Distribution of deep-seated landslides and gentle slopes on the ridge at Hiranabe, Kitagawa, Kochi

Katsuo SASAHARA

Microtopographic examination was conducted to identify geomorphologic factors related to an onset of a deep]seated landslide at Kitagawa, Kochi where several deep]seated landslides occurred in 2011 and 2014 by heavy rainfalls. ELSA Map (Kokusai Kogyo, Co., Ltd.) with 1m mesh was produced from LiDAR Data for the examination. The geology of studied area is made of alternative layers of mudstone and sandstone with faults and fractured zone in accretionary prism. Three kinds of microtopographic characteristics are identified for the slope with the possibility of the onset of deep]seated landslides. The first one is a gentle slope on the ridge with many steps. Landslides are prone to occur below the gentle slope on the ridge. The combination of the gentle slope on the ridge and existing landslides below it is also included in this case. The second one is the combination of small gentle slope at the middle of small ridge and steep slope below it. Several small gentle slopes can be found at almost same altitude in the middle of several ridges along a stream in this case. The third one is that a toe of a slope with landslide configuration is collapsed. The first case is dominant in studied area.