Present earth-surface processes and historical environmental changes inferred from lake-catchment systems

Abstract

Environmental changes in lake-catchment systems due to climatic, tectonic, and anthropogenic activities (processes) have been imprinted on lacustrine sediments. Long continuous observation in a small pond-catchment system at Kobe, Japan following the 1995 Kobe earthquake provides good data on environmental changes. These records are available for establishing a mathematical model in which the rate of sedimentation varies in two stages before arriving at the pre-earthquake stage. The model’s calculations are fairly consistent with observational results, indicating that the model is acceptable. The 1995 earthquake is faintly recorded in the physical properties of sediments obtained in the system (increase in density and slight change in grain size). A combination of grain density (or mineral content) and grain size may be useful as an indicator for the occurrence of comparatively large earthquakes in tectonically active and climatically humid areas. The Tong-hai earthquake of 1970 in Yunnan, China was detected in the combination (density increase and grain size decrease) for the core sediments obtained from Qilu-he. The Kanbun earthquake of 1662 in Lake Biwa catchment was also detected in the corresponding data from some cores obtained from Lake Biwa, Japan.