Tag Archives: Boulder

Gigantic Clifftop Boulder in Tonga Reveals Evidence of an Ancient Tsunami

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Locally referred to as Makarahi, meaning “big rock,” this boulder was displaced over 200 m inland by a tsunami approximately 7,000 years ago.

Limestone rock Makarahi. Image credits: Kohler et al. , doi: 10.1016/j.margeo.2025.107567.

The Makarahi boulder measures 14 x 12 x 6.7 m and weighs nearly 1,200 tons, making it the largest known boulder located atop a cliff and one of the largest vibration-transport boulders globally.

This limestone formation is situated 200 meters away from the coastline on the southern shore of Tongatapu, Tonga.

“Our research focused on the southern part of Tongatapu Island, examining coastal cliffs that show signs of past tsunamis,” stated Martin Kohler, a Ph.D. candidate at the University of Queensland.

“At the end of our fieldwork day, while conversing with some local farmers, they pointed us toward this rock.”

“I was truly astonished. It was found inland, outside our designated research area, indicating it must have been moved there by a massive tsunami.”

“It was remarkable to witness this large boulder enveloped in lush vegetation.”

“We created a 3D model before returning to the coast to identify a location from which boulders could be dislodged from cliffs over 30 meters high.”

Through numerical modeling, the researchers determined that a wave height of roughly 50 m lasting about 90 seconds would be required to transport the Makarahi boulder from its original cliff edge to its new location.

“The University of Queensland has provided a fantastic opportunity to explore the forces shaping our world,” remarked Dr. Annie Lau, a coastal geomorphologist at the institution.

“The recent tsunami in Tonga in 2022 resulted in six fatalities and extensive damage.”

“Gaining insights into extreme past events is crucial for preparing and assessing risks related to current and future hazards.”

“The findings concerning the Makarahi boulder offer evidence of Holocene Pacific tsunamis that have occurred since about 11,700 years ago.”

“This analysis will enhance our understanding of rock wave transport and improve coastal hazard assessments in tsunami-affected regions worldwide.”

The team’s study is published in the journal Marine Geology.

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Martin Kohler et al. 2025. Investigating the world’s highest boulder atop a cliff: preliminary insights and numerical simulations of transport on cliffs ranging from 30-40 m in Tongatapu (Tonga). Marine Geology 487, 107567; doi:10.1016/j.margeo.2025.107567

Source: www.sci.news

The Massive Boulder at Clifftop, Tonga, Was Pulled by 50-Meter High Waves

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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