How a Two-Story Boulder Ended Up on a 120-Foot-High Cliff
Just a stone's throw from the ocean, indeed.
Small family farms dot the southern coast of Tongatapu, the largest island of Tonga in the South Pacific. But something lies amid the cassava and banana plants that doesn't belong: a staggeringly large, off-white boulder.
The rock, which features prominently in Tongan mythology, was recently scrutinized by scientists. New results suggest that the object was transported inland thousands of years ago when tsunami waves breached a 120-foot cliff. That event might have been set in motion by an earthquake in the nearby Tonga-Kermadec Trench, the team reported in the journal Marine Geology.
From Japan to the Bahamas, scientists have spotted hulking rocks that simply don't fit their surroundings. Such boulders were likely transported by moving water, and the powerful waves of tsunamis are often invoked as culprits.
Last July, researchers traveled to Tongatapu to analyze several coastal boulders. The team got a tip from a group of Tongan farmers about a boulder nearby on farmland belonging to the Teisina family.
That boulder turned out to be roughly the size of a two-story house. 'It was unreal,' said Martin Köhler, a geoscientist at the University of Queensland in Australia, who led the research. The rock, made of limestone, was nearly completely camouflaged by vegetation. Köhler's team surveyed the rock, known locally as Maka Lahi or 'Big Rock,' and calculated that it weighed more than 1,300 tons.
Maka Lahi is more than 650 feet inland. As there's nothing taller around, the rock must have been dislodged from its earlier home by one or more enormous waves, the team surmised.
Using computer simulations, the researchers modeled waves of different heights that rolled in anywhere from every 10 to 600 seconds. Waves of at least 160 feet high were needed to dislodge the boulder and send it rolling or sliding to its final resting place. Based on the age of the flowstone growing on the lower half of the boulder, the researchers estimated that the massive waves that transported Maka Lahi struck about 7,000 years ago, before the human occupation of Tonga. — KATHERINE KORNEI /NYT
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How a Two-Story Boulder Ended Up on a 120-Foot-High Cliff
Just a stone's throw from the ocean, indeed. Small family farms dot the southern coast of Tongatapu, the largest island of Tonga in the South Pacific. But something lies amid the cassava and banana plants that doesn't belong: a staggeringly large, off-white boulder. The rock, which features prominently in Tongan mythology, was recently scrutinized by scientists. New results suggest that the object was transported inland thousands of years ago when tsunami waves breached a 120-foot cliff. That event might have been set in motion by an earthquake in the nearby Tonga-Kermadec Trench, the team reported in the journal Marine Geology. From Japan to the Bahamas, scientists have spotted hulking rocks that simply don't fit their surroundings. Such boulders were likely transported by moving water, and the powerful waves of tsunamis are often invoked as culprits. Last July, researchers traveled to Tongatapu to analyze several coastal boulders. The team got a tip from a group of Tongan farmers about a boulder nearby on farmland belonging to the Teisina family. That boulder turned out to be roughly the size of a two-story house. 'It was unreal,' said Martin Köhler, a geoscientist at the University of Queensland in Australia, who led the research. The rock, made of limestone, was nearly completely camouflaged by vegetation. Köhler's team surveyed the rock, known locally as Maka Lahi or 'Big Rock,' and calculated that it weighed more than 1,300 tons. Maka Lahi is more than 650 feet inland. As there's nothing taller around, the rock must have been dislodged from its earlier home by one or more enormous waves, the team surmised. Using computer simulations, the researchers modeled waves of different heights that rolled in anywhere from every 10 to 600 seconds. Waves of at least 160 feet high were needed to dislodge the boulder and send it rolling or sliding to its final resting place. Based on the age of the flowstone growing on the lower half of the boulder, the researchers estimated that the massive waves that transported Maka Lahi struck about 7,000 years ago, before the human occupation of Tonga. — KATHERINE KORNEI /NYT
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