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(Image credit: Martin Köhler, UQ. )
A huge stone set down numerous feet from the edge of a cliff in Tonga appears to have actually been carried by an ancient tsunami, making it among the greatest rocks moved by a wave in the world.
The stone, which was found in 2024 on the southern coast of the Tongan island of Tongatapu, sits 656 feet (200 meters) inland from the cliff edge, at an elevation of 128 feet (39 m) above water level. And it is massive, determining 45.9 x 39.3 x 22 feet (14 x 12 x 6.7 meters) and weighing over 1,300 lots (1,180 metric loads).
It’s the world’s biggest cliff-top stone and was initially recognized by residents. “We had been surveying the southern side of the island of Tongatapu looking along the coastal cliffs at evidence of past tsunamis,” lead author Martin Köhlera scientist at the University of Queensland in Australia, stated in a declaration. “We were talking to some farmers when they directed us to this boulder.”
Precisely how the huge rock ended-up on a cliff was uncertain. “I was so surprised,” Köhler stated. “It is located far inland outside of our field work area and must have been carried by a very big tsunami. It was quite unbelievable to see this big piece of rock sitting there covered in and surrounded by vegetation.”
According to a brand-new research study released online on 21 April in the journal Marine Geologythe stone– called Maka Lahi, which is Tongan for “big rock” — might have been transferred in its not likely home by a big tsunami that struck the island around 7,000 years earlier.
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The scientists determined the stone’s homes then designed how big a wave would require to be in order to deposit such a big rock up until now inland. They recommended that the stone initially sat at the cliff’s edge, however was cleaned inland by a tsunami wave that lasted around 90 seconds and depended on 164 feet (50 m) high– nearly the height of Niagara Falls.
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“We made a 3D model and then went back to the coast and found the spot the boulder could have come from, on a cliff over 30 metres above the sea level,” Köhler stated.
Based upon dating techniques including isotopes present in the rock, Köhler and coworkers think that the stone was most likely cleaned to its existing area a minimum of 6,891 years back, plus or minus 97 years. This date lines up with proof of a big tsunami that struck on New Zealand’s North Island– around 1,300 miles (2,000 kilometers) south west of Tonga– in between 7,240 and 6,940 years earlier.
The Maka Lahi stone might have moved since the wave’s arrival accompanied an earthquake– a “coseismic” occasion. “It is possible that the earthquake not only generated a tsunami that inundated the North Island of New Zealand but also triggered a coseismic landslide, which in turn produced a separate tsunami that deposited Maka Lahi,” the scientists composed in the paper.
The islands of Tonga lie in the South Pacific Ocean, an area that is exceptionally vulnerable to tsunamis due to being surrounded by tectonic plate limits referred to as the “Ring of Fire.”
Subduction zones– where one plate is required under another– or big undersea volcanic eruptions can create effective undersea earthquakes that can activate tsunamis. The Tongan islands lie near the Tonga Trench, where the Pacific Plate is being subducted underneath the Indo-Australian Plate, making it particularly susceptible to tsunamis.
In 2022, Tongatapu was struck by a 62.3 feet (19 m) tsunami activated by the eruption of the Hunga Tonga– Hunga volcano, with water reaching as far as 0.62 miles (1 km) inland.
“Tonga’s most recent tsunami in 2022 killed 6 people and caused a lot of damage,” Annie Laua seaside geomorphologist at the University of Queensland, stated in the declaration.
The scientists hope that this discovery of how far such a big stone was moved by a wave might assist Tonga and surrounding South Pacific countries get ready for big tsunamis.
“Understanding past extreme events is critical for hazard preparation and risk assessment now and in the future,” Lau stated. “The analysis strengthens our understanding of wave transportation of rocks to improve coastal-hazard assessments in tsunami-prone regions around the world.”
Jess Thomson is an independent reporter. She formerly worked as a science press reporter for Newsweek, and has actually likewise composed for publications consisting of VICE, The Guardian, The Cut, and Inverse. Jess holds a Biological Sciences degree from the University of Oxford, where she specialised in animal habits and ecology.
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