Vesiculation and Crystallization of Magma: Fundamentals of the Volcanic Eruption Process

449 Pages·2021·14.716 MB·English

by  Atsushi Toramaru

Advances in Volcanology
Atsushi Toramaru
Vesiculation and
Crystallization
of Magma
Fundamentals of the Volcanic Eruption Process
Advances in Volcanology
fi
An Of cial Book Series of the International
Association of Volcanology and Chemistry
’
of the Earth s Interior
Series Editor
Karoly Nemeth, Institute of Natural Resources, Massey University,
Palmerston North, New Zealand
More information about this series at https://link.springer.com/bookseries/
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Atsushi Toramaru
Vesiculation
and Crystallization
of Magma
Fundamentals of the Volcanic
Eruption Process
123
Atsushi Toramaru
Department ofEarth
andPlanetarySciences
Kyushu University
Fukuoka,Japan
TheJapaneseversionofthisbookwassupportedbyJSPSKAKENHIGrantNumber
JP18HP5236 (Grant-in-Aid for Publication of Scientific Research Results) in
FY2018.TheEnglishversionwassupportedbyKyushuUniversityPracticalVolcano
SpecialEducationBaseProjectoftheMinistryofEducation,Culture,Sports,Science
andTechnology,Japan inFY2019.
ISSN 2364-3277 ISSN 2364-3285 (electronic)
Advances in Volcanology
ISBN978-981-16-4208-1 ISBN978-981-16-4209-8 (eBook)
https://doi.org/10.1007/978-981-16-4209-8
Translation from the Japanese language edition: Magma no Happo to Kesshoka by Atsushi
Toramaru, © Atsushi Toramaru 2019. Published by University of Tokyo Press. All Rights
Reserved.
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To Y. T.
Preface for English Version
This book is the English version of Vesiculation and Crystallization of
Magma—Fundamentals of Volcanic Eruption Process—which was pub-
lished in Japanese in 2018. This book aims at advancing the comprehensive
understanding of fundamental processes, vesiculation and crystallization of
magmas,forresearchersandgraduatestudents.AsImentionintheprefacein
the Japanese version, I feel the need for the detailed illustration of those
fundamental processes in magmatism, because the related works have been
produced at a high rate, covering a wider area. In such circumstances, it is
difficult for the researchers of the field (including the graduate students) to
understandthebaseofthestudiesbygettingbacktofundamentalphysicsand
chemistrybehindthose.Manyerrorsandtypos intheJapaneseversionhave
been corrected in the English version through careful reading by Mizuki
Nishiwaki (Kyushu University), and members of Volcanology seminar of
Earthquake Research Institute, University of Tokyo. Unfortunately, because
of limited number of cited articles, I could not cite a number of important
articles in the reference.
Fukuoka, Japan Atsushi Toramaru
vii
Preface
Studying volcanic phenomena and elucidating their mechanisms and laws
require various types of approaches, including geophysical observation,
geological surveys, geochemical analyses, and modeling. Note that analysis
basedonmaterialsscienceisonesuchapproach,andresearchinthisareahas
been actively ongoing, particularly over the last 20 years. For example,
correspondence between eruption styles, changes in eruption styles, and
eruptive materials have been investigated; moreover, eruption parameters,
suchastheascentvelocityofmagma,havebeenquantitativelyestimated.For
their chemical composition and texture, volcanic products record the vesic-
ulation, crystallization, and movement magma experiences in all their pro-
cesses from generation to accumulation to ascent to eruption. To
quantitativelydeciphertherecordofmagmamovement,anunderstandingof
its key process, i.e., the vesiculation and crystallization of magma, is nec-
essary. However, there isno book comprehensively explaining the scientific
procedure and background for achieving such an understanding; therefore, I
have felt the need for a book such as this.
Using conventional observational research on volcanos, such as geo-
physical monitoring, we can obtain data about the occurrence of volcanic
earthquakes and volcano deformation. However, to interpret these data,
knowledge about the state of magma under the ground is necessary. More-
over,formodelingvolcanicconduitflowusingcomputationalsimulationand
calculating convection and fractional crystallization in magma chambers, a
basic knowledge of materials science is necessary. Furthermore, before
conducting individual observations and developing simulation strategies,
coolingofthemagmaandsolubilityofvolatilesinthemagmaareextremely
fundamental aspects that we should have learned in advance.
This book focuses on the vesiculation and crystallization processes of
magma. Vesiculation and crystallization of magma are basic processes that
appear at every scene of volcanic eruption. In magma chambers deep
underground where cooling crystallization occurs, water as well as other
volatilesthathavenotbeenincorporatedintocrystalsgetconcentratedintoa
liquid and then vesiculate at a certain time point, leading to overpressur-
ization in magma chambers and supply of buoyancy for magma ascent. In
magma that is ascending in a volcanic conduit, decompression-induced
ix
x Preface
vesiculation occurs and expansion of the generated gas governs the ascent
and exit velocities from the vent. Moreover, as a result of the decrease in
water content in liquid caused by decompression-induced vesiculation, the
melting point of minerals increases and decompression-induced crystalliza-
tionoccurs.Theformationofbubblesandcrystalschangestheviscosityand
magma structure, thus providing feedback to magma movement. In eruptive
materials on the surface, temperature and pressure paths the magma has
experienced as well as the rate of changes are recorded as the texture of
bubbles and crystals. Therefore, the appropriate use of a methodology by
which such information is read out from the texture of eruptive materials
allows the estimation of magma movement along with eruption.
Developing this methodology requires both encyclopedic knowledge of
materials such as rocks and minerals and fundamental approaches for
interpreting data obtained by analyzing such materials. For example, New-
tonian mechanics, which we learned in high school, is a fundamental
approach for interpreting data on ball trajectories. Thus, the fundamental
approachesforinterpretingdataonvolcanicmaterialscanberoughlydivided
intotwoconcepts.Oneconceptisreferredtoas“equilibriumtheory,”which
is based on thermodynamics and is integrated into equilibrium phase dia-
grams.Thisconceptisbasedonassumingtheconceptofanequilibriumstate
and discusses the state without motion. “Disequilibrium theory” is the other
concept that discusses motion from one state to another state. It is called
“kinetics.” Focusing on these two concepts, this book explains the founda-
tions offundamental approaches by which we interpret natural materials.
In the fields of applied physics and materials science, a number of text-
books have been published on equilibrium phase diagrams and kinetics.
However, it is somewhat difficult to apply the context of such books to
volcanic materials because they only explain generalities or deal with
materialsandsituationsdifferentfromthoseofvolcanicmaterials.Moreover,
Iamunawareofanybookthatcomprehensivelyexplainskinetictheoriesthat
have been independently developed for magma. This seems to be a major
barrier to advancing research and education to the next step.
On the other hand, textbooks published in Japan, and not only those on
volcanology, are generally compact and often do not contain detailed
explanations of the derivation of equations and the underlying fundamental
physics. In particular, in recent years, while easy-to-understand books are
valued and popular, difficult-to-understand books tend to be avoided. I have
been worrying that this tendency obscures the detailed processes of inquiry
and prevents the understanding of underlying assumptions and fundamental
principles. Aimed at overcoming these demerits, I have attempted to write
thisbookinasmuch detailaspossible andinaneasy-to-understandmanner
as possible. Although Torahiko Terada (physicist in Japan 1878–1935)
commentedonRayleigh'sTheoryofSound,whichcouldbecasuallyglanced
throughwhileensuringhis handsinhispockets,Igained noconfidencethat
this work has turned out to be such a book.
Preface xi
Based on this thinking, this book has the following structure. Part I
introduces instances the author has experienced, to share volcanic phenom-
ena for understanding with readers. Moreover, it contains motivation and
inspiration that we gained from natural phenomena to learn about vesicula-
tionandcrystallizationofmagma.PartIIexplainsthevesiculationofmagma,
whereas Part III describes the crystallization of magma. In both Parts II and
III, the equilibrium theory is first explained, followed by the explanation
of the disequilibrium theory. Note that the equilibrium theory of crystal-
lization isnotexplainedbecause it overlapswith discussion onvesiculation,
andtherearealreadyseveraltextbooksavailableonthesubject,andspaceis
limited. The chapters on the vesiculation process of magma deal with the
conditions of magma vesiculation, mechanism of bubble formation, growth
of bubbles, temporal development of bubble size distribution, and various
processes related to bubbles (secondary growth, coalescence, deformation,
detachment, ascent, as well as shrinkage, collapse, and oscillation of bub-
bles). The chapters on the crystallization process explain the cooling crys-
tallization of magma, crystallization triggered by vesiculation
(decompression-inducedcrystallization), andcrystal sizedistribution (CSD).
PartIV,thelastchapteronapplication,introducesattemptstounderstandthe
behaviorofmagmabyapplyingthediscussioninearlierchapterstoeruptive
materials and rocks obtained from actual volcanos. In Appendix, several
points—derivation and calculation of equations, useful concepts and sum-
maries, an outline of physical properties, and a conceptual basis for textural
analysis—required to understand the contents of the primary text are
explained. Although a number of symbols appear in this book, I have
attempted to not use the same symbol with different meanings and have
provided a list of symbols to help avoid confusion.
Unfortunately, this book cannot cover multiple points that are indis-
pensable to understanding volcanic phenomena from a materials science
viewpoint, and that (one feels) should be comprehensively explained else-
where. These points include a comprehensive introduction to and examina-
tion ofthechemical composition ofobserved crystals, theorigins of various
crystal forms, a detailed explanation of and data on the relevant physical
properties (although they are partly discussed), and the coupling of phase
change and fluid mechanics.
I would like to express my gratitude to Mie Ichihara (University of
Tokyo), Masatoshi Ohashi (University of Tokyo), Kazuya Yamakawa
(University of Tokyo), Takafumi Maruishi (Kyoto University), and Mizuki
Nishiwaki (Kyushu University) who verified the physics and derivation of
equations, thus reporting fundamental mistakes and inappropriate expres-
sionsandprovidingcountlesssuggestionsandpiecesofadviceintworeview
campsthatcoveredcomplete8daysintotal.Withouttheirsupport,thisbook
wouldcertainlyhavebeenafarlessaccurateone;however,itisimpossibleto
deny that many mistakes remain regardless of my best, and the author takes
fullresponsibilityforthisbook.Moreover,IwouldliketothankDr.Ichihara
for useful discussions on the energetics of nucleation, Dr. Ohashi for useful
discussions on the coalescence and deformation of bubbles, Mr. Nishiwaki
for the calculation of viscosity in Appendix, and a technical associate,