A study, published in Science Advances, has suggested the occurrence of a stupendously powerful megatsunami in the Cape Verde Islands off the coast of Africa about 73,000 years back. Scientists believe that around that time a huge flank of the volcanic island of Fogo collapsed into the ocean and unleashed a massive wave over 90m in height. The wave traveled about 50km to the island of Santiago.

The theory suggested that when the wave hit, it was so powerful that it surged over the top of an over 180m-high cliff and eventually attained water levels around 275m above sea level, which were about as high as the Eiffel Tower.

The huge water levels scoured massive boulders from below, carrying them to the top of the plateau where they are expected to be found identified later by modern scientists.

Ricardo Ramalho, lead researcher behind the study, of the University of Bristol in the UK, said, “You're displacing a huge mass, which must generate movement of water. And in the case of volcanic flank collapses they can be very acute, because you have all this mass collapsing basically into the oceans”.

The latest study has originated with a simple mystery that Ramalho was on Santiago in 2007 and had seen huge boulders on top of the high plateau, ending in a steep cliff face. He said that the origin baffled him and he didn’t have any idea about what they meant.

After a few years, other researchers found evidence that suggested a tsunami had hit Santiago long ago. Ramalho and colleagues took inspiration from it and decided to closely observe the boulders and other linked geological evidence at quite higher elevations.

"I was puzzled by their origin. I didn't know what they meant," he says.

"exclusively crop out on the cliff faces and lower slopes of the plateau, implying a source at considerably lower elevations," the researchers write.