Martin Köhler in front of the Maka Rahi Boulder in Tonga
Martin Köhler/University of Queensland
The massive 1,200 tonne boulders of Tonga were carried inland as towering waves of 50 meters crashed against a 30-meter-high cliff.
“This is not just an ordinary boulder. It holds the title of the largest corrugated boulder found on a cliff and ranks as the third largest boulder globally, signifying that an immense force was needed to propel it from such a height,” said Martin Köhler from the University of Queensland, Brisbane, Australia.
Locally known as Maka Rahi, which translates to a large rock, this boulder had yet to be studied by scientists.
During fieldwork in Tonga in July 2024, the villagers pointed the researchers towards some intriguing rocks they might want to examine.
“We never anticipated discovering such a substantial rock at the finale of our field studies. It dawned on us quickly that we had stumbled upon a significant find,” Kohler explained.
Measuring 14 meters in length, 12 meters in width, and approximately 7 meters in height, it was described as a “remarkable” boulder, composed of limestone coral reef horn rec rocks. Previous satellite images missed this potential Monami Boulder, as vegetation had grown atop it, with surrounding forests extending into the woodland.
Upon observing the boulder, researchers identified a massive gouge believed to have been created at the cliff’s top, approximately 200 meters from the ocean.
The team utilized computer models to ascertain how this colossal boulder ended up above sea level.
Shifting it necessitated a wave with a minimum height of 50 meters and a duration of 90 seconds, implying it moved at a velocity exceeding 22 meters per second over a minute and a half, Kohler stated. Such a colossal tsunami is relatively localized and is thought to stem from nearby underwater landslides.
Dating indicated the boulder’s age to be 6,891 years, well before the settlement of humans on the island.
“It’s hard for me to fathom a 50-meter wave since I’ve never witnessed or heard of such massive waves before,” Kohler remarked. “However, the logic follows easily when one considers this enormous boulder positioned 200 meters inland on a 39-meter-high cliff.”
Only two rocks deposited by the tsunami have been found on land: one weighing 3,400 tons and another weighing 1,500 tons.
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Source: www.newscientist.com
