Scientists discovered evidence that a megatsunami hit west Africa's Cape Verde Islands 73,000 years ago, and the findings could have implications for the future.
The 800-foot wave was believed to have been caused by the sudden collapse of a volcano, and now researchers are wondering if a similar monster wave could occur today, the Earth Institute at Columbia University reported. The largest-known recent tsunami that hit the Indian Ocean's coasts in 2004 only reached a height of about 100 feet.
"Our point is that flank collapses can happen extremely fast and catastrophically, and therefore are capable of triggering giant tsunamis," said lead author Ricardo Ramalho, who did the research as a postdoctoral associate at Columbia University's Lamont-Doherty Earth Observatory, where he is now an adjunct scientist. "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 collapse occurred at the Fogo volcano, which now erupts every two decades. The ancient wave caused by the volcano collapse completely swallowed Santiago Island, which is currently inhabited by about 250,000 people.
Several volcanic collapses have triggered tsunamis over the past few centuries, but scientists were unsure if large volcanoes could collapse as suddenly as what this recent study suggests. Researchers believed the collapse of larger volcanoes would occur in gradual stages of landslides, triggering smaller tsunamis, but the new research suggests the 40 cubic miles of rock that Fogo lost during the collapse dropped all at once.
The researchers made their findings on Santiago Island, which sits only 34 miles from Fogo. They noticed some unusual boulders sitting about 2,000 feet inland, some of which were as large as delivery vans. Instead of looking like the volcanic terrain seen in the region, the boulders appeared to be marine-type rocks. The only explanation for the rocks that the scientists could come up with was that an enormous wave ripped them from the coastline and carried them to their current position.
To determine when this incredible event occurred, the researchers measured isotopes of the element helium present in the boulders. The isotopes revealed the wave likely occurred 73,000 years ago.
"[The study] provides robust evidence of megatsunami formation [and] confirms that when volcanoes collapse, they can do so extremely rapidly," said tsunami expert Bill McGuire, a professor emeritus at University College London who was not involved in the research.
McGuire's work has shown megatsunamis probably occur only about once every 10,000 years.
"Nonetheless," he said, "the scale of such events, as the Fogo study testifies, and their potentially devastating impact, makes them a clear and serious hazard in ocean basins that host active volcanoes."
The findings were published in a recent edition of the journal Science Advances.
