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Anak Krakatoa (photo A) is a volcano in Indonesia, one of the most tectonically active countries in the world. It lies in the destructive plate boundary between the Indo-Australian and Eurasian plates (map B).
The volcano forms a small island in the Sundra Strait, between the much larger Indonesian islands of Java and Sumatra. On 22 December 2018, Anak Krakatoa erupted, leading to a deadly tsunami with waves five metres high reaching the island around it. As a result, 437 people died and 14,000 people were injured. It became the world’s most deadly volcanic eruption so far in the twenty-first century.
The history of Anak Krakatoa goes back over a century (see timeline C). Its name means ‘Child of Krakatoa’ and gives a clue to its origins. In recent years, there were frequent eruptions, and steam plumes were often seen coming from the top of it, caused by water heating inside the volcano and rising to the surface. The eruptions became more intense from July 2018.
Finally, on 22 December, there was a violent explosion, when water reacted with magma rising from the mantle, leading to an underwater collapse of the volcano. A huge volume of water in the ocean was displaced by the rock, triggering the tsunami.
What was the tsunami like?
What was the tsunami like?
All the deaths in Indonesia from the eruption of Anak Krakatoa were caused by the tsunami that followed. A tsunami is a large wave created by movement on the seabed, as a result of either an earthquake or volcanic eruption. Tsunami is a Japanese word that means ‘harbour wave’.
In the case of Anak Krakatoa, the collapse of the volcano after the violent eruption led to an underwater landslide that displaced a huge volume of water (diagram F). This created a wave that spread out from the volcano in all directions, a bit like dropping a stone in a pond and watching the ripples spread out in a circle.
Tsunamis travel across the ocean at speeds of hundreds of kilometres an hour. Anak Krakatoa is only about 50 km from the nearest coasts on Sumatra and Java (map G). The tsunami hit within minutes. A tsunami early warning system for the Indian Ocean did not help, as there was not enough time for any warning to be given.
What were the impacts of the tsunami?
What were the impacts of the tsunami?
The tsunami affected about 300 km of coastline in Sumatra and Java around the Sunda Strait. It struck after dark, at 9.30 pm, without any warning, destroying buildings, sweeping away cars and uprooting trees (photo H). The disaster had many impacts on people’s lives:
The death toll was 437 with 14,000 casualties.
40,000 people were made homeless because their homes were destroyed or damaged.
Several tourist resorts were hit, including Tanjung Lesung in Java. The wave hit a marquee where a rock band was playing a concert. Members of the band were washed away.
The main road in Pandeglang was blocked, making it difficult for rescue vehicles to reach the area. Pandeglang is where most of the casualties were treated.
After the tsunami struck, there was confusion about what happened. At first, it was reported as a tidal surge, because there was no earthquake (most tsunamis in Indonesia follow earthquakes).
In 2004, a much bigger tsunami was triggered by a powerful earthquake off the coast of Sumatra in the Indian Ocean. It killed 228,000 people in 13 countries, most of them in Indonesia. After this, a tsunami early-warning system was set in the Indian Ocean to detect tsunamis and to warn people before they reach land (diagram I).
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