The slide, documented in the February 28 issue of the journal Nature, was measured by Global Positioning System satellites in November 2000. A 12- by 6-mile area moved 3.5 inches over a 36-hour period in the first "silent earthquake" ever recorded at an active volcano.
Such earthquakes are virtually undetectable on the surface, but can be measured by GPS recordings. Since the GPS system is relatively new, there is very little data on the phenomenon according to Peter Cervelli of the U.S. Geological Survey. Researchers with the USGS and Stanford University tracked the movement.
The 12- by 6-mile chunk that moved extends five miles into the earth's crust, making its mass roughly equal to that of a quarter-mile thick, Rhode Island-sized object, the researchers said.
An accompanying article in Nature by geophysicist Steven N. Ward, of the University of California at Santa Cruz, speculates that a land mass that size -- if it slid into the ocean in one cataclysmic event -- could trigger an enormous tsunami that could imperil coastlines as far away as California, Chile, or Australia.
A tsunami is a strong, fast-moving wave that can build to 100 feet high or taller as it speeds into shallow water near the shore. Ward said his computer models suggest that a massive slide at Kilauea could touch off an arc of destructive waves in nearly all directions, with the greatest force probably focusing toward the southeast, in the direction of Ecuador.
But Ward, and other scientists, caution that the tsunami risk is minuscule: No such tsunamis of this type have taken place in recorded history. The last such wave of which there is evidence occurred in Hawaii an estimated 200,000 years ago, he said.