Indonesia Warns Volcano Could Erupt at Any Time

Updated at 12:57 a.m. ET

Pressure building beneath a lava dome in the mouth of Indonesia's most volatile volcano could trigger one of its deadliest blasts in years, scientists warned Tuesday, as residents living along the slopes were moved to temporary camps.

Mount Merapi has seen increased volcanic activity in recent days and officials have raised the alert level for the 9,737-foot high mountain to its highest level, said government volcanologist Surono, who uses only one name.

It last erupted in 2006, when it sent an avalanche of blistering gases and rock fragments racing down the mountain that killed two people. A similar eruption in 1994 killed 60 people, while 1,300 people died in an eruption in 1930.

An avalanche of rocks spilled down Merapi's trembling slopes before dawn Tuesday and gusts of hot ash shot 150 feet into the air as the mountain groaned and rumbled.

The greatest concern, Surono told reporters, was pressure building behind a massive lava dome that has formed near the tip of the crater.

"The energy is building up. ... We hope it will release slowly," he said. "Otherwise we're looking at a potentially huge eruption, bigger than anything we've seen in years."

Sri Purnomo, the head of Sleman district on Java island, where Mount Merapi is located, said officials were warning some 11,400 villagers living on the mountain's southern slope to prepare for "urgent evacuation."

Hundreds have already been relocated to makeshift camps set up at government buildings and sports fields more than six miles from the mountain's base, most of them elderly residents and children.

"I just have to follow orders to take shelter here for safety even though I'd rather like to stay at home," said Ponco Sumarto, 65, who arrived at one of the camps with her two grandchildren.

She said her children stayed at home to take care of their livestock and crops.

There are more than 129 active volcanoes to watch in Indonesia, which is spread across 17,500 islands and is prone to eruptions and earthquakes because of its location within the so-called "Ring of Fire" — a series of fault lines stretching from the Western Hemisphere through Japan and Southeast Asia.

The most recent was Mount Sinabung in North Sumatra province. It had been dormant for four centuries before springing to life in August but has since quieted and refugees from its slopes have returned home.

Meanwhile, a strong earthquake hit late Monday off the western coast of Indonesia's Sumatra island, but no damage or casualties were immediately reported.

The 7.5-magnitude temblor struck at a depth of 9 miles on a small island off Sumatra, the U.S. Geological Survey said. A massive earthquake and tsunami struck off the same island in 2004.