Fig. 3: Satellite images showing the resultant landslide following the eruption shown in the photographs.

Comparison of Sentinel-1 SAR image of Anak Krakatau post-collapse on December 22nd, 2018 at 22.33 local time (A), with COSMO-SkyMed (CSK) SAR image of Anak Krakatau post-collapse on December 23rd, 2018 at 10.28 local time (B). Aerial photographs show Anak Krakatau erupting post collapse on morning of December 23rd, 2018. These photographs are used to validate the interpretations of the slide scar in the Sentinel-1 and CSK SAR images, and are used with permission of the photographers. C is credited to Didik Heriyanto taken at 17:01 on December 23rd, 2018; D–F are credited to Nurul Nidayat taken between 08:08 and 08:12 on December 23rd, 2018. Numbered markers are discrete tie points present in Fig. 2A–F. Yellow dashed line in Fig. 2A, B is the interpreted tip-line (cliff top) of the failure plane. Yellow dotted line in Fig. 2A, B is the interpreted cliff base (new coastline) where the failure plane projects underwater. Yellow dot-dashed line in Fig. 2A, B denotes the outline of the vertical plume emitted from the submarine vent following flank collapse. Orange arrows in Fig. 2A, B indicate the line of sight of the satellites. Publicly available Sentinel-1 SAR data is downloaded from the Copernicus Sentinel Hub portal. CSK SAR image is courtesy of the Committee on Earth Observation Satellite’s Earth Observation (CEOS)’s Volcano Demonstrator.