The work is the first global simulation of the Chicxulub impact tsunami to be published in a peer-reviewed scientific journal. It was just released in the journal AGU Advances.

The Chicxulub impact caused a strong tsunami around the world.

The 66 million-year-old asteroid that struck Earth killed off nearly all of the dinosaurs as well as around three-quarters of the planet’s plant and animal species.

A new study led by researchers at the University of Michigan says that it also caused a huge tsunami with waves a mile high that scoured the ocean floor thousands of miles from where it hit, on Mexico’s Yucatan Peninsula.

This study will be the first global simulation of the Chicxulub impact tsunami to appear in a scholarly journal, and it will be published online in the journal AGU Advances on October 4. Also, U-M researchers looked at the geological history of more than 100 places around the world and found evidence that backs up what their models say about the path and power of the tsunami.

Lead author Molly Range, who worked on the modeling study for a master’s thesis under U-M physical oceanographer Brian Arbic and U-M paleoceanographer Ted Moore, said that the tsunami was powerful enough to disturb and erode sediments in ocean basins halfway around the world. This caused either a gap in the sedimentary records or a jumble of older sediments.

The analysis of the geological record concentrated on “boundary sections,” marine sediments laid down immediately before or immediately after the asteroid impact and the ensuing K-Pg mass extinction, which brought an end to the Cretaceous Period.

“The distribution of the erosion and hiatuses that we observed in the uppermost Cretaceous marine sediments are consistent with our model results, which gives us more confidence in the model predictions,” added Range.

The authors of the study estimated that the initial energy of the impact wave was up to 30,000 times more than the energy of the Indian Ocean earthquake tsunami of December 2004, which killed more than 230,000 people and is one of the greatest tsunamis in recorded history.

According to the team’s models, the impact tsunami mostly spread east and northeast into the North Atlantic Ocean and southwest through the Central American Seaway (which once divided North America from South America) into the South Pacific Ocean.

Underwater current velocities in those basins and certain nearby regions probably exceeded 20 centimeters per second (0.4 mph), a velocity powerful enough to destroy fine-grained sediments on the seafloor.

The South Atlantic, North Pacific, Indian Ocean, and what is now the Mediterranean were, however, mostly protected from the worst of the tsunami’s effects, as predicted by the team’s model. The modeled current velocity there were probably below the 20 cm/sec cutoff.

Moore from the University of Michigan looked at published records of 165 marine boundary sections and was able to get useful information from 120 of them for the review of the geological record. The majority of the sediments came from cores that were taken during research initiatives involving ocean drilling.

The South Pacific and North Atlantic have the fewest locations with uninterrupted, complete K-Pg border deposits. In contrast, the South Atlantic, the North Pacific, the Indian Ocean, and the Mediterranean were where the most complete K-Pg boundary sections were discovered.

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

According to the authors, the K-Pg border outcrops on the eastern beaches of New Zealand’s north and south islands, which are more than 12,000 kilometers (7,500 miles) from the Yucatan impact site, are of particular relevance.

Initially, it was believed that the extremely disrupted and unfinished New Zealand sediments, known as olistostromal deposits, were the product of nearby tectonic activity. The U-M-led research team, however, has a different theory about the origin of the deposits because of their age and their proximity to the tsunami’s predicted route after the Chicxulub hit.

The most revealing indication of the event’s global significance, according to Range, is that these deposits appear to be documenting the repercussions of the impact tsunami.

The study’s modeling component employed a two-stage approach. First, the chaotic first 10 minutes of the event—which included the impact, crater creation, and start of the tsunami—were reproduced by a sizable computer program known as a hydrocode. Brandon Johnson, a co-author from Purdue University, carried out the research.

Based on prior research, the researchers created a model of an asteroid 14 kilometers (8.7 miles) in diameter and travelling at 12 kilometers per second (27,000 mph). It collided with granitic crust overlain by thick sediments and shallow ocean waters, ejecting huge clouds of soot and dust into the atmosphere and producing a 100-kilometer-wide (62-mile-wide) crater.

A wall of water was forced outward from the impact site two and a half minutes after the asteroid hit, briefly creating a 4.5-kilometer-high (2.8-mile-high) wave that dissipated when the ejecta plummeted back to Earth.

According to the U-M simulation, a 1.5-kilometer-high (0.93-mile-high) tsunami wave that was ring-shaped and was spreading outward started sweeping across the ocean in all directions ten minutes after the projectile hit the Yucatan, 220 kilometers (137 miles) from the place of impact.

At the 10-minute mark, the outputs of Johnson’s iSALE hydrocode simulations were inputted into two tsunami-propagation models, MOM6 and MOST, in order to track the massive ocean waves. MOM6 has been used to predict tsunamis in the deep ocean, and NOAA’s Tsunami Warning Centers employ the MOST model for operational tsunami forecasting.

“The big result here is that two global models with differing formulations gave almost identical results, and the geologic data on complete and incomplete sections are consistent with those results,” Moore said. “The models and the verification data match nicely.”

The simulation by the team indicates that:

• After impact, the tsunami traveled into the North Atlantic and beyond the Gulf of Mexico.
• The waves entered the Pacific Ocean four hours after impact and traveled via the Central American Seaway.
• The waves entered the Indian Ocean from both the east and the west twenty-four hours after the impact, covering the majority of the Pacific from the east and the majority of the Atlantic from the west.
• Significant tsunami waves had reached the majority of the world’s coastlines 48 hours after the earthquake.

For this study, the researchers did not try to estimate how much the tsunami caused the coast to flood.

But according to their calculations, the Gulf of Mexico would have seen open-ocean waves that were over 10 meters (32.8 feet) high when the tsunami approached the North Atlantic coastline and portions of the Pacific coast of South America.

Wave heights would have substantially increased due to a phenomenon called shoaling as the tsunami approached certain shorelines and came into contact with shallow bottom waters. For most coastal regions across the world, current speeds would have exceeded the 20 millimeters per second limit.

“Depending on the geometries of the coast and the advancing waves, most coastal regions would be inundated and eroded to some extent,” according to the study authors. “Any historically documented tsunamis pale in comparison with such global impact.”

Arbic said that a follow-up study is planned to model the amount of coastal flooding around the world. This investigation will be directed by Vasily Titov of the Pacific Marine Environmental Lab of the National Oceanic and Atmospheric Administration, who is a co-author of the AGU Advances paper.

Image Credit: AGU Advances

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