Scientists aboard the Scripps research vessel Roger Revelle this week solved a 45-year-old geological mystery.
In1960, Scripps oceanographer Dale Krause reported the discovery ofextraordinary deep-sea volcanic rocks in waters off Mexico, nearGuadalupe Island, approximately 200 miles south of San Diego. Whenbrought to the surface, the rocks spontaneously exploded "with a sharpsnapping sound," according to Krause.
Since then, only a fewother sites, mostly along the Mid-Atlantic Ridge, have been reportedwith similar "popping rocks." An attempt by the late Scripps ProfessorHarmon Craig to locate the site in 1984 proved unsuccessful, largelybecause the location of the original discovery lacked the precision oftoday's navigational technologies.
A team of U.S. and Mexicangeologists and student researchers aboard the Oct. 5th to 10th Revelleexpedition explored the region, including the area now known as PopcornRidge, in an attempt to precisely locate the source of Krause's poppingrocks and the unique information these rocks could provide aboutimportant Earth processes.
Three dredge hauls of Popcorn Ridge onOct. 7 recovered some volcanic rocks, though none "popped" on deck. Asonar survey of the seafloor revealed a small mound, which was lateridentified as a volcano, at the base of Popcorn Ridge, 3,200 meters(10,500 feet) below sea level. On Sunday, Oct. 9, the researchers hitthe jackpot with 'D-11,' or the 11th area dredged during theexpedition. D-11 is located along the flank of what the scientists arenow calling "Krause Volcano."
"As soon as we took the rocks outof the water we could hear them popping, much like a firecracker," saidBarry Eakins, a post-doctoral researcher at Scripps and one of thechief scientists on the cruise. "We were very excited because we knewthis was a big find."
Eakins and co-chief scientist DanaVukajlovich, a Scripps graduate student, say the loud popping soundsare due to high concentrations of volcanic gases trapped in bubbleswithin the lava rocks that explode when they escape the confining waterpressure of the deep ocean floor. The scientists consider therediscovery an important achievement because it will give them theopportunity to study these rare rocks in their Scripps laboratories andto compare them with the popping rocks from the Mid-Atlantic Ridge. Italso allows other scientists to return to the site, since the precise,GPS-marked location is now known.
Vukajlovich says that the rocksare important because the volcanic gases (such as carbon dioxide, watervapor, helium and argon) that are trapped in the bubbles did not escapeduring eruption and therefore should represent the concentrations ofthese gases in Earth's mantle. Eakins believes the rocks will not onlygive researchers more information about the inventory of these gaseswithin Earth, but also help them better understand the origin andhistory of Earth's atmosphere. "We expect that these rocks will be thesource of research for decades," Eakins said.
The rediscoveryalso will provide new information about seafloor volcanoes. Theresearchers characterized Krause Volcano that provided the poppingrocks as very young—from decades to a few centuries old—which is a rarefind.
"There are lots of volcanoes on the seafloor but most arequite old," said Vukajlovich. "It's exciting to find one that may bevery, very young and possibly still active."
According to ScrippsProfessor Peter Lonsdale, detailed analyses of the gas chemistry andisotopic composition by Vukajlovich and others in Scripps labs willprovide important information about the composition and origin of themantle beneath oceanic crust.
The Revelle cruise was funded by the University of California Ship Funds Panel of the Marine Operations Committee.
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