Giant boulder on clifftop in Tonga was once carried via a 50-metre-high wave

A 1200-tonne boulder in Tonga was once swept inland when a 50-metre-high wave slammed right into a 30-metre-tall cliff.

“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 Martin Köhler on the University of Queensland in Brisbane, Australia.

While the boulder has lengthy been identified to a few locals as Maka Lahi, because of this huge rock, it had by no means earlier than been studied via scientists.

Köhler and his colleagues have been engaging in fieldwork in Tonga in July 2024 on the lookout for boulders deposited via tsunamis on cliffs. On their ultimate day within the Pacific country, villagers advised them of a boulder they will need to see.

“We were definitely not expecting to find such a large boulder basically during the very last minute of our fieldwork and I knew quite quickly that this was a major discovery,” says Köhler.

At 14 metres lengthy, 12 metres broad and just about 7 metres excessive, it was once a “very striking” boulder, he says, manufactured from coral reef limestone breccia. It had eluded earlier searches for conceivable tsunami boulders in satellite tv for pc pictures because it had plants rising far and wide the highest of it and woodland round it.

After seeing the boulder, the researchers have been in a position to discover a large gash within the clifftop above the sea, 200 metres away, from which they believe the rock was once torn.

Next, the group used laptop fashions to resolve how this type of huge boulder, so excessive above sea stage, may well be moved thus far inland.

Shifting it will have required a wave with a minimal top of 50 metres and a 90-second duration, that means it will have taken a minute and a part to cross and had float speeds of over 22 metres according to moment, says Köhler. It is assumed that such a huge tsunami can have been fairly localised and led to via a close-by underwater landslip.

Dating printed an age of 6891 years, hundreds of years earlier than human agreement of the island.

“It was, for me, hard to believe that it was a 50-metre wave because we hadn’t really seen or known of such a large wave before,” says Köhler. “But if you think that this massive boulder is sitting 200 metres inland on a 39-metre-high cliff, then it’s easier to understand.”

Only two tsunami-deposited boulders which have been discovered on land are larger: the Obiishi rock on Shimoji-shima, Japan, which weighs 3400 tonnes, and Maui rock, which could also be on Tonga, which weighs 1500 tonnes.