Complex hazard cascade culminating in the Anak Krakatau sector collapse

TLDR

Flank instability and sector collapses, major threats on volcanic islands, were exemplified by the 22 Dec 2018 collapse at Anak Krakatau that triggered a deadly tsunami. The study aims to identify precursor processes of Anak Krakatau’s collapse by analyzing multiparametric ground‑based and space‑borne data, revealing elevated activity and seaward flank motion, and to discuss their implications for early detection of flank instability at other volcanoes. The authors employed multiparametric ground‑based and space‑borne observations to detect precursory thermal anomalies, island surface area growth, and seaward motion of the southwestern flank on a dipping décollement. Seismic signals recorded two minutes after a small earthquake marked the 13:55 UTC collapse of Anak Krakatau’s flank, decapitating the cone and triggering a tsunami that killed 430 people, illustrating a complex hazard cascade with implications for early detection of flank instability.

Abstract

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.