A volcanic eruption began three weeks ago in La Palma, in Spain’s Canary Islands, about 300 miles off the African coast. The eruption of the Cumbre Vieja volcano produced lava flows extending three kilometers downstream in populated areas, causing more than 5,000 evacuations. Hundreds of buildings were damaged / destroyed and ash falls covered 14,000 acres.
Much of the media coverage has not focused on the current eruption but has focused on the potential for a catastrophic landslide producing a megatsunami. It is helpful to examine the basis of the hype and the likely results of the current rash.
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 before the pandemic. The islands owe their existence to a geological hotspot, a concentrated plume of hot rock from the depths of the Earth’s mantle, which formed beneath the African plate about 70 million years ago.
The Canary Islands probably formed, succumbed to erosion, and reformed several times since then. The oldest rocks (~ 20 million years old) are found on the island of Fuerteventura in the east. La Palma is one of the most recent; its first rocks date back less than 2 million years. It has also been the most volcanically active with seven historical eruptions documented since 1470.
La Palma is dominated by the Cumbre Vieja, a volcanic ridge that stretches almost the entire length of the island from north to south. The largest historical eruptions occurred in 1677 and 1971 and received a score of two on the Volcanic Explosive 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 as violent as Mount St. Helens.
The current eruption began with the sudden onset of seismic activity on September 11. Spain maintains a network of instruments to monitor volcanic activity in the Canaries. The initial earthquakes were of low magnitude (
Three days after the start of the seismic activity, the regional government raised the volcanic alert level to yellow, the second stage of the Spanish 4-level alert system. Inclinometers and GPS monitoring detected a few centimeters of swelling, confirming a probable rise in magma. Localized evacuations were ordered.
A fissure eruption began on September 19, with lava flows seen in the Cabeza de Vaca area just east of the town of El Paso and the eruption alert level increased to the highest level (Red). The initial flows were effusive (VEI 0), but the proximity of the residences resulted in the evacuation of at least 5,000 people. A week after the start of the eruption, small explosions spread ash over much of the central and southern part of the island and brought the VEI to 2. Involcan, the volcanoes institute of the Canary Islands, estimates that approximately 10,000 tonnes of sulfur dioxide continue to be emitted into the atmosphere. every day as the rash continues.
After that ? If it follows a pattern similar to that of 1971, the eruptive activity will soon slow down and in a few weeks Cumbre Vieja will fall back into dormancy. Evacuation orders will be lifted, structures rebuilt and new ashes will be incorporated into the rich soils that support the many banana plantations in the western part of the island.
But there is always uncertainty about an event taking place. It is entirely possible that the current eruption will last longer than 1971. Some European volcanologists predict that it could continue until November, with continuous lava flows and modest explosive activity. No one predicts that the eruption will become much more explosive.
Where does a tsunami take place? Volcanic eruptions can produce tsunamis. Two of the deadliest tsunamis on record have been linked to volcanism. Thirty-seven thousand years ago, a violent eruption from Santorini into the Aegean Sea triggered a tsunami that devastated Crete and struck a blow to Minoan civilization. In 1883, the eruption of Krakatoa in Indonesia was followed by a tsunami that probably killed 36,000 people.
There is no evidence that a Santorini or Krakatoa scale eruption is likely in the Canary Islands. These were both huge eruptions (~ VEI 6) and the geological setting of the Canaries does not lend itself to an explosion on this scale. The buzz of the La Palma tsunami comes from another source. Tsunamis can also be caused by underwater landslides and some scientists have speculated that the Canary Islands are vulnerable to catastrophic collapse.
In 2001, an article was published on the collapse of the flank of the Cumbre Vieja volcanic system and a large or megatsunami that followed. Geologist Simon Day posited that La Palma was in the early stages of a collapse due to migration of the African plate to the hotspot and changes in the plumbing system. He teamed up with Steven Ward who modeled the tsunami. The story grabbed the headlines and spawned a number of sensational documentaries postulating waves big enough to cause damage along the eastern seaboard of the United States and across Europe.
Since then, the work has attracted much criticism from both the geology and tsunami communities. The modeling assumptions are considered unrealistic and other modelers have not been able to reproduce the results. A credible summary of the Canary Islands tsunami potential is available at https://www.e-education.psu.edu/earth107/node/1609.
Steep oceanic islands are inherently unstable and landslides will occur. Over the course of several millennia, some of the landslides in the Canary Islands will be large enough to produce tsunamis. The largest of these could impact the adjacent African coast and possibly southern Europe, but it is unlikely to make waves as far as the United States. And there is no evidence that the current eruption of Cumbre Vieja has made major landslides more likely in the near future. Stay tuned, I’ll let you know if this review changes.