Fluvial Geomorphology of Active Volcanoes in Costa Rica

Costa Rica, encompassing an area of 51,100 km², features a complex network of streams shaped by its rugged terrain, active volcanism, and tectonic activity. This dynamic drainage system is characterized by diverse erosive and depositional landforms. This study provides a comprehensive examination of Costa Rica's river environments, focusing on channel morphologies and fluvial dynamics across selected reaches. Utilizing advanced remote sensing techniques, including Unmanned Aerial Vehicles (UAVs), hydraulic modeling, and detailed field observations, we characterized significant river sections within distinct geological contexts, including steep volcanic-mountain settings and low-gradient alluvial fans. Focusing on rivers draining from the Irazú-Turrialba Volcanic Complex, we observed rapid channel morphology changes influenced by extreme precipitation, high-magnitude earthquakes, and active volcanic processes. Our analysis of the Sucio River over a 60-year period (1961-2023) revealed significant shifts from island-braided to braided and anabranching systems, illustrating a cyclical pattern of channel dynamics. Increased channel width correlated with a reduction in vegetated islands and sediment bar accumulation, while decreased width facilitated bank stabilization and island consolidation. Additionally, we investigated the Turrialba River, which flows from Turrialba Volcano. This river has a history of causing severe damage to the nearby city, particularly through bank erosion and flooding events, including a significant flood in July 2021 that drastically altered channel morphology. Our analysis of sediment sources and historical evolution highlighted the high hillslope-channel connectivity and sediment load transport characteristics inherent in volcanic environments. Overall, our findings emphasize the critical role of sediment supply from landslides and volcanic activity in shaping channel dynamics, while also addressing the potential hazards posed by these highly dynamic fluvial systems. Furthermore, vegetation plays a vital role in stabilizing channel banks and islands, supporting rapid recovery in disturbed areas. This work contributes to a novel understanding of fluvial geomorphology in active volcanic environments, underscoring the need for further research into the interactions between vegetation and geomorphic processes in these dynamic landscapes.