President Gloria Arroyo late Wednesday declared the evacuation complete and successful, but warned residents against returning to their farms and homes until advised to do so by the government.

They must "heed the advice of experts and disaster officials to stay out of harm's way," she said, pledging that evacuees "will not be kept from their homes a minute longer than is necessary."

Officials said the main problem is dissuading residents from returning to their homes amid an apparent lull in the eruptive phase.

Throughout the day cloud shrouded the 8,070-foot (2,460-meter) volcano in the central Philippines as lava continued to flow slowly down its southeastern face.

The civil defense office in Manila said troops and police have set up checkpoints on Mayon's lower slopes to enforce a "No Human Activity" zone within eight kilometers (five miles) of the crater.

Farmers have been sneaking out of evacuation centers in the morning to work their farms on the fertile volcanic soil and guard their property.

Evacuation efforts were also complicated by communist guerrillas, who attacked an infantry unit evacuating residents near Daraga town close to the slopes of the volcano, the military said. Five soldiers were injured.

Relief agencies and residents are bracing for a long stay in makeshift evacuation centers, mainly schools.

"For the time being, food is not the problem," Legaspi City mayor Noel Rosal said, but appealed for help from the national government.

He said the effort could be sustained until the end of the week but if the evacuation drags on for weeks it will deplete the city's calamity fund.

It costs about 367,000 pesos (7,140 dollars) a day to feed and house the estimated 10,802 people sheltering in Legaspi's schools.

Arroyo on Wednesday ordered her budget department to prepare an extra 250 million pesos (4.86 million dollars) in calamity funds to augment the 76 million pesos earlier disbursed by the national government. She is expected to visit the area this weekend.

Schoolrooms are housing up to 30 evacuees who sleep on the cold concrete floor and are fed with tinned meat and instant noodles.

Local officials though are experienced in dealing with Mayon, which has erupted around 50 times in the past 400 years, most recently in 1993 when 77 people died.

The Philippine Institute of Volcanology and Seismology said that after an upsurge of activity on Monday the volcano was quieter on Tuesday and Wednesday.

From 109 volcanic quakes on Monday, only 21 were recorded on Tuesday. The amount of sulphur dioxide expelled also fell by nearly half. It has been quietly belching out lava since July 15.

However, the institute said such swings in activity were an anomaly and warned that a hazardous eruption could still take place within days.

"Anything above 500 tonnes (of sulphur dioxide emissions) is an indication" of volcanic unrest, said Ernesto Corpuz, head of the volcano monitoring division.

He noted that despite lower readings of sulphur emissions, a column of black, steaming lava was still oozing from the crater and snaking down a channel on its slopes.

This indicates lava is still pushing out toward the crater, which has been largely obscured by clouds since Monday.

Renato Solidum, head of the institute, said such swings in readings were "typical of Mayon" and stressed that they would not lower the alert level until they see about a week of lower volcanic activity.

He also warned that the "gravitational pull" of the full moon this week could trigger an explosive eruption.

The fluid Earth

The conclusion is based on a new computer model that assumes that over timescales of a few years to thousands of years, the surface of the Earth behaves like a very thick fluid.

"Imagine honey or molasses, only a billion, billion times more viscous," said study leader Valentino Barletta of the University of Milan in Italy. If a heavy object is placed on the surface of such a fluid, it sinks until a balance is reached between the forces of gravity pulling it down and the buoyancy keeping it afloat.

"When you remove the weight, the viscous fluid takes some time to refill the depression that's left behind," Barletta told LiveScience.

This is happening in the Alps. As the glaciers melt and the mountains are freed of their heavy burdens, the surface of the Earth springs back very slowly. This effect is well studied and it occurs in North America, too.

The region where the most uplift is occurring is in the French Alps near Mount Blanc, the tallest mountain in Western Europe. The mountains in this region are growing at a rate of about .035 inches per year. In 50 years, they will be about 1.8 inches taller than today. The average maximum growth for the rest of the Alps is a more modest .013 inches per year.

Glacier shrinkage accounts for half of the observed increase, while other geological factors, such as active shifting of the Earth's tectonic plates, drainage and erosion, are responsible for the rest, the researchers say.

The effects of global warming

Glaciers have been shrinking almost continuously since 1850, but the process has sped up in recent decades because of global warming, Barletta said.

Other studies found that from 1850 to the 1970s, glaciers in the European Alps shrunk by 35 percent. In only the past 30 years, however, the rate of melting has accelerated to the point that the 5,150 glaciers now cover only 50 percent of the area they once did.

Some scientists estimate that if summer air temperatures warm by 5 degrees Fahrenheit (3 Celsius) by the end of the century, 80 percent of the Alps' glacial covering will be gone by 2100; if temperatures increase by 9 degrees Fahrenheit (5 Celsius), the Alps will be almost completely ice-free by century's end.

Elsewhere, scientists have found that melting permafrost has caused portions of mountains to crumble and is making the ground sink right out from under buildings and railroads.

Whether the glaciers disappear or not, the Alps will continue to rise, pushed upwards by other geological forces until complete relaxation is reached, something that could take hundreds or thousands of years, Barletta said.

"We will unfortunately keep seeing cases at least until September, when the virus starts to slow down because of the cold weather," said Dr. Onder Ergonul, an associate professor at Marmara University, who has been involved with the government's response to the outbreak.

Most of the cases have occurred in six provinces in the Black Sea and Central Anatolia region: Tokat, Sivas, Gumushane, Amasya, Yozagat and Corum.

Authorities at the World Health Organization are awaiting further information from the Turkish government, including where the other cases have arisen. Turkish authorities say no cases have been reported in the tourist areas along the Mediterranean coast.

By Aug. 4, there were 242 cases of the disease, including 20 deaths, making it the largest reported outbreak since it was first identified in 1944, authorities said.

Last week, a nurse treating Crimean-Congo hemorrhagic fever patients died after being infected accidentally by a needle. To date, four health care workers have been infected, though there have not been any reports of the virus spreading in hospitals.

"There have been large outbreaks of this virus before, but we are concerned about the size of this particular outbreak in Turkey," said Dr. Bernardus Ganter, the World Health Organization's Regional Adviser for Communicable Diseases in the European Region.

One of the reasons for the increased numbers, Ganter said, could be a more sophisticated detection system. Turkey's first outbreak of the disease was in 2002, and surveillance has strengthened considerably since.

"We are reassured that the outbreak appears limited to only one part of Turkey, in Anatolia," said Ergonul. More than 90 percent of cases have been reported in people who have had direct contact with animals, according to Ergonul.

In an attempt to control the outbreak, Turkish authorities have instituted stronger surveillance for the disease across the country, and are attempting to educate the population about how they can minimize the risks of contracting the disease by avoiding contact with ticks.

Veterinarians and entomologists are also looking at ways to control the tick population.

With several previous outbreaks of the disease in recent years, Turkey has considerable expertise in treating patients.

WHO has been in frequent contact with the Turkish Ministry of Health, and is ready to send teams to the region if requested to do so. Ganter said the transmission season was expected to last until October.