T

he Vulcanology and Geological Disaster Mitigation Center (PVMBG) has advised residents living around Mount Semeru in East Java to raise their alertness in the event of an eruption, despite signs that volcanic activity is receding.

PVMBG head Surono said Semeru was currently showing irregular signs, far from its usual activities. Since its alert status was raised to the highest level on March 6 after an eruption, the center recorded a drop in eruptions and tremors from Feb. 6 to March 4, with 873 eruptions, or around 34 tremors daily, with three discharge tremors and 18 volcanic tremors.

Eruptions have further diminished from 63 on March 8 to 58 on March 9 and 41 on March 10, over the past five days.

"We received queries as to why Semeru has not shown signs of eruption visually, such as tremors but its status was instead raised," Surono said in Bandung on Thursday.

He added that Semeru was showing anomalies, evidenced by the drastic drop from up to 150 eruptions on normal days, to less than half that now. When it erupted on March 6, its crater had not emitted a significant amount of volcanic material, but only light smoke which spewed only 50 meters high, which was in stark contrast to its eruption in May last year when it discharged hot clouds up to 700 meters high.

"We have to be vigilant if its activities decline, especially when it is dormant, because lack of activity means Semeru is gathering its energy for a major eruption, although we hope it would vent its energy bit by bit," Surono said.

According to Surono, Semeru's status has not only gotten the attention of local residents but also commercial airlines due to dense flight traffic over the area.

The Australian Meteorological Agency has often request the latest reports on Semeru because it concerns the safety of that country's airline flights, which also pass over the volcano. Flight operators have expressed worry that ash containing high silica could pose risk to flights if it enters plane engines.

Head of PVMBG's western zone station Hendrasto said observations were carried out based on visuals and seismic records. He urged residents to be vigilant, especially when it rained over Semeru, to anticipate the possibility of lava floods in the Besuk Bang, Besuk Kobokan and Besuk Kembar rivers.