Indonesia never saw tsunami coming
Damaged buoys in Java Sea failed to alert scientists a seven-metre high wave was about to hit
PALU, Indonesia — The sun was starting to dip, turning the sky a brilliant orange hue. Then the ground shook.
In Palu, they thought they knew all the risks. Indonesians live along one of the world’s most active fault lines — and Palu, in particular, sits atop a gradually slipping plate.
But a tsunami surge through the narrow bay and mud flows burying villages and residents were never among their fears until last week.
Indonesia has spent millions on disaster preparedness since a massive earthquake and tsunami in December 2004.
But this time, everything that was meant to work did not.
A warning system based on computer simulations failed to gauge the chances of a huge tsunami, estimating waves far smaller. Tsunami detection buoys were not functioning or in the wrong location.
Even the sensors that did work fooled scientists to think the worst was over — even while a third deadly tsunami surge was bearing down on Palu.
Now, the devastation on the western coast of Sulawesi island will now add a new chapter to the understandings of how shifts on the ocean floor can spawn deadly walls of water, and can turn firm soil into muddy rivers that entombed hundreds of people.
Scientists say the back-to-back disasters — which have killed nearly 1,600 people and counting — were among the most complicated they had seen. It began Sept. 28 just after 6 p.m. with a magnitude 7.5 slipstrike quake, where the earth moves side by side.
Normally, quakes that thrust up the seabed prompt a tsunami watch — like the giant dome of sea water that crashed across Asia’s Indian Ocean region in 2004, killing almost 230,000 people, including tens of thousands in Indonesia.
The Sept. 28 quake, located about 48 miles from Palu, wasn’t something that experts think would prompt a powerful tsunami.
“It wasn’t a straightforward event,” said Adam Switzer, principal investigator at the Singapore-based Earth Observatory. “This earthquake was beyond the bounds of the warning systems” available.
The immediate analysis also was compromised by problems with Indonesia’s network of tsunami-detection buoys, which detect changes in the sea even deep below the surface. These work far more accurately than tidal sensors, confirming the height of a wave before it appears.
Dozens of buoys in the Java Sea were broken, damaged or stolen. Others that functioned weren’t at the right spot and estimated the tsunami risk inaccurately — predicting the waves would likely be two feet high, nine feet in an absolute worst case scenario.
Instead, the tsunami sent water as high as seven metres in some places.
With the buoys, “a satellite will immediately receive information that the tsunami has been detected, and we will know which areas would be hit and the height of the waves,” said Sutopo Purwo Nugroho, spokesman for Indonesia’s disaster management agency.
“But,” he added, “the buoys have not operated” fully since 2012.
Soon after 6 p.m., water in Palu’s clear bay started receding, forming rings in the ocean. Miranti Malewa, 35, was driving by the coast to evening prayers. But when she stepped on the pedal to accelerate, her car didn’t seem to move forward.
Across the road, she saw floors of the Mercure Hotel collapse.
“There was a little voice in my head that said, ‘Maybe it’s a tsunami,’” she said.
At 6:10 p.m., the first tsunami surge hit. The next one came in two and a half minutes, even bigger this time. The final wave rose high above the beachfront, crashing down onto houses and kiosks and dragging hundreds of lives along with it.
Cascading secondary effects were devastating areas further inland, turning solid ground into unstable liquid mud. Houses and electricity poles appeared to be chasing people as they were carried by the slurry of soil, witnesses said. Entire neighbourhoods were obliterated.
It was over. But, for Indonesian officials, the problems were just beginning.
Logistical difficulties slowed the initial emergency response. Overwhelmed local officials all but disappeared, raising questions about how Indonesia is prepared for the next inevitable quake-triggered disaster.
Indonesia’s budget for disaster monitoring has fallen in recent years to $46 million from $131 million. The disaster director at Indonesia’s geophysics agency, Rahmat Triyono, said the cuts have left his a “very limited” tsunami-detection system, relying on simulations rather than the more accurate buoys.