River dynamics in an active volcano: The case of the of the Sucio River, Irazú Volcano, Costa Rica

The Sucio River, Costa Rica, composed mainly of boulders, has undergone significant morphological changes, shifting from an island-braided to braided and anabranching system over the last six decades. This study analyzed 12.5 km of the river across three distinct reaches. We examined all available aerial photogrammetric flights and selected satellite imagery from ten key dates (1945-2023) to track morphological transformations following the 1963-1965 eruptions of the Irazú Volcano and to identify key factors influencing these changes, including, besides volcanic eruptions, seismic activity, and precipitation events. Channel morphology exhibited a highly dynamic behavior, with width increases correlating to reduced island presence and sediment bar formation. Conversely, vegetated islands consolidation led to channel narrowing. We noted a progressive increase in landslide area on the northern slopes of Irazú Volcano, particularly post-eruption (1963-1965) and during seismic events in the 1990s. A correlation between increased landslide activity and channel width highlights the sediment supply's role in channel dynamics. Also, vegetation dynamics significantly stabilizes channel banks and islands, facilitating rapid recovery and changes in channel morphology (e.g., from braided to anabranching). Future research should further explore vegetation composition and dynamics, enhancing the understanding of biogeomorphic processes in fluvial volcanic contexts under humid tropical conditions.