QUANTIFYING FLUVIAL EROSION AND LANDSCAPE EVOLUTION OF VOLCANIC ISLANDS

As volcanic islands develop over time, their topographies transform from bare, undissected surfaces to geomorphologically complex and diverse landscapes, dramatically shaped by fluvial erosion. Determining primary influences and controls on this landscape evolution builds stronger knowledge about the past, present, and future of these islands; not only their topography, but also water supply availability, geoecology, and local oceanic geochemistry. Here, we aim to quantify river concavity and volume of basin erosion as metrics of fluvial erosion and landscape evolution, and investigate how these values change over temporal scales, as well as climatic and geologic regimes. Using digital elevation models of 26 islands in Cape Verde, Hawaii, and the Azores, we determine the paths of river channels and extract their longitudinal profiles to calculate normalized concavity indexes. To quantify eroded basin volume, we model an initial topography by interpolating between drainage divide elevations and calculate the total elevation differences normalized by island area. Concavity patterns across these archipelagos demonstrate a pattern of increasing concavity for at least 7.5 million years, after which concavity plateaus, and eventually decreases. We attribute this decrease in concavity to the long-term diffusion of drainage divides. Lower concavity is more prominent in wetter climates, further supporting this theory. We also find a strong relationship between concavity and eroded basin volume, though eroded volume is less correlated to climate and age metrics. Current results demonstrate valuable methods to quantify fluvial erosion and landscape evolution of volcanic islands, and measure trends in their topographic evolution over geologic time. We will compare these observations with models of erosion using Landlab, hypothesizing that the model will display the same patterns of concavity changes as the island ages.