Most of Earth’s volcanic eruptions occur underwater, and these submarine eruptions can significantly impact large-scale earth systems. In this study, we develop a new semi-automated analysis framework to detect submarine eruptions through the supervised classification of satellite images on Google Earth Engine (GEE). We present a case study from the Rabaul caldera region in Papua New Guinea and find a large number of new unreported pumice rafts (in ~16% of images from 2017–present). After analysis of the spatial pattern of raft sightings and ancillary observations, we interpret that these rafts are not the result of a new eruption. Instead, we posit that the observed rafts represent remobilization of pumice clasts from previous historical eruptions. This novel process of raft remobilization may be common at near-shore/partially submarine caldera systems (e.g., Rabaul, Krakatau) and has significant implications for new submarine eruption detection, volcanic stratigraphy, and biological dispersal by rafts.