2002 Volume 41 Issue 4 Pages 253-268
Holocene geomorphic evolution, sea-level change, and tectonic movements around the Aira caldera are discussed based on geomorphic and depositional features, AIMS 14C ages, tephrochronology, archaeological remains, and assemblage analysis of diatom and mollusca of marine terraces and alluvium on the coastal plain along the northwestern coast of Kagoshima Bay. The results show the relative sealevel changes summarized below and uplift which partially affected geomorphic evolution in Holocene time.
Marine terraces which have emerged since the maximum stage of postglacial transgression ca. 8, 000cal BP (ca. 7, 200yrs BP) are distributed in three levels of the lowlands along the northwestern coast of Kagoshima Bay. Emergence dates of these marine terraces are 7, 300cal BP (6, 500yrs BP)-3, 500yrs BP, ca. 3, 000-2, 000yrs BP and ca. 1, 500-1, 000cal BP, respectively.
Previous sea-levels along the northwestern coast of Kagoshima Bay were +4-5m at 8, 500-8, 400cal BP (7, 700yrs BP), +6m at ca. 8, 100cal BP (ca. 7, 300yrs BP), +12m around 7, 300cal BP (6, 500yrs BP: the maximum highstand), and declined stepwise from +5-7m (3, 000-2, 000yrs BP) to +2-3m (1, 500-1, 000cal BP).
Height distributions and ages of the marine terraces and marine top sediments revealed by this study imply the existence of uplift accompanied by tilting toward the center of the Aira caldera. Observed maximum uplift rate is 12m per 7, 300cal yrs.
Coastal landform evolution has been greatly affected by the volcanic products that erupted from the maars around the Aira caldera. Reclamation of the inlets by the Yonemaru base surge (8, 100-8, 000cal BP) was particularly large-scale.
