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Natural hazards afflict all corners of the Earth; often unexpected, seemingly unavoidable and frequently

catastrophic in their impact.This revised edition is a comprehensive, inter-disciplinary treatment of the full range of natural hazards.Accessible, readable and well supported by over 150 maps, diagrams and photographs, it is a standard text forstudents and an invaluable guide for professionals in the field.

Clearly and concisely, the author describes and explains how hazards occur, examines prediction methods,considers recent and historical hazard events and explores the social impact of such disasters. This revised editionmakes good use of the wealth of recent research into climate change and its effects.

Edward Bryant is Associate Dean of Science at Wollongong University in Australia. Among his other publicationsis Tsunami: The Underrated Hazard (Cambridge University Press, 2001). He has particular interest in climaticchange and coastal evolution.

Praise for the First Edition:Professor Bryants heroic compilation is an excellent guide.Scientific American

NATURAL HAZARDS


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EDWARD BRYANT

S E C O N D E D I T I O N

NATURALHAZARDS


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Cambridge, New York, Melbourne, Madrid, Cape Town, Singapore, So Paulo

Cambridge University PressThe Edinburgh Building, Cambridge , UK

First published in print format

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Edward Bryant 2005

2005

Information on this title: www.cambridge.org/9780521537438

This book is in copyright. Subject to statutory exception and to the provision ofrelevant collective licensing agreements, no reproduction of any part may take place

without the written permission of Cambridge University Press.

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Cambridge University Press has no responsibility for the persistence or accuracy of

s for external or third-party internet websites referred to in this book, and does notguarantee that any content on such websites is, or will remain, accurate or appropriate.

Published in the United States of America by Cambridge University Press, New York

www.cambridge.org

paperback

eBook (EBL)

eBook (EBL)

paperback
http://www.cambridge.org/http://www.cambridge.org/9780521537438http://www.cambridge.org/


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To Dianne, Kate and Mark


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List of illustrations ixPreface xiiiAcknowledgements xv

1 Introduction to Natural Hazards 1

Rationale 1

Historical background 2Chapter outlines 10References and further reading 13

Climatic Hazards

2 Mechanisms of Climate Variability 17

Introduction 17Models of atmospheric circulation and change 17Astronomical cycles 37

Concluding comments 41References and further reading 42

3 Large-scale Storms as a Hazard 44

Introduction 44Tropical cyclones 44Extra-tropical cyclones 58Snowstorms, blizzards and freezing rain 67Storm surges 73Probability of occurrence 76

Dust storms 78Concluding comments 83References and further reading 83

4 Localized Storms 85

Introduction 85Thunderstorms, lightning and hail 85Tornadoes 93Concluding comments 102References and further reading 102

5 Drought as a Hazard 103

Introduction 103Pre-colonial response to drought 103Post-colonial response 105Drought conditions exacerbated bymodern societies 106

Modern response to droughts 106International response 113Private responses: Bob Geldof 115Concluding comments 118References and further reading 119

6 Flooding as a Hazard 120

Introduction 120Flash floods 120High-magnitude, regional floods 131

Contents


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7 Fires in Nature 139

Introduction 139Conditions favoring intense bushfires 140

Causes of fires 143Bushfire disasters: world perspective 144Concluding comments 153References and further reading 154

8 Oceanic Hazards 155

Introduction 155Waves as a hazard 156Sea-ice as a hazard 162Sea level rise as a hazard 166

Beach erosion hazard 170Concluding comments 174References and further reading 175

Geological Hazards

9 Causes and Prediction of

Earthquakes and Volcanoes 179

Introduction 179Scales for measuring earthquake intensity 179Distribution of earthquakes and volcanoes 182Causes of earthquakes and volcanoes 184Prediction of earthquakes and volcanoes 189Concluding comments 200References and further reading 200

10 Earthquakes and Tsunami as

Hazards 202

Types of shock waves 202

Seismic risk maps 204Earthquake disasters 204Liquefaction or thixotropy 211Tsunami 214


11 Volcanoes as a Hazard 227

Introduction 227

Types of volcanic eruptions 229Volcanic hazards 230Volcanic disasters 238Concluding comments 247References and further reading 247

12 Land Instability as a Hazard 249

Introduction 249Soil mechanics 249Shear strength of soils 251

Classification of land instability 254Subsidence 267Concluding comments 268References and further reading 269

Social Impact

13 Personal and Group Response

to Hazards 273

Introduction 273Before the event 273Dealing with the event and its aftermath 277Additional impacts 283References and further reading 286

14 Epilogue 288

Changing hazard regimes 288Modern consequences of natural hazards 290References and further reading 291

Select glossary of terms 292Index 304

viii Contents


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1.1 Incidence of natural hazards by region

19752001 7

1.2 Reporting incidence of natural hazards

19002001 8

1.3 Deaths from natural hazards 19002001 9

2.1 Wind movements relative to isobars 18

2.2 PalmnNewton schematic model of

general air circulation 192.3 Mid-latitude westerly and easterly trade

wind belts 20

2.4 Path of jet stream in the northern hemisphere 21

2.5 Mobile polar highs and resulting trade wind

circulation 23

2.6 Dynamic structure of mobile polar highs 24

2.7 El NioSouthern Oscillation event 25

2.8 Indices of atmospheric pressure oscillations 26

2.9a Fans deposited during La Nia event 30

2.9b Landslides and washouts resulting from

La Nia 302.10 Southern Oscillation index, drought and

rainfall indices and river discharges 31

2.11 Time series of Southern Oscillation index 33

2.12 Hurricane days in North AtlanticCarribean

Sea region 34

2.13 Phases of North Atlantic Oscillation 36

2.14 Winter storms in north Atlantic 36

2.15a Zurich sunspot numbers, 15002002 38

2.15b Zurich sunspot record between 1860

and 2002 38

2.16 Precession of the Moons orbit 39

2.17 The 18.6-year lunar orbit relative to the Earth 40

3.1 Hazards related to occurrence of tropical

cyclones 45

3.2 Location map 46

3.3 Origin and number of tropical cyclones 46

3.4 Potential temperature structure in

Hurricane Inez 473.5 Wind and pressure cross sections through

Hurricane Anita 48

3.6 Damage caused by Cyclone Tracy 52

3.7 Satellite image of Hurricane Andrews path 53

3.8 Sheet of plywood driven through a

Royal Palm 53

3.9a Effects of wind damage caused by

Cyclone Tracy 55

3.9b Building peeled back to beams by high winds 55

3.10 Path of 1970 cyclone in Bay of Bengal 58

3.11 Development of an extra-tropical depression 593.12 Incidence of severe North Sea and English

Channel storms 60

3.13 Historical, erosive North Sea storms 61

3.14 Pressure pattern over northern Europe, 1588 62

3.15 Schematic development of an east-coast low 63

3.16 Satellite image of Halloween storm, 1991 64

3.17 Ash Wednesday storm damage, 1962 65

3.18 Storms of 25 May15 June 1974, Sydney 66

3.19a Undermining and collapse of beachfront

houses 66

Illustrations


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3.19b Collapsed picnic shelter 66

3.20 Precipitation patterns, mid-latitude cyclonic

depression 68

3.21 Pressure patterns for 1984 snowstorm 69

3.22 Effect of a heavy snowstorm, Newfoundland 69

3.23 Equivalent temperature or wind chill chart 72

3.24 Effect of freezing precipitation and wet snow 733.25 Track of Hurricane Carol 75

3.26 Effect of wave shoaling on long wave height 75

3.27 Recurrence intervals of North Sea storm

surges 77

3.28 Probability exceedence diagram for Fig 3.27

data 78

3.29 Dust storm bearing down on Melbourne 79

3.30 Trajectories of dust storms 80

3.31 Extent and frequency of dust storms in

United States 82

4.1 Annual frequency of thunder days in

United States 86

4.2 Average annual thunder days in Australia 87

4.3 Location map 88

4.4 Separation of charged water droplets 89

4.5 Annual frequency of hailstorms in

United States 91

4.6a Large hailstones 92

4.6b Layered hailstone 92

4.7 Tornado generation within a supercell

thunderstorm 94

4.8 Development of a mountainado 95

4.9 Waterspout striking the Trombes 95

4.10 First tornado captured by NSSL 96

4.11 Model for multiple-vortex formation in a

tornado 96

4.12 Average tornadoes per year and preferred

paths 98

4.13 Tornadoes and tornado deaths in United

States 98

4.14 Effect of topography on passage of a tornado 101

5.1 Map of semi-arid regions and the Sahelin Africa 104

6.1 Maximum rainfall amounts versus time 121

6.2 Location map 121

6.3 Stream power per unit boundary area 123

6.4 Channel depth verus current velocity 124

6.5 Abnormal patterns of airflow, leading to

flash flooding 125

6.6 Maximum probably rainfalls per unit time 126

6.7 Forty-eight-hour isohyets for the Dapto flood 128

6.8 Synoptic pattern for Sydney flash floods 129

6.9 Isohyets for three flash flood events in Sydney 130

6.10 Flood locations 19852003 131

6.11 Mississippi River drainage basin and flood

extents 132

6.12 Occurrence of major floods on Mississippi

River 132

6.13 Major rivers of eastern Australia 1336.14 Hwang Ho River channel: 2300 BC to

present 136

7.1 William Strutts painting Black Thursday 139


7.3 Synoptic weather pattern conducive to

bushfire 141

7.4a Crown fire in aEucalyptus forest 142

7.4b Crown fire in a boreal forest 142

7.5 Whirlwind associated with a clearing

after burning 143

7.6 Destruction caused by southern Californian

fires 148

7.7 Pattern of seasonal bushfires in Australia 149

7.8 Extent of bushfires, location of spot fires 150

7.9 Devastation of Fairhaven following Ash

Wednesday 152


8.2 Schematic representation of wave

characteristics 157

8.3 Wave behavior in shallow water 158

8.4 Worldwide distribution of altimeter wave

heights 160

8.5 Deep-water swell waves, Wollongong 162

8.6 Worldwide distribution of sea-ice 163

8.7 Composite April sea-ice extent 163

8.8 Pack-ice Cornwall Island, Canadian Arctic 166

8.9 Annual sea level changes 167

8.10 Changes in global sea level 168

8.11 Global sea level change 19922002 169

8.12 The Bruun Rule for shoreline retreat with

sea level rise 171

8.13 Difference in beach volume, Stanwell Park 1738.14 Linear regression lines, Stanwell Park Beach 174

9.1 Plate boundaries 181


9.3 Return intervals of earthquakes 183

9.4 Origin of volcanism: mid-ocean plate

spreading 184

9.5 Origin of volcanism over a subduction zone 185

9.6 Movement of Hawaiian Islands drifting over

hot spot 186

9.7 Hot spots and island strings on Pacific Plate 187

x Illustrations


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TABLES

1.1 Frequency of natural hazards during thetwentieth century 7

1.2 Cost of natural hazards, 19002001 71.3 Number of people killed, injured or displaced

due to natural hazards 91.4 Ranking of hazard characteristics

and impact 112.1 Comparison of drought in Indonesia with

El NioSouthern Oscillation events 32

xi

2.2 Timing of flood and drought with18.6 year lunar tide 41

3.1 Lowest central pressures recorded intropical cyclones 49

3.2 Scales for measuring cyclone intensity 504.1 Fujita Tornado Intensity Scale and

frequency of tornadoes in the USA 978.1 Wave energy and power for typical

ocean waves 159

Illustrations

9.8 Faults associated with earthquake activity 188

9.9 Probability of eruptions of individual

volcanoes per century 190

9.10 Recent volcanism (16002000) 191

9.11 Magnitude on the Richter scale of major

earthquakes 193

9.12 Major seismic gaps in the Pacific ringof fire 194

10.1 Seismic waves and their travel behavior 203

10.2 Global seismic risk map 204


10.4 Earthquake and tsunami characteristics 207

10.5 Head scarp of landslide, Anchorage, Alaska 207

10.6 Historically active fault systems of southern

California 208

10.7 Collapsed sections of Cypress viaduct 209

10.8 Distribution of faulting for Tokyo

earthquake, 1923 210

10.9 Cumulative effect of compressional P-waves

on pore water pressure 212

10.10 Liquefaction following 1964 Niigata

earthquake 213

10.11a Spatial distribution of tsunami since 47 BC 215

10.11b Source areas for Pacific-wide events 215

10.12 Plots of tsunami wave trains in Pacific region 217

10.13 Tsunami wave refraction pattern 217

10.14 Sequential photos of 1957 tsunami, Hawaii 218

10.15 Ships stranded by tsunami, 1868 218

10.16 Run-up heights of tsunami, Hawaiian

Islands 219

10.17 Pacific Tsunami Warning System 223


11.2 Tephra ejecta from Mt St Helens 233

11.3 Beginning of pyroclastic flow 234

11.4 Location map of Mt St Helens 236

11.5 Lahar following eruption of Mt Pinatubo 237

11.6 Region affected by Santorini eruption 239

11.7 Location map of Mt Vesuvius 241

11.8 Sundra Strait coastline affected by tsunami 242

11.9 Volcanoes and earthquakes in Carribean

region 244

11.10 Location map of Mt Pele 245

11.11 St Pierre after eruption of Mt Pele 24611.12 North side of Mt St Helens after 1980

eruption 247

12.1 Effect of gravity on an object 250

12.2 Strength of bonding on particles of

different sizes 251

12.3 Schematic representation of MohrCoulomb

equation 252


12.5 Schematic representation of Atterberg limits 254

12.6 Classification of land instability 255

12.7 Extent of expansive soils in the United

States 256

12.8 Effect of alternate wetting and drying of

expansive soils 257

12.9 Downhill movement caused by soil creep 258

12.10 Widespread debris flows in Kiwi Valley area 260

12.11 Erosion and debris flow deposition after

urban flood 261

12.12 Process of rotational sliding 261

12.13 Complexity of landslide initiation over time 262

12.14 Mega-landslide, northern slopes of

Nakanai Range 263

12.15 Extent of landslides in the coterminous

United States 264

12.16 Process and impact forces generated by

snow avalanche 266

13.1 Drinkers in Lorne watching Ash Wednesday

bushfire 274

14.1 Imbricated boulders stacked against cliff face 288


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8.2 Factors controlling beach erosion 1729.1 Annual frequency of earthquakes 1809.2 Some of the largest earthquakes 1809.3 The Mercalli scale of earthquake intensity 18110.1 Major historical earthquakes by death toll 20510.2 Percentage of tsunami in the worlds

oceans and seas 21510.3 Earthquake magnitude, tsunami magnitude

and tsunami run-up heights in Japan 219

10.4 Solovievs scale of tsunami magnitude 22010.5 Causes of tsunami in the Pacific 22010.6 Large death tolls from tsunami in the Pacific

Ocean region 22012.1 US Highway Research Board Landslide

Committee classification of mass

movements 25513.1 Frequency of psychological problems

amongst young survivors of Cyclone Tracy 285

xii Illustrations


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I have reread the preface to the first edition manytimes: extreme events, dire warnings about Green-house warming, El NioSouthern Oscillation predic-tion . . . Little has changed in the fifteen years sinceI wrote about them. I am still perplexed becauseextreme events continue to happen and global

warming is no closer to occurring. As Sydney in

February 2004 experienced a heat wave of a magnitudeunprecedented since at least 1939, I was chasing myfavourite research topic cosmogenically inducedmega-tsunami on Stewart Island, New Zealand sometwo thousand kilometres away where an unprece-dented cold snap was occurring. One event witnessedby four million people got all the publicity; the otherplayed out in a remote cabin in front of half of dozentrekkers got none. Yet both climatic extremes wereproduced by the same pattern of atmospheric circula-tion controlled by the same sequence of mobile polar

highs. Sydney lay on the equatorial greenhouse side ofthe highs and Stewart Island lay on the poleward IceAge side. This book covers two of the phenomenaI experienced in my February of extremes mobilepolar highs and tsunami. As with the first edition, thebook does not cover the third phenomena, Green-house warming. This book is about everyday climaticand geological hazards that can be explained, pre-dicted, and alleviated. Global warming is mentionedand is covered by the concept of changing hazardregimes. However, heat waves and cold snaps are

about everyday hazards that we have lived with, willcontinue to experience, and hopefully can survive.These concepts are what this second edition is about.

In order to convey this point of view clearly in thebook, adherence to academic referencing has been keptto a minimum. Usually each section begins by listing themajor papers or books on a topic that have influenced

my thinking and writing. Full reference to these publi-cations can be found at the end of each chapter. I apol-ogize to anyone who feels that their crucial work hasbeen ignored; but the breadth of coverage in thistextbook precluded a complete review of the literatureon many topics including some of my own.

Manuscript preparation is quite different now fromwhat it was in the late 1980s when the first edition wasbeing published. For one thing, the software programsfor scanning, image enhancement, graphics, and wordprocessing are far more comprehensive and efficient

at doing tasks. The diagrams in the first edition werehand-drawn, a technique that is rarely used today.Readers will find that many of those diagrams remainin this version. However, many have been revampedusing graphics software. New computer-prepareddiagrams have also been added. Word processingpackages now allow spelling and grammar to bechecked uniformly without the assistance of a copy-editor. Minor changes have been made to text retainedfrom the first edition using this capability. TheInternet was in it infancy when the first edition was

Preface


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prepared. It is now very easy to capture all the argu-ments or theories related to a hazard topic via thismedium. Where the Internet was used to prepare thecurrent edition, the web sites have been referenced inthe text and their full addresses appended to individ-ual chapters. The reader should be aware that some of

these addresses may not be available to them becausethey have changed, or because of the lack of anarchival tradition on the Internet.

Ted Bryant9 August 2004

xiv Preface


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Several people generously provided data from theirown research as follows: Jane Cook, formerly of theFaculty of Education, University of Wollongong for herKiama landslip data in figure 2.11; Professor Eric Bird,formerly of the Department of Geography, Universityof Melbourne for updating table 8.2; Dr. GeoffBoughton, TimberED Services Pty Ltd., Glengarry,

Western Australia, for information on the lowerlimits of seismically induced liquefaction; Col Johnson,New South Wales South Coast State EmergencyServices for pointing out the importance of CriticalIncident Stress Syndrome amongst rescue workers;Rob Fleming, Australian Counter Disaster College,Mt Macedon, Victoria for access to photographic fileson hazards in Australia; and Bert Roberts, Schoolof Earth and Environmental Sciences, University of

Wollongong for pointing out the relative literature onuniformitarianism.

The following people or publishers permitteddiagrams or tables to be reproduced: University ofWisconsin Press, for figure 2.4; Methuen, London forfigures 3.12 and 3.14; Harcourt Brace JovanovichGroup, Academic Press, Sydney for figures 9.9 and11.7; Butterworths, Sydney for figures 12.2 and 12.13;and Dr. John Whittow, former at the Department ofGeography, University of Reading for figures 12.12 and12.16. Acknowledgment is made to the following orga-nizations who did not require permission on copy-righted material: NOAA for figures 3.7, 3.8, 4.6a & b,

4.9, 4.10, and 11.5; United States Jet PropulsionLaboratory for figure 8.4; the United States GeologicalSurvey for figures 10.5, 10.7, 10.10, 10.14, 10.15, 11.2,11.3, and 12.11; the United States Marine FisheriesService, Seattle for Table 2.1; and the American Geo-physical Union for Table 2.2. All of the above diagramsand tables are acknowledged fully in the text.

The following people or organizations providedphotographic material: John Fairfax and Sons Limited,for figures 3.6, 7.9 and 13.1; Dr. Geoff Boughton,TimberED Services Pty Ltd., Glengarry, WesternAustralia, for figures 3.9a & b; the Canadian Atmos-pheric Environment Service for figures 3.22 and 3.24;the Australian Bureau of Meteorology for figure 3.29;John Telford, Fairymeadow, New South Wales forfigure 8.5; Dr. Ann Young, for figure 8.13; Bob Webb,Mal Bilaniwskyj and Charles Owen, New South WalesDepartment of Main Roads, Wollongong and Bellambi

Offices for figure 2.9a and b; the State Library of Victoria who kindly permitted the reproduction of William Strutts painting entitled Black Thursdayappearing as figure 7.1; N.P. Cheney, Director, andA.G. Edward, National Bushfire Research Unit,CSIRO, Canberra for figures 7.4a and 7.5 respectively;Jim Bryant, for figure 7.4b; Director Naval VisualNews Service, US Navy Office of Information forfigure 7.6; J.L. Ruhle and Associates, Fullerton, Cali-fornia for figure 11.12; A.G. Black, Senior Soil Conser-

vator, Hawkes Bay Catchment Board (Hawkes Bay

Acknowledgements


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Regional Council), Napier, New Zealand for figure12.10; and Dr. Peter Lowenstein for figure 12.14,courtesy C.O. McKee, Principal Government Volca-nologist, Rabaul Volcanological Observatory, Depart-ment of Minerals and Energy, Papua New GuineaGeological Survey.

I am indebted to the staff and associates of Cam-bridge University Press, Melbourne: Peter Debus whoencouraged a second edition of the hazards text, SusanKeogh who oversaw the publishing process, MoniqueKelly who processed the figures, and Malory Weston

who copyedited the manuscript. The majority of this

text has been presented as lecture material. I wouldlike to thank many students in my first and second

year Hazards and Climatology classes who challengedmy ideas or rose enthusiastically to support them.Unfortunately, current students have no access to thesesubjects. I hope that this textbook makes up for the

deficiency. Finally, I would like to thank my familywho kindly tolerated my next textbook and deflectedmany of the requests upon my time by friends whodid not realize the magnitude of the task of writing asecond edition.

xvi Acknowledgements


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RATIONALE

The field of environmental studies is usually intro-duced to students as one of two themes. The firstexamines human effects upon the Earths environ-ment, and is concerned ultimately with the question of

whether or not people can irreversibly alter that envi-ronment. Such studies include the effect of humanimpact on climate, of land-use practices on the land-scape in prehistoric and recent times, and of nuclear

war upon the Earths environment. The second themetotally disregards this question of human impact on theenvironment. It assumes that people are specks of dustmoving through time subject to the whims of nature.In this sense, calamities are acts of God, events thatmake the headlines on the evening news, events youmight wish on your worst enemy but would never wantto witness yourself.

University and college courses dealing with this lattertheme usually treat people as living within a hostileenvironment over which they have little control. Suchcourses go by the name of Natural Hazards. The dif-ference between the two themes is aptly summarizedby Sidle et al. (2003). Both themes describe hazards.The first theme can be categorized as chronic while thesecond is episodic or periodic. Chronic hazards wouldinclude desertification, soildegradation, and melting ofpermafrost. The causes could be due to humans orglobal warming. Periodic hazards are large magnitude

events that appear over a short time period. Theyinclude phenomena such as earthquakes, tsunami,

volcanic eruptions and flashfloods. This book dealsmainly with episodic hazards, events that wreak havocupon humans. However, the message is not one of totaldoom and gloom. Humans choose hazardous areasbecause they often offer benefits. For example, ashfrom volcanoes produces rich soils that can grow threecrops per year in the tropics, and floodplains provideeasily cultivated agricultural land close to a watersupply. Humans in these environments are forced topredict and avoid natural calamities such as landslides,cyclones, earthquakes, and drought. Or as Middleton(1995) states, a hazard should be seen as an occasion-ally disadvantageous aspect of a phenomenon, whichis often beneficial to human activity over a differenttimescale. For those hazards that cannot be avoidedby humans, this book also examines how people

can minimize their effects and rectify their negativeconsequences.The book is organized around climatic and geologi-

cal hazards. Intense storms and winds, oceanographicfactors such as waves, ice and sea level changes,together with extreme precipitation phenomena, areall investigated under the heading of climatic hazards.Earthquakes, volcanoes, and land instability areexamined under the topic of geological hazards. Thisbook is not concerned overly with biological hazardssuch as plague, disease, and insect infestations; but one

Introduction toNatural Hazards

C H A P T E R 1


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should realize that death and property loss from theselatter perils can be just as severe as, if not worse than,those generated by geological and climatic hazards. Afinal section examines the social impact of hazards.

HISTORICAL BACKGROUND

The world of myths and legends(Holmes, 1965; Day, 1984; Myles, 1985; Milne, 1986;

Bryant, 2001)

Myths are traditional stories focusing on the deeds ofgods or heroes, often to explain some natural phenom-enon, while legends refer to some historical eventhanded down usually by word of mouth in traditionalsocieties. Both incorporate natural hazard events. Pre-historic peoples viewed many natural disasters with

shock and as a threat to existence. Hazards had to beexplained and were often set within a world of animisticgods. Such myths remain a feature of belief systems formany peoples across the world from Aborigines inAustralia and Melanesians in the South Pacific, to theindigenous inhabitants of the Americas and the ArcticCircle. With the development of written language,many of these oral myths and legends were incor-porated into the writings of the great religions of the

world. Nowhere is this more evident than with storiesabout the great flood. Along with stories of Creation,the Deluge is an almost ubiquitous theme. The biblicalaccount has remarkable similarities to the BabylonianEpic of Gilgamesh. In this epic, Utnapishtim, whoactually existed as the tenth king of Babylon, replacesNoah, who was the tenth descendant of Adam. Thebiblical account parallels the epic, which tells of thebuilding of an ark, the loading of it with different animalspecies, and the landing of the ark upon a remotemountaintop. Babylonian civilization was founded in

what was called Mesopotamia, situated in the basin of

the Euphrates and Tigris Rivers, which historically havebeen subject to cataclysmic flooding. Clay deposits inexcess of 2 m have been found at Ur, suggesting atorrential rain event in the headwaters of the valley thatcaused rivers to carry enormous suspension loads athigh concentrations.

Such an event was not unique. The epic and biblicalaccounts are undoubtedly contemporaneous and, infact, a similar major flood appears in the writtenaccounts of all civilized societies throughout MiddleEastern countries. For example, broken tablets found in

the library of Ashurbanipal I (668626 BC) of Assyria, atNippur in the lower Euphrates Valley, also recount theBabylonian legend. The Deluge also appears worldwidein verbal and written myths. The Spanish conquista-dores were startled by flood legends in Mexico that borea remarkable similarity to the biblical account. Because

these staunchly Catholic invaders saw the legends asblasphemous, they ordered the destruction of all writtennative references to the Deluge. The similarities weremost remarkable with the Zapotecs of Mexico. The heroof their legend was Tezpi, who built a raft and loaded it

with his family and animals. When the god Tezxatlipocaordered the floodwaters to subside, Tezpi released firstlya vulture and then other fowl, which failed to return.

When a hummingbird brought back a leafy twig,Tezpi abandoned his raft on Mt Colhuacan. A Hawaiianlegend even has a rainbow appearing, which signals

a request for forgiveness by their god Kane for hisdestructiveness. Almost all legends ascribe the flood tothe wrath of a god. The Australian Aborigines have astory about a frog named Tiddalik drinking all the waterin the world. To get the water back, all the animals tryunsuccessfully to get the frog to laugh. Finally, a cavort-ing eel manages the task. However, the frog disgorgesmore water than expected and the whole Earth isflooded. In some myths, floods are attributed to animalsurinating after being picked up. Many myths areconcerned with human taboo violations, womensmenstruation, or human carelessness. Almost all storieshave a forewarning of the disaster, the survival of achosen few, and a sudden onset of rain. However, theBible has water issuing from the ground, as do Chinese,Egyptian, and Malaysian accounts. The latter aspectmay refer to earthquakes breaking reservoirs orimpounded lakes. Many Pacific island and Chileanlegends recount a swelling of the ocean, in obvious ref-erence to tsunami. Despite the similarities of legendsglobally amongst unconnected cultures, there is no geo-

logical evidence for contemporaneous flooding of theentire world, or over continents. It would appear thatmost of the flood myths recount localized deluges, andare an attempt by human beings to rationalize the floodhazard.

Almost as ubiquitous as the legends about flood areones describing volcanism or the disappearance ofcontinents. North American natives refer to sunken landto the east; the Aztecs of Mexico believed they weredescended from a people called Az, from the lost landof Aztln. The Mayas of Central America referred to a

2 Natural Hazards


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church. John Wesley viewed the earthquake as Godspunishment for the licentious behavior of believersin Lisbon, and retribution for the severity of thePortuguese Inquisition. Immanuel Kant and Jean-Jacques Rousseau viewed the disaster as a naturalevent, and emphasized the need to avoid building in

hazardous places.The Lisbon earthquake also initiated scientific study

of geological events. In 1760, John Mitchell, GeologyProfessor at Cambridge University, documented thespatial effects of the earthquake on lake levels through-out Europe. He found that no seiching was reportedcloser to the city than 700 km, nor further away than2500 km. The seiching affected the open coastline ofthe North Sea and shorelines in Norwegian fjords,Scottish lochs, Swiss alpine lakes, and rivers and canalsin western Germany and the Netherlands. He deduced

that there must have been a progressive, wave-liketilting movement of the Earth outward from the centerof the earthquake, different to the type of waveproduced by a volcanic explosion.

Mitchells 1760 work on the Lisbon earthquake effec-tively represents the separation of two completely dif-ferent philosophies for viewing the physical behavior ofthe natural world. Beforehand, the Catastrophists dom-inated geological methodology. These were the people

who believed that the shape of the Earths surface, thestratigraphic breaks appearing in rock columns, andthe large events associated with observable processes

were cataclysmic. Catastrophists believed events had tobe cataclysmic to allow the geological record to fit withthe date for the Earths creation of 4004 BC, as deter-mined by Biblical genealogy. Charles Lyell, one of thefathers of geology, sought to replace this catastrophetheory with gradualism the idea that geological andgeomorphic features were the result of cumulative slowchange by natural processes operating at relativelyconstant rates. This idea implied that processes shaping

the Earths surface followed laws of nature as defined byphysicists and mathematicians as far back as Bacon.William Whewell, in a review of Lyells work, coined thetermuniformitarianism, and subsequently a protracteddebate broke out about whether or not the slowprocesses we observe at present apply to past unobserv-able events. The phrase The present is the key to thepast also arose at this time and added to the debate.

In fact, the idea of uniformitarianism involves twoconcepts. The first implies that geological processesfollow natural laws applicable to science. There are no

acts of God. This type of uniformitarianism wasestablished to counter the arguments raised by theCatastrophists. The second concept implies constancyof rates of change or material condition through time.This concept is nothing more than inductive reasoning.The type and rate of processes operating today charac-

terize those that have operated over geological time.For example, waves break upon a beach today in thesame manner that they would have one hundredmillion years ago, and prehistoric tsunami behave thesame as modern ones described in our written records.If one wants to understand the sedimentary deposits ofan ancient tidal estuary, one has to do no more than goto a modern estuary and study the processes at work.Included in this concept is the belief that physical land-scapes such as modern floodplains and coastlinesevolve slowly.

Few geomorphologists or geologists who study earthsurface processes and the evolution of modern land-scapes would initially object to the above concept ofconstancy. However, it does not withstand scrutiny.For example, there is no modern analogy to thenappe mountain building processes that formed theEuropean Alps or to the mass extinctions and suddendiscontinuities that have dominated the geologicalrecord. Additionally, no one who has witnessed a

fault line being upthrusted during an earthquake, orMt St Helens wrenching itself apart in a cataclysmiceruption, would agree that all landscapes developslowly. As Thomas Huxley so aptly worded it, gradual-ists had saddled themselves with the tenet ofNatura

non facit saltum Nature does not make suddenjumps. J. Harlen Bretz from the University of Chicagochallenged this tenet in the 1920s. Bretz attributed theformation of the scablands of eastern Washington tocatastrophic floods. For the next forty years, he borethe ridicule and invectiveness of the geological estab-lishment for proposing this radical idea. It was not until

the 1960s that Bretz was proved correct when VicBaker of the University of Arizona interpreted spaceprobe images of enormous channels on Mars asfeatures similar to the Washington scablands. At theage of 83, Bretz finally received the recognition of hispeers for his seminal work.

Convulsive events are important climatic and geolog-ical processes, but are they likely to occur today? This isa major question cropping up throughout this book.The climatic and geological processes responsible formost hazards can be described succinctly. However, do

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major disasters, simply are unfortunate to be living inareas experiencing large-scale climatic change or

tectonic activity. After all, European populations werebadly decimated by the climatic cooling that occurredafter the middle of the fourteenth century andeveryone knows that the Los Angeles area is well

overdue for a major earthquake. One might also arguethat Third World countries bring much of the disasterupon themselves. In many countries afflicted by largedeath tolls due to drought or storms, the politicalsystems are inefficient, corrupt, or in a state of civil war.If governments in Third World countries took nationalmeasures to change their social structure, they wouldnot be so vulnerable to natural disasters. For example,Japan, which occupies a very hazardous earthquakezone, has performed this feat through industrializationin the twentieth century. One might further argue that

Australians or Americans cannot be held responsiblefor the misery of the Third World. Apart from foreignaid, there is little we can do to alleviate their plight.

The Marxist view disagrees with all these views.Marxism stipulates that western, developed nations arepartially responsible for, and perpetuate the effect ofdisasters upon, people in the Third World because weexploit their resources and cash-cropping modes of pro-duction. The fact that we give foreign aid is irrelevant. Ifour foreign aid is being siphoned off by corrupt officials,or used to build highly technical projects that do notdirectly alleviate the impoverished, then it may only bekeeping underprivileged people in a state of povertyor, it is suggested, further marginalizing the alreadyoppressed and thus exacerbating their risk to naturalhazards. Even disaster relief maintains the status quoand generally prohibits a change in the status of peasantsregarding their mode of production or impoverishment.

The basis of Marxist theory on hazards can be sum-marized as follows: the forms of exploitation in Third World countries

increase the frequency of natural disasters as socio-economic conditions and the physical environmentdeteriorate;

the poorest classes suffer the most; disaster relief maintains the status quo, and works

against the poor even if it is intentionally directed tothem; and

measures to prevent or minimize the effects ofdisasters, which rely upon high technology, reinforcethe conditions of underdevelopment, exploitation andpoverty.

Marxist philosophy does not form the basis of thisbook. It has been presented simply to make the readeraware that there are alternative viewpoints about theeffects of natural hazards. The Marxist view is basedupon the structure of societies or cultures, and howthose societies or cultures are able to respond to

changes in the natural environment. The frameworkof this book, on the other hand, is centered on thedescription and explanation of natural hazards that canbe viewed mainly as uncontrollable events happeningcontinually over time. The frequency and magnitude ofthese events may vary with time, and particular typesof events may be restricted in their worldwide occur-rence. However, natural hazards cannot be singled outin time and space and considered only when they affecta vulnerable society. An understanding of how, whereand when hazards take place can be achieved only by

studying all occurrences of that disaster. The arrival ofa tropical cyclone at Darwin, with the loss of 64 lives,is just as important as the arrival of a similar-sizedcyclone in Honduras, with the loss of 8000 lives.Studies of both events contribute to our knowledge ofthe effects of such disasters upon society and permit usto evaluate how societies respond subsequently.

Hazard statistics (Changnon & Hewings, 2001;CRED, 2002; Balling & Cerveny, 2003)

Figure 1.1 plots the number of hazards by region overthe period 19752001. The map excludes epidemics orfamine. Despite its large population, Africa is relativelydevoid of natural hazards. This is due to the tectonicstability of the continent and the fact that tropicalstorms do not develop here, except in the extremesouth-east. However the African population is affecteddisproportionately by drought. The frequency ofevents over the rest of the world reflects the domi-nance of climate as a control on the occurrence ofnatural hazards. This aspect is illustrated further for

the twentieth century in Table 1.1. The most frequenthazards are tornadoes, the majority of which occur inthe United States. Over the latter half of the twentiethcentury, their frequency more than 250 events per

year exceeds any other natural hazard. Climaticallyinduced floods and tropical cyclones follow this phe-nomenon in frequency. Tsunami, ranked fourth, is themost frequent geological hazard, followed by damagingearthquakes with nine significant events per year. Alltotalled, climatic hazards account for 86.2 per cent ofthe significant hazard events of the twentieth century.

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The economic relevance of the biggest hundred ofthese hazard events is summarized over the sameperiod in Table 1.2. Values are reported in US dollarsand do not include inflation. Earthquakes, while

ranking only fifth in occurrence, have been the costli-est hazard ($US249 billion), followed by floods($US207 billion), tropical storms ($US80 billion), and

windstorms ($US44 billion). In total, the hundred most

expensive natural disasters of the twentieth centurycaused $US631 billion damage. The single largestevent was the Kobe earthquake of 20 January 1995,

which cost $US131.5 billion. While this event isfamiliar, the second most expensive disaster of thetwentieth century floods in the European part ofthe former Soviet Union on 27 April 1991 costing$US60 billion is virtually unknown.

Figure 1.2 presents the number of hazards reportedeach year over the twentieth century. Apparently,natural hazards have increased in frequency over this

7Introduction to Natural Hazards

1000

500

250

No. of Events

Fig. 1.1 Incidence of natural hazards by region 19752001 (based on CRED, 2002).

Type of Hazard No of Events

Tornadoes (US)1 9476

Flood 2389Tropical Cyclone 1337

Tsunami 986

Earthquake 899

Wind (other) 793

Drought 782

Landslide 448

Wild fire 269

Extreme temperature 259

Temperate winter storm 240

Volcano 168

Tornadoes (non-US) 84Famine 77

Storm surge 18

1 for F2F5 tornadoes 19501995

Table 1.1 Frequency of natural hazards during the twentieth

century. Tsunami data comes from the Intergovernmental

Oceanographic Commission (2003). Tornado statistics for

the USA are for the 19901995 period only and derived

from the High Plains Regional Climate Center (2003). All

other data based on WHO (2002).Type Cost

Earthquake $248,624,900,000

Flood $206,639,800,000

Tropical storm $80,077,700,000

Wind Storm $43,890,000,000

Wild Fire $20,212,800,000Drought $16,800,000,000

Cold wave $9,555,000,000

Heat wave $5,450,000,000

Total $631,250,200,000

Table 1.2 Cost of natural hazards, summarized by type of hazard

for the 100 biggest events, 19002001 (based on

WHO, 2002).


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time span from around ten events per year at the begin-ning of the century to over 450 events at the end. Whileincreased vigilance and perception of natural hazardsaccounts for part of this increase, other data suggest thatnatural hazards are on the increase. The fact that thesefigures include both geological and climatic hazardsrules out such a simple explanation as global warming as

a major cause of this increased incidence. On the otherhand, these figures should be treated with some cautionbecause they do not always hold under scrutiny. Forexample, in the United States, the magnitude and fre-quency of thunderstorms, hailstorms, intense tornadoes,hurricanes and winter storms have not increased, butmay have decreased. Over the same period, there is noincrease in the cost of climatic hazards after the figuresare adjusted for inflation. Instead, damaging eventsappear to recur at twenty-year intervals around19501954, 19701974, and 19901994. This timing

coincides with the peak of the 18.6 MN lunar cycle,which will be described in Chapter 2.Figure 1.3 presents the number of deaths due to

natural hazards over the twentieth century. The timeseries does not include biological hazards such as epi-demics or insect predation; however, it does includedrought-induced famines. The number of deaths isplotted on a logarithmic scale because there have beenisolated events where the death toll has exceeded thelong-term trend by several million. On average 275 000people have died each year because of natural hazards.

If famine is removed from the data set, this numberdeclines to 140 200 deaths per year. This reductionsuggests that famine kills 134 800 people per year,roughly 50 per cent of the total number. Although thegreatest number of deaths occurred in the 1930s afigure that can be attributed to political upheaval andcivil war there is no significant variation over the

twentieth century. This fact suggests that improved warning and prevention of natural hazards hasbalanced population increases resulting in a constantdeath toll. Many world organizations would considerseveral hundred thousand deaths per year due tonatural hazards as unacceptable.

Table 1.3 presents the accumulated number ofdeaths, injuries and homeless for each type of hazardfor the twentieth century. Also presented is the largestevent in terms of death for each category. The greatesthazard during the twentieth century was flooding;

however much of this was due to civil unrest. Halfof the 6.9 million death toll occurred in China inthe 1930s where neglect and deliberate sabotageaugmented deaths. Earthquakes and tropical cyclonesaccount for the other significant death tolls of thetwentieth century. Interestingly, during the first three

years of the twenty-first century 4242 deaths werecaused by cold waves. This is 60 per cent of the totalfor the whole of the twentieth century despite the per-ception of global warming. In contrast, the death tollfrom a heat wave in France in 2003 resulted in 15 000

8 Natural Hazards

100

200

300

400

500

0

Num

bero

fdisas

tersreporte

d

1900 1920 1940 1960 1980 2000Year

Exponential trend line

Fig. 1.2 Reporting incidence of natural hazards over time 19002001 (based on CRED, 2002).


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deaths, more than could be attributed to this causeduring the whole of the twentieth century. Obviously,the statistics presented in Table 1.3 underestimateactual deaths, mainly because data were simply notcollected for some hazards until recent times.

Table 1.3 also presents the number of injured anddisplaced people due to natural catastrophes in thetwentieth century. Often hazard statistics concentrate

upon death, not taking into account the walking wounded and the homeless who put a greater, more

lasting burden, upon society. Eighteen times morepeople were made homeless by floods in the twentiethcentury than were killed. This ratio rises to 30 and344 times respectively for tropical cyclones and extra-tropical storms. For example, the January 1998 icestorm that paralyzed Montreal killed twenty-five people.However up to 100 000 people were made homelessfor up to a month afterwards because of the failure of

electricity supplies as temperatures dipped to 40C.


10

100

1000

10000

100000

1000000

10000000

Numberofannualdea

ths

1900 1920 1940 1960 1980 2000Year

Significant deaths due to drought or famine

Fig. 1.3 Deaths from natural hazards over time 19002001 (based on CRED, 2002).

Type of Hazard Deaths Injuries Homeless Largest death toll event and date Death toll

Floods 6 851 740 1 033 572 123 009 662 China, July 1931 3 700 000

Earthquakes 1 816 119 1 147 676 8 953 296 Tangshan, China, July 1976 242 000

Tropical cyclones 1 147 877 906 311 34 272 470 Bangladesh, Nov 1970 300 000

Volcano 96 770 11 154 197 790 Martinique, May 1902 30 000

Landslides,

avalanches,

mud flows 60 501 8 071 3 759 329 Soviet Union, 1949 12 000

Extra-tropical storms 36 681 117 925 12 606 891 Northern Europe, Feb 1953 4 000

Heat wave 14 732 1 364 0 India, May 1998 2 541

Tsunami 10 754 789 Sanriku Japan, Mar 1933 3 000

Cold wave 6 807 1 307 17 340 India, Dec 1982 400

Tornado 7 917 27 887 575 511 Bangladesh, Apr 1989 800

Fires 2 503 1 658 140 776 USA, Oct 1918 1 000

Total 10 052 401 3 257 714 183 533 065

Table 1.3 Number of people killed, injured or displaced due to natural hazards during the twentieth century (based on WHO, 2002).


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CHAPTER OUTLINES

While this book has been written assuming little priorknowledge in Earth science at the university level,there are occasions where basic terminology (jargon)has had to be used in explanations. More explicit

definitions of some of these terms can be found in theglossary at the end of the book. You may have noticedalready that some words in this book have beenitalicized. These terms are defined or explained furtherin the glossary. Note that book titles, names of shipsand botanical names are also italicized, but they do notappear in the glossary.

Individual chapters are arranged around a specificconcept or type of hazard. The mechanisms controllingand predicting this particular hazards occurrence areoutlined and some of the more disastrous occurrences

worldwide are summarized. Where appropriate, someof humankinds responses to, or attempts at mitigating,the hazard are outlined.

The hazards covered in this book are summarized inTable 1.4, with a chapter reference for each hazardshown in the last column. The hazards, assessedsubjectively, are listed in the order that reflects theemphasis given to each in the text. Table 1.4 also gradesthe hazards, on a scale of 1 to 5, as to degree of severity,time span of the event, spatial extent, total death toll,

economic consequences, social disruption, long-termimpact, lack of prior warning or suddenness of onset,and number of associated hazards. The overall socio-economicphysiological impact of the hazard is rankedusing these criteria. The most important global hazardis drought, followed by tropical cyclones, regionalfloods, and earthquakes. Three of these four tophazards rank highest for cost (Table 1.2) and humanimpact (Table 1.3). These latter two tables do notevaluate drought because it develops so slowly andinsidiously that it is often ignored when event statistics

are collected. Of the top ten hazards, six are climaticallyinduced. Table 1.4 has been constructed for worldhazards. The ranking differs for individual countriesand latitudes. For example, the ranking of hazards inthe United States in terms of economic loss is tropicalstorms, floods, severe thunderstorms, tornadoes, extra-tropical storms, hail, and wind.

The hazards in the book are organized under twomain parts: climatic hazards and geological hazards.Climatic hazards are introduced in Chapter 2, whichoutlines the mechanisms responsible for climatic vari-

ability. This chapter covers the basic processes of airmovement across the surface of the globe, the conceptof mobile polar highs, airocean temperature inter-actions resulting in the Southern, North Atlantic andNorth Pacific oscillations, and the effect of astronomicalcycles (such as sunspots and the 18.6-year lunar tide) on

the timing of climate hazard events.A description of large-scale storms is then covered

in Chapter 3. This chapter discusses the formation oflarge-scale tropical vortices known as tropical cyclones.Tropical cyclones are the second most importanthazard, generating the greatest range of associatedhazard phenomena. Familiar cyclone disaster eventsare described together with their development, magni-tude and frequency, geological significance, andimpact. The response to cyclone warnings in Australiais then compared to that in the United States and

Bangladesh. Extra-tropical cyclones are subsequentlydescribed with reference to major storms in thenorthern hemisphere. These storms encompass rain,snow, and freezing rain as major hazards. Storm surgesproduced by the above phenomena are then described.Here, the concepts of probability of occurrence andexceedence are introduced. The chapter concludes

with a description of dust storms as a significant factorin long-term land degradation.

Chapter 4 summarizes smaller hazards generatedby wind. Attention is given to the description of thun-derstorms and their associated hazards. These includetornadoes, described in detail together with some ofthe more significant events. The chapter concludes

with a description of the measures used to averttornado disasters in the United States.

These chapters set the scene for two chapters dealing with longer lasting climatic disasters, namely droughtand floods. Chapter 5 deals with impact of humanactivity in exacerbating drought and peoples subsequentresponses to this calamitous hazard. Emphasis is placed

on pre- and post-colonial influences in the Sahel regionof Africa, followed by a discussion of modern impacts forcountries representative of a range of technologicaldevelopment. The second half of the chapter deals withhuman response by a variety of societies, from those

who expect drought as a natural part of life, to those whoare surprised by its occurrence and make little effort tominimize its impact. These responses cover Third WorldAfrican countries as well as developed westernizedcountries such as the United States, England, andAustralia. The chapter concludes by describing the way

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the international community alleviates drought. It isonly apt that this section emphasizes the inspirationaland enthusiastic role played by Bob Geldof during theEthiopian drought of the mid-1980s. The reaction to his

initiatives by individuals, regardless of their economic orpolitical allegiance, gives hope that the effects of eventhe worst natural calamities affecting humanity can beminimized.


1 largest or most significant 5 smallest or least significantNumber of

Degree of Length of Total areal Total loss Total Social Long term associated ChapterRank Event severity event extent of life economic loss effect impact Suddenness hazards location

1 Drought 1 1 1 1 1 1 1 4 3 5, 6

2 Tropical 1 2 2 2 2 2 1 5 1 2cyclone

3 Regional 2 2 2 1 1 1 2 4 3 5, 8flood

4 Earthquake 1 5 1 2 1 1 2 3 3 10, 11

5 Volcano 1 4 4 2 2 2 1 3 1 10, 12

6 Extra- 1 3 2 2 2 2 2 5 3 2tropicalstorm

7 Tsunami 2 4 1 2 2 2 3 4 5 11

8 Bushfire 3 3 3 3 3 3 3 2 5 9

9 Expansive 5 1 1 5 4 5 3 1 5 13soils

10 Sea-level 5 1 1 5 3 5 1 5 4 4rise

11 Icebergs 4 1 1 4 4 5 5 2 5 4

12 Dust storm 3 3 2 5 4 5 4 1 5 4

13 Landslides 4 2 2 4 4 4 5 2 5 13

14 Beach 5 2 2 5 4 4 4 2 5 4erosion

15 Debris 2 5 5 3 4 3 5 1 5 13avalanches

16 Creep & 5 1 2 5 4 5 4 2 5 13solifluction

17 Tornado 2 5 3 4 4 4 5 2 5 3

18 Snowstorm 4 3 3 5 4 4 5 2 4 7

19 Ice at shore 5 4 1 5 4 5 4 1 5 4

20 Flash flood 3 5 4 4 4 4 5 1 5 8

21 Thunderstorm 4 5 2 4 4 5 5 2 4 7

22 Lightning 4 5 2 4 4 5 5 1 5 7strike

23 Blizzard 4 3 4 4 4 5 5 1 5 7

24 Ocean waves 4 4 2 4 4 5 5 3 5 4

25 Hail storm 4 5 4 5 3 5 5 1 5 7

26 Freezing rain 4 4 5 5 4 4 5 1 5 7

27 Localized 5 4 3 5 5 5 5 1 5 3strong wind

28 Subsidence 4 3 5 5 4 4 5 3 5 13

29 Mud & debris 4 4 5 4 4 5 5 4 5 13flows

30 Air supported 4 5 5 4 5 5 5 2 5 13flows

31 Rockfalls 5 5 5 5 5 5 5 1 5 13

Table 1.4 Ranking of hazard characteristics and impact.


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Chapter 6 examines flash flood and regional floodingevents that are usually severe enough to invoke statesof emergency. In addition, regional flooding accountsfor the largest death toll registered for any type ofhazard. This chapter begins by introducing the climaticprocesses responsible for flash flooding. This is

followed by examples of flash flooding events in theUnited States and Australia. Regional flooding is dis-cussed in detail for the Mississippi River in the UnitedStates, the Hwang Ho River in China, and Australia

where floods are a general feature of the country.Drought-induced bushfires or forest fires are then

treated as a separate entity in Chapter 7. The conditionsfavoring intense bushfires and the causes of such disas-ters are described. Major natural fire disasters, includingin the United States and Australia, are then presented.Two of the main issues discussed in this chapter are the

continuing debate overprescribed burning as a strategyto mitigate the threat of fires (especially in urban areas),and the regularity with which fire history repeats itself.Both the causes of fires and the responses to themappear to have changed little between the ends of thenineteenth and twentieth centuries.

These climatic chapters are followed by Chapter 8sdiscussion of aquatic hazards encompassing a varietyof marine and lacustrine phenomena. Most of thesehazards affect few people, but they have long-termconsequences, especially if global warming becomessignificant over the next 50 years. Because of theirspatial extent and long period of operation, most ofthe phenomena in this chapter can be ranked asmiddle-order hazards. Waves are described first withthe theory for their generation. The worldwide occur-rence of large waves is discussed, based upon ship andsatellite observations. This is followed by a briefdescription of sea-ice phenomena in the ocean and atshore. One of the greatest concerns today is theimpending rise in sea level, supposedly occurring

because of melting of icecaps or thermal expansion ofoceans within the context of global warming. World- wide sea level data are presented to show that sealevels may not be rising globally as generally believed,but may be influenced in behavior by regional climaticchange. Finally, the chapter discusses the variousenvironmental mechanisms of sandy beach erosion(or accretion) caused mainly by changes in sea level,rainfall, or storminess. This evaluation utilizes anextensive data set of shoreline position and environ-mental variables collected for Stanwell Park Beach,

Australia. Much of the discussion in this chapter drawsupon the authors own research expertise.

Geological hazards forming the second part of thisbook are covered under the following chapterheadings: causes and prediction of earthquakes and

volcanoes; earthquakes and tsunami; volcanoes; and

land instability. Chapter 9 presents the worldwide distri-bution of earthquakes and volcanoes and a presentationof the scales for measuring earthquake magnitude. Thisis followed by an examination of causes of earthquakesand volcanoes under the headings of plate boundaries,hot spots, regional faulting, and the presence of reser-

voirs or dams. Next, the presence of clustering in theoccurrence of earthquakes and volcanoes is examined,followed by a discussion of the long-term prediction of

volcanic and seismic activity. The chapter concludeswith a presentation of the geophysical, geochemical, and

geomagnetic techniques for forecasting volcanicand seismic activity over the short term.

Two chapters that are concerned separately withearthquakes and volcanoes then follow this introductorychapter. Both hazards, because of their suddenness andhigh-energy release, have the potential to afflict humanbeings physically, economically, and socially. Both rankas the most severe geological hazards. Chapter 10 firstdescribes types of seismic waves and the global seismicrisk. Earthquake disasters and the seismic risk forAlaska, California and Japan are then described. Theassociated phenomenon of liquefaction or thixotropy,and its importance in earthquake damage, is sub-sequently presented. One of the major phenomenagenerated by earthquakes is tsunami. This phenomenonis described in detail, together with a presentationof major, worldwide tsunami disasters. The prediction oftsunami in the Pacific region is then discussed. Chapter11, on volcanoes, emphasizes types of volcanoes andassociated hazardous phenomena such as lava flows,tephra clouds, pyroclastic flows and base surges, gases

and acid rains, lahars (mud flows), and glacier bursts.The major disasters of Santorini (~1470 BC), Vesuvius(79 AD), Krakatau (1883), Mt Pele (1902), and Mt StHelens (1980) are then described in detail.

The section on geological hazards concludes, inChapter 12, with a comprehensive treatment of landinstability. This chapter opens with a description ofbasic soil mechanics including the concepts of stressand strain, friction and cohesion, shear strength ofsoils, pore-water pressure, and rigid, elastic, and plasticsolids. Land instability is then classified and described

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under the headings of expansive soils, creepandsolifluction, mud and debris flows, landslides andslumps, rockfalls, debris avalanches, and air-supportedflows. Many of these hazards rank in severity andimpact as middle-order events. For example, expansivesoils, while not causing loss of life, rank as one of the

costliest long-term hazards because of their ubiqui-tousness. For each of these categories, the type of landinstability is presented in detail, together with adescription of major disasters. The chapter concludes

with a cursory presentation on the natural causes ofland subsidence.

Because the emphasis of the previous chapters hasbeen on the physical mechanisms of hazards, the bookcloses in Chapter 13 with a discussion of the socialimpact of many of these phenomena. Here is empha-sized the way hazards are viewed by different societies

and cultures. This section is followed by detaileddescriptions of responses before, during, and after theevent. As much as possible, the characterization ofresponses under each of these headings is clarifiedusing anecdotes. It is shown that individuals or familieshave different ways of coping with, or reacting to,disaster. The chapter concludes by emphasizing thepsychological ramifications of a disaster on the victims,the rescuers, and society.

REFERENCES AND FURTHERREADING

Balling, R.C. and Cerveny, R.S. 2003. Compilation and discussion oftrends in severe storms in the United States: Popular perception

v. climate reality.Natural Hazards 29: 103112.Blong, R.J. 1982. The Time of Darkness, Local Legends and

Volcanic Reality in Papua New Guinea. Australian NationalUniversity Press, Canberra.

Bryant, E.A. 2001. Tsunami: The Underrated Hazard. CambridgeUniversity Press, Cambridge.

Changnon, S.A. and Hewings, G.J.D. 2001. Losses from weatherextremes in the United States. Natural Hazards Review 2:113123.

CRED 2002. EM-DAT: The OFDA/CRED International DisastersData Base. Center for Research on the Epidemiology of Disas-

ters, Universit Catholique de Louvain, Brussels,

Day, M.S. 1984. The Many Meanings of Myth. Lanham, NY.High Plains Regional Climate Center 2003. Annual average number

of strongviolent (F2F5) tornadoes 19501995. University ofNebraska, Lincoln, http://www.hprcc.unl.edu/nebraska/USTORNADOMAPS.html

Holmes, A. 1965. Principles of Physical Geology. Nelson, London.Huggett, R. 1997. Catastrophism: Asteroids, Comets and Other

Dynamic Events in Earth History. Verso, London.Intergovernmental Oceanographic Commission 2003. On-line

Pacific, Atlantic, and Mediterranean Tsunami Catalog.

Tsunami Laboratory, Institute of Computational Mathematicsand Mathematical Geophysics, Siberian Division, RussianAcademy of Sciences, Novosibirsk, Russia,

Middleton, N. 1995. The Global Casino. Edward Arnold, London.Milne, A. 1986. Floodshock: the Drowning of Planet Earth. Sutton,

Gloucester.Myles, D. 1985. The Great Waves. McGraw-Hill, NY.Sidle, R.C., Taylor, D., Lu, X.X., Adger, W.N., Lowe, D.J., de Lange,

W.P., Newnham, R.M. and Dodson, J.R. 2003. Interaction ofnatural hazards and society in Austral-Asia: evidence in past andrecent records. Quaternary International 118119: 181203.

Susman, P., OKeefe, P. and Wisner, B. 1983. Global disasters, a

radical interpretation. In Hewitt, K. (ed.) Interpretations ofCalamity. Allen and Unwin, Sydney, pp. 263283.

Watts, M. 1983. On the poverty of theory: natural hazards researchin context. In Hewitt, K. (ed.) Interpretations of Calamity. Allenand Unwin, Sydney, pp. 231261.



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CLIMATICHAZARDSP A R T 1


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INTRODUCTION

Climatic hazards originate with the processes thatmove air across the Earths surface due to differentialheating and cooling. Surprisingly, examination of theseprocesses has focused upon heating at the tropics anddownplayed the role of cold air masses moving out of

polar regions due to deficits in the radiation balance inthese latter regions. Fluctuations in the intensity ofpulses of cold air moving out of polar regions orof heating at the equator and the location of theinteraction between these cold and warm air masses,are crucial factors in determining the magnitude, fre-quency, and location of mid-latitude storm systems.

While most of these factors are dictated by internalfactors in the Earthatmosphere system, modulationby 11-year geomagnetic cycles linked to solar activityand by the 18.6 year MN lunar tide also occurs. This

chapter examines these processes and mechanisms.The responses in terms of centers of storm activity willbe examined in the following chapter.

MODELS OF ATMOSPHERICCIRCULATION AND CHANGE

(Bryson & Murray, 1977; Lamb, 1982)

How air moves

Barometric pressure represents the weight of air abovea location on the Earths surface. When the weight of airover an area is greater than over adjacent areas, itis termed high pressure. When the weight of air islower, it is termed low pressure. Points of equalpressure across the Earths surface can be contouredusing isobars, and on weather maps contouring isgenerally performed at intervals of 4 hectopascals (hPa)or millibars (mb). Mean pressure for the Earth is1013.6 hPa. Wind is generated by air moving fromhigh to low pressure simply because a pressure gradient

exists owing to the difference in air density (Figure 2.1):the stronger the pressure gradient, the stronger thewind. This is represented graphically on weather mapsby relatively closely spaced isobars. In reality, wind doesnot flow down pressure gradients but blows almostparallel to isobars at the surface of the Earth because ofCoriolis force (Figure 2.1). This force exists becauseof the rotation of the Earth and is thus illusionary. Forexample, a person standing perfectly still at the pole

would appear to an observer viewing the Earth fromthe Moon to turn around in a complete circle every

Mechanisms ofClimate Variability

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18 Climatic Hazards

24 hours as the Earth rotates. However, a personstanding perfectly still at the equator would always

appear to be facing the same direction and not turningaround. Because of Coriolis force, wind tends to bedeflected to the left in the southern hemisphere and tothe right in the northern hemisphere. Coriolis force canbe expressed mathematically by the following equation:

Coriolis force = 2 sin 2.1where = rate of spin of the Earth

sin = latitude= wind speed

Clearly, the stronger the pressure gradient, thestronger the wind and the more wind will tend to bedeflected. This deflection forms a vortex. Also, thestronger the wind, the smaller and more intense isthe resulting vortex. Very strong vortices are known ashurricanes, typhoons, cyclones, and tornadoes. Coriolisforce varies across the surface of the globe because oflatitude and wind velocity. Coriolis force is zero at theequator (sin 0 = 0), and maximum at the pole(sin 90 = 1). The equator is a barrier to inter-hemispheric movement of storms because vortices

rotate in opposite directions in each hemisphere. Forexample, tropical cyclones cannot cross the equator

because they rotate clockwise in the southern hemi-sphere and anti-clockwise in the northern hemisphere.

PalmnNewton model of globalcirculation

Upward movement of air is a prerequisite for vortexdevelopment, with about 10 per cent of all airmovement taking place vertically. As air rises, it spiralsbecause of Coriolis force, and draws in adjacent air atthe surface. Rising air is unstable if it is warmer thanadjacent air, and instability is favored if latent heat can

be released through condensation. The faster air rises,the greater the velocity of surface winds spiraling intothe center of the vortex. Of course, in the oppositemanner, descending air spirals outward at the Earthssurface. These concepts can be combined to account forair movement in thetroposphere. The PalmnNewton

general air circulation model is one of the morethorough models in this regard (Figure 2.2). Intenseheating by the sun, at the equator, causes air to rise andspread out poleward in the upper troposphere. As thisair moves towards the poles, it cools through long wave

1012

hPa

1008

1004

1000

1012

hPa

1008

1004

1000

Weak

Strong

Potential wind

Actual wind

Wind strengthWind direction

Low

Low

High

High

wind deflected to the rightNorthern hemisphere

wind deflected to the leftSouthern hemisphere

Fig. 2.1 Wind movements relative to isobars, with and without Coriolis force (i.e. potential and actual).


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emission and begins to descend back to the Earthssurface around 2030 north and south of the solar

equator, forming high pressure at the ground. Uponreaching the Earths surface, this air either movespoleward or returns to the equator to form a closed cir-culation cell, termed a Hadley cell. Because of Coriolisforce, equatorial moving air forms two belts of easterly

trade winds astride the equator. Air tends to convergetowards the solar equator, and the uplift zone here istermed the intertropical convergence. Over the westernsides of oceans, the tropical easterlies pile up warm

water, resulting in convection of air that forms lowpressure and intense instability. In these regions, intense

vortices known as tropical cyclones develop preferen-tially. These will be described in Chapter 3.At the poles, air cools and spreads along the Earths

surface towards the equator. Where cold polar air meetsrelatively warmer, subtropical air at mid-latitudes, a cold

polar front develops with strong uplift and instability.Tornadoes and strong westerlies can be generated nearthe polar front over land, while intense extra-tropicalstorms develop near the polar front, especially over

water bodies. Tornadoes will be described in Chapter 4, while extra-tropical storms are described in the next

chapter. A belt of strong wind and storms dominatedby westerlies poleward of the polar front forms around

40 latitude in each hemisphere. These winds, known asthe roaring forties, are especially prominent in thesouthern hemisphere where winds blow unobstructedby land or, more importantly, by significant mountainranges. Maps of global winds support these aspects ofthe PalmnNewton model (Figure 2.3).

The PalmnNewton model has two limitations.First, the location of pressure cells within the modelis based upon averages over time. Second, becausethe model averages conditions, it tends to be static,

whereas the Earths atmosphere is very dynamic.

Additionally, the concept of Hadley circulation isoverly simplistic. In fact, rising air in the tropics is notuniform, but confined almost exclusively to narrowupdrafts within thunderstorms. At higher latitudes,large-scale circulation is distorted by relatively smalleddies. Other factors also control winds. For example,over the Greenland or Antarctic icecaps, enhancedradiative cooling forms large pools of cold air, whichcan accelerate downslope under gravity because of thelowfrictional coefficient of ice. Alternative models thatovercome some of these limitations will be presented.

19Mechanisms of Climate Variability

air flow

heat transport

Polar front

Polar jet

Subtropicaljet

Intertropicalconvergence

Tropopause

HADLEYCELL

Easterlytrades

Roaringforties

Polareasterlies

90 60 30 0

POLAR HIGH

SUB TROPICAL

HIGHEXTRATROPICAL

LOW MONSOONAL

LOW

Fig. 2.2 PalmnNewton schematic model of general air circulation between the pole and the equator.


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20 Climatic Hazards

Ice Ice

Ice Ice

January

2 4 6 8 10 12 14 16

Meters s-1

A

Ice Ice

Ice Ice

July

2 4 6 8 10 12 14 16

Meters s-1

B

Fig. 2.3 Location of mid-latitude westerly and easterly trade wind belts based on TOPEX/POSEIDON satellite observations A) January 1995,

B) July 1995 (Jet Propulsion Laboratory, 1995a, b).


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Changes in jet stream paths

Strong winds exist in the upper atmosphere adjacentto the tropopause boundary (Figure 2.2). The moresignificant of these is the polarjet stream on the equa-torial side of the polar front. This jet stream consists of

a zone of strong winds no more than 1 km deep and100 km wide, flowing downwind over a distance of1000 km or more. Wind speeds can reach in excessof 250 km hr1. The polar jet stream is most prominentand continuous in the northern hemisphere. Here, itforms over the Tibetan Plateau, where its position islinked with the seasonal onset and demise of theIndian monsoon. The jet loops northward over Japanand is deflected north by the Rocky Mountains. It thenswings south across the Great Plains of the UnitedStates, north-eastward (parallel to the Appalachian

Mountains), and exits North America off Newfound-land, dissipating over Iceland. Both the TibetanPlateau and the Rocky Mountains produce a resonanceeffect in wave patterns in the northern hemisphere,locking high pressure cells over Siberia and NorthAmerica with an intervening low pressure cell over thenorth Pacific Ocean. Barometric pressure, measuredalong the 60N parallel of latitude through these cells,reveals a quasi-stable planetary or Rossby wave.

In the northern hemisphere, the jet stream tends toform three to four Rossby waves extending through510 of latitude around the globe (Figure 2.4). Rossby

waves move a few hundred kilometres an hour fasterthan the Earth rotates and thus appear to propagatefrom west to east. Any disturbance in a Rossby wavethus promulgates downwind, such that a change in

weather in North America appears over Europeseveral days afterwards. This aspect gives coherenceto extreme events in weather across the northernhemisphere. Because there is a time lag in changes toRossby waves downwind from North America, fore-

casters can predict extreme events over Europe days inadvance. In some winters, the waves undergo amplifi-cation and loop further north and south than normal.Many researchers believe that changes in this loopingare responsible, not only for short-term drought(or rainfall), but also for semi-permanent climaticchange in a region extending from China to Europe.Sometimes the looping is so severe that winds in the jetstream simply take the path of least resistance, andproceed zonally (parallel to latitude), cutting off theloop. In this case, high and low pressure cells can be

left stranded in location for days or weeks, unable tobe shifted east by the prevailing westerly airflow.High-pressure cells are particularly vulnerable to thisprocess and form blocking highs. Blocking highsdeflect frontal lows to higher or lower latitudes thannormally expected, producing extremes in weather.Blocking is more characteristic of winter, especially inthe northern hemisphere. It also tends to occur overabnormally warm seas, on the western sides of oceans.

Expansion of the westerlies because of enhancedlooping of Rossby waves can be linked to recent failure


A

B

Fig. 2.4 Path of jet stream in the northern hemisphere showing

likely Rossby wave patterns A) for summer, B) for extreme

winter (Bryson & Murray, 1977 with the permission of

The University of Wisconsin Press).


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of monsoon rains and resulting drought in the Sahel inthe early 1970s. In the Sahara region, rain normallyfalls as theintertropical convergence moves seasonallynorthward. If westerlies expand, then such movementof the intertropical convergence is impeded anddrought conditions prevail. Drought in Britain can also

be linked to displacement northward of the jet streamand polar-front lows shifting into the Arctic insteadof crossing Scotland and Norway. This displacementleaves Britain under the influence of an extension ofthe Azores high-pressure system that is stable andrainfall-deficient. Blocking of this high leads to droughtfor several months. Blocking highs off the Californiancoast were also responsible for drought in the mid-United States in 1997, while highs over easternAustralia have led to some of the worst droughts in thatcontinents recorded history. The social response to

these types of droughts will be examined in Chapter 5.

Mobile polar highs (Leroux, 1993, 1998;Bryant, 1997)

The monsoonal circulation described above does notfit well within the PalmnNewton general circulationmodel. In fact, the positioning of Hadley cells, and thesemi-permanency of features such as the Icelandic orAleutian Lows, are statistical artefacts. There is not anIcelandic Low, locked into position over Iceland. Norare there consistent trades or polar easterlies. Aircirculation across the surface of the Earth is dynamic,as is the formation and demise of pressure cells. Inreality, the Icelandic Low may exist as an intense cell oflow pressure for several days, and then move eastwardtowards Europe within the westerly air stream.Climate change in the PalmnNewton model impliesthe movement, or change in magnitude, of thesecenters of activity. For example, weakening of the Ice-landic Low conveys the view that winter circulation isless severe, while expansion of Hadley cells towards

higher latitudes suggests that droughts shoulddominate mid-latitudes.There are other problems with terminology in the

PalmnNewton model; these have an historical basis.The depression, extra-tropical cyclone, or polar low

was initially explained as a thermal phenomenon, andthen linked to frontal uplift along the polar front, toupper air disturbances, and recently to planetary wavesor Rossby waves. The jet stream is supposedly tiedto the polar front, and related to cyclogenesis at mid-latitudes. However, the connection between the jet

stream and the polar front is approximate, and a clearrelationship has not been established between the jetstream in the upper troposphere and the formation oflow pressure at the Earths surface. Indeed, no onetheory adequately explains the initial formation of lowsat mid-latitudes. The PalmnNewton general circula-

tion model is a good teaching model, but it is not anideal model for explaining the causes of climatechange.

Conceptually, the PalmnNewton model in itssimplest form has two areas of forcing: upward airmovement at the equator from heating of the Earthssurface, and sinking of air at the poles because ofintense cooling caused by long wave emission. At theequator, air moves from higher latitudes to replacethe uplifted air, while at the poles subsiding air movestowards the equator as a cold dense mass hugging

the Earths surface. The lateral air movement at theequator is slow and weak, while that at the poles isstrong and rapid. Polar surging can reach within 10 ofthe equator, such that some of the lifting of air in thisregion can be explained by the magnitude and locationof polar outbursts. Hence, the dominant influence onglobal air circulation lies with outbursts of cold air

within polar high-pressure cells. Each of these out-bursts forms an event termed a mobile polar high.There is no separate belt of high pressure or Hadleycell in the subtropics. These cells, as they appear onsynoptic maps, are simply statistical averages over timeof the preferred pathways of polar air movementtowards the equator.

Mobile polar highs developing in polar regions areinitially maintained in position by surface cooling, airsubsidence and advection of warm air at higher alti-tudes. When enough cold air accumulates, it suddenlymoves away from the poles, forming a 1500 m thicklens of cold air. In both hemispheres, polar high out-breaks tend to move from west to east, thus conserving

vorticity. Additionally, in the southern hemisphere,pathways and the rate of movement are aided by theformation ofkatabatic winds off the Antarctic icecap(Figure 2.5). In the northern hemisphere, outburstpathways are controlled by topography with mobilepolar highs tending to occur over the Hudson Baylowland, Scandinavia and the Bering Sea (Figure 2.5).The distribution of oceans and continents, with theirattendant mountains, explains why the mean trajectoriesfollowed by these highs are always the same. Forinstance, over Australia, a polar outbreak always

22 Climatic Hazards


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approaches the continent from the southwest, and thenloops across the continent towards the equator, anddrifts in the Hadley belt out into the Tasman Sea.Highs rarely move directly northward across the conti-nent, or sweep up from the Tasman Sea. In NorthAmerica, mobile polar highs regularly surge southwardacross the Great Plains for the same reason.

Because mobile polar highs consist of dense air, theydeflect less dense, warm air upward and to the side.The deflection is greatest in the direction they aremoving. Hence, the polar high develops an extensivebulbous, high-pressure vortex, surrounded downdriftby a cyclonic branch or low-pressure cell (Figure 2.6).Typically, the high-pressure cell is bounded by anarching, polar cold front with a low pressure cell

attached to the leading edge. However, in the northernhemisphere, individual outbreaks tend to overlap sothat the low-pressure vortex becomes containedbetween two highs. This forms the classic V-shaped,

wedged frontal system associated with extratropicallows or depressions (Figure 2.6). Thus lows, and upper

westerly jet streams, are a product of the displacementand divergence of a mobile polar high. The intensity ofthe low-pressure cell becomes dependent upon thestrength of the polar high, and upon its ability todisplace the surrounding air. Strong polar highs

produce deep lows; weak highs generate weak lows. Ina conceptual sense, a deeper Icelandic or Aleutian Lowmust be associated with a stronger mobile polar high.If a mobile polar high is particularly cold, it can causethe air above to cool and settle. This creates lowpressure above the center of the high-pressure cell,

which can develop into a trough and then a cell asupper air flows inwards. If a mobile polar high has lostits momentum and stalled forming a blocking high,the low-pressure cell can intensify, propagate to theground, and generate a surface storm. This processoccurs most often on the eastern sides of continentsadjacent to mountain ranges such as the Appalachiansin the United States and the Great Dividing Range inAustralia. These storms will be discussed further in the

next chapter.Mobile polar highs tend to lose their momentumand stack up or agglutinate at particular locations overthe oceans. A blocking high is simply a stagnant mobilepolar high. Air pressure averaged over time thusproduces the illusion of two stable, tropical high-pressure belts known as Hadley cells on each sideof the equator. Mobile polar highs can propagate intothe tropics, especially in winter. Here, their arrivaltends to intensify the easterly trade winds. Moreimportant, yet little realized, is the fact that strong


Main outburstsMPH pathways

MPH boundaries mid-latitudes

Trade WindsMPH boundaries in tropics

Relief affecting MPH pathways

Fig. 2.5 Pathways for mobile polar highs (MPH) and resulting trade wind circulation in the tropics (based on Leroux, 1993).


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polar highs produce stronger monsoons, although in amore restricted tropical belt.

The Southern Oscillation

Introduction

The Earths general atmospheric circulation in thetropics and subtropics, as shown above, can be simplydescribed. However, the actual scene is slightly morecomplex. The intensity of mobile polar highs withina hemisphere varies annually with the apparent

movement of the sun north and south of the equator.There is also a subtle, but important, shift in the inten-sity of heating near the equator. In the northernhemisphere summer, heating shifts from equatorialregions to the Indian mainland with the onset of theIndian monsoon. Air is sucked into the Indian subcon-tinent from adjacent oceans and landmasses, to return

via upper air movement, to either southern Africa orthe central Pacific

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