A huge earthquake that struck off the Solomons Islands today was another reminder of the power of the volatile "Ring of Fire", a vast zone of volcanic instability that encircles the Pacific Ocean.
The 8.0-magnitude earthquake was feared to have flattened villages in the Solomons, and generated small tsunami waves that reached Pacific nations' coasts, triggering emergency sirens and evacuations.
Australia's earthquake monitoring agency and the Pacific Tsunami Warning Centre said a wave measuring 90 centimetres had been recorded at Lata, on one of the Santa Cruz islands in the Solomons.
The Ring of Fire reaches from Indonesia to the coast of Chile in a 40,000 kilometre arc of seismic violence that unleashes earthquakes and volcanoes around the Pacific rim almost every day.
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.
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.
A 9.0-magnitude undersea earthquake off Japan in 2011 triggered a tsunami that left about 19,000 people dead or missing, and caused a meltdown at the Fukushima nuclear power plant in the world's worst atomic disaster in 25 years.
In 2007 a tsunami following an 8.0-magnitude earthquake killed at least 52 people in the Solomons and left thousands homeless.