Fundamental study on microparticle tephra

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Usually tephras are decreasing in grain size and thickness from the source to distal area. In the more distal area, only microparticle tephras are scattered in the soil, peat, snow, and ice. In this study, microparticles in 20 to 5 μm included in Antarctic surface snow and ice core, and in 100 to 20 μm in Japanese soils were investigated through analyses of shape, size, and chemical properties.Colorless microparticles from surface snow near Dome F in Antarctica, include tephra grains similar to two types of pumice samples from the Pinatubo 1991 eruption. Colorless microparticles rich in the peak of aerozol signal of H15 ice core near Showa Station, Antarctica, are identified to be volcanic glass shards from the Tambora 1815 eruption.In the Usu volcano 2000 eruption, generation and dispersion of fine tephras were investigated based on the distribution and grain size from the proximal area to distal area.On the age determination for tephras, single grain method using Thermoluminescence dating were tried for quartz grains included in Chichibuyama pyroclastic surge deposit, Kozushima. The result is consistent with the ages by radiocarbon dating method.