EGU General Assembly 2020
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

Precursors and processes culminating in the Anak Krakatau December 2018 sector collapse and tsunami

Thomas R. Walter1 and the Rapid Response Team*
Thomas R. Walter and the Rapid Response Team
  • 1GFZ Potsdam, Geophysics, Potsdam, Germany (
  • *A full list of authors appears at the end of the abstract

It is 135 years after the 1883 volcano-triggered tsunami disaster, when Krakatau volcano became once more the source of a deadly tsunami striking without warning. We use data recorded on the ground and by satellite, to show that the volcano was in an elevated stage of activity throughout the year 2018, producing thermal anomalies associated with volcanic deposits, an increase of the island area and ground movement of the southwestern sector of the island towards the sea, increasing in June 2018. Following further intense activity on 22 December 2018, seismic data reveal the timing and duration when this sector collapsed. The landslide removed 102 million m³ of material subaerially, which was followed by ~15 minutes of phreatic explosions. This study allows better understanding of the complex hazard cascades, including precursory thermal anomalies, island growth and deformation, followed by sector collapse, tsunami waves, and finally explosive volcanic eruptions, and has important implications for designing early warning systems.

Rapid Response Team:

Thomas R. Walter (1), Mahmud Haghshenas Haghighi (1,2), Felix M. Schneider (1), Diego Coppola (3), Mahdi Motagh (1,2), Joachim Saul, Andrey Babeyko, Torsten Dahm; Valentin R. Troll; Frederik Tilmann, Sebastian Heimann; Sébastien Valade; Rahmat Triyono; Rokhis Khomarudin; Nugraha Kartadinata; Marco Laiolo; Francesco Massimetti; Peter Gaebler

How to cite: Walter, T. R. and the Rapid Response Team: Precursors and processes culminating in the Anak Krakatau December 2018 sector collapse and tsunami , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2602,, 2020

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Presentation version 1 – uploaded on 01 May 2020
  • CC1: Questions and answers from the live chat during EGU2020, Michael Heap, 11 May 2020

    Q: The flank sliding had remained unnoticed before the event, right? Any thoughts on how to improve the detection of such precursors?

    A: Def was unnoticed bcause noone looked at it. New observations suggest it was going on for a decade

    Q: Hi Thomas; interesting work. Similar question. Could you clarify the meaning of the rows (a) b) and c) in slide 4 ? Indeed, I’m wondering if there is some information about the evolution of the deformation rate before the collapse. In slide 4 it seems to me that the 3 rows show images of differnt time; is that the case? there is an evolution?

    A: These rows are different sar viewing geometries

    Q: Has Krakatau now entered another re-building stage?

    A: It seems reload the collapsed flank again

    Q: Important study of this devastating event. You talk about precursors, do you mean the 6 months of increased thermal flux and flank moment? Were there any short-term precursors (other than the 2 min EQ) that could have been used as warning?

    A: Precursors are: temp increase, def change associated with this, and the little eq

    Q: Presentation mentions using MODIS to track thermal precursors: could this also be used to determine collapse volumes?

    A: Modis isnt a good tool for volume estimations.

    Q: Does flank reloading means repeat of collapse is expected soon? Any estimates of time build up to next collapse event? Any continuous monitoring planned?

    A: Not sure. we continue the insar study, and as written in the paper: the collapse affected only half of the mobile flank (subaerially!)