Eruptive Volume and Age of Large-Scale Pumice Eruptions of the Asama-Maekake Volcano, Central Japan, as Revealed by Detailed Trench Surveys: Implications for Future Volcanic Hazards

抄録

The eruptive volumes and ages of the large-scale pumice eruptions of the Asama-Maekake volcano were obtained from extensive trench-based surveys. The calibrated radiocarbon age unit (CRAU) was adopted instead of each calibrated radiocarbon age. From the high-resolution tephro-stratigraphy of large-scale pumice eruptions and CRAU dating, the eruptive history of the Asama-Maekake volcano is divided into three active and two moderately active stages as follows: active stage I (9430 to 7260 ycalBP), moderately active stage 1 (7261 to 6446 ycalBP), active stage II (6447 to 3160 ycalBP), moderately active stage 2 (3161 to 1819 ycalBP), and active stage III (1820 ycalBP to present). The eruptions of the Asama-Maekake volcano consists of small-scale (phreatic to phreato-magmatic), intermediate-scale (Vulcanian), and large-scale pumice eruptions (sub-Plinian). The active stages were characterized by the occurrence of large-scale pumice eruptions. In the moderately active stages, pumice producing eruptions were lacking but instead Vulcanian eruptions dominated. A step diagram showing the relationship between eruption volumes (DRE) and ages (CRAU) is proposed, which indicates that active stage III is not time-predictable but is volume-predictable; if the large-scale pumice eruption occurs in 2022 AD, the forecasted eruptive volume is approximately 0.21 km³. The eruption rate is not constant and changes in each stage, and the average eruption rate of active stage III (0.0011 km³/year) is larger than those of active stage I (0.00006 km³/year) and II (0.0001 km³/year).