Indonesia on tsunami watch after volcano erupts, prompting mass evacuation
More than 11,000 people have been ordered to evacuate a 6km zone around Mount Ruang.
More than 11,000 people have been ordered to evacuate a 6km exclusion zone around Mount Ruang volcano in North Sulawesi after a series of explosive eruptions that Indonesian authorities have warned could trigger a tsunami.
At least four explosions since Tuesday have sent columns of ash and smoke billowing as high as 3km into the sky and deposited showers of gravel and volcanic rocks on to neighbouring islands, prompting fears part of the volcano could collapse into the ocean and cause an abrupt sea level rise.
Indonesia’s volcanology agency issued a level four alert late on Wednesday (early Thursday AEST) – the highest possible warning – for the 725m-high mountain after continued explosions during the day, and expanded an exclusion zone from 4km to 6km.
“At least 11,615 residents who are in the risk area must evacuate to a safe place. Because the status has been upgraded to four, islands in the Tagulandang region have become areas that must be vacated,” Abdul Muhari, the head of the agency’s disaster data, communications and information centre said on Thursday.
More than 800 people were initially evacuated from Ruang to nearby Tagulandang Island, 100km north of the provincial capital, Manado, but the exclusion zone was expanded after showers of rocks and gravel projected from the volcano’s chamber reached the Tagulandang coastline.
All those evacuated would now be relocated to Manado, a six-hour boat journey away.
Aviation officials ordered a shuttering of the province’s main airport in Manado until at least Thursday evening “due to the spread of volcanic ash, which could endanger flight safety”, disrupting air travel across the region.
Flights to and from Malaysia’s Kota Kinabalu International Airport on the northern tip of Borneo island some 1100km away have also been affected by the activity, which Indonesia’s volcanology agency said had been triggered by two earthquakes in recent weeks
Mr Muhari said authorities were not yet issuing a formal early tsunami warning, but were “alert to the potential because historically there has been a tsunami caused by the eruption of Mount Ruang”.
At least 400 people were killed in 1879 after a major eruption from Mount Ruang caused part of the volcano to collapse into the sea, triggering a tsunami that raised local sea levels by some 25m.
ANU emeritus professor of geology Richard Arculus said a similar event could not be ruled out as a result of the current eruptions, given the possibility that the explosions could be contributing to Mount Ruang’s instability, though “the difficulty is predicting the mechanical failure of a (volcano) edifice”.
Any tsunami caused by a volcanic collapse would likely be a steady rise rather than one single massive ocean wave, Professor Arculus said. “The build-up can take a while but the main problem is when the first part of the wave arrives, it can keep increasing over seconds and minutes.”
In 2018, the eruption of Indonesia’s Anak Krakatoa volcano triggered a tsunami along the coasts of Sumatra and Java. Hundreds of people were killed.
Mount Ruang sits on the Sangihe island arc which is currently colliding with the Halmahera island arc – the earth’s only example of a collision between facing volcanic arcs.
Additional reporting: Dian Septiari
Ash and sulfur dioxide blasts from the Ruang volcano following its explosive eruption earlier today, climbing thousands of feet into the atmosphere. pic.twitter.com/cYxPkqAPqB
— CIRA (@CIRA_CSU) April 17, 2024