It may not happen anytime soon, but the Cumbre Vieja volcano in the Canary Islands is bound to erupt againand when it does, it may well set in motion a tsunami wave more massive than any in recorded history. According to a new model by Simon Day of University College London and Steven Ward of the University of California, this mega-tsunami, which they describe in the September 2001 issue of Geophysical Research Letters, would rouse waves 100 meters high along the West Saharan shore, seas more than 40 meters high on the north coast of Brazil, and water walls towering 50 meters in the air off the coast of Florida and in the Caribbean. Britain, Spain, Portugal and France would also face sizeable waves.

Day and his colleagues predicted earlier that a future eruption of Cumbre Vieja would most likely prompt a serious landslide on the volcano's western side. They guessed that a chunk of rock twice the volume of the Isle of Man might break off, rush into the sea and create a debris avalanche deposit extending as far as 60 kilometers from the island. The new model adds to this picture, forecasting that Cumbre Vieja's collapse would send up a dome of water 900 meters high and tens of kilometers wide. As that dome collapsed and rebounded, giant waves would form and build, fueled by what is known as a tsunami wave train, itself created as the landslide sped away from the island underwater. In 10 minutes, such a tsunami would travel almost 250 kilometers.

"Anyone planning a holiday to the Canary Islands and the islanders themselves need not panic," Day says. "Cumbre Vieja is not erupting, so the short-term and medium-term risks are negligible. Eruptions of Cumbre Vieja occur at intervals of decades to a century or so and there may be a number of eruptions before its collapse. Although the year-to-year probability of a collapse is therefore low, the resulting tsunami would be a major disaster with indirect effects around the world. Cumbre Vieja needs to be monitored closely for any signs of impending volcanic activity and for the deformation that would precede collapse."