Mega Tsunami that struck 73000 years ago may strike again

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.

The event occurred 73,000 years ago in the Cape Verde Islands off west Africa, long before there were any coastal cities that might have been flattened by the deluge. Scientists suggest that it is a rarity but can not be ignored altogether.

Tsunamis are monster waves that are often caused by earthquakes.

Seaside towns are under threat from strikes in the North Sea and the Atlantic Ocean, which could trigger tsunamis with the potential to kill thousands of people. In 2011, a massive quake struck Japan, causing vast flooding and loss of life, and resulting in the partial meltdown at a nuclear power plant that resulted in a huge humanitarian crisis. A volcanic collapse about 100,000 years back in Hawaii reportedly generated a megatsunami that flooded the land as high as 300 meters. In 1958, an natural disaster sent a landslide into Alaska’s isolated Lituya Bay, generating a titanic wave 1,724 feet high (525 m), the largest ever recorded. Two fishermen and their boat were reportedly held aloft for the whole event. When they realized that the only possible explanation for the structures’ origin was a great tsunami impact, they got excited. All this was due to what’s called a “flank collapse” and such collapses could pose threats even today. It has been argued that in the open ocean, waves created by geological collapse quickly lose energy simply because of all the surface area their momentum has to cover. Then there’s the possibility that the Cumbra Vieja volcano on the Canary Islands could collapse in such a way to send a megatsunami all the way to the United States – certainly a sobering thought, as if they’ve happened before, they can certainly happen again.

(Photo: Ricardo Ramalho) A researcher collects samples from Cape Verde’s mysterious boulders.

Around 73,000 years ago, the towering predecessor of the Fogo volcano – one of the most active in the world – collapsed.

Clues left by the mega-tsunami include boulders the size of lorries that had been carried up to 600 metres inland and almost 200 metres above sea level on Santiago island, 34 miles from Fogo. Rather, they match marine-type rocks that ring the island’s shoreline: limestones, conglomerates and submarine basalts.

“At first, we were quite puzzled by what we found in the field – why were such large boulders stranded on the landscape?”

Most of us are aware about the destruction that tsunamis can inflict. The size of the wave was determined by calculating how much energy it would have taken to move the boulders-some weighing up to 770 tons-up and over so far across the island.

“We estimate that the wave was possibly about 170 m (557 feet) high upon arrival to Santiago’s coastline”, Ramalho said. Ramalho also stressed at finding realistic solutions.

To date the event, in the lab Ramalho and Lamont-Doherty geochemist Gisela Winckler measured isotopes of the element helium embedded near the boulders’ surfaces.

In the early 2000s, other researchers started publishing evidence that the Cape Verdes could generate large tsunamis. The ancient wave caused by the volcano collapse completely swallowed Santiago Island, which is now inhabited by about 250,000 people. The sudden collapse generated waves of water as high as 800 feet and wiped off a neighboring island 30 miles away. “But I don’t know the geology of La Palma, and so I can not comment on the validity of Simon Day’s assumptions”.