The tsunami was caused by the collapse of a 64-hectare (158-acre) section of the Anak Krakatau volcano.
This caused an underwater landslide, Dwikorita Karnawati, head of the Indonesian meteorological agency, told The Guardian .
The collapse transformed Anak Krakatau.
ystein Lund Andersen, a nature photographer who documents Indonesian volcanoes, shared the following before-and-after images on Twitter last week. One photo of the volcano was taken August 5, 2018, while the other was captured January 11, 2019.
The following images, many taken by the WorldView-2 satellite, show Anak Krakatau's stunning transformation. The collapse reduced the 1,100-foot-tall volcano to a crater a quarter of the size.
Anak Krakatau is one of the worlds most famous volcanoes.
Riau Images/Barcroft Images/Getty
In 1883, the Krakatau (Krakatoa) volcano erupted in a series of four explosions that destroyed the surrounding island and killed more than 30,000 people. The eruption wreaked havoc on global weather patterns for the next five years.
Some 50 years later, the island of Anak Krakatau (Anak Krakatoa) emerged from the site of Krakatoa's fiery death.
Anak Krakatau grew steadily each year until the partial collapse in December 2018. This is what it looked like in November 2017.
Anak Krakatau had been growing taller by an average of about 5 meters (16 feet) per year, according to EarthSky .
Satellite imagery shows what the volcano looked like after the collapse its as if a giant thumb pushed down on Anak Krakatau.
This image is more zoomed out than the previous one, so it also includes the islands that surround the volcano. But it's clear that, at the top of Anak Krakatau, there's now a gaping hole. The trees and wildlife that once lived there are also gone.
After the collapse, Anak Krakatau shrank to just a quarter of its original height.
Anak Krakatau spewed so much ash into the air that planes had to be re-routed around the Sunda Strait area.
Anak Krakatau is still active; the collapse didn't stop its volcanic activity.
Subsequent eruptions will help to rebuild the volcano, forming a new island.
Indonesia needs to be prepared for future tsunamis, experts say.
M. Tohir/Barcroft Media/Getty
The December 22 tsunami came without warning.
Richard Teeuw of the University of Portsmouth told The Guardian that the likelihood of further tsunamis in the Sunda Strait will remain high while Anak Krakatau volcano is going through its current active phase, because that might trigger further submarine landslides.
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