The asteroid that caused a global tsunami with giant waves

66 million years ago, an asteroid more than 10 km wide crashed into what is now the Yucatan Peninsula (Mexico) with a force equivalent to that of ten billion atomic bombs like the one on Hiroshima. The impact set fire to forests and expelled so much sulfur into the atmosphere that it blocked out sunlight.

As a result, a winter that lasted years and during which three quarters of the species of animals and plants that existed then became extinct, including almost all the dinosaurs. But in addition, the blow unleashed a monstrous tsunami with waves over a kilometer and a half high that swept the ocean floor thousands of kilometers from the impact site. 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 older sediments.”explains Molly Range, responsible for the study published in ‘AGU Advances’.

The asteroid caused a global tsunami

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

The team’s simulations show that the tsunami radiated mainly east and northeast into the North Atlantic Ocean, and southwest through the Via Maritima Centroamericana (which used to separate North and South America) into the South Pacific Ocean. .

In those basins and some adjoining areas, undersea current speeds probably exceeded 20 centimeters per second (0.4 mph), a speed that is strong enough to erode fine-grained sediments on the seafloor.

In contrast, the South Atlantic, North Pacific, Indian Ocean, and the region that is now the Mediterranean were largely shielded from the tsunami’s strongest effects, according to the team’s simulation. At those locations, the current modeled velocities were likely below the threshold of 20 cm per second.

The researchers reviewed the geological record at more than 100 locations around the world. The results agreed with the models. Of particular importance, according to the authors, are highly disturbed and incomplete sediments on the eastern shores of New Zealand’s North and South Islands, which are more than 12,000 kilometers from the Yucatan impact site. “We believe that these deposits are recording the effects of the impact tsunami, and this is perhaps the strongest confirmation of the global importance of this event”Range says.

4.5 km high wave caused by the asteroid

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, which included the impact, the formation of the crater, and the start of the tsunami.

Based on the findings of previous studies, the researchers modeled an asteroid that was 14 kilometers in diameter and moving at 12 kilometers per second (27,000 mph). It struck a granitic crust covered by thick sediments and shallow ocean waters, opening a crater roughly 100 kilometers wide and ejecting dense clouds of soot and dust into the atmosphere.

Two and a half minutes after the asteroid impacted, a curtain of ejected material pushed a wall of water away from the impact site, briefly forming a 4.5-kilometer-high wave that subsided as the ejecta fell back to Earth. . Ten minutes after the projectile hit the Yucatan and 220 kilometers from the point of impact, a 1.5-kilometer-high tsunami wave in the shape of a ring and propagating outward began to sweep the ocean 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 MOST model operationally for tsunami forecasts at its Tsunami Warning Centers.

Two global models with different formulations

“The big result here is that two global models with different formulations gave almost identical results, and the geological data in complete and incomplete sections are consistent with those results.”says study co-author Ted Moore, a professor of earth and environmental sciences.

According to the team’s simulation, an hour after impact, the tsunami had spread out of the Gulf of Mexico and into the North Atlantic. Four hours after impact, the waves had crossed the Central American seaway into the Pacific. Twenty-four hours after impact, they had crossed most of the Pacific from the east and most of the Atlantic from the west, and had entered the Indian Ocean on both sides. And within 48 hours of 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 the tsunami. However, their models indicate that open-ocean wave heights in the Gulf of Mexico would have exceeded 100 meters, with wave heights exceeding 10 meters as the tsunami approached coastal regions of the North Atlantic and the American Pacific coast.

wave height

As the tsunami approached those shorelines and encountered shallow bottom waters, the height of the waves would have increased dramatically through a process called banking. Current speeds would have exceeded the threshold of 20 centimeters per second for most of the world’s coastal areas.

“Depending on the geometries of the coastline and advancing waves, most coastal regions would be flooded and eroded to some extent”according to the study authors. “Any historically documented tsunami pales in comparison to such a global impact”they add.

Font: J. DE JORGE / ABC

Reference article: https://www.abc.es/ciencia/asteroid-acabo-dinosaurs-levanto-oceano-mexico-nueva-20221003162835-nt.html