New Rock Forms from Our Trash: Plastiglomerate

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Melted plastic trash on beaches can sometimes mix with sediment, basaltic lava fragments and organic debris (such as shells) to produce a new type of rock material, new research shows.

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The new material, dubbed plastiglomerate, will forever remain in Earth's rock record, and in the future may serve as a geological marker for humankind's impact on the planet, researchers say.

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Plastic pollution is a worldwide problem affecting every waterway, sea and ocean in the world, according to the Natural Resources Defense Council. First produced in the 1950s, plastic doesn't break down easily and is estimated to persist in the environment for hundreds to thousands of years. Plastic debris is also lightweight, allowing it to avoid being buried and becoming a part of the permanent geological record.

But while at Hawaii's Kamilo Beach, Capt. Charles Moore, an oceanographer with the Algalita Marine Research Institute in California, found that plastic, if melted, can actually become one with rocks, sediment and other geologic materials. (See Images of the Plastiglomerate Rock at Kamilo)

"He found some plastic had been melted to rocks, and other pieces of natural material had also been stuck on it," said study lead author Patricia Corcoran, a geologist at the University of Western Ontario (UWO) in Canada. "He didn't know what to call it. It's possible other people have found [the plastic conglomerates] at other locations before Captain Moore did, but nobody had thought to report it or identify it."

Corcoran attended a presentation Moore gave about his find, and she became immediately interested in investigating the material. So she, along with Moore and Kelly Jazvac, a visual artist at UWO, headed to Kamilo Beach to analyze the plastic formations.

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Kamilo Beach, located on the southeastern tip of the Big Island of Hawaii, is often considered to be one of the dirtiest beaches in the world. Because of the current flow and high wave energy of the area, the beach is covered with plastic debris pulled in from the ocean, including fishing gear, food and drink containers and multicolored plastic fragments called "plastic confetti." (Photos: Tsunami Debris & Trash on Hawaii's Beaches)

The researchers discovered there are two types of plastiglomerates at Kamilo Beach: In situ and clastic.

In situ plastiglomerate is more rare than the clastic variety, and forms when "plastic melts on rock and becomes incorporated into the rock outcrop," Corcoran told Live Science, adding that the melted plastic can also get into the rock vesicles, or cavities. Clastic plastiglomerates, on the other hand, are loose rocky structures, composed of a combination of basalt, coral, shells, woody debris and sand that have been glued together by melted plastic.