Scientist Find Evidence of Megatsunami in Cape Verde Islands

Posted on October 3, 2015

Boulder washed up by megatsunami in Santiago Island

Scientists have found evidence of an ancient megatsunami in the Cape Verde Islands off west Africa. The research say the sudden collapse of part of the Fogo volcano 73,000 years ago generated an 800-foot wave that engulfed a nearby island. The image above shows a boulder swept up into the highlands of Santiago Island by the giant wave.

Ricardo Ramalho, the study's lead author and adjunct scientist at Columbia University's Lamont-Doherty Earth Observatory, says in a statement, "Our point is that flank collapses can happen extremely fast and catastrophically, and therefore are capable of triggering giant tsunamis. They probably don't happen very often. But we need to take this into account when we think about the hazard potential of these kinds of volcanic features."

The volcano stands 2,829 meters (9,300 feet) above sea level. It erupts about every 20 years. The most recent eruption was last year. The researchers say that volcanic flanks present a megatsunami threat in the Cape Verdes and elsewhere today. Santiago Island is currently home to 250,000 people.

Recent modern tsunamis such as the one that devastated the Indian Ocean's coasts in 2004 and eastern Japan in 2011 reached a height of about 100 feet (30 meters). Simon Day, a senior researcher at University College London, has been warning that a future eruption of the Canary Islands' active Cumbre Vieja volcano could set off a flank collapse that might generate a wave 3,000 feet high. This wave would still be 300 feet high when it reached west Africa an hour later and about 150 feet high along the coasts of North and South America.

There is recent evidence for megatsunamis. The 1958 Lituya Bay megatsunami reached a staggering 1,722 feet (525 meters) above the height of the bay. The megatsunami was generated when earthquake shook 90 million tons of rock into the isolated Alaskan bay. In this case the tsunami was contained in a small body of water compared to a vast ocean.

Bill McGuire, a professor emeritus at University College London, believes megatsunamis probably come only once every 10,000 years. He was not involved in the new research but says in a statement that the study "provides robust evidence of megatsunami formation [and] confirms that when volcanoes collapse, they can do so extremely rapidly."

Ricardo Ramalho explains the significance of the large displaced boulders found on Santiago Island in the following video. Take a look:

A research paper on the study was published here in the journal, Science Advances.

Photo: Ricardo Ramalho