Shinmoedake volcano started a sub-plinian eruption after an interval of 300 years, since its latest magmatic eruption in 1716-1717. In 2003, the committee for volcanic disaster prevention consisting of local governments has been established. The committee published the Kirishima volcano disaster prevention handbook in March, 2008. Soon after, a series of precursory events of the 2011 eruption began. The media reported that pyroclastic flows were generated in all directions, but, actually, only one small pyroclastic flow occurred. Also an oblique eruption deposit was recognized on the upper slope of the volcano consisting of pumice-fall deposit showing slightly elliptic to concentric wrinkle pattern. The information provided by researchers were sometimes inaccurate and generated unnecessary concerns among the public. The main reasons for these are: 1) the disaster prevention map was not easy to understand, 2) the sense of impending crisis was unnecessarily increased by the announcements of a potential for sector collapse of the volcanic edifice, and 3) the eruptive history of the volcano was not reasonably understood among researchers, hence, it took a few days before researchers recognized that this is actually “an apparent magmatic eruption after 300 years interval”. These issues are some of the challenges that the research community should consider during future eruptions.

JMA (Japan Meteorological Agency) applies the Volcanic Aler t Levels to Kirishimayama Shinmoedake, based on disaster mitigation measures required in target areas. Each level corresponds to action to be taken. Observing small eruptions and seismic activity from 2008, Shinmoedake’s alert level was set as 2 (do not approach the crater) before 2010. When its level was risen to 3 (do not approach the volcano) after the sub-plinian eruption of Shinmoedake on 26 January 2011, it reveals some problems such as underestimate of plume height, lack of appropriate information, late issuance of warnings and discommunication among organizations. Based on lessons learned through this event, some progress have been made on volcanic disaster management such as realtime evaluation of eruption, improvement of the Volcanic Ash Fall Forecast, quick evaluation of ash deposit and reinforcement of local Volcanic Disaster Management Councils..

The 2011 Kirishima Shinmoe-dake eruption brought pumice fall deposits to the south-eastern flank of the Kirishima Volcanoes. This study aims to confirm the processes of tephra deposits movements which followed to the eruption and to catch the trend of the valley bottom topographic change after the eruption. The method of this work is to observe the topographic change at the same point repeatedly to clarify the changing pattern of micro-topography on the valley slope, and to measure elevation of the valley floor repeatedly to clarify the volumetric and topographic change of the valley floor deposits using GIS. Study area is located at the south-eastern foot of Takachihonominepeak, where the 2011 air-fall pumice deposits about 10cm thick mantled the valley slope and the valley floor. These observation and measurements lead to the conclusions as follows. Sheet wash eroded surface tephra particles on the upper part of valley slope and transport them downslope. This process formed lobe-like micro-topography on the original air-fall tephra surface. Another process is gully erosion, which started from the middle part of valley slope and washed away tephra layer linearly, but never eroded subsurface of buried soil. These two erosional processes started in the first summer rainy season after the eruption. On the valley floor, rapid deposition appeared in the first summer rainy season. Depositional tendency on the valley floor continued in August 2012, then the valley floor changed to erosional condition to form two steps of terrace-like topography. In 2015, the valley floor condition changed to equilibrium of erosion/deposition. The secondary movement of tephra deposits occurred rapidly in the first rainy season but reached the equilibrium in several years.

Mount Kirishima is a cluster of volcanoes situated in the boundary between Kagoshima and Miyazaki Prefectures, Japan, and includes the Shinmoedake Volcano which erupted violently in January 2011, ejecting a large amount of volcanic ash and pumice onto surrounding land. In this paper, I describe the effects of volcanic activity on sediment transport phenomena and the potential for development of related hazards in relation to Mount Kirishima. First, I examine sediment transport phenomena that followed the volcanic eruption, such as covering by volcanic ash, lowering of infiltration capacity, increase in surface runoff, and rapid progress of erosion and related occurrence of debris flows. The thickness and grain size of the volcanic ash deposits, and the infiltration capacity on the hillside slope covered with volcanic ash, were investigated in terms of the potential for debris flow hazard posed to the area surrounding Shinmoedake. Second, I examine the bedrock aquifer that is widely distributed in the Mount Kirishima area and the deep-seated landslides which have been mobilized by the groundwater. Recently, such deep-seated landslides have caused serious damage, such as in Ebino in Miyazaki in 1972, Izumi in Kagoshima in 1997, and Minamata in Kumamoto in 2003. These landslides resulted from rising groundwater levels caused by heavy rainfalls and deeply weathered rocks. Some methods for onsite prediction and early-warning of potential deep-seated landslides are also examined, based on geomorphological, geological and hydrological surveys.