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Scientists marvel at “asphalt” volcanoes

April 27, 2010
Courtesy of the National 
Science Foundation
and World Science staff

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.”

A topographic map shows ex­tinct as­phalt vol­ca­noes on the sea­floor off Cali­fornia. (Cre­dit: Dana Yoer­ger, WHOI)


The larg­est of these un­der­sea 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.


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Some 10 miles (16 km) off the coast of Santa Barbara, Calif., a series of strange landmarks rise from the sea floor. They’ve been there for 40,000 years, hidden in the Pacific Ocean’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 on-line this week in the journal Nature Geoscience. “They’re larger than a football-field-long and as tall as a six-story building.” The largest of these undersea 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. 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. 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.