1:45 PM - 2:05 PM
[O06-01] Investigating the Causes of Nishinoshima's Continuous Growth Through Geophysical Observations
★Invited Papers
Keywords:Nishinoshima, Aeromagnetic survey, Magnetiation structure, OBEM, Electrical conductivity structure
In November 2013, Nishinoshima, located in the Bonin Arc, resumed volcanic activity for the first time in approximately 40 years. Since then, the island has significantly expanded, incorporating the pre-existing landmass from before 2013. As many of you may know, the Izu-Bonin Arc is formed by numerous volcanic islands and seamounts, which have developed due to the subduction of the old Pacific Plate beneath the trench on the eastern side of the arc. However, even after more than ten years since 2013, Nishinoshima remains the only volcano in the region that continues to experience large-scale and prolonged eruptive activity. Why is Nishinoshima the only one exhibiting such persistent volcanic activity?
We hypothesize that investigating the internal structure of Nishinoshima can help us trace the origin of its eruptive magma and unravel the factors driving its ongoing volcanic activity. Furthermore, Tamura et al. (2016) proposed that Nishinoshima may hold the key to understanding the formation mechanisms of the Earth's continental crust. This suggests that Nishinoshima could be a precursor to continental crust, with the potential to eventually evolve into a continent. To test this hypothesis, it is essential to clarify how water, dehydrated from the subducted Pacific Plate and supplied to the upper mantle, travels and transforms into magma.
To investigate the internal structure of Nishinoshima, the distribution of magma associated with volcanic activity, and the location of water that contributes to magma generation, we have been conducting electromagnetic observations since 2016. In June 2019, we carried out an aerial magnetic survey using a multicopter (commonly known as a drone) to reveal the near-surface structure of Nishinoshima. As a result, we identified an anomalous region of magnetization intensity, which is thought to be associated with lava erupted before the 2013-2015 eruptions (Tada et al., 2021, JVGR). We deployed approximately 20 OBEMs (ocean-bottom electromagnetometers) around Nishinoshima to investigate its deep structure. The primary goal of this study was to examine the electrical conductivity distribution in three-dimension within Nishinoshima, allowing us to detect the presence of magma and water. The OBEMs were deployed on the seafloor in multiple phases between 2016 and December 2020. However, due to phenomena likely associated with submarine volcanic activity, some OBEMs became trapped on the seafloor and could not be recovered, while others moved as far as 3.5 km during the deployment period. These instruments have provided invaluable information about Nishinoshima's volcanic activity that could not have been obtained through aerial observations alone. Additionally, one OBEM was carried away by ocean currents and drifted an astonishing 1,700 km to Iriomote Island in the Ryukyu Archipelago.
Observations targeting Nishinoshima have involved groundbreaking efforts, such as conducting the world's first aerial magnetic survey over a remote oceanic island and unprecedented experiences in OBEM-based research. These observations continue to be conducted today. In this presentation, we will introduce how researchers are attempting to unravel the mysteries of Nishinoshima, using observational data and photographs. We also hope to engage in active discussions with the audience regarding new perspectives that we may not have yet considered.
We hypothesize that investigating the internal structure of Nishinoshima can help us trace the origin of its eruptive magma and unravel the factors driving its ongoing volcanic activity. Furthermore, Tamura et al. (2016) proposed that Nishinoshima may hold the key to understanding the formation mechanisms of the Earth's continental crust. This suggests that Nishinoshima could be a precursor to continental crust, with the potential to eventually evolve into a continent. To test this hypothesis, it is essential to clarify how water, dehydrated from the subducted Pacific Plate and supplied to the upper mantle, travels and transforms into magma.
To investigate the internal structure of Nishinoshima, the distribution of magma associated with volcanic activity, and the location of water that contributes to magma generation, we have been conducting electromagnetic observations since 2016. In June 2019, we carried out an aerial magnetic survey using a multicopter (commonly known as a drone) to reveal the near-surface structure of Nishinoshima. As a result, we identified an anomalous region of magnetization intensity, which is thought to be associated with lava erupted before the 2013-2015 eruptions (Tada et al., 2021, JVGR). We deployed approximately 20 OBEMs (ocean-bottom electromagnetometers) around Nishinoshima to investigate its deep structure. The primary goal of this study was to examine the electrical conductivity distribution in three-dimension within Nishinoshima, allowing us to detect the presence of magma and water. The OBEMs were deployed on the seafloor in multiple phases between 2016 and December 2020. However, due to phenomena likely associated with submarine volcanic activity, some OBEMs became trapped on the seafloor and could not be recovered, while others moved as far as 3.5 km during the deployment period. These instruments have provided invaluable information about Nishinoshima's volcanic activity that could not have been obtained through aerial observations alone. Additionally, one OBEM was carried away by ocean currents and drifted an astonishing 1,700 km to Iriomote Island in the Ryukyu Archipelago.
Observations targeting Nishinoshima have involved groundbreaking efforts, such as conducting the world's first aerial magnetic survey over a remote oceanic island and unprecedented experiences in OBEM-based research. These observations continue to be conducted today. In this presentation, we will introduce how researchers are attempting to unravel the mysteries of Nishinoshima, using observational data and photographs. We also hope to engage in active discussions with the audience regarding new perspectives that we may not have yet considered.