Bathymetry and Shallow Seismic Imaging of the 2018 Flank Collapse of Anak Krakatau

Abstract

The flank failure and collapse of Anak Krakatau on December 22nd, 2018 triggered a destructive tsunami. Whether the prior activity of the volcano led to this collapse, or it was triggered by another means, remains a challenge to understand. This study seeks to investigate the recent volcano submarine mass-landslide deposit and emplacement processes, including the seafloor morphology of the flank collapse and the landslide deposit extent. Bathymetry and sparker seismic data were used during this study. Bathymetry data collected in August, 2019 shows the run-out area and the seafloor landslide deposit morphology. Bathymetry data acquired in May, 2017, is used as the base limit of the collapse to estimate the volume of the flank collapse. Comparisons between seismic data acquired in 2017 and 2019 provide an insight into the landslide emplacement processes, the deposit sequence, and structure below the seafloor. From these results we highlight two areas of the submarine-mass landslide deposit, one proximal to Anak Krakatau island (∼1.6 km) and one distal (∼1.4 km). The resulting analysis suggests that the submarine-mass landslide deposit might be produced by a frontally compressional, faulted, landslide, triggered by the critical stability slope, and due to the recent volcanic activity. Blocky seabed features clearly lie to the southwest of Anak Krakatau, and may represent the collapse blocks of the landslide. The seismic analysis of the data acquired in August, 2019 reveals that the blocky facies extends to ∼1.62 km in the width around Anak Krakatau, and the block thicknesses vary up to 70.4 m. The marine data provides a new insight into the landslide run out and extent, together with the landslide deposit morphology and structure that are not available from satellite imagery or subaerial surveys. We conclude that the landslide run out area southwest of the recent collapse, is ∼7.02 ± 0.21 km2.

The Hidden Giant: How a rift pulse triggered a cascade of sector collapses and voluminous secondary mass‐transport events in the early evolution of Santorini

“…the hazardous Krakatau volcanic system at the Sunda strait or the volcano‐tectonic Kagoshima graben at the northern end of the Ryukyu Arc in the East China Sea (Harjono et al, 1991; Kamata & Kodama, 1999). Both are volcanic back‐arc systems that lie in an extensional marine setting and comprise large volcanoes and calderas (Harjono et al, 1991; Priyanto et al, 2021; Tatsumi et al, 2018).…”

Submarine Landslides and Their Tsunami Hazard

“…The Sulawesi tsunamis were up to 10-11 m in elevation, much larger than expected from the earthquake mechanism, but observations from field studies suggested that coastal landslides could have contributed to the tsunami. At Anak Krakatau, a flank collapse generated the tsunami, with most data published on the subaerial features but little on the submarine part (Hunt et al 2021, Priyanto et al 2021.…”

“…Based on hydroacoustic MBES and seismic data acquired in August, 2019, the landslide formed mainly of large blocks of subaerially erupted lavas (Figure 13) that were emplaced on friable submarine erupted pyroclastics, which were therefore inherently unstable (Hunt et al 2021, Priyanto et al 2021. The eruption triggered the collapse.…”

Modeling of the Dec. 22nd 2018 Anak Krakatau volcano lateral collapse and tsunami based on recent field surveys: Comparison with observed tsunami impact

“…The subaerial data on the collapse has been published (e.g., Williams et al, 2019;Novellino et al, 2020;Perttu et al, 2020) and provided the basis for previous tsunami modelling (e.g., Grilli et al, 2019). The new numerical modeling presented hereafter is also based on this remote (mainly satellite) subaerial data but also, for the first time, on a hydroacoustic data set of multibeam echosounder (MBES) bathymetry and seismic data acquired to the southwest of the volcano after AK's eruption, in August 2019 (Priyanto et al, 2020;Hunt et al, 2020).…”