Integrated Research on Large-Scale Eruption at Sakurajima Volcano

Abstract

The 1914 eruption with VEI 4 Plinian pumice falls and the lava flow at Sakurajima Volcano is the largest-scale eruption in Japan after the 20th century. From the uplift of the ground of Aira Caldera where the main magma reservoir of Sakurajima is located and long-term recurrence interval of VEI 4 eruption, a large-scale eruption is expected to occur on the volcano in the near future. For such a large-scale eruption, it is important to (1) understand the precursory activity, (2) forecast eruption, (3) evaluate hazards, and (4) improve disaster prevention literacy. Respectively, (1) the intrusion of magma induces elastic deformation and fracture of rock (volcano-tectonic (VT) earthquake). This may be followed by an opening tensile crack. Evolution of magma intrusion may appear as a conjugate crack. (2) Magma intrusion rate is a key factor to forecast scale and type of eruption. Magma intrusion rate increased up to >10⁸ m³/day before the Plinian eruption. Very high seismicity of low-frequency earthquake follows VT earthquake swarm. (3) Simulation tools have been developed for various kinds of volcanic hazards. A key parameter is allocation of intrusive magma to tephra, pyroclastic flow, and lava flows. (4) Evacuation from volcanoes is an essential countermeasure against volcanic disaster risk. A large eruption, especially pumice fall, requires a wide alert zone. Since awareness of evacuation from the massive tephra fall is low in areas far from the volcano, workshops for residents were repeated to enhance awareness of evacuation from the massive tephra.