Direct comparison of site-specific and basin-scale denudation rate estimation by in situ cosmogenic nuclides: an example from the Abukuma Mountains, Japan

Accurate determination of denudation rates is important in understanding Earth surface system dynamics. In situ produced cosmogenic nuclides, such as Be and Al, provide a valuable insight but are not entirely free from complications. In this study, denudation rates are determined for the Abukuma Mountains, Japan, using both site-specific and basin-scale methods. Considered with density measured in the field, distinct and systematic differences between the two methods are identified. Site-specific rates calculated from depth profiles of cosmogenic nuclides (Be and Al) at topographic highs indicate a rate of 67 to 85 mm/kyr, whereas basin-scale averaged denudation rates derived from the concentration of cosmogenic nuclides in fluvial sediments show 114 to 180 mm/kyr. This is the first comparison of these two commonly used methods in the same region in Japan, where the entire study area is characterized by well-developed saprolite. These results indicate that differential denudation rates between topographic highs and valleys reflect increasing local topographic relief of the study area. Comparison between rates derived from depth profiles and those applicable to the entire basin is important for understanding landscape development.