5:15 PM - 7:15 PM
[SVC32-P22] Continuous observations on soil diffuse degassing of carbon dioxide at Izu-Oshima volcano, Japan
Keywords:Diffuse soil degassing, Carbon dioxide, Izu-Oshima volcano
Volcanic gas is primarily emitted in the form of plumes and fumaroles, as well as through soil diffuse degassing, which is an unseen type of emission from the soil of volcanic edifices. The gas species of interest is primarily carbon dioxide. Soil diffuse degassing was first identified in the late 1980s (Baubron et al., 1990; Allard et al., 1991) and has since been observed at volcanoes around the globe (Burton et al., 2013; Werner et al., 2019).
On Izu-Oshima volcano, eight repeat observations have been conducted over the 10 years since 2007 (Hernández Pérez et al., 2016), with the 2007 observations covering the entire island and subsequent repeat observations focused on the summit area of Mt. Mihara. A high flux of carbon dioxide was observed around the rim of Mt. Mihara, particularly near the fumaroles on the southwest side of Crater A and the west side of Kenkagamine, as well as around Crater B, with flux ranging from several hundred to several thousand g m–2 day–1. The total emission rate in the summit area of Mt. Mihara seems to correlate roughly with the increase in the number of earthquakes, with values of 15–30 tons day–1 recorded in 2007, 2010, and 2011, but dropping to as low as 5 tons day–1 in 2009 and from 2012 onward. It is interpreted that stress fluctuations in the deep part of the volcano cause variations in fluid pressure within the volcanic body.
Repeated observations have limitations in the temporal resolution of the data, making it challenging to assess the impact of meteorological conditions on the observed emission rates. Therefore, in September 2018, continuous observation equipment was installed at the edge of the fumarolic zone on the southwest side of Crater A as part of the Integrated Program for Next Generation Volcanic Research and Human Resource Development. Data is collected hourly and transmitted to a server at the University of Tokyo. Additionally, meteorological factors (eight items: air temperature, atmospheric pressure, humidity, wind speed, wind direction, precipitation, soil temperature, and soil water content) that contribute to fluctuations in the flux are also measured. Observations were suspended in 2020 due to equipment failure caused by severe weather conditions at the summit and COVID-19 but were restored in December 2023. However, it broke down again in September 2024, and we are working to recover it again.
The data covering the ten months from September 2018 and the ten months from December 2023, when meteorological observations were available, indicate that the baseline flux has remained around 50–200 g m–2 day–1. Additionally, the flux increased by a factor of several to ten during low-barometric-pressure and high-wind-speed events. These fluctuations are similar to the relationship observed in previous studies between the decrease in atmospheric pressure, the increase in wind speed, and the rise in flux (Viveiros et al., 2008; Carapezza et al., 2009; Laiolo et al., 2016; Morita et al., 2019). This suggests that fluctuations in meteorological conditions significantly impact soil diffuse degassing on Izu-Oshima volcano.
It will be necessary to quantitatively assess the variation caused by meteorological conditions through ongoing observations and to evaluate the changes in flux due to volcanic activity by continuing repeated observations and installing new continuous monitoring equipment.
On Izu-Oshima volcano, eight repeat observations have been conducted over the 10 years since 2007 (Hernández Pérez et al., 2016), with the 2007 observations covering the entire island and subsequent repeat observations focused on the summit area of Mt. Mihara. A high flux of carbon dioxide was observed around the rim of Mt. Mihara, particularly near the fumaroles on the southwest side of Crater A and the west side of Kenkagamine, as well as around Crater B, with flux ranging from several hundred to several thousand g m–2 day–1. The total emission rate in the summit area of Mt. Mihara seems to correlate roughly with the increase in the number of earthquakes, with values of 15–30 tons day–1 recorded in 2007, 2010, and 2011, but dropping to as low as 5 tons day–1 in 2009 and from 2012 onward. It is interpreted that stress fluctuations in the deep part of the volcano cause variations in fluid pressure within the volcanic body.
Repeated observations have limitations in the temporal resolution of the data, making it challenging to assess the impact of meteorological conditions on the observed emission rates. Therefore, in September 2018, continuous observation equipment was installed at the edge of the fumarolic zone on the southwest side of Crater A as part of the Integrated Program for Next Generation Volcanic Research and Human Resource Development. Data is collected hourly and transmitted to a server at the University of Tokyo. Additionally, meteorological factors (eight items: air temperature, atmospheric pressure, humidity, wind speed, wind direction, precipitation, soil temperature, and soil water content) that contribute to fluctuations in the flux are also measured. Observations were suspended in 2020 due to equipment failure caused by severe weather conditions at the summit and COVID-19 but were restored in December 2023. However, it broke down again in September 2024, and we are working to recover it again.
The data covering the ten months from September 2018 and the ten months from December 2023, when meteorological observations were available, indicate that the baseline flux has remained around 50–200 g m–2 day–1. Additionally, the flux increased by a factor of several to ten during low-barometric-pressure and high-wind-speed events. These fluctuations are similar to the relationship observed in previous studies between the decrease in atmospheric pressure, the increase in wind speed, and the rise in flux (Viveiros et al., 2008; Carapezza et al., 2009; Laiolo et al., 2016; Morita et al., 2019). This suggests that fluctuations in meteorological conditions significantly impact soil diffuse degassing on Izu-Oshima volcano.
It will be necessary to quantitatively assess the variation caused by meteorological conditions through ongoing observations and to evaluate the changes in flux due to volcanic activity by continuing repeated observations and installing new continuous monitoring equipment.