The devastating tsunamis that struck the coastlines of Chile, Haiti, Indonesia, and Japan in recent decades produced waves tens of meters high, unimaginable to most people accustomed to gentle seas. But millions of years ago, a truly inconceivable set of waves—the tallest roughly 1,500 meters high—rammed through the Gulf of Mexico and spread throughout the ancient ocean, producing wave heights of several meters in distant waters, new simulations show.
The enormous waves were triggered by a large asteroid slamming into the shallow waters of the modern-day Yucatán Peninsula. That asteroid impact, which occurred about 66 million years ago and created the Chicxulub crater, contributed to the demise of the dinosaurs.
A Global Look
Molly Range, a paleoceanographer working at the University of Michigan when this research was conducted, and her colleagues have now modeled how the ensuing tsunami propagated in the Gulf of Mexico and beyond. “As far as we know, no one has done a global simulation of this impact,” said Range.
Range and her collaborators used two models: one simulating the initial impact of an asteroid 14 kilometers in diameter into shallow water and one modeling the ensuing propagation of displaced water throughout the ancient ocean. It was necessary to use the two models in tandem, explained Brian Arbic, a physical oceanographer at the University of Michigan who was involved in the study. “A typical ocean model just can’t handle an asteroid,” he noted.
The first effect of the asteroid impact, the researchers found, would have been a roughly 1,500-meter-high tsunami wave. This wave represented the “initial blast of water away from the impact,” said Range.
A simulation is shown in the video below. Crustal material is shown in brown, sediments are shown in yellow, and the ocean is shown in blue.
A few minutes later, the models show that water began refilling the gaping crater formed by the impact. “You have a steep wall of water that rushes back in,” said Arbic. This rapid inflow likely triggered yet another set of waves. Although the strongest effects from the tsunami were felt in the Gulf of Mexico, the waves would have propagated globally, Range and her team found. Thanks to the seaway that existed between North America and South America at the time of the dinosaurs, the tsunami waves would have rushed freely into the Pacific Ocean.
Range and her colleagues calculated that the tsunami wave heights in the Pacific and Atlantic basins would have been as large as 14 meters. As these waves approached land and slowed down, they would have gotten even larger. But because the researchers’ models didn’t include the topography of the continents 66 million years ago, it wasn’t possible to calculate actual wave run-up heights, Arbic said.
The video below provides a look at how the waves propagated around the world as well as an estimate of their heights.
The scientists also showed that the tsunami waves would have pushed water at the seafloor by more than 20 centimeters per second. Such strong water flows are sufficient to scour sediments from the bottom of the ocean, the researchers said. Scouring would have occurred in the South Pacific and the North Atlantic, the modeling revealed. Tantalizingly, in-progress research by the same team is showing that these very places are also where sediment coring experiments have found dislodged and displaced sediments.
These results were presented last week at AGU’s Fall Meeting 2018 in Washington, D. C.
The implications of this work are significant, said Timothy Bralower, an Earth scientist at Pennsylvania State University who was not involved in the research. “Geologists can now glean the sediments at sites far afield from the crater to detect the fingerprints of the tsunami.”
This modeling provides a glimpse into a cataclysmic part of Earth’s history that, thankfully, hasn’t been repeated. But more advanced simulations—incorporating, for example, higher spatial resolution or estimates of on-land topography so wave run-ups can be estimated—would improve our understanding of this tsunami, Arbic explained.
But one thing is very clear: The Chicxulub tsunami was clearly a force to be reckoned with. As Arbic said, “It must have been one of the biggest tsunami ever.”