Permeability and pore-connectivity variation of pumices from a single pyroclastic flow eruption: Implications for partial fragmentation     

Michihiko Nakamura  Keiichi Otaki  Shingo Takeuchi 《Journal of Volcanology and Geothermal Research》2008

The relationship between permeability and vesicularity in volcanic rocks has been used to infer the degassing behavior of hydrous magma. Recent data on natural samples from various eruptions show a wide variation, fitting a power–law relationship of the percolation models with low (< 30%) critical vesicularity (Ф_C). In this study, we present data on permeability and pore-connectivity of juvenile rhyolitic pumice clasts in a pyroclastic flow around Onikobe volcano, NE Japan, and investigate their relationship with vesicularity developed in a single eruption event. The permeability of the pumices having a relatively low abundance of microlites and microphenocrysts shows a trend increasing by 4 orders of magnitude (from 10^− 13.8 to 10^− 10.1 m²) in a high and narrow vesicularity range (from 72 to 80%). This trend intersects at a high angle with the fit to the permeability–vesicularity data in the previous studies that has a low Ф_C, and is located on the extension of the trend for the products of isotropic decompression experiments. The two-dimensional (2D) connectivities of pores for the pumices were also measured from thin sections. From the point of view of percolation theory, connectivity provides information about the probability of percolation. They showed a steep increase from ca. 0 to 0.7 in an almost similar vesicularity range, as compared to their permeabilities. We attribute the increase in 2D connectivity to the increasing amount of ruptured bubble walls, which might have provided less-tortuous paths through larger apertures for gas flow. This, in turn, would cause an effective increase in the permeability. Aggregates of bubble-wall-shaped glass shards were found in the pumices, and their amount and degree of welding are higher in the pumices that have a higher abundance of microlites and microphenocrysts. These pumices have relatively high permeability and 2D connectivity at low vesicularity, which is accounted for by the existence of large irregularly shaped pores. These textural characteristics suggest that a series of partial fragmentation processes, including local rupturing of bubble walls and subsequent foam-collapse with permeable gas flow, might have occurred before the ultimate bulk fragmentation, thus resulting in the increase in permeability. We suggest that the 2D connectivity of pores is a useful parameter to quantify the degree of fragmentation of bubble walls and has the potential for use to assess their permeability.  相似文献   

Regional variations in trace element concentrations in tissues of black tiger shrimp Penaeus monodon (Decapoda: Penaeidae) from South Vietnam     

Tu NP  Ha NN  Ikemoto T  Tuyen BC  Tanabe S  Takeuchi I 《Marine pollution bulletin》2008,57(6-12):858-866

The goal of the present study was to examine the specific bioaccumulation of 22 trace elements in muscle, exoskeleton and hepatopancreas of black tiger shrimp Penaeus monodon from the Mekong River Delta (MRD), and the South Key Economic Zone (SKEZ), South Vietnam. The general tendency in most trace element concentrations among different tissues were hepatopancreas>exoskeleton>muscle. Comparisons of trace element levels in tissues between the two regions showed that concentrations of Se in muscle and As in all three tissues were higher in SKEZ; whereas in MRD, the higher concentrations of most elements such as Mn, Cu, Cd, Ba, Hg, were observed in tissues. These geographical variations in trace element levels may reflect the differences in human activities between the two regions of South Vietnam. The target hazard quotient (THQ) values for trace elements (<1) indicate that local residents are not exposed to potential health risks via the consumption of shrimp.  相似文献   

A quadratic element method for evaluating groundwater flow by the inversion of surface tilt with application to the Tono Area, Japan     

Koji Matsuki  Katsuya Nakatani  Takashi Arai  Kazuo Ohmura  Ryuji Takeuchi  Yasushi Arai  Shinji Takeuchi 《Journal of Hydrology》2008,360(1-4):217-229

By modifying a previous method with constant elements, we developed a quadratic element method for more accurately estimating groundwater flow by the inversion of tilt data. In this method: (1) a region of groundwater flow is divided into quadratic elements in which the change in groundwater volume per unit volume of rock (Δv) and the Skempton coefficient (B) vary in a quadratic manner with the coordinates, (2) the values of Δv are set to zero at the boundaries of the region of groundwater flow and (3) the sum of the squared second derivatives of Δv is adopted as a constraining condition that is weighted and added to the sum of the squared errors in tilt. First, analyses were performed for a flow model to determine the accuracy of this method for estimating groundwater flow and also to clarify the effect of the assumed size of a region of groundwater flow. These analyses showed that the quadratic element method proposed in this study gives a much better estimation of Δv than the constant element method and that a large region of groundwater flow should be assumed, rather than a small region, since the values of Δv at points outside of the actual region of groundwater flow are estimated to be nearly zero when a large region is assumed while these values are greatly overestimated when an excessively small region is assumed. Finally, the quadratic element method was applied to the site of the Mizunami Underground Research Laboratory in the Tono area, Japan. Inverse analyses were performed for tilt data measured by four tiltmeters with a resolution of 10⁻⁹ radians during the excavation of two shafts under the assumption that the rock mass is an isotropic and homogeneous half- space. The results showed that the method proposed in this study reproduced the tilt data very accurately. Thus, the distribution of Δv was estimated without sacrificing the reproducibility of the tilt data. The contour maps of B(1 + ν)Δv (ν: Poisson’s ratio) showed that the heterogeneous flow of groundwater occurred at the site and that groundwater volume decreased mainly in the area surrounded by two faults. The latter result is consistent with the finding obtained by previous investigations that these faults have low permeability in the direction perpendicular to the strike and may act as a flow barrier.  相似文献   

Regional variations in trace element concentrations in tissues of black tiger shrimp Penaeus monodon (Decapoda: Penaeidae) from South Vietnam     

Nguyen Phuc Cam Tu  Nguyen Ngoc Ha  Tokutaka Ikemoto  Bui Cach Tuyen  Shinsuke Tanabe  Ichiro Takeuchi   《Marine pollution bulletin》2008,57(6-12):858

The goal of the present study was to examine the specific bioaccumulation of 22 trace elements in muscle, exoskeleton and hepatopancreas of black tiger shrimp Penaeus monodon from the Mekong River Delta (MRD), and the South Key Economic Zone (SKEZ), South Vietnam. The general tendency in most trace element concentrations among different tissues were hepatopancreas > exoskeleton > muscle. Comparisons of trace element levels in tissues between the two regions showed that concentrations of Se in muscle and As in all three tissues were higher in SKEZ; whereas in MRD, the higher concentrations of most elements such as Mn, Cu, Cd, Ba, Hg, were observed in tissues. These geographical variations in trace element levels may reflect the differences in human activities between the two regions of South Vietnam. The target hazard quotient (THQ) values for trace elements (<1) indicate that local residents are not exposed to potential health risks via the consumption of shrimp.  相似文献   

Bifurcation current along the southwest coast of the Kii Peninsula   总被引：1，自引：0，他引：1  

Junichi Takeuchi  Naoto Honda  Yoshitaka Morikawa  Takashi Koike  Yutaka Nagata 《Journal of Oceanography》1998,54(1):45-52

Along the southwest coast of the Kii Peninsula, a bifurcation current is regularly observed. By using ADCP data taken on board the R/V Wakayama of the Wakayama Prefectural Fisheries Experimental Station, characteristics of this bifurcation current are analyzed. The occurrence frequency of the bifurcation current reaches about 70% in the period from 1988 to 1996. The bifurcation point appears to be changeable and occurs almost evenly between Cape Ichie and Cape Shionomisaki. The current divergence in the alongshore direction was also investigated. Positive divergence values dominated in the whole analyzed area, and an onshore current appears to be dominant along the southwest coast of the Kii Peninsula, except in 1990 when the Kuroshio flowed in a large meandering path.  相似文献   

改进的BTOPMC模型及其在水文模拟中的应用   总被引：2，自引：0，他引：2  

王国强  周买春  竹内邦良  石平博 《地理学报(英文版)》2007,17(1):73-84

In this paper, a grid-based distributed hydrological model BTOPMC （Block-wise use of TOPMODEL） is introduced, which was developed from the original TOPMODEL. In order to broaden the model＇s application to arid regions, improvement methodology is also implemented. The canopy interception and soil infiltration processes were incorporated into the original BTOPMC to model event-based runoff simulation in large arid regions. One designed infiltration model with application of time compression approximation method is emphasized and validated for improving model＇s performance for event hydrological simulations with a case study of Lushi River basin.  相似文献   

Tracing the origin of Southwest Japan using the Hf isotopic composition of detrital zircons from the Akiyoshi Belt     

Xiaojing Zhang  Makoto Takeuchi  Hao‐Yang Lee 《地学学报》2019,31(1):11-17

The Permian Akiyoshi Belt, which is the oldest unmetamorphosed accretionary complex in Southwest Japan, plays an important role in understanding the origin of the Japanese Islands; however, its tectonic affinity is still not well constrained. Herein, we present the first Hf isotopic data for U–Pb dated detrital zircons of the Late Permian sandstones in the Akiyoshi Belt. Almost all the late Palaeozoic detrital zircons yielded highly positive ?_Hf (t) values compatible with a juvenile source, suggesting that the major provenance of the trench sediments was from the South China block and not from the Bureya‐Jiamusi‐Khanka massif. We propose that in the late Palaeozoic, a block of juvenile lower crust existed outboard of the South China block, and it was being melted during the westward subduction of the Palaeo‐Pacific oceanic plate to produce voluminous volcanic and plutonic rocks with positive ?_Hf (t) values.  相似文献   

Estimating groundwater residence time using multiple regression model based on fluoride dissolution: an exploration of possibilities     

Abdelrahman Mohamed Abdelgawad  Kunio Watanabe  Mebruk Mohammed  Shinji Takeuchi 《Environmental Earth Sciences》2010,60(3):449-462

High levels of fluoride concentration were observed in deep groundwater of the Mizunami area in Central Japan. Fluoride occurs mainly due to the reaction between granitic basement rock and groundwater. Granites were collected, crushed to powder, and then allowed to react with purified water for 80 days. Water–rock interaction results showed that the major factor affecting fluoride concentration is the residence time of the groundwater. Coexisting ions have also some contribution toward fluoride concentration. The groundwater residence time in the Mizunami area was estimated by applying results of water–rock interaction to correspond with field data. A regression model relating fluoride concentration, residence time, and coexisting ions was developed. The parameters of the regression model were determined using the genetic algorithms technique. Residence time was estimated by extrapolating experimental data to correspond with filed data. Near the recharge area, residence times in the potential fluoride source rock varied between 1 and 2,000 years, whereas near the discharge area residence times were in excess of tens of thousands of years. The groundwater residence time was also estimated by the groundwater particle-tracking-flow model. The estimates of groundwater residence time based on geochemical regression model were often larger than estimates of groundwater residence time developed by particle-tracking analysis using a groundwater flow model. There were large uncertainties—on the order of 10–10,000 years—in the estimates based on geochemical data.  相似文献   

The origin of fluoride-rich groundwater in Mizunami area, Japan — Mineralogy and geochemistry implications     

Abdelrahman M. Abdelgawad  Kunio Watanabe  Shinji Takeuchi  Takashi Mizuno 《Engineering Geology》2009,108(1-2):76-85

The aim of this paper was to explore new factors that might be reasons for the occurrence of fluoride-rich groundwater in the area around a construction site. During the construction of two deep shafts of the Mizunami Underground Research Laboratory (MIU) in Mizunami city, central Japan, a large quantity of groundwater with high fluoride concentration was charged into the shafts. Chemical investigation carried out during the excavation revealed that fluoride concentrations in the area around the MIU site greatly exceeded those prescribed by Japanese standards. Therefore, the origin of fluoride ion was experimentally investigated. Samples were collected from the core of a deep borehole drilled in the study area. The weathering - and alteration levels of the collected granites varied greatly. Granitic powders were used to measure fluoride content in the granitic rock mass. The fluoride content ranged between 200 and 1300 mg/kg. The powders were reacted with purified water for 80 days. The results of water–rock interaction showed granitic rock to be one of the main sources of fluoride-rich groundwater in Mizunami area. Fluoride concentrations in these solutions that were shaken for 80 days varied between 2 and 7 mg/l. This change may have occurred as a result of the spatial distribution of fluoride ions in the granite mass as evidenced by mineralogical analysis of fluoride content in several specimens. X-ray powder diffraction analysis of the rock before- and after the water–rock interaction tests manifested that the presence of fluorite mineral was relatively small compared to other minerals. The degree of weathering and alteration might be an additional factor causing dissolution of fluoride-rich minerals. However, it was difficult to interpret the change in fluorite composition by X-ray diffraction analysis.  相似文献   

Upper mantle can in-situ fracture: an implication from a cataclastic peridotite xenolith from Megata,Northeast Japan arc     

Miyuki Takeuchi  Shoji Arai 《Mineralogy and Petrology》2015,109(2):283-294

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