World’s Largest Cliff-Top Rock Moved by Ancient Tsunami

There's a humongous boulder on a cliff in Tonga. Now we know how it got there.

A massive boulder perched hundreds of feet from the edge of a cliff in Tonga appears to have been transported by an ancient tsunami, making it one of the biggest rocks moved by a wave on Earth. The boulder, which was discovered in 2024 on the southern coast of the Tongan island of Tongatapu, sits 656 feet (200 m) inland from the cliff edge, at an elevation of 128 feet (39 m) above sea level. As you can see from the photo below, it's enormous - and weighs over 1,300 tons (1,180 metric tons). LiveScience says it's the world's largest cliff-top boulder.

Credit: Martin Kohler, University of Queensland

According to a new study published in the journal Marine Geology, the boulder - named Maka Lahi, which is Tongan for "big rock" - may have been deposited in its unlikely home by a huge tsunami that struck the island around 7,000 years ago, suggests the study's lead author Martin Köhler, a researcher at the University of Queensland in Australia. The islands of Tonga are located in the South Pacific Ocean, a region that is extremely prone to tsunamis due to being surrounded by tectonic plate boundaries known as the 'Ring of Fire'.

The researchers measured the boulder’s properties then modeled how large a wave would have needed to be in order to deposit such a large rock so far inland. They suggested that the boulder originally sat at the cliff's edge, but was washed inland by a tsunami wave that lasted around 90 seconds and was up to 164 feet (50 m) tall.

This date aligns with evidence of a huge tsunami that hit on New Zealand's North Island - around 1,300 miles (2,000 km) south west of Tonga - at the same time around 7,000 years ago.

The researchers hope that this discovery of how far such a large boulder was moved by a wave may help Tonga and surrounding South Pacific nations prepare for large tsunamis.

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