Spain's Cumbre Vieja Volcano and the Megatsunami Threat: Could a Catastrophic Wave Hit the Atlantic?

The Cumbre Vieja volcano, located on La Palma, one of Spain's Canary Islands, has for some time been a subject of intense study and debate among scientists. One concern of geologists is that the western wall or mountain slope of this volcano, referred to in the language of physics as a flank, could become unstable and collapse into the Atlantic Ocean in the future. If such a catastrophic landslide were to occur, the resulting displacement could create a massive wave in the ocean, known in scientific terms as a megatsunami.

According to volcanologist Professor Bill McGuire, a massive section of the Cumbre Vieja mountain is slowly moving toward the ocean. Based on his article published in 'BBC Science Focus', computer simulations show that if this entire slope were to collapse into the ocean at once, the resulting destructive waves would travel at speeds of hundreds of kilometers per hour. In a worst-case scenario, these waves could reach heights of up to 65 feet and strike the US Eastern Seaboard within just 9 hours. The extremely large and anomalous boulders found on the coast of the Bahamas provide evidence that tsunami waves caused by landslides on the Canary Islands in prehistoric times crossed the entire Atlantic Ocean to reach the other side.

There is a fundamental physical difference between a regular tsunami and a megatsunami. A regular tsunami is caused by the movement of tectonic plates or earthquakes on the ocean floor. In this process, the entire water column is displaced as the sea floor rises or falls. Such regular tsunamis have a height of only 30 centimeters (12 inches) in the deep ocean and are often imperceptible even if a ship passes over them; however, when they reach the coast, their height can increase to a maximum of 30 meters (100 feet) due to the shallow water. In contrast, a megatsunami is created when an enormous quantity of soil, rock, or debris suddenly crashes into the water or onto the shore. In this process, the water is violently splashed upward and outward, which causes the initial height of these waves to be extremely large, reaching hundreds of meters.

From a historical perspective, there is abundant documented evidence of megatsunamis caused by landslides. On July 9, 1958, a 7.8 magnitude earthquake in Lituya Bay, Alaska, caused 80,000,000 metric tons of rock and ice to crash directly into deep water. This impact caused water to surge up the opposite mountain to an incredible height of 524.6 meters (1,721 feet), which is the highest megatsunami run-up height (run-up height: the height to which water climbs on land at the coast) recorded in human history.

Cumbre Vieja is an active volcanic ridge stretching 25 kilometers across the southern half of the island of La Palma, Spain. Geological maps show that in the past, this volcano possessed a triple rift system, which has since changed and transformed into a single north-south rift. Due to magma channels or dykes that have penetrated parallel to the mountain's interior, the western slope has become extremely steep and unstable. Scientists believe that a detachment fault (a crack separating the mountain from the base rock) is developing at the base of this mountain.

The foundation of this fear was laid during the 1949 eruption or the San Juan volcanic event. During the eruption that began on June 24, 1949, intense earthquakes occurred on July 1 and 2. Following these earthquakes, a crack ranging from 1.5 kilometers to 2.5 kilometers long was observed on the summit of Cumbre Vieja. Due to this crack, the western half of the mountain shifted 1 meter to the side and 2 meters downward toward the Atlantic Ocean. In some areas, this vertical displacement was recorded up to 4 meters. This 1949 crack is still visible there today, which has sparked intense debate among scientists as to whether this is the preliminary beginning of the collapse of the western slope.

To understand the process of how landslides generate tsunamis, scientists use the Froude number. This number represents the ratio between the speed of the landslide and the speed of wave propagation. Waves formed by landslides in the ocean are generally short in wavelength. According to the laws of physics, waves with short wavelengths lose their energy quickly (radial damping). Therefore, landslide tsunamis show highly destructive run-ups near the coast, but their intensity decreases as they move into the deep ocean. In the landslide that occurred in Papua New Guinea on July 17, 1998, 15-meter-high waves claimed the lives of 2,200 people along 20 kilometers of coastline, but there was no significant impact in distant areas.

In the 20th century, the Cumbre Vieja volcano experienced major eruptions in 1949, 1971 (the Teneguía eruption), and most recently on September 19, 2021. In the 10 days leading up to the 2021 eruption, more than 25,000 earthquakes were recorded. This eruption lasted until December 13, 2021, forcing the evacuation of over 7,000 people and destroying thousands of homes. This event once again raised questions regarding the stability of the mountains of La Palma.

But will the east coast of America truly be destroyed? The scientific community is divided on this matter. According to the theory proposed by Day et al. (1999), the flank of Cumbre Vieja would collapse into the sea as a single monolithic block, creating a catastrophic megatsunami. However, many modern geologists and experts in hydrodynamics disagree with this simulation. They argue that instead of collapsing all at once, the mountain would slide into the sea in a piecemeal collapse, which would not generate a massive, terrifying wave. Furthermore, it remains unclear whether the cause behind the 1949 fissure was magma pressure or surface displacement.

Experts agree that even if such a cataclysmic event were to occur, the possibility of it happening tomorrow or in the near future is negligible. Professor McGuire himself admits that it could take centuries or millennia for this event to occur. Therefore, there is no immediate danger to people living on the Atlantic coast at the present time, but Cumbre Vieja is becoming an extremely important natural laboratory for understanding the Earth's geological history and the destructive potential of active volcanoes.