RIVER LOADS AND MODERN DENUDATION OF THE ALPS - A REVIEW

We present the first comprehensive analysis of sediment and dissolved load across an entire mountain range such as the Alps based on a compilation of data about river loads and reservoir sedimentation from 202 drainage basins that are between ca. 1 to 10 000 km² large. The study basins cover about 50% of the total area of the Alps. Modern glaciated basins show the highest total denudation rates with up to 3 mm a^-1, on average being 5 to 10 times higher than in non-glaciated basins and a significant positive correlation exists between sediment yield and glacial cover. Instead, relief is a relatively weak predictor of sediment yield. The strong glacial impact is due to glacier recession since the 19^th century as well as due to glacial conditioning during repeated Quaternary glaciations producing a strong transient state of the Alpine landscape. We suggest that this is the major cause for ca. 3 fold enhanced denudation of the western compared to the eastern Alps. Chemical denudation rates are highest in the outer Alps dominated by sedimentary rocks where they make up about one third of total denudation. The high rates can not be explained without anhydrite dissolution. We estimated that only 45% of the sediments mobilised in headwaters are exported out off the Alps, most sediments being trapped in artifical reservoirs. When corrected for sediment storage we receive an area-weighted mean total denudation rate for the Alps of about 0.32 mm a^-1. The pre-dam rate might be as high as 0.42 mm a^-1. In total, ca. 58*10⁶ t of mass are exported each year out of the Alps. These rates are not enough to pace out modern rock uplift. Thus the Alps are topographically growing at present, in contrast to the Quaternary mean. Nevertheless, the coincidence between rock uplift, glacial imprint and the pattern of modern denudation rates supports the hypothesis of an erosion-driven uplift of the Alps.