The Cumbre Vieja volcano on the Canary Islands' La Palma island may not erupt again for centuries, but when it does disaster could spread across oceans. Shaken loose by the eruption, a gigantic chunk of the mountain's western flank could slide into the Atlantic - shoving massive tsunamis toward the coasts of Africa, Europe, South America, Newfoundland and even the United States.
In the worst-case scenario (detailed in an article in the Sept. 1 issue of Geophysical Research Letters by geophysicists Steven Ward of the University of California at Santa Cruz and Simon Day of University College, London) half a trillion tons of volcanic rock would slip into the ocean.
Map courtesy of the BBC. Within five minutes, a wall of water would rise to 1,500-feet high and travel at high-speed 30 miles out to sea. The wave would weaken before it reached land, but it still could be 900 feet high when it would slam into nearby islands.
Over the next five to 45 minutes, a series of waves would ripple outward, their crests reaching 150 feet before barreling into the African coast, Spain and England.
Six hours after the eruption, waves reaching 30 feet would arrive in Newfoundland and 45- to 60-foot waves would bombard South America, swamping large parts of land. Nine hours after the eruption, crests reaching 30 to 70 feet would collide into the East Coast of the United States.
However, scientists say the entire area of unstable slope may not fall at once. Instead, smaller landslides may occur over time. These landslides would produce waves one-fourth to half the height of the mega tsunami. Moreover, the disaster is not expected to happen anytime soon. The Cumbre Vieja Volcano last erupted in 1949 and has shown no signs of activity.
"Let's not scare people," Ward told the Associated Press. "Certainly there is no indication that this will happen anytime soon." Even if an eruption occurs, a landslide is not inevitable, he added.
However, the possibility remains. A giant crack stretches up and down the volcano's western flank, threatening to break loose. The threat comes as no surprise. Landslides make up the volcano's history. A pile of debris from past landslides lies on the seafloor at the base of the volcano.
"Volcanoes try to continuously add lava to a steep slope, and eventually the slope becomes so heavy it fails," Peter Lipman, a volcanologist with the U.S. Geological Survey, told the Associated Press. "I don't see this as something that is likely to happen very often at La Palm. But it had a failure like this half a million years ago and will again in the future."
Tsunamis, often incorrectly called tidal waves, reach all the way to the sea floor. Out at sea, they look like regular waves. However, as they approach land, the sea floor rises, pushing the wave upward.
Such an event is not expected to occur anytime soon, but if a tsunami were to strike the U.S. coast, it could be extremely destructive.
Earthquakes or landslides under the ocean cause most tsunamis. In 1998, more than 2,200 people lost their lives when 20- to 30-foot waves - generated by undersea earthquakes -- crashed into Papua New Guinea.
