[Abstract]

In this report, we review prediction researches on the recent eruptions at Usu and Miyakejima volcanoes, based on three points of view: 1) basic understanding of magma-plumbing system, 2) detection of magma accumulation processes, 3) detection of magma movements by extensive observations. Each volcano showed contrasting long-term precursors. Usu volcano showed no remarkable inflation before the eruption, while Miyakejima showed quasi-continuous inflation. Before both eruptions, we could clearly detect remarkable precursors and contributed to dispatch actual warnings leading to quick evacuation of inhabitants. After the beginning of the eruption, however, it was difficult to predict the time developments of the activities, especially in case of Miyakejima volcano where a caldera collapse was accompanied by repeated explosive hydromagmatic eruptions, and followed by a huge amount of continuous degassing. In order to make a successful long-term prediction or to predict a scale, style and time developments of volcanic eruption, we further need to elucidate magma-plumbing system and to understand particular processes operating in magma. E-mail: watanabe@eri.u-tokyo.ac.jp