Reconstruction of volcanic eruptive history using tephrochronological and geomorphological methods

为了重建高分辨率的爆发历史，在常规地质方法和测年法的基础上，对九州的4座火山进行了地貌学和地表年代学的调查。通过地层研究揭示了九州南部艾拉火山口100 ka ~ 30 ka的喷发历史。在此期间，火山口爆发了七次。最后的0.1 Ma（=100 ka）是活跃期，发生了许多爆炸性和喷涌性喷发。27 ka的艾拉火山碎屑喷发（体积超过411 km^3）将这一活跃期分开。100 ka-30 ka喷发岩浆的总质量为63.3×10^<12>kg。平均速率为0.9×10^<12>kg/ky。艾拉火山口以大约7500年的间隔重复其岩浆喷发。福岛的鬼宿火山群是具有玄武岩熔岩流和火山锥的单生火山群之一，由11座单生火山组成。K-Ar和^<14>C定年结果表明，这些火山在0.5 ~ 0.018 Ma期间活跃。单成因火山形成爆发的平均间隔为5万至3万年。竹野土寺火山位于岛的南部，是伊基岛最年轻的火山之一，该岛有晚中新世至更新世的火山，包括火山锥、盾状火山和碱性和亚碱性岩石的熔岩高原。我们识别并描述了连续形成的共14个单元。K-Ar测年表明该火山发生于0.9 ~ 0.6 ma。在最后一次形成破火山口的Aso-4喷发之后，Aso火山中心的层状火山在过去800 ka中一直处于活跃状态。在没有300-250ka的情况下，活动持续不断，形成了浮石瀑布、矿渣瀑布、岩屑瀑布、火山灰瀑布、火山碎屑涌流等100多个火山单元，显示出在火山中心发生的各种喷发方式。

The four volcanoes in Kyushu were surveyed using tephrochronological and geomorphologyical methods in addition to the ordinary geological one and dating in order to reconstruct high-resolution explosive eruptive histories.The eruptive history during 100 ka-30 ka of Aira caldera, southern Kyushu, is revealed by tephrostratigraphical studies. In this period, seven explosive eruptions of the caldera are identified. The last 0.1 Ma(=100 ka) is the active period occurring many explosive and effusive eruptions. The Aira pyroclastic eruption at 27 ka(more than 411 km^3 in bulk volume) separates this active period. Total mass of erupted magma during 100 ka-30 ka is 63.3×10^<12>kg. And the average rate is 0.9×10^<12>kg/ky. The Aira caldera had repeated its magmatic eruptions at intervals of ca.7500 years. The Onidake volcano group on Fukue island is one of the monogenetic volcano groups with basaltic lava flows and scoria cones, and contains eleven monogenetic volcanoes. The K-Ar and ^<14>C dating results show that these volcanoes were active during 0.5-0.018 Ma. The average interval of monogenetic volcano-forming eruption is fifty thousand to thirty thousand years. Takenotuji volcano located in the southern part of the island is one of the youngest volcanoes in the Iki island which has late Miocene to Pleistocene volcanoes including scoria cones, shield volcanoes and lava plateau of alkalic and subalkalic rocks. We recognize and describe a total of 14 units formed successively. The K-Ar dating indicates that the volcano occurred in 0.9-0.6Ma. The central strato-volcanoes of Aso volcano have been active during the last 800 ka after the last caldera-forming Aso-4 eruption. The activity has been so continuous without 300-250ka and formed more than 100 tephra units including pumice falls, scoria falls, lithic falls, ash falls, and pyroclastic surges which show various eruption styles occurred in volcanic centers.