Santiago is the largest and most populated island belonging to the Cape Verde Islands off the coast of South Africa. There’s no doubt that Santiago’s scenery is striking—a mixture of mountains and plains covered in thick vegetation. On top of that, there are also huge boulders that can be found sitting nearly 2,000 feet inland and 650 feet above sea level. But how did they get there?
This is what Ricardo Ramalho found himself asking back in 2007—and ultimately what led to the findings of evidence of an ancient megatsunami, a study recently published in the journal Science Advances on October 2nd.
Ramalho led and conducted the research project while at Lamont-Doherty Earth Observatory at Columbia University. He and his research team analyzed the boulders, which didn’t match Santiago’s terrain; rather, they resembled marine-type rocks found in the waters surrounding the Cape Verde archipelago. The team of geologists also used cosmogenic techniques to arrive at the conclusion of mystery of the massive rocks. Approximately 73,000 years ago, a large flank of the volcanic island Fogo—which last erupted in 2014—collapsed into the ocean, causing a wave up to 270 metres high. The mind-boggling wave—tall enough to submerge the Statue of Liberty—traveled 50 kilometres to Santiago, where it tore off chunks of the island’s mountains and hurled them overtop of 180-metre-high cliffs.
The idea of a megatsunami has been debated by scientists, but all evidence points to the occurrence of the catastrophic natural disaster—and not just in the Cape Verde Islands; evidence also suggests a megatsunami occurred in the Hawaiian Islands, Canada’s west coast, and Madagascar, to name a few, all thousands of years ago.
So, when will the next megatsunami happen?
Experts predict potential future megatsunamis in the regions of Canada’s west coast, the Canary Islands, the Hawaiian Islands, and Cape Verde Islands. “The potential energy for a new collapse therefore exists but what we don’t know is if or when this is ever going to happen,” says Ramalho. “We need to be vigilant. These findings stand as a warning that the hazard potential of volcanic island lateral collapses should not be underestimated, and consequently our society needs to do more to improve its resilience to such a threat.”