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

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

DOI： 10.1029/2020JB019711

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DOI： 10.1016/j.jvolgeores.2019.106760

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DOI： 10.1126/science.aay9070

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DOI： 10.1029/2019GL085009

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DOI： 10.1130/G45323.1

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DOI： 10.1186/s40623-018-0914-5

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DOI： 10.1002/2017GL074845

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DOI： 10.1002/2016GC006472

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

DOI： 10.1016/j.jvolgeores.2016.03.010

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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

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

DOI： 10.1002/2015JB012364

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

DOI： 10.1016/j.jvolgeores.2015.01.002

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

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

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

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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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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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

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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

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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

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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

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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

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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

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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

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Language：English   Presentation type：Oral presentation (general)  

Venue：New Orleans