Research Topics

Research introduction pamphlets for each academic year can be found here.

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Past Research Topics2014-2019

Master's and Doctoral Theses of Graduates

Introduction

Volcanic eruption mechanisms and the associated wave phenomena are the main focus of our laboratory’s research. Volcanic eruptions can essentially be understood as thermodynamic phenomena; however, magma exhibits properties that transition between fluid and solid states. While 'solid flow' is a significant topic in solid Earth sciences, such as mantle convection, in volcanoes, the issue lies in 'fluid fracture.' We have been studying the nature of this process through theoretical and experimental approaches. In addition, various vibrational phenomena are observed in active volcanoes, manifesting as seismic activity, ground deformation, and airwaves (sound waves). Even when, in our daily lives, we can interpret a wide range of information from sounds, our ability to 'listen' to volcanic reverberations is still poorly developed. By observing volcanic ‘sounds’ in the field and conducting model experiments, we are attempting to understand the meaning of these vibrations.

Fluid fracture experiments to understand the mechanism of magma fracture and air vibration generation

Magma is molten rock, exhibiting both liquid and solid properties. This duality means that if a sudden force is applied, magma can shatter into fragments, much like glass. Such explosive fragmentation causes significant dangers. If magma consistently behaved like glass, volcanic eruptions would be far more violent and hazardous. In reality, magma often exists in an intermediate state between liquid and solid. However, the mechanisms by which such “intermediate substance” breaks apart and the physical properties governing these processes remain poorly understood. Our research group explores the complex physical properties of magma by conducting deformation and fracture experiments using fluids that mimic its characteristics. The video on the left demonstrates an experiment in which bubbles are injected into a soft, jelly-like substance possessing both viscosity and elasticity. To visualize elastic deformation, the property of photoelasticity was used. While these experiments cannot be directly applied to magma, they help us gain a deeper understanding of the physics underlying these phenomena and contribute to the development of more sophisticated models of volcanic processes. (Sanchez)

Eruption observation using a ultra-small infrasound temporary array

Air vibrations are low-frequency sound waves that are inaudible to the human ear. Occasionally, strong airwaves occur that can be felt physically or even break window glass. However, in most cases, even when examining data measured by sensors, it is difficult to clearly identify the waveforms or pinpoint their onset. On the other hand, understanding when, where, and how the airwaves occurred is crucial for effectively grasping the starting point and progression of an eruption.

The direction of a sound source can be estimated using an observation and analysis method called an 'array,' which involves measuring sound waves with multiple sensors arranged in a specific pattern. Conventional air vibration arrays used sensors spaced approximately 100 meters apart, which made installation and maintenance challenging. However, using the latest sensors, we demonstrated that sound source direction can be determined with sufficient accuracy even with sensors spaced just 10 meters apart. Additionally, we found that arranging sensors in a slightly three-dimensional configuration significantly improves the accuracy of height estimation for the sound source. The figure on the left shows an example of a miniature air array deployed at Stromboli Volcano in Italy. This method has also been applied to volcano observations at Sakurajima and Kirishima, as well as avalanche monitoring at Mt. Fuji.(Yamakawa/Ikeda)

Understanding Eruptive Activity and Monitoring Volcanoes Using Satellite Data

Satellites observe the Earth continuously, 24 hours a day, 365 days a year．For this reason, they are used as an observational tool that can detect volcanoes and eruptive activity even in areas with few ground-based observation stations, such as infrasound sensors or seismometers, and at night, when visual observation of volcanic plumes is difficult． Japan’s geostationary meteorological satellite Himawari observes, or scans, Japan, Kamchatka, Southeast Asia, South Asia, and the surrounding regions once every 10 minutes．From these observational data, we can obtain information such as how volcanic plumes produced by eruptions evolve over time and when extremely hot materials, such as lava, appear at the Earth’s surface．For volcanic eruptions that occurred at volcanoes without nearby observation stations, we analyzed these satellite observation data and compared them with distant ground-based observation data to reveal the eruption sequence in greater detail．Furthermore, by improving methods for analyzing satellite data, we have found that it is also possible to understand conditions within and beneath volcanic plumes．The figure on the left is a satellite image captured from above of the volcanic plume formed by the large-scale eruption of Hunga Tonga-Hunga Haʻapai volcano in Tonga in 2022．A new eruption can be seen near the center of the image． By applying these methods, we are working not only to understand the status of volcanic activity in Japan, but also to monitor activity at submarine volcanoes in cooperation with overseas institutions．（Horiuchi）

Ocean-area Volcano Monitoring Using DAS

Ocean-area volcanoes, such as submarine volcanoes and volcanoes on volcanic islands, are difficult to equip with observation stations, and the development of observation networks has lagged behind．We focus on DAS（Distributed Acoustic Sensing）, a technology that uses optical fibers as seismometers, and are conducting observations of submarine volcanoes in Tonga using submarine communication cables．DAS enables dense observations that were not possible with conventional seismometers． On the other hand, DAS has characteristics that differ from those of conventional seismometers, and it can sometimes be difficult to analyze earthquakes using existing methods．Therefore, we are working to develop analytical methods that take advantage of the characteristics of DAS while detecting weak seismic activity occurring at volcanoes．（Nakao）