Sept. 22 (Bloomberg) -- Indonesia raised an alert for a volcano in the eastern part of Java, its most densely populated island, to its highest since the last eruption in 1990, amid signs that it may erupt.

Mount Kelud, in Kediri, ``has been showing increasing activity,'' Surono, director of volcanology and mitigation of geological disasters at the Department of Energy and Mineral Resources, said today. ``It's difficult to predict when the eruption may happen. The activity may even subside.''

The 1,731-meter (5,679-foot) volcano has emitted more than 300 metric tons of carbon dioxide a day in the past few days, or triple the normal measure, Surono said in a telephone interview. The alert was raised more than a week ago, and the volcano has been closed to tourists. If the alert is raised to its highest level, the government will evacuate residents.

Indonesia is located on the western side of the so-called Pacific Rim of Fire, an arc of volcanoes and geologic fault lines surrounding the Pacific Basin. The country has had two of the world's biggest volcanic eruptions in the past 200 years, Mount Tambora in 1815 and Krakatau in the Sunda Straits in 1883.

Earthquakes, which shook buildings as far away as in Singapore, have also struck near Indonesia's island of Sumatra in the past two weeks. An 8.4 magnitude quake, the world's strongest in 2 1/2 years, hit the region on Sept. 12, leaving at least 23 people dead.

Lava and Gas

Last month, Mount Karangetang, on Siau island in North Sulawesi, was given the highest alert status as it spewed lava and gas, forcing the evacuation of 600 people from the area.

Kelud had been erupting at intervals of about 15 years, or between 24 and 30 years, before 1990, Surono said by phone from Bandung, West Java province. Kelud's worst eruption in 1586 killed about 10,000 people.

A system to curb the flow of Kelud's lava has been in place since 1926, using seven rivers that function as canals to drive the lava into man-made lakes, Koran Tempo daily reported today, citing Umar Rosyadi, head of Kediri's volcano monitoring center.

Other signs that show Kelud may erupt include the change in the color of its crater, the report said. Its magma is at a depth of 4.2 kilometers (2.6 miles) below the ground now, compared with as deep as 10 kilometers normally, the newspaper reported, citing Rosyadi.

Still, Surono said that lower water levels in the volcano may reduce the impact of an eruption.

``Kelud used to have a very large body of water in its crater, as much as 40 million cubic meters of water. Now there is only 2 million cubic meters,'' Surono said. ``When lava is mixed with a great volume of water, the result would be greater devastation. The lower liquid levels would cut down the distance covered by the lava, implying less damage.''

To contact the reporter on this story: Wahyudi Soeriaatmadja in Jakarta at wahyudi@bloomberg.net.

Last Updated: September 22, 2007 02:53 EDT