Threshold flow depths to move large boulders by the 2011 Tohoku-oki tsunami

Abstract Around the world, numerous coastal boulders with weight of few thousand tons are suspected to have been transported by very large tsunamis, although their origins remain enigmatic. For clarifying origins of these boulders, the relation between the tsunami flow depth and the movement of mete...

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Autores principales:	Shohei Iwai, Kazuhisa Goto
Formato:	article
Lenguaje:	EN
Publicado:	Nature Portfolio 2021
Materias:	Medicine R Science Q
Acceso en línea:	https://doaj.org/article/b054d67be5d64f0da27c690f83a21247
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spelling	oai:doaj.org-article:b054d67be5d64f0da27c690f83a212472021-12-02T18:18:58ZThreshold flow depths to move large boulders by the 2011 Tohoku-oki tsunami10.1038/s41598-021-92917-22045-2322https://doaj.org/article/b054d67be5d64f0da27c690f83a212472021-06-01T00:00:00Zhttps://doi.org/10.1038/s41598-021-92917-2https://doaj.org/toc/2045-2322Abstract Around the world, numerous coastal boulders with weight of few thousand tons are suspected to have been transported by very large tsunamis, although their origins remain enigmatic. For clarifying origins of these boulders, the relation between the tsunami flow depth and the movement of meter-size boulders should be clarified but there is no proper field dataset. Here we collected first comprehensive dataset of both moved and unmoved boulders as well as the maximum flow depths along the Sanriku coast of Japan, where was affected by the 2011 Tohoku-oki tsunami based on satellite image analyses and field survey. The dataset revealed that up to ca. 1500 tons of boulders and concrete blocks were moved by the 2011 tsunami with approx. 28 m flow depth. We further revealed that most unmoved boulders were not moved because of the local setting rather than their heavy weights. The threshold of moved/unmoved boulders is estimated against the flow depth. The threshold predicted that approx. > 20 m flow depths are required to move approx. > 1000 tons boulders. The results imply that even a few thousand tons of enigmatic boulders in the world could have been moved by these sizes of the tsunami flow depths, although applicability of our results to other examples should be evaluated in the future work. We further tested the validity of an earlier proposed inverse model. Although the model result is consistent with the field observation, assumption of the appropriate parameters is problematic and further improvement of the model is required to estimate hydrodynamic features of the tsunami and to discriminate tsunami boulders from storm ones. Regarding such future work, our dataset is expected to be important for the evaluation of the improved numerical models.Shohei IwaiKazuhisa GotoNature PortfolioarticleMedicineRScienceQENScientific Reports, Vol 11, Iss 1, Pp 1-10 (2021)
institution	DOAJ
collection	DOAJ
language	EN
topic	Medicine R Science Q
spellingShingle	Medicine R Science Q Shohei Iwai Kazuhisa Goto Threshold flow depths to move large boulders by the 2011 Tohoku-oki tsunami
description	Abstract Around the world, numerous coastal boulders with weight of few thousand tons are suspected to have been transported by very large tsunamis, although their origins remain enigmatic. For clarifying origins of these boulders, the relation between the tsunami flow depth and the movement of meter-size boulders should be clarified but there is no proper field dataset. Here we collected first comprehensive dataset of both moved and unmoved boulders as well as the maximum flow depths along the Sanriku coast of Japan, where was affected by the 2011 Tohoku-oki tsunami based on satellite image analyses and field survey. The dataset revealed that up to ca. 1500 tons of boulders and concrete blocks were moved by the 2011 tsunami with approx. 28 m flow depth. We further revealed that most unmoved boulders were not moved because of the local setting rather than their heavy weights. The threshold of moved/unmoved boulders is estimated against the flow depth. The threshold predicted that approx. > 20 m flow depths are required to move approx. > 1000 tons boulders. The results imply that even a few thousand tons of enigmatic boulders in the world could have been moved by these sizes of the tsunami flow depths, although applicability of our results to other examples should be evaluated in the future work. We further tested the validity of an earlier proposed inverse model. Although the model result is consistent with the field observation, assumption of the appropriate parameters is problematic and further improvement of the model is required to estimate hydrodynamic features of the tsunami and to discriminate tsunami boulders from storm ones. Regarding such future work, our dataset is expected to be important for the evaluation of the improved numerical models.
format	article
author	Shohei Iwai Kazuhisa Goto
author_facet	Shohei Iwai Kazuhisa Goto
author_sort	Shohei Iwai
title	Threshold flow depths to move large boulders by the 2011 Tohoku-oki tsunami
title_short	Threshold flow depths to move large boulders by the 2011 Tohoku-oki tsunami
title_full	Threshold flow depths to move large boulders by the 2011 Tohoku-oki tsunami
title_fullStr	Threshold flow depths to move large boulders by the 2011 Tohoku-oki tsunami
title_full_unstemmed	Threshold flow depths to move large boulders by the 2011 Tohoku-oki tsunami
title_sort	threshold flow depths to move large boulders by the 2011 tohoku-oki tsunami
publisher	Nature Portfolio
publishDate	2021
url	https://doaj.org/article/b054d67be5d64f0da27c690f83a21247
work_keys_str_mv	AT shoheiiwai thresholdflowdepthstomovelargebouldersbythe2011tohokuokitsunami AT kazuhisagoto thresholdflowdepthstomovelargebouldersbythe2011tohokuokitsunami
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Threshold flow depths to move large boulders by the 2011 Tohoku-oki tsunami

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