Some parts of Indonesia that do not have early warning systems in place for earthquakes could be at increased risk of tsunamis, according to a new study.
Analysis of more than 2.5million years’ worth of geological data revealed 19 enormous ancient underwater landslides around the island nation.
The submarine landslides happened, on average, once every 160,000 years.
Should one of these events happen in the modern world, the most at-risk locations would be the cities of Balikpapan and Samarinda, with a combined population of over 1.6 million people.
Researchers say the proposed new capital city of Indonesia at Balikpapan Bay would also be heavily affected.
The research team, led by Heriot-Watt University in Edinburgh, said the findings suggest coastal communities in the country without tsunami warning or mitigation systems could be at risk from tsunamis generated by similar landslides.
Researcher Rachel Brackenridge said: ‘The largest of the landslides comprised 600 kilometres cubed of sediment, while the smallest we identified were five kilometres cubed.’
The debris produced by the largest landslides identified would fill Sydney harbour 1,000 times over.
Ms Brackenridge said the team mapped underneath the seabed using seismic data.
She said: ‘We can see a layered and orderly seabed, then there are huge bodies of sediment that appear chaotic.
‘We can tell from the internal characteristics that these sediments have spilled down a slope in a rapid, turbulent manner.