Late Holocene Coastal Morphology and Sea-level Records on Three Small Islands, the South Ryukyus, Japan

Abstract

The Holocene coastal morphology of three small islands, Kohama, Kuro and Hateruma, of the southern part of the Ryukyu Islands, Southwest Japan, is discussed in relation to paleo sea-level indicators. Three islands are located between about 24•‹0•L N and 24•‹20•L N, and are largely under lain by Pleistocene coral limestones. They are fringed by emergent coastal features such as marine terraces and marine notches. Emergent marine deposits and fossils are also preserved. Present elevations of these landforms and fossils generally range from 1.0 to 1.5m above mean sea level (AMSL) and C-14 dates for five samples are younger than ca. 4,200yBP. Sea level was slightly higher than at present, about 1m AMSL from ca. 3,300 to 800yBP in Kohama and Hateruma and about 1.5m AMSL at about 4,200yBP in Kuro Island. No definite evidence is found to con firm the culmination of postglacial sea-level rise which is usually observed on the Japanese coast at about 6,000yBP. Age of placement and orientation of large boulders scattered on the terrace up to 22m high on Hateruma Island probably suggest their tsunami origin, associated with the 1771 earthquake.

Possible tsunami deposits from the 1855 earthquake, North Island, New Zealand

“…Optical dating (OSL) is the best method available assuming the sediments were exposed to daylight during reworking by the tsunami Foster et al 1991;Dawson 1994Ota et aI. 1985Moore & Moore 1988;Clague & Bobrowsky 1994Moore & Moore 1988Dawson et al 1996Dawson et al 1988Moore & Moore 1988Dawson 1994Moore et al 1994Foster et al 1991Minoura & Nakaya 1991Ota et al 1985Moore & Moore 1988;Minoura & Nakaya 1991;Dawson 1994;Minoura et al 1994;Young et al 1996Dawson et al 1988Minoura et al 1994;Hemphi11-Haley 1996Patterson et al 1996Sherman et al 1996Minoura et al 1994Goff & Chagu&Goff 1998Moore & Moore 1988Bryant et al 1992Clague & Bobrowsky 1994Dawson 1994Albertho & Martins 1996Imamura et al 1997Dawson et al 1988Hansom & Briggs 1991;Clague & Bobrowsky 1994;Dawson 1994;Huntley & Clague 1996 could account for 80-100% of the strain rate measured in Wellington. The most recent movements of faults in the Cook Strait region occurred on the southern portion of the Wellington fault c. AD 1350, c. AD 1250 and c. AD 1450 (Best 1923;Stirling 1992;Van Dissen et al 1992;…”

Tsunami Deposits

“…However, although palaeotsunamis have been considered in this case as a possible depositional agent, similar boulders were also considered to have been deposited as a result of storm surges (TEISSIER, 1969;PIRAZZOLI et al, 1988). Boulder fields attributable to tsunamis have been observed elsewhere in the world (e.g., Japan) (OTA et al, 1985;KAWANA and PIRAZZOLI, 1990;NAKATA and KAWANA, 1993 4). Hindson noted that at several locations on the Algarve coastline the palaeotsunami was associated with the deposition of both continuous and discontinuous sediment sheets, some of which contained boulders.…”

Relative Sea‐Level Changes Over the Past Centuries in the Central Ryukyu Arc Inferred From Coral Microatolls

“…We present here the first study using the annual record preserved in coral microatolls in Japan to accurately reconstruct RSL changes related to tectonic processes at subduction zones and to the climate. Previous works were dedicated to the survey and the C dating of the edges of mid‐ to late‐Holocene fossil microatolls in south Ryukyus (Ota et al, ) and on the east of Okinawa (Fujita et al, ).…”