Morphological changes of Anak Krakatau after the 22 December 2018 flank collapsed

Series of hydrothermal events and a large phreatomagmatic which shortly followed by an effusive eruption has changed the morphology of Anak Krakatau between 2019 and 2020. The large phreatomagmatic and effusive events that occurred on April, 10th 2020, produced tephra and lava flow deposit that enlarged the west flank area. Here, we investigated the morphological changes of Anak Krakatau between August 2019 and May 2020 using UAV SfM photogrammetry, Sentinel and Pleiades satellite imageries, and fieldworks photographs data. Our UAV orthomosaic image captured the morphology of Anak Krakatau in August 2019, while temporal Sentinel 2 and High-resolution Pleiades satellite images observed the morphology of Anak Krakatau between September 2019 and May 2020. We manually digitized the edifice of Anak Krakatau from UAV, sentinel 2, and Pleiades images to investigate morphological changes of Anak Krakatau. The high-resolution Pleiades satellite image was processed using supervised classification to automatically delineate the deposit of lava flow, altered rocks and tephra. Result shows volcaniclastic deposit due to the hydrothermal and/or phreatomagmatic eruptions that covered 0.08 km2 around an active crater lake at Anak Krakatau between January and February 2020. The large phreatomagmatic and effusive eruptions produced tephra that covered 0.815 km2 at the north–north west flanks of Anak Krakatau and lava flow that emplaced 0.2 km2 and elongated around 742 m from the pre-existing crater lake to the west shoreline of Anak Krakatau. The lava flow has blocky surface and highly fractured that possibly formed due to compression—extension stresses during lava flow emplacement and has widened the Anak Krakatau volcanic island from 2.99 km2 to 3.027 km2. We infer that Anak Krakatau is currently on reconstruction phase after the destructive flank collapse on December 22th, 2018. © The Author(s) 2025.