Mount Raung on Java island blasted ash and debris up to 2,000 meters (6,560 feet) into the air after rumbling for several weeks, government volcanologist Surono said.
Ash erupted also from Gamalama and Dukono mountains on the Moluccas islands chain, Sinabung volcano on Sumatra island and Mount Karangetang on Siau island, darkening the skies, Surono said.
A total of more than 13,000 people have been evacuated due to the volcanic eruptions since last month, mostly from around the slopes of Sinabung in Tanah Karo District, added Surono, who uses a single name.
“Our evaluation showed there is no extraordinary natural phenomenon that triggered simultaneous eruptions of the five volcanoes,” Surono said, adding that all the eruptions are natural and normal occurrences in a nation with about 130 active volcanoes.
Transport Ministry spokesman Julius Adravida Barata said Jember and Banyuwangi airports closed late Tuesday and Bali’s international airport was closed for several hours on Wednesday, disrupting flights. Media reports said 37 flights to and from Bali’s Ngurah Rai airport were cancelled.
An eruption of Raung early this month sparked chaos as the airport in the tourist hotspot of Bali and four other airports in the region were shutdown, stranding thousands of holiday-goers.
Last week, the ministry closed Sultan Babullah airport in North Maluku’s Ternate town after eruptions at Gamalama and Dukono sent volcanic ash up to 1,700 meters (5,570 feet) into the sky.
Indonesia, a chain of 17,000 islands where millions of people live in mountainous areas or near fertile flood-prone plains, is prone to seismic upheaval due to its location on the Pacific “Ring of Fire,” an arc of volcanoes and fault lines encircling the Pacific Basin.