Volcanic plume measurements using a UAV for the 2014 Mt. Ontake eruption

Abstract

A phreatic eruption of Mt. Ontake, Japan, started abruptly on September 27, 2014, and caused the worst volcanic calamity in recent 70 years in Japan. We conducted volcanic plume surveys using an electric multirotor unmanned aerial vehicle to elucidate the conditions of Mt. Ontake's plume, which is flowing over 3000 m altitude. A plume gas composition, sulfur dioxide flux and thermal image measurements and a particle sampling were carried out using the unmanned aerial vehicle for three field campaigns on November 20 and 21, 2014, and June 2, 2015. Together with the results of manned helicopter and aircraft observations, we revealed that the plume of Mt. Ontake was not directly emitted from the magma but was influenced by hydrothermal system, and observed SO 2 /H 2 S molar ratios were decreasing after the eruption. High SO 2 flux of >2000 t/d observed at least until 20 h after the onset of the eruption implies significant input of magmatic gas and the flux quickly decreased to about 130 t/d in 2 months. In contrast, H 2 S fluxes retrieved using SO 2 /H 2 S ratio and SO 2 flux showed significantly high level of 700-800 t/d, which continued at least between 2 weeks and 2 months after the eruption. This is a peculiar feature of the 2014 Mt. Ontake eruption. Considering the trends of the flux changes of SO 2 and H 2 S, we presume that majority of SO 2 and H 2 S are supplied, respectively, from high-temperature magmatic fluid of a deep origin and from hydrothermal system. From the point of view of SO 2 /H 2 S ratios and fumarolic temperatures, the plume degassing trend after the 2014 eruption is following the similar course as that after the 1979 eruptions, and we speculate the 2014 eruptive activity will cease slowly similar to the 1979 eruption.

Opal-A in Glassy Pumice, Acid Alteration, and the 1817 Phreatomagmatic Eruption at Kawah Ijen (Java), Indonesia

“…Immediately after the eruption, SO 2 emission rates of >2,000 t/d were measured, and rapidly decreased thereafter, though hydrothermal H 2 S emissions continued (Mori et al, 2016). It appears likely that the eruption was at least partially triggered by input of magmatic gas at the base of the acidaltered hydrothermal system (Sano et al, 2015;Mori et al, 2016;Yamaoka et al, 2016).…”

Review article: the use of remotely piloted aircraft systems (RPASs) for natural hazards monitoring and management

“…The combination of these sensors enabled the estimation of fluxes of SO 2 and CO 2 , which are crucial for revealing the geochemical condition of erupting volcanoes. The monitoring of gas composition including CO 2 , SO 2 , H 2 S and H 2 , as well as air temperature, can be used for the quantification of the degassing activities and prediction of the conduit magma convection, as suggested by the tests at several volcanoes in Japan (Shinohara, 2013;Mori et al, 2016) and in Costa Rica (Diaz et al, 2015).…”

UAV- based Photogrammetry and Geocomputing for Hazards and Disaster Risk Monitoring – A Review

“…The problems solved by UAV therefore concerns keeping scientists and researchers at a reasonable distance from danger, with duties spanning from visual observation of disasters (Sato and Nakanishi, 2014), measure of evolution from visual imagery and photogrammetry (Nakano et al, 2014), gas sampling (Mori et al, 2016), to sediment sampling using robotic sampling devices (Yajima et al, 2014).…”

“…For instance, researchers have used a fix-wing UAV to collect SO2 gas emission over Kirishima Volcano in South Japan (Shinohara, 2013), a multi-rotor to collect plume data during the 2014 Mt. Ontake eruption (Mori et al, 2016), different fix-wings and balloons at Costa Rica Volcano (Diaz et al, 2015).…”