Abstract
This study describes volcanic structures of four drilling cores obtained from the Takanoobane rhyolite lava distributed in Aso caldera, Japan and discuss on development of the structures of the lava. The Takanoobane lava is divided into three parts: Alternation of the pumiceous layers and the obsidian layers (the upper part), the crystalline rhyolite layer (the central part), and the obsidian layer (the lower part). This variation of internal structures is interpreted to have been formed as a result of cooling and degassing processes during flowage. The central crystalline rhyolite layer contains many minute cavity parts defined as crystalline with many minute cavities. The minute cavity parts were formed immediately before or after the extrusion. At distal drilling site, the minute cavity parts were flattened and show flow layering. The flow layering shows high tilt angle in upper part of the crystalline rhyolite layer, suggesting a ramp structure.
