Government volcanologists have raised the status of Mount Soputan in Minahasa, which straddles two regencies in North Sulawesi, while issuing a lahar-flow warning to people living near Mt. Gamalama in North Maluku and Mt. Merapi in Yogyakarta.
National Disaster Mitigation Agency (BNPB) spokesperson Sutopo Purwo Nugroho said the status of Mt. Soputan was raised a tier higher to alert, the second-highest level, as of Friday.
Sutopo said the local Volcanology and Geology Disaster Mitigation Center (PVBMG) reported white smoke reaching 50-200 meters high emitting from Soputan's crater and increased frequency of volcanic tremors. "We urge residents to not go within a 6.5-km radius of the crater," he said.
The BNPB said evacuations were not necessary as the nearest residential area was located 8 km from the crater.
With the increased warning level for Soputan, six volcanoes are now on alert status; the others are Mt. Gamalama in North Maluku, Mt. Slamet in Central Java, Mt. Sinabung in North Sumatra, and Mt. Karangetang and Mt. Lokon in North Sulawesi.
Mt. Lokon has been on alert status since July 2011, Mt. Karangetang since September 2013, Mt. Sinabung since April, Mt. Slamet since August and Mt. Gamalama since mid-December.
According to the agency's classification, the second-highest warning level indicates that a volcano has moved toward eruption, with seismic activities and related data showing that eruption or disaster resulting from its conditions is expected.
Following Mt. Gamalama's eruption last week, the Ternate Disaster Mitigation Agency (BPBD) issued a lahar-flood warning to residents of Ternate city, specifically those living near riverbanks.
"Rain has started falling in Ternate; there is possibility that lahar floods may occur like in 2011 and 2012," local BPBD head Hasyim Yusuf said as quoted by Antara news agency in Ternate on Saturday.
The volcano's eruption has resulted in volcanic ash piling up on the mountain's slope. The ash is expected to slide down into the rivers with rainfall.
Amid heavy rains on Thursday night, some residents in three subdistricts in North Ternate began preparing to evacuate as water containing volcanic material overflowed into the Tugurara River.
Hasyim said that although evacuations were not necessary, the agency called on the residents to remain cautious. Government officials and personnel had been notified to monitor river flows, he added.
The Yogyakarta Geological Disaster Investigation Agency has also issued a lahar warning to residents on the slope of Indonesia's most active volcano, Mt. Merapi.
The agency's officer Agus Budi Santoso said there was only a small possibility a lahar flood would occur.
"There is about 30 billion cubic material near Merapi's crater, which is quite small. The material has also hardened, making it more difficult to be flushed down by rain," Agus said.
With rainfall intensifying, residents living near riverbanks had been asked to remain cautious, he said.
Merapi, located on the border between Yogyakarta and Central Java provinces, last erupted in September 2013, spewing volcanic material reaching 2 km into the air.