The deadly tsunami in Indonesia was triggered by a chunk of the Anak Krakatau volcano slipping into the ocean, officials have confirmed, amid calls for a new early warning system that can detect volcanic eruptions.
At least 373 people were killed and many buildings were heavily damaged when the tsunami struck, almost without warning, along the rim of the Sunda Strait between Java and Sumatra islands late on Saturday.
Anak Krakatau had been spewing ash and lava for months before a 64-hectare (158-acre) section of its south-west side collapsed, an Indonesian official said. “This caused an underwater landslide and eventually caused the tsunami,” said Dwikorita Karnawati, the head of the meteorological agency.
Images captured by the European Space Agency’s Sentinel-1 satellite showed a large portion of the southern flank of the volcano had slid off into the ocean, scientists said.
The fact that the tsunami was triggered by a volcano rather than an earthquake meant no tsunami warning was triggered, scientists said. Coastal residents reported not seeing or feeling any warning signs before waves of up to three metres high surged in.
Hundreds of military personnel and volunteers spent Monday scouring beaches strewn with debris in search of survivors. At least 1,459 people were injured and more than 600 homes, 60 shops and 420 vessels damaged when the tsunami struck.
Sutopo Purwo Nugroho, the chief spokesman for the Indonesian disaster agency, said the country had no early warning system for landslides or volcanic eruptions. “The current early warning system is for earthquake activity,” he wrote on Twitter.
“Indonesia must build an early warning system for tsunamis that are generated by underwater landslides and volcanic eruptions … Landslides triggered the 1992 Maumere tsunami and the Palu 2018 tsunami.”
He also said Indonesia’s tsunami buoy network had not been operational since 2012. “Vandalism, a limited budget and technical damage mean there were no tsunami buoys at this time,” Sutopo said. “They need to be rebuilt to strengthen the Indonesian tsunami early warning system.
“Anak Krakatau has been erupting since June 2018 until now. Yesterday’s eruption was not the biggest. The October-November 2018 period had a larger eruption.”
The death toll is expected to rise as 128 people were still missing on Monday. At least 1,600 people have also been displaced. Dody Ruswandi, a senior official at the disaster agency, added that the rescue effort was likely to last a week.
Sutopo warned locals to stay away from the coast. “People should not carry out activities on the beach and stay away from the coast for a while,” he told reporters.
The University of Queensland volcanologist Teresa Ubide said Anak Krakatau had been erupting for the past few months, which was not unusual. “It seems like the volcano is active at the moment and it may happen again,” Ubide said.
“The volcano is very close to the shoreline so … there wouldn’t be much time to warn because it’s close and the tsunamis can travel very fast.” The lack of seismic activity that would accompany an earthquake was also significant, she added.
Richard Teeuw of the University of Portsmouth said sonar surveys were needed to map the seafloor around the volcano, but that work usually took months. “The likelihood of further tsunamis in the Sunda Strait will remain high while Anak Krakatau volcano is going through its current active phase, because that might trigger further submarine landslides,” he said.
Kathy Mueller from the International Federation of Red Cross and Red Crescent Societies said aid workers were helping evacuate injured people, bring in clean water and tarpaulins, and provide shelter.
She said the group was preparing for the possibility of diseases breaking out in the tsunami zone, adding: “The situation, and the death toll, will remain fluid over the next days and even weeks.”
The water washed away an outdoor stage where a local rock band, Seventeen, were performing, killing their bassist and manager. Other people who had been watching the band on the beach were missing.
Azki Kurniawan, 16, said his first warning about the tsunami was when people burst into the lobby of the Patra Comfort hotel shouting: “Sea water rising.”
Kurniawan, who was undergoing vocational training with a group of 30 other students, said he was confused because he had not felt a big earthquake. He said he ran to the car park to try to reach his motorbike but discovered it was already flooded.
“Suddenly, a one-metre wave hit me,” he said, his eyes red and swollen from crying. “I was thrown into the fence of a building about 30 metres from the beach and held on to the fence as strong as I could, trying to resist the water, which felt like it would drag me back into the sea. I cried in fear … ‘This is a tsunami?’ I was afraid I would die.”