A crater collapse on the volcanic island at high tide on Saturday sent waves up to 5 metres high smashing into the coast on the Sunda Strait, between the islands of Java and Bali.
Authorities have warned that the crater of Anak Krakatau, or child of Krakatau, remains fragile, raising fears of another collapse and tsunami, and have urged residents to stay away from the coast.
There are also fears of a bigger eruption.
The volcano has been rumbling on and off since July but has been particularly active since Sunday, spewing lava and rocks, and sending huge clouds of ash up to 3,000 metres into heavily overcast skies.
The national geological agency, in raising the alert level to the second-highest, set a 5-km exclusion zone around the island.
Since December 23, activity has not stopped, we anticipate a further escalation, said Antonius Ratdomopurbo, secretary of the geological agency.
A thin layer of volcanic ash has been settling on buildings, vehicles and vegetation along the west coast of Java since late on Wednesday, according to images shared by the national disaster mitigation agency.
Authorities said the ash was not dangerous, but advised residents to wear masks and goggles when outside, while aircraft were ordered away.
All flights are rerouted due to Krakatau volcano ash on red alert, the government air-traffic control agency AirNav said in a release.
The civil aviation authority said no airports would be affected. The capital, Jakarta, is about 155 km east of the volcano.
In 1883, the volcano then known as Krakatoa erupted in one of the biggest blasts in recorded history, killing more than 36,000 people in a series of tsunami and lowering the global surface temperature by one degree Celsius with its ash.
A tsunami in Indonesia’s Sunda Strait struck two of the country’s islands without warning, killing at least 222 people and injuring more than 700, officials said here yesterday.
Hundreds of buildings were destroyed by the three-foot wave, which hit the coast of southern Sumatra and the western tip of Java about 14.30pm GMT (6.30pm UAE time) on Saturday after a volcano known as the “child” of Krakatoa erupted, national disaster agency spokesman Sutopo Purwo Nugroho said.
No earthquake was recorded and no tsunami warning was issued, said Rahmat Triyono, earthquake and tsunami chief at Indonesia’s Meteorology, Climatology and Geophysics Agency. We don’t know what caused the tsunami yet, he said.
Search and rescue teams were scouring rubble for survivors, with 222 people confirmed dead, 843 people injured and 28 missing, Nugroho said.
Tsunamis triggered by volcanic eruptions are relatively rare, caused by the sudden displacement of water or slope failure, according to the International Tsunami Information Centre.
Unlike those triggered by earthquakes, they give authorities no time to warn residents of the impending threat. Ben van der Pluijm, an earthquake geologist and a professor in the University of Michigan, said the tsunami may have been caused by a partial collapse of Anak Krakatoa.
Instability of the slope of an active volcano can create a rock slide that moves a large volume of water, creating local tsunami waves that can be very powerful. This is like suddenly dropping a bag of sand in a tub filled with water, he said.
Videos from the regency of Pandeglang in Java’s Banten province showed extensive damage. More than 400 homes, nine hotels and at least ten vessels were damaged or destroyed in Pandeglang, Sutopo Purwo Nugroho, the spokesman for Indonesia’s disaster management agency, said on Twitter.
The area hit by the tsunami is popular with tourists from Jakarta, the capital, and many people were at the beach on Saturday when the wave struck around 9.30pm (local time).
Rahmat said no tsunami warning had been issued because such warnings are prompted by tectonic activity and no earthquake had occurred.
In September, an earthquake struck the island of Sulawesi, setting off an underwater landslide and tsunami that struck the city of Palu and surrounding areas. More than 2,100 people died.
TV images showed the seconds when the tsunami hit the beach and residential areas in Pandeglang on Java island, dragging with it victims, debris and large chunks of wood and metal.
On December 26, 2004, an Indian Ocean tsunami triggered by an earthquake killed 226,000 people in 13 countries, including more than 120,000 in Indonesia.
The eruption of Krakatoa in 1883 killed more than 36,000 people in a series of tsunamis. Anak Krakatoa is the island that emerged from the area once occupied by Krakatoa, which was destroyed in 1883. It first appeared in 1927 and has been growing ever since.
Saturday’s tsunami was the latest in a series of tragedies that have struck Indonesia, a vast archipelago, this year.
Successive earthquakes flattened parts of the tourist island of Lombok, and a double quake-and-tsunami killed thousands on Sulawesi island. Nearly 200 people died when a Lion Air passenger plane crashed into the Java Sea in October.
President Joko Widodo, who is running for re-election in April, tweeted that he had ordered all relevant government agencies to immediately take emergency response steps, find victims and care for the injured.
Neighbouring Malaysia and Australia both said they were ready to provide assistance if needed.
Another tsunami could strike Indonesia, experts have warned, after a powerful wave caused by a volcanic eruption killed hundreds when it swallowed coastal settlements, taking earthquake-focused disaster monitors by surprise.
While tsunamis are often triggered by earthquakes, in this case experts believe the deadly waves were generated by an eruption of the Anak (or "child of") Krakatoa volcano, which could have caused a large undersea landslide or flow of molten rock into the water.
The tsunami appears to have been caused by an underwater collapse of part of the volcano, said David Rothery, a professor of planetary geosciences at Britain's Open University.
Anak Krakatoa is an island that emerged around 1928 in the crater left by Krakatoa, whose massive 1883 eruption killed at least 36,000 people.
The tsunami that struck on Saturday was the third natural disaster to hit Indonesia in six months.
The country has 127 active volcanoes and lies on the Pacific Ocean's "Ring of Fire" where earthquakes and volcanic eruptions are frequent.
Anak Krakatoa, located in the Sunda Strait between Java and Sumatra islands, is close to densely populated areas.
The volcano has been particularly active since June, noted Jacques-Marie Bardintzeff at the University of Paris-South.
We were helpless given how sudden the event took place, Bardintzeff said. The time between cause and effect was a few dozen minutes, which was too short to warn the population.
The killer wave struck at night, sweeping across tourist beaches and low-lying settlements on both sides of the Sunda Strait and catching both residents and disaster monitors totally unawares.
Signs that a tsunami was coming weren't detected and so people did not have time to evacuate, said Indonesia's disaster agency spokesman Sutopo Purwo Nugroho, who blamed vandalism, technical problems and limited budgets for the lack of warning buoys.
But the Open University's Rothry said such buoys, normally positioned to monitor earthquakes at underwater tectonic plate boundaries, would still have had limited efficacy.
Even if there had been such a buoy right next to Anak Krakatoa, this is so close to the affected shorelines that warning time would have been minimal given the high speeds at which tsunami waves travel.
Simon Boxall of Southampton University said the region was in spring tide, and it would appear that the wave hit some of the coastal areas at the highest point of this high tide, exacerbating the damage done.
While the tsunami was relatively small, Richard Teeuw, a disaster risk reduction expert at the University of Portsmouth in England said: Such waves - laden with debris - can be deadly for coastal communities, especially if there is no warning.
Devastating tsunami caused by volcanic eruptions are rare; one of the most famous and deadly was caused by the eruption of Krakatoa in 1883, Teeuw said.
The likelihood of further tsunamis in the Sunda Strait will remain high while Anak Krakatoa volcano is going through its current active phase because that might trigger further submarine landslides, he said.
Sonar surveys would now be needed to map the seafloor around the volcano, but unfortunately submarine surveys typically take many months to organise and carry out, he added.
Bardintzeff warned we must be wary now that the volcano has been destabilised.
Tourism Observer
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