Bali’s highest volcano was pictured giving off a red glow and sending up a huge plume of steam into the night sky over the holiday destination last night.
The eery photograph was taken by Magma Indonesia and shared on Twitter by National Agency for Disaster Management (BNPB) spokesman Sutopo Purwo Nugroho.
A translation of Sutopo’s tweet said that Mount Agung remains under the highest possible alert, which is known as level four or Awas.
He said that the danger zone still covers a radius of 8-10km from the summit but the rest of Bali is safe and the airport is operating normally.
David A Rothery, professor of planetary geosciences at The Open University, said that the night-time glow was from red hot cracks in the lava dome being reflected off the plume of gas.
Prof Rothery said that the plume seen coming out of the towering volcano was now mostly condensed steam and it was carrying up little, if any ash, at present.
He said: “Agung IS currently erupting, but currently there seem to be few major explosions.
“Most of the erupted material is being extruded onto/intruded in a lava dome that is growing on the floor of the crater.”
An aerial photograph, shared by Sutopo on Sunday, showed that magma had created a lava dome which fills up a third of Mount Agung’s crater.
Prof Rothery said: “Lava domes tend to grow when the gas supply is insufficient to fragment the magma explosively into ash.
“However the effect of the dome could now be to act as a ‘stopper’ that inhibits the escape of the gas that is arriving near the surface with the magma that continues to arrive from below, so there could be a build up of gas below the dome followed by an explosion that destroys the dome and sends it skywards as an eruption column.
“This means that the risk of a major eruption has not passed.
“Another scenario is that the supply of magma (and gas) will wane, and the crater will be left with an intact lava dome on its floor after the eruption has petered out.”
The BNPB Facebook page has also shared an image of the lava dome on Saturday alongside another photograph of the empty crater in late October.
Professor David Pyle, from the University of Oxford, said: “Mount Agung remains active, and satellite images show how a blocky pile of lava is growing slowly within the crater.
“At night, the radiant glow from this hot lava appears to light up the crater, and the steam plume above the volcano.
“This behaviour is typical of many erupting volcanoes, and is mainly a reminder that the activity at Agung has not yet died down.”
He confirmed that Mount Agung was currently erupting with occasional emissions of ash and intermittent effusion of lava into the crater. This kind of volcanic activity could continue for some time.
Asked if the build-up of lava was sign that there could be a major eruption, he said: “No.
“The eruption of lava shows that there is an active supply of molten magma from within the volcano to the crater; but it doesn’t indicate whether, or how, the activity might change in the future.”
In late November, Bali was put on high alert when the volcano erupted and sent ash columns into the sky. Cold lava also poured down the volcano’s slopes.
Thousands of tourists were stranded due to flight cancellations and the temporary closure of airports on Bali and the neighbouring island of Lombok.
This month the volcano has been intermittently erupting and sending up plumes of steam and ash, but on a much smaller scale than before.