Formation and distribution Asphalt volcano

a bathymetric depiction of 7 asphalt volcanoes discovered west of santa barbara in 2007.

the tar relatively hot when comes out of seafloor, undersea lava flows, cooled colder seawater around it. produces forms similar distinctive a , pahoehoe types of basalt lava flow seen in places hawaii. similarity tar heats methane hydrate , causes explode free gas, similar action hot lava has on groundwater in phreatomagmatic eruptions.

the team proposed asphalt volcano formation theory in paper published in eos. article suggested water heated past critical point underneath seafloor found passageway surface, salt dome, , carried heavy load of hydrocarbons , dissolved minerals. special property of such critically heated water can mix oils, whereas normal water cannot. same process attributed formation of black smokers. once water reaches surface, cools, , carrying capacity drops. lighter compounds in mixture escape surface, while tar , other heavier materials remain on seafloor, building asphalt volcano s structure.

in 2007, 7 more such structures discovered off coast of santa barbara, california. largest of these domes lies @ depth of 700 ft (213 m). structures larger football field , tall six-story building, made out of asphalt. unusual features first noted ed keller on bathymetric surveys conducted in 1990s, , first viewed team led david valentine in 2007, utilizing dsv alvin. samples brought testing @ university campus , woods hole oceanographic institution.

two further dives dsv alvin in 2009 , detailed photographic survey of area autonomous underwater vehicle sentry showed many similarities volcanic flows, including flow texture , cracking of asphalt layers. carbon dating puts structures @ between 30 , 40 thousand years old. had @ 1 time been prolific source of methane. 2 largest structures, less 1 km (1 mi) apart, pocked pits , depressions, sign of methane gas bubbling long ago. although structures still emitting residual gas, @ present amounts small have effect. amount of crude oil in largest of structures alone enough fuel honda civic half billion miles. [however] quality of material poor...it s not worth light sweet crude, said valentine. petroleum in structure more viscous found in underground wells. because has had less time bake under earth s heat before being released. in addition, as 20% of mass made of junk —microscopic organisms, sand, , miscellaneous materials gradually accumulated in oil.

analysis of samples collected mounds suggest required several decades, centuries, build current bulk, , volcanoes last erupted around 35,000 years ago. in addition may account mysterious spike in oceanic methane concentrations around 35,000 years ago. methane forms naturally alongside petroleum underneath structure, , while petroleum flows have long abated, residual methane continues bubble up. burst of methane have caused rapid increase in population of methane-eating bacteria, in turn caused decrease in oxygen in water, possibly causing dead zone, in addition large amounts of crude oil released environment.

the presence of these structures provides hard surface on life can grow, surrounding ocean floor muddy. similar happens on seamounts, resulting in place ecological hub.