Magma-hydrothermal system interaction inferred from volcanic gas measurements obtained during 2003–2008 at Meakandake volcano, Hokkaido, Japan

Abstract

2008. We conducted geochemical surveillance that included measurements of temperature, SO 2 emission rates, and volcanic gas composition from 2003 to 2008 at the Nakamachineshiri (NM), Northwest (NW), and Akanuma (AK) fumarolic areas, and the 96-1 vent, where historical eruptions had occurred. The elemental compositions of the gases discharged from the different areas are similar compared with the large variations observed in volcanic gases discharged from subduction zones. All the gases showed high apparent equilibrium temperatures, suggesting that all these gases originated from a common magmatic gas. The gases discharged from each area also exhibited different characteristics, which are probably the results of differences in the conditions of meteoric water mixing, quenching of chemical reactions, and vapor-liquid separation. The highest apparent equilibrium temperatures (about 500°C) were observed in the case of NW fumarolic gases, despite the low outlet temperature of about 100°C at these fumaroles. Since the NW fumaroles were formed as a result of the 2006 phreatic eruption, the high-temperature gas supply to the NW fumarole suggests that the phreatic eruption was caused by the ascent of high-temperature magmatic gases. The temperatures, compositions, and emission rates of the NM and 96-1 gases did not show any appreciable change after the 2006 eruption, indicating that each fumarolic system had a separate magmatic-hydrothermal system. The temperatures, compositions, and emission rates of the NM fumarolic gases were apparently constant, and these fumaroles are inferred to be formed by the evaporation of a hydrothermal system with a constant temperature of about 300°C. The 96-1 gas compositions showed large changes during continuous temperature decrease from 390°to 190°C occurred from 2003 to 2008, but the sulfur gas emission rates were almost constant at about four tons/day. At the 96-1 vent, the SO 2 /H 2 S ratio decreased, while the H 2 /H 2 O ratio remained almost constant; this was probably caused by the rock-buffer controlled chemical reaction during the temperature decrease.

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

“…Thus, we modified the system to fulfill the requested payload. For SO 2 and H 2 S electrochemical sensors and an H 2 S semiconductor sensor, we used the same ones as in Shinohara et al (2011) andShinohara (2013). For CO 2 and H 2 O, a small instrument (TR-76Ui-H, T&D Corp., Japan) including a diffusion-type NDIR CO 2 sensor, a capacitive relative humidity sensor and a platinum resistance thermometer with a data logger was used to minimize the total weight of the system.…”

“…Background is Mt. Ontake emitting volcanic plume A SO 2 scrubber filter was placed in front of the H 2 S sensor to avoid the cross-sensitivity for SO 2 as in Shinohara et al (2011). For SO 2 , H 2 S and H 2 sensors, the gas was pumped at a rate about 700 mL/min through 0.45-μm membrane filter.…”

“…The highest H 2 S value of 10.5 ppm was recorded during the flight. Considering the response time of about 30 s for the sensors (Shinohara et al 2011), real concentration in the plume was likely to be much higher.…”

“…Molar ratios of SO 2 over H 2 S for all the flights were calculated from correlation plots as in previous MultiGAS studies (Shinohara 2005(Shinohara , 2013Shinohara et al 2011;Aiuppa et al 2005a, b). Figure 8a-d shows SO 2 versus H 2 S scatter plots of the four MultiGAS flights.…”

Development of a portable active long-path differential optical absorption spectroscopy system for volcanic gas measurements

“…At the same time, the low power consumption and lack of moving parts make the instrument significantly more portable and durable than FTIR spectrometers, which previously represented the only remote sensing approach to obtaining this geochemical parameter. Despite the difficulties involved with making measurements in the past, monitoring the CO 2 / SO 2 ratio at active volcanoes throughout the world has already led to significant insights into volcanic processes (Duffell et al, 2003;Allard et al, 2005;Aiuppa et al, 2007;Burton et al, 2007;Shinohara et al, 2008Shinohara et al, , 2011Ohba et al, 2011;Werner et al, 2012Werner et al, , 2013 and allows the estimation of CO 2 input into the atmosphere from global volcanism (Burton et al, 2013). In the future, mobile LP-DOAS instruments could help quantify this parameter at hitherto inaccessible volcanic systems.…”