The Fogo volcano, which stands on the island of the same name in the Cape Verde archipelago (located in the Atlantic Ocean, off the coast of Senegal), erupted on November 23, devastated several nearby villages and forced the evacuation of the population. Things could have been much worse if the same thing happened as 73,000 years ago, when a side of this mountain collapsed into the sea and raised a gigantic 170-meter high wave that hit the island of Santiago, 55 kilometers from there. .
Scientists already had evidence of that prehistoric tsunami, but did not know its exact date – they dated it to about 100,000 years ago – and they thought it had been modest in size. Now, the geophysicist Ricardo Ramalho and his collaborators from the University of Bristol (United Kingdom) have revealed the exact data of the event.
Ramalho’s team has analyzed large rocks – the size of motorhomes – scattered over a plateau that extends 200 meters above sea level on the island of Santiago. The stones, coming from the cliffs, reach 650 meters inland. Only a megatsumani could have led them there. According to calculations, the wave originating in Fogo would have measured about 170 meters high and when it hit the ground the water levels would have risen more than 270 meters .
To date the catastrophe, the researchers measured the concentration of helium isotopes on the surface of the rocks studied. When the sun’s rays hit certain minerals, helium-3 is produced. By measuring its presence on rock surfaces exposed to light from the tsunami, the time elapsed since the impact of the wave can be calculated. In this case, 73,000 years.
This work will allow to create models of volcanic collapses in islands and the consequent tsumanis that could cause, something very important to specify in the Azores, the Canaries or Hawaii, islands with young, tall and steep volcanoes, which generates a potential danger of collapse.
