Introduction Under natural conditions, sediment loads in rivers are primarily a function of climate and geology. Climate is expressed through the amount, seasonality and intensity of precipitation. Geology is expressed through the surface rocks of the catchment area and the tectonic style of the terrain over which the catchment has developed. The influence of these interactions between climate and geology will be discussed here at both the fundamental continental and major river basin scale and the local catchment scale. The continental scale analysis considers variations in the fundamental drivers of sediment delivery: the supply of erosive energy and the resistance to erosion. The local catchment scale analysis examines how flows and activities within the ecosystems produced by these climatic and geologic drivers influence the sources and delivery of sediment. INFLUENCE OF TECTONICS AND LITHOLOGY. Although tropical rainforests cover many parts of the Equatorial regions, they extend over great geological diversity, with wide variations in sediment yield. Where tectonics are active, earth movements frequently trigger landslides and thus supply large quantities of sediments to rivers. Active volcanic areas also create large sediment supplies, particularly through ejected ash and its mobilisation in lahars. Lahar flows can contain sediment concentrations as high as 66% by volume and peak discharges of several hundred m3 s-1 (Major et al., 1996; Pierson et al., 1992).