Kyushu University Academic Staff Educational and Research Activities Database
List of Papers
Atsushi Toramaru Last modified date:2021.06.21

Professor / Dynamics, Structure and Evolution of the Earth and Planets / Department of Earth and Planetary Sciences / Faculty of Sciences

1. T. MitsuokaA. ToramaruA. HarijokoH. E. Wibowo , Eruption types and conduit dynamics of Kukusan and Genteng volcanoes of the Ijen volcanic vomplex, Indonesia, Memoirs of the Faculty of Sciences, Kyushu University, Series D Earth and Planetary Sciences, Volume XXXV, No. 1,, XXXV, 1, 1-17, 2021.03.
2. Shunsuke YamashitaAtsushi Toramaru, Control of Magma Plumbing Systems on Long‐Term Eruptive Behavior of Sakurajima Volcano, Japan: Insights from Crystal‐Size‐Distribution Analysis, Dynamic Magma Evolution, Geophysical Monograph Series, 2020.07.
3. Ai HamadaAtsushi Toramaru, Analogue experiments on morphological transition from colonnade to entablature of columnar joints, Journal of Volcanology and Geothermal Research, 2020.07.
4. Mizuki Nishiwaki, Atsushi Toramaru,, Inclusion of Viscosity Into Classical Homogeneous Nucleation Theory forWater Bubbles in Silicate Melts: Reexamination of Bubble Number Density in Ascending Magmas, Journal of Geophysical Research: Solid Earth, /10.1029/2019JB017796, 124, 8, 88250-8266, 2019.09, To evaluate the effect of melt viscosity on bubble nucleation, we formulated the homogeneous nucleation rate of water bubbles to explicitly include melt viscosity. The viscosity coefficient appears in the preexponential factor of the nucleation rate in terms of the Péclet number: the ratio of the bubble growth timescale by molecular diffusion and the viscous relaxation timescale. The preexponential factor is almost constant when viscosity is low (or a high Péclet number), whereas it linearly decreases with increasing viscosity (or a decreasing Péclet number) exceeding the crossover value of viscosity, under a given supersaturation. The crossover point depends on whether homogeneous or heterogeneous nucleation takes place.We numerically solved the evolution of bubble nucleation and growth processes in ascending magmas by using the new nucleation rate formula and a precise approximation of moment equations of the bubble size distribution function. The resultant bubble number density has two regimes, similar to the previous study, but the transition point between the diffusion-controlled regime and the viscosity-controlled regime moves to higher viscosity or higher decompression rates by 0.6 log units at the maximum. In the viscosity-controlled regime, the effect of the better approximation of bubble size distribution moment equations reduces bubble number density by a few orders of magnitude compared with the previous study. As a result of compiling the past laboratory experimental data, it turned out that all the experiments are conducted under the conditions equivalent to the diffusion-controlled regime.We
propose an experimental condition to confirm the presence of the viscosity-controlled regime..
5. Masatoshi Ohashi,Mie Ichihara,Atsushi Toramaru, Bubble deformation in magma under transient flow conditions, Journal of Volcanology and Geothermal Research,, 364, 15, 59-75, 2018.09.
6. Yu Iriyama, Atsushi Toramaru, Tetsuo Yamamoto, Theory for Deducing Volcanic Activity From Size Distributions in Plinian Pyroclastic Fall Deposits, Journal of Geophysical Research: Solid Earth, 10.1002/2017JB014782, 123, 3, 2199-2213, 2018.03, Stratigraphic variation in the grain size distribution (GSD) of plinian pyroclastic fall deposits reflects volcanic activity. To extract information on volcanic activity from the analyses of deposits, we propose a one-dimensional theory that provides a formula connecting the sediment GSD to the source GSD. As the simplest case, we develop a constant-source model (CS model), in which the source GSD and the source height are constant during the duration of release of particles. We assume power laws of particle radii for the terminal fall velocity and the source GSD. The CS model can describe an overall (i.e., entire vertically variable) feature of the GSD structure of the sediment. It is shown that the GSD structure is characterized by three parameters, that is, the duration of supply of particles to the source scaled by the fall time of the largest particle, ts/tM, and the power indices of the terminal fall velocity p and of the source GSD q. We apply the CS model to samples of the Worzel D ash layer and compare the sediment GSD structure calculated by using the CS model to the observed structure. The results show that the CS model reproduces the overall structure of the observed GSD. We estimate the duration of the eruption and the q value of the source GSD. Furthermore, a careful comparison of the observed and calculated GSDs reveals new interpretation of the original sediment GSD structure of the Worzel D ash layer..
7. Kyohei Sano, Atsushi Toramaru, Cooling and crystallization of rhyolite–obsidian lava
Insights from micron-scale projections on plagioclase microlites, Journal of Volcanology and Geothermal Research, 10.1016/j.jvolgeores.2017.05.012, 341, 158-171, 2017.07, To reveal the cooling process of a rhyolite–obsidian flow, we studied the morphology of plagioclase microlites in the Tokachi–Ishizawa lava of Shirataki, northern Hokkaido, Japan, where the structure of the lava can be observed from obsidian at the base of the flow to the innermost rhyolite. Needle-like micron-scale textures, known as “projections” occur on the short side surfaces of the plagioclase microlites. Using FE–SEM we discovered a positive correlation between the lengths and spacings of these projections. On the basis of the instability theory of an interface between melt and crystal, and to understand the length and spacing data, we developed a model that explains the positive correlation and allows us to simultaneously estimate growth rates and growth times. Applying the model to our morphological data and the estimated growth rates and growth times, we suggest that the characteristics of the projections reflect the degree of undercooling, which in turn correlates with lava structure (the obsidian at the margin of the flow experienced a higher degree of undercooling than the interior rhyolite). The newly developed method provides insights into the degree of undercooling during the final stages of crystallization of a rhyolitic lava flow..
8. O. Namur, Bénédicte Abily, Alan E. Boudreau, Francois Blanchette, John W.M. Bush, Georges Ceuleneer, B. Charlier, Colin H. Donaldson, Jean Clair Duchesne, M. D. Higgins, D. Morata, Troels F.D. Nielsen, B. O’Driscoll, K. N. Pang, Thomas Peacock, Carl J. Spandler, Atsushi Toramaru, I. V. Veksler, Igneous layering in basaltic magma chambers, Layered Intrusions, 10.1007/978-94-017-9652-1_2, 75-152, 2015.01, Layering is a common feature in mafic and ultramafic layered intrusions and generally consists of a succession of layers characterized by contrasted mineral modes and/or mineral textures, including grain size and orientation and, locally, changing mineral compositions. The morphology of the layers is commonly planar, but more complicated shapes are observed in some layered intrusions. Layering displays various characteristics in terms of layer thickness, homogeneity, lateral continuity, stratigraphic cyclicity, and the sharpness of their contacts with surrounding layers. It also often has similarities with sedimentary structures such as crossbedding, trough structures or layer termination. It is now accepted that basaltic magma chambers mostly crystallize in situ in slightly undercooled boundary layers formed at the margins of the chamber. As a consequence, most known existing layering cannot be ascribed to a simple crystal settling process. Based on detailed field relationships, geochemical analyses as well as theoretical and experimental studies, other potential mechanisms have been proposed in the literature to explain the formation of layered igneous rocks. In this study, we review important mechanisms for the formation of layering, which we classify into dynamic and non-dynamic layer-forming processes. Dynamic processes occur during filling of the magma chamber or during its crystalliztion. They include differential settling or flotation of crystals with contrasted densities and/or grain sizes, flow segregation of crystal-laden magma and crystal segregation during convective liquid movement into the magma chamber. Double diffusive convection, which produces a stratified liquid column in the magma chamber, can also produce layering. Other dynamic processes include magma injection into the chamber, which results in magma stratification or magma mixing, and silicate liquid immiscibility either in the main magma chamber or within the solidifying crystal mush. Non-dynamic layer-forming processes mainly include rapid changes in intensive conditions of crystallization (e.g. pressure, oxygen fugacity) that disrupt and change the stable liquidus assemblages, and transitory excursions about cotectic curves. Layering can also result from variation in nucleation rates and from mineral reorganization in a crystal mush through grain rotation, dissolution-precipitation due to initial heterogeneity in terms of grain size distribution, mineral modes or differential pressure. Many of these processes are driven by dissipation of energy and can be referred to as equilibration or self-organization processes..
9. Atsushi Toramaru, On the second nucleation of bubbles in magmas under sudden decompression, EARTH AND PLANETARY SCIENCE LETTERS, 10.1016/j.epsl.2014.07.035, 404, 190-199, 2014.10.
10. Takahiro Miwa, Atsushi Toramaru, Conduit process in vulcanian eruptions at Sakurajima volcano, Japan: Inference from comparison of volcanic ash with pressure wave and seismic data, Bulletin of Volcanology, 75 (2013) 685:DOI 10.1007/s00445-012-0685-y, 2013.01, To elucidate the conduit processes controlling the amplitude of air pressure waves (Apw) from vulcanian eruptions at the Sakurajima volcano, Japan, we examine ash particles emitted by eruptions preceded by swarms of lowfrequency B-type earthquakes (BL-swarms). We measure the water content of glassy ash, an indicator of shallow magma storage pressure, and vesicle textures, such as vesicle number density (VND). These data allow us to reconstruct the shallow conduit by comparing vesicularity with inferred pressure, and therefore depth, of magma storage. The results show that VND increases with depth, implying formation of a dense, outgassed magma cap underlain by more-vesicular, less-outgassed, magma. The VND and water content in the glassy ash positively correlate with the duration of BL-swarms, suggesting that such seismic signals reflect upward migration of deep gas- and vesicle-rich magma. Finally, it is determined that Apw positively correlates
with VND, suggesting that the amplitude of the air pressure waves is controlled by the amount of accumulated gas- and bubble-rich magma below the dense magma cap..
11. Atsushi Toramaru, 前田一樹, Mass and style of eruptions in experimental geysers, Journal of Volcanology and Geothermal Reserches, 257 (2013) 227–239., 2013.04, In the present study, we conducted laboratory experiments of geysers to reproduce the time predictability of
natural geysers in Yellowstone and other geothermal areas. We measured pressure and temperature in a hot
water chamber, flux from a cold water reservoir, and mass erupted by each eruption (total number of eruptions
are up to 100), varying experimental conditions such as the heating rate, water quality, and system
geometry. We observed two styles of eruptions, “jet” and “flow” depending on the maximum height reached.
Under some conditions, only jet events occurred, while under other conditions, jet and flow events
co-occurred. Based on the statistical analysis of the erupted mass, an experiment setup that produces only
jet events exhibits a narrower frequency distribution with a relatively large average mass. As the proportion
of flow events increases, the frequency distribution of the erupted mass widens with relatively small average
mass. The temperature measurements indicated that jet-dominated experimental setups had smaller
temperature fluctuations than flow-dominated setup. We proposed a triggering condition involving boiling
of water that defined the onset of an eruption. We assumed two thresholds of the efficiency of decompression
boiling that defined explosivity and eruption development on the basis of hydrodynamic energetics. Using
the triggering condition and the two thresholds, to explain experimental correlations between erupted
mass, eruption style, and the magnitude of thermal fluctuation, we conducted a Monte Carlo simulation in
a square consisting of 256 × 256 parcels with the superheating temperature as a stochastic variable by a
Gaussian probability density function (PDF). The results showed that when the PDF has a larger average
and smaller standard deviation, the event tends to be explosive and large fraction of water is evacuated, as
in jet events. Decreasing the average temperature or increasing the standard deviation of the PDF shifts the
events to an explosive style followed by an effusive event and to an event that produces only effusive flow.
This transition of eruption styles from explosive to effusive and the relationship with the erupted mass is
consistent with results of the laboratory experiments, suggesting that the spatial distribution pattern of
supersaturated portions just prior to an eruption is a factor controlling the style and transition of the
12. A. Toramaru and M. Matsumoto, Numerical experiment of cyclic layering in a solidified binary eutectic melt, Journal of Geophysical Research, VOL. 117, B02209, doi:10.1029/2011JB008204, 2012, 2012.02, In shallow magmatic intrusions, a characteristic layering structure (hereafter referred to as cyclic layering) can sometimes be observed.
This cyclic layering is different from what is observed as rhythmic layering caused by gravity.
Here, we present examples of cyclic layering in Japan and Scotland.
The cyclic layering is visualized as differential weathering in response to the differential stiffness caused by textural variations such as those in the volume fraction, number density, and size of vesicles or crystals.
The spacing of layers seems to increase according to a geometric progression, like as in Liesegang bands of a diffusion-precipitation system.
Their geological occurrences suggest an origin in which the interplay between double diffusion (mass and heat) and the kinetics of crystallization or vesiculation has an important role.
In order to understand the development condition for cyclic layering and the characteristics of textural variations, such as the spacing of layering in crystallized multi-component melts by conductive cooling, we carried out a numerical experiment on the 1D crystallization process of a binary eutectic melt.
This simulation took into account the cooling from contact with country rock as well as the compositional and thermal diffusion and the kinetics of diffusion-limited crystallization.
The governing equations include dimensionless control parameters describing the relative importance of thermal diffusion or compositional diffusion (Lewis number, $Le$) and the effective latent heat release (Stefan number, $St$).
From the results of the numerical experiments, it was found that the layering develops through eutectic oscillation (compositional and thermal oscillation below the eutectic point), suggesting that the bi-activating condition, whereby both phases cooperatively activate their crystallization rates, is essential for the development of layering.
No layering is observed at the margin, and the length of the region with no layering increases exponentially with decreasing $St$.
The amplitude of textural oscillation decreases with decreasing $St$.
Thus, practically no layering develops at small latent heat release.
Three types of layering structure or oscillatory profiles of spatial texture are observed (short, long and multiple types), depending mainly on $Le$.
Realistic values of $Le$ and $St$ suggest that natural cyclic layering is the multiple or long type of layering.
Assuming that the spacing of natural layering corresponds to the distance between adjoining local maxima of textural quantities, such as crystal number density or mean crystal radius, the spacing in numerical experiments is mathematically well described by a geometric progression with common ratios that are functions of the controlling parameters,namely $Le$, $St$, nucleation barrier, and crystal growth rate scale.
The common ratios converge with increasing $Le$ to constants in the range of approximately 1.02 - 1.05, which is similar to the range of the natural observations.
Experiments with no latent heat release by the second-phase simulated vesicles show similar oscillatory behaviors, suggesting that the latent heat release of the first crystallizing phase is an essential factor for the development of vesicle layering.
Applying the results to vesicle layering, we propose a revised formation scenario in which the thermal effect of first-phase crystallization below the eutectic point dominates the effect of volatile diffusion..
13. T. Miwa, M. Iguchi, A. Toramaru, Correlations of volcanic ash texture with explosion earthquakes from vulcanian eruptions at Sakurajima volcano, Japan, Journal of Volcanology and Geothermal Research, 10.1016/j.jvolgeores.2009.05.012, 184, 3-4, 473-486, 2009.07.
14. A. Toramaru, T. Miwa, Vesiculation and crystallization under instantaneous decompression: Numerical study and comparison with laboratory experiments, Journal of Volcanology and Geothermal Research, Volume 177, Issue 4, 20 November 2008, Pages 983-996
, 2008.11.
15. Satoshi Noguchi, Atsushi Toramaru, Setsuya Nakada, Groundmass crystallization in dacite dykes taken in Unzen Scientific Drilling Project (USDP-4), Journal of Volcanology and Geothermal Research, Volume 175, Issues 1-2, 30 July 2008, Pages 71-81, 2008.11.
16. Satoshi Noguchi, Atsushi Toramaru, Setsuya Nakada, Relation between microlite textures and discharge rate during the 1991–1995 eruptions at Unzen, Japan, Journal of Volcanology and Geothermal Research, Volume 175, Issues 1-2, 30 July 2008, Pages 141-155, 2008.11.
17. Toramaru, A., S. Noguchi, S. Oyoshihara, A. Tsune, MND(microlite number density) water exsolution rate meter, Journal of Volcanology and Geothermal Research, Volume 175, Issues 1-2, 30 July 2008, Pages 156-167
, 2008.07.
18. Akira Tsune, Atsushi Toramaru, Observation and quantitative description of oscillatory zoning in basaltic to dacitic plagioclases, Earth Planets Space, 60, 653–660, 2008.06.
19. A. Tsune and A. Toramaru, A simple model of oscillatory zoning in magmatic plagioclase: Development of an isothermal undercooling model, Americal Mineralogist, 92, 1071-1079., 2007.07.
20. A. Toramaru, BND (bubble number density) decompression rate meter for explosive volcanic eruptions, Journal of Volcanology and Geothermal Research, 154 (2006) 303–316, 2006.05.
21. S. Noguchi, A. Toramaru and T. Shimano, Crystallization of microlites and degassing during magma ascent: Constraints on the fluid mechanical behavior of magma during the Tenjo Eruption on Kozu Island, Japan, Bulletin of Volcanology, 68, 432-449, 2006. DOI: 10.1007/s00445-005-0019-4, 2006.02.
22. Corrections for Na-loss on micro-analysis of glasses by electron probe
X-ray micro amalyzer.
23. Magmatic differentiation process inferred from plagioclase zoning and its pattern.
24. A. Toramaru and T. Matsumoto, Columnar joint morphology and cooling rate: a starch-water mixture experiment, Journal of Geophysical Research, 109, B02205, doi:10.1029/2003JB002686, 2004.02.
25. A. Toramarau, A numerical experiment of crystallization for a binary eutectic system with application to igneous textures, J. Geophys. Res., 106, 4037-4060, 2001.03.
26. A. Toramaru, E. Takazawa, T. Morishita, and K. Matsukage, Model of layering formation in a mantle peridotite (Horoman, Hokkaido, Japan), Earth Planet Sci. Lett., 185, 299-313, 2001.02.
27. A. Toramaru, T. Harada and T. Okamura, Experimental pattern transitions in a Liesegang system, Physica D, 183, 133-140, 2003.09.
28. A. Toramaru, A. Iochi, Transition between periodic precipitation and tree-like crystal aggregates: a detail experimental study, Forma, 15, 365-376, 2000.01.