[S-VC28] Active Volcanism

[SVC28-P06] Monitoring of underground temperature in Jigokudani, Midagahara volcano using LPWA devices

*Tohru Watanabe¹ (1.Faculty of Sustainable Design, University of Toyama)

Keywords:Midagahara volcano, Jigokudani, underground temperature

Jigokudani is an active geothermal area in Midagahara volcano, Toyama prefecture, central Japan. It was formed as a result of repeated phreatic eruptions over 40,000 years. Increased volcanic activity in this area has been observed since 2011. In order to detect a precursory signal of a phreatic eruption, observations should be conducted on seismicity, ground deformation, geothermal activity, volcanic gas, etc. A monitoring system of underground temperature using LPWA (Low Power, Wide Area) devices has been tested since 2018. LPWA devices (netvox, R718CX2) for measuring underground temperature were deployed at 8 points in Jigokudani. One device has two thermocouples at the depths of 10 and 50 cm. Underground temperature is sent every 30 minutes to a gateway to the internet situated in Hotel Tateyama. Short-period (~10 hours) variations in temperature are remarkable at 10 cm, while quite weak at 50 cm. Short-period variations come from the temporal change in the surface temperature. The heat flux can be estimated from temperatures at different depths. Jigokudani has heavy snow fall in winter. The operation of this system has been tested since October 2020. Temperature data can still be received at least until February 2021.