5:15 PM - 6:30 PM
[SVC29-P08] Ground surface Heat balance measurements at Izu-Oshima volcano
Keywords:Izu-Oshima volcano, heat balance measurement
1. Introduction
During the 1986 eruption of Izu-Oshima volcano, phenomena suggesting the development of the underground hydrothermal system were observed. Thus, thermal observation is important for grasping such the transitions of volcanic activities. In order to understand the thermal activity, underground and surface temperature measurements are often performed. However, the temperature near the ground surface strongly affected by external factors such as radiation from the sun and atmosphere and meteorological factors. Therefore, in order to detect and quantify thermal signs associated with volcanic activity, it is necessary to understand the effect of these external factors. For the purpose of clarifying these factors, heat balance observation devices were installed at two locations in caldera area of the Izu-Oshima volcano.
2. Measurement System
The system consists of sensors that measure not only the surface and underground temperatures, but also the radiations from the sun and the atmosphere and meteorological factors that can affect them. Further, as auxiliary information, the soil moisture and the thermal conductivity in the ground are measured.
Sensors
T-type thermocouple thermometers (CHINO SCHS1-5) are installed at 5 depths (10, 30, 50, 70 and 100 cm) for the underground temperatures. For ground surface temperature, infrared radiation thermometer (Apogee SI-431) is installed. The meteorological parameters (wind speed and direction, atmospheric pressure, temperature, relative humidity, precipitation, and hail) are measured by the weather transmitter Vaisala WXT536. The albedometer (Hukseflux SRA01) is used to measure short-wave radiations (solar radiation and its reflection from the ground surface), and the long-wave radiometer (Hukseflux IR02) is used to measure atmospheric radiation (infrared radiation). The sensors of the soil moisture meter (Sentek EnviroSMART) were installed at the same depth of 5 as the underground temperature. In addition, the thermal properties sensor (Huluseflux TP01) is installed at a depth of about 20 to 30 cm in order to estimate the effective thermal conductivity of the medium.
Data Record and Transmission
Measurements were performed at a minimum interval of 10 seconds, and these were recorded with a data logger (Campbell Scientific CR-1000X). In addition, data is transmitted to the Meteorological Research Institute using a mobile phone line.
3. Observation
This device was installed at two locations inside the caldera of Izu-Oshima volcano. One is in a fumarolic area and the other is in a non-fumarolic area. Both were set up in March 2020.
HB01 (Eastern Crater Floor of Mt. Mihara)
It was installed in a steaming ground distributed along a crack in the eastern crater floor of Mt. Mihara. It is near a fixed point where the Japan Meteorological Agency has been continuously measuring fumarolic temperature since 1991. According to this, what was about 80 °C in 1991 has decreased over time, and has been around 45 to 50 °C in recent years.
HB02 (Southeastern Caldera Floor)
While HB01 was installed in a the fumarolic area, this site was selected from areas where thermal signs associated with volcanic activity were not observed, because the purpose was to understand the heat balance due to external factors such as radiation and meteorological conditions. It was installed in the bare land in the southeastern caldera floor. The ground surface is covered with scoriaceous silt, sand and lapilli.
4. Characteristics of Observed Data
Characteristics of changes in the surface and underground temperatures are totally different between two sites. At the HB02 in non-fumarolic area, diurnal and seasonal (that are considered to be annual) changes are clearly observed. In particular, it is strongly affected by solar radiation, and the amplitude of temperature changes attenuate and the phase is delayed as it gets deeper. On the other hand, at HB01 in the fumarolic area, such the changes are not prominent in the underground temperatures, although diurnal changes in temperature are observed on the ground surface. The underground temperatures are almost constant at about 45 to 48 °C at depths from 10 cm to 100 cm during the seasons. However, when the average wind speed for 10 minutes exceeds approximately 5 m/s, the temperature decreases from the surface to the deeper often occur, suggesting that sensible heat transport or latent heat transport is promoted.
In this presentation, we show the outlines of the measurements and characteristics of observed data.
During the 1986 eruption of Izu-Oshima volcano, phenomena suggesting the development of the underground hydrothermal system were observed. Thus, thermal observation is important for grasping such the transitions of volcanic activities. In order to understand the thermal activity, underground and surface temperature measurements are often performed. However, the temperature near the ground surface strongly affected by external factors such as radiation from the sun and atmosphere and meteorological factors. Therefore, in order to detect and quantify thermal signs associated with volcanic activity, it is necessary to understand the effect of these external factors. For the purpose of clarifying these factors, heat balance observation devices were installed at two locations in caldera area of the Izu-Oshima volcano.
2. Measurement System
The system consists of sensors that measure not only the surface and underground temperatures, but also the radiations from the sun and the atmosphere and meteorological factors that can affect them. Further, as auxiliary information, the soil moisture and the thermal conductivity in the ground are measured.
Sensors
T-type thermocouple thermometers (CHINO SCHS1-5) are installed at 5 depths (10, 30, 50, 70 and 100 cm) for the underground temperatures. For ground surface temperature, infrared radiation thermometer (Apogee SI-431) is installed. The meteorological parameters (wind speed and direction, atmospheric pressure, temperature, relative humidity, precipitation, and hail) are measured by the weather transmitter Vaisala WXT536. The albedometer (Hukseflux SRA01) is used to measure short-wave radiations (solar radiation and its reflection from the ground surface), and the long-wave radiometer (Hukseflux IR02) is used to measure atmospheric radiation (infrared radiation). The sensors of the soil moisture meter (Sentek EnviroSMART) were installed at the same depth of 5 as the underground temperature. In addition, the thermal properties sensor (Huluseflux TP01) is installed at a depth of about 20 to 30 cm in order to estimate the effective thermal conductivity of the medium.
Data Record and Transmission
Measurements were performed at a minimum interval of 10 seconds, and these were recorded with a data logger (Campbell Scientific CR-1000X). In addition, data is transmitted to the Meteorological Research Institute using a mobile phone line.
3. Observation
This device was installed at two locations inside the caldera of Izu-Oshima volcano. One is in a fumarolic area and the other is in a non-fumarolic area. Both were set up in March 2020.
HB01 (Eastern Crater Floor of Mt. Mihara)
It was installed in a steaming ground distributed along a crack in the eastern crater floor of Mt. Mihara. It is near a fixed point where the Japan Meteorological Agency has been continuously measuring fumarolic temperature since 1991. According to this, what was about 80 °C in 1991 has decreased over time, and has been around 45 to 50 °C in recent years.
HB02 (Southeastern Caldera Floor)
While HB01 was installed in a the fumarolic area, this site was selected from areas where thermal signs associated with volcanic activity were not observed, because the purpose was to understand the heat balance due to external factors such as radiation and meteorological conditions. It was installed in the bare land in the southeastern caldera floor. The ground surface is covered with scoriaceous silt, sand and lapilli.
4. Characteristics of Observed Data
Characteristics of changes in the surface and underground temperatures are totally different between two sites. At the HB02 in non-fumarolic area, diurnal and seasonal (that are considered to be annual) changes are clearly observed. In particular, it is strongly affected by solar radiation, and the amplitude of temperature changes attenuate and the phase is delayed as it gets deeper. On the other hand, at HB01 in the fumarolic area, such the changes are not prominent in the underground temperatures, although diurnal changes in temperature are observed on the ground surface. The underground temperatures are almost constant at about 45 to 48 °C at depths from 10 cm to 100 cm during the seasons. However, when the average wind speed for 10 minutes exceeds approximately 5 m/s, the temperature decreases from the surface to the deeper often occur, suggesting that sensible heat transport or latent heat transport is promoted.
In this presentation, we show the outlines of the measurements and characteristics of observed data.