The tsunami is thought to have been triggered by the eruption of the neighbouring Anak Krakatoa volcanic island.

Medan, North Sumatra, Indonesia – Hundreds of people have been killed and many more injured following a powerful tsunami that hit the Sunda Strait in Indonesia on Saturday evening, sending waves crashing into the islands of Sumatra and Java with no warning.

Samsul Hidayat is a local guide who has been taking tourists to watch the eruptions of neighbouring active volcano Anak Krakatoa since 1993.

“I was so surprised when the tsunami hit. There was no earthquake and the weather was good. There was no rain or wind and we could see the full moon,” said Hidayat, who lives close to one of the worst affected areas of Carita Beach in Banten on the island of Java.

Hidayat was at home when the waves surged some 20 metres inland and said he didn’t hear about the damage until the next morning when he was roused from his home by neighbours.

At least 30 people are also believed to be missing according to the Indonesian Disaster Management Agency, but these figures are likely to rise as some areas have been difficult to reach following the mass destruction caused by walls of water.

“I spent all morning helping other local residents with the clean-up,” Hidayat said.

“I saw some 30 bodies strewn around Carita Beach. One woman was washed inland and buried under a pile of rubbish, so we originally couldn’t see her until we moved the debris and found her corpse.

“We couldn’t identify her and all her possessions had washed away, so we guessed she was a tourist from Jakarta. All we could do was send her to the local health clinic,” he explained.

Little to no warning

The tsunami is thought to have been triggered by the eruption of the neighbouring Anak Krakatoa volcano, a volcanic island formed from the nearby Krakatoa volcano.

According to Eddie Dempsey, a lecturer in structural geology at the School of Environmental Sciences, the University of Hull, even if warning systems had been in place they would have been unlikely to have had much effect.

“These events happen with very little to no warning,” he told Al Jazeera. “They are very powerful, so there is little that can be done from an engineering point of view and when these events happen close to populations, there is no early warning system quick enough”.

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Daniel Quinn runs the Gunung Bagging website, which researches peaks in Indonesia and Malaysia, and visited Mount Anak Krakatoa in November this year.

He told Al Jazeera he is not surprised by the death toll, given the proximity of the volcano to inhabited areas.

“An event like this caught everyone by surprise,” he said. “When I went there in November you could still do a day trip to camp at Rakata [the most significant remnant of the original Krakatau volcano] to watch the eruptions from a normally safe distance. There is no tsunami shelter at Rakata that I know of, but I’m not sure a normal shelter would be of great use.”

Indonesia’s Meteorological, Climatological, and Geophysical Agency (BMKG) has pointed to a possible underwater landslide caused by the eruption of Anak Krakatoa, which is thought to have then triggered the tsunami.

It’s a theory that Dempsey agrees with, although he is cautious to point out that it is still too early to be sure.

“The likely cause is a significant submarine landslide relating to the ongoing eruption of Anak Krakatoa,” he told Al Jazeera.

“Volcanos like this grow very quickly, so can become very structurally unstable, leading to collapse and landslides. When this happens in water, the moving earth causes huge amounts of water to be displaced, leading to tsunami,” he said.

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“The tragic events in Indonesia seem to have all the hallmarks of this kind of scenario,” he added. “The narrow inlets typical of the Indonesian coast unfortunately have the effect of amplifying tsunamis and making the waves bigger than they normally would be.”

As local authorities scramble to deal with the damage to homes and roads in both Java and Sumatra, other organisations are also preparing to offer assistance.

Peter Holtsberg, deputy country director of the World Food Programme in Indonesia, told Al Jazeera that the “WFP is ready to support the Indonesian government response to the tsunami triggered by the eruption of Mount Anak Krakatoa.

“We have teams in the country specialised in disaster response, and our logistics experts can help bring aid supplies and aid workers to the affected areas. Upon request we will support the Indonesian government to assess the damage and assist in the response,” Holtsberg said.

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But while local organisations such as aid agencies and search-and-rescue teams are still trying to gain access to the worst-affected areas, questions continue to be asked about what could have been done to prevent this tragedy.

Dempsey stressed it was important for people in Indonesia to remain vigilant.

“Sadly in that part of the world, volcanoes are an everyday hazard, which is very easy to turn a blind eye to,” he said. “The key thing always to remember in Indonesia is that if you notice anything strange about the ocean, get as inland and as high as you can. Don’t wait for a warning. Just do it.”