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Plastic rocks! 

 (plastiglomerate)
A whole rainbow of bizarre colourful rocks are washing up all along our Dorset coastlines. They might look kind of pretty, or in more muted tones, be almost indistinguishable from the surrounding geology. But are they really just another disturbing example of the plastic crisis close to home?

PLASTIGLOMER…WHAT?

Plastiglomerate was first discovered in 2006 on Kamilo Beach, Hawaii. It was here that Oceanographer, Charles Moore discovered and collected samples of porous volcanic rock filled with molten plastic.

Years later, inspired by the photographs of Charles Moores plastic-rock conglomerates, Dr Patricia Corcoran and Professor Kelly Jazvac decided to visit Kamilo Beach and find out more about the mysterious rocks for themselves.

Kamilo Beach, Hawaii

Kamilo Beach, Hawaii

WHY KAMILO?

Kamilo Beach is well known for the vast array of plastics that wash up there. If you look up Kamilo Beach images on any search engine, you’ll be confronted with page upon page of horrifying pictures of plastic-coated beaches.

Being nearly 12km from the nearest paved road, visitors often camp there overnight and burn detritus on the beach to cook and keep warm. The remoteness and difficult access also makes beach clean-up operations rather tricky.

Hawaii and the Great Pacific Garbage Patch

Ocean gyres are huge systems of circular ocean currents, formed by both the Earth’s rotation and global wind patterns. There are 5 major ocean gyres, of which the North pacific subtropical gyre is that largest.

As ocean currents move the water around, waste and debris from the surrounding ocean is drawn into the calm centre of the gyre. Ocean gyres encircle vast areas of calm water, where the lack of movement means waste easily accumulates.

The Hawaiian Islands are located within the North Pacific subtropical gyre (aka the Great Pacific Garbage Patch). Ocean currents move in a clockwise direction here (anti-cyclone), depositing detritus along the eastern and south-eastern shorelines of the Hawaiian islands, which includes Kamilo Beach. It has been estimated that up to 90 per cent of the waste that washes up there is plastic!

Ocean Clean-up project estimated that the garbage patch in the North Pacific now covers over 1.6 million square kilometres! 

WHY ARE THEY ON THE BEACH?

When the two Geologists first noticed the plastic rocks in situ on Kamilo Beach, they assumed that it was the result of nearby volcanoes melting beach waste. However, the geologists soon realised that it was actually human action to blame.

The sand and plastic conglomerate the geologists found were the result of deliberate beach fires. The bonfires had melted the plastic detritus onto the sand and through the porous holes of the island’s volcanic rock, creating a kind of polymer amygdale. 

Corcoran and Jazvac took samples away and analysed them. This new discovery was thereon named ‘plastiglomerate’

Fossils of our future

burning plastic 

These strange, plastic rocks form when plastic melts and becomes stuck to hard organic material like stone, sand, shells and coral. Beach fires like those on Kamilo, waste burning (commonplace until fairly recently in the UK) or natural disasters are all causative factors in the formation of plastiglomerate. 

Plastic that melts into the porous holes of rock (vesicles) is also called a plastic amygdale. The long-term fate of plastiglomerate or plastic amygdale is still unknown. Some scientists and geologists believe these will become the fossils of our age. However, others have suggested that given the right conditions, they could become oil once again. Either way though, they definitely shouldn’t be part of the legacy we leave behind! 

THE LIFE OF A PLASTIC ROCK

  • Plastic is burnt
  • Heats melts it into molten plastic goo
  • Molten plastic goo sticks to sand, stones, shells and other plastic pieces on the beach
  • The plastic cools and hardens
  • Organic material is now trapped within the plastic, creating plastiglomerate
  • Plastiglomerate then becomes buried on the beach or is washed out to sea
  • Wave action wears away at the plastiglomerate, smoothing its surface or breaking it down into smaller pieces called ‘Clastic Plastiglomerate’
  • Heavier pieces, containing more stone and less plastic can then sink to the sea bed, lighter pieces will be more buoyant and float, occasionally sinking and resurfacing
  • Some pieces are thrown out by the sea and deposited on the beach at low tide. These plastic rocks will then either be collected by people, be washed back out to sea at high tide, or become buried.
  • These sunken and buried pieces of plastiglomerate could well end up being the fossils of today

 

NOT JUST KAMILO…COMING TO A BEACH NEAR YOU!

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Plastiglomerate may have been discovered and named in Hawaii, but it’s a global occurrence. The images used in this post show examples of some of the plastiglomerate found along our local Dorset coastline. The rocky beaches along Dorset’s Jurassic Coast, where washed up plastic was burnt until fairly recently is the perfect place to hunt for these rainbow rocks. Like nurdles, once you spot one, you’ll keep finding more! 

  • Have you found any plastic rocks on the beach?
  • What natural material can you identify in it?
  • Can you identify any of the plastic pieces within it?

References

Newer R, June 2014, Future fossils:plastic stone, The New York Times, Viewed 2 June 2021 <Future Fossils: Plastic Stone – The New York Times (nytimes.com)>

Trinastic J, July 2015, Plastic rock: the new anthropogenic marker in the geologic record, Nature Education, viewed 2 June 2021 <Plastic rock: the new anthropogenic marker in the geologic record | Eyes on Environment | Learn Science at Scitable (nature.com)>

Corcoran P L et al, June 2014, An anthropogenic marker horizon in the future rock record, GSA Today, viewed  2 June 2021. <GSA Today – An anthropogenic marker horizon in the future rock record (geosociety.org)>

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