Review of Coral Reef Terrace Studies at Kikai Island, Ryukyu Islands, Southwestern Japan

Abstract

Kikai Island, one of the northern most of the Ryukyu Islands, is 80km from the Ryukyu Trench, which marks the boundary between the overriding Eurasian plate and the subducting Philippine Sea plate. A flight of Quaternary coral reef terraces, up to 224m above sea level, forms much of the island's landscape. A symposium on recent findings about coral terraces on Kikai Island was held in February 1998. The findings were obtained by four projects in the preceding several years. Here we provide background for these findings by reviewing earlier studies of the terraces. We also present new maps of terrace distribution and initial extent of each terrace, which were reconstructed based on the relationship between terrace topography and radiometric data as well as on faults displacing terraces. We also compare Kikai Island, which is at 28°N and is near the northern limit of coral growth, with the Huon Peninsula, Papua New Guinea, which is at 6°S and is within the core region for coral growth and moreover is one of the type areas for the study of coral terraces.