Volcano may blow again, experts warn

Mayon has been increasingly active since January

By staff and wire reports

LEGAZPI, Philippines -- Authorities fear a lull in eruptions by a Philippines volcano may deceive thousands of residents into believing it is safe to return to their homes.

Many villagers have already started going back, despite a declaration of a state of calamity in the region around cone-shaped Mayon, which has a history of deadly eruptions.

Fountains of bright red lava and towering clouds of ash shot skywards as car-sized boulders tumbled down its slopes, leading Philippine Airlines to suspend all nearby flights at least a week.

A single massive explosion from the volcano -- one of the Philippines most active -- spewed ash more than nine miles (14.5 kilometers) high, with continuous columns of nearly 2,000 feet (600 metres), officials said.

VIDEO Maria Ressa on the Mount Mayon Volcano eruption in the Philippines Play video (QuickTime, Real or Windows Media)

Visibility dropped to near zero within hours as the enormous mushroom cloud began to settle, turning the green landscape gray.

About 23,000 villagers were evacuated overnight, and many returned Monday morning despite warnings from the government, civil defense authorities said.

But the volcano could spit lava and red-hot boulders for several days or even weeks, said Raymundo Punongbayan, director of the Philippine Institute of Volcanology and Seismology.

VIDEO CNN's Kathy Quiano reports on the eruption of Philippines' Mayon volcano (June 24) Play video (QuickTime, Real or Windows Media)   MORE STORIES ANALYSIS: A restless giant in a volcanic land      CNN.com Asia More news from our Asia edition

"I left because it was making strong noises," said Lorna Azona, among hundreds of villagers at an evacuation center. "The lava flow was getting strong."

Depending on lava flow, as many as 60,000 could be forced to evacuate to Legazpi, the biggest town nearby, said Jason Aragon, officer in charge of the evacuation. Legazpi is 12 kilometers (7.5 miles) from the volcano summit.

An elderly woman died of a heart attack during the evacuation and another died in an auto accident during the explosions.

On Monday, the danger zone was broadened to a five-mile radius of Mayon, and authorities called for the evacuation of residents within that area.

With the threat of rain remaining in the wake of a tropical storm, concerns rose over the possibility of flows of mud and ash like those that buried a town and killed 1,200 people in the volcano's worst known eruption in 1814.

The southeast portion of the crater showed visible signs of weakening Sunday and may give way in days, sending more lava down the slope of the volcano, scientists said.

Eduardo Laguerta, resident vulcanologist, said a lava dome about 100 feet wide had formed on the crater.

Collapsed domes have continuously been expelling rocks and pyroclastic flows -- superheated clouds of volcanic ash that travel down a volcano's slopes at up to 50 mph -- which instantly incinerate anything in their path.

Audible explosions shook the ground more than eight miles away as officials were preparing emergency shelters and evacuation plans, said emergency coordinator Cedric Dive.

The 8,118-foot Mayon, a well-known tourist attraction because of its near-perfect shape, began acting up in January, but had been at alert level 3 -- of a possible 5 -- for weeks.

After a brief 160-foot fountain of lava late Saturday, authorities raised the alert to 4, then quickly put it at 5 early Sunday afternoon, meaning an eruption was in progress.

Following past eruptions, farmers have often worked in their fields during the day and then returned to their families in evacuation centers at night. Mayon, 200 miles southeast of Manila, towers over farming communities in the Bicol region. The Philippines is in the Pacific "Ring of Fire," with frequent earthquakes and volcanic activity.

The Associated Press & Reuters contributed to this report.