a spot called Cumbre Vieja.3 Rift is a seismologist’s term for a fissure or plane along which rock may most easily split. Since the island has erupted seven times in the historic past (since 1585), and recently in 1949 and 1971, it is not unreasonable to assume it will erupt at some time in the future. The danger is that if molten lava interacts with seawater penetrating the lower level of the island, the resulting steam explosion could dislodge the side of the caldera, or a volcanic eruption itself could blow away the steep side of the island, as happened in Mount St. Helens and Krakatoa. If this occurred, millions of tons of rock, sliding down nearly 2.5 miles to the bottom of the ocean, could create a tsunami. Alternatively, underwater landslides of weak material could occur.
No one can predict whether this would be limited to a local tsunami or could affect a wider area. In an extreme scenario, a wave racing west at around 380 knots would wash over Bermuda in seven hours and would reach the East Coast of the United States in around nine hours. As the wave emerged from the deep waters of the Atlantic onto the continental shelf, its height would increase dramatically, potentially towering over buildings along the waterfront from Jacksonville to Boston. While the travel time of the wave would allow some warning to be given, it is doubtful that a mass evacuation of the entire East Coast of the United States could be carried out in a matter of hours. The damage to buildings and infrastructure, as well as the loss of life, would be appalling and unprecedented if this extreme event were to occur.
We know, in the case of tsunami, how massive forces and a huge release of energy deep beneath the ocean generate waves that are modest in size as they race across the ocean, but become powerful and extremely high as they reach shallower waters. Also, storms in midocean acting on near-surface waters produce large waves. In the next chapter I want to discuss what happens when several storms occur in different locations, their waves radiating out and dispersing and at some point meeting each other. To a vessel located at the intersection of several wave paths, the seas can be chaotic, with waves of all heights seeming to approach from a bewildering mix of directions. This condition is known as a confused sea.