抄録
With respect to mineral and chemical compositions, microstructure, x-ray powder diffraction and grain-size distribution of volcanic ashes from Sakurajima Volcano, Kyushu, Japan, greyish black-colored “black ashes”, reddish dark grey-colored “red ash” and greyish white-colored “white ash” are compared with one another, and mechanisms of their formation are discussed.
Many evidences show that the black ashes came from solidifying lavas, by which the summit crater had been buried, those which were explosively crushed and ejected by gas pressure which was accumulating within the vent. The red ash is considered possible to be a mixture of the preexisted and recent ashes which were affected by alteration due to action by volanic gases. Meantime, the white ash characterized by abundant vesiculated volcanic glasses seems to be that which was ejected continuously from magma which came up to the craters.
