for National Geographic News
The magnitude-6.3 earthquake that shook the Indonesian island of Java this weekend has so far killed about 5,700 people and left more than 100,000 homeless.
The devastating quake is at least the fourth geological disaster to strike Indonesia in 18 months (Indonesia map, music, and profile), highlighting the constant threat faced by residents of the Pacific Ocean zone known as the Ring of Fire. This tectonically active region rims the Pacific and includes Mount St. Helens, now erupting in Washington State.
The event also puts a spotlight on scientists' efforts to understand how and why quakes can cause different kinds and levels of damage.
On December 26, 2004, the Indonesian island of Sumatra was hit by the largest earthquake the world had seen in 40 yearsa magnitude 9.3.
The massive quake triggered a tsunami that left about 131,000 dead in Indonesia alone (news reports: "Tsunami in Southeast Asia: Full Coverage").
That event was followed on March 28, 2005, by another enormous earthquake, with a magnitude of 8.7, sparking fears of a second tsunami. But the deadly wave didn't materialize, and the death toll was about 320.
More recently one of Indonesia's many volcanoes, Mount Merapi, began erupting only a few dozen miles from the epicenter of this weekend's quake (related photo: Volcano Eruption Countered With Dance, Food).
The latest quake occurred on Saturday at 5:54 a.m. local time and had a magnitude of 6.3, the U.S. Geological Survey (USGS) reported on its Web site.
Same Plates, Different Results
Earthquakes and volcanoes are produced by the forces of plate tectonics, which cause the vast plates that form the Earth's crust to slowly but steadily collide.
Just south of Java, for example, the Australian plate is moving northward at about two and a half inches (six centimeters) a year.
When the Australian plate collides with the Sunda plate, which includes Java, the Australian plate is forced beneath the Sunda plate in a process called subduction.
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