An ancient volcano once caused an 800-foot tsunami, and it could happen again

The sudden collapse of a volcano off the coast of Cape Verde in Africa roughly 73,000 years ago caused a tsunami wave larger than anything ever witnessed by humans – a massive, 800-foot-tall wave that swallowed up an island located 30 miles away, researchers have discovered.

The tsunami, which took place when the eastern flank of the Fogo volcano collapsed into the sea, would have been roughly two-thirds as tall as the Empire State Building, according to Gizmodo. If such a massive wave were to hit a coastal city in this day and age (which scientists claim could be a distinct possibility), the results would most likely not be pretty.

“Flank collapses can happen extremely fast and catastrophically, and therefore are capable of triggering giant tsunamis,” lead author Ricardo Ramalho at Columbia University’s Lamont-Doherty Earth Observatory explained in a statement Friday. “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.”

At least eight smaller volcanic flanks have collapsed worldwide over the past several hundred years, Ramalho and his colleagues said, and some of them have generated dangerous tsunamis. While many studies question whether or not a larger volcano can collapse suddenly, as the new study suggests, the authors assert that “flank collapses may indeed catastrophically happen and are capable of triggering tsunamis of enormous height and energy.”

Sudden, destructive mega-tsunamis may not be rare after all

Writing in the journal Science Advances, Ramalho’s team explained that their deductions were based on the recent discovery and dating of rock deposits discovered on Cape Verde’s Santiago Island. These deposits are evidence that 40 cubic miles (160 cubic kilometers) that Fogo lost in the collapse came down all at once, resulting in the generation of the giant tsunami.

Several years ago, Ramalho and colleagues spotted unusual boulders located as far as 2,000 feet inland and upwards of 650 feet above sea level. Some of the massive rocks were the size of vans, and their composition more closely matched marine-type rocks along the island’s shoreline than the volcanic terrain where they were found, suggesting that they were deposited by a giant wave.

They determined how large the wave was by calculating how much energy would have been needed to carry the rocks to their current location, and then dated the event by measuring helium isotopes embedded near the boulders’ surfaces. That revealed that the date of origin was about 73,000 years ago, which matched-up with prior estimates suggesting a smaller event occurred.

The analysis “provides the link between the collapse and impact, which you can make only if you have both dates,” said co-author and Columbia geochemist Gisela Winckler. While experts indicate that the discovery provides evidence that volcanoes can collapse suddenly, causing these massive mega-tsunamis to occur, Ramalho said there is no immediate cause for concern.

“It doesn’t mean every collapse happens catastrophically,” he said, “but it’s maybe not as rare as we thought.”

—–

Feature Image: NASA