A collapsing flank of a Canary Islands volcano could send a wave racing across the Atlantic

On the small Spanish island of La Palma sits a volcano whose western flank has become the subject of one of the most debated hazard scenarios in earth science. If a large section of that slope ever slid into the sea at once, some researchers have argued, it could launch a wave capable of crossing the entire Atlantic Ocean.

The volcano and the ridge in question

Cumbre Vieja is an active volcanic ridge that makes up the southern half of La Palma, in the Canary Islands off the northwest coast of Africa. Like many ocean volcanoes, it has grown through repeated eruptions that pile up steep, unstable slopes of rock. Volcanic islands around the world bear the scars of past flank collapses, in which enormous chunks of a mountainside have broken away and tumbled into the ocean.

Such large-scale collapses are a recognized volcanic hazard, a process documented across many settings by the U.S. Geological Survey. The concern at Cumbre Vieja centers on its western flank, where studies of the ridge have suggested that a future eruption could, in a worst case, destabilize a large volume of rock along a pre-existing weakness and send it sliding seaward.

The scenario that started the alarm

The dramatic version of the threat came from a modeling study published in 2001 that imagined a catastrophic failure dropping on the order of 150 to 500 cubic kilometers of rock into the Atlantic. As explained in a Penn State overview of Canary Island landslides and potential megatsunamis, the authors calculated that such a collapse could generate waves traveling at roughly the speed of a jet, tall enough near the source to devastate the Canaries and still substantial after crossing the ocean to the Americas.

In that scenario, waves might arrive on the far side of the Atlantic still tens of feet high, striking coastlines in western Europe, northwest Africa, and the eastern seaboard of North America. It was this vision of a transoceanic megatsunami that captured public attention and spawned countless documentaries.

Why many scientists say the threat is overstated

The megatsunami scenario has drawn substantial pushback. Critics argue that the original model relied on assumptions that do not match how such collapses actually behave. Rather than failing as a single coherent block moving at high speed, real flank collapses tend to break apart into multiple stages and pieces, which would produce smaller and more localized waves.

Later modeling suggested that near-field waves, while still formidable enough to endanger the Canary Islands themselves, would be far more moderate than the earliest predictions, and that the energy reaching distant coasts would be greatly reduced. Several researchers have described the assumptions behind the most alarming forecasts as unrealistic regarding the size, speed, and coherence of the failure.

The record of past collapses supports the more cautious view. Study of the seafloor around the Canary Islands and other volcanic archipelagos has revealed the debris of numerous ancient flank failures, and the deposits suggest that many of them broke apart in stages, spread over time, rather than dropping as a single giant block. A staggered collapse displaces far less water at once than an instantaneous one, which is exactly the difference between a catastrophic transoceanic wave and a serious but more contained regional tsunami.

What is actually known about the slope

What is not in dispute is that Cumbre Vieja is an active volcano capable of erupting, as it did during a lengthy eruption in 2021 that destroyed thousands of buildings on La Palma without triggering any collapse of the flank. Instrument monitoring during that eruption did not reveal the kind of large-scale slope movement that a catastrophic failure would require.

Geologists generally agree that a major flank collapse, if it happens at all, is likely to be a rare event separated from the next by many thousands of years, and one that would probably unfold in stages rather than in a single instantaneous slide. That framing turns a doomsday image into a low-probability hazard worth studying rather than an imminent catastrophe.

How the risk is monitored and weighed

Because the stakes of even a rare event are high, the volcano is closely watched. Networks of seismometers, ground-deformation sensors, and satellite measurements track any sign that the western flank is moving, giving scientists a chance to detect instability long before a collapse. Tsunami warning systems around the Atlantic add another layer of protection for distant coasts.

That monitoring matters because flank collapses, while rare, are genuine hazards. Even a partial failure could threaten the roughly 80,000 residents of La Palma and nearby islands, along with coastal communities across the region, so the goal is not to dismiss the danger but to size it accurately. Overstating the threat can breed complacency once the alarming version is debunked, while understating it leaves people unprepared.

The lasting lesson of Cumbre Vieja is less about a specific wave than about how hazard science handles uncertainty. A single striking model can dominate the public imagination, while the slower work of testing its assumptions reveals a more measured picture, one in which the possibility of an Atlantic-crossing wave remains real in principle but far less likely than the most frightening headlines once implied.

This article was produced with the assistance of AI and reviewed by Morning Overview editors prior to publication.

More from Morning Overview