Morphological Changes of Anak Krakatau after the 22 December 2018 Flank Collapsed

Abstract

\n After the 22 December 2018 flank collapse, series of hydrothermal, phreatomagmatic, and effusive eruptions occurred and changed the morphology of Anak Krakatau. The ejected volcanic materials enlarge and increase the elevation of the west flank, which may indicate a reconstruction phase of the Anak Krakatau edifice. Here, we investigated the morphological changes of Anak Krakatau between 2019 and 2020 by using drone SfM photogrammetry, Sentinel and Pleiades satellite imageries, and fieldworks photograph data. The 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 February and January 2020. The large phreatomagmatic and effusive eruptions on 10 April 2020 produced tephra and lava flow deposits that significantly changed the morphology of Anak Krakatau. The deposit of tephra covered 0.815 km2 at the north – northwest flanks of Anak Krakatau, while the lava flow 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 a blocky surface and highly fractured that possibly formed due to compression – extension stresses during lava flow emplacement. The emplacement of the massive lava flow at the pre-existing crater lake may change the future eruption style at Anak Krakatau, which was previously dominated by hydrovolcanism activities, such as hydrothermal and phreatomagmatic events.