Krakatoa volcano (Sunda Strait, Indonesia): scientists had explained and warned about the tsunami risk 6 years earlier - prediction came true

Tue, 25 Dec 2018, 11:58
11:58 AM | BY: T
Exaggerated  cross section and bathymetry of the Krakatau caldera, showing the flank collapse modeled in 2012 (image: Giachetti et al, 2012)
Exaggerated cross section and bathymetry of the Krakatau caldera, showing the flank collapse modeled in 2012 (image: Giachetti et al, 2012)
Screenshot from the video from 23 Dec 2018 showing the fresh scar of the flank collapse behind the explosion plumes in the center image left and right (image: Adam Sidiq/Kumparan / youtube)
Screenshot from the video from 23 Dec 2018 showing the fresh scar of the flank collapse behind the explosion plumes in the center image left and right (image: Adam Sidiq/Kumparan / youtube)
Comparision of the Krakatau between 2007 and 2018 Oct - before the 22 Dec landslide, the growth of Anak Krakatau to the SW was even more pronounced
Comparision of the Krakatau between 2007 and 2018 Oct - before the 22 Dec landslide, the growth of Anak Krakatau to the SW was even more pronounced
Model of the propapagion of the tsunami wave (image: Giachetti et al, 2012)
Model of the propapagion of the tsunami wave (image: Giachetti et al, 2012)
Sometimes, science has already answers for tragic events, but their voice is not heard or underestimated at the time. The Indonesia tsunami disaster two days ago is such an example: What happened on 22 Dec 2018 had actually already been described and warned about for years in amazing detail:
In January 2012, scientist around volcanologist Dr Thomas Giachetti from the University of Oregon published results of numerical modelling simulating a flank collapse and associated tsunami at Anak Krakatau island and warned about the devastating effects it would have on nearby coasts:
In their paper adequately called "Tsunami hazard related to a flank collapse of Anak Krakatau Volcano, Sunda Strait, Indonesia", they "numerically simulate a sudden southwestwards destabilization of a large part of the Anak Krakatau Volcano, and the subsequent tsunami formation and propagation."


Anak Krakatau island - the intra-caldera complex called "Child of Krakatau" - has been growing rapidly growing since it first breached the surface of the sea in 1928. Since then, in less than 100 years, it built an overlapping cone during several eruptions, the latest being the one that started May 2018 and still continues. What makes the island particularly prone to gravitational flank failure is that it has been constructed close and above a steep submarine slope, the NE margin of the caldera basin left by the massive 1883 eruption.
As a consequence of this underwater topography, combined with strong sea currents, the western slope of Anak Krakatau has developed to be much steeper than the eastern. Giachetti et al. observed that as the volcano continues to grow towards the SW (which it had done particularly well visible during the recent eruption, s. attached image comparing 2007 and 2018), "landslides along its southwestern flank cannot be excluded. Such a landslide would be directed southwestwards into the 1883 caldera and would trigger waves that would propagate into the Sunda Strait, possibly affecting the Indonesian coasts".

The modeled waive heights in various location correspond amazingly well with what had been observed. At Anyer, for example, waves of up to 1.5 meters would arrive in 38 minutes. Inside the caldera, neighboring islands such as Rakata or Sertung would be hit by waves 15-30 meters in height in less than a minute after the event.

Since the local tsunami warning systems in place was built only with earthquakes as trigger in mind, no warning could be given to the people on the beaches. In addition, the flank collapse occurred at night and the resulting large ash plume (which eventually reached about 15 km altitude), and violent steam explosions as result of sudden interaction of water with magma and hot rocks could not be seen by people. When the tsunami waves arrived they caught everyone by surprise.

It should be noted that the report was written 6 years ago. Since then, the new eruption, everything described in there had even become more true: compared to the situation described in 2012, the cone of Anak Krakatau had significantly been enlarged to the SW and grown in height by estimated 30%.

Change in activity style
The eruption style changed drastically right after the landslide occurred, as it exposed the conduit and the rising magma to the water. As it no longer erupted from the now-gone summit crater, but at or below sea level in the new scar left by the landscape (which can be seen in the video below), violent steam explosions were the result. As seawater interacted with hot exposed rocks and the magma continuing to rise in the conduit, these so-called phreatomagmatic explosions ejected dense jets of steam, debris and ash, and produced a very large plume. Small surges of overheated steam can be seen traveling over the water as well, in the video by Adam Sidiq/Kumparan published on youtube:


As of now, it appears that the activity at the volcano itself has calmed down again, following the pattern since June of phases of increased magma supply occurring rhythmically about once every 4 weeks, followed by quieter phases.

Previous news

Mon, 24 Dec 2018, 15:46
A version with the start of the explosion filmed in Oct slowed down 10x where you can see how it breaks through the cone itself: ... Read all
Mon, 24 Dec 2018, 14:58
The triggering cause of Saturday's tsunami is still being discussed. A common and likely interpretation is a landslide, which could have been caused by either, or a combination of: ... Read all
Show more
Try our free app!
Volcanoes & Earthquakes - new app for Android
Android | iOS version

More on VolcanoDiscovery

Why is there advertising on this site?
Support us - Help us upgrade our services!
We truly love working to bring you the latest volcano and earthquake data from around the world. Maintaining our website and our free apps does require, however, considerable time and resources.
We need financing to increase hard- and software capacity as well as support our editor team. We're aiming to achieve uninterrupted service wherever an earthquake or volcano eruption unfolds, and your donations can make it happen! Every donation will be highly appreciated. If you find the information useful and would like to support our team in integrating further features, write great content, and in upgrading our soft- and hardware, please make a donation (PayPal or Online credit card payment).

Planned features:
  • Improved multilanguage support
  • Tsunami alerts
  • Faster responsiveness
Thanks to your past donations, these features have been added recently:
  • Earthquake archive from 1900 onwards
  • Detailed quake stats
  • Additional seismic data sources
Download and Upgrade the Volcanoes & Earthquakes app to get one of the fastest seismic and volcano alerts online:
Android | IOS
Thank you!
Copyrights: VolcanoDiscovery and other sources as noted.
Use of material: Most texts and images, in particular photographs, on this website are protected by copyright. Further reproduction and use of without authorization is usually not consented. If you are not sure or need licensing rights for photographs, for example for publications and commercial use, please contact us.
Home | Travel | Destinations | Volcanoes | Photos | Earthquakes | About | Glossary | News | Contact | Privacy | Imprint | EN | DE | EL | ES | FR | IT | RU
Follow us:Follow us on facebookFollow us on InstagramFollow us on TwitterVisit our Youtube channel