Candra Malik & Dessy Sagita
Yogyakarta. More than five weeks since Mount Merapi began erupting, the government has downgraded the alert level for the volcano but is maintaining the 2.5-kilometer exclusion radius.
Surono, head of the Volcanology and Geological Disaster Mitigation Agency (PVMBG), announced the downgrade from level four to level three on Friday, adding it was based on visual and instrument monitoring of the volcano, whose eruptions since Oct. 26 have killed 353 people.
“There has been a significant reduction in seismic activity,” he said. “The deformation of the volcanic cone has also been observed as being stable.”
He warned, however, that there was still the danger of lahar, or volcanic mud, swamping places downstream.
“There’s still about 1.5 million cubic meters of volcanic material lying loose on the slopes,” he said. “Heavy rains there could cause landslides and lahar that would hit Cangkringan, Ngemplak and Pakem subdistricts in Sleman, Yogyakarta, via the Gendol and Boyong rivers.”
Surono did not rule out the possibility of more eruptions in the near future.
“Toward the end of the eruption phase, a lava dome usually forms to block the flow of magma,” he said. “Such a dome had already formed earlier, but was destroyed in the November 5 eruption.”
That blasts have thrown rocks and ash more than 10 kilometers into the atmosphere, making them Merapi’s biggest eruptions in more than 100 years.
Surono added that without a lava dome to contain its explosive power, a future eruption could send rock and lava flowing in all directions.
For these reasons, the PVMBG has maintained the 2.5-kilometer exclusion zone around the crater of the volcano and has advised residents to stay at least 300 meters away from the rivers flowing down its flanks.
“We also recommended that the local governments revise their zoning plans by identifying those areas that are prone to threats from Merapi’s eruptions,” Surono said.
“If an area is considered too risky for settlement, we also recommend relocation to some place safer. The eruptive characteristics of Merapi have changed, and it would be wise to take note.”
The call to stay alert for lahar has been echoed by the National Disaster Management Agency (BNPB).
“There are 12 rivers that flow into Yogyakarta and Central Java from Merapi,” Sutopo Purwo Nugroho, BNBP’s director of disaster risk reduction, said on Friday.
“Anyone living within 300 meters of these rivers must remain alert at all times.”
He added that authorities had set up early warning systems along some of the rivers to give notice of the muddy torrents, which are likely to happen until at least March next year, when the rainy season is expected to end.
On Tuesday, Yogyakarta Mayor Herry Zudianto declared emergency status in the city after lahar brought by the Code River flooded hundreds of homes and forced thousands of residents to evacuate.
The BNPB is also overseeing the construction of 2,613 temporary homes in villages damaged by the eruptions in Yogyakarta and 366 in Central Java.
BNPB Chairman Syamsul Maarif said construction of the homes would be finished this month.
“The families occupying them will each get Rp 5,000 and 400 grams of rice daily for a month,” he said.
With the alert status for Merapi now downgraded, Mount Bromo in East Java becomes the only volcano in the country still on level-four alert. The volcano began erupting on Nov. 26. Since then, however, there has been a lull in volcanic activity.