Death of the dinosaurs: First an asteroid, next a terrifying 1.5 km-high tsunami

Animation of the change in sea surface height tsunami propagation over 48 hours model. Shown in ten-minute increments. Credit: Range et al. in AGU Advances, 2022.

What could possibly be worse than dying from a 14-km wide asteroid hitting Earth at 12 kilometres per second? How about surviving that and then dealing with a mile-high tsunami afterwards?

For lifeforms left loitering after the impact 66 million years ago of an asteroid near the Gulf of Mexico town of Chicxulub (pro.: Chix-ah-lubb) – thought to be responsible for the extinction of around 75% of life on the planet (including most of the dinosaurs) – this would have been the terrifying reality.

For the first time, a global simulation of the Chicxulub impact tsunami has reached the shores of a peer-reviewed scientific journal. University of Michigan researchers were able to input the characteristics of the impactor, impact site and models of the Earth and sit back and watch the simulated waves roll around the globe.

What’s more, an investigation of over 100 sites has unearthed evidence supporting the predictions of the simulations.

One of the largest and most destructive tsunamis in recorded history is the 2004 Indian Ocean earthquake tsunami, which killed more than 230,000 people.

Researchers estimate the Chicxulub impact tsunami had up to 30,000 times the energy of the 2004 Indian Ocean earthquake tsunami, making it truly colossal.

The simulations show the tsunami mainly radiated east and northeast into the North Atlantic Ocean and to the southwest, with the South Atlantic, North Pacific, Indian Ocean and the Mediterranean region relatively protected.

The first ten minutes of the impact were modelled using a complex computer program called a hydrocode. The results of the hydrocode at the ten-minute mark were inserted into two different codes, both designed to model tsunami propagation across the ocean. The first model, MOM6, is used to model tsunamis travelling through deep oceans, while the second model, MOST, is used by the NOAA (National Oceanic and Atmospheric Administration, USA) for tsunami forecasting.

The results from MOM6 and MOST were remarkably similar. “The big result here is that two global models with differing formulations gave almost identical results,” said Ted Moore, a palaeoceanographer and co-author of the study.

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Two minutes after impact, the simulation shows a large ‘curtain’ of material ejected from the impact site which pushes a wall of water outward and away from the site. This wall of water would have been around 4.5 km high for a short time, until the ejected material fell back to Earth.

Animation of the hydrocode simulation for the first ten minutes post-asteroid impact (crustal material is brown, sediments are yellow, and the ocean is blue. The origin marks the point of impact and black curves mark material interfaces. Credit: Range et al. in AGU Advances, 2022.

Eight minutes later, a 1.5-kilometre-high tsunami radiated outwards from about 220 km from the shallow-watered granite-laden Yucatán Peninsula impact site in Mexico. This swept around the ocean in all directions.

Over the course of the next 48 hours, the tsunami made its way from the Gulf of Mexico and reached most of the world’s coastlines – including Australia’s.

The researchers also calculated open-ocean wave heights, finding waves in the Gulf of Mexico would have likely been over 100 m, and over 10 m in regions near the coastlines of the North Atlantic and the Pacific near South America. As tsunamis reach shallower waters, the wave heights would have increased, although researchers did not specifically calculate the extent of inland flooding.

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

Animation of the change in sea surface height tsunami propagation over 48 hours from the MOST model. Shown in five-minute increments. Credit: Range et al. in AGU Advances, 2022.

Another important result of this research is that geological samples taken from over 100 sites around the globe support the predicted power and reach of the tsunami.

Looking at 165 published records of marine sediments from two different times in the geological record – either side of the impact and subsequent extinction – the researchers found gaps in the record, or regions of jumbled-up older sediments. These sediments confirmed simulation results showing the main radiation path of the tsunami, along which underwater currents would have reached velocity strong enough to erode the fine-grained seafloor.

“We found corroboration in the geological record for the predicted areas of maximal impact in the open ocean,” said Brian Arbic, professor of earth and environmental sciences and a co-author of the paper.

Interestingly, the research also sheds new light on rocky outcrops on the eastern shores of New Zealand’s north and south islands. Dating from the impact period, these sediments are highly disturbed and incomplete – characteristics originally attributed to tectonic activity in the region. (New Zealand lies along a margin, where the Australian and Pacific tectonic plates converge, making it geologically very active.)

This research suggests that given the age and the simulation results, the New Zealand deposits at 12,000 km away from the impact site, are a record of the power and extent of the Chicxulub event.

“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.

The researchers are keen to investigate the extent of coastal inundation from the impact tsunami using these results.

You can watch more about these discoveries from the University of Michigan below.