Bali's Mt Agung volcano erupting but alert level remains unchanged

Bali's Mt Agung volcano erupting but alert level remains unchanged

Bali's Mt Agung volcano erupting but alert level remains unchanged

Updated 23 November 2017, 10:35 AEDT

Bali's Mt Agung volcano begins erupting with an ash cloud rising 800 metres above the summit, but authorities say the eruption is small so far and locals are being urged to remain calm.

Bali's Mt Agung has finally erupted, two months after tens of thousands of local residents were evacuated from their homes around the volcano.

Key points:

  • No plans to expand evacuation zone to take in more villages
  • Bali's international airport remains open
  • People near Mt Agung should be "on alert" but eruption is small

But the initial eruption was small — so far there have been no new evacuations, and the island's airport remained open.

Bali's police chief Petrus Golose said there was no panic anywhere on the island.

The volcano's initial eruption was an 800-metre-high plume of steam and pulverised rock that was blowing to the east, away from the island.

The ash cloud is dangerous to breathe and hazardous to aircraft engines, but it is so small — so far — and has not yet affected operations at Ngurah Rai International Airport.

There was an "orange" aviation alert status, warning pilots of an ash cloud close to the volcano no higher than 3,900 metres.

The head of the volcano monitoring post at Mt Agung, I Dewa Made Mertayasa, said the eruption was a "phreatic explosion" and there was no reason yet to broaden the evacuation zone around the volcano which extended for between 6-7.5 kilometres from the crater.

"Phreatic means that the water in the crater surface collected because of heavy rain recently combined with ascending magma," Mr Mertasaya said.

"The dangers are for [the people] living within a 6km to 7.5km radius from the crater. That evacuation zone should remain clear because the ash clouds are heading in that direction.

"The people should be on alert, as the volcano has been spewing ash cloud — though in small size and non-pyroclastic — but still the ash will affect the people surrounding Mt Agung."

Agung's alert status was recently lowered to the second-highest warning level after several weeks at the highest level.

'This is playing out like they said it could'

US-based volcanologist Dr Janine Krippner has been following Mt Agung's rumblings since September.

"This is what they said might have happened," she said.

"They said if something did happen it was likely to be small — it might be larger afterwards but it would start out small. This is playing out like they said it could.

"A phreatic eruption is basically one where there is no magma involved. We've all seen the steaming, the steam plume at the top of the volcano.

"And what can happen with volcanos is some of the steam can get trapped, and it can be pressurised, and it can cause an explosion."

In September more than 150,000 locals were evacuated from their homes, partly because of what happened the last time Agung erupted, in 1963.

Back then, more than 1,000 people died on the slopes of the volcano — many killed by clouds of hot gas called "pyroclastic flows".

The other big risk to human life comes after the eruption when rain sends waves of mud and rock washing down the mountain — these are called lahars.

About 30,000 people remain in evacuation centres. So far, there's no plans to expand the evacuation zone to take in more villages.