Indonesian volcano Anak Krakatau is now only about a quarter of its pre-eruption size

Plumes rise from Mount Anak Krakatau as it erupts in the Java Strait, Indonesia on Sunday, December 23. Photo / AP

Scientists say Indonesia's Anak Krakatau volcano island, which erupted and collapsed a week ago triggering a deadly tsunami, is now only about a quarter of its pre-eruption size.

Anak Krakatau now has a volume of 40-70 million cubic metres (1.4 billion-2.4 billion cubic feet) and lost 150-180 million cubic metres (5.2 billion-6.3 billion cubic feet) of volume since the December 22 eruption and tsunami, according to Indonesia's Centre for Volcanology and Geological Disaster Mitigation.

Mount Anak Krakatau spews volcanic material during an eruption as seen from an Indonesian Navy ship in the waters of Sunda Strait. Photo / AP

The analysis shows the scale of the island's collapse, shedding light on the power of the tsunami that crashed into more than 300km of coastline in Sumatra and Java. More than 420 people died in the waves that were 2 metres (6.6 feet) or higher and 40,000 were displaced.

The centre said that the crater peak was 110 metres (360 feet) high as of Friday compared with 338 metres (1,108 feet) in September.

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 from more visual inspections.

Authorities have warned residents to stay a kilometre away from the coastline of the Sunda Strait, which separates Java and Sumatra, because of the risk of another tsunami.

But experts now say another potential tsunami triggered by the volcano collapsing again would be less severe due to its reduced mass.

Before and after images from Aug. 20, 2018, left, and on Dec. 24, 2018, right, respectively show a deformation on the volcano. Photo / AP

People inspect the damage at a tsunami-ravaged village in Sumur, Indonesia. Photo / AP

Anak Krakatau, which means Child of Kratakau, is the offspring of the infamous Krakatau volcano whose monumental eruption in 1883 triggered a period of global cooling.

- AP