[H-TT13] HIGH-DEFINITION TOPOGRAPHIC SURFACE DATA FOR CONNECTIVITY IN THE ANTHROPOCENE

[HTT13-P05] Long-term monitoring and visualization of rocky coast erosion by three-dimensional measurements: A case study at Suzumejima Island, eastern Japan

*Yuichi S. Hayakawa¹ (1.Faculty of Environmental Earth Science, Hokkaido University)

Keywords:uncrewed aerial system, photogrammetry, three dimensional

Repeated measurements of three-dimensional (3D) morphological data of changing rocky coasts can facilitate people to recognize the ongoing geomorphological processes therein, and the data can be utilized for the protection of coastal areas or the recognition of environmental landscape changes. We have been working on the acquisition of 3D data of a small rocky island, namely Suzumejima Island, on the Pacific coast in eastern Japan for nearly ten years since 2013. The measurements have been based on terrestrial laser scanning (TLS), uncrewed aerial system (UAS)-based structure-from-motion (SfM) photogrammetry, and UAS-based light detection and ranging (Lidar), and UAS-SfM was found to be the best appropriate approach to continuously capture the 3D topographic data at an interval of several months if the aircraft has an ability of high-precision positioning by realtime-kinematic global navigation satellite system (RTK-GNSS). From the obtained point cloud and 3D mesh data, volumetric changes of the rocky island by erosional processes are quantified, and the temporal analysis revealed spatially variable rockfalls and wave cuts on the order of 10⁰ to 10³ m³ in several months, likely affected by the frequency of high (> 3 m) tidal waves rather than ground acceleration by earthquakes. Moreover, it seems that the wave erosion appears effectively on weak portions in the bedrock of weakly-consolidated Pleistocene sedimentary rocks, particularly along the joints rather than bed planes. In fact, it is observed that holes (caves) are actually being formed along the joints in the island. These observations suggest that the island will shrink and disappear in decades. Such 3D changes can be visualized in various ways, including virtual reality (VR) platforms and 3D print models. In particular, small "copies" of the island in the real world with 3D prints can support people in understanding the past, present, and future of the coast.