Fundamentals of Physical Volcanology E-Book

Elisabeth Parfitt

• Herausgeber: John Wiley & Sons
• Kategorie: Wissenschaft und neue Technologien
• Sprache: Englisch

Seitenzahl: 704

Veröffentlichungsjahr: 2025

Beschreibung

The world’s leading student text on physical volcanology offers an unmatched introduction to the field

In the revised second edition of Fundamentals of Physical Volcanology, the authors provide a comprehensive introduction to the processes that control when and how volcanoes erupt. Understanding these processes involves bringing together ideas from a number of disciplines, including branches of geology, such as petrology and geochemistry, and aspects of physics, such as fluid dynamics and thermodynamics.

With the help of new and improved illustrations, this new edition explains eruption types and mechanisms, subsurface processes, volcanic eruption products, and how volcanoes affect their surrounding environment.

Readers will also find:

• Quantitative treatment of physical volcanological processes
• A review of the historical development of volcanology
• Examples of current research trends and topics in volcanology

Perfect for undergraduate earth sciences students and graduate students starting research programs in volcanology, Fundamentals of Physical Volcanology will also earn a place in the libraries of researchers in related fields seeking an accessible introduction to the principles of physical volcanology.

Leseprobe

Table of Contents

Cover

Table of Contents

Title Page

Copyright Page

Dedication

Preface

Acknowledgments

Glossary

1 Volcanic Systems

1.1 Introduction

1.2 Styles of Volcanic Eruptions

1.3 Volcanic Systems

1.4 The Structure and Aims of This Book

1.5 Further Reading

1.6 Questions to Think About

2 Magma Generation and Segregation

2.1 Introduction

2.2 Rock‐Melting Mechanisms

2.3 Volcanism and Plate Tectonics

2.4 Melting and Melt Segregation in the Mantle

2.5 Summary

2.6 Further Reading

2.7 Questions to Think About

3 Magma Migration

3.1 Introduction

3.2 Diapiric Rise of Melt

3.3 The Change From Diapir Rise to Dike Formation

3.4 Dike Propagation

3.5 Trapping of Dikes

3.6 Consequences of Dike Trapping

3.7 Summary

3.8 Further Reading

3.9 Questions to Think About

4 Magma Storage

4.1 Introduction

4.2 Evidence for Magma Storage Within the Crust

4.3 Formation and Growth of Magma Reservoirs

4.4 Magma Reservoirs and Their Impact on Volcanic Systems

4.5 Summary

4.6 Further Reading

4.7 Questions to Think About

5 The Role of Volatiles

5.1 Introduction

5.2 Volatiles in Magma

5.3 The Solubility of Volatiles in Magma

5.4 Bubble Nucleation

5.5 Bubble Growth

5.6 Influence of Volatiles on Magma Dynamics

5.7 Magma Fragmentation and the Influence of Volatiles on Eruption Styles

5.8 Summary

5.9 Further Reading

5.10 Questions to Think About

6 Steady Explosive Eruptions

6.1 Introduction

6.2 Influence of Gas Bubbles Prior to Magma Fragmentation

6.3 Acceleration of the Gas–Magma Mixture

6.4 Controls on Exit Velocity

6.5 Eruption Plumes in Steady Eruptions

6.6 Fallout of Clasts from Eruption Plumes

6.7 Unstable Eruption Columns

6.8 Summary

6.9 Further Reading

6.10 Questions to Think About

7 Transient Volcanic Eruptions

7.1 Introduction

7.2 Magmatic Explosions

7.3 Transient Eruptions Involving External Water

7.4 Summary

7.5 Further Reading

7.6 Questions to Think About

8 Pyroclastic Falls and Pyroclastic Density Currents

8.1 Introduction

8.2 Fallout of Clasts from Eruption Columns

8.3 The Application of Eruption Column Models

8.4 Pyroclastic Density Currents and Their Deposits

8.5 Summary

8.6 Further Reading

8.7 Questions to Think About

9 Lava Flows

9.1 Introduction

9.2 Origin of Lava Flows

9.3 Types of Lava Flows

9.4 Lava Flow Rheology

9.5 Rheological Control of Lava Flow Geometry

9.6 Lava Flow Motion

9.7 Lengths of Lava Flows

9.8 Surface Textures of Lava Flows

9.9 Effects of Ground Slope and Lava Viscosity

9.10 Summary

9.11 Further Reading

9.12 Questions to Think About

10 Eruption Styles, Scales, and Frequencies

10.1 Introduction

10.2 Chemical Composition and Styles of Volcanic Activity

10.3 Chemical Composition and Effusive Eruptions

10.4 Chemical Composition and Explosive Eruptions

10.5 Summary of Compositional Controls on Eruption Character

10.6 Magnitudes and Frequencies of Volcanic Eruptions

10.7 Elastic and Inelastic Eruptions and the Contribution of “Mush”

10.8 Eruptions of Exceptional Magnitude

10.9 Summary

10.10 Further Reading

10.11 Questions to Think About

11 Volcanic Hazards and Volcano Monitoring

11.1 Introduction

11.2 Types of Volcanic Hazards

11.3 Hazard Assessment

11.4 Monitoring Volcanoes and Short‐term Eruption Prediction

11.5 Hazard Mitigation

11.6 Summary

11.7 Further Reading

11.8 Questions to Think About

12 Volcanoes and Climate

12.1 Introduction

12.2 Evidence for the Impact of Volcanic Eruptions on Climate

12.3 Satellite Monitoring of Climate Change After Volcanic Eruptions

12.4 The Effects of Volcanic Eruptions on Climate

12.5 Volcanoes and Mass Extinctions

12.6 Summary

12.7 Further Reading

12.8 Questions to Think About

13 Volcanism on Other Planets

13.1 Introduction

13.2 Volcanically Active Bodies in the Solar System

13.3 The Effects of Environmental Conditions on Volcanic Processes

13.4 The Moon

13.5 Mars

13.6 Venus

13.7 Mercury

13.8 Io

13.9 Europa

13.10 Differentiated Asteroids

13.11 Summary

13.12 Further Reading

13.13 Questions to Think About

Answers to Questions

Index

End User License Agreement

List of Tables

Chapter 2

Table 2.1 Summary of the main types of magma and the trends of their physic...

Chapter 3

Table 3.1 The influences of the densities of magmas and the tectonic settin...

Table 3.2 The average widths of the dikes containing the columns of magma d...

Chapter 4

Table 4.1 The size of calderas formed during a selection of volcanic erupti...

Table 4.2 Magma chamber depths and sizes inferred from geophysical observat...

Chapter 6

Table 6.1 Basaltic magma with a total gas content of 2 wt% water rises thro...

Table 6.2 Plume heights generated during selected 20th‐century volcanic eru...

Table 6.3 The terminal velocity,

U

T

, is given for three clasts of different...

Table 6.4 The bulk density,

ρ

B

, of a gas–magma mixture as it is erupte...

Chapter 7

Table 7.1 Parameters obtained for a number of transient explosive eruptions...

Chapter 8

Table 8.1 Values of the magma eruption speed, the corresponding magma water...

Table 8.2 Parameters of pyroclastic fountains forming pyroclastic density c...

Chapter 10

Table 10.1 Typical total water contents (wt%) in various magmas.

Table 10.2 Calculations of the minimum water and carbon dioxide contents in...

Table 10.3 The Volcanic Explosivity Index (VEI) classification scheme.

Table 10.4 The magnitude, intensity, and Volcanic Explosivity Index (VEI) o...

Table 10.5 Examples of some of the largest volcanic eruptions occurring in ...

Chapter 11

Table 11.1 Data on eruption frequency and probability for 92 eruptions of M...

Table 11.2 Volcano alert systems.

Chapter 12

Table 12.1 Comparison between volcanic activity and occurrence of frost rin...

Table 12.2 The relationship between atmospheric aerosol loading and erupted...

Chapter 13

Table 13.1 The consequences of erupting a basaltic magma containing 1 wt% w...

Table 13.2 Comparison of conditions in eruptions of basalt containing 0.25 ...

List of Illustrations

Chapter 1

Fig. 1.1 An approximately 300 m high lava fountain eruption from the Puʻu ʻŌ...

Fig. 1.2 Eruption cloud from the sustained phase of the May 18, 1980 eruptio...

Fig. 1.3 An approximately 160 m high, 400 m wide lava dome slowly growing in...

Fig. 1.4 Part of a dense, sheet‐like lava flow erupted on the ocean floor, w...

Fig. 1.5 Lava fountain forming lava flows at the Puʻu ʻŌʻō vent on the East ...

Fig. 1.6 Spatter ramparts along either side of a fissure vent on the East Ri...

Fig. 1.7 Tephra blanket from the Puʻu Puaʻi vent near the summit caldera of ...

Fig. 1.8 Map showing the global distribution of flood basalt deposits, marke...

Fig. 1.9 A Plinian fall deposit from the ∼3.3 ka Waimihia rhyolitic ...

Fig. 1.10 A pyroclastic density current formed by partial collapse of an eru...

Fig. 1.11 This type of pyroclastic density current is called a pyroclastic s...

Fig. 1.12 Approximately 120 m high ash‐rich eruption cloud from a Strombolia...

Fig. 1.13 Pyroclasts following ballistic trajectories from a Strombolian exp...

Fig. 1.14 Clots of fragmented magma ejected as gas bubbles burst on the surf...

Fig. 1.15 Walker (1973) devised this classification scheme for different typ...

Fig. 1.16 Coarse pyroclasts deposited by a pyroclastic density current forme...

Fig. 1.17 Basaltic pillow lavas on the northeast rim of Kamaʻehuakanaloa vol...

Fig. 1.18 Lava from Kīlauea volcano, Hawaiʻi, enters the sea through a lava ...

Fig. 1.19 Image of cock’s tail plumes, transient explosive tephra jets gener...

Fig. 1.20 Maar crater in Death Valley, California, USA, formed during phreat...

Fig. 1.21 Four stages involved in the formation of a volcanic system. Stage ...

Chapter 2

Fig. 2.1 The temperatures and pressures (and hence depths below the surface)...

Fig. 2.2 The solidus and liquidus curves and the zones of partial melting (s...

Fig. 2.3 The distribution on Earth of subaerial volcanoes and of hot spots (...

Fig. 2.4 Cross‐sectional representation (vertically exaggerated) of the topo...

Fig. 2.5 The consequences of the head of a mantle plume impinging on contine...

Fig. 2.6 Hot spots near the mid‐Atlantic ridge that helped to initiate sprea...

Fig. 2.7 Updoming and faulting of the African continental crust by the Afar ...

Fig. 2.8 The two types of subduction zones that can occur on Earth. In (a), ...

Fig. 2.9 The first stages in the formation of melt as the temperature of a r...

Fig. 2.10 Increasing amounts of melt formation in the spaces between mineral...

Fig. 2.11 Settling of mineral crystals in a partially molten region concentr...

Chapter 3

Fig. 3.1 The arrows indicate the directions of convective movement occurring...

Fig. 3.2 The variation of the stress intensity at the growing tip of a dike ...

Fig. 3.3 The variation of density with depth through the crust and mantle in...

Fig. 3.4 Diagram showing magma in a dike penetrating crust of thickness

z

cru

...

Fig. 3.5 Three likely scenarios for the fate of magma rising in a dike from ...

Fig. 3.6 A reconstruction of the North American, South American, and African...

Chapter 4

Fig. 4.1 The summit caldera complex of Kīlauea Volcano, Hawaiʻi, seen from t...

Fig. 4.2 Variation of liquidus temperatures of two melts with pressure. In e...

Fig. 4.3 Distribution with depth, and with position in a vertical plane‐orie...

Fig. 4.4 Comparison of the seismic signals from a volcanic earthquake (trace...

Fig. 4.5 (a) Measurements of seismic tremor and ground uplift rate over a 25...

Fig. 4.6 Contours of the percentage of melt present in the region beneath th...

Fig. 4.7 Measurements of (a) ground tilt and (b) surface elevation made at K...

Fig. 4.8 (a) Contours of surface uplift in meters in the summit region of Kī...

Fig. 4.9 The result of fitting a Mogi model to surface uplift at the summit ...

Fig. 4.10 Illustrations of the relationships between a feeder dike, the host...

Fig. 4.11 (a) An outcrop of the Whin Sill beneath Bamburgh Castle, Northumbr...

Fig. 4.12 Schematic of the shape of the Skaergaard layered intrusion in Gree...

Fig. 4.13 Cross‐section through the Cadillac Mountain Intrusive Complex in M...

Fig. 4.14 The Mull and Ardnamurchan Tertiary intrusive complexes on the west...

Fig. 4.15 The patterns of lateral dike emplacement from Tertiary intrusive c...

Fig. 4.16 The times needed for heat loss to cause the solidification of intr...

Fig. 4.17 An example of a dike intruding into the interior of a previously e...

Fig. 4.18 The magmatic system thought to underlie Kīlauea Volcano in Hawaiʻi...

Fig. 4.19 The relationship between the magnitude of eruptions, expressed as ...

Fig. 4.20 The relationship between the size of a magma chamber, expressed as...

Chapter 5

Fig. 5.1 Scientists R. Okamura and K. Honma making measurements at a fumarol...

Fig. 5.2 The solubility of H

2

O in rhyolite and basalt as a function of press...

Fig. 5.3 A comparison of the solubility of H

2

O in rhyolite and basalt and of...

Fig. 5.4 Migration of the molecules of a volatile into a gas bubble from the...

Fig. 5.5 The variation of gas bubble radius with depth beneath the surface i...

Fig. 5.6 The typical distribution of bubble sizes within magma rising toward...

Fig. 5.7 A sequence of four frames extracted from a movie showing the rise o...

Fig. 5.8 The influence of magma rise speed on bubble growth for initial magm...

Fig. 5.9 Four stages in the growth of gas bubbles in a magma leading to magm...

Fig. 5.10 Pumice clast with many small bubbles taken from the Campo de Piedr...

Fig. 5.11 Scoria clast consisting of many bubbles of various sizes. Ruler is...

Chapter 6

Fig. 6.1 Schematic view of a dike of length

l

along strike and width

t

in wh...

Fig. 6.2 The variation with depth beneath the surface of the rise speed of m...

Fig. 6.3 (a) A number of possible shapes of dikes in the vicinity of the sur...

Fig. 6.4 The turbulent convection cells at the edge of the eruption plume fr...

Fig. 6.5 The shape of an eruption column seen from a direction at right angl...

Fig. 6.6 The eruption plume from the March 22, 1915, eruption of Lassen Peak...

Fig. 6.7 The relationship between the heights of some observed eruption plum...

Fig. 6.8 Two examples of the variation of eruption plume rise speed with hei...

Fig. 6.9 Diagram of a “control volume” used to relate the flux of atmospheri...

Fig. 6.10 Diagrams showing the variations of the velocity of gas and pyrocla...

Chapter 7

Fig. 7.1 The maximum speed of the solid rock fragments ejected in a transien...

Fig. 7.2 Diagram showing the progressive fragmentation and dispersal of the ...

Fig. 7.3 Lobes of pillow lava erupted on the ocean floor. Displacement of th...

Fig. 7.4 The final velocity and temperature of fragments ejected in hydromag...

Chapter 8

Fig. 8.1 A Plinian eruption cloud viewed from upwind of the vent. The progre...

Fig. 8.2 A Plinian eruption cloud viewed obliquely from a direction at right...

Fig. 8.3 Volcanic eruption clouds can circle the globe. The top panels show ...

Fig. 8.4 Terminal velocities in the atmosphere at sea level of typical dense...

Fig. 8.5 (a) Isopach and (b) isopleth data for the main Plinian fall deposit...

Fig. 8.6 The theoretically predicted variation of the product of clast diame...

Fig. 8.7 Data for four well‐studied eruptions plotted on the theoretical dia...

Fig. 8.8 Diagram showing the formation of a pyroclastic fountain over a vent...

Fig. 8.9 Sequence of images of the collapse of the front of a short lava flo...

Fig. 8.10 A pyroclastic density current erupted from the crater of Mount St....

Fig. 8.11 A thin (~1 m thick) nonwelded ignimbrite flow unit, part of a depo...

Fig. 8.12 Cross‐bedding in surge deposits from hydromagmatic eruptions at th...

Fig. 8.13 Possible vertical variations in particle concentration,

C

, and hor...

Fig. 8.14 The deposit from a pyroclastic density current erupted from Mount ...

Chapter 9

Fig. 9.1 A pāhoehoe toe lobe advancing over older lava. Note the rope‐within...

Fig. 9.2 A dacite dome formed during the eruption of Unzen volcano, Japan, t...

Fig. 9.3 A rhyolite flow forming the ~80 m high Novarupta dome marking the s...

Fig. 9.4 An unwelded deposit of scoria clasts. The scale is in centimeters....

Fig. 9.5 View of one side of a welded spatter rampart on Kīlauea volcano, Ha...

Fig. 9.6 A rootless lava flow being formed from a lava fountain at the Puʻuʻ...

Fig. 9.7 Diagram showing how the mass flux erupted from the vent and the exs...

Fig. 9.8 A rheomorphic ignimbrite deposit in the Trans‐Pecos volcanic provin...

Fig. 9.9 A basaltic sheet flow forming from a breakout from a pāhoehoe lava ...

Fig. 9.10 Compound pāhoehoe lava flow forming on January 18, 2005, on the so...

Fig. 9.11 Two scientists from the Hawaiian Volcano Observatory prepare to ta...

Fig. 9.12 The relationship between shear stress and strain rate for various ...

Fig. 9.13 The stresses acting on a lava flow levee. (a) In the downslope dir...

Fig. 9.14 Models of the internal structures of lava flow lobes. (a) The stru...

Fig. 9.15 Illustration of the changing properties of the lava in a lava flow...

Fig. 9.16 The classic ropy texture of a pāhoehoe lava flow surface.

Fig. 9.17 The rough, clinkery texture of an ʻaʻā lava flow surface.

Fig. 9.18 A series of pāhoehoe toes forming a compound lava field.

Fig. 9.19 A sequence of pillows formed by undersea eruptions, now exposed in...

Fig. 9.20 A very rough toothpaste‐textured lava surface forming on the south...

Fig. 9.21 Lava cascading into the ʻAlae pit crater during the eruption of Ma...

Fig. 9.22 A perched lava pond forming near the prehistoric cinder cone Puʻu ...

Chapter 10

Fig. 10.1 Diagram showing the classification of magma types in terms of thei...

Fig. 10.2 Viscosity as a function of temperature for a range of common magma...

Fig. 10.3 Variation of the size of the largest gas bubble that can form in a...

Fig. 10.4 Variation of the viscosities of various magmas with their dissolve...

Fig. 10.5 View of the ruins of the Roman city of Herculaneum, destroyed in t...

Fig. 10.6 A thin lava flow surrounding a house in the town of Kalapana on th...

Fig. 10.7 Part of the Deccan Volcanic Province, western India, an enormous s...

Fig. 10.8 Illustration of the strong correlation between the area of the cal...

Fig. 10.9 Summit tilt changes reflecting a series of inflation and deflation...

Fig. 10.10 Map of a portion of the island of Hawaiʻi showing the subaerial a...

Chapter 11

Fig. 11.1 Buildings in the village of Kalapana on the southeast flank of Kīl...

Fig. 11.2 Building in the village of Kalapana on the southeast flank of Kīla...

Fig. 11.3 The St. Mary’s Star of the Sea Catholic Church, Kalapana, Hawaiʻi,...

Fig. 11.4 An accumulating pyroclastic fall deposit from the 1991 eruption of...

Fig. 11.5 A World Airways DC‐10 aircraft tilted onto its tail by the weight ...

Fig. 11.6 Damage to the interior of a jet engine from a

DC

‐8 aircraft that e...

Fig. 11.7 A Roman column knocked down by the first pyroclastic density curre...

Fig. 11.8 A dilute pyroclastic surge cloud crossing a ridge. The top of the ...

Fig. 11.9 A lahar deposit from an eruption of Mount Pinatubo, Philippines. T...

Fig. 11.10 The jökulhlaup from the 1996 Gjálp eruption, Iceland. The flood h...

Fig. 11.11 Probability of a given Volcanic Explosivity Index (VEI).

Fig. 11.12 A compact, three‐component broadband seismometer system. The thre...

Fig. 11.13 A Fourier transform infrared spectrometer taking data during an e...

Chapter 12

Fig. 12.1 Occurrences of sudden increases (spikes) of acidity in polar ice c...

Fig. 12.2 Typical example of global temperature changes for a few years befo...

Fig. 12.3 The extent of atmospheric dispersal of tephra from the 1883 explos...

Fig. 12.4 The apparent correlation between the timing of named flood basalt ...

Chapter 13

Fig. 13.1 Shown to scale, from left to right, are the planets Mercury, Venus...

Fig. 13.2 (a) A suspected cryovolcanic mountain on the dwarf planet 1 Ceres....

Fig. 13.3 (a) Plumes on Enceladus from the Cassini spacecraft. (b) Enceladus...

Fig. 13.4 Some of the lava flow units that flooded the interior of the Mare ...

Fig. 13.5 The central part of the lunar linear rille Hyginus. The numerous c...

Fig. 13.6 The lunar sinuous rille called

Vallis Schroeteris

(Schroeters Vall...

Fig. 13.7 The area of the Moon known as the Marius Hills, a region in

Oceanu

...

Fig. 13.8 The ∼120 km diameter lunar crater

Alphonsus

. The small, da...

Fig. 13.9 The region around the lunar sinuous rille

Rima Bode

. The low refle...

Fig. 13.10 The summit region of

Arsia Mons

, one of the giant shield volcanoe...

Fig. 13.11 A portion of the Medusae Fossae Formation. The formation ranges f...

Fig. 13.12 A young lava flow from the Cerberus Plains on Mars. The Cerberus ...

Fig. 13.13 Mosaic of RADAR scans of a 210 km by 140 km area of volcanic plai...

Fig. 13.14 The shield volcano Sapas Mons on Venus stands 1.5 km above the su...

Fig. 13.15

Bahet Corona

, in the Fortuna region of Venus, is about 230 by 150...

Fig. 13.16 So‐called “pancake domes” in the Eistla region of Venus, probably...

Fig. 13.17 Distinct volcanic plains on the surface of Mercury (represented h...

Fig. 13.18 A pyroclastic deposit on Mercury represented in orange, located i...

Fig. 13.19 This comparison image shows changes in lava flow field being form...

Fig. 13.20 Near the north pole of Io a 290 km high eruption plume rises from...

Fig. 13.21 Near the left edge of this 250 km‐wide image, a mildly explosive ...

Fig. 13.22 A 100 by 140 km area of Europa showing complex ridges and fractur...

Fig. 13.23 An image of the asteroid 4 Vesta, taken by NASA’s Dawn mission. N...

Guide

Cover Page

Table of Contents

Title Page

Copyright Page

Dedication

Preface

Acknowledgments

Glossary

Begin Reading

Answers to Questions

Index

Wiley End User License Agreement

Pages

iii

iv

v

xiii

xv

xvi

xvii

xviii

xix

xx

xxi

xxii

xxiii

xxiv

1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

16

17

19

20

21

22

23

24

25

26

27

28

29

30

31

32

33

34

35

36

37

38

39

40

41

42

43

44

45

46

47

48

49

50

51

52

53

54

55

56

57

58

59

60

61

62

63

64

65

66

67

68

69

70

71

72

73

74

75

76

77

78

79

80

81

82

83

84

85

86

87

88

89

90

91

92

93

94

95

96

97

98

99

100

101

102

103

104

105

106

107

108

109

110

111

112

113

114

115

116

117

118

119

120

121

122

123

124

125

126

127

128

129

130

131

133

134

135

136

137

138

139

140

141

142

143

144

145

146

147

148

149

150

151

153

154

155

156

157

158

159

160

161

162

163

164

165

166

167

168

169

170

171

172

173

174

175

176

177

178

179

180

181

182

183

184

185

186

187

188

189

190

191

192

193

194

195

196

197

198

199

200

201

203

204

205

206

207

208

209

210

211

212

213

214

215

216

217

218

219

220

221

222

223

224

225

226

227

228

229

230

231

232

233

234

235

236

237

238

239

240

241

242

Fundamentals of Physical Volcanology

Second Edition

Elisabeth Parfitt

Conwy Archive ServiceConwy County Borough CouncilConwy, UK

Lionel Wilson

University of LancasterLancaster, UK

Laura Kerber

Jet Propulsion Laboratory / California Institute of TechnologyPasadena, CA, USA

This second edition first published 2025© 2025 John Wiley & Sons Ltd

Edition HistoryWiley‐Blackwell (1e, 2008)

All rights reserved, including rights for text and data mining and training of artificial technologies or similar technologies. No part of this publication may be reproduced, stored in a retrieval system, or transmitted, in any form or by any means, electronic, mechanical, photocopying, recording or otherwise, except as permitted by law. Advice on how to obtain permission to reuse material from this title is available at http://www.wiley.com/go/permissions.

The right of Elisabeth Parfitt, Lionel Wilson, and Laura Kerber to be identified as the authors of this work has been asserted in accordance with law.

Registered Office(s)John Wiley & Sons, Inc., 111 River Street, Hoboken, NJ 07030, USAJohn Wiley & Sons Ltd, New Era House, 8 Oldlands Way, Bognor Regis, West Sussex, PO22 9NQ, UK

For details of our global editorial offices, customer services, and more information about Wiley products visit us at www.wiley.com.

The manufacturer’s authorized representative according to the EU General Product Safety Regulation is Wiley‐VCH GmbH, Boschstr. 12, 69469 Weinheim, Germany, e‐mail: [email protected].

Wiley also publishes its books in a variety of electronic formats and by print‐on‐demand. Some content that appears in standard print versions of this book may not be available in other formats.

Trademarks: Wiley and the Wiley logo are trademarks or registered trademarks of John Wiley & Sons, Inc. and/or its affiliates in the United States and other countries and may not be used without written permission. All other trademarks are the property of their respective owners. John Wiley & Sons, Inc. is not associated with any product or vendor mentioned in this book.

Limit of Liability/Disclaimer of WarrantyWhile the publisher and authors have used their best efforts in preparing this work, they make no representations or warranties with respect to the accuracy or completeness of the contents of this work and specifically disclaim all warranties, including without limitation any implied warranties of merchantability or fitness for a particular purpose. No warranty may be created or extended by sales representatives, written sales materials or promotional statements for this work. This work is sold with the understanding that the publisher is not engaged in rendering professional services. The advice and strategies contained herein may not be suitable for your situation. You should consult with a specialist where appropriate. The fact that an organization, website, or product is referred to in this work as a citation and/or potential source of further information does not mean that the publisher and authors endorse the information or services the organization, website, or product may provide or recommendations it may make. Further, readers should be aware that websites listed in this work may have changed or disappeared between when this work was written and when it is read. Neither the publisher nor authors shall be liable for any loss of profit or any other commercial damages, including but not limited to special, incidental, consequential, or other damages.

Library of Congress Cataloging‐in‐Publication Data Applied for:

Paperback ISBN: 9781119266419

Cover Design: WileyCover Images: © An iconic aerial view of the eruption of Mount St. Helens. Skamania County, Washington. May 18, 1980, U.S. Geological Survey (color modified by Wiley)

Dedication

In memory of George Walker, who was an inspiration to us all.

Preface

Our knowledge of the physics of how volcanoes work has expanded enormously over the past 60 years, as have our methods of studying volcanic processes. In the late 1960s, George Walker conducted experiments into the fall‐out of volcanic particles from eruption clouds by using stopwatches to time the fall of pieces of tephra dropped down a stairwell at Imperial College, London. Now, technology exists which uses radar interferometry from satellites to monitor tiny changes in the shape of volcanoes, and broadband seismometers can detect the “heartbeat” (and “indigestion”) of volcanoes as magma moves around deep inside them. Sometimes, however, as we gain increasingly in‐depth knowledge of a subject, it becomes all too easy to focus on the minute details and hard to see the fundamental principles underlying all the complex behaviours that we observe. In this book we have attempted to step back from the details, and to view volcanoes as systems governed by some basic physical principles. Our approach is to consider the physical processes that control the formation, movement and eruption of magma, starting in the source region and following the magma upwards. Our intention is to show that, for all the apparent complexity of volcanoes, a little basic physics can go a long way in explaining how they work, and that often eruptions that may at first sight look remarkably different from one another are, in fact, physically much the same.

Acknowledgments

EAP: This book developed out of an undergraduate course that I taught for a number of years at the University of Leeds. That course benefited from and evolved due to the feedback of the students who took it, and I thank them all for their enthusiasm. A number of colleagues at Leeds – Joe Cann, Sue Bowler, Jane Francis, Mike Leeder and Pete Baker – offered their time and thoughts to that course and I thank them very much for their input and support. My knowledge of Strombolian activity was greatly improved by a trip to Stromboli with staff and students at Leeds, and I thank Jurgen Neuberg, Graham Stuart and Roger Clark for taking me along with them. Much of the writing of the book took place while I was working at the State University of New York at Buffalo, and I thank Marcus Bursik, Tracy Gregg and Mike Sheridan for discussions and ideas shared during that time. Nigel Burrows offered invaluable help converting my many old slides to digital format. This book would never have been finished without the treatment I received from the Chronic Fatigue Syndrome Service at Ysbyty Eryri, Caernarfon: a huge thank you to Dr Helen Lyon Jones, Marian Townsend, Anne the nutritionist and Dr Paul Nickson for their dedication and encouragement. Many thanks to my mother for the constant nagging to get this book finished, and for the belief that it could be done. To my son, James, a big thank you for putting up with my hours at the computer. Most of all to David, who always reminded me of the importance of punctuation and who enthusiastically applied red ink to the many drafts of this book, my innumerable thanks for providing the support, emotional and financial, needed to make the completion of this book possible.

LW: When my co‐author suggested that we collaborate on this book I was very happy to agree, as I have devoted most of my time since 1968 to understanding the physics of volcanic processes. During that year, while I was working on a pre‐Apollo study of the mechanical structure of the surface of the Moon, we began to get spacecraft images showing very long lava flows in the lunar mare areas, and in an effort to learn more about lava eruptions I visited the eminent British volcanologist George Walker, then at Imperial College London, to ask what was known about the physics of eruptions. George patiently, and with some amusement, explained to me just how little was known about this subject at that time, and by the end of my visit my career path was decided. My interest in the Moon remained, and broadened as spacecraft visited other solar system objects. Indeed, the study of how planetary environments control the boundary conditions (e.g., acceleration due to gravity, atmospheric pressure) under which volcanoes operate has been a major source of ideas. An equally important source of inspiration for me has been my interaction with the more than 30 graduate students who have worked with me on volcanic topics over the last 35 years. I must also thank my immediate colleagues at Lancaster, Harry Pinkerton, Steve Lane, Jennie Gilbert and Ray MacDonald, for their unfailing willingness to enlighten a mere physicist on the finer points of geology and geochemistry, and I am indebted to the numerous other scientists with whom collaboration has been so stimulating over the years, especially Stephen Sparks, James Head, Peter Mouginis‐Mark and, of course, my co‐author Elisabeth Parfitt. Thanks for logistic help in locating and manipulating images go to Peter Neivert at Brown University and Ian Edmondson at Lancaster University. Last, but very much not least, thanks to my wife Dorothy for her unfailing tolerance and support.

LK: I appreciate the opportunity provided by my co‐authors to work with them on the new edition of this textbook, from which I learned a great deal as a graduate student, and from which I continued to learn in the process of updating it. I hope that this version will likewise provide help to future students and researchers. I would like to acknowledge my husband Ben, who married into this project, my daughter Anna, who was born into it, and my dear friend Juan Pablo, whom we lost along the way.

All: We wish to thank John Guest, Michael Branney, Tracy Gregg for their helpful comments on parts of this book; and Jim Head and several anonymous reviewers for providing suggestions for the new version. As ever, errors and omissions remain our responsibility.

Glossary

ʻaʻā

A type of lava having a very rough surface texture.

absolute temperature

The thermodynamic temperature of a substance, measured on a scale where zero corresponds to the molecules forming the substance having no motion. The unit of absolute temperature is the Kelvin (K); the Kelvin has the same size as the degree Celsius (ºC) and 0K corresponds to –273.15ºC.

accidentally breached

An accidentally breached lava flow is one in which an overflow or breakout from the main channel occurs when the channel is blocked by material breaking off its walls.

accretionary lapilli

Small (between 4 and 32 mm in diameter) rounded particles formed by the accretion of large numbers of smaller particles in a volcanic eruption plume. The small particles may be held together by water, ice, or electrostatic forces.

acidity spikes

Localized high concentrations of sulfuric acid found at certain depths in ice cores drilled in polar regions. These correspond to the deposition of snow soon after volcanic eruptions which released large amounts of sulfate aerosols into the atmosphere.

active continental margin

The edge of a continental land mass at which one of the platetectonic processes of subduction or faulting is taking place.

aerosols

Small droplets of water in the atmosphere in which volatile species, especially sulfur dioxide, are dissolved.

air drag

The force exerted on a particle moving through the atmosphere as a result of the friction between the surface of the particle and the air.

andesite

A rock type of intermediate silica content, commonly associated with subduction zones.

arachnoids

Tectonic structures up to many hundreds of kilometers in diameter, with complex central parts and radiating fracture systems, seen in the crust of Venus. The name suggests that they look like spiders.

ash cluster

A collection of ash particles loosely held together by moisture, ice, or electrostatic forces.

ash pellet

A collection of ash particles strongly held together by moisture, ice, or electrostatic forces.

basalt

A rock type with a low silica content, commonly associated with ocean floor spreading.

basaltic andesite

A rock type of low to intermediate silica content.

base surge

A cloud of hot gas and entrained particles flowing out close to the ground from the site of a volcanic (or nuclear) explosion.

billion

Used in this book in its American context to mean the number 10

9

, i.e., one thousand million.

Bingham plastic

A liquid that has not only a viscous resistance to deformation and flow, but also a finite strength that must be overcome by any applied force before any flow takes place.

block lava

A type of viscous lava in which the surface fractures into large blocks.

block‐and‐ash flow deposit

A mixture of coarse and fine pyroclasts. deposited from a pyroclastic density current.

bulk modulus

The property of a material expressing the way the density changes with pressure.

buoyancy

The phenomenon whereby a lowdensity body surrounded by a higher‐density fluid in a gravitational field experiences an upward force.

caldera

A steep‐walled depression, commonly found at the summit of a volcano, formed when a large volume of magma is removed quickly from an underlying magma reservoir and the overlying rocks slide down along faults to fill the vacated space.

canali

Long (many hundreds of kilometers), narrow (a few kilometers wide) channels seen on the surface of Venus.

carbonatite

A rare type of magma consisting mainly of liquid carbonates rather than liquid silicates, produced in the mantle beneath some continental areas.

channelized lava flow

A lava flow in which liquid lava moves in a central region bordered on either side by a bank (called a levee) of stationary lava.

choked flow

The flow of a fluid under conditions such that the speed of the fluid is equal to the speed of sound within the fluid. This is the maximum speed that can be reached by the fluid unless special conditions apply.

coalescence

The joining together of two separate gas bubbles within a liquid (or of two droplets of liquid in a gas).

cock’s tail plume

The distinctive “feather‐edged” jet of ash and steam formed in an explosion when a large amount of water gains access to a vent.

co‐ignimbrite ash fall deposit

A fine‐grained deposit of pyroclasts settling out on the ground from a co‐ignimbrite cloud.

co‐ignimbrite cloud

An eruption cloud of gas and small pyroclasts formed as gas rising through an ignimbrite carries small particles upward with it as it escapes.

column collapse

The condition in which an eruption column fails to be positively buoyant in the atmosphere, so that a lower fountain of gas and entrained particles forms over the vent instead.

compound lava flow field

A region containing many lava flow units, most of which have formed by new flows breaking out from the margins of earlier‐emplaced flows.

conservation of momentum

The physical law that asserts that the momentum of a system (the product of mass and velocity) cannot be destroyed, only redistributed among the components of the system.

continental arc

An arcuate chain of volcanoes at the margin of a continent.

convective region

Part of the interior of a fluid or plastic solid within which convection (relative movement of different parts of the fluid due to density differences) is taking place.

convergent margin

A location where the edges of two tectonic plates are being driven into collision.

cooling unit

One or more layers of pyroclastic particles (or lava) emplaced so soon after one another that they cool as though they had been emplaced at the same time.

cooling‐limited

Description of a lava flow that ceases to move because the front of the flow has cooled to the point of effectively being a solid.

corona

(plural:

coronae

)

One of a number of large (many hundreds of kilometers) roughly circular regions on Venus where tectonic forces have fractured and folded the surface rocks.

country rock

Pre‐existing rock into which magma intrudes.

cryovolcanism

A volcanic process in which liquid water rather than liquid rock is the moving fluid.

dacite

A type of magma with intermediate to high silica content.

dark halo deposit

A roughly circular region on the Moon where dark pyroclasts are deposited around an explosive vent.

de Lavalle nozzle

Part of a volcanic conduit or dike where the shape changes from converging upward to diverging upward, thus allowing magma flowing through the conduit to accelerate from subsonic to supersonic speeds.

decompression

The expansion of a material, especially a gas, when the pressure acting on it decreases.

decompression melting

The process whereby solid rock begins to melt when the pressure acting on it decreases even if the temperature does not change.

diapir

A body of plastic material that rises buoyantly as a coherent mass within a larger body of plastic material.

diffusion

The process whereby the atoms or molecules of a volatile compound migrate by moving between the atoms or molecules of a host material.

dike

A fracture filled with volcanic material cutting through earlier‐emplaced host rocks.

dilatant

Description of a type of non‐Newtonian fluid in which the viscosity increases as the applied stress increases.

divergent margin

A boundary between two tectonic plates, almost always on the ocean floor, at which new crustal material is being supplied by volcanic eruptions or intrusions as the plates move apart.

dome

A deposit of (commonly viscous) lava where the width and maximum thickness are of the same order because the lava has not spread far from the vent.

dusty gas

A gas containing solid particles so small that frictional drag forces effectively force the particles to travel at the same speed as the gas.

ejecta

Any material thrown out from a vent (rather than flowing away from it) during volcanic activity.

elastic

Description of any material that changes its shape when a stress is applied to it but recovers its original shape when the stress is removed.

energy equation

An equation describing the law that says that the total energy of a system cannot be destroyed, only redistributed among its parts.

entrainment

The process whereby the flow of one material through or past another surrounding material causes some of the surrounding material to be mixed into the flowing material.

equivalent diameter

A geometric property of a flowing fluid in a channel equal to four times the cross‐sectional area at right angles to the direction of flow divided by the length of the perimeter in contact with the floor and walls.

exit velocity

The speed at which volcanic materials emerge through a surface vent.

expansion wave

A moving zone within a fluid across which the pressure decreases significantly.

explosive

Description applied to any process that takes place suddenly, or that involves a very large pressure change.

exsolution level

The depth at which gas dissolved in a rising magma first starts to come out of solution and form gas bubbles in response to the decreasing pressure.

exsolve

Release a gas from solution in a liquid. The opposite of dissolve.

fiamme

Pumice clasts in the interior of an ignimbrite deposit that have become stretched sideways while still hot as the deposit is compressed by the weight of overlying material.

filter‐pressing

The process whereby magma is squeezed out of its partly molten source rocks when stress causes compaction of the unmelted material.

fissure

A fracture in rock, more particularly an elongate surface vent from which magma is erupted.

flood basalt eruption

A rare kind of basaltic eruption in which a very large volume (thousands of cubic kilometers) of basalt is erupted in a geologically short space of time.

flow unit

A lava flow which is the product of a single eruptive event from a single vent.

focus

The location beneath the surface where an earthquake takes place.

fractional crystallization

The formation of crystals in a cooling liquid. One or more types of crystal may form at any one time, but each forms over its own characteristic temperature range.

fragment

A piece of material broken from a larger piece of material.

fragmentation

The process of breaking a material into smaller pieces. The material may be a solid or a liquid.

fragmentation level

The depth below the surface at which shearing stresses tear a magma containing gas bubbles apart into clots of liquid carried along by the gas released from the bubbles broken by the tearing process.

friction

A force that opposes the motion of any two materials in contact and sliding past one another.

frost ring

A layer inside the trunk of a tree, forming parallel to the bark and marking a time when the growth of the tree was inhibited by unusually cold weather.

fumaroles

Places where volatile compounds being released from the interior of a volcanic deposit reach the surface and settle to form deposits on the ground as they cool.

Gas Laws

The laws describing the way the pressure, temperature, density, and internal energy of gases are related.

gas‐thrust region

The lowest part of an eruption column, where the inertia of the erupted materials, which has been determined by the expansion of volcanic gases beneath the surface, is the main control on their motion.

giant dike swarm

A group of dikes radiating for great distances (at least many hundreds of kilometers) away from some region where a very large magma reservoir has existed at some time.

graben

A trench‐like depression formed in an area of extensional forces. The crust is forced apart and breaks along two parallel normal faults dipping toward one another, with the ground between the faults moving downward.

grading

The variation of the average grain size of a deposit with vertical position within it. In normal grading the mean size increases downward, whereas in reverse (or inverse) grading it increases upward in the deposit.

granular flow

The flow of a body of material consisting of discrete solid clasts in which only the interaction between clasts controls the motion – any gas or liquid between the clasts has no important effects.

Hawaiian

Description applied to eruptions like those common in Hawai’I, where basaltic lava is erupted, commonly explosively.

heat pipes

Regions where heat is transported upward through the crust mainly by the frequent passage of magma through the surrounding rocks.

heterogeneous nucleation

The process of the formation of gas bubbles in a liquid supersaturated in a dissolved volatile compound when the bubbles nucleate on crystals in the liquid or irregularities in the boundary between the liquid and its solid surroundings.

hindered settling

The settling of solid particles in a fluid where the particles are so close together that they either collide with one another or interfere with the smooth flow of the fluid around them.

homogeneous nucleation

The process of the formation of gas bubbles in a liquid supersaturated in a dissolved volatile compound when the bubbles have no solid surfaces on which to nucleate and so appear at random within the liquid.

hot spot

Place where there is an unusually large upward flow of heat from the mantle toward the surface. Generally a location of significant volcanic activity.

hyaloclastite

A type of fragmental and chemically altered rock produced when erupting lava interacts strongly, generally explosively, with surface water.

hyaloclastite ridge

A ridge composed of fragmental and chemically altered rock produced when a fissure eruption occurs in shallow water, most commonly beneath a glacier.

hydromagmatic

Description of any eruption process in which magma or lava interacts with external water.

hydrothermal

Description of any process involving the circulation of water at shallow depths in the crust as a result of heat supplied by intruded magma.

ignimbrite

A large body of rock formed from the deposition of pyroclasts that have traveled from a vent as a pyroclastic density current.

ignimbrite‐forming

A type of explosive eruption that produces large volumes of pyroclasts emplaced as pyroclastic density currents.

inertial region

An alternative description (see “gas‐thrust region”) of the lowest part of an eruption column where the inertia of the erupted material dominates the motion.

inflation

The word has two uses in volcanology: (i) the enlargement of a magma chamber as new magma is added to it from the mantle; (ii) the process whereby a lava flow gets thicker after it has been emplaced as a result of additional magma being forced into its interior.

intraplate

Any process that occurs within, i.e., well away from the boundaries of, a tectonic plate.

inversely graded

Description of a deposit of pyroclasts in which the average grain size increases upward in the deposit.

island arc

An arcuate group of volcanic islands formed above a subduction zone at the edge of a tectonic plate.

isopach

A contour line on the map of a volcanic deposit joining places where the thickness of the deposit is the same.

isopleth

A contour line on the map of a volcanic deposit joining places where the grain size of the deposit is the same.

jökulhlaup

The Icelandic word for a “glacierburst,” the sudden release of a very large volume of water that has accumulated under a glacier as a result of melting caused by an eruption there.

juvenile

In volcanology, the word implies material that has come directly from the deep interior of the planet.

kimberlite

A rare type of mafic rock resulting from the eruption or intrusion of magma coming from unusually great depth in the mantle. Economically important because some kimberlites bring with them diamonds from the mantle.

kinetic energy

The type of energy associated with the movement of material.

komatiite

A type of ultramafic magma forming low‐viscosity lava flows, common in early Earth history.

laccolith

An intrusion of magma that has a relatively large vertical extent compared with its horizontal width.

Large Igneous Province

A region where large volumes of basaltic lava have been erupted – essentially a more general term for a region in which a flood‐basalt eruption has happened.

lava breakout

A place where lava breaks out from the edge of an existing lava flow deposit.

lava dome

A relatively thick and short lava flow deposit.

lava flow

An individual deposit of a discrete phase of an effusive eruption.

lava flow field

A group of lava flow deposits emplaced in successive phases of a prolonged eruption.

lava fountain

A jet of hot pyroclasts ejected from an explosive volcanic vent, rising to a significant height, and then falling back to the surface. Also called a fire fountain.

lava tube

The interior of a lava flow where the surface layers of the flow have ceased to move and thus form an insulating roof reducing heat loss from lava still flowing beneath.

levee

The stationary edge of a lava flow.

level of neutral buoyancy

See “neutral buoyancy level.”

linear rille

A type of graben found on the Moon.

liquidus

The temperature at which a magma is completely molten.

lithic clast

A fragment of rock broken from the rocks through which a volcanic event has taken place and incorporated into the erupted volcanic materials.

lithosphere

The outer part of a planet where the rocks behave as brittle solids, consisting of the crust and the upper part of the mantle.

lithostatic load

The pressure at a given depth below the surface due to the weight of the overlying layers of rock.

littoral cone

A cone‐shaped accumulation of pyroclasts on land close to the ocean, built up by explosions when lava enters the water.

maar

A crater formed by an explosive interaction between magma approaching the surface and surface or near‐surface water.

magma

Molten or partly molten rock beneath the surface of a planet.

magma chamber

a subsurface region with a large proportion of molten magma.

magma ocean

A layer of molten rock on the surface of a planet, formed when the outer layers of the planet accumulate so fast that heat from the impact of each added asteroid cannot be radiated away completely before the next impact happens.

magma reservoir

A long‐lived magma storage system beneath the surface consisting of a collection of liquid magma chambers, or melt lenses, and semi‐solid mush regions.

magmon

A localized concentration of magma in the pore space of host rocks. The rocks deform to allow the magma concentration to pass through, so that it moves like a wave through the host rocks.

mantle plume

A part of the mantle where buoyancy causes the mantle rocks to rise toward the surface. Commonly the site of pressure‐release melting.

maria

(singular:

mare

)

The latin name for the dark areas on the Moon, consisting of floods of basaltic lava filling very large impact craters.

mass extinction

A biological event in which large numbers of species die out in a geologically relatively short space of time.

mass flux

The mass of magma passing though a volcanic system every second.

meteoric

Generally, description of any phenomenon associated with the atmosphere. In volcanology, applied to near‐surface water that has collected as a result of rain or snow.

mid‐ocean ridge

The ridge formed along a constructive tectonic plate margin by the accumulation of lavas erupted onto the ocean floor.

mush column

A zone within the crust where magma passes through so often that the host rocks are partly molten.

negatively buoyant

Description of material that is denser than the material surrounding it, so that it will tend to sink through its surroundings.

neutral buoyancy level

Any location above or below ground where volcanic materials have the same density as their surroundings.

Newtonian

Description of a fluid with the property that any change in applied stress produces a directly proportional change in rate of deformation.

non‐Newtonian

Description of a fluid in which the rate of deformation is not directly proportional to a change in the applied stress.

normally graded

Description of a pyroclastic deposit in which the grain size increases downward in the deposit.

nova

(plural:

novae

)

A type of tectonic structure on Venus in which fractures radiate out from a central zone.

nuclear winter

A prolonged period of cooling when heat reaching the surface from the Sun is greatly reduced by dust in the atmosphere thrown up from the explosion of a large number of nuclear weapons.

nuée ardente

French for “burning cloud,” one of the possible names for a pyroclastic surge.

ophiolite

A body of rock consisting of the subsurface part of an old spreading center now uplifted and exposed at the Earth’s surface by tectonic forces.

p waves

Primary waves, compressive waves spreading out from an earthquake focus into the surrounding rocks. These waves travel faster than any other type of seismic waves.

pāhoehoe

A type of lava where the surface is smoothly folded into a series of ripples called ropes.

pāhoehoe toe

A small lava flow unit consisting entirely of pāhoehoe lava extending for a short distance from a larger flow unit.

partial melting

The process in which part of a mass of rock melts, the liquid still containing the mineral grains that have not yet melted.

perched lava pond

A lava flow that has spread out sideways so that it has a similar width to its length. The shape is sometimes controlled by pre‐existing topography but can be selfgenerated by a suitable combination of eruption rate and very shallow ground slope.

peridotite

A type of rock rich in olivine, found in the Earth’s mantle.

petrology

The general term for the study of all aspects of rocks.

phoenix cloud

Alternative term for a coignimbrite cloud.

phreatomagmatic

Description of an eruption involving interaction between magma and surface, near‐surface or ground water.

phreato‐Plinian

Description of a sustained explosive eruption in which magma interacts with surface or ground water, generally resulting in more fragmentation of the magma than in a Plinian eruption.

pillow

A lava flow lobe that is approximately as wide as it is thick, produced by a low lava extrusion rate under water.

pillow lava

A lava flow consisting of a pile of pillows.

plastic

Description of a fluid that is capable of deforming smoothly in response to an applied stress.

plastic viscosity

The property of a non‐Newtonian fluid expressing the ratio between a change in applied stress and a corresponding change in rate of deformation.

plate

One of a series of sections of the Earth’s lithosphere behaving as a rigid solid.

plate tectonics

The term applied to our current understanding of the structure of the Earth’s lithosphere, with rigid plates sliding as discrete structures on top of the plastic mantle and interacting at their edges.

Plinian

Description of a sustained explosive discharge of volcanic gas and pyroclasts forming a large eruption cloud in the atmosphere.

Poisson’s ratio

An elastic property of a solid, specifically the ratio of transverse to longitudinal strain (i.e., fractional deformation) when a tensional force is applied.

poroviscoelastic

Related to a spongy substance where stress imposed by a liquid can be accommodated by elastic stretching, viscous deformation, or porous flow.

potential energy

Generally, a form of energy associated with the position of an object in a force field. In volcanology this is the planetary gravitational field.

pressure‐balanced

Description of a volcanic fluid emerging from a vent in such a way that the pressure within the fluid is equal to the atmospheric pressure at the level of the vent.

pressure‐release melting

An alternative term for decompression melting.

pumice

A piece of volcanic rock containing vesicles.

pyroclastic density current

A mixture of gas and suspended or entrained solids released in a sustained explosive eruption and forming a dense fluid that moves along the ground at high speed.

pyroclast

General term for any fragment of volcanic material produced in an explosive eruption.

pyroclastic fountain

A mixture of gas and pyroclasts erupted explosively though a vent, traveling upward, and then falling back to the surface.

pyroclastic surge

A relatively short‐lived form of pyroclastic density current.

regolith

A fragmental layer on the surface of a planet. If a biological component is present, as on Earth, the regolith is called soil.

residence time

The time that particles or aerosols spend in the atmosphere before settling to the ground. More generally the time taken for any particles suspended in a fluid to settle out.

rheology

The study of the way fluids deform in response to applied stresses.

rhyolite

A rock type with a high silica content.

Ring of Fire

The regions around the rim of the Pacific Ocean dominated by volcanic activity.

rootless lava flow

A lava flow formed by the accumulation and coalescence of hot pyroclasts falling from a lava fountain.

rootless vent

The site of a volcanic explosion that is not directly underlain by a volcanic vent, for example a place where an explosion occurs in a lava flow advancing over waterlogged ground.

s waves

Secondary waves, shear waves spreading out from an earthquake focus into the surrounding rocks. These waves can propagate in solids but not in liquids.

saltate

To bounce over the ground, as when particles are almost suspended in a strong wind.

saturated

Description of a fluid containing the maximum amount of volatiles allowed by the current pressure and temperature.

sedimentation

The settling of particles from a fluid to form a layer at the base of the fluid.

seismic gap

A subsurface region within which no sources of seismic waves occur because the region is occupied by magma.

seismic velocity

The speed of a seismic wave, a sound wave in rock generated by an earthquake.

shear modulus

The elastic property of a solid expressing the fractional amount by which it deforms in response to a shearing stress.

sheet flow

A lava flow that is very wide compared with its thickness.

sill

A sheet‐like body of magma, often approximately horizontal, intruded at some depth below the surface along the interface between two preexisting rock layers.

sinuous rille

A meandering type of channel found on the Moon and Mars where hot turbulent lava has eroded the surface over which it has flowed.

slug

A body of gas rising through a volcanic dike or conduit where the vertical extent of the gas is much greater than the width of the dike or conduit.

solidus

The temperature below which a magma is completely solid.

soliton

A solitary wave, i.e., a wave that travels without changing its size or shape.

solubility law

The law specifying how much of a given volatile compound can be dissolved in a magma at a given pressure and temperature.

spatter rampart

A ridge parallel to a fissure vent consisting of pyroclasts ejected from the fissure.

spreading center

A boundary between two tectonic plates at which new crust is being created by volcanic eruptions and intrusions and the plates are moving apart.

stoping

The process whereby blocks of country rock become detached from the roof or walls of a magma reservoir and fall into the magma.

strain rate

The rate at which a solid or liquid changes its length, expressed as a fraction of its original length, as a result of an applied stress.

stratosphere

The second layer of the Earth’s atmosphere, lying above the troposphere.

Strombolian

A style of explosive volcanic activity characterized by the intermittent arrival, at the surface of the magma in a vent, of giant gas bubbles that burst, throwing out the disrupted liquid skin of the bubble.

subaerial

Description of any process taking place in an atmosphere.

subduction

The process whereby some tectonic plates are forced down into the Earth’s interior beneath other plates.

sub‐Plinian

Description of a class of sustained explosive volcanic activity producing relatively small eruption plumes in the atmosphere.

supersaturated

Description of a fluid containing more of a dissolved volatile compound than it should be capable of dissolving under its current pressure and temperature conditions. This is an unstable state leading to bubble formation by exsolving gas.

surface tension

A molecular attraction force acting parallel to any interface between two fluids and tending to reduce the area of contact.

tensile strength

The strength of a material when subject to a tensional force.

tephra