10:45 AM - 11:00 AM
[SVC34-06] Importance of observations of island or submarine volcanoes
★Invited Papers
Keywords:Island or submarine volcanoes, volcanic eruptions, tsunami
Japan is a volcanic country with an estimated 111 active volcanoes, about 30 of which are offshore volcanoes. Because most of the offshore volcanoes are located far from populated areas, the impact of an eruption is often thought to be less severe than that of an inland volcanic eruption. However, when eruptions occur on inhabited islands, they can cause serious damage due to the limited evacuation options, such as the Aogashima eruption in 1785 and the Izu-Torishima eruption in 1902. Depending on the size and style of eruption, volcanic eruptions can also have a large social impact over a wide area outside of the island, with the release of large amounts of volcanic ejecta or the generation of tsunamis. For example, the 1741 eruption of Oshima-Oshima caused the edifice collapse, which triggered a massive and damaging tsunami. A recent example is the August 15, 2021 eruption of Fukutoku Okanoba, which initially drew little public attention because there were no inhabited islands nearby. However, the large amount of pumice generated by the massive phreatomagmatic eruption was carried westward on ocean currents and drifted to Okinawa and other areas, causing significant impact on fishing and tourism. As an overseas example, the Hunga Tonga-Hunga Ha'apai eruption on January 15, 2022, is still fresh in our memory. The large-scale atmospheric wave caused by the gigantic phreatic eruption excited a tsunami, which reached Japan and overturned fishing boats. From a disaster prevention perspective, tsunami excitation by atmospheric wave was not anticipated, and the arrival time and scale of the tsunami could not be forecasted by conventional methods. Thus, depending on the magnitude and eruption style, offshore volcanic activities can cause various kinds of damage even in areas far from populated areas.
Although it is effective to conduct multi-parameter observations at target volcanoes in order to understand volcanic activity, it is often more difficult at offshore volcanoes than at inland volcanoes. If an island volcano is active, it is dangerous to approach or land on the volcano, and it is difficult to conduct observations. Seismic and crustal deformation observations are effective for understanding magma accumulation, movement, and ascent in the subsurface of volcanoes before eruption, but it is not easy to develop a wide-span observation network for offshore volcanoes, and it is more difficult to obtain information at great depth than for inland volcanoes. Although ocean bottom seismographs and magnetometers have been used to observe the sea area, it is not easy to conduct such observations on a large scale, and there are also difficulties in real-time data acquisition. Currently, visible and infrared image data, volcanic gas data, and crustal deformation data such as SAR obtained from satellites are the most promising means of observing and monitoring offshore volcanoes, but it is difficult to increase the frequency, and the time resolution is limited.
Thus, despite the great importance of offshore volcano observations, their implementation is not easy. In recent years, however, technological progress has been made to solve the problems mentioned above. Specifically, a new technique called Distributed Acoustic Sensing (DAS), which uses optical cables to detect ground strain, has emerged. Since this method can be implemented using existing optical cables, it can be applied not only to inland volcanoes but also to offshore volcanoes, and examples of observations using submarine cables for communication have begun to appear. This method enables observations that are not bound by the limitations of real-time and multi-channel seismic observation, which have been problems with conventional ocean bottom observations, and has the potential to play an important role in future observations of offshore volcanoes.
In this presentation, I will review the current status of offshore volcano observation and discuss its future direction.
Although it is effective to conduct multi-parameter observations at target volcanoes in order to understand volcanic activity, it is often more difficult at offshore volcanoes than at inland volcanoes. If an island volcano is active, it is dangerous to approach or land on the volcano, and it is difficult to conduct observations. Seismic and crustal deformation observations are effective for understanding magma accumulation, movement, and ascent in the subsurface of volcanoes before eruption, but it is not easy to develop a wide-span observation network for offshore volcanoes, and it is more difficult to obtain information at great depth than for inland volcanoes. Although ocean bottom seismographs and magnetometers have been used to observe the sea area, it is not easy to conduct such observations on a large scale, and there are also difficulties in real-time data acquisition. Currently, visible and infrared image data, volcanic gas data, and crustal deformation data such as SAR obtained from satellites are the most promising means of observing and monitoring offshore volcanoes, but it is difficult to increase the frequency, and the time resolution is limited.
Thus, despite the great importance of offshore volcano observations, their implementation is not easy. In recent years, however, technological progress has been made to solve the problems mentioned above. Specifically, a new technique called Distributed Acoustic Sensing (DAS), which uses optical cables to detect ground strain, has emerged. Since this method can be implemented using existing optical cables, it can be applied not only to inland volcanoes but also to offshore volcanoes, and examples of observations using submarine cables for communication have begun to appear. This method enables observations that are not bound by the limitations of real-time and multi-channel seismic observation, which have been problems with conventional ocean bottom observations, and has the potential to play an important role in future observations of offshore volcanoes.
In this presentation, I will review the current status of offshore volcano observation and discuss its future direction.