allison chinchar weather explainer tsunami
How the tsunami occurred without warning
02:13 - Source: CNN
CNN  — 

The disaster hit without warning.

Many of the hundreds of people who died when a tsunami struck the Indonesian coast Saturday night were nowhere near shelter. Quite simply, they had no idea it was coming.

That’s because despite a history of tsunamis caused by volcanoes and earthquakes, Indonesia has not had an effective early warning system for years.

Saturday’s disaster isn’t the first time Indonesia’s disaster readiness has been criticized this year. In September, more than 2,000 people were killed after a tsunami and earthquake struck western Sulawesi, with many complaining they were caught unawares. Also, over July and August, a series of earthquakes hit the northern Lombok region, sparking landslides and collapsing buildings that left over 400 people dead.

On Monday, Indonesian President Joko Widodo ordered the country’s Meteorology, Climatology and Geological Agency (BMKG) to purchase tsunami detectors “that can provide early warnings to community.”

Widodo claimed the tsunami which struck over the weekend was beyond Indonesia’s currently ability to predict.

“Usually it was preceded by earthquake. That’s why the residents and visitors in Carita and Labuan beaches and Tanjung Lesung and Sumur beaches were not prepared to escape,” he said.

BMKG chief Dwikorita Karnawati said the agency would look to install tidal gates to detect waves near land, admitting the existing system was unable to warn of the tsunami ahead of time.

“This (tsunami) is caused by several factors. Our censors did not sound early warning because they are for tectonic activity not volcanic activity. That’s why we are in coordination with other agencies such as the maritime and geology agencies,” Dwikorita said.

Ring of Fire

Saturday’s tsunami was caused when molten rock pouring out of the Anak Krakatau volcano prompted a series of underwater landslides, pushing water up and causing a wave which grew as high as three meters (10 feet).

Anak Krakatau sits on the Ring of Fire, an area of high tectonic activity which spans much of the Pacific.

Volcanoes along the “ring” are formed when one plate is shoved under another into the mantle – a solid body of rock between the Earth’s crust and the molten iron core – through a process called subduction. Large earthquakes which can trigger tsunamis also occur in subduction zones.

Indonesia, the world’s largest island nation, was formed in part by the Ring of Fire’s volcanoes. It has more than 1,115 in total, more than 125 of which are still active, according to the Smithsonian’s Global Volcanism Program.

Most tsunami detection systems feature a pressure recorder anchored to the ocean floor and a buoy on the surface. When a tsunami passes over the recorder, the instruments detect and record changes in water pressure. That data is then transmitted to the surface buoys, which relay the message to the wider tsunami detection system.

“In most cases, the first sign of a potential tsunami is an earthquake,” according to the National Oceanic and Atmospheric Administration (NOAA).

The group concedes that it is far more difficult to forecast non-seismic tsunamis, such as those caused by landslides, “which can arrive with little to no warning.”

Current system inadequate

Writing on Twitter after Saturday’s disaster, Sutopo Purwo Nugroho, a spokesman for Indonesia’s National Board for Disaster Management, called on the government to build a new system which could monitor for non-seismic tsunamis.

“Indonesia does not yet have a tsunami early warning system for those caused by underwater landslides and volcanic eruptions. The current early warning system is for earthquake activity,” he said.

“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.”

Sutopo also noted that the existing buoy network “has not been operational since 2012.”

“Vandalism, a limited budget, and technical damage mean there were no tsunami buoys at this time,” he added. “They need to be rebuilt to strengthen the Indonesian tsunami early warning system.”

After the deadly Sulawesi tsunami in September, allegations were made that the detection system did not function correctly, with many pointing to the fact that a tsunami warning was lifted 36 minutes after it was first raised. A spokesman for the disaster agency said the warning was canceled after the waves made land.

Unconfirmed reports also claimed that sirens did not sound in some areas because they were left without power due to the initial earthquake and did not have a secondary source of energy.

After the devastating 2004 tsunami, multiple countries – including the UK, Germany and Malaysia – donated detection buoys and other equipment to Indonesia to help warn of future disasters.

Since then, calls have been made to upgrade and replace that system. They were made in 2012, when the final buoys stopped working. The same calls were made in the wake of September’s tsunami, and are being made again now.

Until they are finally answered, Indonesians are left nervously watching the seas.

CNN’s Azieza Uhnavy, Jamaluddin Masrur, Dakin Andone, Hilary Clarke and Yosef Riadi contributed reporting.