Abstract
Kuchinoerabu-jima is a volcanic island in southern Kyushu, Japan. On August 3, 2014, a moderate summit eruption occurred, destroying all the observation stations near the summit. By using an unmanned aerial vehicle (UAV), a helicopter in our case, we installed four stations in the summit area in April 2015. We also conducted multi-parameter observations including an aero-magnetic survey, visual and infrared observation, and gas measurements and sampling. A summit eruption occurred again on May 29, 2015. It was far larger than the previous one and the entire island was evacuated. The seismometers installed in April were all destroyed but they detected changes in seismic activity a few days before the eruption.
In September 2015, we installed five seismometers again. We also conducted multi-parameter observations as in April. A comparison of the two observations in April and September shows a clear decline in volcanic activity. Proximal data are sensitive to the volcanic activity, but difficult to acquire. UAV observation clearly compensates for the lack of data near the summit of the volcano. Together with other information, the UAV-acquired information contributed to reducing the alert level by the local government (Yakushima Town), and thus contributed to the evacuees being able to return in December 2015.
