Images Show Landslide Likely Caused Indonesian Tsunami

Radar images appear to show the southwestern flank of the Anak Krakaktau volcano sheared off into the sea

Anak Krakakau
Geospatial Information Authority of Japan

For Indonesia, 2018 has been a year characterized by natural disasters. In late September an earthquake and tsunami hit the island of Sulawesi killing almost 2,000 people, mostly in the city of Palu. A few days later, the nearby volcano Soputan erupted.

Last Saturday brought more devastation when a tsunami hit Indonesia’s Sunda Strait between the islands of Java and Sumatra. The disaster, which appears to have been triggered by an underwater landslide set off by volcanic activity, killed at least 430 people and displaced upwards of 16,000.

New satellite images taken of the Anak Krakatau volcano before and after the explosion suggests that the massive landslide destroyed the volcano’s entire southwest flank, reports George Dvorsky at Gizmodo.

The close-up look comes from JAXA. While cloud cover made taking direct satellite images impossible, the Japanese space agency’s ALOS-2 satellite used radar readings converted to images to capture the changes in the landscape, according to the Associated Press.

Japan’s Geospatial Information Authority analyzed images, which were taken before and after the disaster hit, and revealed a significant portion of the volcano had been sheered off. The after images also showed concentric circles in the water around the volcano, an indicator of seismic activity.

Dave Petley, head of research and innovation at Sheffield University, who writes about landslides at his blog hosted by the American Geophysical Union, analyzed similar images from the European Space Agency, concluding that the tsunami was likely caused by an underwater landslide at the volcano. “The challenge now is to interpret what might be happening on the volcano, and what might happen next,” he writes.

As a precaution, authorities have warned people to stay at least a kilometer away from the coastline of the Sunda Strait in case another landslide and tsunami take place. On Thursday, the BBC reports that Indonesian authorities also raised the volcano alert level to the second highest option, due to the activity at Anak Krakatau and diverted all flights from the volcano exclusion zone.

Anak Krakatau has been showing signs of activity since July, when it began shooting out rocks and lava in short bursts known as Strombolian eruptions.

Volcanic eruptions are fairly common with an average of one per week somewhere on the globe. But when Anak Krakatau stirs, people take notice. That’s because the Sunda Strait volcano itself is a remnant of one of the worst volcanic eruptions in recorded history. Anak Krakatau emerged almost five decades after the volcano it got its name from, Krakatoa, blew its top in 1883, creating a massive ash plume and major tsunami. At least 35,000 people died from the explosion, and the massive blast changed the global climate in the northern hemisphere for years, leading to unusual weather events and cooler temperatures.

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