Signatures of lithology, climate, and exhumation in river networks on Earth and Titan

Branching river networks are among the most widespread and recognizable erosional features in the Solar system, yet we have much to learn about how material properties, climate, and life influence the erosional processes that shape river networks. I will share three stories illustrating how river networks reveal different aspects of a planet’s geologic past. First, we will visit the east and west coasts of the US to uncover an explanation for why rivers form fine-scale tributary networks, and will see that the instability that generates this pattern occurs at a spatial scale that is sensitive to rock strength. Next, we will travel to Titan, where the challenge is to use coarse observations of drainage networks to reconstruct erosional and climatic processes. Images of small-scale fluvial networks and surface sediment permit an estimate of short-term methane rainfall rates, an aspect of Titan’s climate that is difficult to infer even from spacecraft observations of the atmosphere. Finally, a numerical model of large-scale landscape evolution reveals how the shapes of drainage networks constrain the amount of erosional exhumation that has occurred on Titan’s icy surface. I will end by describing key unknowns that currently limit the information we can extract from landscapes shaped by river networks.