The characteristic of January-February 2023 Eruption of Marapi Volcano

After a long paused of eruption, Marapi Volcano in West Sumatra, Indonesia, started to erupt on 7 January 2023.  The eruption lasted for a couple of months.  It is followed by several months of quite period, the new, more violent eruption episodes occurred starting Dec 3, 2023 which are ongoing.  The study focus on episodes of January-February 2023 eruption to understand the volcano process, eruption behaviour compared to the past eruption and whether, in the hindsight there are precursors to the eruption that followed.  Compared to last recent episodes of eruptions, The January-February 2023 Marapi eruption consist of many explosions and degassing events. The time interval between explosions of Marapi in the beginning of eruptions, almost every hour there was an explosion, after a week time, the time interval became longer until no explosion occurred a month the first explosion.  We will also explore the mechanism of explosions from the infrasound data because the infrasound waveforms are simpler than those of the seismic waveforms. We observed the waveforms and the amplitude of infrasound in the beginning of eruption was simpler and very large at the station 300m from the active vent (> 50 Pa peak-to-peak) then the later explosions the amplitudes became smaller, and the waveforms became more oscillating coda.  This suggest the source, in the beginning it is filled with gas and fragmented magma and later the source is partially filled.  The explosions were also recorded by 4 other infrasound stations installed around the volcano up to the distance of 10 km from the vent.  Based on the observation seismicity several months prior to the first explosion of January-February 2023 Marapi eruption, there were distal volcano tectonic earthquakes clustered 4-5km the NW of the active crater.  The seismicity migrates to shallower depth below the active crater. This is supported by the observation of the tilt data from summit station and flank station, the tilt showed migration of pressure source for several months before the eruptions and that the magma pathway may probably located near the active fault zone.