MANILA, Sept. 16 (Xinhua) -- A Philippines volcano spewed ash on Friday, the Philippines Institute of Volcanology and Seismology said.
The institute said in its bulletin that Bulosan volcano in Sorsogon province "generated a steam-driven explosion" at 4:54 p.m. local time that lasted approximately four minutes.
Based on the seismic record it produced approximately 1,500-meter high dark gray ash plume that drifted towards the northeast of the volcano, the institute said.
Philippines disaster authorities in nearby Legazpi City said at least four towns were affected by the volcanic dust, urging them to be vigilant against sediment-laden stream flows and lahars in the event of heavy and prolonged rainfall.
The institute said alert level one remains in effect over the volcano. "This indicated that hydrothermal processes are underway beneath the volcano that may lead to more steam-driven eruptions," it said.
It also advised residents around the area not to enter with the 4-km radius permanent danger zone "due to the possibility of sudden and hazardous steam-driven or phreatic eruptions."
Moreover, the institute advised airline pilots "to avoid flying close to the volcano's summit as ash from any sudden phreatic eruption can be hazardous to aircraft."
Bulosan last erupted in November 1994, according to the institute records.
The Philippines also raised last week the alert level for the Mayon volcano after it exhibited "abnormal" signs that may trigger rockfalls and avalanches.
Bulosan volcano is about 70 km southeast of Mt. Mayon, which last erupted in November 2009, the institute records said.
Mt. Mayon and Bulosan are among the Philippines' most active volcanoes.
