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The Southeastern nation of Indonesia, which sits on the Pacific Ring of Fire, is no stranger to earthquakes, many of which trigger tsunamis – powerful waves capable of immense destruction. However, the towering 18-foot wave that crashed into the island of Sulawesi on September 28, 2018 is one of the deadliest to hit the country in recent years.
The perfect storm of the disastrous events began after a 7.5 magnitude earthquake struck off the coast of Sulawesi at 6:02 pm local time. The powerful tremor and the numerous aftershocks resulted in landslides that destroyed or buried hundreds of homes and buildings in the city of Palu and caused power outages that crippled communications. Among the most impacted is the Balaroa neighborhood where over 1,747 homes have collapsed, with many residents buried underneath. According to experts, the widespread damage was the result of soil liquefaction. As the name indicates, the phenomenon occurs when saturated, or partially saturated, soil loses strength due to the stress created by an earthquake and starts to behave like a liquid, causing all the structures above to be reduced to rubble.
The powerful earthquake was also followed by a tsunami warning. However, based on the information available at the time, the Indonesian Agency for Meteorology, Climatology, and Geophysics (BMKG) decided there was no imminent danger and retracted it about 34 minutes later. Believing the threat had been averted, hundreds of Palu residents, from areas not affected by the earthquake, gathered at the beach for a local festival.
As it turned out, the experts had been wrong. Just about the time the tsunami warning was canceled, the residents began noticing, and recording, a series of massive waves crashing into the shoreline. Then, at 7:58 pm local time, the monstrous 18-foot arose sweeping away everything in its path. Though the tsunami impacted many areas along the stretch of the shore, including the city of Donggala, it was Palu that bore the brunt of its wrath. As of October 4, 2018, the earthquake and the ensuing tsunami are believed to be responsible for the deaths of over 1400 residents, including 86 children who were attending bible camp in a remote region when the disaster struck.
Though nothing could have been done about the tragedy in Balaroa, many people believe that hundreds of deaths could have been prevented if the tsunami warning had not been lifted. BMKG officials say they followed standard protocol based on the data received from the closest tidal sensor, which lies about 200 km from Palu. "We have no observation data at Palu. So we had to use the data we had and make a call based on that," said Mr. Rahmat Triyono, head of the earthquakes and tsunami center at BMKG. "If we had a tide gauge or proper data in Palu, of course, it would have been better. This is something we must evaluate for the future." The agency also argues that the massive waves witnessed on the Palu coastline should have served as a warning for residents to move to higher grounds.
Given that the 7.5 magnitude earthquake was the result of a strike-slip fault - two blocks of crust rubbing against each other in a horizontal direction – the tsunami also caught other experts by surprise. That’s because the destructive phenomenon is usually the result of a vertical movement in the crust, which disrupts the ocean water and causes massive waves to land onshore. ”It is definitely a surprise,” says Baptiste Gombert, a geophysicist at the University of Oxford.
Gombart believes the culprit behind the tsunami’s strength may be the earthquake-caused landslides that disturbed the bay waters, causing them to rise. Janine Krippner, a volcanologist at Concord University, thinks the shape of the narrow Palu Bay may have also played a part in magnifying the already large waves as they entered the smaller area. Both experts caution that these are just hypotheses and the real answer will only be revealed once a complete investigation has been conducted.
Regardless of the reason the tsunami occurred, the survivors in Palu are now dealing with the aftermath. Thousands of homes have been leveled, power lines downed, and streets washed away. All local shops have either been destroyed or looted, leaving residents struggling to get necessities like food and water. The roads to the city of about 350,000 people remain partially closed. While many countries, including Australia and the United States, have sent funds to help those in need, few supplies are being delivered to the affected areas. Our thoughts are with Indonesians and we hope the country is able to recover soon
Resources: Nationalgeographic.com, Vox.com, CNN.com, Forbes.com