Scientists believe a megatsunami happened in the Cape Verde Islands of Africa about 73,000 years ago. They came to this theory after studying a big rock made of basalt and limestone previously formed at sea level, that ended 30 miles away on Santiago Island. The research was made by scientists from Columbia University, as well as other universities in Portugal and Japan, and it was published in the journal Science Advances.

Researchers think that a large flank of the Island of Fogo fell into the ocean, causing a big powerful wave that drove more than seven hundred tons of stone to the island, ending in the place where scientists found it recently. According to these scientists, submarine earthquakes are not the only cause of large tsunamis. In this sense, the energy created by the addition of a large mass to the water can do it.

Boat dragged inland in Akahama, Japan by the 2011 tsunami (Credit: Stephen Vaughan)

“You’re displacing a huge mass, which must generate movement of water,” said Ricardo Ramalho, the lead researcher of the study, from Lamont-Doherty Earth Observatory at Columbia University, according to the Washington Post. “And in the case of volcanic flank collapses they can be very acute, because you have all this mass collapsing basically into the oceans.” he added.

In 2007, Ramalho was on the islands when he saw the large boulders ending in a steep cliff face, and he was so amazed that he had to find their origins. 

“You can only explain the existence of those deposits from the impact of a giant tsunami approaching from the western side of the island, and of course, that’s where Fogo is,” said Ramalho.

Ramalho and his colleagues found previous information about a tsunami hitting the Santiago island long ago, and they decided to do further research on the boulders. They found that the island of Fogo, just near by, showed evidence of a big piece of its volcano that could have collapsed causing the tsunami, although researchers cannot be sure of this because it could have happen through various stages and not just once.

Another fact supporting their theory is that the origins of the rock found on Santiago Island had to come from a geological shape formed at low heights, so they assume it came from the side of a sheer vertical cliff.

Scientists believe that volcanic islands are capable of producing similar events, because of their potential of flanks collapsing. They explain this is more common on volcanic islands because they are formed from the seafloor to incredible heights, making them vulnerable. Nevertheless, they don’t intend to alarm people, they just want to point out that it has happened before and it could happen again.

“They are some of the tallest features on Earth […] The big island of Hawaii, if you take into account from the base of the seafloor up to the summit, it’s even higher than Mount Everest,” Ramalho added.

Source: The Washington Post