5:15 PM - 7:15 PM
[HGM04-P13] The Emergent Coastal Landforms of Chigoki Cape, Happo Town, Akita Prefecture
Keywords:horizontal shore platform, schmidt hammer, unmanned aerial vehicle (UAV), weathering
A horizontal shore platform is a flat coastal landform that develops due to wave erosion in rocky coasts. This landform develops within the intertidal zone, which lies between the high tide and low tide levels. The landforms are also said to be formed in relation to the resistance (hardness) of the rock and the erosive force of waves. The objective of this study is to estimate the formation age and process of horizontal shore platforms in a region where multiple platforms have developed, using high-precision topographic surveys and rock property measurements.
The study area is Chigoki Cape, located in Happo Town, Akita Prefecture, Japan. The Nishitsugaru region, including Chigoki Cape, has undergone intermittent uplift since the Holocene. Nakata et al. (1976) reported that the area surrounding Chigoki Cape experienced approximately 2 meters of uplift due to earthquakes in 1704 and 1793. In this study, we conducted elevation measurements, UAV-based topographic surveys, rock strength assessments, and fracture density analyses in the region. Elevations were measured using RTK-GNSS. The topographic survey was conducted using an unmanned aerial vehicle (UAV) equipped with RTK-GNSS, from which a high-precision 3D topographic model was generated. Rock strength values were measured using a Schmidt hammer with both continuous-impacts and single-impacts methods. Additionally, weathering indices were calculated by the obtained rock strength values. Fracture densities were defined as the number of fractures per meter, and the average values were determined from three measurements.
Cross-sectional profiles were extracted from the high-precision 3D topographic model. As the result, three distinct horizontal shore platforms were identified based on the elevation. These platforms were designated as the L surface (upper), B surface (middle), and C surface (lower). Additionally, two notches were observed at elevation of 4.2 m. The presence of the L surface beneath the notch suggests that it represents a former horizontal shore platform formed during the notch development. The B surface, located at a lower elevation of approximately 2 m, corresponds to the uplift height reported by Nakata et al. (1976), indicating that it was uplifted during the 1704 and 1793 earthquakes. The C surface is situated within the present intertidal zone, suggesting that it represents an active wave-cut platform.
Rock strength, weathering indices, and fracture density measurements indicate that the C surface, as an active horizontal shore platform, is currently subjected to erosional processes, whereas the L and B surfaces exist within a weathering environment. Furthermore, the L surface exhibits weathering accompanied by extensive fracturing, while the B surface primarily undergoes weathering without significant fracture development.
Future research will focus on more detailed chronological analysis and investigations of weathering processes to further elucidate the formation mechanisms of wave-cut platforms.
Nakata, T., Imaizumi, T. and Matsumoto, H. (1976): Late Quaternary Tectonic Movements on the Nishi-tsugaru Coast, with Reference to Seismic Crustal Deformation. Sci.Rep.Tohoku Univ.,7th Ser. (Geogr), 26, 101-112
The study area is Chigoki Cape, located in Happo Town, Akita Prefecture, Japan. The Nishitsugaru region, including Chigoki Cape, has undergone intermittent uplift since the Holocene. Nakata et al. (1976) reported that the area surrounding Chigoki Cape experienced approximately 2 meters of uplift due to earthquakes in 1704 and 1793. In this study, we conducted elevation measurements, UAV-based topographic surveys, rock strength assessments, and fracture density analyses in the region. Elevations were measured using RTK-GNSS. The topographic survey was conducted using an unmanned aerial vehicle (UAV) equipped with RTK-GNSS, from which a high-precision 3D topographic model was generated. Rock strength values were measured using a Schmidt hammer with both continuous-impacts and single-impacts methods. Additionally, weathering indices were calculated by the obtained rock strength values. Fracture densities were defined as the number of fractures per meter, and the average values were determined from three measurements.
Cross-sectional profiles were extracted from the high-precision 3D topographic model. As the result, three distinct horizontal shore platforms were identified based on the elevation. These platforms were designated as the L surface (upper), B surface (middle), and C surface (lower). Additionally, two notches were observed at elevation of 4.2 m. The presence of the L surface beneath the notch suggests that it represents a former horizontal shore platform formed during the notch development. The B surface, located at a lower elevation of approximately 2 m, corresponds to the uplift height reported by Nakata et al. (1976), indicating that it was uplifted during the 1704 and 1793 earthquakes. The C surface is situated within the present intertidal zone, suggesting that it represents an active wave-cut platform.
Rock strength, weathering indices, and fracture density measurements indicate that the C surface, as an active horizontal shore platform, is currently subjected to erosional processes, whereas the L and B surfaces exist within a weathering environment. Furthermore, the L surface exhibits weathering accompanied by extensive fracturing, while the B surface primarily undergoes weathering without significant fracture development.
Future research will focus on more detailed chronological analysis and investigations of weathering processes to further elucidate the formation mechanisms of wave-cut platforms.
Nakata, T., Imaizumi, T. and Matsumoto, H. (1976): Late Quaternary Tectonic Movements on the Nishi-tsugaru Coast, with Reference to Seismic Crustal Deformation. Sci.Rep.Tohoku Univ.,7th Ser. (Geogr), 26, 101-112