Collapse of a volcanic island and generation of a giant tsunami wave in cape verde 73000 years ago
2015-10-05 (IPMA)
The research now published in the journal Science Advances (http://advances.sciencemag.org/content/1/9/e1500456) shows that a sudden prehistoric collapse of one of the highest and active oceanic islands - the island of Fogo in Cape Verde - produced a giant tsunami with catastrophic consequences. The evidence, documenting the impact of waves up to at least 220 m above present sea level, was found on the island of Santiago, 55 km east of the island of Fogo. This study reopens the debate that has lasted for decades about whether the collapse of volcanic islands occur suddenly and in a catastrophic way, capable of generating large tsunamis. This study confirms that the collapse of volcanic islands can indeed generate tsunamis of gigantic proportions.
The evidence found on the island of Santiago include boulders, some the size of caravans, as well as marine sediments covering the surface of the island, deposited a great height above sea level. These deposits involve the occurrence of a catastrophic marine flooding compatible only with the impact of a giant tsunami coming from the west, i.e., the island of Fogo. By using state-of-the-art techniques for dating rocks, it is estimated that the tsunami occurred at about 73,000 years ago. This age is age compatible with pre-existing dates of the collapse of the eastern flank of the neighboring island of Fogo. This study thus, establishes a causal link between deposits found in Santiago and the collapse of Fogo, indicating that the collapse has occurred in a catastrophic manner and produced a huge tsunami. Since sea level was at the time about 50 meters lower than the current level, it can be inferred that the tsunami flooded the coast of the island of Santiago, in some places up to 270 meters or more.
The Fogo Island rises 2829 meters above current sea level and erupts every 20 years on average, the most recent of which was the eruption that took place between November 2014 and February this year. The active volcano that can be seen today was built inside the scar of this collapse, being so tall and steep as the previous volcano before the collapse. The potential energy for a future collapse, therefore, continues to exist. We do not know yet or when it will happen again. What we know is that we need to remain vigilant.
This study was led by Ricardo Ramalho, currently at the University of Bristol and had the participation of the Portuguese researchers José Madeira, from the Universidade de Lisboa, Rui Quartau from the Instituto Português do Mar e da Atmosfera and Ana Hipólito from the Universidade dos Açores.
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