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