Excavation of a Limestone Cave Preserving Evidence of Tsunami Events that can Devastate an Island Society: Karadagi Cave, Yaeyama Islands, SW Japan

ISHIHARA Yoshiro1*, NARUSE Hajime2, ONO Rintaro3, YAMAGIWA Kaishi4, GUSHIKEN Seita5, KAMESHIMA Shingo5, KATAGIRI Chiaki5, and YOSHIMURA Kazuhisa6

Island societies are highly vulnerable to environmental instability, and catastrophic events such as large tsunamis that can trigger demographic decline, settlement abandonment, and cultural discontinuity. In the Yaeyama Islands of southwestern Japan, geological and historical evidence indicate that major tsunamis have struck the region at intervals of several centuries. The best-documented event is the 1771 Meiwa Tsunami, which devastated coastal settlements on Ishigaki Island. An earlier large-scale event, the Okinawa–Sakishima Tsunami (ca. 2000 years ago), is inferred from widespread tsunami boulders across the Miyako and Yaeyama islands. Archaeological records suggest a cultural discontinuity around this period, raising the question of whether catastrophic marine inundation reshaped island settlement systems. Karadagi Cave, developed in uplifted coral limestone approximately 500 m from the Shiraho- Saonetabaru Cave Site at 30-40 m above sea level, preserves a stratified record of repeated interaction between extreme marine events and human activity. Excavations reveal, from top to bottom: modern soil and guano deposits; sediments attributed to the 1771 Meiwa Tsunami deposits; a layer containing Early Modern burials; reworked and primary deposits of the Okinawa-Sakishima Tsunami deposits; and superimposed hearth features dated to ca. 3000 and 4000 years ago. Although occupation evidence is spatially limited, the sequence documents repeated alternations between tsunami deposition and human use. Tsunami deposits preserved above a sea level of 30 m indicate substantial inland inundation. Karadagi Cave thus provides rare geoarchaeological evidence for how extreme coastal hazards repeatedly disrupted and reorganised settlement systems in the northern Indo-Pacific.