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Asphalt Volcanoes
Regarding current Fun Times In The Gulf, it's certainly true that Deepwater Horizon has a long way to go before it's even close to the scale of Ixtoc 1 and other oil spills around the world, but that didn't stop me yelling "GODDAMN ****ING ****!" when I had a look at this website, which takes the current size of the oil slick and plots it over your home country.
And although it no way excuses those responsible for the current disaster, there are a fair number of natural oil leaks around the world - the famous tar pits of La Brea, and Pitch Lake in Trinidad, for example. Both of these have been around for tens of thousands of years ( which is not, admittedly, very reassuring ).
And on top of these, there's also the recent discovery of asphalt volcanoes deep underwater, where molten tar erupts from the sea bed, cools, and sets into mounds very like the A'a and pahoehoe lava flows of Hawaii. At the same time it boils the methane clathrates on the sea bed there, so it gets quite explosive.
The first were discovered in 2003 in a field of salt domes known as the Campeche Knolls in the Gulf of Mexico, where salt bodies rise from underlying rock.
One model that fits the Campeche volcanoes involves supercritical water - water from deep underground, very very hot, under extremely high pressure, melting its way at high speed up through the salt. Supercritical water can, unlike water under normal conditions, hold a great deal of dissolved hydrocarbons and other minerals. But the moment it hits the open water, the temperature and pressure drop, and the outer layers of the plume instantly set into solid asphalt, and the asphalt flow spreads rapidly across the surrounding sea floor, bubbling and bursting. Another report, with photo of tube worms on the asphalt, here.
In 2007, seven more were discovered near Santa Barbara, California. These, the result of a huge natural leak, were larger than a football field and as tall as a six-storey building, all made completely out of asphalt.
To quote one of the researchers, regarding the quantity of oil in the largest -
"enough to fuel my Honda Civic for about half a billion miles. [However] the quality of the material is very poor...It's not worth something like light sweet crude," said Valentine. The petroleum in the structure is more viscous than that which is usually found in underground wells. This is because it has had less time to "bake" under the Earth's heat before being released. In addition, as much as 20% of its mass is made of "junk"-microscopic organisms, sand, and miscellaneous materials that gradually accumulated in the oil."
Samples from the California mounds suggest that they took decades, or even centuries, to build up to their current size, and that they last erupted around 35,000 years ago - suspiciously close to a sudden spike in oceanic methane concentrations at that time. Some residual methane continues to bubble up, but at the time the lighter oils in the mix would have made for a huge oil spill at the surface, at the same time the heavier constituents were piling up into the volcanoes and contributing to a methane-fed bacterial Dead Zone surrounding the site.
Ecologically, both kinds of asphalt volcano are highly important to the deep-sea life in the area. Methane-eating bacteria, and chemosynthetic tube-worms thrive on the hydrocarbons, and the hard asphalt surface is colonised by clams and anything else that can't attach to soft mud. Photos of the Campeche mounds and lifeforms from them here.
And although it no way excuses those responsible for the current disaster, there are a fair number of natural oil leaks around the world - the famous tar pits of La Brea, and Pitch Lake in Trinidad, for example. Both of these have been around for tens of thousands of years ( which is not, admittedly, very reassuring ).
And on top of these, there's also the recent discovery of asphalt volcanoes deep underwater, where molten tar erupts from the sea bed, cools, and sets into mounds very like the A'a and pahoehoe lava flows of Hawaii. At the same time it boils the methane clathrates on the sea bed there, so it gets quite explosive.
The first were discovered in 2003 in a field of salt domes known as the Campeche Knolls in the Gulf of Mexico, where salt bodies rise from underlying rock.
One model that fits the Campeche volcanoes involves supercritical water - water from deep underground, very very hot, under extremely high pressure, melting its way at high speed up through the salt. Supercritical water can, unlike water under normal conditions, hold a great deal of dissolved hydrocarbons and other minerals. But the moment it hits the open water, the temperature and pressure drop, and the outer layers of the plume instantly set into solid asphalt, and the asphalt flow spreads rapidly across the surrounding sea floor, bubbling and bursting. Another report, with photo of tube worms on the asphalt, here.
In 2007, seven more were discovered near Santa Barbara, California. These, the result of a huge natural leak, were larger than a football field and as tall as a six-storey building, all made completely out of asphalt.
To quote one of the researchers, regarding the quantity of oil in the largest -
"enough to fuel my Honda Civic for about half a billion miles. [However] the quality of the material is very poor...It's not worth something like light sweet crude," said Valentine. The petroleum in the structure is more viscous than that which is usually found in underground wells. This is because it has had less time to "bake" under the Earth's heat before being released. In addition, as much as 20% of its mass is made of "junk"-microscopic organisms, sand, and miscellaneous materials that gradually accumulated in the oil."
Samples from the California mounds suggest that they took decades, or even centuries, to build up to their current size, and that they last erupted around 35,000 years ago - suspiciously close to a sudden spike in oceanic methane concentrations at that time. Some residual methane continues to bubble up, but at the time the lighter oils in the mix would have made for a huge oil spill at the surface, at the same time the heavier constituents were piling up into the volcanoes and contributing to a methane-fed bacterial Dead Zone surrounding the site.
Ecologically, both kinds of asphalt volcano are highly important to the deep-sea life in the area. Methane-eating bacteria, and chemosynthetic tube-worms thrive on the hydrocarbons, and the hard asphalt surface is colonised by clams and anything else that can't attach to soft mud. Photos of the Campeche mounds and lifeforms from them here.