Mount Agung volcano on the island resort of Bali has reached a "critical stage" with about 500 tremors recorded a day compared with just two in previous weeks, Indonesian national disaster management agency BNPB said yesterday.
The tremors are caused by magma rising closer to the surface, BNPB spokesman Sutopo Purwo Nugroho told reporters.
When asked if an eruption is imminent, he said: "No one can predict when exactly. But for now, we can say all measuring instruments show there is growing pressure towards the surface."
The government has evacuated more than 48,000 of the 62,000 people living within the "danger zone" - a 12km exclusion zone around the crater.
Some families, however, have decided to stay put, even though they have been urged to leave. "Their reason is Mount Agung has not erupted yet, while others said they were worried about their cattle and farms, saying no one would look after them," Dr Sutopo said.
As for Bali's capital Denpasar, Dr Sutopo said it is far from the danger zone because it is located 75km away from the mountain.
The volcano last erupted in 1963, killing 1,549 people and forcing 100,000 others to flee their homes.
"Mount Agung's eruption has always been explosive, but the last eruption was 100 years from the previous eruption. So if it erupts again now, it should not be as big. But this is just a prediction," said Dr Sutopo.
Indonesia, which sits on the Pacific Ring of Fire, has 127 active volcanoes, or 13 per cent of the total number of volcanoes around the world. Mount Agung in Karangasem regency and Mount Sinabung in North Sumatra province are both at the highest alert level - Stage 4 - which means an eruption is imminent.
Dr Sutopo said that if Bali's main Ngurah Rai airport has to be closed, flights there will be diverted to nearby airports, including those in Semarang, Yogyakarta and Solo in the central part of Indonesia's main island of Java, Surabaya in East Java province, and Lombok, an island to the east of Bali.
If Mount Agung erupts between now and next month, the volcanic ash is expected to travel south-west towards Surabaya, following the wind direction trend.
If the volcano erupts between November and January, the ash would travel easterly, going in the direction of West Nusa Tenggara province as well as East Nusa Tenggara, where popular tourist spots Komodo island and Labuan Bajo are located.
Dr Sutopo said President Joko Widodo will travel to Bali today to check the situation on the ground and meet the evacuees.
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