5:15 PM - 7:15 PM
[MIS12-P02] Formation period and maintenance conditions of mires located at the top and hillside of Naeba volcano
Keywords:Mountain mire, Hypsithermal period, Recharge water, Quaternary volcano
Quaternary volcanoes are important sites for mountain mire formation in Japan. These mires primarily develop in craters, within landslides, and on original volcanic surfaces. Mires on original volcanic surfaces exist in snow patches and also in flat areas near the summits of mountains and foothills that receive relatively less snowfall. In this study, we focused on the Komatsubara and Naeba Mire, which are located at different elevations on the lava plateau of Mount Naeba. Our aim was to clarify their formation periods through sediment analysis and to examine the environmental conditions based on observations of soil moisture properties and temperature.
Mount Naeba is a quaternary stratovolcano located on the border between the Nagano and Niigata prefectures. The Komatsubara Mire is located at the hillslope of a lava plateau, whereas the Naeba Mire extends across a flat area on the southern slope of the summit. In this study, four sites in the Naeba Mire and three sites in the Komatsubara Mire were drilled. Additionally, we monitored the soil temperature, soil moisture, and electrical conductivity (EC) in the peat layers at depths of 4 and 8 cm in Shimonosiro (1,334 m) in Komatsubara and Ryunomine (2,052 m) in Naeba Mire. We also monitored the air temperature at 5 m above ground level. The observation period was from November 26, 2020, to October 1, 2021, at the Komatsubara Mire, and from October 20, 2020, to August 6, 2022, at the Naeba Mire. Changes in soil moisture were analyzed in relation to precipitation data obtained from the AMeDAS Tsunan station.
The radiocarbon dating results indicated that the wetland formation was synchronized with climatic changes. In the Komatsubara Mire, peat deposition began approximately 5,000–4,500 years ago, or approximately 3,300 years ago. In the Naeba Mire, peat deposition began approximately 7,000–4,500 years ago, with the wetlands forming earlier at two locations closer to the summit. It has been reported that many peat bogs in the snowy regions of Japan were formed during the hypsithermal period, and it has become evident that the mires on Mt. Naeba also formed during the same period.
The results of the observations of soil temperature and moisture in the peat layer clarified that the maintenance conditions were different between the Naeba and Komatsubara Mires. The snow cover period, estimated from the soil temperature data, extended from late November to mid-late May, with no significant differences observed between the two mires. The soil moisture content and EC at a depth of 8 cm fluctuated primarily in response to snow-covered and snow-free periods. In the Komatsubara Mire, EC increased immediately after snow cover began and decreased rapidly once snowmelt was complete, exhibiting a substantial change. In contrast, the Naeba Mire showed a smaller rate of increase and a lesser degree of change. Data collected at a depth of 4 cm indicated changes in response to precipitation. In the Komatsubara Mire, a rapid decrease in soil moisture was observed on consecutive days without rain, whereas EC tended to decrease during precipitation events. A decrease in soil moisture corresponding to periods of no rainfall was also observed in the Naeba Mire; however, its frequency was low. EC generally exhibited higher values in groundwater than in meteoric water, suggesting that groundwater contributed more significantly to the Komatsubara Mire, whereas meteoric water played a greater role in the Naeba Mire.
While the Komatsubara Mire is expected to receive a substantial supply of groundwater from the slope behind it, the Naeba Mire is expected to receive less recharge water. An estimation of the global solar radiation revealed that solar radiation levels in the Naeba Mire were low throughout the snow-free season. Consequently, the suppression of evapotranspiration due to localized cloudy days, fog, or rainfall near the summit is also crucial for the maintenance of the Naeba Mire.
Mount Naeba is a quaternary stratovolcano located on the border between the Nagano and Niigata prefectures. The Komatsubara Mire is located at the hillslope of a lava plateau, whereas the Naeba Mire extends across a flat area on the southern slope of the summit. In this study, four sites in the Naeba Mire and three sites in the Komatsubara Mire were drilled. Additionally, we monitored the soil temperature, soil moisture, and electrical conductivity (EC) in the peat layers at depths of 4 and 8 cm in Shimonosiro (1,334 m) in Komatsubara and Ryunomine (2,052 m) in Naeba Mire. We also monitored the air temperature at 5 m above ground level. The observation period was from November 26, 2020, to October 1, 2021, at the Komatsubara Mire, and from October 20, 2020, to August 6, 2022, at the Naeba Mire. Changes in soil moisture were analyzed in relation to precipitation data obtained from the AMeDAS Tsunan station.
The radiocarbon dating results indicated that the wetland formation was synchronized with climatic changes. In the Komatsubara Mire, peat deposition began approximately 5,000–4,500 years ago, or approximately 3,300 years ago. In the Naeba Mire, peat deposition began approximately 7,000–4,500 years ago, with the wetlands forming earlier at two locations closer to the summit. It has been reported that many peat bogs in the snowy regions of Japan were formed during the hypsithermal period, and it has become evident that the mires on Mt. Naeba also formed during the same period.
The results of the observations of soil temperature and moisture in the peat layer clarified that the maintenance conditions were different between the Naeba and Komatsubara Mires. The snow cover period, estimated from the soil temperature data, extended from late November to mid-late May, with no significant differences observed between the two mires. The soil moisture content and EC at a depth of 8 cm fluctuated primarily in response to snow-covered and snow-free periods. In the Komatsubara Mire, EC increased immediately after snow cover began and decreased rapidly once snowmelt was complete, exhibiting a substantial change. In contrast, the Naeba Mire showed a smaller rate of increase and a lesser degree of change. Data collected at a depth of 4 cm indicated changes in response to precipitation. In the Komatsubara Mire, a rapid decrease in soil moisture was observed on consecutive days without rain, whereas EC tended to decrease during precipitation events. A decrease in soil moisture corresponding to periods of no rainfall was also observed in the Naeba Mire; however, its frequency was low. EC generally exhibited higher values in groundwater than in meteoric water, suggesting that groundwater contributed more significantly to the Komatsubara Mire, whereas meteoric water played a greater role in the Naeba Mire.
While the Komatsubara Mire is expected to receive a substantial supply of groundwater from the slope behind it, the Naeba Mire is expected to receive less recharge water. An estimation of the global solar radiation revealed that solar radiation levels in the Naeba Mire were low throughout the snow-free season. Consequently, the suppression of evapotranspiration due to localized cloudy days, fog, or rainfall near the summit is also crucial for the maintenance of the Naeba Mire.