櫻島の新熔岩

概要

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The volcano Sakurajima began its latest eruption on 11th, March, 1946., At first it ejected the considerable amount of ash with some breccias and bombs, and then began the gush out of lava., The action with the effusion of lava was continued through the period from 13th, March to 24th, May, and the total amount of lava effused in this period reached to 130,000,000 cc., In this report was given the petrographic description on the new lava, the specimen of which was collected from the front of the lava flow, at 1 km., N., from the Kurokami village on 17 th, March, 1946., It is black and porous but comparatively compact, with some glassy lustre., It has phenocrysts and microphenocrysts of plagioclase (An55-83), hypersthene, augite and magnetite, scattering inthe dark glassy or cryptocrystalline groundmass., Optical constants of hypersthene and augite are shown as follows : Hypersthene: (-)2V=68°, 66°, 61°, 60°, 59°, 55°, β=1,700-1.,704- Augite: (+)2V=55°, 50.,5°, 50°, β=1.,697-1.,704- The chemical composition was not determined, but SiO_2 (61%) was measured by Assist., Prof., I., IWASAKI., At the end it may be said that the new lave is two-pyroxene andesite similar to the so called "the Taisho Lava (I)" belonging to the eruption of 1914.,
日本地質学会の論文
1948-07-20