Prehistrical and Historical Tsunamis of Ryukyu Islands Estimated Thgrough Tsunami Deposits

Nakaza, Eizo; Iribe, Tsunakiyo; Tokuhisa, Uzoru; Miyazato, Nao; Inagaki, Kento; Savou, Rusila

doi:10.2208/jscejoe.69.i_515

Cited by 2 publications

(3 citation statements)

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“…In either case, considering our results along with those of earlier studies (Kawana and Nakata 1994;Omoto 2012;Araoka et al 2013;Hisamatsu et al 2014;Ando et al 2018;Kitamura et al 2018a, b), we conclude that large tsunamis repeatedly struck both the Miyako and Yaeyama Islands. Consequently, the hypothesis that the 1771 Meiwa tsunami was the only extraordinary event of the past (Nakaza et al 2013) is less likely.…”

Section: Age Of Paleotsunami At Minna Islandmentioning

confidence: 99%

Millennial paleotsunami history at Minna Island, southern Ryukyu Islands, Japan

Fujita

Goto

Iryu

et al. 2020

Prog Earth Planet Sci

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Huge tsunami waves have repeatedly bombarded the southern end of the Ryukyu Islands (Miyako and Yaeyama Islands, southwestern Japan) at several-hundred-year intervals. Therefore, clarifying the islands’ paleotsunami history is important for risk assessment. Nevertheless, discrepancies of paleotsunami histories exist among regional studies of tsunami boulders and sandy tsunami deposits. Radiocarbon ages of tsunami boulders indicate that tsunami events of the last 2400 years have occurred every 150–400 years, most recently the historical 1771 Meiwa tsunami. Sandy tsunami deposits at Yaeyama Islands show that four tsunami events of the last 2000 years struck the islands at approximately 600-year intervals. Sandy tsunami deposits of the Miyako Islands have been studied only rarely. Therefore, studying sandy tsunami deposits in the Miyako Islands is crucially important for clarifying the paleotsunami history of this region. We conducted a trench survey on Minna Island, located among the westernmost Miyako Islands, which revealed two sandy tsunami deposits under a coral tsunami boulder transported by the 1771 tsunami. The upper tsunami deposit was likely deposited by the 1771 tsunami, as inferred from stratigraphic correlation to the tsunami boulder. However, the lower tsunami deposit was probably deposited 700–1000 years ago, which is consistent with the age range of the paleotsunami reported for Yaeyama Islands. Because sandy tsunami deposits found in this and earlier studies are thick and deposited at high elevation and far inland, these are useful markers of large tsunami events similar to the 1771 event. However, the reported tsunami boulders of various sizes are deposited along the coast and reefs: they can be formed not only by large tsunami events but also by small ones. It is noteworthy that each tsunami deposit is coarse and thick (40–48 cm) relative to the island elevation (about 12 m maximum, 7 m above the mean sea level at the study site). By assuming that tsunamis have affected this region repeatedly during the past few thousand years at around 600-year intervals, tsunamis might have been important geomorphic agents for building up small reef-surrounded islands such as Minna Island.

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Section: Age Of Paleotsunami At Minna Islandmentioning

confidence: 99%

Millennial paleotsunami history at Minna Island, southern Ryukyu Islands, Japan

Fujita

Goto

Iryu

et al. 2020

Prog Earth Planet Sci

View full text Add to dashboard Cite

show abstract

“…Possible sandy tsunami deposits, especially relating to 1771 CE, were previously reported by archaeologists (e.g., Yamamoto, 2008;Kugai, 2011;Nakaza, 2017) and coastal engineers (Nakaza et al, 2013) following the work done by Kawana and Nakata (1994) but their detail history had remained uncertain. Recently, Ando et al (2018) performed a 120 m-long trench survey and found that paleotsunamis may have occurred at approximately 600-year intervals over the last 2000 years (Fig.…”

Section: Paleotsunamis On the Sakishima Islandsmentioning

confidence: 95%

“…Alternatively, this discrepancy might also reflect the small number of studies carried out on sandy deposits in this region so further research is required. Although some researchers have suggested the absence of a predecessor to the 1771 CE tsunami (Nakaza et al, 2013(Nakaza et al, , 2015, geological evidence of both boulders and sandy deposits provides crucial evidence that either small or large tsunamis have repeatedly occurred over the last few thousand years around the Sakishima Islands.…”

Section: Paleotsunamis On the Sakishima Islandsmentioning

confidence: 99%