Eruption in Atlantic raises tsunami fears

A volcanic eruption began three weeks ago on La Palma in Spain’s Canary Islands, about 300 miles off the coast of Africa. The eruption of Cumbre Vieja volcano has produced lava flows extending two miles downslope into populated areas resulting in more than 5,000 evacuations. Hundreds of buildings have been damaged/destroyed and ashfall has covered 14,000 acres.

Much of the media coverage has not been about the current eruption but focused on the potential for a catastrophic landslide producing a megatsunami. It is useful to look at the basis of the media hype and what the likely outcomes of the current eruption.

The Canaries include seven inhabited islands and a number of smaller islets that are home to over 2.1 million people. It is a major tourist destination with at least 4 million annual visitors in prepandemic times. The islands owe their existence to a geologic hotspot, a concentrated plume of hot rock originating deep within the earth’s mantle, that formed beneath the African plate about 70 million years ago.

The Canary Islands likely formed, succumbed to erosion, and reformed many times since then. The oldest rocks (~20 million years) are on the island of Fuerteventura on the east. La Palma is one of the newest; its earliest rocks are less than 2 million years. It has also been the most volcanically active with seven documented historic eruptions since 1470.

La Palma is dominated by Cumbre Vieja, a volcanic ridge running nearly the length of the island from north to south. The largest historic eruptions were in 1677 and 1971 and rated a two on the Volcanic Explosivity Index (VEI), a qualitative measure of the size and vigor of an eruption. Two means modest explosions — more ejecta than a typical Hawaiian eruption but not nearly as violent as Mt. St. Helens.

The current eruption began with the sudden onset of seismic activity on Sept. 11. Spain maintains a network of instruments to monitor volcanic activity in the Canaries. The initial earthquakes were small in magnitude (Three days after the onset of seismic activity, the regional government raised the volcanic alert level to yellow, the second stage of Spain’s 4-stage alert system. Tilt meters and GPS monitor