1:45 PM - 3:15 PM
[O11-P110] A Study on the Hydrological Characteristics of a Crater Lake Based on Field Surveys : Lake Tairo, Miyake Island, Izu Islands
Keywords:Crater Lake, Hydrological Characteristics, Miyake Island
Lake Tairo is located in the southern part of Miyake Island, Izu Islands, and was formed in a marl about 2,500 years ago (Tsukui et al., 2005), and does not interact with seawater(Arai et al., 1977) (Fig.1).
Arai et al. (1977), Arai (1978), and Aoki et al.(1977) reported that Lake Tairo does not receive water from surface rivers and suggested that Lake Tairo is an outcrop of groundwater (Fig.2). Kodera et al. Kodera(2014) and Sato et al. (2020) suggested that the quality of Miyake Island's terrestrial water, including Lake Tairo, is influenced by volcanic activity.
This study aimed to elucidate the hydrological characteristics of Lake Tairo , including how water is supplied to the crater lake.
Six water sampling points (Fig.1) were set at Lake Tairo on January 17 and July 31, 2024, and February 23 and 24, 2025. Water quality was investigated by measuring air temperature, water temperature, pH, electrical conductivity, Na+ concentration. I also conducted fixed-point observations of temperature and water temperature (Fig.3). On February 23, 2025, I used a water sampler (Fig. 4) that I had made by myself.
The results showed that in January 2024, water temperature was higher and ion levels were lower in the northwestern part of the pond than at other sites at all times (Figs. 5, 6 ,7). On the morning of February 23, 2025, high water temperature and low ion values were observed in the northwestern part of the pond (Figs. 8,9,10), and in the afternoon of February 23, the distribution was uniform among sites (Figs. 11,12,13). In the bottom layer of the pond, pH and conductivity were almost the same as in the surface layer, and water temperature was about 0.3°C lower than in the surface layer (Table.1).
Lake Mashu was chosen for comparison because, like Lake Tairo, it is a closed lake and a crater lake. Lake Mashu is a caldera lake formed by an eruption about 7,000 years ago in eastern Hokkaido, and high water temperatures and ion concentrations have been observed in the bottom layer (Fig.14) due to the high temperature and high ion concentration of spring water gushing from the lake bottom (Nojiri et al., 1990; National Institute for Environmental Studies, 2004). This suggests that Lake Mashu is an example of a lake that is particularly affected by spring water in the bottom layer, and that the northwestern part of Lake Tairo is affected by spring water in the surface layer as Lake Mashu is. In addition, Tsuchi (2017) revealed that groundwater flows through the clinker part of the lava flow and gushes out from the end of the lava flow as spring water as it descends down the mountain body under pressure (Fig.15).
The high water temperature and low ion concentrations observed in the northwestern part of Lake Tairo may be due to the inflow of groundwater into the pond through the basaltic lava flow that originated from Mt Oyama in the central part of the island in the 9th century (Fig. 16).
In the future, we intend to elucidate the hydraulic characteristics of crater lakes in general by comparing them with other crater lakes.
Arai et al. (1977), Arai (1978), and Aoki et al.(1977) reported that Lake Tairo does not receive water from surface rivers and suggested that Lake Tairo is an outcrop of groundwater (Fig.2). Kodera et al. Kodera(2014) and Sato et al. (2020) suggested that the quality of Miyake Island's terrestrial water, including Lake Tairo, is influenced by volcanic activity.
This study aimed to elucidate the hydrological characteristics of Lake Tairo , including how water is supplied to the crater lake.
Six water sampling points (Fig.1) were set at Lake Tairo on January 17 and July 31, 2024, and February 23 and 24, 2025. Water quality was investigated by measuring air temperature, water temperature, pH, electrical conductivity, Na+ concentration. I also conducted fixed-point observations of temperature and water temperature (Fig.3). On February 23, 2025, I used a water sampler (Fig. 4) that I had made by myself.
The results showed that in January 2024, water temperature was higher and ion levels were lower in the northwestern part of the pond than at other sites at all times (Figs. 5, 6 ,7). On the morning of February 23, 2025, high water temperature and low ion values were observed in the northwestern part of the pond (Figs. 8,9,10), and in the afternoon of February 23, the distribution was uniform among sites (Figs. 11,12,13). In the bottom layer of the pond, pH and conductivity were almost the same as in the surface layer, and water temperature was about 0.3°C lower than in the surface layer (Table.1).
Lake Mashu was chosen for comparison because, like Lake Tairo, it is a closed lake and a crater lake. Lake Mashu is a caldera lake formed by an eruption about 7,000 years ago in eastern Hokkaido, and high water temperatures and ion concentrations have been observed in the bottom layer (Fig.14) due to the high temperature and high ion concentration of spring water gushing from the lake bottom (Nojiri et al., 1990; National Institute for Environmental Studies, 2004). This suggests that Lake Mashu is an example of a lake that is particularly affected by spring water in the bottom layer, and that the northwestern part of Lake Tairo is affected by spring water in the surface layer as Lake Mashu is. In addition, Tsuchi (2017) revealed that groundwater flows through the clinker part of the lava flow and gushes out from the end of the lava flow as spring water as it descends down the mountain body under pressure (Fig.15).
The high water temperature and low ion concentrations observed in the northwestern part of Lake Tairo may be due to the inflow of groundwater into the pond through the basaltic lava flow that originated from Mt Oyama in the central part of the island in the 9th century (Fig. 16).
In the future, we intend to elucidate the hydraulic characteristics of crater lakes in general by comparing them with other crater lakes.