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Experts warn eruption at Bali volcano Mount Agung is ‘more likely than not’

A decrease in the energy with which the magma has been rising has raised speculation that the threat may be subsiding, but vulcanologists say it could mean it is rebuilding pressure

PUBLISHED : Friday, 29 September, 2017, 1:35pm
UPDATED : Wednesday, 04 October, 2017, 3:39pm

Throughout the morning, vulcanologists at a small monitoring post on the Indonesian island of Bali go back and forth between checking instruments to detect volcanic activity and surveying visually for signs of a possible eruption of Mount Agung.

Located in the hilly village of Rendang, about 13km southwest of the mountain, the post has seen an influx of vulcanologists after the highest eruption alert was issued September 22 by the country’s Centre for Volcanology and Geological Hazard Mitigation.

Vulcanologist Devy Kamil Syahbana came from the centre in the West Java provincial capital of Bandung soon after the 3,142 metre volcano showed signs of anomalous activity.

“Gassing ... for some volcanoes is normal, but for Mount Agung, it’s different,” Devy told Kyodo News, referring to gases released by active, or in some cases dormant, volcanoes.

Since July, Mount Agung has been discharging small amounts of volcanic gases after being inactive for 53 years.

The volcano last erupted in 1964. But it was in 1963 that a major eruption killed 1,549 people, with cold lava triggered by heavy rain later claiming another 200 lives, according to National Disaster Mitigation Agency spokesman Sutopo Purwo Nugroho.

Threat of volcanic eruption triggers evacuation of nearly 50,000 on holiday island of Bali

No vulcanologist in the world knows whether this volcano will erupt or not, [but] we don’t want to wait until the first eruption occurs
Devy Kamil Syahbana

“Also we found that the area of hotspots [around the volcano] has increased between July and September, indicating heat from the magma is intensifying and the level of seismicity is increasing quite significantly,” Devy, the vulcanologist, said.

These abnormal activities led to the heightened alert status and warnings for residents who live on the volcano to seek safety elsewhere.

By Thursday night, more than 134,000 local residents had been evacuated from the danger zone – a radius ranging from 9km to 12km from the peak.

Over the past few days, however, a slight decrease in the energy with which the magma has been rising to the top of the mountain has raised speculation among residents that volcanic activities may be subsiding.

But Devy was quick to point out that this does not mean the possibility of an eruption has disappeared.

“It can also mean the volcano is rebuilding the pressure,” he said, citing last week’s seismicity data, which showed a decrease in energy followed by a sharp increase.

The magnitude 4 earthquakes recorded over the past few days, in addition to the increasing volume of magma, provides statistical indication that “an eruption is more likely than not”, Devy said.

With a volcanic explosivity index of five, he said Mount Agung is one of just seven volcanoes in the world to have consecutive eruptions – as it did in 1843 and 1963.

This level of explosivity has not been seen in Indonesia since the eruption of Mount Lokon in 2011.

Devy, who heads the Eastern Region Volcano Mitigation Division at the volcanology centre, stressed that there is still a chance Mount Agung might not erupt, but that preparation for the worst-case scenario is important in mitigation efforts.

“No vulcanologist in the world knows whether this volcano will erupt or not, [but] we don’t want to wait until the first eruption occurs, because by then it will be too late for everyone,” Devy said.

Despite the danger, some people living on the slopes of the volcano have refused to leave their villages, saying they will only flee if the volcano erupts and believing they would have enough time to escape.

According to Devy, the hot clouds released by an eruption would engulf 10km of surrounding areas in under two and a half minutes, while “ballistic bombs” formed by the ejection of viscous fragments of lava would travel at speeds of up to 300 metres per second.

“Hopefully, they can run faster than the hot clouds and ballistic bombs,” he said.