Abstract
Flank instability and sector collapses, which pose major threats, are common on volcanic islands. On 22 Dec 2018, a sector collapse event occurred at Anak Krakatau volcano in the Sunda Strait, triggering a deadly tsunami. Here we use multiparametric ground-based and space-borne data to show that prior to its collapse, the volcano exhibited an elevated state of activity, including precursory thermal anomalies, an increase in the island’s surface area, and a gradual seaward motion of its southwestern flank on a dipping décollement. Two minutes after a small earthquake, seismic signals characterize the collapse of the volcano’s flank at 13:55 UTC. This sector collapse decapitated the cone-shaped edifice and triggered a tsunami that caused 430 fatalities. We discuss the nature of the precursor processes underpinning the collapse that culminated in a complex hazard cascade with important implications for the early detection of potential flank instability at other volcanoes.
Highlights
Flank instability and sector collapses, which pose major threats, are common on volcanic islands
An analysis of infrared data recorded by the thermal sensors of the Moderate Resolution Imaging Spectroradiometer (MODIS)[32] indicates that a new intense eruptive phase initiated at Anak Krakatau on 30 June 2018 (Fig. 1b)
This eruptive phase was the most intense recorded since systematic data acquisition began in 2000 and was characterized by a mean volcanic radiative power (VRP) of ~146 MW, which is ~100 times the long-term thermal emission (~1.6 MW) recorded between 2000 and June 2018 (Fig. 1b)
Summary
Flank instability and sector collapses, which pose major threats, are common on volcanic islands. A common problem of such events is that they are rare[16], and volcanic islands introduce numerous recognizable threats such as instability, sector collapse and tsunamis[21,22], little is known about their precursor activity and possible strategies to mitigate the associated risks. A gradual shift in activity occurred toward the southwest, resulting in further growth of the edifice over the cliff and toward the deep submarine caldera basin[27] This was leading to recent concerns about a possible landslide from the southwestern island flank and the corresponding generation of a tsunami[22]. The cumulative erupted volume (red line) indicates a gradual decline in effusive activity after Oct 2018 a 6°5′30′′ S
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