66 million years ago, an asteroid 10 km wide hit what is now the Yucatan Peninsula (Mexico) with a force equivalent to ten billion atomic bombs like the one at Hiroshima. The impact set forests on fire and released enough sulfur into the atmosphere to block sunlight. A winter that lasted for years Three-quarters of the animal and plant species that existed during that time became extinct, including almost all dinosaurs. But in addition, the blow unleashed a monstrous tsunami, with waves over one and a half kilometers high, that swept the ocean floor thousands of kilometers from the point of impact. They reached New Zealand.
This is the conclusion of a team of researchers from the University of Michigan (USA) who carried out a global simulation of the tsunami after the Chicxulub impact.
“This tsunami was strong enough to disturb and erode sediments in ocean basins on the other side of the world, leaving a gap in the sedimentary record or a jumble of old sediments,” explains Molly Range, who was responsible for the study published in AGU Advances’.
Researchers have calculated that the initial energy of the tsunami was 30,000 times greater than the tsunami energy of the December 2004 Indian Ocean earthquake, which killed more than 230,000 people and was one of the largest tsunamis in modern history.
The team’s simulations showed that the tsunami propagated mainly east and northeast into the North Atlantic Ocean and southwest through the Maritima Centroamericana (used to separate North and South America) into the South Pacific Ocean.
In those basins and some surrounding areas, undersea current speeds can exceed 20 centimeters (0.4 mph) per second, strong enough to erode fine sediments on the seafloor.
In contrast, the South Atlantic, North Pacific, Indian Ocean and what is now the Mediterranean Sea were largely shielded from the strong effects of the tsunami, according to the team’s simulations. At those locations, current model velocities may be below the 20 cm/s threshold.
The researchers reviewed the geological record from more than 100 locations around the world. The results are consistent with the models. Of particular importance, according to the authors, are the highly disturbed and incomplete sediments on the east coast of New Zealand’s North and South Islands, more than 12,000 kilometers from the Yucatan impact site. “We think these deposits record the effects of a tsunami impact, and this may be a strong confirmation of the global importance of this event,” says Range.
4.5 km high tide
The modeling part of the study used a two-stage strategy. First, a large computer program called Hydrocode simulated the chaotic first 10 minutes of the event, including impact, crater formation and the onset of the tsunami.
Based on the findings of previous studies, the researchers modeled an asteroid with a diameter of 14 kilometers and a speed of 12 kilometers (27,000 miles) per second. It struck a granite crust covered by thick sediment and shallow seawater, opening a crater about 100 kilometers wide and spewing thick clouds of soot and dust into the atmosphere.
Two and a half minutes after the asteroid hit, a curtain of ejected material pushed a wall of water away from the impact site, briefly creating a 4.5-kilometer-high wave that subsided as the emission returned to Earth.
Ten minutes after the projectile hit the Yucatan, 220 kilometers from the point of impact, a 1.5 kilometer high tsunami wave formed a ring and spread outwards, sweeping the sea in all directions. , according to the simulation.
At the 10-minute mark, the results of the simulations were fed into two tsunami propagation models, MOM6 and MOST, to track rogue waves across the ocean. MOM6 has been used to model tsunamis in the deep ocean, and NOAA uses the model extensively in its Tsunami Warning Centers for operational tsunami forecasts.
“The big conclusion here is that the two global models with different formulations gave almost identical results, and the geologic data in complete and incomplete sections are consistent with those results,” says Ted Moore, professor of earth and environmental sciences.
According to the team’s simulation, about an hour after impact, the tsunami spread from the Gulf of Mexico to the North Atlantic. Four hours after the attack, waves crossed the Central American coast and entered the Pacific. Twenty-four hours after impact, they crossed most of the Pacific Ocean from the east and most of the Atlantic Ocean from the west, entering the Indian Ocean on both sides. Within 48 hours of the impact, significant tsunami waves reached most of the world’s coastlines.
For the current study, the researchers did not attempt to estimate the extent of coastal flooding caused by the tsunami. However, their models show that open ocean wave heights in the Gulf of Mexico exceed 100 m, and wave heights exceed 10 m as the tsunami approaches coastal areas of the North Atlantic and US Pacific coasts.
As the tsunami approached those shorelines and encountered shallower bottom water, the height of the waves would have increased dramatically through a process known as banking. Current velocities exceed 20 centimeters per second for most coastal areas of the world.
“Depending on coastal geometry and advancing tides, most coastal areas are inundated and eroded to some extent,” the study authors report. “Historically documented tsunamis pale in comparison to such a global impact,” they add.
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