The Mount Agung volcano on the Indonesian tourist island of Bali spewed ash and steam Tuesday, but authorities said its alert level remained unchanged.

National Disaster Mitigation Agency spokesman Sutopo Purwo Nugroho said the minor eruption began at about 5 p.m. and the plume rose about 700 meters (2,300 feet) from the volcano.

Bali's international airport remained open. Volcanologists say the eruption was caused by magma heating water, which is called a phreatic eruption, rather than a generally more dangerous eruption of magma itself, Nugroho said.

Agung's alert status was recently lowered to the second-highest warning level after several weeks at the highest level.

More than 140,000 people evacuated the region around the volcano when it was on high alert, though authorities urged some to return home who had left areas not in the official danger zone.

The number of evacuees dropped to about 30,000 after the alert level was lowered.

Nugroho said people should stay out of an exclusion zone that in places extends 7.5 kilometers (4.5 miles) from the volcano.

He said there hasn't been an increase in seismic tremors from the volcano. An escalation in tremors can indicate magma is rising inside the mountain.