A 164-Foot Tsunami Pushed This Enormous Boulder Atop a Cliff in Tonga 7,000 Years Ago
The hulking rock, called Maka Lahi, is the size of a two-story house and sits on a 120-foot-tall cliff, covered in vegetation
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At the top of a 120-foot-high cliff in Tonga sits a humongous rock—and at more than 650 feet inland, it’s staggeringly out of place. Now, scientists have modeled how this massive boulder could have ended up in such a strange location: a powerful tsunami roughly 7,000 years ago. They describe the scenario in a new paper published in the journal Marine Geology.
“This is not just a boulder; it’s the biggest wave-lifted boulder ever found on a cliff and the third largest boulder in the world, so it really needed gigantic forces to move it that far across such a high place,” says lead author Martin Köhler, a geoscientist at the University of Queensland in Australia, to New Scientist’s James Woodford.
The hulking boulder is well-known to the people of Tonga, who call it Maka Lahi, or “big rock.” In Tongan mythology, coastal boulders like Maka Lahi were deposited by the demigod Maui as he chased chickens between two islands. They are known as “Maui throwing stones.”
But scientists only learned of Maka Lahi in 2024, while they were conducting field work on the southern side of Tongatapu, Tonga’s largest and most populated island. They were looking for evidence of past tsunamis by examining coastal boulders that didn’t seem to fit with their surroundings. Late in the afternoon on the last day of their trip, the scientists mentioned their project to some farmers.
“They said, ‘Why aren’t you looking at the much larger boulder farther inland?’” Köhler tells Yahoo News’ Michael Dahlstrom.
When the farmers took the researchers to Maka Lahi, the team knew right away it was “a major discovery,” Köhler tells New Scientist. Before them, they saw an enormous limestone rock measuring 46 feet by 39 feet by 22 feet—about the same size as a two-story house. The scientists estimated its weight to be more than 1,300 tons.
“Boulders this size are rare,” says Ricardo Ramalho, a geologist at Cardiff University in Wales who was not involved with the research, to the New York Times’ Katherine Kornei.
Maka Lahi was perched 128 feet above sea level and sitting some 656 feet inland from the edge of the coastal cliff. The boulder was covered in vegetation, which was probably why researchers hadn’t previously spotted it on satellite imagery.
“I was so surprised,” Köhler says in a university statement. “It is located far inland outside of our field work area. … It was quite unbelievable to see this big piece of rock sitting there.”
But how did such a hefty rock end up so far inland? The researchers knew a tsunami was probably responsible, but they wanted to know the size of the wave that was capable of moving such an immense object.
Based on modeling, the researchers concluded the tsunami wave was approximately 164 feet tall—roughly the same height as Niagara Falls—and lasted about 90 seconds. Using this information, they revisited the coast and pinpointed the place where the boulder likely originated: a spot on a cliff some 98 feet above sea level.
Scientists were able to figure out when the boulder had been deposited by dating the layers of secondary limestone that had formed on its sides during rainstorms. Those layers could only have formed once the rock was in its current location, Köhler tells IFLScience’s Stephen Luntz.
This analysis revealed Maka Lahi had been washed inland at least 6,891 years ago—nearly 4,000 years before humans first arrived on Tonga.
That timeline makes sense, given that a large tsunami hit New Zealand’s North Island between 6,940 and 7,240 years ago. Tonga is more than 1,000 miles away from North Island, but they’re both located along the Tonga-Kermadec Trench, an underwater point where two tectonic plates meet. More specifically, in this part of the South Pacific Ocean, the edge of the Pacific Plate is being forced under the edge of the Australian Plate through a process known as subduction. This can incite large underwater volcanic eruptions, which in turn can cause earthquakes that result in tsunamis.
The scientists suspect the same earthquake that caused the tsunami in New Zealand may have also triggered a landslide that produced a separate tsunami on Tongatapu.
Tsunamis caused by landslides tend to be larger than those caused by earthquakes. Since the wave that moved Maka Lahi was very large, scientists think a landslide-triggered tsunami is the best explanation. To prove that hypothesis, however, they’ll need to find evidence of a landslide.
That might be tough to do, because the landslide most likely occurred underwater, Köhler tells Cosmos magazine’s Richard Musgrove. But it may have occurred on Tongatapu or some other nearby island, he adds.
Deadly and destructive tsunamis are common in Tonga because of its position near the Tonga-Kermadec Trench. But scientists hope that by learning more about historic tsunamis, they might help coastal communities better prepare for future disasters.
“Tonga’s most recent tsunami in 2022 killed six people and caused a lot of damage,” says study co-author Annie Lau, a coastal geomorphologist at the University of Queensland, in the statement. “Understanding past extreme events is critical for hazard preparation and risk assessment now and in the future.”
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