Indonesia's deadly tsunami predicted by experts in 2012

An aerial view shows the Anak Krakatau volcano erupting in Lampung, Indonesia, on Dec 23, 2018. PHOTO: EPA-EFE

JAKARTA - A study carried out six years ago by the Geological Society of London which accurately predicted a possible major hazard emerging from Anak Krakatau volcano could have been used as a basis to prevent Indonesia's latest natural disaster which has killed more than 400 people.

The 2012 study said a tsunami could be triggered by a collapse of Anak Krakatau's flank as the volcano is partly built on a steep wall of the caldera resulting from the 1883 eruptions.

Using a numerical model, it simulates both Anak Krakatau landslides and the tsunami propagations, detailing the tsunami's possible travel time and wave amplitude when hitting various coastal areas including Sumur, Carita, Labuan and Anyer in Banten province - in the western tip of Indonesia's most populous island, Java - and parts of Lampung province, in the southern tip of the country's second most populous island, Sumatra.

On Dec 22, the calamity happened, with the highlighted areas mentioned in the study being those with the highest level of devastation.

A section of the volcano's slope collapsed after the Dec 22 eruption and slid into the ocean, which displaced massive amounts of water, generating waves up to 5m high that then inundated the nearby coastlines of Java and Sumatra.

At least 426 people have been killed, over 7,000 others injured and another 23 are still unaccounted for.

Sumur district, which consists of seven coastal villages, became the worst hit and rescuers are still searching for victims' bodies under the rubble of houses and fallen trees, and more excavators are needed.

The 2012 study - jointly prepared by T. Giachetti, R. Paris, K. Kelfoun, and B. Ontowirjo of the Geological Society of London - was called "Tsunami hazard related to a flank collapse of Anak Krakatau volcano, Sunda Strait, Indonesia".

It underlined that the volcano is largely built on the steep north-eastern wall of the 1883 Krakatau eruption caldera and is growing towards the south-west, which makes the structure quite unstable, thus landslides, involving a debris avalanche volume of more than 200 million cubic m, can be unavoidable.

The volcanic island, the name of which means "Child of Krakatau", emerged around 1927 after its "parent" Krakatau erupted 44 years previously, killing more than 36,000 people.

The study report also elaborates that a hypothetical flank collapse directed southwestwards could trigger giant waves that would then spread across the Sunda Strait at an average speed of 80kmh-100kmh.

"The tsunami would reach the areas on the western coast of Java, 35-45 minutes after the onset of collapse...These waves present a non-negligible risk," the report warns.

It also makes a bold recommendation:"A rapid detection of the collapse by the volcano observatory, together with an efficient alert system on the coast, would possibly prevent this hypothetical event from being deadly."

The tsunami struck at night without warning. Indonesian authorities said the country's early warning system can only be activated if a tsunami is preceded by earthquake.

The London geological society report presents a table detailing, among other things, that Carita could be hit by waves as high as 2.9m, Labuan 3.4m, and Sumur 1.2m. The tsunami travel time to these places, respectively, could be within 37 minutes, 40 minutes and 36 minutes. This was calculated partly based on the distance and water depth in various parts of Sunda Strait - the shallower the faster the speed.

When asked by The Straits Times on Friday (Dec 29) about this Sunda Strait tsunami hazard, Indonesia's national geological agency's secretary Antonius Ratdomopurbo said that the agency would be overwhelmed if it were to keep track of all the studies that have been made.

"There are a lot of them," Mr Antonius said. "One thousand pieces of research, and one of them is correct. How could we go about this?"

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