This one was without warning. They think it was due to a submarine landslide caused Krakatoa erupting.
It was near Java and Sumatra. Many people dead, many people missing.
Here’s a link - can’t block and embed links in the text anymore.
The Tsunami Warning System has one fatal flaw. It is supposed to warn of an impending tsunami, but it is not based upon detection of a tsunami, but detection of an earthquake.
Most tsunamis are caused by earthquakes, so that seems to make sense. But some earthquakes do not cause tsunamis (for reasons best known by seismologists):
… and some tsunamis are caused by non-earthquakes, at least in the “conventional” sense of continental plates slipping, sliding or faults adjusting – they may be caused by landslides, as the latest Indonesian one seems to have been.
So the TWS suffers from both false positives and false negatives, which doesn’t lend an air of certainty to the warning system.
This recent Indonesian event was exacerbated by geography. If the tsunami began at Anak Krakatoa as is currently believed, Bandar Lampung, one of the worst victims, could not be in a worse place. As waves head toward shore, if they are funneled into an increasingly narrow bay, they tend to rise. By the time they reach land, they are much bigger than when they started. This appears to be the case in several places around Anak Krakatoa (see map).