Natural controls of fluvial denudation rates in major world drainage basins

Abstract

We present a new compilation of estimates of modern rates of mechanical and chemical denudation for externally drained basins exceeding 5×105 km2 in area. These estimates are based on sediment and solute load data selected in order to represent natural rates as far as possible. Chemical denudation rates have been calculated by deducting the nondenudational component of solute load. Mechanical denudation rates range from 1 mm kyr−1 for the St. Lawrence and Dnepr basins to 670 mm kyr−1 for the Brahmaputra basin. Chemical denudation rates vary from 1 mm kyr−1 (Kolyma, Niger, Nile and Rio Grande basins) to 27 mm kyr−1 (Chiang Jiang basin). The Kolyma basin has the lowest (4 mm kyr−1), and the Brahmaputra basin the highest, overall rate of denudation (688 mm kyr−1). Relationships between denudation rates and a range of morphometric, hydrologic, and climatic variables are investigated through correlation and regression analysis. Morphometric variables, such as mean local relief, are accurately calculated for large basins for the first time by using the National Geophysical Data Center 10‐minute topographic database. Variables expressing basin relief characteristics and runoff are found to be most strongly associated with both mechanical and chemical denudation rates, with more than 60% of the variance in total denudation being accounted for by basin relief ratio and runoff. Basin area, runoff variability, and mean temperature, however, are only weakly associated with rates of denudation. Although direct comparisons cannot be made, it appears that rates of basin denudation derived from present‐day mass flux estimates are not, overall, significantly different from estimates of long‐term rates based on sediment volume and thermochronologic data. It therefore appears that the key factors identified as controlling denudation rates here are also applicable to the geological time spans relevant to the interaction between tectonic and denudational processes.