Vesiculation and Calcium Hydrosulfate Crystals in Volcanic Ashes From Sakurajima Volcano and their Environmental effects

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Volcanic ashes from Sakurajima Volcano can be grouped into three major classes : black ashes, i. e., most common volcanic ashes ; red ashes characterized by the high-content of ferric iron oxide and the presence of cristobalite, gypsum and anhybrite ; and white ashes characterized by abundant grains of vesiculated volcanic glass. The presence of grains of volcanic glass in the vesiculation state and that of crystals of calcium hydrosulfate in common volcanic ashes are significant in that volcanic ashes were subjected to the adiabatic expansion, and to some chemical reaction due to volcanic gases at the time of eruption.The natural and social environments are affected by two major factors due to volcanic ashes and their accompanying volcanic gases ; physical factors attributed to the substantial nature and grain size of volcanic ash-composing materials, and chemical factors to volcanic gases.Discussions were given to mechanisms that farm products, human health and debris flows are effected by the physical and chemical factors due to volcanic ashes and their accompanying volcanic gases.Farm products are resulted into killing down by a composite factor of the physical factor that volcanic ash-micrograins fill epidermal stomata and, as a result, respiration is stopped or hypofunction takes place, and the chemical factor that volcanic gases behave as acids when they are encountered with water. Meantime, when man continues to inspire a considerable amount of volcanic ash every day, man showing respiratory diseases such as silicosis or pneumoconiosis and/or their similar diseases, will surely come out in not so far future. A close relationship is demonstrated between characteristics of volcanic ash itself and the cause of debris flows. There are eighteen dry rivers at Sakurajima Volcano. Even if it is light rain, dry rivers very often cause a big scale of debris flow down-stream due to physicochemical features of volcanic ash itself.