A mile-wide asteroid that slammed into Earth 66 million years ago wiped out nearly all of the dinosaurs and about three-quarters of the planet’s plant and animal species.
It also caused a terrible tsunami with mile-high waves sweeping the ocean floor thousands of miles from the impact site on Mexico’s Yucatan Peninsula, according to a new study by the University of Michigan.
The study is scheduled for online publication in the journal Oct. 4 AGU Advances, presents the first global simulation of the Chicxulub impact tsunami to be published in a peer-reviewed scientific journal. In addition, the UM researchers examined geological annals at more than 100 sites around the world and found evidence to support their models’ predictions of the path and power of the tsunami.
“This tsunami was strong enough to disturb and erode the sediments ocean basins halfway around the globe, leaving either a gap in the sedimentary record or a jumble of older sediments,” said lead author Molly Range, who conducted the modeling study for her master’s thesis under the guidance of physical oceanographer and study co-author Brian Orbick and UM paleoceanographer and study co-author Ted Moore .
The review of the geologic record focused on “margins,” marine sediments deposited just before or immediately after the asteroid impact and the subsequent K-Pg mass extinction that closed the Cretaceous.
“The distribution of erosion and hiatus we observed in the uppermost Cretaceous marine sediments match the results of our model, giving us more confidence in the model’s predictions,” said Range, who began the project as an undergraduate in the Orbick lab in the Department of Earth and Environmental Sciences.
The study authors estimated that the initial energy of the impact tsunami was 30,000 times greater than that of the December 2004 Indian Ocean earthquake, which killed more than 230,000 people and was one of the largest tsunamis on record.
Modeling by the team shows that the impact tsunami propagated mainly east and northeast into the North Atlantic Ocean and southwest through the Central American Seaway (which used to separate North America from South America) into the South Pacific.
In these basins and some adjacent areas, submarine currents probably exceeded 20 centimeters per second (0.4 mph), a velocity strong enough to erode fine-grained sediments on the seafloor.
In contrast, the southern Atlantic, northern Pacific, Indian Ocean and the region that is today the Mediterranean Sea were largely shielded from the worst effects of the tsunami, according to the team’s simulations. At these locations, the simulated current velocities were probably less than the 20 cm/s threshold.
To review the geologic record, UM’s Moore analyzed the published records of 165 marine boundary sites and was able to extract usable information from 120 of them. Much of the sediment comes from cores collected during scientific ocean drilling projects.
The North Atlantic and South Pacific had the fewest sites with complete, continuous K-Pg boundary deposits. In contrast, the highest numbers of complete K-Pg boundary sections were found in the South Atlantic, North Pacific, Indian Ocean, and Mediterranean Sea.
“We found confirmation in the geologic record of predicted zones of maximum impact in the open ocean,” said Orbick, a professor of earth and environmental sciences who oversaw the project. “The geological evidence certainly strengthens the paper.”
Of particular importance, according to the authors, are the outcrops of the K-Pg boundary on the eastern coasts of the North and South islands of New Zealand, which are more than 12,000 kilometers (7,500 miles) from the Yucatan impact site.
New Zealand’s highly disturbed and incomplete sediments, called olistostromal sediments, were originally thought to be the result of local tectonic activity. But given the age of the deposits and their location directly in the simulated path of the Chicxulub tsunami, the UM-led research team suspects a different origin.
“We believe that these deposits record the effects of an impact tsunami, and this is perhaps the strongest confirmation of the global significance of this event,” Range said.
The simulated 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, which included an impact, cratering, and tsunami initiation. This work was conducted by co-author Brandon Johnson of Purdue University.
Based on the findings of previous studies, the researchers modeled an asteroid with a diameter of 14 kilometers (8.7 miles) moving at a speed of 12 kilometers per second (27,000 miles per hour). It collided with granitic crust covered in thick sediments and shallow ocean waters, blasting a crater about 100 kilometers (62 mi) wide and spewing dense 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 (2.8 mi) high wave that subsided as the ejecta fell back to Earth.
Ten minutes after the projectile hit the Yucatan and 220 kilometers (137 mi) from the point of impact, a 1.5-kilometer (0.93 mi) tsunami wave—circular and spreading outward—began to sweep across the area. of the ocean in all directions, according to UM simulations.
After 10 minutes, Johnson’s iSALE hydrocode simulation results were fed into two tsunami propagation models, MOM6 and MOST, to track giant waves across the ocean. MOM6 has been used to model deep-ocean tsunamis, and NOAA actively uses the MOST model for tsunami forecasts at its Tsunami Warning Centers.
“The big takeaway here is that the two global models with different formulations produced nearly identical results, and the geologic data at full and incomplete sections are consistent with those results,” said Moore, emeritus professor of earth and environmental sciences. “Models and validation data agree well.”
According to the simulation team:
- An hour after the impact, the tsunami spread beyond the Gulf of Mexico to the North Atlantic.
- Four hours after the impact, the waves passed through the Central American Seaway and entered the Pacific Ocean.
- Within 24 hours of the impact, the waves had crossed most of the Pacific Ocean from the east and most of the Atlantic Ocean from the west and entered the Indian Ocean on both sides.
- Within 48 hours of the impact, significant tsunami waves had 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 tsunamis.
However, their models show that open-ocean wave heights in the Gulf of Mexico would exceed 100 meters (328 ft) and wave heights of more than 10 meters (32.8 ft) as the tsunami approaches coastal regions of the North Atlantic and parts of the South Pacific coast of America.
As the tsunami approached these shores and encountered shallow bottom waters, the height of the waves increased dramatically through a process called shoaling. Current velocities would exceed the threshold of 20 centimeters per second for most coastal areas of the world.
“Depending on the geometry of the coast and the incoming waves, most coastal regions will be inundated and eroded to some extent,” the study authors state. “Any historically documented tsunami pales in comparison to such a global impact.”
A follow-up study is planned to model the extent of coastal inundation around the world, Orbick said. This study will be led by Vasyl Titov of the National Oceanic and Atmospheric Administration’s Pacific Marine Environmental Laboratory, who is a co-author AGU Advances paper
The impact of Chicxulub caused a powerful global tsunami, AGU Advances (2022). agupubs.onlinelibrary.wiley.co … 10.1029/2021AV000627
University of Michigan
Citation: Dinosaur-killing Asteroid Triggers Global Tsunami That Ripples Sea Floor Thousands of Miles From Impact Site (2022, October 4) Retrieved October 4, 2022, from https://phys.org/news/2022-10- dinosaur-killing-asteroid-triggered- global-tsunami.html
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