29 December 2018
First visual satellite images of Anak Krakatau show the enormous extent of the landslide
For reference, this is an image also collected by Sentinel-2, of the island before the landslide:-
I have tried to improve the Sentinel-2 image to bring out the main features:-
So, there appears to be a huge scar on the west side of the island. This is consistent with the reported deformation from the radar images, as analysed by PVMBG and reported by the BBC. They report that the landslide had a volume of 150-170 million cubic metres, which is a huge landslide. Note that most of the slide was a terrestrial (i.e. above water) slide, not the underwater event that was initially reported. A very substantial proportion of the volcanic cone is missing, including all of the higher elements. PVMBG report that the come elevation has decreased from 338 metres to about 100 metres. Around the southwest part of the island there appears to be an extensive shallow marine deposit – is this landslide material, perhaps moved by the currents, or ash fall from the volcanic eruptions? Or both of course.
It seems likely that this failure was a single large event, although it might have had several phases in short succession. The seismic data, once properly analysed should help with the interpretation of the failure sequence. A key question will be whether INSAR data could have detected precursory deformation of this flank prior to the main landslide event?