Potentially deadly pyroclastic flows, a briefly cooler climate and flight disruptions are on the cards

Bali volcano: will Mount Agung erupt and what happens if it does?

An eruption at Bali’s Mount Agung volcano is imminent, according to experts.



Hundreds of tremors are being recorded at the site each day, and more than 75,000 people evacuated in the past few days after local authorities declared a state of emergency.

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But will it erupt? If it does, what’s likely to happen? And what will it mean for the tens of thousands of Australians who plan to travel to the popular tourist destination in the next week?

Will Mount Agung erupt?

Last week Indonesian authorities announced the highest possible alert warning, and besides the evacuations they’ve also set up an exclusion zone that stretches 12km from the crater in some places.

Scott Bryan, an associate professor from the Queensland University of Technology, says there have been “very good indications” that an eruption is imminent.

“The fact that the seismic tremors beneath the volcano are increasing in number, intensity, and the reduction in their depth in the last week or so, is a very good indication that magma is moving up to the surface,” he said.

As well as seismic activity, Bryan said there are two other signs that an eruption is imminent: gas emissions from the summit, and bulging on the volcano’s surface.

He said gas emissions were a sign that pressure under the ground had become too great, sending magma towards the summit of the volcano and releasing gas and steam in the process.



“It’s like a bottle of Coke or champagne, if you shake them up the pressure builds until you release the lid,” he said.

If it does, what happens next?

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Mount Agung hasn’t erupted for more than 50 years. The last time it did, in 1963, more than 1,000 people were killed and hundreds more were injured.

Lava flowed for 7km from the crater, and the ABC reports that survivors of the catastrophe recall a “rain of ashes”.

But the most deadly feature of the volcano were the devastating pyroclastic flows: waves of superheated gas containing gas, ash and rock that can travel hundreds of kilometres an hour.

“Pyroclastic flows are the main hazard and threat in terms of killing a lot of people very quickly with little to no warning,” Bryan said.

“If it’s at night and people are in bed they have literally seconds or minutes to move and people get caught and trapped and die. It’s what caused the deaths in 1963, and at Mount Merapi in 2010.”

This time authorities have taken plenty of precautions, but Bryan said there was no way to be totally sure of its impact.

“What we need to worry about when it does erupt is how much of the gasses have been able to escape from magma,” he said.

“If you think about your bottle of Coke again, if you shake it up and take the lid off you get it all foaming out, but, if you take the lid off, let it stand there for a day and then shake it, all the gas has escaped and nothing happens.”

What will it mean for travellers?

About 1.2 million Australians visit Indonesia each year, and tens of thousands are expected to flock to Bali in the next few weeks as most states break for school holidays.

So should travellers be worried?

The short answer is not unless you were planning a trip to see the summit of a volcano. Mount Agung is located in Bali’s northeast, about 75 kilometres away from Kuta.

Jetstar, Qantas and Virgin all say they’re monitoring the situation, but are still flying as usual.

That could change in the event of an eruption though.

In 2015 thousands of Australian holidaymakers were stranded and flights were disrupted for months after Mount Raung erupted. Bryan said that could easily occur again.

“As a rule, any ash in the atmosphere means it becomes a no-fly zone,” he said.

“As soon as there is an eruption there’s a big ash column there will most likely see air space closed to traffic and planes diverted.

“Depending on the wind and how long the eruption goes for there could easily be a shutdown of air space over Denpasar.”

It’s worth noting though that while Australia’s Department of Foreign Affairs and Trade has told travellers to check with their airline before travelling, the overall level of travel advice to Bali has not changed.

What will an eruption mean for the climate?

When volcanoes erupt, the Earth actually gets cooler.

Teresa Ubide, a lecturer in volcanology from the University of Queensland, explained that the cooling was caused by sulphur emissions from the volcano.

“Basically what happens is volcanoes such as this one generate sulphur-based aerosols which block radiation from the sun and therefore the climate is affected by a decrease in global temperatures,” she said.

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In 1963, when Mount Agung last erupted, global temperatures dropped by between 0.1C and 0.4C.

And in 1991 the eruption of Mount Pinatubo in the Philippines created a significant dip in global temperatures of about 0.5C.

That might not sound like much, but Ubide explains that it can have a “significant impact”.

“Obviously you will not feel a massive change personally but it’s going to affect everything on Earth because everything responds to climate,” she said.