The Tectonic Clock – Part 4: Skyscraper Waves: When Oceanic Collapse Devastates Continents

The Deceit of Volcanic Stability

The Earth’s crust beneath the oceans holds threats far exceeding routine earthquakes or storms. The horrific Asian tsunami of 2004, which killed 300,000 people, demonstrated the catastrophic potential of displaced water. Yet, an even rarer and more terrifying oceanic hazard is the colossal volcanic landslide, capable of generating tsunamis that span entire ocean basins. Most people perceive volcanoes as rigid, static sentinels; however, they are often nothing more than unstable piles of ash and lava rubble, “rotten to the core,” constantly shifting and primed for collapse. This process, known as volcano lateral collapse, is a normal part of a volcano’s lifecycle and occurs globally about half a dozen times per century. The danger escalates exponentially when this collapse occurs into a massive body of water.

A Thesis of Megatsunamis and Systemic Coastal Destruction

The central claim is that the episodic, near-unpredictable collapse of oceanic island volcanoes presents a low-frequency, high-consequence risk capable of generating continent-spanning megatsunamis, an acute threat magnified by rising sea levels and global coastal urbanization. While routine tsunamis are typically triggered by submarine earthquakes, the sheer volume of rock displaced by a massive volcanic flank collapse generates waves orders of magnitude greater.

An Analytical Core of Landslides, Water, and Coastal Vulnerability

Foundation & Mechanism: The Scale of Oceanic Landslides

The Mount St Helens eruption in 1980 was scientifically pivotal because it highlighted the mechanism of lateral collapse, although that event involved a landslide of less than one cubic kilometer. By comparison, underwater surveys around Hawaii reveal nearly 70 identified giant landslides, some exceeding 1,000 cubic kilometers in volume. The last massive collapse in Hawaii, roughly 120,000 years ago from the Mauna Loa volcano, generated giant tsunamis that surged an astonishing 400 meters up the flanks of the neighboring Kohala volcano—significantly higher than the Empire State Building. These massive waves remain tens of meters high even when they hit land half an ocean away, posing a direct threat to the entirety of the Pacific Rim. Since tsunamis travel at the speed of a Jumbo Jet in deep water, major coastal cities in North America and Asia would have barely 12 hours warning before being hit.

The Crucible of Context: The Cumbre Vieja Threat

The threat is not confined to the Pacific. Scientific research indicates that the western flank of the Cumbre Vieja volcano on the Canary Island of La Palma is primed and ready for collapse. This gigantic chunk of volcanic rock, estimated at several hundred cubic kilometers, dropped four meters toward the Atlantic during the 1949 eruption and then stopped, but is believed to be now detached and slowly creeping seawards. Although the precise timing is unknown—it could be next year or 10,000 years from now—the collapse is almost certain to occur, likely triggered by a new eruption. Modelling of a worst-case scenario collapse (500 cubic kilometers) shows that the immediate entry of the rock mass would generate an initial dome of water nearly 900 meters high.

Cascade of Effects: The Atlantic Meltdown Scenario

The subsequent series of gigantic waves would scour the Canary Islands and African mainland before heading across the Atlantic. Barely nine hours after the landslide, the east coast of the United States—including Boston, New York, Baltimore, Washington, and Miami—would bear the full brunt of waves, with focusing effects in harbors and estuaries potentially increasing heights to 50 meters or more. Unlike wind-driven waves, tsunamis have wavelengths hundreds of kilometers long, meaning they crash into the coast as a solid wall of water and keep coming for ten or fifteen minutes before receding. Without massive, effective evacuation during the nine-hour window, the death toll could run into millions. Furthermore, such an event would wipe out the insurance industry instantly, leading to a swift global economic meltdown. Researchers also worry that the current climate crisis accelerates this risk. My own research suggests a link between increased volcanic collapse and periods of changing sea level. As global warming is forecast to continue raising sea levels and bringing heavier rainfall to volcanic island chains, the collapse events might be brought forward.

A Shift in Planetary Risk Calculation

The frequency of major collapse events at volcanic islands may be as high as one every 10 millennia, a very frequent occurrence on a geological timescale that provides serious cause for concern. The risk calculation is no longer theoretical, but is actively evolving in response to human-induced climate change. Increased rainfall, combined with melting permafrost caused by warmer temperatures, is already destabilizing mountainous regions in the Alps and Pyrenees, leading to more rockfalls and mudflows. Crucially, the warming ocean may cause the rapid dissociation of gas hydrates—methane solids found in marine sediments—into gaseous states, potentially leading to the destabilization and collapse of massive sediment masses, similar to the ancient Storegga Slides off Norway. The future promises a “fiery” scenario driven not just by internal geology, but by the destabilizing feedback loops between the atmosphere, the oceans, and the Earth’s crust. We must adapt by moving inland and uphill, or prepare to face the combined wrath of Vulcan and Neptune.