s ca le ,

w hich rang es from one to 12, depending upon t he intensity (see Tab le

1.2). This is a semi-qua ntita tive linear sca le.

Earthquake m a g n i t u d e is measured on the Rich te r s ca le (named after

the seismologist who devised it), which rates them on a scale of one to

nine. It is a logarithmic scale where each step represents a tenfold increase

in measured w ave a mplitude. Tran slated int o energy, each w hole number

represents a 31.5-fold increase in energy release. Thus a magnitude 3.0

on the Richter scale is 31.5 more energy than a 2.0 and 992 times more

energy than a 1.0. A value greater than 7.0 denotes a ma jor earthqua ke.

Since 1993 the Richter scale has been improved, as it was difficult tomeasure or differentiate between quakes at high intensity. The m o m e n t

m a g n i t u d e s c a le is more accurate than the original Richter amplitude

magnitude scale. For example, the 1964 earthquake at Prince William


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16

Sound in Alaska had an amplitude magnitude of 8.6 but on the moment

magnitude scale it increased to a 9.2. The largest ea rthquake recorded

occurred in Chile, in 1960, and reached 9.6 on the moment Richter scale

(see Table 1.2). This earthq uake is closely followed by t he ma gnitude 9.0

which occurred in northern Sumatra on 26 December 2004, causing the

most destructive tsunami ever. Most major earthquakes have magnitudes

of ~ 6.5. The Richter scale is a qua ntitative logarithmic scale.

Modified

Mercalli scale

(intensity)

Descript ion of effects on land Richter scale

(magnitude)

I Vibrat ions show up on inst rum ents; how ever, m ovem ent is not felt by hum ans. 0 .0 4.3

II M ovem ent felt by those rest ing and/o r on the upper f loors o f tall bu ild ings.

III Sh ak in g felt in sid e b uild in gs. Han gin g o bject s sw in g. Peo ple o ut sid e m ay n ot

realise earthquake is taking place.

IV M ost people indo ors feel m ovem ent . Hanging ob jects m ay sw ing. W indow s,

doo rs and dishes ratt le. Parked cars may rock. Som e people o utside m ay feel

movement .

4 .34.8

V M ovem en t not iced by all. Doors sw ing open and closed, l iqu ids sp il l, d ishes

break, etc. Pictures and wall hangings swing. Small objects may move/fall over.

Those sleeping may w ake up. Trees may shake.

VI Peo ple h ave d if f icu lt y w alk in g. M o vem en t felt by all. W in do w s b reak , p ict ures

fall off w alls, furniture m oves, objects fal l from shelves. Plaster in w alls may

begin t o crack. Trees and bushes shake. No majo r structural dam age, althoug h

i t m ay be sl ight in po orly constructed bui ldings.

4.86.2

V II Peo ple h ave d if ficu lt y st an din g. Dr ivers feel t heir cars sh ak in g. So m e f urn it ur e

breaks. Large b ells ring. Plaster, loose bricks and t i les fal l from buildin gs. Slight-

to-m oderate damage in w el l -constructed bui ldings, considerable damage inpoorly constructed buildings.

V III Car st eerin g may be aff ect ed . Tree bra nch es b reak . W ell- co nst ru ct ed bu ild in gs

may suf fer sl ight dam age. Houses that are no t secured dow n m ay begin to

move off their foundations. Poorly constructed buildings may experience severe

dam age. Tall structures (including t ow ers and chimn eys) may fall . Cracks

appear in w et groun d, hi l lsl ides may take place in w et groun d. Water levels in

wells may change.

6.27.3

IX General panic am ong pop ulat ion s. Sand and m ud may bu bble from the gro und.

Well-constructed buildings may be severely damaged. Houses that are not

secured down may move off their foundations. Reservoirs experience damage.

Some u nderground pipes are broken. Cracks appear on the grou nd.X M o st b uild in gs co llap se, so me b rid ges m ay b e affect ed . Railw ay t rack s b eg in t o

bend. Dams seriously damaged. Large landslides may occur, and water may be

thro w n on to t he ban ks of rivers, canals, lakes, etc. Large cracks appear o n th e

ground.

XI Larg e crack s ap pear o n t he g ro un d. Ro ck s fall . Railw ay t rack s b en d an d ro ad s

break up. M ost bui ldings destroyed (some earthquake-proof bui ldings may

withstand tremors up to 8.5 on the Richter scale). Some bridges may collapse.

Underground pipel ines destroyed.

7.38.9

XII To tal d est ru ct io n. Gro un d m oves in a w ave-l ike m ot io n. Larg e am ou nt s o f ro ck

may be moved. Rivers change their course. Objects are thrown into the air.

Vision is blurred.

Table 1.2: The M ercalli and Richte r scales


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1 7

Often severe earthquakes are so deep in the Earth that no surface

displacements are seen. However, as the shockwaves reach the surface,

landw aves may roll across the terrain, w hich may trigger events such a s

mass movements and ava lanches.

By their nat ure, earthqua kes are often q uite difficult to predict, and so

they are ca pable of causing much da mage should they strike w ithout

w arning. Earthqua kes take place a ll the time, but it is the size and location

of the ea rthquake w hich w ill determine the scale of destruction. Often,

the extent to w hich a n earthq uake is termed dama ging depends upon its

locat ion in relation to human populations.

Note that much of the dama ge associated w ith earthqua kes may not

be due to the tremors themselves, but to the after-effects, such as fires

from broken gas pipes, disruption of transport and other services, poor

sanitation, disease (e.g. from broken sew ers and contaminat ed w at er

supplies), exposure caused by lack of shelter, food shorta ges, lack of

medical equipment, etc.

Earthquake f eatures

There are three main stag es to an eart hqua ke:

F o re s h o c k s relate to the initial shattering of obstructions or bonds

along t he failure plane.

P r in c i p a l s h o c k is the most severe shock. It may last from just a few

seconds to a couple of minutes.

Af te rshocks recur as the shockw aves tra vel around t he Earth. They

generally d ecrease in frequency a nd intensity over time, but ma y

occur over a period of several days to several months. They have great

potential to cause dama ge, as structures have a lread y been w eakened

by t he principal shock.

Types of shockw ave

Earthquakes produce three different types of shockwave, which become

progressively weaker with distance from the Earthquake focus, like ripples

on a pond. The nature of the w ave a lso determines how it travels through

the Earths interior (see Figure 1.4).


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Figure 1.4: The movement of t he different earthquake wa ves through the

structure of the Earth

The three ma in types of w ave and their differences are outlined in Tab le

1.3:

W ave typ e Wave

character

Speed How it passes

through the

Earths inter ior

Figure

Primary (P) Longitud inal3 Fastest waves,

travell ing at an

average speed of

5 km per second.

Are able to pass

through sol ids and

liquids, so can travel

through the core.

Figure 1.5a

Secondary (S) Tra nsv er se4 Slow er, travell ing at

an average speed of

3 km per second (i.e.

60 per cent of the

speed of P w aves).

Are not able to

t ravel through

liquids, so cann ot

pass through the

outer core.

Figure 1.5b

Surface/long(L) waves

Transverse Slow est w a ves,w i th greatest

wavelength 5, but

they carry most of

earthq uakes energy.

Travel around thesurface of the Earth

the surf ace w av es

of the Chilean

earthquake of

1960 t ravel led 20

t imes around th e

Earth, and w ere

sti l l registering on

seismometers 60

hours af ter the main

shock.

Figure 1.5c

Table 1.3: The ma in types of e arthquake wa ve

3 Longitudinal waves

have a push-pull

motion where particles

travel in the same

direction as the wave.

4In t ransverse waves

particles oscillate on a

vertical plane about the

direction of travel (i.e.

undulating like rolling

ocean w aves).

5 The wavelength is the

distance between tw o

peaks within a w ave (or

two troughs).


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1 9

Figure 1.5: The diff erent t ypes of earthquake w ave

Tsunamis

These are huge tidal waves caused by the displacement of the sea bed.

Displacement ma y be caused by an ea rthqua ke, but may also be caused by

the slumping of sediments around the coast, or especially near to deep-sea

trenches. Whole series of waves may be set up, which have wavelengths of

several hundred kilometres. Because they posses so much energy, they may

race across the ocean for thousands of kilometres at speeds of up to 900

km per hour a large tsunami can cross the Pacific in about 24 hours.

The height of a tsuna mi is directly proportional to t he depth of the w at er

across which it is travelling. In the middle of the deep ocean, a tsunami

wave may be relatively unnoticeable. Therefore its effects are at their most

intense in shallow waters, so shelving coastlines are particularly vulnerable

to da mage should a tsunami hit.

Most dangerous tsunamis occur in the Pacific Ocean, as it is surrounded

by t ectonic plate margins. The Pacific Tsunami Warning System ha s been

set up, w hich triggers w arning ala rms if an ea rthqua ke greater than 6.5

on the Richter scale is detected by one of its 69 seismic stations a cross the

area. Tsunami w arnings can t hen be issued, and appropriate a ction taken

in areas at risk.


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20

However, as was discovered on 26 December 2004, a tsunami originating

from a magnitude 9.0 ea rthqua ke in northern Sumatra killed over 100,000

people in countries surrounding the Indian Ocean. There are now moves

to set up tsunami w arning systems in the Indian and Atlantic Oceans.

Activity

Earthquakes take place all the t ime, but the ones w e hear about in th e news tend t o be

those occurring near to major p opulat ion centres. Search th e internet or read through old

newspapers for art icles about earthquakes that have taken p lace. When you read th em,

pay at tent ion t o th e sequence of events that have taken place and t ry to dist inguish th e

three different types of earthquake shock. Also consider the location of the earthquake,

and compare i t w i th Figure 1.3 is there a connect ion w i th tectonic plate boundaries? I f

so, what sort of boundary is it related to (constructive/destructive/ passive)?

Vulcanicity

Lava

There are tw o types of lava , and th ese are compared in Tab le 1.4.

Ba sa lt ic, or ba sic la va And esit ic, o r a cid ic la va

Hot (1 ,20 0C) Less hot (80 0C)

Low er si lica content Higher silica content

Low v i scosi t y, so f l ows qu ick ly and f ar V iscous, so f lows sl ow l y, and l ess fa r

Takes longer to cool and solidify, so f low s

considerable d istances as lava rivers.

Cools and solidif ies quickly, so f low s over

shorter distances

Ret ain s g as, g ivin g it m ob ili t y Lo ses g as q uick ly, so b eco mes even m ore

viscous

Produces large-scale landforms of gentle

slope angles

Produces more localised features, with

steeper slope angles

Eruptions are frequent, but relatively

gent le

Eruptions less frequent, but violent due to

viscous lava and b uild u p of g ases.

Ejecta: lava and steam Ejecta: ash (tephra), rocks (pyroclasts),

lava and steam

Found at construct ive plate boun daries

w here magm a rises f rom the mant le, e.g.Heimaey, Iceland (a f issure along the Mid

Atlantic Ridge); and over hotspots, e.g.

M auna Loa, Hawai i

Found at d estruct ive plate boun daries

where oceanic crust subducts, melts andrises, e.g. Mt St Helens, USA (subduction

zone), M t Fuji, Japan (island arc)

Table 1.4: A comparison of the different types of lava

Note that there a re tw o different types of basic lava:

a a cools into extremely irregular clinker-like surface of sharp edges

p a h o e h o e rope lava buckles up into series of cord-like pleats.

Although the two lavas are chemically the same, these differences are

thought to arise from differing flow mechanisms, speed of cooling and theshape of the enclosed gas bubbles.


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2 1

Intrusive landform s

These formwithin the Earths crust; however, they may become visible at

the Earths surface due to erosion and weathering (see Chapter 5). When

molten rock is forced up through the crust, it may solidify in a number of

forms (see Figure 1.6).

Figure 1.6: The diff erent types of int rusive landform s and their ef fect on relief

Laccoliths, e.g. Eildon Hills, Scottish Borders (200 m above

surrounding area )

Loppoliths

Batholiths (e.g. underlying Britains southwest peninsula and Brittany)

Phacoliths

Bysmaliths

Dykes (e.g. Cleveland Dyke, stretching 40 km across North Yorkshire

Moors) Sills (e.g. Great Whin Sill, northeast England)

Phacoliths.


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Note that due to the high heat w hich may have been released as the

magma intruded, it may have a ltered the surrounding country rock.

Therefore such features listed above may be surrounded by halos of

metamorphic rock. For example, the great batholith underlying southwest

England is surrounded by kaolin (otherw ise know n a s china clay, a nd

hence the china-clay pits commonly found in Cornwall).

Ext rusive landf orms: volcanoes

Extrusive landforms are those which are formed above the Earths surface

as a result of the lava being extruded . Volcanoes a re mostly associated

w ith tectonic plate boundaries, and it is thought tha t 80 per cent of the

worlds presently active volcanoes are found above subduction zones.

Because the a sh ejected from volca noes is often very rich in minerals, it is

usually extremely fertile. For this reason, huma ns w ill quite often risk the

chance of eruption for the opportunity to farm the fertile soils of volcanic

areas. In other cases, it is the volcanic activity itself which provides the

land upon which people can live (for example volcanic islands such as

Iceland on the Mid Atlantic Ridge). In Iceland, geothermal energy isharnessed from the volcanic activity, and is used to provide heating for the

nation.

Activity

Visi t the w ebsite ht tp: / /geothermal.marin.org/pw rheat .html of th e Geothermal Educat ion

Off ice. M ake notes on how geothermal energy can be exploi ted by hum an society.

The basic structure of a volcano is shown in Figure 1.7, and the different

types of volcano are listed below.

Figure 1.7 The ba sic str ucture of a volcano

Hotspots

Not all volcanoes a re found a bove plate margins. Hotspots are areas of

the Earths crust where there is an unusually high flow of heat, marked by

volcanic activity. They are usually found on oceanic crust, although they

may also occur on continental crust. For example, it is thought that there

is a superplume (extremely large hotspot) underlying Yellowstone Park,

Wyoming, USA. Of the 125 hotspots that are thought to have been active

over the past ten million years, most are located a w ay from the boundaries

of tectonic plates, a nd it is generally thought tha t they result from hot

plumes of molten rock in the mantle that rise to the surface. Should thehotspot be stationary, chains of volcanoes may develop on the overlying

crust a s it is moved by tectonic a ctivity. Therefore these chains of islands

can be used to monitor long-term movements of tectonic plates. Good

Crater

Pipe

Viscous Lavasform steep-sided

dumpy cones


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examples include the Haw aiian Islands, Pacific Ocean; and Runion, near

Madag ascar in the Indian Ocean.

Fissure erupt ions

At constructive margins, lava may erupt through fissures, rather than

through a central vent. Heimaey, Iceland (1973), began as fissure

eruption, 2 km in length, but Laki, Iceland (1783), was 30 km in length.

As the lava is basic, it flows great distances, a nd ma y form large plateaux,

for example those that can be seen as basaltic columns in Iceland,

Greenland , a nd most fa mously in Northern Ireland (the Giant s Causewa y)

and northwest Scotland (Fingals Cave on t he Isle of Staffa ).

Lava cones

These are show n in Figure 1.8. The slope of the cone d epends on w hether

the molten lava was fluid or viscous (basic or acidic), and cones are built

up from repeated lava flows. Fluid, basic lavas give rise to more gently

sloping cones (e.g. Mauna Loa, Haw aii, ~ 400 km in diameter at t he sea

floor and 112 km at sea level). Viscous acidic lavas give rise to more

steeply sloping cones, which may be convex (dumpy) in appearance as

the lava tends to solidify close to the equator. In the case of Mont Pele,

Martinique, the la va w as so viscous and solidified so q uickly a s it w as

coming up the vent that it w as extruded as a s p i n e or p l u g . How ever, it

broke up rapidly on cooling.

Figure 1.8: Lava cone f orme d fro m ba sic lava

Ash and cinder volcanoes

These are show n in Figure 1.9. In violent eruptions, lava is ejected t o grea t

heights, where it breaks into small fragments. These then fall back to Earth

and build up a symmetrical cone with slightly concave sides, composed

of layers of fine ash and larger cinders. Good examples include Paracutn,

Mexico; and Volcano d el Fuego, Gua tema la.

Figure 1.9: Ash and cinder volcano

Sea

about 400 km (250 miles)

112 km (70 miles)

Crater

Layers of lava4115 m (13 000 f t )9 1 1 4 m(30 000 f t )Sea

Earth'sSurface

Crater

Cone is made of

layers of ash

3 0 4 8 m(10 000 f t )


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Composite volcanoes

These are show n in Figure 1.10. Composite volcanoes a re composed of

alternating la yers of ash and lava usually resulting from alternating t ypes

of eruption, where first ash (from initial violent eruption) and then lava

(usually acidic) are ejected. Dykes may extend out from the central pipe,

allowing lava to escape from the sides of the cone, where it may build up

small conelets (pa rasitic cones). A good example is Mount Etna, Sicily.

Figure 1.10: Compo site volcano

Calderas

Occasionally, volcanic eruptions are so violent that they clear the magma

chamber beneath the volcano. The summit of the cone may then sink

into the empty ma gma chamber beneath the vent, creating a huge crater

tha t ma y be severa l kilometres in diameter (see Figure 1.11). These

caldera s may lat er become flooded (e.g. Lake Toba , northern Suma tra ),

and later eruptions may create conelets in these lagoons (e.g. Wizard

Island in Crater Lake, USA; Anak Krakatoa w ithin Krakatoa , Sunda Strait,

Indonesia).

Underwat er volcanoes

If volcanoes erupt under the sea (e.g. at plate margins), the lava cools very

quickly due to the cool temperatures of the surrounding water. This may

give rise to interesting forms, such as pi l low lava , so called as it a ppears

to billow outwards.

Types of volcanic eruption

In ascending order of magnitude (gentlest to most explosive):

Icelandic

Haw a iian

Strombolian

Vulcanian

Vesuvian

Krakatoan

Pelan

Plinian.

Pyroclasts

Volcanoes a lso eject fra gmented (or pyroc las t i c , mea ning fire broken)

material of various sizes including:

tephra (volcanic glass shards)

a sh

Crater

Dyke

Pipe

ConeletAsh Layer

Lava Layer

Lava Flow

Earth'sSurface


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2 5

Figure 1.11: The formation of a caldera

lapilli (small stones)

bombs (larger material)

pumice (solidified foam/scum on the top of the lava flow).These may then form pyroclasticflows, w hich may take the form of either

a fast-moving cloud of very hot toxic gas, known as a n u e a r d e n t e

(e.g. Mont Pele, Martinique, 8 May 1902), which then deposits a

material known as i g n i m b r i t e , or it may fa ll to Earth a nd be tra nsported

dow n the side of a volcano as a l a h a r , or mud slide (e.g. Mt Pinatubo,

Philippines, 1991).

Other feat ures

Geysers

These develop when w at er in an und erground cavern with a restricted

opening becomes superheated by the surrounding rock and pressure builds

up. Once a pressure threshold is crossed, t he w a ter is ejected violently a s

steam, a nd t he process starts a gain. Water ma y be ejected straight out of

1. Before violent eruptions take place

2. Violent eruption s

3. Violent eruptions have ceased

Formation of a Caldera:

Caldera with new cones

Caldera

Gases andlava

bombs

ejected

Top of conebreaks up

Top of cone has sunk

into the magma


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26

the cavern, or it may be ejected from a sump in a pipe. A good example is

Old Faith ful at Yellowstone Nationa l Park, USA, w hich releases every 30

minutes.

Fumaroles

These are small volcanic vents through w hich hot gases an d steam are

continuously emitted a t low pressure. If the ga s is rich in sulphur, yellow

sulphurous deposits may form around the vent, which becomes known as

a solfatara .

Hot springs

These are formed w hen superheated w at er flows gently out of t he rocks.

The water often contains minerals dissolved from the rocks, and these

are believed to be good for ailments such as rheumatism. Because of this,

many hot springs have spas (health resorts) nearby.

M ud volcanoes

These form w hen hot w a ter mixes w ith mud an d surface deposits.

Activity

Look in an atlas and locate the examples of the volcanoes given above. Can you see a

relat ionship w i th the b oundaries of plate tectonics given in Figure 1.3?

Search the internet for accounts of volcanic eruptions that have taken place. Compile case

studies of how volcanic activity has impacted human l i fe. Volcanoes are a natural hazard,

yet wh y do people st i l l choose to l ive near to them?

Rock types

The volume of the Earths crust is composed of 95 per cent igneous rocks

and only 5 per cent sedimentary and metamorphic rocks, combined.

However, at least 74 per cent of the rocks exposed at the surface are

sedimenta ry shales, san dstones a nd limestones. We w ill examine these

different rock ty pes below.

Igneous

See Figure 1.12. This is the original rock type from w hich all ot hers are

derived. Igneous rocks are of volcanic origin, and are usually crystalline.

There are various methods of classification, including the degree of acidity

and location of cooling, both of which are relevant to rocks structure and

resistance. The most common are granite, basalt a nd ga bbro. Rocks may

contain parallel horizontal planes (known as pseudo-bedding planes orsheet joints) due to the expansion of the rock after the overlying layers

have been removed by denudation. J ointing (fractures in a ny direction)

is also common, formed by contraction of rock as it cools, e.g. hexagonal

jointing in basalt (e.g. Giants Causeway, Northern Ireland). Such joints/

fractures may provide potential zones of w eakness for w eathering, and so

are important for the development of the rock outcrop.


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Figure 1.12: The classificatio n o f igneous rocks

Sedimentary

See Figure 1.13. Sedimenta ry rocks are composed of:

particles of other rocks derived from denudat ion, e.g. sand, clay or

gravel, which may be held together by a na tural cement, chemically

precipitated in the gaps between the particles (e.g. s a n d s t o n e ,

c o n g l o m e ra t e , brecc ia ) .

organic matter, e.g. microscopic marine organisms, such as

foraminifera, coccoliths and sponge spicules (e.g. l i m e s t o n e , fl int ,

c h e r t ); a ncient plants

physical geography 1

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