Have you ever seen a giant boulder sitting somewhere and wondered how it got there? Well, most of the time it is from the natural movement of land that occurred during ice ages, Earthquakes, landslides, and other events that are easy to understand. Sometimes, however, a massive boulder is found in a place that is so unbelievable that it is hard to imagine exactly how it got there.

That is what happened with a massive boulder named Maka Lahi by the people of Tongatapu. The boulder can be found about 200 meters (700 feet) inland from the ocean on top of a 30-meter (100-foot) cliff. Normally, the only explanation for this would be either an ice age or possibly an Earthquake if there were mountains nearby (which there aren’t).

So, researchers set out to figure out exactly how the boulder got there, and they published their findings in Marine Geology. What they discovered was that this boulder was moved here about 7000 years ago by a massive tsunami.

They were able to determine this by looking at the boulder itself and the limestone sediment that attached to it over the years. Martin Kohler is part of the research team and a PhD student at the University of Queensland. In a statement, he explained how they found this boulder in the first place.

“It was late in the day, and we were talking to some farmers when they directed us to this boulder. I was so surprised; it is located far inland outside of our field work area and must have been carried by a very big tsunami. It was quite unbelievable to see this big piece of rock sitting there covered in and surrounded by vegetation.”

The boulder itself is quite large, measuring about 14 by 12 by 6.7 meters (45x40x22 feet), so it doesn’t seem possible that a tsunami would have moved it here, but that is where the evidance was pointing, so the team ran some models to determine just how large the tsunami would have to be. They came to the conclusion that to move this boulder, the wave would have to be 50 meters (170 feet) high and last around 90 seconds.

That is significantly larger than the biggest tsunami ever measured, but not outside how big experts believe tsunamis can be.

Discovering how this boulder got here is not just a matter of curiosity. Looking at these types of boulders can help experts estimate how often tsunamis strike a given location and how large the waves may be. This can help them to plan how to keep the people and property of an area as safe as possible.

While a tsunami of this size is extremely rare and hasn’t happened here since this one 7000 years ago, the area does get hit with them relatively often. Knowing that tsunamis of this size are possible will help with future planning.

If you thought that was interesting, you might like to read about 50 amazing finds on Google Earth.