It’s being called the “Mega-Tsunami” — an 800-foot wave that smashed the Cape Verde Islands 73,000 years ago — and its power was simply unbelievable.

A new study published in the journal Science Advances found that a megatsunami in the Cape Verde Islands, which sits off the coast of Africa, formed when a huge piece of the volcanic island of Fogo collapsed, blasting rock into the water and creative a huge wave that started out at more than 300 feet high, according to a Washington Post report.

The wave then traveled 30 miles to the the island of Santiago and struck it with such power that it flew up over a 600-foot cliff and eventually reached 800 and nearly 900 feet above sea levels, which would have made it higher than the Eiffel Tower.

As a result, scientists have found huge boulders on top of the island that were carried by this gigantic wave.

It was these gigantic boulders up on this high plateau on the island that first piqued the curiosity of Ricard Ramalho, who was the lead researcher on the study at Lamont-Doherty Earth Observatory at Columbia University. Ramalho first noticed them in 2007, and was puzzled at to how they got up there.

So he decided to dig deeper, and thanks to the help of a team of research, they were able to uncover evidence of a truly tremendous tsunami striking Santiago tens of thousands of years ago.

But the problem was that most tsunamis strike areas of low elevation, whereas there was evidence of it being at a high plateau. Surely this couldn’t be right. So they started to look at those boulders and other geological evidence, and then zeroed in on nearby Fogo, which even today has an active volcano that is four miles off the seafloor. They determined that this volcano had undergone a partial collapse, and they were able to spot evidence on the seafloor of a gigantic avalanche of rock that could have produced a truly epic tsunami, or a megatsunami if you will.

Still, the very existence of megatsunami is fraught with controversy in scientific circles, and some argued that while Fogo had indeed collapsed, it may not have happened all at once. That’s one of the reasons why many scientists don’t believe in megatsunamis, because they don’t believe these kinds of collapses are sudden.

But Ramalho wasn’t convinced of this theory, and the geological evidence he collected at Santiago and in the vicinity of Fogo have convinced him that there must have been a megatsunami that carried these boulders up to the very top of the island, hundreds of feet up. He argues that the composition of the boulder indicates that it came from a cliff face at a much lower elevation. He and his researchers also dated the rock with cosmogenic techniques to determine how long the rock had been exposed at that location to the sun, and determined it dated back to around the time of the Fogo collapse, further bolstering his theory.

Volcanoes are good candidates for sudden collapses because of how they are created: turmoil deep below the Earth thrusts up massive columns of rock dramatically off the sea floor, resulting in the sudden creation of some of the tallest structures on Earth. As a result, they’re more likely to suddenly collapse, and that’s what Ramalho believes happens in Fogo’s case.

And there’s evidence of other megatsunamis happening in world history, with some scientists opining that a megatsunami struck the Hawaiian islands about 100,000 years ago. Then there’s the possibility that the Cumbra Vieja volcano on the Canary Islands could collapse in such a way to send a megatsunami all the way to the United States — certainly a sobering thought, as if they’ve happened before, they can certainly happen again.

A tsunami, which is also known as a seismic sea wave, is a series of waves that is produced when a large volume of water becomes suddenly displaced. The most common cause of this is either an earthquake or a volcanic eruption. Contrary to their depiction in films, tsunamis generally don’t resemble typical waves, mostly because their wavelength is a lot longer. Rather than breaking, a tsunami looks more like a suddenly rising tide, and that is why people often refer to them as tidal waves even though they have absolutely no relationship to the tides. A tsunami can involve a series of waves that can last over a period of either minutes or hours.

Most of the time, tsunamis only cause problems in coastal areas, but sometimes they can be so massive that they cause untold disaster. Just in the last few years, mankind has experienced two extremely brutal tsunami events. The first was the 2004 Indian Ocean earthquake and tsunami, which caused massive flooding and killing tens of thousands of people in Thailand and other parts of Southeast Asia. In 2011, a massive earthquake struck Japan, causing immense flooding and loss of life, and resulting in the partial meltdown at a nuclear power plant that resulted in a huge humanitarian crisis.

The understanding that tsunamis come from undersea earthquakes stretches all the way back to Greek historian Thucydides in the late 5th century BC, who wrote the History of the Peloponnesian War. However, not much was known about tsunamis until the 20th century. Even today, scientists have difficulty predicting when a tsunami might strike after an earthquake. Many times, tsunamis catch the scientific community completely off guard, while in other cases a tsunami is predicted that never shows itself.