A massive 1,200-ton boulder stranded far inland in Tonga has been revealed as one of the world's largest wave-transported rocks, shedding a light on the history of tsunamis in the region. The Maka Lahi ("Big Rock") boulder—which farmers directed the researchers to—came as a "surprise," study author Martin Köhler says in a press release. "It is located far inland and outside of our field work area and must have been carried by a very big tsunami." How far and how big? It was moved more than 650 feet from the coastline of Tongatapu island by a tsunami that likely struck about 7,000 years ago. The study, published in Marine Geology, notes it sits at an elevation of roughly 130 feet.
Using 3D modeling, the boulder's likely origin was determined to be a cliff nearly 100 feet above sea level; numerical modeling indicated that a wave about 150 feet high and lasting a minute and a half would be required to transport the boulder from the cliff to its current position. Per the study, it "notably ... represents the earliest known Holocene [our current geological epoch, which started 11,700 years ago] tsunami in the Pacific, offering new insights into the long-term history of extreme wave events in the region." It's also far greater than any tsunami on record that impacted Tongatapu island.
The largest historically recorded tsunami happened after the 2022 eruption of the Hunga volcano and produced top flow heights of about 60 feet on the island's northwestern side (read one incredible story of survival from the time). Researchers say the analysis enhances the global understanding of how rocks can be moved by tsunami forces, providing valuable information that can "improve coastal-hazard assessments in tsunami-prone regions around the world," says co-author Annie Lau. (This content was created with the help of AI. Read our AI policy.)
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