A Moment of Science

Oil Spills , Naturally

It's a big deal when an oil tanker spills its contents into the ocean. And for good reason. But what about oil spills that aren't caused by humans?

Dead sea bird in oil contaminated water

Photo: davepatten (flickr)

Hundreds of thousands of animals including this sea bird have died during the Exxon Valdez disaster and other man-made oil spills, but naturally-made oil spills also pollute Earth's waters

When the Exxon Valdez dumped ten million gallons of oil into waters off the Alaskan coast, the massive slick killed hundreds of thousands of animals. Casualties included salmon, sea birds, seals, and bald eagles.

Oil Spills Made Natural

Not all oil spills are man-made. According to one study, the ocean floor off the coast of Santa Barbara, California has leaked the equivalent of as many as eighty Exxon Valdez-volume spills over the past several hundred thousand years.

Now, there are important differences between spills caused by poorly piloted tankers and natural seepage. When a ship dumps its load, almost all the oil is let loose at once, coating and contaminating everything in sight.

Natural spills, on the other hand, occur relatively slowly over long periods of time and are confined to a smaller area. So animals either avoid natural slicks or learn to live with them.

Where Did All The Oil Go?

One question that intrigues scientists about natural oil spills is what ultimately happens to all that crude? When it first seeps out, most of the oil rests on the water’s surface, creating natural slicks that can extend for miles. Some of the oil washes up on shore, some dissolves into the surrounding water, and some is eaten by microbes.

But scientists suspect that a good portion of the crude eventually sinks, and settles on the ocean floor. The next step in this research is to figure out how and why oil sinks and settles, and how it affects animals in the area.

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