Keynote Presentation: Nel Caine

Geochemical Denudation in Alpine Environments

The last 50 years have seen increased recognition of the importance of geochemical processes in many alpine systems. In this paper, I treat solute dynamics in a geomorphic context on a variety of scales. Solute yields (on the order of 10 mm ka^-1) from large, high mountain drainage basins are usually lower than corresponding sediment yields (which may exceed 100 mm ka^-1). However, solute yields are still often greater than the global average, even in non-carbonate terrains. This level of geochemical activity is associated with characteristics common to high mountain environments: glacial areas; freshly-fractured rock debris; and high rates of water flux. Rates of solute yield from small drainage basins within mountain systems are even more highly variable and reflect contrasts in soil and bedrock materials; geomorphic history; glacierized areas; precipitation amounts, and landscape dynamics. Within such small basins, variability probably continues to increase, though there are relatively few studies which treat more than basin averages. In Green Lakes Valley, Colorado Front Range, yields of cations and Si derived from the basin materials decrease with increasing basin area and are closely correlated to water yields. However, we still need to identify better the sources from which the solutes are derived; the reaction rates in its generation, and the pathways through which it is transported to the basin outlet. These influences are presumed to reflect the local bedrock and soil structure; the location of geomorphically active sites within the basin, and the spatially variable contributions of "aggressive" water. In turn, these contrasts may have long-term significance for the development of the mountain landscape.