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Yoshihiro Kuwahara Last modified date:2017.06.01

Associate Professor / Course for Earth Changes
Department of Environmental Changes
Faculty of Social and Cultural Studies

Graduate School
Other Organization

Introduction to ykuwa's world .
Academic Degree
Dr. of Science
Field of Specialization
Research Interests
  • Dissolution and crystal growth mechanisms of carbonate and sulfate minerals as the index of climate and environmental changes: nanoscale analysis by hot/cool-stage AFM
    keyword : climate change, environmental change, AFM, dissolution and crystal growth mechanisms, carbonate mineral, sulfate mineral
  • In-situ AFM study for smectite dissolution under alkaline conditons
    keyword : smectite, dissolution, kinetics, alkaline solutions, Atomic Force Microscopy, Bentonite, buffer materials
  • Reconstruction of paleoclimatic and paleoenvironmental variations recorded in clay minerals in the Kathmandu Basin sediments
    keyword : clay minerals, crystallinity, paleoclimate, paleoenvironment, the Kathmandu Basin, Hymalaya
  • AFM study on surface structure of micas
    keyword : micas, Atomic Force Microscopy, surface structure, surface relaxation
  • AFM study for the growth mechanism and process of mica clay minerals
    keyword : illite, Atomic Force Microscopy, crystall growth, spiral growth pattern
  • Dissolution process and mechanism of micas under acid conditons
    keyword : micas, acid condition, dissolution, weathering, alteration, kinetics
Current and Past Project
  • Carbonate and sulfate minerals serve as an important indicator of climate and environmental changes because they dissolve and/or precipitate by slight change of temperature even at low temperature. However, the mechanisms are not well understood. In-situ AFM studies on mineral dissolution make it possible to characterize the reactive surfaces and to estimate the essential dissolution rate. Furthermore, AFM with a temperature-controlled fluid-cell system enables in situ observations of mineral dissolution at elevated and lowered temperatures. So far, no in situ AFM study of carbonate and sulfate mineral dissolution at elevated and lowered temperature has been reported. In this study, we attempt an in situ AFM study of carbonate and sulfate mineral dissolution and precipitation at elevated and lowered temperature.
Academic Activities
1. Reconstruction of paleoclimate recorded in clay minerals.
1. Y. Kuwahara, W. Liu, M. Makio, K. Otsuka, In Situ AFM Study of Crystal Growth on a Barite (001) Surface in BaSO4 Solutions at 30°C, Minerals, Special Issue Nucleation of Minerals: Precursors, Intermediates and Their Use in Materials Chemistry), 117, 2016.11.
2. Y. Kuwahara, M. Makio, In situ AFM study on barite (001) surface dissolution in NaCl solutions at 30 C, Applied Geochemistry, 51, 12, 2014.12.
3. Y. Kuwahara, K. Ishida, S. Uehara, I. Kita, Y. Nakamuta, T. Hayashi, and R. Fujii, Cool-stage AFM, a new AFM method for in situ observations of mineral growth and dissolution at reduced temperature: Investigation of the responsiveness and accuracy of the cooling system and a preliminary experiment on barite growth, Clay Science, 16, 4, 111-119, 2012.12.
4. Yoshihiro Kuwahara, In situ hot-stage AFM study of the dissolution of the barite (001) surface in water at 30–55 °C, American Mineralogist, 97, 10, 1564-1573, 2012.10.
5. Yoshihiro Kuwahara, In situ Atomic Force Microscopy study of dissolution of the barite (001) surface in water at 30°C, Geochimica et Cosmochimica Acta, 75, 41-51, 2011.01.
6. Kuwahara, Y., Masudome, Y., Paudel, M.R., Fujii, R., Hayashi, T., Mampuku, M., Sakai, H., Controlling weathering and erosion intensity on the southern slope of the Central Himalaya by the Indian summer monsoon during the last glacial, Global and Planetary Change, 71, 1-2, 73-84, Vol. 71, 73-84., 2010.03.
7. Yoshihiro Kuwahara and Seiichiro Uehara, AFM Study on Surface Microtopography, Morphology and Crystal Growth of Hydrothermal Illite in Izumiyama Pottery Stone from Arita, Saga Prefecture, Japan, The Open Mineralogy Journal, Vol. 2, 34-47., 2008.12.
8. Yoshihiro Kuwahara, In situ observations of muscovite dissolution under alkaline conditions at 25-50°C by AFM with an air/fluid heater system, American Mineralogist, Vol.93, 1028-1033, 2008.08.
9. Yoshihiro Kuwahara, In-situ AFM study of smectite dissolution under alkaline conditions at room temperature, American Mineralogist, Vol. 91, 1142-1149., 2006.07.
10. Yoshihiro Kuwahara, In-situ,real time AFM study of smectite dissolution under high pH condtions at 25°-50°C., Clay Science, Vol. 12, Supplement 2, 57-62., 2006.04.
11. Yoshihiro KUWAHARA, Seiichiro UEHARA, and Yoshikazu AOKI, Atomic force microscopy study of hydrothermal illite in Izumiyama pottery stone from Arita, Saga prefecture, Japan, Clays and Clay Minerals, 49, 4, Vol.49, 300-309, 2001.04.
12. Yoshihiro KUWAHARA, Comparison of the surface structure of the tetrahedral sheets of muscovite and phlogopite by AFM, Physics and Chemistry of Minerals, 28, 1, Vol.28, 1-8, 2001.01.
13. Yoshihiro KUWAHARA and Yoshikazu AOKI, Dissolution kinetics of phlogopite under acid conditions, Clay Science, Vol.11, 31-45, 1999.01.
14. Yoshihiro KUWAHARA and Yoshikazu AOKI, Dissolution process of phlogopite in acid solutions, Clays and Clay Minerals, 43, 1, Vol.43, 39-50, 1995.01.
1. This paper reports the results of clay mineral analysis (the amount of clay fraction, clay mineral assemblages, illite crystallinity) of samples collected from a drilled core (Rabibhawan (RB) core) located in the westcentral part of the Kathmandu Basin on the southern slope of the Central Himalaya. The amount of clay fraction in the core sediments between 12 m and 45 m depth (corresponding to ca. 17–76 ka), which belong to the Kalimati Formation, is variable and shows three clay-poor zones (19–31 ka, 44–51 ka, and 66–75 ka). The variations correspond with those of illite crystallinity index (Lanson index (LI) and modified Lanson index (MLI)) and kaolinite/illite ratio as well as the fossil pollen and diatom records reported by previous workers. These data reveal the following transformations occurring during the weathering process in this area:

micas (mainly muscovite)→illite(→illite−smectitemixedlayer mineral(R = 1))→kaolinite

The sedimentation rate (~50 cm/kyr) of clay-poor zones that correspond to dry climate intervals is only half that of clay-rich zones (~120 cm/kyr) that correspond to wet climate intervals, indicating weakened chemical weathering and erosion and low suspended discharge during dry climate intervals. The clay-poor zones commonly show unique laminite beds with very fine, authigenic calcite, which was probably precipitated under calm and high calcite concentration conditions caused by low precipitation and run-off. The variations between dry and wet conditions in this area as deduced from clay minerals appear to follow the Indian Summer Monsoon Index (ISMI) (30°N–30°S, 1 July) and northern hemisphere summer insolation (NHSI) signals (30°N) at 1 July, especially during the dry climate zones, whereas the wet maxima of the wet climate zones somewhat deviate from the strongest NHSI. On the other hand, the dry–wet records lead markedly the SPECMAP stack (by about 5000 years). These results suggest that the Indian summer monsoon precipitation was strongly controlled by the NHSI or summer insolation difference between the Himalayan–Tibetan Plateau and the subtropical Indian Ocean, showing a major fluctuation on the 23,000 years precessional cycle, and that it was not driven by changes in high-latitude ice volume, although the records of clay mineral indices during the wet intervals leave a question that other factors, in addition to insolation forcing, may play important roles in weathering, erosion, and sedimentation processes..
2. The dissolution behavior of the barite (001) surface in pure water at 30°C was investigated using in situ AFM, to better understand the dissolution mechanism and the microtopographical changes that occur during the dissolution. The dissolution of the barite (001) surface could be divided into three stages. The first stage of the dissolution was characterized only by the retreat of various steps that were formed mechanically by the initial cleaving. During the second stage, the change in the retreat behavior (from a step with one layer to a “f” step with an upper half-unit cell layer and a “s” step with a lower half-unit cell layer) and the formation of etch pits were observed. The last stage of the dissolution was characterized by an increase of the stable steps parallel to the [010] direction, followed by a decrease of steps parallel to , and the development of angular deep etch pits..
3. In-situ AFM observations on muscovite dissolution at 20-50C under alkaline conditions.
4. Mineral behavior in Paleoclimate and paleoenvironment changes in the Kathmandu Basin sediments, Central Nepal Himaraya during the last 50kyr.
5. In situ AFM study on smectite and muscovite dissolutions under high pH conditions.
6. The dissolution behaviors of muscovite and smectite under alkaline conditions at 25°C to 50°C were investigated using in-situ atomic force microscopy (AFM) with an air/fluid heater system, in order to understand the dissolution mechanism and to derive reliable dissolution rates of these minerals.The both minerals showed the same dissolution behavior in which the reactive surface was only the edge surfaces and any new etch pits were not formed on the basal surfaces within the experimental durations. The dissolution rates normalized to the edge surface area (ESA) of these minerals were also approximately the same. In addition, the effects of temperature on the ESA-normalized dissolution rates were very similar each other. These results suggest that the dissolution mechanisms (e.g., reactive surface, the rate-limiting step) of muscovite and smectite are identical each other. The dissolution rates normalized to the total surface area (TSA) of initial particle size (smectite) or initial etch pit size (muscovite) varied with the particle or etch pit size, respectively..
7. Variations of paleoclimate and paleoenvironment during the last 50 kyr in the Kathmandu Valley, Central Nepal, Himalayas: From the results of clay mineral study.
Membership in Academic Society
  • Mineralogical Society of America