A dinosaur-killing asteroid triggered a global tsunami that eroded the seafloor thousands of kilometers from the impact site

The mile-wide asteroid that struck Earth 66 million years ago wiped out nearly all of the planet’s dinosaurs and about three-quarters of the planet’s plant and animal species.

It also unleashed a monstrous tsunami with miles-high waves that ripped through the ocean floor thousands of miles from the impact site on Mexico’s Yucatan Peninsula, according to a new study from the University of Michigan.

The study, which is scheduled to be published online in the journal on October 4 AGU progress, presents the first global simulation of the Chicxulub impact tsunami to be published in a peer-reviewed scientific journal. In addition, UM researchers reviewed the geological record at more than 100 locations worldwide and found evidence supporting their models’ predictions of the tsunami’s path and magnitude.

“This tsunami was powerful enough to disrupt and erode sediments in ocean basins halfway around the world, leaving either a gap in the sediment record or a jumble of older sediments,” said lead author Molly Range, who conducted the modeling study for a master’s thesis under UM oceanographer and study co-author Brian Arbic; and UM paleoceanographer and study co-author Ted Moore.

Review of the geological record focused on “boundary stretches,” marine sediments deposited just before or just after the asteroid impact and subsequent K-Pg mass extinction event that ended the Cretaceous.

“The distribution of erosion and gaps we observed in Upper Cretaceous marine sediments are consistent with our model results, giving us more confidence in the model predictions,” said Range, who started the project as a student in Arbic’s lab in the department Earth and Environmental Sciences.

The study authors calculated that the initial energy of the impact tsunami was up to 30,000 times greater than the energy of the December 2004 Indian Ocean earthquake tsunami, which killed more than 230,000 people and is one of the largest tsunamis in the modern record .

The team’s simulations show that the impact tsunami radiated primarily east and northeast into the North Atlantic and southwest through the Central American Sea Route (which used to separate North America and South America) into the South Pacific.

In these basins and some adjacent areas, underwater current speeds likely exceeded 20 centimeters per second (0.4 mph), a speed strong enough to erode fine-grained sediments on the sea floor.

In contrast, according to the team’s simulation, the South Atlantic, North Pacific, Indian Ocean and what is now the Mediterranean Sea were largely shielded from the strongest effects of the tsunami. At these locations, the modeled flow velocities were probably below the 20 cm/s threshold.

To review the geological record, Moore analyzed UM’s published records from 165 sea boundary sections and was able to obtain actionable information from 120 of them. Most of the sediments came from drill cores collected during scientific marine drilling.

The North Atlantic and South Pacific had the fewest sites of complete, uninterrupted K-Pg boundary sediments. In contrast, most complete K-Pg boundary sections have been found in the South Atlantic, North Pacific, Indian Ocean, and Mediterranean Sea.

“We found confirmation in the geological record for the predicted areas of maximum impact in the open ocean,” said Arbic, a professor of earth and environmental sciences who oversaw the project. “The geological evidence definitely strengthens the paper.”

Of particular importance, according to the authors, are outcrops at the K-Pg boundary on the east coast of the North and South Islands of New Zealand, more than 12,000 kilometers (7,500 miles) from the Yucatan impact site.

The severely disturbed and incomplete New Zealand sediments, called olistostromal deposits, were originally thought to be the result of local tectonic activity. But given the age of the deposits and their location directly in the modeled path of the Chicxulub impact tsunami, the UM-led research team suspects a different origin.

“We believe these deposits are recording the effects of the impact tsunami, and this is perhaps the most telling confirmation of the global significance of this event,” Range said.

The modeling part of the study used a two-step strategy. First, a large computer program called Hydrocode simulated the chaotic first 10 minutes of the event, which included impact, cratering and tsunami release. This work was conducted by co-author Brandon Johnson of Purdue University.

Based on the results of previous studies, the researchers modeled an asteroid 14 kilometers (8.7 miles) in diameter, moving at 12 kilometers per second (27,000 miles per hour). It struck a granite crust covered by thick sediments and shallow ocean water, blasted a crater about 100 kilometers wide (62 miles wide) and ejected dense clouds of soot and dust into the atmosphere.

Two and a half minutes after the asteroid’s impact, a curtain of ejected material pushed a wall of water outward from the impact site, briefly forming a 4.5-kilometer (2.8-mile) wave that subsided as the ejecta fell back toward Earth.

Ten minutes after the projectile struck the Yucatan, and 220 kilometers (137 miles) from the impact site, a 1.5-kilometer-tall (0.93-mile-tall) tsunami wave began — annular and spreading outward — across the Yucatan to sweep ocean in all directions, according to the UM simulation.

Maximum tsunami wave amplitude in centimeters after the asteroid impact 66 million years ago. Credit: Von Range et al. in AGU progress2022.

At the 10 minute mark, results from Johnson’s iSALE hydrocode simulations were fed into two tsunami propagation models, MOM6 and MOST, to track the giant waves across the ocean. MOM6 has been used to model deep sea tsunamis and NOAA uses the MOST model operationally for tsunami forecasts in their tsunami warning centers.

“The big result here is that two global models with different formulations gave almost identical results, and the geological data on complete and incomplete intervals agree with these results,” said Moore, professor emeritus of earth and environmental sciences. “The models and the verification data fit well together.”

According to the team’s simulation:

• An hour after impact, the tsunami had spread outside the Gulf of Mexico into the North Atlantic.
• Four hours after impact, the waves had made their way through the Central American Seaway and into the Pacific.
• 24 hours after impact, the waves had crossed most of the Pacific from the east and the Atlantic from the west, entering the Indian Ocean from both sides.
• 48 hours after impact, significant tsunami waves had reached most of the world’s coasts.

For the current study, 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 would have exceeded 100 meters (328 ft), with wave heights in excess of 10 meters (32.8 ft) as the tsunami approached the North Atlantic coastal regions and parts of the south America’s Pacific Coast.

As the tsunami approached these shorelines and encountered shallow groundwater, wave heights would have increased dramatically through a process called swarming. Current speeds would have exceeded the 20 centimeters per second threshold for most coastal areas worldwide.

“Depending on the geometry of the coast and the waves, most coastal regions would be partially flooded and eroded,” the study authors said. “Any historically documented tsunami pales in comparison to such global impacts.”

A follow-up study is planned to model the extent of global coastal flooding, Arbic said. This study is led by Vasily Titov of the National Oceanic and Atmospheric Administration’s Pacific Marine Environmental Lab, who is a co-author of the study AGU progress Paper.