Mount Mayon: Restless giant in a volcanic land

More than half a million people live on or around Mt Mayon's slopes

By CNN's Joe Havely

(CNN) -- Mount Mayon is the most volatile of more than 50 volcanoes -- 22 of which are considered active -- that are scattered across the Philippine archipelago.

An almost perfect cone-shape, Mayon last erupted in February 2000, forcing some 68,000 people to flee their homes.

Since 1616 when records began the 2,464 meter volcano has erupted at least 47 times.

Its most violent episode occurred in 1814 when more then 1,200 people were killed as an entire town was buried in mud and rocks.

Mayon's slopes, like many volcanoes in the country, are home to thousands of farming communities who make use of the fertile soils provided by the volcanic activity despite the occasional risk of eruption.

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Over the centuries flows of mud and hot volcanic gases -- known pyroclastic flows -- from the volcano's eruptions have wreaked devastation on lowland population centers that surround Mount Mayon.

Powerful typhoons which hit the country on a regular basis add to the deadliness of Philippine volcanoes with heavy rains often turning fields of volcanic ash into raging mudflows.

Nonetheless, for most people who make their living from the mountain, the extraordinary fertility of the area is attractive for farming.

An estimated 560,000 people live within 15 kilometers of Mayon's summit. The largest township is Legazpi City with a population of around 120,000.

Ring of fire

The extent of volcanic activity in the Philippines is governed by the country's location at the meeting point of several of the earth tectonic plates -- massive fields of rock that form the surface of the Earth floating on top of molten magma beneath.

The 1991 eruption of Mt Pinatubo left more than 840 people dead

Situated in the western Pacific, the Philippines forms part of the Pacific rim's co-called 'ring of fire'.

Most volcanoes in the country are located on the eastern side of the archipelago where the oceanic Philippine Plate is sliding -- or subducting -- under the Asian Plate.

The most devastating eruption in recent Philippine history occurred in June 1991 when Mount Pinatubo, a volcano many thought to be extinct, suddenly and violently burst back into life.

Having been dormant for more than 400 years, the eruption sent more than 5 billion cubic meters of ash and other debris into the atmosphere.

The explosion -- the second most powerful volcanic eruption of the twentieth century -- and subsequent devastating mudflows killed at least 840 people and displaced more than a million.

In the days that followed, a series of explosions sent clouds of debris more than 20 km into the sky, blanketing towns in the area with layers of ash so thick that many buildings simply collapsed under the weight.