© baliglory.comMount Agung
More than 75,000 people have been evacuated in the last few days as Agung, the highest point of the island, has experienced hundreds of internal volcanic earthquakes. "Instrumentally we have never recorded such high energy or seismicity from Mount Agung," Devy Kamil Syahbana, a seismologist from Indonesia's centre for volcanology and geological hazard mitigation, told the Guardian.
Data showed that Mount Agung experienced 844 volcanic earthquakes on Monday, and 300 to 400 earthquakes by midday on Tuesday, he said. "We need to pay attention because these kinds of earthquakes indicate the movement of magma and increase the probability of an eruption."
Evacuated people have sought shelter in hundreds of village halls and sports centres and in the homes of relatives in more than nine districts. President Joko Widodo is scheduled to visit evacuees at several camps on Tuesday. Authorities have urged people to stay out the danger zone, a designated five-to-seven-mile radius of the volcano.
The increasing frequency of deep and shallow volcanic earthquakes, as well as local tectonic tremors, is an indication that magma continues to move toward the surface. The alert status of Agung was raised to the highest levelon Friday evening following a significant spike in seismic activity. Kasbani, the head of the volcanology centre, told local media that if tremors continued, an eruption - the first in more than half a century - could be a "matter of hours" away.
The volcanology agency is also drawing data from GPS and satellite imagery, including a thermal camera. Readings from these measurements are in line with the increase in volcanic tremors.
Syahbana said it was impossible to say that Agung would definitely erupt, only that the data showed there was an increasing probability that it would. "There is no volcanologist in the world who could predict precisely when a volcano will erupt," he said. "Volcanoes are a stochastic system, many complexities are unknown by the human brain and technology."
Mount Agung last erupted in 1963, when more than 1,000 people were killed. That event was preceded by an increased frequency in earthquakes.
One of the difficulties in predicting the likelihood and timing of an eruption on Agung is that monitoring of the volcano began only after the 1963 eruption. Other volcanoes in Indonesia that have erupted more recently offer a greater wealth of data for seismologists to compare and assess.
"But for Agung we have no instrumental documentation," said Syahbana. "The only records that we have is of the phenomena that were observed and reported by people around the volcano prior to the 1963 eruption."
Bali's Ngurah Rai international airport, which is about 47 miles from the volcano, remains open, with flights running as normal on Tuesday. In the event of an eruption and ash clouds that could disrupt air travel, authorities have made preparations for flights to be diverted to seven regional airports, including on Java and Lombok islands.
The UK, Australia and the US are among several countries that have issued travel advisories in recent days, warning that volcanic activity on Agung could interfere with travel plans.
Mount Agung is one of many active volcanoes in the ring of fire, a string of volcanoes and seismic activity that runs through the Indonesian archipelago and the edges of the Pacific Ocean.
James Wilson, 28 from Bristol, is staying near Mount Agung with his fiancé and they have plans to climb the nearby Mount Batur on Wednesday morning. He said: "It's always been our plan to come to Bali and go up Mount Batur so we're quite keen to continue if we can."
Wilson, who is staying in the Volcano Terrace Bali hotel around 10km from Agung, said there are mixed feelings in the local community. He said: "Some people are quite relaxed and others are quite worried because of the evacuations. "We did see smoke this morning above Agung though, and our hotel shook a bit earlier in what I assume was a tremor. I'm not sure why we haven't been evacuated. In some respects it might be foolhardy to stay and in another we want to get on with our holiday as much as we can."
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