Largest Oil Spills
Over two decades after the devastating Exxon Valdez oil spill off the coast of Alaska, significant quantities of oil can still be found covering the state's shores and beneath gravel beaches, a new study has discovered.
Over 21,000 gallons of crude oil remains of the 11 million gallons of crude oil that gushed from the stranded tanker Exxon Valdez on the night of 23 March 1989. Traces of Valdez's oil have been detected as far as 724km away from the spill-site in Prince William Sound, and the toxic film that coats Alaska's shores remain a danger to wildlife, entire eco-systems and the lives of local people.
Writing in Nature Geoscience, a team of scientists found that oil just a few inches down was dissipating up to 1000 times slower than oil on the surface.
Despite Valdez not being up there with the largest oil spills of all time, it is one of the most high-profile and considered to be one of the worst environmental disasters of its kind, covering more than 2000km of coastline and killing thousands upon thousands of seabirds,fish and other water-dwelling creatures.
"Damage beyond anyone's imagination"
The economic impact was also significant as the region's fishing industry was heavily impacted, not to mention the money spent on clean-up efforts. Most clean-up operations in the area ended in 1992 with millions of dollars having been spent, because the remaining oil was expected to disperse within a few years.
However, a study a number of years after the spill discovered that the oil was disappearing at a rate of just four percent each year, far less than people expected and the new study compounds environmental concerns.
"The damage that [the spill] created is something beyond anyone's imagination," said Michel Boufadel, Temple University's Civil and Environmental Engineering chair, who has just completed research on why the oil persists.
As explained by National Geographic, oil naturally "disappears" through two processes: As the tide rises over an oil patch, the water sloughs off bits of oil, which then disperse into the ocean as tiny, less harmful droplets that can biodegrade easily. Secondly, bio-degradation occurs when bacteria or other microorganisms break down oil as part of their life cycle. However both these processes are slowed when oil is trapped among sand grains beneath the surface.
Exxon Valdez remains relevant today
In their paper, the team who conducted the new study observed that the upper layer temporarily stored the oil, while it slowly and continuously filled the lower layer, "You have a high amount of oxygen in the seawater, so you would think that the oxygen would diffuse in the beach and get down 2-4 inches (5-10cm) into the lower layer and get to the oil," said Prof Boufadel.
"But the outward movement of [fresh groundwater] in the lower level is blocking the oxygen from spreading down into that lower level."
The Exxon Valdez oil spill remains extremely relevant today. Last year, off the coast of Australia, a tanker grounded spilling 52,000 gallons of oil and shutting down local fisheries.San Francisco also saw the terrible effects of an oil spill in the bay in 2007.
Here NG Oil & Gas take a look at the world's largest oil spills.
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