5:15 PM - 7:15 PM
[HCG21-P12] Potholes and regional Joint at Taki-no-hai in Kozagawa Town, Wakayama Prefecture, using UAV photography
Keywords:potholes, joints, structural control, Taki-no-Hai, UAV
Taki-no-Hai, located in Kogawa River, Kozagawa Town has been designated as a natural monument of Wakayama Prefecture. It is situated approximately 16 km upstream from the confluence of the Kozagawa River. On the rock terrace, numerous potholes of varying sizes are densely concentrated for 200 meters. The bedrock of Taki-no-Hai is composed of the Kumano Group from the Middle Miocene epoch, consisting of interbedded sandstone and sandstone-siltstone layers with thicknesses ranging from 0.1 to 2 meters. The strata strike NNW-SSE and dip 12 degrees to the northeast, and some areas exhibit hydrothermal alteration, giving the rocks a gray-to-white coloration.
In March 2024, we conducted a field survey and UAV imaging to observe and describe the geomorphological features of the potholes and joints, and to explore their relationship with the geological structures. We utilized the DJI Air 2S drone for aerial photography, capturing panoramic images from an altitude of about 80 meters and detailed images over a 40-meter square area at around 20 meters. Using Structure from Motion (SfM) analysis, we generated 3D models and orthophotos.
Extensive joints on the bedrock terrace occur at intervals ranging from several tens of centimeters to several meters in two perpendicular directions. Their orientations change to align with the curvature of the river channel. Additionally, according to Ito's (1979) classification, both groove-type and spoon-type potholes are arranged in parallel on the bedrock terrace. The groove-type potholes display a pattern formed by the accumulation of spoon-type potholes due to plucking. These groove-type potholes closely follow the extensive joints along the river channel direction, with their extension parallel to the joints' orientation. These findings suggest that groove-type pothole groups were formed along the joint orientations by plucking from floodwaters and that the microtopography facilitated structural control of the river's direction by the joints. Further investigation is required to understand the causes behind the changing orientations of joints along the curving river channel and their broader applicability to the overall
river channel systems.
In March 2024, we conducted a field survey and UAV imaging to observe and describe the geomorphological features of the potholes and joints, and to explore their relationship with the geological structures. We utilized the DJI Air 2S drone for aerial photography, capturing panoramic images from an altitude of about 80 meters and detailed images over a 40-meter square area at around 20 meters. Using Structure from Motion (SfM) analysis, we generated 3D models and orthophotos.
Extensive joints on the bedrock terrace occur at intervals ranging from several tens of centimeters to several meters in two perpendicular directions. Their orientations change to align with the curvature of the river channel. Additionally, according to Ito's (1979) classification, both groove-type and spoon-type potholes are arranged in parallel on the bedrock terrace. The groove-type potholes display a pattern formed by the accumulation of spoon-type potholes due to plucking. These groove-type potholes closely follow the extensive joints along the river channel direction, with their extension parallel to the joints' orientation. These findings suggest that groove-type pothole groups were formed along the joint orientations by plucking from floodwaters and that the microtopography facilitated structural control of the river's direction by the joints. Further investigation is required to understand the causes behind the changing orientations of joints along the curving river channel and their broader applicability to the overall
river channel systems.