'Ring of Fire' strikes again

The Ring of Fire stretches along the western coast of the Americas and through the South Pacific and on through Southeast Asia.

A massive earthquake that struck off Chile on Saturday revealed anew the ferocity of the volatile "Ring of Fire", a massive zone of volcanic instability that encircles the Pacific Ocean.

The 8.8-magnitude quake struck some 115 kilometers (70 miles) northeast of the city of Concepcion, killing 122 people, toppling buildings and triggering a tsunami that experts said was roaring across the Pacific.

Most of history's deadliest quakes, tremors and volcanic explosions have occurred along this weak line in the Earth's crust, including the eruptions of Krakatoa near Java and Mount St Helens in the United States, as well as the massive quake that sparked the Indian Ocean tsunami of December 2004.

The Ring of Fire stretches along the western coast of the Americas and through the island nations of the South Pacific and on through Southeast Asia.

It is an interconnected circle of fault lines -- cracks in the Earth's hardened upper crust -- which are under constant pressure from super-hot molten rock beneath.

Occasionally the fissures give in and explode, creating volcanic eruptions and causing the land on either side of the fault line to shift and buckle violently, triggering earthquakes.

The fault lines are actually the margins of huge plates of rock on which the continents sit. These plates are in constant motion.

According to the US Geological Survey, which studies seismic activity, there have been an average of 19.4 quakes of 7.0-plus strength on the Ring each year.

The 9.3-magnitude quake that struck Indonesia on December 26, 2004 unleashed tsunamis that crashed into Indian Ocean shorelines, killing more than 220,000 people.

The world's largest-ever registered tremor, the 9.5-magnitude Valdiva quake, shook Chile in 1960 and churned up a tsunami that killed scores in Japan and Hawaii.