Experts voiced guarded optimism Monday that a life-threatening eruption of Mount Sakurajima is not imminent, despite the volcano’s dramatic outburst in Kagoshima Prefecture the previous day.

Sakurajima, a quasi-island next to the city of Kagoshima, is in a virtually constant state of eruption and has logged 500 outbursts so far this year.

Sunday afternoon’s explosion sent a plume of smoke and ash 5 km into the sky, this time from the volcano’s Showa vent, which became active in 2006 after years of dormancy. The plume’s altitude was the highest from the Showa vent ever recorded, said the Meteorological Agency, which started collecting data in 2006.

Ash from the towering plume caused minor disruptions to local transportation as the JR Nippo Line was halted to clear the tracks, JR Kyushu officials said, adding some 500 passengers were affected.

The eruption also caused a lava flow spanning about 1 km, according to a local meteorological observatory.

Media reports said huge boulders were spotted rolling down the mountain.

No injuries or fatalities have been reported, and a no-go zone of 2 km has been set up around the crater.

When contacted by The Japan Times, a meteorological official in Kagoshima described the eruption as testament to the mountain’s “increasingly active status” over the years. But the official, who didn’t want his name released, said Sunday’s outburst should not be regarded as a direct harbinger of a bigger event, such as the 1914 Taisho eruption, which, along with a 7.1-magnitude earthquake, claimed 58 lives and left 112 people injured.

A huge caldera north of the Showa vent shows no sign of a magma buildup that would signal an imminent eruption, the official said.

Masato Iguchi, a chief researcher at Kyoto University’s Disaster Prevention Research Institute, agreed that a deadly eruption is not in the offing.

“The eruption Sunday is already subsiding, and there has been no report of a surge in quake frequency,” he said, adding the accumulated magma in the caldera beneath the volcano “is hardly enough to provoke a large-scale eruption.”

But he nonetheless stressed that the volcano could have a mammoth eruption “sometime in the future,” although he stopped short of suggesting when that may occur.

Toshitsugu Fujii, a volcanologist at the Crisis & Environment Management Policy Institute, likewise downplayed the danger, noting an aerotonometer set up by the Meteorological Agency near the mountain showed the eruption caused a shock wave that did not merit special attention. He also attributed the 5-km-high plume to a lack of wind that would normally carry the smoke away.

Sakurajima’s eruptions are just part of everyday life for local residents, said a Kagoshima municipal official who asked to remain anonymous for privacy reasons.

If an imminent violent eruption is detected, especially after a strong earthquake, the city would take immediate evacuation measures, he said.

Information from Kyodo added