Despite Bali’s Mount Agung volcano spewing huge plumes of volcanic ash, and lava, experts warn complacency is the island’s biggest enemy and that the worst is yet to come, including blinding ashfall and flying rocks that spew out of the volcano.

“This is an eruption, this is 100 per cent an eruption,” volcanologist Dr Janine Krippner told news.com.au.

“Lava is coming out of the volcano, there’s definitely enough to cause trouble. This can get much worse, you can’t outrun this.”

For months, magma inside Bali’s giant, belching volcano has been gradually rising to the top of the volcano, forcing the gigantic structure to rumble and shake.

In August, the volcano slowly began to rumble back to life, and through September the number of tremors recorded at Mount Agung reached about a thousand a day.

Agung’s last eruptions in 1963 produced deadly clouds of searing hot ash, gases and rock fragments that travelled down its slopes at great speed. About 1100 people died in total. There are serious fears the same will happen again.

Lava spread for several kilometres and people were also killed by lahars — rivers of water and volcanic debris also described as cold lava.

“If those come, they can travel 10km within three minutes,” Dr Krippner said.

“You can’t outrun these.”

In Mount Agung’s case, molten rock, which has been accumulating for the past 50 years, has heated up and slowly — thanks to the overwhelming pressure — pushed through the volcanic rock above, finding weaker points to penetrate.

But Dr Krippner said what has changed in recent weeks is that the molten rock has nothing left to push through - it’s reached the top. Now that the lid has quite literally been blown off, the future is an uncertain one.

“The danger is that this is now an open system. Before, it was a closed system which means that there was no easy open access between the magma and the surface,” she explained.

“Now that that has completely made its way through, this can change quickly. It doesn’t have to force its way through the rock any more, now it’s just coming out.”

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Increased temperature in the groundwater created steam filled with gases like sulphur dioxide; it’s been steaming away quite strongly over the last months. Dangerous volcanic gases also fill the air. It’s getting thicker, pulsating.

As it’s doing that, the mountain is shaking as rocks interact with water and ocean sediment, melting, bubbling their way up to their source.

“It’s like shaking up a bottle of Coke and then taking the lid off,” Dr Krippner said.

“It’s the same process before you open a bottle of Coke; there’s gas in it, but you can’t see it because it’s pressurised when they bottle it in the factory. But if you shake that up you’ve agitated the gases and then as soon as you relieve that pressure the gases are coming out so quickly that it’s blowing the Coke into tiny fragments.

“That’s exactly what is happening with Agung. The pressure is being released quickly as it comes out because its coming from below the surface of the earth so there’s a lot of rock and gravity. As it’s being released the gases are coming out very quickly and expanding and just blowing the rock apart as fragments of ash and glass and crystals.”

Authorities had already raised the alert for Mount Agung to the highest level and ordered 100,000 residents living within a 12 kilometre exclusion zone to leave. The exclusion zone has since been downgraded within 8-10 kilometres.

But not everyone has left - and even those who are within Bali still face dangerous perils form the erupting volcano.

“The concern is we know the history of Agung and knowing what a volcano has done in the past, you know what it can do in the future. You know what you need to prepare for.

“Agung has shown us in the past this volcano can produce a very large ash column but more importantly for people close to the volcano, it can produce what has changed in recent weeks, as pyroclastic flows and lahars. That is the main issue now, everyone has to get out of those exclusion zones. It’s very serious that everyone stays out of the exclusion zone.

“People everywhere all through Bali need to be prepared for ashfall because it can cause respiratory issues. You know how you can’t function as a human being if you had an eyelash in your eye? Imagine if that was rock and glass.”

Indonesia is the world’s most active volcanic region with 127 active volcanoes. The Southeast Asian archipelago lies on the Pacific “ring of fire” where tectonic plates collide, causing frequent seismic and volcanic activity.

Mount Agung, about 70 kilometres to the northeast of the Kuta tourist mecca, is among more than 120 active volcanoes in Indonesia. Another volcano, Mount Sinabung on Sumatra, has been erupting since 2010.

The issue for experts attempting to map out a possible timeline in Bali is the fact that no one really knows when the worst will come - if at all.

“The sad part about that is often times people have moved back inside the danger zone because they say, ‘it hasn’t erupted, it will be fine’ — and then it erupts,” Emile Jansons, aviation services manager at the Volcanic Ash Advisory Centre (VAAC), a section of the Australian Bureau of Meteorology, previously told news.com.au.

“We hope for the best and we prepare for the worst,” Mr Jansons said.

Meanwhile, young Australian school leavers stranded in Bali due the ash cloud spewing from Mt Agung say they’ve been abandoned by their travel insurance companies.

Insurers have limited financial and other support for Australians trapped on the Indonesian resort island, in the shadow of the smoking volcano.

The international airport on Bali is likely to remain closed for a second full day on Wednesday, and airlines have cancelled inbound and outbound flights due to the danger posed by the ash cloud.

— Australian travellers to Bali should visit the Australian Government’s Smart Traveller website.