Abstract

Alluvial rivers are the main mechanism by which sediment is moved from eroding source regions to downstream basins. In response to changing climatic or tectonic boundary conditions, they aggrade, incise and adjust the rates at which they transport sediment. Their lateral migration also builds fertile floodplains that large populations inhabit and cultivate. I will present results from two modelling studies. First, I explore how changing sediment supply, precipitation rate or base level is recorded in fluvial terrace sequences and variations in downstream basin accumulation rates. I will discuss some general insights as well as preliminary results from a case study focused on major pro-glacial rivers in southern Patagonia. Second, I present a new model for the lateral evolution of alluvial valleys, which is based on random walk theory, and provides analytical descriptions of how valleys widen over time and the age distributions of sediment they deposit. This work moves us closer to quantitative interpretation of alluvial landforms and stratigraphic archives in terms of past climatic and tectonic environments, and to accurate predictions of how these systems will evolve in the future.