In the 1990s, several scientists carefully examined the then dormant volcano and even went inside, discovering that the entire southwest flank had become unstable and could slide into the Atlantic Ocean. This unstable land mass is the size of Manhattan Island in New York City and would trigger a tsunami wave.
Computer models showed that the tsunami would hit the east coast of the USA within 7 to 8 hours and inundate almost all large cities with a high wall of water. That would mean a massive wave that would last 5 to 45 minutes while flooding occurred inland. The current quake may have started naturally, but as of 11:45 pm Eastern US time on Friday, October 22, 2021, “doesn’t look natural” according to some watchers.
In 2004, German daily the FAZ reported that a tsunami after a volcanic eruption on La Palma would devastate New York, 6000 kilometers away, with 25 meter high breakers.
Up to 500 billion tons of rock on the western flank of the Cumbre Vieja could break loose in further volcanic eruptions, plunge into the Atlantic devastating parts of the North American East Coast. On Cumbre Vieja, which towers almost 2000 meters above sea level, geologists found a huge crack in the rock that stretches for a few kilometers along the mountain ridge from north to south. This crack could have occurred during the last major eruptions of the volcanoes up there in July 1949.
Simon Day of the Benfield Greig Hazard Research Center in London took a closer look at the geology of this area. The Cumbre Vieja is one of the most active volcanic zones on earth. Since 1493, seven of the 120 volcanoes have erupted on this 14-kilometer ridge, and since 1949 alone, four eruptions occurred. However, the more frequent such eruptions are, the steeper the flanks of the volcano become and the easier it is to slide away from the land mass.
Day, who conducts research at the University of California in Santa Cruz, discovered that deep in the subsurface of the Cumbre Vieja there are also some rock layers that contain a lot of water. If the magma rises in the volcanic vent before an eruption, the heat of this water evaporates. This creates a lot of pressure that could enlarge the existing crack. Under certain circumstances, the entire mountain flank along the fissure could come loose, and up to 500 billion tons of rock would then fall into the sea.