Tephrostratigraphy and eruptive history of Shinmoedake volcano of the Kirishima volcanoes, Kyushu, Japan

Abstract

The Kirishima volcanoes comprise more than 20 volcanic edifices. The volcanic ejecta cover an elliptical area of approximately 330 km², elongated in the NW-SE direction. The latest eruption of the Shinmoedake volcano in January 2011 was accompanied by pumice falls. The presence of Sm-St tephra (10.4 cal ka BP), Sm-My tephra (5.6 cal ka BP), and Sm-Kp tephra (AD 1716-1717) indicate that three magmatic eruptions must have occurred before the 2011 eruption. In this study, we detected three new tephras, namely, Sm-Sy tephra (4.5 cal ka BP), Sm-SrB tephra (2.7 cal ka BP), and Sm-SrA tephra (2.3 cal ka BP). Moreover, we discovered two lava flows, Ryobuike B and A, above the Sm-Sy tephra originating from the summit of Shinmoedake. In addition, we found Ryobuike C lavas beneath the Sm-Sy tephra. Ryobuike D lavas underlie the Otk-UsA tephra near the southern flank of the volcano. The crater was filled with Shinmoedake crater lava from an eruption that occurred after the Sm-Kp tephra eruptions, but before AD 1822.
The repose time between the 2011 eruptions and the Sm-Kp tephra is approximately 300 years, and that between the Sm-Kp tephra and the Sm-SrA tephra is 2,000 years. The Shinmoedake volcano has experienced repeated active and quiescent periods. The eruption intervals indicate that the recent age may be the active period.
The age of the Sm-Sy tephra, which erupted in the center part of the Kirishima volcanoes, is close to the ages of the Ebino D and Miike tephra that erupted in the northwestern part and southeastern part of the Kirishima volcanoes, respectively. The occurrence of these three pyroclastic eruptions from vents at distances of 4-8 km from each other during the same period indicates the higher volcanic activity of the entire Kirishima volcanic complex area.