Use of Unmanned Aircraft System (UAS) in Response to the 2014 Eruption of Ontake Volcano, Japan

Abstract:

On Sept. 27, 2014, a phreatic eruption occurred at Ontake volcano (3067 m a.s.l.), central Japan. The eruption caused an unprecedented volcanic disaster in the last 70 years in Japan. Search and rescue operations started soon after the eruption until they were suspended due to snowfall in late October. Considering the potential hazards of further explosive events and the severe winter condition, an approach to the summit area after late October was very difficult. To reveal the condition of the volcanic activity and foresee the trend, we considered it important to carry out volcanic gas surveys for the dense plumes in the vicinity of the vents using an unmanned aircraft system (UAS).

For the surveys at Ontake volcano, the UAS was expected to fly about 8 km roundtrip distance at an altitude of over 3000 m. A multicopter with 8 rotors was adopted and we targeted four types of plume monitoring using the UAS; in-plume monitoring of multiple gas concentrations, SO₂ flux measurement with UV spectroscopy, thermography of the vents, and in-plume particle sampling. In order to meet the 1 kg payload of the multicopter, some of the instruments were slimmed down.

The UAS campaigns at Ontake volcano were carried out on Nov. 20-21, 2014 and on Jun. 2, 2015 from the safety distance of 3-3.5 km away from the crater. With the UAS surveys, we revealed that the SO₂/H₂S ratios of volcanic gas were closer to the hydrothermal origin instead of direct magma degassing. The second survey also pointed out that the SO₂ emission decreased down below 10 ton/day by June 2015, by taking an advantage of flying the vicinity of the vents before the plume was diluted. Our surveys showed decreasing activity of the volcano, together with the advantages of using UAS in volcano monitoring for inaccessible conditions.