Primary controls in incipient erosion: A tale of two volcanic landscapes

Volcanic islands constitute some of the best natural laboratories to investigate the processes that dictate landscape evolution. Due to their simplified lithologies, known initial topography, and datable surfaces, these systems are ideal for isolating the primary drivers of fluvial erosion at a variety of spatial and temporal scales. Fogo island (Cape Verde) and the Kohala Peninsula (Hawai'i) boast an additional two characteristics that allow us to directly explore the relationship between climate and fluvial erosion: a substantial orographic precipitation gradient and young (O[100 ka]) surfaces with limited confounding processes of landscape modification. Here we combine high-resolution topographic analysis with climate datasets to compare the relationship between precipitation and erosion across these two regions. Results suggest that although there is a strong coupling between rainfall and erosion within each island, Fogo erosion rates are systematically an order of magnitude larger than expected based on rainfall alone when compared to Kohala. Differences in rainfall/storm intermittency do not account for this observation, nor do differences in erodibility of the rock. We find instead that surface gradient is likely to be responsible for this behavior, implying that the steepness of the initial topography may be the strongest control on the incipient rates of landscape evolution. An improved understanding of incipient basaltic terrain evolution could inform how fluvial systems on other planets may have developed and persisted, particularly in Fogo as it is analogous to the generally steep topography on the martian surface.