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[SVC34-09] History of rapid subsidence and uplift associated with magma eruption at 2.7 ka in Iwoto (Iwo Jima) Island, Ogasawara Islands, Japan
Keywords:Iwoto(Iwo Jima), Izu-Ogasawara Arc, eruption, uplift, resurgent dome, coral fossil
Iwoto (Iwo Jima) Island, in the Izu-Ogasawara Arc, is a volcanic island located 1200 km south of Tokyo. The island is formed by the connection of Mt. Motoyama (139 m above sea level), which has a flat summit with a diameter of about 5km, and Mt. Suribachi (172 m above sea level), a small cone-shaped mountain with a diameter of about 600m. Mt. Motoyama was made by the Motoyama-forming eruption (>1.3 km3) at 2.7 ka. Since human settlement in the late 19th century, This Island has experienced significant uplift and frequent small eruptions.
In this study, based on sedimentary facies analysis and 14C dating of coral fossils, we have reconstructed the uplift and subsidence history from just before the largest eruption of Iwoto Island, the Motoyama-forming eruption (2.7 ka), to the present. The results are as follows:
Just before the Motoyama-forming eruption 2.7 ka, the area near the eastern coast of present-day Iwoto Island was in a beach (backshore) environment, similar to today. The eruption materials from the Motoyama-forming eruption, which overlies this, was deposited in a submarine environment. Based on the eruption materials of the Motoyama-forming eruption thick, indicating subsidence of more than 140 meters just before or during the eruption. Based on the 14C dating of coral fossils of the terrace surface at the top of Mt. Motoyama, the island re-emerged above sea level and became land again between the 13th to 15th centuries (ca. 700-400 years ago). In addition, Iwoto Island was first discovered in AD 1543. When humans first settled on the island in the late 19th century, Mt. Motoyama was an elevation of about 100 m above sea level. The highest point of Mt. Motoyama in AD2023 is 139 m above sea level.
Iwoto Island experienced rapid subsidence before and after the Motoyama eruption, followed by rapid uplift continuing to the present. This study is suggested that eruptions of the scale of the Motoyama-forming eruption could cause rapid subsidence on this island.
In this study, based on sedimentary facies analysis and 14C dating of coral fossils, we have reconstructed the uplift and subsidence history from just before the largest eruption of Iwoto Island, the Motoyama-forming eruption (2.7 ka), to the present. The results are as follows:
Just before the Motoyama-forming eruption 2.7 ka, the area near the eastern coast of present-day Iwoto Island was in a beach (backshore) environment, similar to today. The eruption materials from the Motoyama-forming eruption, which overlies this, was deposited in a submarine environment. Based on the eruption materials of the Motoyama-forming eruption thick, indicating subsidence of more than 140 meters just before or during the eruption. Based on the 14C dating of coral fossils of the terrace surface at the top of Mt. Motoyama, the island re-emerged above sea level and became land again between the 13th to 15th centuries (ca. 700-400 years ago). In addition, Iwoto Island was first discovered in AD 1543. When humans first settled on the island in the late 19th century, Mt. Motoyama was an elevation of about 100 m above sea level. The highest point of Mt. Motoyama in AD2023 is 139 m above sea level.
Iwoto Island experienced rapid subsidence before and after the Motoyama eruption, followed by rapid uplift continuing to the present. This study is suggested that eruptions of the scale of the Motoyama-forming eruption could cause rapid subsidence on this island.