Yogyakarta. Lava from Mount Merapi in Central Java began flowing down the Gendol River over the weekend, signaling an eruption could be imminent, a geologist said on Sunday.
The volcano, one of the world’s most active, last erupted in June 2006 shortly after the Yogyakarta earthquake, when a pyroclastic flow, or a fast-moving cloud of superheated gas, ran down its slopes and killed two people.
But Surono, head of the Volcanology and Geological Disaster Mitigation Agency (PVMBG), said the distension of the mountain’s slopes was much more rapid this time around, indicating a higher-pressure build-up of gas and hence a much more explosive eruption.
“We believe Merapi will erupt explosively, as it did in 1930, and not just spew gas like in 2006,” he said.
“However, that scenario is only a guess. No one really knows when Merapi will erupt and how much volcanic material it will spew out.”
The eruption in 1930 wiped out 13 villages on the slopes of the mountain, killing around 1,400 people.
The alert status for Merapi is currently “standby,” just one level below the alert for an eruption.
Sri Sumarti, the Merapi section head at the Volcano Investigation and Technology Development Institution (BPPTK), said thick clouds and mist over the weekend had prevented her team from measuring the mountain’s distension.
On Thursday, the volcanic cone was observed to be expanding by 8.5 centimeters a day, while on Friday the rate had picked up to 16.4 centimeters a day.
“We’ve also seen a dramatic increase in the number of multiphase volcanic earthquakes, from 321 on Friday to 525 on Saturday,” Sumarti said, referring to the tremors from volcanic activity.
“Lava spurts have also increased, from 93 on Friday to 183 on Saturday. We’re now on standby mode around the clock.”
She said there were two types of eruption, the first a Pelean eruption that has a pyroclastic flow with lava streams.
The second is a Plinian or Vesuvian eruption, which is far more explosive, throwing ash and rock more than 25 kilometers into the atmosphere, but does not always have a pyroclastic flow.
“Whichever we get, we must prepare for the worst,” she said.
Djarot Nugroho, head of the Central Java Regional Disaster Management Board, said about 53,600 people in the districts of Magelang, Boyolali, Klaten and Sleman were at risk and would have to be evacuated.
He added that 22 temporary shelters had been set up.
Hadi Prabowo, the Central Java provincial secretary, said Rp 25 billion ($2.8 million) had been allocated to respond to an eruption.
“We’re working with the police and the military, and we’re ready to face the threat from Merapi, which is quite frequent,” he said.
“We hope residents are ready to evacuate at a moment’s notice, to minimize casualties.”
Yogyakarta’s governor, Sri Sultan Hamengkubuwono X, said there was no evacuation order yet.
“We’re going to see the latest developments with the volcanic activity before issuing an evacuation order,” he said.
“The mountain never really fully erupts, it just kind of melts. I hope Mount Merapi doesn’t erupt this time. But we’ll still prepare evacuation plans for residents.”