Jane J. Lee in Honolulu

The Exxon Valdez oil spill is not just an awful memory. Oil from one of the most devastating environmental disasters in U.S. history still clings to boulder-strewn beaches in the Gulf of Alaskaand could stick around for decades. Researchers presented evidence of a lingering, foamy, mousse-like emulsion this week at the Ocean Sciences meeting in Honolulu, Hawaii.

Chemical analyses find that this 25-year-old oil is from the Exxon Valdez spill, when the tanker ran aground on Bligh Reef in Prince William Sound (map) in 1989. And to the surprise of the scientists, the oil still has most of the same chemical compounds as oil sampled 11 days after the initial spill. (See "Exxon Valdez Anniversary: 20 Years Later, Oil Remains.")

The oil's presence in areas that were cleaned right after the spill 25 years ago points to the need to monitor certain environments long after the visible effects disappear, the researchers say.

It's Like Mayonnaise

There are two main reasons why there's still oil on some of the beaches of the Kenai Fjords and Katmai National Parks and Preserves in the Gulf of Alaska, explains Gail Irvine, a marine ecologist with the U.S. Geological Survey and lead researcher on the study.

When the oil first spilled from the tanker, it mixed with the seawater and formed an emulsion that turned it into a goopy compound, she says.

"When oil forms into the foam, the outside is weathering, but the inside isn't," Irvine explains. It's like mayonnaise left out on the counter. The surface will crust over, but the inside of the clump still looks like mayonnaise, she explains.

When that foamy oil met the boulders and cobbles of beaches in the Gulf of Alaska, it plopped down between and under the rocks, and it's still there.

PHOTOGRAPH BY GAIL IRVINE, U.S. GEOLOGICAL SOCIETY

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Oil From the Exxon Valdez Spill Lingers on Alaska Beaches