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ount Merapi is showing interesting signs in its activities, says the Volcanic and Geological Disaster Mitigation Center (PVMBG).

Surono, the center head, said the new pattern was marked by significant numbers of low frequency (LF) earthquakes, considered a good sign of greater predictability.

He said observations on Merapi between midnight and 6 a.m. Sunday recorded seven LF earthquakes.

“These are what we have been expecting,” Surono said on Sunday.

These LF earthquakes, he said, indicated that there are still huge amounts of magma in the volcano, trying to get out. It indicates the gas in the magma is being released without enormous pressure.

This, he added, would probably be followed by the formation of a lava dome, as in past eruptions. Lava from the volcano would then be released slowly and not explosively as during last week’s eruptions, which claimed over 30 lives including that of Merapi’s spiritual gatekeeper — Mbah Maridjan.

Merapi has long been known for its specific type of behavior, resulting in a classic type of eruption with its own style. This is characterized by the slow expulsion of lava following the formation of a lava dome.

Last Tuesday and Saturday, however, the volcano showed unusual eruption styles that were explosive, accompanied by thundering sounds, sending out hot clouds as high as 3.5 kilometers up into the sky. Pyroclastic flows of ash, or ash clouds also traveled up to 10 kilometers down the mountain at high speed.

Head of Volcanic Technology Development and Research Center (BPPTK) Yogyakarta, Subandrio, said that his team had found high concentrations of up to 57 percent of silica in the material from Merapi, indicating high acid content.

“This probably is what has made the eruptions this time so explosive,” said Subandrio over the weekend, adding that the normal content of silica in Merapi’s volcanic ash was between 52 and 54 percent.

He also said that Tuesday’s and Saturday’s eruptions could have sent out some 2 million cubic meters of volcanic material, meaning that some five to six million cubic meters more of material were still inside the volcano, waiting to be released.

He said this prediction was based on the volume of volcanic materials Merapi discharged during a previous eruption, which was between seven and eight million cubic
meters.

Considering that Merapi was still showing high volcanic activity, the top alert status was still imposed on the area around the volcano. The PVMBG very strongly recommended that the areas within 10 kilometers of the peak of the volcano should be kept totally free of human activity.

Surono said that apart from Merapi, second top alert status has also been imposed on Mount Karangetan in Sangihe Talaud and on Mount Ibu in Halmahera.

“Nineteen other volcanoes have been in the third highest alert status for quite some time, some even before the same alert status was imposed on Mount Merapi,” he said.

Among the volcanoes in the third highest alert status, he said, were included Mount Papandayan, Mount Bromo and Mount Anak Krakatau. He said these alert status warnings had been imposed due to various local considerations.

“Each has nothing to do with the others. They have their own characteristics and they are located far from one another,” he said, adding that Indonesia was home to 129 active volcanoes.