2:30 PM - 2:45 PM
[SVC32-04] Real-time and drone-based observations of rockfalls on Mt. Fuji
Keywords:rockfall, Mt. Fuji, field observation, drone
The movement of gravel is a phenomenon commonly observed on all rocky bodies, including Mars, the Moon, and asteroids. We are interested in rockfalls from a planetary perspective, in particular because rockfalls may play a key role in the gravel accumulations of rubble-pile asteroids, and because commonly observed traces of rockfalls on Mars and the moons of Earth and Mars may provide clues for estimating geotechnical parameters.
Rockfalls are common in mountainous regions on Earth and are triggered by various factors such as erosion, weathering, seismic activity, and human activities. Because rockfalls can be dangerous to people and property, considerable works have been done through monitoring of rock movements, laboratory to full-scale experiments, theoretical studies, and numerical reconstructions, leading to significant advances in the physical understanding of rockfalls. However, the triggering mechanism of large-scale rockfalls and the physical conditions under which rocks stop moving are still not well understood due to the lack of accurate large-scale observations in an area without vegetation and man-made objects.
Mt. Fuji is a unique environment in this regard because it has little vegetation and few developed areas above 2,500m, where rockfalls are reported in the media almost every year. We set up an observation station at the bottom of the No. 1 Hoei volcanic vent, which is a volcanic crater about 1km in diameter with a steep slope of more than 48 degrees. We installed 6 independent cameras (2 video cameras and 4 time-lapse cameras) connected to a portable lithium battery supported by a solar panel. The seismometer and the infrasound monitoring instrument were also placed separately. The observation was performed unmanned from July 8th, 2022 to October 12th, 2022, with 10 visits for maintenance. Despite occasional technical problems, we were able to successfully obtain observation data for a total of 74 days during this period and identify more than 100 rockfall events, including some giant ones, where movements of a few meters in diameter are recorded at high-resolution videos/images. The seismometer and infrasound monitor generally show consistent results with the optical observations, though noice often hinders detecting the rock fall signals. Working together with NHK (Japan Broadcasting Corporation), we also flew a drone on September 6th and October 3rd to precisely map the surface gravel inside the crater. 8301 optical images from the drone were used to reconstruct 3D shape models for each day, which were projected to 2.5cm resolution orthographic images to critically compare the differences in gravel in this region. These collectively indicate that the gravel in this region is much more actively moving than previously thought.
Rockfalls are common in mountainous regions on Earth and are triggered by various factors such as erosion, weathering, seismic activity, and human activities. Because rockfalls can be dangerous to people and property, considerable works have been done through monitoring of rock movements, laboratory to full-scale experiments, theoretical studies, and numerical reconstructions, leading to significant advances in the physical understanding of rockfalls. However, the triggering mechanism of large-scale rockfalls and the physical conditions under which rocks stop moving are still not well understood due to the lack of accurate large-scale observations in an area without vegetation and man-made objects.
Mt. Fuji is a unique environment in this regard because it has little vegetation and few developed areas above 2,500m, where rockfalls are reported in the media almost every year. We set up an observation station at the bottom of the No. 1 Hoei volcanic vent, which is a volcanic crater about 1km in diameter with a steep slope of more than 48 degrees. We installed 6 independent cameras (2 video cameras and 4 time-lapse cameras) connected to a portable lithium battery supported by a solar panel. The seismometer and the infrasound monitoring instrument were also placed separately. The observation was performed unmanned from July 8th, 2022 to October 12th, 2022, with 10 visits for maintenance. Despite occasional technical problems, we were able to successfully obtain observation data for a total of 74 days during this period and identify more than 100 rockfall events, including some giant ones, where movements of a few meters in diameter are recorded at high-resolution videos/images. The seismometer and infrasound monitor generally show consistent results with the optical observations, though noice often hinders detecting the rock fall signals. Working together with NHK (Japan Broadcasting Corporation), we also flew a drone on September 6th and October 3rd to precisely map the surface gravel inside the crater. 8301 optical images from the drone were used to reconstruct 3D shape models for each day, which were projected to 2.5cm resolution orthographic images to critically compare the differences in gravel in this region. These collectively indicate that the gravel in this region is much more actively moving than previously thought.