OCCURRENCE AND MINERALOGY OF TAAL-INFLUENCED VOLCANIC ASH SOILS IN BATANGAS PROVINCE, PHILIPPINES(International symposium on volcanic ash soils and field workshop in the Mt. Fuji area)

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概要

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• The mineralogical properties of five soil profiles formed from tephra deposits of Taal volcano during the pre- and post-caldera eruptions were investigated. These deposits were identified as pyroclastic deposits from pre-caldera eruption, scoria pyroclastic flow deposits during caldera formation and volcanic ash during post caldera eruption. Three stages of weathering were determined : 1) Slightly weathered soils, which consists of greater amount of volcanic glass than pyroxene, plagioclase, altered (weathered minerals) and quartz in heavy and light minerals of fine sand fractions. Allophane predominates the clay fractions of these soils ; 2) Moderately weathered soils contain more pyroxene than plagioclase, volcanic glass and weathered minerals. The clay fractions consist of halloysite, with mica and vermiculite ; 3) More weathered soils contain more alterites (weathered minerals) than plagioclase, pyroxene, volcanic glass and quartz. Montmorillonite was predominant in the clay fraction of soils in the lowlands, while kaolinite was predominant in the uplands.Results of the soil mineral identification were evaluated with respect to the environmental factors, the type of tephra deposits and their age of deposition. Primary and secondary minerals revealed that they originated from Taal tephra deposits. Those from Taal ignimbrites had more advanced stages of weathering compared to volcanic ash. More colored volcanic glass, amphibole, Ca-plagioclase, and pyroxene were found in the fine sand fractions, thus, tephra deposits from Taal were more basalt to basaltic andesite rather than dacitic. Very few quartz and almost no olivine minerals were found indicating that the minerals have undergone less weathering process.Based on the five pits, it is concluded in the study that as affected by age and type of tephra, climate, vegetation, and topography, the clay transformation of the parent material follows two path ways : (1) the first is that the basalt to basaltic andesite is transformed to mica (illite), then to vermiculite, then to smectite, and finally to kaolinite ; and (2) the second pathway is that the basalt to basaltic andesite is transformed to allophane, then to halloysite, then to smectite, and finally to kaolinite.

• 明治大学の論文
• 2007-02-28

著者

• OHKURA Toshiaki

  National Institute for Agro-Environmental Sciences

• Carating Rodelio

  Integrated Soil Resources Information Section, Agricultural Land Management and Evaluation Division,

• Juico Purisima

  Department of Soil Science, Central Luzon State University

• Juico Purisima

  Department Of Soil Science Central Luzon State University

• Carating Rodelio

  Integrated Soil Resources Information Section Agricultural Land Management And Evaluation Division B

• Ohkura Toshiaki

  National Inst. Agro‐environmental Sci. Ibaraki Jpn

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