On December 22, 2018 the south-western flank of Anak Krakatau collapsed into the sea, removing 93.8×106m3of subaerial lavas, and generated a tsunami. Synchronously with the collapse, a large volcanic plume of SO2andash (14–15 km in height) has formed, marking the onset of a paroxysmal eruption lasting from December 22, 2018to January 06, 2019. From remote sensing analysis, we show that the eruption can be divided into three mainphases. Phase I and II show both tephra and gas emissions while phase III is mostly degassing. The total amount ofSO2injected in the atmosphere is 173±52 kt, while the minimum bulk magma volume emplaced, estimated from atopographic reconstruction, is∼45×106m3. This value compares well with a petrologic-based estimate of 56.4×106m3, making the existence of external sulphur sources and sinks quite unlikely. The ice-rich ash plume formationshows that a strong sea-water/magma interaction was responsible for the phreatomagmatic activity throughout theeruption. However, we distinguish a first Vulcanian blast-derived eruption (lasting 40 min) just after the collapsehaving a Mass Eruption Rate (MER) of 9×105kg s−1, followed by a sustained lower-intensity eruption resultingin ash emissions over hours (MER = 5×105kg s−1). From December 23, daytime photos show typical Surtseyan activity.