Indonesia tsunami: Not enough data to determine if volcanic eruptions caused huge waves, says geology agency

Residents inspecting damaged buildings in Carita, after the area was hit by a tsunami, on Dec 23, 2018.
Residents inspecting damaged buildings in Carita, after the area was hit by a tsunami, on Dec 23, 2018.PHOTO: AFP

JAKARTA - Indonesia's geology agency said it has yet to collect adequate data to determine whether the eruptions of the Anak Krakatau volcano caused, or partly caused, the high waves on Saturday night (Dec 22) that crashed into houses and other buildings on the coastal areas in the western tip of Java and southern tip of Sumatra.

Indonesia's disaster management agency (BNPB) said the tsunami was caused by "an undersea landslide resulting from volcanic activity on Anak Krakatau" and was exacerbated by an abnormally high tide because of the current full moon.

Indonesian Tsunami Expert Association chairman Gegar Prasetya said that based on the meteorological data, there was no earthquake or storm on Saturday, and therefore, the tsunami was linked to the activities of Mount Anak Krakatau in the Sunda Strait.

It was likely caused by a flank collapse, triggered by the increasing geological activities of the volcano, he added.

"The eruption of Anak Krakatau potentially had made the slope unstable and then the flank collapsed," Dr Gegar told The Straits Times.

He further said that such a tsunami might have likely occurred in the past as part of the formation process of Anak Krakatau, but the incident was unmonitored and no casualties were recorded, as local people did not erect buildings close to the seashore.

Going forward, the Meteorology, Climatology and Geophysics Agency must enhance its early warning system by covering other phenomena other than tectonic earthquakes, Dr Gegar added.

But the head of Indonesia's geology agency, Mr Rudi Suhendar, said such high waves may not be related to Anak Krakatau's volcanic activity.

"From a volcanology point of view, such chances are small," Mr Rudi told The Straits Times by telephone.


"Anak Krakatau's eruption yesterday measured at amplitude 58 and an eruption of such measurement did not only happen (on Saturday)," he said, adding that Anak Krakatau has been acting up since end-June.

Anak Krakatau, or Child of Krakatoa, is originally a new island in the Sunda Strait that emerged in 1927 from the caldera, or huge hollow, formed by the Krakatoa volcano after its massive eruptions in 1883.

Anak Krakatau was initially a bump on the sea bed before it surfaced above sea level, and it has since gradually developed into what it is now, Mr Rudi explained.

"Its perfect conical shape today is owed to this gradual development," Mr Rudi also said, stressing that Saturday night's tsunami could be solely attributed to bad weather. "There are two schools of thought currently regarding Saturday night."

His agency is waiting out the bad weather in the area, which is currently also marked by pouring rain, to do further assessment to determine what caused the calamity.

"The weather is not favourable now, our team cannot get good visual," he added.

Additional reporting by Linda Yulisman