Scientists marvel at “asphalt” volcanoes

Some 10 miles (16 km) off the coast of San­ta Bar­ba­ra, Calif., a se­ries of strange land­marks rise from the ocean floor. They’ve been there for 40,000 years, hid­den in the Pa­cif­ic’s murky depth­s—un­til now, sci­en­tists say.

They’re called as­phalt vol­ca­noes.

“They’re mas­sive fea­tures, and are made com­pletely out of as­phalt,” said Da­vid Val­en­tine, a geo­sci­en­tist at Uni­vers­ity of Cal­i­for­nia at San­ta Bar­ba­ra and the lead au­thor of a pa­per pub­lished on­line this week in the jour­nal Na­ture Ge­o­sci­ence. “They’re larg­er than a football-field-long and as tall as a six-story build­ing.”


sea Ice Age domes lies at a depth of 700 feet (220 me­ters), too deep for scu­ba div­ing, which ex­plains why hu­mans haven’t seen them, said Don Rice, di­rec­tor of the U.S. Na­tional Sci­ence Founda­t­ion’s Chem­i­cal Ocean­og­ra­phy Pro­gram, which funded the re­search.

Asphalt is a sticky black sub­stance found in pet­ro­leum and often used for pav­ing. In so-called “as­phalt” roads, though, grav­el or sand are mixed with the true as­phalt, which sol­id­ifies at cooler temp­er­atures.

Val­en­tine and col­leagues first viewed the vol­ca­noes dur­ing a 2007 dive on a re­search sub­ma­rine dubbed Al­vin. Val­en­tine cred­its Ed Kel­ler, an earth sci­ent­ist at the uni­vers­ity, with guid­ing him and col­leagues to the site. “Ed had looked at some ba­thym­e­try [sea floor to­pog­ra­phy] stud­ies con­ducted in the 1990s and not­ed some very un­usu­al fea­tures,” Val­en­tine said.



A slab from an as­phalt vol­ca­no dis­covered on the sea-floor of the San­ta Bar­bara Chan­nel. (Cre­dit: Os­car Piz­ar­ro, U. of Syd­ney)

Based on Kel­ler’s re­search, Val­en­tine and oth­er sci­en­tists took Al­vin in­to the ar­ea in 2007 and dis­cov­ered the source of the mys­tery. Us­ing the sub’s robotic arm, the re­search­ers broke off sam­ples and brought them to labs for test­ing. In 2009, Val­en­tine and col­leagues con­ducted a de­tailed sur­vey of the ar­ea us­ing an au­ton­o­mous un­der­wa­ter ve­hi­cle, Sen­try, which takes pho­tos as it glides about nine feet above the ocean floor.

“When you ‘fly’ Sen­try over the sea floor, you can see all of the crack­ing of the as­phalt and flow fea­tures,” said Val­en­tine. “All the tex­tures are vis­i­ble of a once-flowing liq­uid that has so­lid­i­fied in place. That’s one of the rea­sons we’re call­ing them vol­ca­noes, be­cause they have so many fea­tures that are in­dic­a­tive of a la­va flow.”

Tests showed that these aren’t your typ­i­cal la­va vol­ca­noes, how­ev­er, found in Ha­waii and else­where around the Pa­cif­ic Rim. Us­ing an ar­ray of tech­niques, the sci­en­tists de­ter­mined that the struc­tures are as­phalt, formed when pe­tro­le­um flowed from the sea-floor about 30,000-40,000 years ago.

“The vol­ca­noes un­der­score a little-known fact: half the oil that en­ters the coast­al en­vi­ron­ment is from nat­u­ral oil seeps like the ones off the coast of Cal­i­for­nia,” said Chris Reddy of the Woods Hole Oce­a­no­graphic In­sti­tu­tion in Woods Hole, Mass., a co-au­thor of the pa­per.

world-science.net