19 October 2018
Landslide tsunamis from the Sulawesi earthquake
Posted by Dave Petley
Landslide tsunamis from the Sulawesi earthquake
Our understanding of the Sulawesi earthquake continues to improve as more information becomes available. This has shown Twitter at its very best, with a range of people bringing different expertise, and techniques to bear on the problem of what has proven to be a very complex event. I would like to recommend in particular Austin Elliott, John O’Leary, Xiaohua Xu, Eric Fielding and (most impressive of all) Sotiris Valkaniotis, all of whom have been very proactive in interpreting and synthesising the data, and making the information available online.
New videos continue to appear on Youtube. One is particularly interesting, taken from a boat located just offshore when the tsunami struck:-
.
There is so much in this video that it is hard to know where to start. The video opens with a view roughly southwards (corrected from earlier version) up the bay, showing an enormous landslide generated displacement wave from the western side of the bay:-
A landslide tsunami from the Sulawesi earthquake. Still from a video on Youtube.
.
The view then switches to the east side, where another landslide tsunami has been generated:-
A second landslide tsunami generated by the Sulawesi earthquake. Still from a video on Youtube.
.
Incidentally, as the camera pans from one to the other, a third wave, generated from the eastern side of the bay, can also be seen. Meanwhile, in the background the multiple dust plumes generated by landslides in the hills can be seen:-
Multiple dust clouds generated by landslides triggered by the Sulawesi earthquake. Still from a video on Youtube.
.
On Twitter, Austin Elliott managed to tie down the location of the boat to -0.8303, 119.8133, and John O’Leary confirmed that there was a landslide at that point.
This video aligns nicely with the remarkable video taken by a pilot of an aircraft that had just left Palu airport when the earthquake struck. This video also shows the generation of landslide tsunamis by the Sulawesi earthquake:-
A landslide generated by the Sulawesi earthquake. Still from a video tweeted by Gerry Soejatman.
.
We have never had such a detailed and nuanced view of the way that coastal landslides generate local tsunamis during an earthquake.
Dave Petley is the Vice-Chancellor of the University of Hull in the United Kingdom. His blog provides commentary and analysis of landslide events occurring worldwide, including the landslides themselves, latest research, and conferences and meetings.
At 1:06 you can see more shoreline collapsing.
Waves on both sides of the bay do not necessarily imply two landslides. The tsunami from a single landslide will break on both sides but be subdued in the middle where the water is deeper.
I find it interesting that the waves start to be generated at the same time that the landslides commence and then dust starts to rise. Does this indicate that maybe the tsunami was actually just a localised event cause by coastal land shifts in the bay itself?
Also this doesn’t seem to align with what I hear, here on the ground. I spoke to families in Petobo etc. who describe the earthquake hitting and then they evacuated their houses. to safe areas. One then described their husband running back into then house to rescue their daughter a few minutes after the earthquake had ended, and then suddenly the landslide event occurred and he and the house were gone.
This video confuses e regarding timing of events
Interesting plume or cloud at the 1:30 mark in the background.
Regarding the shoreline collapsing at 1:06 – I wondered that too, but I think it is just the edge of a carbonate wave-cut platform. I don’t see the edge changing.
FWIW, the ‘authoritative’ write up in ‘Scientific American’…
https://www.scientificamerican.com/article/indonesian-tsunami-was-powered-by-a-deadly-combo-of-tectonics-and-geography1/
… doesn’t seem convinced by land-slide induced tsunami claims.
Disclaimer: IMHO, SA stopped being a serious publication when their new owners dropped the ‘Amateur Scientist’ and ‘Math Puzzles & Diversions’ departments…
( My very first SA, which I think I still have, was the ‘Cities’ special, with its wondrous feature on Piet Hein ‘Super Ellipses’ aka ‘squarcicles’… )