Identifying the vulnerable landforms toward climate change-related hazards on small islands using geological-geomorphological and social approaches (Kei Kecil-Tual Carbonate Islands, Southeast Maluku, Indonesia)

Indonesia hosts an extremely large number of small islands and most of these are inhabited by humans. Such small islands are considerably prone to climate change-related hazards; however, until the present day, the study related to the assessment of coastal vulnerability to climate change hazards on small islands in Indonesia is still limited. This research focuses on studying carbonate islands in the Southeast Maluku (Indonesia), named Kei Kecil-Tual. Three rock facies were identified: the Quaternary stratified limestone (QSL; mainly rudstone intercalated with wackestone and grainstone layers), Quaternary massive limestone (QML; diagenetic crystalline limestone), and recent loose deposits (RLDs; sand, silt, and mud breccia). The prevalence of coral reef fragments in the QSL facies suggests a paleoenvironment of shallow ocean (in association with extensive carbonate platforms, possibly patch reefs) and subsequently uplifted due to the compressional stress from the Banda subduction; this is why most faults and folds are exclusively observed with the QSL. As the limestones had risen to the surface, the interaction with surface water became intense thus allowing the karstification process to take place, forming the QML facies. However, the Kei Kecil-Tual Islands are still in the early stages of karstification because the typical karst features (e.g., karst tower/cone) are still underdeveloped. The ongoing sedimentation in the coastal and estuarine-lake-fluvial area produces the recent sand and silt deposits, respectively, while the recent ‘eruption’ of mud volcanoes produces the mud breccias. Furthermore, the combination of geological information with morphometric parameters (i.e., elevation and slope) allowed us to classify the landform into 11 units: (KS 1) incipiently karstified structural ridges, (KS 2) incipiently karstified structural flank, (KS 3) incipiently karstified sloping plain, (K 1) moderately karstified plateau, (K 2) moderately karstified terraces, (S 1) pull-apart structural basins, (FM 1) estuarine, (M 1) shore, (M 2) tombolo, (F 1) fluvial plain, and (F 2) point bar. People living in landform units KS 1-3 and K 1-2 are facing threats from extreme weather and drought because these areas are made up of porous limestones, and the transition from flat land to hilly terrain creates localized pressure differences and further intensifies wind speeds. Meanwhile, landform units K 2 S 1, FM 1, M 1-2, and F1-2 are the most vulnerable to extreme waves and abrasion due to the direct contact with the ocean. Interpretation regarding the vulnerable landforms is further confirmed by the questionnaire surveys and field evidence. Our study becomes the first that captures the detailed geological conditions and genesis of the Kei Kecil-Tual Islands. Both types of information are not only useful for regional study but also fundamental for risk evaluation because each landscape poses a different response in facing climate change-related hazards. © The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature 2025.