垂木台地における雲仙普賢岳1990-1995年噴火堆積物の重要露頭(＜特集＞火山噴火史解明のための露頭データベース構築の検討(3))

抄録

There are two significant outcrops that can be observed at Tarukidaichi (Taruki Height) located around 2.5 km NW of Heiseishinzan lava dome generated by the 1990-1995 eruption of Unzen Volcano. This paper discussed the dates and time of eruptions based from the observations on the pyroclastic deposits exposed at these outcrops. Pyroclastic deposits observed at Tarukidaichi can be divided into 5 layers based on their occurrences. Layer 1 corresponds to mainly ash fall deposits resulting from pyroclastic flows that occurred from May 20, 1991 to early September 1991. Layer 2 is composed of pyroclastic surge deposits that are accompanied by large-scale pyroclastic flows that happened on September 15, 1991. Layer 3 is composed of deposits caused from the series of pyroclastic surges and ash falls that occurred from January to March 1992. Layer 4 is ash falls accompanied with pyroclastic flows, pyroclastic surges and their reworked deposits from March 1992 to middle June 1993. Layer 5 is composed of deposits from pyroclastic flows that occurred on June 23, 1993. These outcrops are very useful for students who want to learn volcanic geology. These sites should be conserved and protected through effective collaboration between the scientific community and local residents.