Fluvial Marine Dynamics and Volcanic Sediment Supply in Barrier Beach and Mangrove Formation, Santen Island Banyuwangi

The Banyuwangi Regency is distinguished by substantial volcanic activity, which has contributed to the formation of the region’s coastal landforms. On Santen Island, the barrier island is a morphological feature formed primarily by fluvial–marine dynamics, with volcanic deposits serving as a significant sediment source. These processes also support the protection and growth of mangrove ecosystems. The present study analyses the interaction between volcanic sediment supply and fluvial–marine processes in barrier formation, and their relation to mangrove sustainability. An explanatory–descriptive approach was applied, integrating geological analysis with Sentinel-2 imagery from 2018 to recent monitoring. The results of the study indicate that the formation of barriers is influenced by volcanic materials derived from Mount Ijen, Mount Ranti, and Mount Merapi. These materials are transported through the Bendo watershed and deposited in the intertidal zone. Sentinel-2 imagery reveals a barrier extending longitudinally from north to south, with mangroves expanding both landward and laterally. Between 2018 and the most recent observations, mangrove cover has generally increased, although recent data suggest minor fluctuations that require further investigation. These findings underscore the combined role of volcanic sediment supply and fluvial– marine dynamics in shaping and sustaining vulnerable coastal ecosystems.