Abstract
Kaimondake volcano is an active volcano located on the southeastern end of the Satsuma Peninsula, Kyushu Island. Its volcanic activity started about 4,400 years ago and erupted in the Heian period about 1,150 years ago. The eruptions of the Heian period occurred in year 16 of the Jogan era (874 AD) and the first year of Nin-na era (885 AD). The houses and farmland of the Hashimuregawa and the Shikiryo archaeological sites located in Ibusuki city were significantly damaged by the eruption of Kaimondake volcano, in year 16 of the Jogan era. Based on the results of excavations at the two archaeological sites, herein, we document the eruption of Kaimondake volcano and the subsequent human responses to this disaster in year 16 of the Jogan era. In addition, the ejecta (Km12a3～4, Murasaki-Kora) from these two sites appears to support details from the historic document “Nihon-Sandai-Jitsuroku”. This document noted that it rained during the eruption followed by a Lahar deposit. Ejecta from year 16 of the Jogan era eruption appears in the Hashimuregawa archaeological site as a 50cm to 80cm thick deposit ; consequently, people abandoned the village instead of trying to remove the ejecta. In the Shikiryo archaeological site, located about 1km north of Hashimuregawa, the ejecta deposition is about 30cm thick. At this site, people attempted without success to remove the deposits, but ultimately abandoned the village. Restoration was unsuccessful at Hashimuregawa and Shikiryo archaeological sites because the ejecta deposits and rainwater created a very firm matrix. People attempted restoration because public facilities and paddy fields were essential to life in this area at this time.
