73,000 years ago, the volcano on the Cape Verde island of Fogo caused a super tsunami as high as 170 meters. If you look at the island of Fogo, you immediately notice that part of the island has been broken off. The crater of the volcano Pico do Fogo seems to be only partially intact. The facts that the eastern side of the volcano’s crater broke of the made 167 cubic kilometers of rock to fall into the ocean. This caused a wave of 170 meters high that flooded the neighboring Cape Verde islands – including the island of Santiago at 50 kilometers away. The Fogo tsunami is one of the largest the world has ever seen.
Investigation of the Fogo tsunami
In general, tsunamis are caused by seaquakes as happened in Southeast Asia in 2004. This tsunami caused waves of about 30 meters. The fact that Fogo’s tsunami was much higher is due to the collapse of much of the volcano. This was much more at one specific place, so the waves were also higher.
In the past, there were often indications that there had been tsunamis around Fogo and the Cape Verde islands. The breaking off of part of the Fogo volcano was said to have caused a small number of tsunamis, according to French geologists (Sedimentary Geology, 2011). Researcher and geologist Dr. Ramalho recently came to a different conclusion. The strength and size of the tsunami must have been much greater than the researchers first concluded. In his doctoral research (2007), Dr. Ramalho finds some 40 lonely boulders on the island of Santiago at an altitude about 270 meters. The boulders on Santiago are 8 meters wide and lie 600 meters inland. They consist of lime and basalt and were originally part of the Santiago coastline. This means that the boulders were dragged along a few hundred meters. By calculating the force required to move these boulders along this distance, the height of the tsunami could be estimated.
Tsunami in the future
Dr. Ramalho indicates that a super tsunami of this magnitude might occur again in the future. For any volcano that resembles the volcano on Fogo (height, steepness), a collapse is realistic. The chance is very small, but it is possible. The scale and impact will then be significant.