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AYUMI NAKANISHI / STAR-BULLETIN
Tourists watched a lava flow from Kilauea volcano as it crossed an untouched part of Chain of Craters Road at sunrise on Aug. 19.




Prehistoric Kilauea blast
sent rocks 15 miles high



By Rod Thompson
rthompson@starbulletin.com

HILO >> Sometime around 800 A.D., Kilauea volcano, acting like a huge cannon, shot rocks 15 miles into the atmosphere, says Hawaiian Volcano Observatory scientist-in-charge Don Swanson.

The rocks, one weighing nearly 10 pounds, went so high they were caught by the jet stream and carried several miles before falling back to Earth, said Swanson, who has been studying the event.

An analysis of the rocks shows they were shot from 2 1/2 to 4 miles below the surface of the earth.

The force that produced the blast seems to have been carbon dioxide, Swanson said.

Recent studies have shown that Kilauea produces nearly twice as much of the gas as previously thought, he said.

But he and other scientists can't figure out how enough pressure built up to produce the blast, since carbon dioxide normally escapes through the tiniest cracks.

Its hard for even geologists to imagine rocks shooting four miles through the earth just to get to the surface.

Other volcanic vents in the world show signs of similar cannonlike behavior, but their action is theoretical.

"No one has seen this kind of thing happen, except maybe the Hawaiians," Swanson said.

The clues that led Swanson to envision a volcano-cannon were golf ball- and baseball-size rocks found as far as 10 miles south of Kilauea.

His first guess was that the rocks were shot out by a kind of eruption that includes a lot of lightweight pumice, which would carry them.

But when Swanson looked, the pumice wasn't there.

Next came the cannon idea, but since most of the rocks fell to the south, the cannon "barrel" would have sloped southward.

A 4-mile sloped "barrel" just doesn't fit geologists' information about Kilauea's interior.

So the theory was revised to a straight shot upward to where winds move at 40 to 70 mph.

How certain is all this? "We're in the early phases of our thinking and investigation of this," Swanson said.



Hawaii Volcanoes National Park

County of Hawaii


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