Cumbre Vieja volcano in the Canary Islands looks peaceful now. Undersea surveys have found a 400 cubic km landslide, the debris of a prehistoric eruption. Previous activity has caused the Western slope to come loose, creating a North-South fracture. Another large eruption would cause 500 cubic kilometres of mountain to crash into the sea. Dr. Simon Day and Steven Ward have modelled what would happen next.
The initial impact would create a water dome 900 meters high, collapsing and spreading like a stone creating ripples. A massive tsunami would race across the Atlantic at nearly 800 km/hr. The coast of Morocco would be struck by waves 100 meters high. Waves up to 50 meters from crest to trough would strike the US East Coast. Water would inundate coasts from Britain to Brazil.
The Indian Ocean tsunami of 2004 produced waves up to 30 m high. Krakatoa's eruption in 1883 created 6 m waves, killing 30,000 people. The damage in New York City alone would make 9/11 look like a college prank. The Northeastern US is also vulnerable to earthquakes. As recently as 1925 a magnitude 7 quake struck the region. Unlike California or Hawaii, New York has never prepared for a major earthquake.
Before Einstein and Planck some scientists believed they knew everything about physics. Even today some will tell you that they have inventoried everything in the Universe. It is the height of folly to think we know everything in nature. Previously humans did not suspect what lies beneath their feet. The hiccoughs of a Black Hole less than a millimetre across can wipe out whole coastlines. The Universe has power and mysteries far beyond human understanding.