Updated on 2022/03/07

写真a

 
NAMIKI Atsuko
 
Organization
Graduate School of Environmental Studies Department of Earth and Environmental Sciences Earth and Planetary Physics Associate professor
Graduate School
Graduate School of Environmental Studies
Undergraduate School
School of Science Department of Earth and Planetary Science
Title
Associate professor
Contact information
メールアドレス

Degree 1

  1. Ph. D ( 2002.3 ) 

Research Areas 1

  1. Natural Science / Solid earth sciences  / Volcanology, Earthquake, Rheology

Current Research Project and SDGs 1

  1. Rheology and fragmentation of the molten magma

Awards 1

  1. 特別研究員等審査会専門委員(書面担当)表彰

    2015  

    並木 敦子

 

Papers 33

  1. Coalescence of two growing bubbles in a Hele-Shaw cell. Reviewed

    Ohashi M, Toramaru A, Namiki A

    Scientific reports   Vol. 12 ( 1 ) page: 1270   2022.1

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    Language:English   Publishing type:Research paper (scientific journal)   Publisher:Scientific Reports  

    An understanding of the dynamics of growth-driven coalescence is important in diverse fields across natural science and engineering. Motivated by the bubble coalescence in magma during volcanic eruptions, we study both experimentally and theoretically the coalescence of two growing bubbles in a Hele–Shaw cell. In our system, bubbles grow by gas expansion due to decompression and the diffusional influx of dissolved gas in the liquid. Our experiments show that the evolution of film thickness and bubble shape depends on viscosity, decompression rate, and cell gap. Through a scaling analysis and a perturbation approximation, we find that the hydrodynamic interaction between two bubbles is characterized by a film capillary number Caf= (ηR˙ / σ) (R/ D) 2 depending on viscosity η, bubble radius R, growth rate R˙ , interfacial tension σ, and cell gap D. The experimental results demonstrate that the film capillary number solely determines the bubble distortion just before coalescence. Under our experimental conditions, bubble coalescence occurs below a critical value of a nominal film capillary number defined as a film capillary number evaluated when two undeformed circular bubbles come into contact.

    DOI: 10.1038/s41598-022-05252-5

    Scopus

    PubMed

  2. The build-up and triggers of volcanic eruptions Invited Reviewed

    Luca Caricchi, Meredith Townsend, Eleonora Rivalta, Atsuko Namiki

    NATURE REVIEWS EARTH & ENVIRONMENT   Vol. 2 ( 7 ) page: 458 - 476   2021.7

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    Language:Japanese   Publishing type:Research paper (scientific journal)   Publisher:SPRINGERNATURE  

    More than 800 million people live in proximity to active volcanoes and could be directly impacted by potential eruptions. Mitigation of future volcanic hazards requires adequate warning of a pending eruption, which, in turn, requires detailed understanding of the fundamental processes driving volcanic activity. In this Review, we discuss the processes leading up to volcanic eruptions, by following the journey of magma from crustal storage zones to the surface. Magma reservoirs can feed volcanic eruptions if they contain sufficiently hot and mobile magma and are able to supply sufficient energy for the magma to reach the surface. Young volcanic plumbing systems favour volcanic activity, whereas storage becomes more likely in mature volcanic systems with large reservoirs (hundreds of cubic kilometres). Anticipating volcanic activity requires a multidisciplinary approach, as real-time monitoring and geophysical surveys must be combined with petrology and the eruptive history to understand the temporal evolution of volcanic systems over geological timescales. Numerical modelling serves to link different observational timescales, and the inversion of data sets with physics-based statistical approaches is a promising way forward to advance our understanding of the processes controlling recurrence rate and magnitude of volcanic eruptions.Anticipating the timing, style and size of volcanic eruptions is essential for hazard mitigation. This Review discusses the accumulation and evolution of magma storage regions, the processes that trigger magma reservoir failure and the ascent of magma through the crust.

    DOI: 10.1038/s43017-021-00174-8

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    Scopus

  3. Brittle fragmentation by rapid gas separation in a Hawaiian fountain Reviewed

    Namiki Atsuko, Patrick Matthew R., Manga Michael, Houghton Bruce F.

    NATURE GEOSCIENCE   Vol. 14 ( 4 ) page: 242 - +   2021.4

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    Authorship:Lead author, Last author, Corresponding author   Language:English   Publishing type:Research paper (scientific journal)  

    DOI: 10.1038/s41561-021-00709-0

    DOI: 10.1038/s41561-021-00709-0

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    Other Link: https://rdcu.be/chG2J

  4. Origin and Properties of Hydrothermal Tremor at Lone Star Geyser, Yellowstone National Park, USA Reviewed

    Nayak Avinash, Manga Michael, Hurwitz Shaul, Namiki Atsuko, Dawson Phillip B.

    Journal of Geophysical Research: Solid Earth   Vol. 125 ( 12 )   2020.12

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    Language:English   Publishing type:Research paper (scientific journal)  

    DOI: 10.1029/2020JB019711

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  5. Fragility and an extremely low shear modulus of high porosity silicic magma Reviewed

    Namiki Atsuko, Tanaka Yukie, Okumura Satoshi, Sasaki Osamu, Sano Kyohei, Takeuchi Shingo

    JOURNAL OF VOLCANOLOGY AND GEOTHERMAL RESEARCH   Vol. 392   2020.2

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    Language:English   Publishing type:Research paper (scientific journal)  

    DOI: 10.1016/j.jvolgeores.2019.106760

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  6. Cyclic lava effusion during the 2018 eruption of Kilauea Volcano Reviewed

    Patrick M. R., Dietterich H. R., Lyons J. J., Diefenbach A. K., Parcheta C., Anderson K. R., Namiki A., Sumita I., Shiro B., Kauahikaua J. P.

    SCIENCE   Vol. 366 ( 6470 ) page: 1213-+   2019.12

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    Language:English   Publishing type:Research paper (scientific journal)  

    DOI: 10.1126/science.aay9070

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  7. A Model Experiment of Fracture Induced Long-Period Events: Injection of Pressurized Gas Into a Viscoelastic Rock Analog Reviewed

    Namiki Atsuko, Takahashi Makoto, Tsutsui Ryo

    GEOPHYSICAL RESEARCH LETTERS   Vol. 46 ( 21 ) page: 11906-11914   2019.11

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    Language:English   Publishing type:Research paper (scientific journal)  

    DOI: 10.1029/2019GL085009

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  8. Volcanic activities triggered or inhibited by resonance of volcanic edifices to large earthquakes Reviewed

    Namiki Atsuko, Rivalta Eleonora, Woith Heiko, Willey Timothy, Parolai Stefano, Walter Thomas R.

    GEOLOGY   Vol. 47 ( 1 ) page: 67-70   2019.1

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    Language:English   Publishing type:Research paper (scientific journal)  

    DOI: 10.1130/G45323.1

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  9. Physical characteristics of scoriae and ash from 2014-2015 eruption of Aso Volcano, Japan Reviewed

    Namiki Atsuko, Tanaka Yukie, Yokoyama Tadashi

    EARTH PLANETS AND SPACE   Vol. 70 ( 1 )   2018.9

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    Language:English   Publishing type:Research paper (scientific journal)  

    DOI: 10.1186/s40623-018-0914-5

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  10. Oscillatory rheology measurements of particle- and bubble-bearing fluids: Solid-like behavior of a crystal-rich basaltic magma Reviewed

    Namiki Atsuko, Tanaka Yukie

    GEOPHYSICAL RESEARCH LETTERS   Vol. 44 ( 17 ) page: 8804-8813   2017.9

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    Language:English   Publishing type:Research paper (scientific journal)  

    DOI: 10.1002/2017GL074845

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  11. An experimental study of the role of subsurface plumbing on geothermal discharge Reviewed

    Namiki Atsuko, Ueno Yoshinori, Hurwitz Shaul, Manga Michael, Munoz-Saez Carolina, Murphy Fred

    GEOCHEMISTRY GEOPHYSICS GEOSYSTEMS   Vol. 17 ( 9 ) page: 3691-3716   2016.9

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    Language:English   Publishing type:Research paper (scientific journal)  

    DOI: 10.1002/2016GC006472

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  12. Sloshing of a bubbly magma reservoir as a mechanism of triggered eruptions Invited Reviewed

    Namiki Atsuko, Rivalta Eleonora, Woith Heiko, Walter Thomas R.

    JOURNAL OF VOLCANOLOGY AND GEOTHERMAL RESEARCH   Vol. 320   page: 156-171   2016.6

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    Language:English   Publishing type:Research paper (scientific journal)  

    DOI: 10.1016/j.jvolgeores.2016.03.010

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  13. 室内実験による火山現象の解明(<特集>日本火山学会60周年「火山学の最新動向と今後の展望」) Invited Reviewed

    並木 敦子

    火山   Vol. 61 ( 1 ) page: 171-182   2016

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    Language:English   Publishing type:Research paper (scientific journal)  

    Magmas include phenocrysts and bubbles, and sometimes fragment under rapid deformation. Ascent of such a complicated magma generates and destroys surfaces between the melt and other phases. In this system, magma dynamics and physical properties of magma are coupled. The interaction between the magma dynamics and physical properties has not yet explained well, and prevents our understanding of eruption dynamics. Recently, several laboratory experiments have performed, describing interaction between dynamics and physical properties quantitatively. Here, I would like to review those experiments.

    DOI: 10.18940/kazan.61.1_171

  14. Geyser eruption intervals and interactions: Examples from El Tatio, Atacama, Chile Reviewed

    Munoz-Saez Carolina, Namiki Atsuko, Manga Michael

    JOURNAL OF GEOPHYSICAL RESEARCH-SOLID EARTH   Vol. 120 ( 11 ) page: 7490-7507   2015.11

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    Language:English   Publishing type:Research paper (scientific journal)  

    DOI: 10.1002/2015JB012364

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  15. Dynamics within geyser conduits, and sensitivity to environmental perturbations: Insights from a periodic geyser in the El Tatio geyser field, Atacama Desert, Chile Reviewed

    Munoz-Saez Carolina, Manga Michael, Hurwitz Shaul, Rudolph Maxwell L., Namiki Atsuko, Wang Chi-Yuen

    JOURNAL OF VOLCANOLOGY AND GEOTHERMAL RESEARCH   Vol. 292   page: 41-55   2015.2

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    Language:English   Publishing type:Research paper (scientific journal)  

    DOI: 10.1016/j.jvolgeores.2015.01.002

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  16. El Cobreloa: A geyser with two distinct eruption styles Reviewed

    Atsuko Namiki, Carolina Munoz-Saez, Michael Manga

    JOURNAL OF GEOPHYSICAL RESEARCH-SOLID EARTH   Vol. 119 ( 8 ) page: 6229 - 6248   2014.8

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    Publishing type:Research paper (scientific journal)   Publisher:AMER GEOPHYSICAL UNION  

    We performed field measurements at a geyser nicknamed "El Cobreloa," located in the El Tatio Geyser Field, Northern Andes, Chile. The El Cobreloa geyser has two distinct eruption styles: minor eruptions and more energetic and long-lived major eruptions. Minor eruptions splash hot water intermittently over an approximately 4 min time period. Major eruptions begin with an eruption style similar to minor eruptions, but then transition to a voluminous liquid water-dominated eruption, and finally end with energetic steam discharge that continues for approximately 1 h. We calculated eruption intervals by visual observations, acoustic measurements, and ground temperature measurements and found that each eruption style has a regular interval: 4 h and 40 min for major eruptions and similar to 14 min for minor eruptions. Eruptions of El Cobreloa and geochemical measurements suggest interaction of three water sources. The geyser reservoir, connected to the surface by a conduit, is recharged by a deep, hot aquifer. More deeply derived magmatic fluids heat the reservoir. Boiling in the reservoir releases steam and hot liquid water to the overlying conduit, causing minor eruptions, and heating the water in the conduit. Eventually the water in the conduit becomes warm enough to boil, leading to a steam-dominated eruption that empties the conduit. The conduit is then recharged by a shallow, colder aquifer, and the eruption cycle begins anew. We develop a model for minor eruptions which heat the water in the conduit. El Cobreloa provides insight into how small eruptions prepare the geyser system for large eruptions.

    DOI: 10.1002/2014JB011009

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  17. Earthquake model experiments in a viscoelastic fluid: A scaling of decreasing magnitudes of earthquakes with depth Reviewed

    Atsuko Namiki, Tetsuo Yamaguchi, Ikuro Sumita, Takehito Suzuki, Satoshi Ide

    JOURNAL OF GEOPHYSICAL RESEARCH-SOLID EARTH   Vol. 119 ( 4 ) page: 3169 - 3181   2014.4

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    Publishing type:Research paper (scientific journal)   Publisher:AMER GEOPHYSICAL UNION  

    We performed shear deformation experiments using quasi-Maxwell fluids. We found that, depending on the strain rates, the same material generates earthquakes associated with the elastic rebound and deforms viscously. Around the threshold, elastic rebound releases a certain fraction of the interseismic displacement, but the other fraction remains as a result of the viscous relaxation. We applied our experimental results to a subduction zone, in which the upper part of the hanging wall behaves as an elastic layer and generates seismicity, while the deeper part behaves as a viscous fluid and subducts with the slab. Our experimental results suggest that, around the boundary of the elastic and viscous layers, seismicity can occur, but only some part of the interseismic displacements is released. The experimentally obtained threshold of the seismic activity is determined by the combination of the subduction velocity v(s), the viscosity of the hanging wall eta, the fault length W, and the adhesive stress sigma(a), V-s eta/(W sigma(a)) > 1. This threshold suggests that if the viscosity of the hanging wall decreases with depth, the maximum size of the earthquakes also decreases with depth, and, finally, seismicity disappears. This hypothesis is consistent with the observed fact that slow earthquakes, characterized by their small magnitudes, are observed at the downdip limit of the seismogenic zone.

    DOI: 10.1002/2014JB011135

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  18. Intermittent and efficient outgassing by the upward propagation of film ruptures in a bubblymagma Reviewed

    Atsuko Namiki, Takanori Kagoshima

    JOURNAL OF GEOPHYSICAL RESEARCH-SOLID EARTH   Vol. 119 ( 2 ) page: 919 - 935   2014.2

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    Publishing type:Research paper (scientific journal)   Publisher:AMER GEOPHYSICAL UNION  

    We simulated the ascent of bubbly magma in a volcanic conduit by slow decompression experiments using syrup foam as a magma analogue. During decompression, some large voids appear in the foam. The expansion of one void deep in the foam leads to another void expansion, and the void expansion then propagates upward. The void expansion finally reaches the surface of the foam to originate outgassing. The velocity of the upward propagation of void expansions is essentially the same as the rupturing velocity of the bubble film, suggesting that the rupture of films separating each void propagates upward to create the pathway for outgassing. The calculated apparent permeability of decompressed foam can become higher than that measured for natural pumices/scoriae. The upward propagation of film ruptures thus allows for efficient outgassing. This may also appear as the mechanism for energetic gas emissions originating at a depth, such as Strombolian eruptions.

    DOI: 10.1002/2013JB010576

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  19. A laboratory model for melting erosion of a magma chamber roof and the generation of a rhythmic layering Reviewed

    Yasuko Shibano, Ikuro Sumita, Atsuko Namiki

    JOURNAL OF GEOPHYSICAL RESEARCH-SOLID EARTH   Vol. 118 ( 8 ) page: 4101 - 4116   2013.8

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    Publishing type:Research paper (scientific journal)   Publisher:AMER GEOPHYSICAL UNION  

    A hot magma chamber can ascend by melting the roof rock, a process which in turn affects the magma composition. The disaggregated mineral particles which consisted the roof rock will descend in the magma chamber to form a sedimentary cumulate. However, the fluid dynamics leading to the formation of the sediment, and how we can decipher them is unknown. Here we conducted a series of experiments modeling melting erosion of the roof with particle size consisting the roof rock as the parameter. We find that there is a critical particle size below which the melting erosion occurs rhythmically. Melting erosion stops because the disaggregated particles are suspended in the magma chamber and suppress the vertical heat transfer. The suspension then separates into an upper clear layer and a lower suspension layer. Eventually, the heated stratified layers become unstable. An overturn occurs, and melting erosion resumes. When the particles consist of two sizes such that at least one of them is smaller than the critical size, a rhythmic erosion occurs. Particles are sorted during each erosion period, and a size-graded rhythmic layering is spontaneously generated. We estimate that rhythmic layering can be generated from melting erosion in a basaltic magma chamber when the grain size of the roof rock is 0.6 mm, assuming a vertical temperature difference of 10 degrees C. We suggest that rhythmic roof melting coupled with particle settling is one possible mechanism for generating the rhythmic layering which is commonly observed in solidified magma chambers.

    DOI: 10.1002/jgrb.50295

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  20. Can a sheet-like low-velocity region form an elongated Large Igneous Province? Reviewed

    Atsuko Namiki, Kenta Sueyoshi, Nozomu Takeuchi

    GEOCHEMISTRY GEOPHYSICS GEOSYSTEMS   Vol. 14 ( 8 ) page: 3053 - 3066   2013.8

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    Publishing type:Research paper (scientific journal)   Publisher:AMER GEOPHYSICAL UNION  

    High-resolution tomography of the lower mantle has revealed the existence of another chemically distinct region with low-velocity and a sheet-like structure beneath the western Pacific. On the other hand, Large Igneous Provinces (LIPs) sometimes have elongated shapes. If a sheet-like upwelling reaches the Earth's surface while maintaining its shape, an elongated LIP may form. In order to test this hypothesis, we perform a series of experiments and investigate the stability of a buoyant sheet. The experimental results show that the buoyant fluid accumulates at the top of the sheet to form a buoyant cylinder. The gravitational instability divides the cylinder into several plume heads. We develop a model to explain the growth of the buoyant cylinder and the time scale until instability begins. Our model shows that a thin sheet-like upwelling with a width of 200 km, a small density difference from the ambient mantle, 10 kg m(-3), and a high supply rate of buoyant fluid, 0.1 m yr(-1), can reach the Earth's surface while maintaining its shape. We thus infer that LIPs with an elongated shape can be generated by sheet-like upwellings. The width of the observed sheet-like low-velocity region beneath the western Pacific is 500 km and is marginally sufficient to form an elongated LIP.

    DOI: 10.1002/ggge.20182

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  21. An empirical scaling of shear-induced outgassing during magma ascent: Intermittent magma ascent causes effective outgassing Reviewed

    Atsuko Namiki

    EARTH AND PLANETARY SCIENCE LETTERS   Vol. 353   page: 72 - 81   2012.11

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    Publishing type:Research paper (scientific journal)   Publisher:ELSEVIER SCIENCE BV  

    Outgassing, which changes the distribution of volcanic gases in magmas, is one of the most important processes to determine the eruption styles. Shear deformation of ascending bubbly magmas at the vicinity of the volcanic conduit wall has been considered as an efficient mechanism of outgassing. On the other hand, seismological observations of volcanic eruptions reveal the gas bursting associated with long-period (LP) earthquakes and tremors, suggesting the existence of a large void space in the conduit. However both, the quantitative features of shear-induced outgassing and a mechanism to make a large void space, have still remain unknown. Here I perform a series of model experiments in which shear localization of syrup foam causes outgassing by making large bubbles or a crack-like void space, likely a gas bursting source. There is a critical strain, gamma, above which outgassing occurs depending on the Capillary number, Ca, gamma > 1 for Ca < 1 and gamma > Ca-1 for Ca >= 1. The width of the region in which outgassing occurs is described as a function of gamma Ca-0.48(0.24). Outgassing occurs efficiently at the very beginning of the deformation, suggesting that intermittent magma ascent causes effective outgassing such that the eruption style becomes effusive. This hypothesis is consistent with the fact that cyclic activity has been observed during effusive dome eruptions. (C) 2012 Elsevier B.V. All rights reserved.

    DOI: 10.1016/j.epsl.2012.08.007

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  22. Experiments on upward migration of a liquid-rich layer in a granular medium: Implications for a crystalline magma chamber Reviewed

    Yasuko Shibano, Atsuko Namiki, Ikuro Sumita

    GEOCHEMISTRY GEOPHYSICS GEOSYSTEMS   Vol. 13   2012.3

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    We perform a series of experiments to investigate the situation in which a melt-rich layer formed by a magma intrusion ascends through a crystalline magma chamber. The initial condition is such that a heavier granular layer overlies a liquid layer. The particles consisting the upper granular layer are in a jammed state, and only the particles near the interface can move to form a dilated boundary layer. The dilated layer detaches from the upper granular layer, and forms downwelling plumes which drive a cellular convection within the liquid-rich layer. The convection erodes the upper granular layer, and the liquid-rich layer migrates upwards with time. This upward migration of the liquid-rich layer differs from the previously known mechanisms of liquid transport; permeable flow in which the liquid migrates at the Darcy velocity, the Stokes settling in which the individual particle settles, and diapirs formed by the Rayleigh-Taylor instability. We find that the velocity of the upward migration of the liquid-rich layer can be scaled by the volumetric flux of the liquid ascending through the narrow channel between the particles. The upward migration of the liquid-rich layer is faster than the Darcy velocity. In a mushy magma chamber whose crystals are in a jammed state, neither the Stokes settling nor the Rayleigh-Taylor instability can occur. We propose that the upward migration of the melt-rich layer observed in our experiments can become an efficient mechanism of melt transport in a crystalline magma chamber.

    DOI: 10.1029/2011GC003994

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  23. Excitation of airwaves caused by bubble bursting in a cylindrical conduit: Experiments and a model Reviewed

    Tsukasa Kobayashi, Atsuko Namiki, Ikuro Sumita

    JOURNAL OF GEOPHYSICAL RESEARCH-SOLID EARTH   Vol. 115   2010.10

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    Strombolian eruptions are considered to be a consequence of the bursting of a large bubble. In order to understand the relation between the style of bubble bursting and the resulting airwave, we perform experiments of bubble bursting at the top of the surface of viscous liquid contained in an acrylic pipe which acts as an air column and observe it visually and acoustically. We find that when the liquid viscosity is less than 1 Pa s, the bubble vibrates before bursting. The major source of the airwave during the sequence of the bubble bursting is the bubble vibration. On the other hand, when the liquid viscosity is greater than 1 Pa s, the bubble does not vibrate. During bubble bursting, an aperture appears on the bubble film. The aperture growth first accelerates and later decelerates before finally stopping. The major source of the airwave is the aperture growth. We calculate a synthetic waveform of the airwave generated by the aperture growth which explains the experimentally observed airwave well. When the frequency of the airwave generated by the aperture growth matches the eigenfrequency of the air column, resonance occurs. Applying this model to the Strombolian eruption, the characteristic low frequency (<20 Hz) is explained if the velocity of the aperture growth is several meters per second. The model also explains the asymmetrical initial rise of the airwave observed in the Strombolian eruptions as a result of the accelerating growth of the aperture.

    DOI: 10.1029/2009JB006828

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  24. Transition between fragmentation and permeable outgassing of low viscosity magmas Reviewed

    Atsuko Namiki, Michael Manga

    JOURNAL OF VOLCANOLOGY AND GEOTHERMAL RESEARCH   Vol. 169 ( 1-2 ) page: 48 - 60   2008.1

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    Publishing type:Research paper (scientific journal)   Publisher:ELSEVIER SCIENCE BV  

    Explosive volcanic eruption requires that magma fragments into discrete parcels. Silicic magma can fragment through brittle failure or other processes that depend on the viscoelasticity of the melt. Owing to the low viscosity of basaltic magmas, however, the fragmentation mechanism must be different and will be governed by fluid mechanics alone. We perform a series of decompression experiments on bubbly Newtonian fluids with viscosities and surface tensions similar to those of basaltic magmas. For sufficiently rapid expansion, the bubbly fluid expands continuously, eventually tearing into several pieces. We find that the fragmentation threshold is governed by a critical Reynolds number of similar to 1, indicating that it is the inertia of the expanding fluid that drives the continued expansion and ultimate breakup into discrete parcels. Experiments in which the fluid does not fragment allow us to determine the gas permeability of the bubbly fluid as the bubbles expand. Permeability remains small until the volume fraction of bubbles exceeds about 70%. We scale the results of the laboratory experiments to basaltic eruptions and find that the predicted fragmentation threshold is consistent with the exit velocities that characterize effusive and explosive eruptions. Our experimental results suggest that the mechanism for fragmentation of low viscosity basaltic magma is fundamentally different from that of high-viscosity silicic magma, and that magma with low viscosities can fragment easily. (C) 2007 Elsevier B.V. All rights reserved.

    DOI: 10.1016/j.jvolgeores.2007.07.020

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  25. Influence of decompression rate on the expansion velocity and expansion style of bubbly fluids Reviewed

    Atsuko Namiki, Michael Manga

    JOURNAL OF GEOPHYSICAL RESEARCH-SOLID EARTH   Vol. 111 ( B11 )   2006.11

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    The decompression rate of magma is correlated with explosivity of volcanic eruptions. We present a series of decompression experiments in a shock tube apparatus to investigate the effect of decompression rate on the expansion and eruption style of bubbly fluids. We also consider the effects of the pressure change Delta P and initial vesicularity phi(i). As an analogue for magma we use viscoelastic polymer solutions. For fast decompression, we observe fragmentation and rupture of bubble walls only for large Delta P and large phi(i). For slow decompression, however, bubbles maintain spherical shapes, and the bubbly fluid does not fragment, irrespective of Delta P and phi(i). We consider two theoretical estimates for the expansion of bubbles, which we refer to as "equilibrium expansion,'' in which the pressures inside and outside the bubbles are assumed to be equal, and "disequilibrium expansion,'' in which the enthalpy change caused by the pressure change is converted into kinetic energy. The observed expansion velocity is governed by the slower estimate. For slow decompression, where bubbles expand while maintaining their spherical shape, the measured expansion is well explained by equilibrium expansion. In contrast, for fast decompression, in which we observe the rupture of bubble walls and fragmentation, the expansion follows disequilibrium expansion. We conclude that the disequilibrium estimate is an upper limit velocity for the bubble expansion and fragmentation and the rupture of bubble walls require disequilibrium expansion. The calculated threshold decompression rate for disequilibrium expansion is consistent with the estimated decompression rate for the explosive/effusive transition in natural basaltic eruptions.

    DOI: 10.1029/2005JB004132

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  26. Influence of a basal thermal anomaly on mantle convection Reviewed

    Nayuta Matsumoto, Atsuko Namiki, Ikuro Sumita

    PHYSICS OF THE EARTH AND PLANETARY INTERIORS   Vol. 157 ( 3-4 ) page: 208 - 222   2006.8

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    Publishing type:Research paper (scientific journal)   Publisher:ELSEVIER SCIENCE BV  

    We perform laboratory experiments to study the effects of a variable basal thermal anomaly on convection. In the regime of cellular convection (Ra < 10(7)), the convection pattern changes as the horizontal temperature variation in the bottom boundary increases. When the temperature variation is less than the critical value, there is no effect to the convection pattern. Above this critical value, an upwelling is fixed at the site of the thermal anomaly. For a larger temperature variation, the upwelling region becomes wider. For the cases above the critical value, the time-averaged temperature in the isothermal core above the thermal anomaly becomes higher than that in the other regions. In the regime of plume dominant convection (Ra >= 107), when the horizontal temperature variation exceeds the critical value, the location of a hot plume is similarly affected. For this case, the plume generated by the thermal anomaly straddles around the site of the thermal anomaly rather than being fixed. For a larger temperature variation, multiple plumes cluster together which also straddle around the anomaly. The straddling nature of the hot plumes generated by the thermal anomaly causes the time-averaged temperature above the thermal anomaly to remain unchanged. We also find that different from the cellular convection cases, the temperature variation less than critical is capable of generating intermittent hot plumes, but they do not dominate the convection pattern. The critical horizontal temperature variation needed to affect the convection pattern is found to be scaled by the maximum standard deviation of the time variation of the temperature sigma(max)* around the lower thermal boundary layer in the absence of thermal anomaly. We estimate the possible temperature variation which can be generated by a partially molten region at the CMB. We find that assuming that sigma(max)* for mantle is the same as that obtained from the experiment, a region less viscous than the surrounding region by an order of magnitude, can generate a hotspot. (c) 2006 Elsevier B.V. All rights reserved.

    DOI: 10.1016/j.pepi.2006.04.005

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  27. Response of a bubble bearing viscoelastic fluid to rapid decompression: Implications for explosive volcanic eruptions Reviewed

    A Namiki, M Manga

    EARTH AND PLANETARY SCIENCE LETTERS   Vol. 236 ( 1-2 ) page: 269 - 284   2005.7

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    Publishing type:Research paper (scientific journal)   Publisher:ELSEVIER SCIENCE BV  

    We conducted rapid decompression experiments using bubble-bearing viscoelastic fluid in a vertical shock tube. We varied vesicularity phi and pressure difference between the inside P-g and the outside P-o of the bubbles, Delta P=P-g-P-o, to understand the behavior of bubbly-magmas under rapid decompression. We find that the potential energy, which depends on the initial vesicularity phi, P-g, and P-o, determines the expansion velocity of the bubbly fluid during rapid decompression. Higher potential energy, caused by a higher phi and a larger Delta P, leads to faster expansion. the expansion style also depends on the vesicularity phi and on the pressures P-g and P-o. We observe five different styles of expansion during the rapid decompression that depend on phi and Delta P. When both phi and Delta P are small, "nothings' occurs. As phi and Delta P increase, the bubbly fluid reacts more violently. First, the surface of the bubbly fluid "deforms" and the fluid elongates in the vertical direction. For sufficient elongation the fluid can "detach" from the tube wall. As phi and Delta P continue to increase, bubble walls can break, a process we refer to as "partial rupture". Finally, for still larger Delta P and phi, both bubble walls and plateau borders break allowing the fluid to "fragment" into discrete pieces and erupt explosively. Our experiments show that a larger potential energy, which results from higher phi and larger Delta P, causes a faster expansion of magma which in turn promotes fragmentation and thus explosive eruption. If we assume that the pressure inside bubbles P-g scales with the depth of bubbly magma, measuring the magma vesicularity in conduits or domes as a function of the depth before eruption would help assess volcanic hazard. (c) 2005 Elsevier B.V. All rights reserved.

    DOI: 10.1016/j.epsl.2005.02.045

    Web of Science

  28. Can the mantle entrain D ''? Reviewed

    A Namiki

    JOURNAL OF GEOPHYSICAL RESEARCH-SOLID EARTH   Vol. 108 ( B10 )   2003.10

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    Publishing type:Research paper (scientific journal)   Publisher:AMER GEOPHYSICAL UNION  

    [1] A series of laboratory experiments for mixing between the more viscous upper layer and the less viscous lower layer has been performed to study how the less viscous D" mixes with the overlying more viscous mantle. Experimental results show that the style of entrainment when the more viscous layer overlies the less viscous layer is different from the opposite case. In the latter case the interface between the two layers moves upward, indicating that the more viscous lower layer asymmetrically entrains the less viscous upper layer. However, in the former case, an interfacial layer develops between the two layers and the interface does not move, indicating that the volumetric ratio of the two layers remains unchanged. It has been suggested that the compositional difference between mid-ocean ridge basalts (MORB) and ocean island basalts (OIB) originates from the entrainment of D" by the mantle plumes. The experimental results suggest that the mantle plume entrains only the interfacial layer, thus modifying the composition of OIB. The volume of D" would remain unchanged since D" is formed.

    DOI: 10.1029/2002JB002315

    Web of Science

  29. Bubble size distributions in a convecting layer Reviewed

    A Namiki, T Hatakeyama, A Toramaru, K Kurita, Sumita, I

    GEOPHYSICAL RESEARCH LETTERS   Vol. 30 ( 15 )   2003.8

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    Publishing type:Research paper (scientific journal)   Publisher:AMER GEOPHYSICAL UNION  

    [1] We have conducted a series of laboratory experiments to explore the bubble size distribution coupled with convection in a magma chamber. Boiling liquid heated from below exhibits two types of convection pattern depending on the viscosity. When the viscosity is sufficiently high, bubbles are distributed uniformly in the liquid, and the bubble size distribution becomes the power law type for large bubbles and exponential distribution for small bubbles. On the other hand, when the viscosity is low, bubbles are separated from the liquid layer, making a foam, and their size distribution is exponential for large bubbles and unimodal for small bubbles. These experimental results suggest that the bubble size distribution is determined whether the viscous drag of the magma is sufficiently high to trap bubbles.

    DOI: 10.1029/2003GL017156

    Web of Science

  30. Heat transfer and interfacial temperature of two-layered convection: Implications for the D ''-mantle coupling Reviewed

    A Namiki, K Kurita

    GEOPHYSICAL RESEARCH LETTERS   Vol. 30 ( 1 )   2003.1

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    Publishing type:Research paper (scientific journal)   Publisher:AMER GEOPHYSICAL UNION  

    [1] We performed laboratory measurements of the heat flux and the interfacial temperature of two-layered thermal convection. Experiments show that the scaling law of the heat flux (Nu-Ra relation) can be classified by the buoyancy number B. The heat flux under B > 1 follows the well-known Nu-Ra relation. However, under B < 1, undulations develop at the interface, and heat flux is systematically enhanced. The interfacial temperature is determined only by the ratio of physical properties between the upper and lower layers. Our results suggest that the existence of less viscous and slightly denser D" than the overlying mantle would enhance the heat transfer from the core to the mantle.

    DOI: 10.1029/2002GL015809

    Web of Science

  31. Rayleigh-Benard convection with an inclined upper boundary Reviewed

    A Namiki, K Kurita

    PHYSICAL REVIEW E   Vol. 65 ( 5 )   2002.5

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    Publishing type:Research paper (scientific journal)   Publisher:AMER PHYSICAL SOC  

    We report experiments on thermally driven convection of a high-Prandtl-number fluid with an inclined upper boundary. For an inclined angle greater than the critical value, we observed a few new convection patterns, in which laterally migrating convection cells and plumes appear simultaneously and a large-scale flow is induced from the inclined upper boundary. The plumes induced from the inclined upper boundary activate the temperature fluctuations, resulting in the formation of a large-scale horizontal heat transfer with a lateral scale larger than that of each convection cell. The critical angle for the onset of the lateral migration of the cells is determined by comparing the two length scales: the height difference in one convection cell imposed by the inclined upper boundary and the thickness of the viscous boundary layer.

    DOI: 10.1103/PhysRevE.65.056301

    Web of Science

  32. The influence of boundary heterogeneity in experimental models of mantle convection with internal heat sources Reviewed

    A Namiki, K Kurita

    PHYSICS OF THE EARTH AND PLANETARY INTERIORS   Vol. 128 ( 1-4 ) page: 195 - 205   2001.12

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    Language:English   Publishing type:Research paper (scientific journal)   Publisher:ELSEVIER SCIENCE BV  

    The lateral variations in the thickness of the D" layer observed by recent global seismology are suspected to control mantle dynamics. Namiki and Kurita (1999) performed laboratory experiments to explore how undulations of various sizes in the D" layer affect convection patterns. In addition, we found that the undulation at the lower boundary can induce plumes and that there is a critical height above which the undulation controls convection patterns. Observed undulations at the top of the W layer exceed this critical height, suggesting that they may control the mantle convection patterns. The previous work, however, assumed basal heating. Since internal heating is an important source which drives mantle convection, we extend our previous study to a case incorporating internal heat sources using laboratory experiments. Internal heat generation is simulated by lowering the boundary temperatures at a constant rate. We observed that the undulation, which has the comparable thickness to the critical height determined in the purely basal heating case, can fix the location of the upwelling although the magnitude of the intensity of the upwelling is weaker. This situation is similar to the Earth's hotspots and suggests that the undulation at the top of the D" layer is the source region of the hotspots. (C) 2001 Elsevier Science B.V. All rights reserved.

    DOI: 10.1016/S0031-9201(01)00286-2

    Web of Science

  33. The influence of boundary heterogeneity in experimental models of mantle convection Reviewed

    A Namiki, K Kurita

    GEOPHYSICAL RESEARCH LETTERS   Vol. 26 ( 13 ) page: 1929 - 1932   1999.7

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    Language:English   Publishing type:Research paper (scientific journal)   Publisher:AMER GEOPHYSICAL UNION  

    Recent global seismological observations have revealed lateral variations in the thickness of the D " layer. We have performed laboratory experiments to explore how undulations of various sizes in the D " layer affect convection patterns. We find that topography on the lower boundary can induce plumes and that there is a critical height above which topography controls convection patterns. Observed undulations in the D " layer exceed this critical height, suggesting that they may control mantle convection patterns.

    DOI: 10.1029/1999GL900427

    Web of Science

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Presentations 1

  1. Brittle Fragmentation by Rapid Gas Separation in a Hawaiian Fountain International coauthorship International conference

    Atsuko Namiki, Matthew R Patrick, Michael Manga, Bruce F Houghton

    AGU Fallmeeting  2021.12.14  AGU

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    Language:English   Presentation type:Oral presentation (general)  

    Venue:New Orleans  

KAKENHI (Grants-in-Aid for Scientific Research) 4

  1. Catastrophic caldera forming eruption revealed by petrological and experimental study of lubrication of crystal-mush

    Grant number:21KK0055  2021.10 - 2024.3

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    Authorship:Coinvestigator(s) 

  2. 火山直下のマグマの状態と将来を知る方法の提案:粘弾性測定と浸透流・破砕の実験

    Grant number:19H00721  2019.4 - 2024.3

    基盤研究(A)

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    Authorship:Principal investigator  Grant type:Competitive

  3. 粘弾性体中で起き得る地震の最大サイズの実測と地震波形の観察:モデル実験と理論

    Grant number:19H04625  2019.4 - 2022.3

    スロー地震学: 新学術領域研究(研究領域提案型)

    並木敦子

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    Authorship:Principal investigator  Grant type:Competitive

  4. Constructing a model of outgassing from basaltic magma based on observations and experiments

    Grant number:17KK0092  2017.4 - 2023.3

    Atsuko Namiki

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    Authorship:Principal investigator  Grant type:Competitive

 

Teaching Experience (On-campus) 4

  1. Introduction to Earth Science

    2021

  2. Introduction to Earth and Planetary Physics

    2021

  3. Geophysics and Planetary Physics Experiments I

    2021

  4. Earth and Planetary Physics 2

    2021

 

Social Contribution 2

  1. 名大MIRAI GSC 講義

    Role(s):Lecturer

    2021.7

  2. 2018年ハワイ島の噴火でわかったマグマの破砕

    Role(s):Lecturer

    2021.6