Article in german newspaper from 2004
Tsunami simulation: danger from the Canary Islands
"We would be right there on the edge of the massive landslide that could devastate the Canary Islands and the east coast of the United States." Doris and Heinz Birkemeier have been looking up at Cumbre Vieja from their El Sombrero restaurant on the outskirts of the mountain village of El Paso on the Canary Island of La Palma since 2002 with quite mixed feelings. This fourteen-kilometer-long volcanic chain attracts quite a few mountain hikers from Europe every year, some of whom stop off at the German chef's and his Swiss wife's restaurant in the evening after the long march between the rather fresh craters. For almost three years, however, the couple has also known that one day they could slide into the Atlantic with all their belongings.
Up to 500 billion tons of rock from the western flank of Cumbre Vieja could break loose in the event of further volcanic eruptions, plunge into the Atlantic and throw such huge waves that parts of New York would be devastated by 25-meter-high breakers even 6,000 kilometers away.
Huge crack in the rock
High up on Cumbre Vieja, which rises almost 2,000 meters above sea level, geologists have found a huge crack in the rock that runs for several kilometers along the ridge from north to south. This crack could have been formed during the last major eruptions of the volcanoes up there in July 1949. Simon Day of the Benfield Greig Hazard Research Center in London has studied the geology of this area in more detail. Cumbre Vieja is considered one of the most active volcanic zones on Earth. Since 1493, seven of the 120 volcanoes on this 14-kilometer-long mountain range have erupted; since 1949 alone, four eruptions have terrified the population. The more frequent such eruptions are, however, the steeper the flanks of the volcano become and therefore slide more easily.
Deep underground on Cumbre Vieja there are also some rock layers that contain a lot of water, as Simon Day, a researcher at the University of California in Santa Cruz, has discovered. If the magma in the volcanic vent rises before an eruption, the heat vaporizes this water. This creates a large pressure that could enlarge the existing crack. Under certain circumstances, the entire mountain flank along the crack could even break away, and up to 500 billion tons of rock would then fall into the sea.
Landslide on El Hierro
On the neighboring island of El Hierro, the director of the Canary Islands Institute of Volcanology, Juan Carlos Carracedo, has found evidence that a similar landslide was caused there 120,000 years ago. At that time, the entire northwestern part of a 1500-meter-high volcano plunged into the sea. Even today, a 15-kilometer-wide, strikingly rugged bay bears witness to this event. The tidal wave that was thrown up at that time hit the Bahamas, among other places, and heave rocks weighing 2,000 tons twenty meters above sea level there.
Hans-Erwin Minor and Willi Hager of the Swiss Federal Institute of Technology in Zurich recreate such landslides in their laboratory. They are using a natural disaster from July 8, 1958, as a model: In Lituya Bay on the southern coast of Alaska, an earthquake caused a steep cliff to sway and plunge into the sea. At first, the rock displaced lots of water, but it quickly sloshed back, creating a 160-meter-high wave. On the beach on the opposite shore of the bay, this wave then ran up to a height of 524 meters, washing away soil and vegetation down to bare rock.
650 meter high wave simulated
After the Swiss researchers used the data from this landslide to calibrate their experimental apparatus, they were also able to simulate the effects of a similar landslide on La Palma, where up to ten thousand times more rock could travel into the Atlantic at the speed of a high-speed train. The result of these calculations makes not only Doris and Heinz Birkemeier in their restaurant under the Cumbre Vieja thoughtful: 650 meters high a wave should pile up directly near La Palma. At jet speed of 720 kilometers per hour, this wave would chase across the ocean, weakening as it did so. When it reached the coast of Morocco after an hour, it would be a hundred meters high. A few hours later, waves 25 meters high would pile up off New and devastate the U.S. East Coast up to twenty kilometers inland.
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https://www.faz.net/aktuell/gesellschaft/tsunami-simulation-gefahr-von-den-kanaren-1194921.html