Indonesia’s Anak Krakatau volcano island, which erupted and collapsed a week ago triggering a deadly tsunami, is now only about a quarter of the size it was before its eruption, according to scientists.

Anak Krakatoa, which used to stand 338 metres high is now just 110 metres tall and has a volume of 40-70 million cubic metres after losing 150-180 million cubic metres since the December 22 eruption and tsunami, according to Indonesia’s Centre for Volcanology and Geological Disaster Mitigation.

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Its analysis shows the scale of the island’s collapse, shedding light on the power of the tsunami that crashed into more than 300 kilometres of coastline in Sumatra and Java.

Authorities said at least 426 people were killed and 23 have gone missing in the waves that were two metres or higher. Forty thousand people have been displaced.

Experts have largely relied on satellite radar images to work out what happened to the volcano because cloud cover, continuing eruptions, and high seas have hampered inspections. The centre said it would get more precise results after more visual inspections.