Just off of the western coast of Mexico’s Yucatán peninsula lies the 12 mile deep, 6.2 mile wide Chicxulub crater. The 66 million year-old impact crater is the site where a massive asteroid struck the Earth, wiping out the dinosaurs and about three quarters of all life on Earth. But new evidence shows that it was even more destructive than previously realized.
A study published today in the journal AGU Advances shows that the asteroid also triggered a monstrous tsunami with mile-high waves that scoured the ocean floor thousands of miles from the impact site in Mexico. A team of researchers built the a first global simulation of the Chicxulub impact tsunami to be published in a peer-reviewed journal and reviewed the geological record at over 100 sites around the world to determine the tsunami’s path and power.
“This tsunami was strong enough to disturb and erode sediments in ocean basins halfway around the globe, leaving either a gap in the sedimentary records or a jumble of older sediments,” lead author Molly Range, who conducted the modeling study for a master’s thesis at the University of Michigan, said in a press release.
The team estimates that the initial energy in the Chicxulub impact tsunami was up to 30,000 times larger than the energy of the 2004 Indian Ocean earthquake tsunami—a devastating disaster killed more than 230,000 people and was one of the largest tsunamis in the modern record.
To determine just how powerful the tsunami was, the team analyzed the published records of 165 marine boundary sections, or marine sediments in the geologic record deposited around the time the asteroid struck the earth, and sediment cores. The cores act as a terrestrial timeline that scientists can use to analyze the layers or rock, sand, and ice to better understand what the Earth was like millions of years ago.
The K–Pg boundary (also called the K-T boundary) marks around the time where the astroid hits—ending the Cretaceous Period. Through the sediment in these boundary sections, they found that the impact tsunami radiated mainly to the east and northeast (into the North Atlantic Ocean), then later to the southwest through the Central American Seaway which used to separate the continents of North America and South America. Lastly, the tsunami diffused into the South Pacific Ocean.
“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,” said Range.
The authors also used the boundary section sediment to determine the speed of underwater currents in those basins. In some nearby spots, the current was likely 0.4 miles per hour (20 centimeters per second), a velocity that is strong enough to erode fine-grained sediments on the seafloor. By comparison, the South Atlantic, the North Pacific, the Indian Ocean, and the region that is today the Mediterranean appear to have been largely protected from the strongest effects of the tsunami.
Outcrops of the K-Pg boundary were found on the eastern shores of New Zealand’s north and south islands, over 7,500 miles (12,000 km) from the crater impact site. “We feel 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.
[Related: It was probably springtime when an asteroid did the dinosaurs in.]
To create the computer model of the mass extinction event, a large computer program called a hydrocode simulated the chaotic first 10 minutes of the extinction event. The asteroid in the simulation was modeled after previous studies that found the dinosaur-killing space rock to be 8.7 miles in diameter and moving at 27,000 mph After it struck the Earth’s crust under shallow ocean waters, a 62 mile (100 km) wide crater ejected dense clouds of dust and soot into the atmosphere.
According to the simulation, ejected material formed a 2.8 mile (4.5 km) high wave two and a half minutes after impact which then subsided when the material fell back to Earth. Ten minutes after the projectile hit the Yucatan, a 0.93 mile (1.5 km) high tsunami wave began rolling across the ocean in all directions.
This 10-minute simulation was entered into two tsunami-propagation models (called MOM6 and MOST) used by the National Oceanic and Atmospheric Administration (NOAA) to track and understand these enormous waves. “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,” University of Michigan paleoceanographer and study co-author Ted Moore said in a press release. “The models and the verification data match nicely.”
The simulation mirrored geologic findings, showing that about one hour after impact, the wave had spread outside the Gulf of Mexico and into the North Atlantic. Four hours after impact, the tsunami passed through the Central American Seaway and into the Pacific, and by the end of day one, the waves had crossed most of the Pacific Ocean and entered the Indian Ocean from both sides. By 48 hours after impact, significant tsunami waves had reached most of the coastlines on Earth.
“Depending on the geometries of the coast and the advancing waves, most coastal regions would be inundated and eroded to some extent,” the authors said. “Any historically documented tsunamis pale in comparison with such global impact.”
