Ancient Mega-Tsunami Moved 1,300-Ton Boulder Up Tonga Cliff

Imagine a 1,300-ton boulder, roughly the size of a two-story house, perched on a 100-foot cliff. Now imagine that boulder traveling over 650 feet inland, carried not by human hands but by the sheer force of a colossal tsunami. This is exactly what scientists uncovered in Tonga, revealing a dramatic story of ancient natural power.

In July 2024, a research team led by PhD candidate Martin Kohler from the University of Queensland was investigating Tonga’s cliffs for evidence of past tsunamis. Local farmers pointed them to a massive limestone boulder known as Maka Lahi, or “large rock,” which had escaped prior scientific attention due to its thick vegetation cover.

The boulder’s composition—coral reef limestone breccia—indicated a coastal origin. Nearby, the team found a massive gash in a 100-foot cliff, about 650 feet from the boulder’s current resting place. Radiocarbon dating revealed the boulder was deposited approximately 6,891 years ago, predating human settlement in Tonga.

Using computer simulations, researchers estimated the ancient tsunami’s height at a minimum of 164 feet, with speeds exceeding 70 miles per hour. The wave likely lasted about a minute and a half, powerful enough to carry the massive boulder uphill and inland. Intriguingly, the tsunami was probably triggered by a landslide rather than an earthquake.

Why does this matter today? Tonga is a hotspot for geologic activity, including the devastating 2022 tsunami. Understanding the mechanics of ancient mega-tsunamis helps scientists improve coastal hazard assessments and prepare communities for future events.

This discovery also adds Maka Lahi to the list of the world’s largest tsunami-transported boulders and marks it as the largest known to have surfed a tsunami from a cliff. It’s a geological testament to the immense forces shaping our planet’s coastlines over millennia.

Unlocking the Past to Protect the Future

The study of Maka Lahi exemplifies how geological detective work can reveal hidden histories of natural disasters. By combining field observations with modern computer modeling, scientists reconstruct events that occurred thousands of years ago, offering crucial insights into tsunami dynamics.

For regions like Tonga, where seismic and volcanic activity is frequent, such research informs early warning systems and disaster preparedness strategies. It also underscores the importance of integrating geological data with advanced analytics to anticipate and mitigate the impacts of future tsunamis.