After that eruption, scientists said the volcano island was reduced to about a quarter of its pre-eruption size.
AP reported at the time that Anak Krakatau had 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 2018 eruption and tsunami, according to Indonesia's Centre for Volcanology and Geological Disaster Mitigation.
The analysis showed 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 two metres (6.6 feet) or higher and 40,000 were displaced.
The centre said that the crater peak was 110 metres (360 feet) high after the 2018 eruption, compared with 338 metres (1,108 feet) two months previously.
Experts initially relied on satellite radar images to work out what happened to the volcano because cloud cover, continuing eruptions and high seas hampered inspections.
At the time, authorities 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.
Experts at the time said another potential tsunami triggered by the volcano collapsing again would be less severe due to its reduced mass.
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.
More to come
