Indonesia raises alert, widens danger zone

Indonesia raised the danger level for an island volcano that triggered a tsunami last weekend, killing at least 430 people in Sumatra and Java, and widened its no-go zone.

The country’s volcanology agency increased the Anak Krakatau volcano’s alert status to the secondhighest and more than doubled the exclusion zone to a 5km radius. The eruption caused part of the island in the Sunda Strait to collapse into the sea, apparently generating tsunami waves of more than 2m. Most tsunamis are caused by earthquakes.

The Government has warned communities in the strait to stay a kilometre away from the coastline because of the risk of another tsunami. A navy vessel was expected to pass by the island, which could give scientists more information about the risks.

“There’s still a chance of a landslide,” said Rudy Sunendar, head of the Energy Ministry’s Geology Department. “Based on the satellite imagery interpretation, there is collapse of some area of Mount Anak Krakatau.”

Radar data from satellites shows Anak Krakatau had shrunk dramatically following the eruption.

Satellite photos aren’t available because of cloud cover but radar images from a Japan Aerospace Exploration Agency satellite taken before and after the eruption show the volcano’s southwestern flank has disappeared. JAXA’s post-eruption image shows concentric waves radiating from the island, which experts say is caused by its ongoing eruptions.

Dave Petley, head of research and innovation at Sheffield University who analysed similar images from an ESA satellite, said they support the theory that a landslide caused the tsunami.

“The challenge now is to interpret what might be happening on the volcano, and what might happen next.”