Hydrological and Chemical Budgets of Okama Crater Lake in Active Zao Volcano, Japan

Kazuhisa A Chikita,Mare Yamamoto,Takashi Yamaguchi,Jun Okada,Akio Goto,Satoshi Miura

doi:10.3390/hydrology9020028

Abstract

The Okama Crater Lake is located in the highly active Zao Volcano on the boundary of Miyagi and Yamagata Prefectures, Japan. At present, the lake stays relatively calm with neither bubbling, steaming nor gas smell at a pH of 3.2–3.4, though the lake did change color with steaming from the water surface in 1939 as the result of one of Zao’s volcanic activities. In order to clarify the geothermal effect on Okama and the groundwater flow system below or around Okama, field observations were performed in 2019 and 2020. Groundwater inflow and outflow in Okama were separately evaluated by estimating the hydrological and chemical budgets of the lake, based on the hydrometeorology, water temperature and river inflow measured in the field. The average groundwater inflow and outflow were estimated at 0.012 m3/s and 0.039 m3/s during the non-rainfall periods of 2020, respectively. A surplus of groundwater outflow makes the lake level consistently decrease during non-rainfall periods or the completely ice-covered season. In the completely ice-covered periods, the water temperature consistently increased at 0–15 m above the lake bottom, which is probably due to thermal leakage from a hydrothermal reservoir below the lake bottom. The heat fluxes averaged over December 2019–April 2020 and December 2020–March 2021 were calculated at 2.5 and 2.9 W/m2, respectively. A coupling between the estimated groundwater inflow and the calculated geothermal heat flux was used to evaluate the temperature of inflowing groundwater.

Highlights

When a volcano has high potential to produce a disaster, its volcanic activity is monitored at present by video cameras, seismometers, gravimeters, tiltmeters and a GNSS (GlobalNavigation Satellite System) survey (US Geological Survey; URL https://www.usgs.gov/media/images/volcanic-monitoring-types-and-methods-employed-usgs-vhp)
2020 and 15 December 2020–29 March 2021 in Figure 10 were selected for the calculation, since the water temperature at the surface increased after 27 April 2020 and 29 March 2021, indicating the incidence of solar radiation via a partial loss of covered ice from spring ice melt
In order to explore the geothermal effect on Okama Crater Lake in the active Zao

Summary

Introduction

When a volcano has high potential to produce a disaster, its volcanic activity is monitored at present by video cameras, seismometers, gravimeters, tiltmeters and a GNSS (GlobalNavigation Satellite System) survey (US Geological Survey; URL https://www.usgs.gov/media/images/volcanic-monitoring-types-and-methods-employed-usgs-vhp (accessed on 4December 2021)). When a volcano has high potential to produce a disaster, its volcanic activity is monitored at present by video cameras, seismometers, gravimeters, tiltmeters and a GNSS The prediction of volcanic eruptions is sometimes very difficult and, has produced many serious disasters, even in the 21st century (e.g., the 2010 eruption of Merapi Volcano, Indonesia [1,2], and the 2014 eruption of Mt. Ontake, Japan [3]). If a lake or pond exists in an active volcano, the volcano carries a high risk of producing phreatic/phreatomagmatic explosions and lahars at the time of eruptive activity Volcanic lakes provide a place for a research that can directly address the states of the heat source beneath volcanoes. It is important to establish methods for directly exploring the interaction between the heat source and the lake

Methods

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Discussion

Conclusion