Researchers at the University of Tsukuba have discovered that rainwater runoff in the highly rugged sedimentary rock mountains of Japan's Southern Alps is governed by two processes: "deep infiltration" and "shallow drainage via landslides." These processes are dictated by the inclination of geological strata. Based on these findings, the researchers propose a conceptual framework, termed the "structural ground system," to explain how the bedding structure regulates rainwater runoff.