30-05-2025
Hidden inland boulder is proof of massive tsunami that hit Tonga 7,000 years ago
On the island of Tongatapu, the main island of Tonga, researchers scoured the southern coastline for evidence of violent weather events that occurred thousands of years ago.
They were specifically looking for boulders, as they can only be carried ashore or moved by massive waves in 'high-energy events, such as tsunamis or storms,' according to a May 14 study published in the journal Marine Geology.
Aerial photo revealed several boulders, but the largest was hidden from view.
Local farmers speaking with the researchers told them of a boulder deep inland atop a cliff, covered by dense vegetation that obscured it from aerial view, and led them to it.
'I was so surprised; it is located far inland outside of our field work area,' study author and Ph.D. candidate Martin Köhler said in a news release from The University of Queensland's School of the Environment.
'It was quite unbelievable to see this big piece of rock sitting there covered in and surrounded by vegetation,' Köhler said.
Researchers said 7,000 years ago, a tsunami about 164 feet tall— the height of the Arc de Triomphe, or a giant sequoia — dislodged the enormous rock and moved it 656 feet inland.
At 45 feet long, 22 feet tall, 39 feet wide and weighing 1,300 tons, the 'exceptional' Maka Lahi is the world's largest cliff-top boulder, according to the study.
Models suggest the tsunami was triggered by a landslide caused by an earthquake near the Tonga-Kermadec Trench, according to the study.
'Understanding past extreme events is critical for hazard preparation and risk assessment now and in the future,' coastal geomorphologist Annie Lau said in the release.
According to Lau, the region has a 'long history of tsunamis triggered by volcanic eruptions and earthquakes along the underwater Tofua Ridge and the Tonga Trench.'
The research team included Martin Köhler, Annie Lau, Koki Nakata, Kazuhisa Goto, James Goff, Daniel Köhler, Mafoa Penisoni.
