Asteroid that wiped out the dinosaurs also triggered a global tsunami

By Ashley Strickland, CNN

When a city-size asteroid slammed into Earth 66 million years ago, it wiped out the dinosaurs — and sent a monster tsunami rippling around the planet, according to new research.

The asteroid, about 8.7 miles (14 kilometers) wide, left an impact crater about 62 miles (100 kilometers) across near Mexico’s Yucatan peninsula. In addition to ending the reign of the dinosaurs, the direct hit triggered a mass extinction of 75% of animal and plant life on the planet.

When the asteroid hit, it created a series of cataclysmic events. Global temperatures fluctuated; plumes of aerosol, soot and dust filled the air; and wildfires started as flaming pieces of material blasted from the impact re-entered the atmosphere and rained down. Within 48 hours, a tsunami had circled the globe — and it was thousands of times more energetic than modern tsunamis caused by earthquakes.

Researchers set out to gain a better understanding of the tsunami and its reach through modeling. They found evidence to support their findings about the path and power of the tsunami by studying 120 ocean sediment cores from across the globe. A study detailing the findings published Tuesday in the journal American Geophysical Union Advances.

It’s the first global simulation of the tsunami caused by the Chicxulub impact to be published in a peer-reviewed scientific journal, according to the authors.

The tsunami was powerful enough to create towering waves more than a mile high and scour the ocean floor thousands of miles away from where the asteroid hit, according to the study. It effectively wiped away the sediment record of what happened before the event, as well as during it.

“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,” said lead author Molly Range, who began working on the study as an undergraduate student and completed it for her master’s thesis at the University of Michigan.

Researchers estimate that the tsunami was up to 30,000 times more energetic than the December 26, 2004 Indian Ocean tsunami, one of the largest on record, that killed more than 230,000 people. The energy of the asteroid impact was at least 100,000 times larger than the Tonga volcanic eruption earlier this year.

Tracing an ancient tsunami’s path

Brandon Johnson, study coauthor and an associate professor at Purdue University, used a large computer program called a hydrocode to simulate the first 10 minutes of the Chicxulub impact, including the formation of the crater and the beginning of the tsunami.

He included the size of the asteroid and its speed, which was estimated to be moving at 26,843 miles per hour (43,200 kilometers per hour) when it hit the granite crust and shallow waters of the Yucatan peninsula.

Less than three minutes later, rocks, sediments and other debris pushed a wall of water away from the impact, creating a 2.8 mile (4.5 kilometer) tall wave, according to the simulation. This wave subsided as exploded material fell back to Earth.

But as the debris fell, it created even more chaotic waves.

Ten minutes after impact, a ring-shaped wave about a mile high began traveling across the ocean in all directions from a point that was located 137 miles (220 kilometers) away from the impact.

This simulation was then entered into two different global tsunami models, MOM6 and MOST. While MOM6 is used to model deep ocean tsunamis, MOST is part of tsunami forecasting at the National Oceanic and Atmospheric Administration’s Tsunami Warning Centers.

Both models delivered almost the exact same results, creating a timeline of the tsunami for the research team.

An hour after impact, the tsunami had travel beyond the Gulf of Mexico into the North Atlantic Ocean. Four hours post-impact, the waves passed through the Central American Seaway and into the Pacific Ocean. The Central American Seaway once separated North and South America.

Within 24 hours, the waves entered the Indian Ocean from both sides after traveling across the Pacific and Atlantic oceans. And by 48 hours after impact, large tsunami waves had reached most of Earth’s coastlines.

A changing ocean floor

The underwater current was strongest in the North Atlantic Ocean, the Central American Seaway and the South Pacific Ocean, exceeding 0.4 miles per hour (643 meters per hour), which is strong enough to blast away sediments on the ocean floor.

Meanwhile, the Indian Ocean, North Pacific, the South Atlantic and the Mediterranean were shielded from the worst of the tsunami, with lesser underwater currents.

The team analyzed information from 120 sediments that largely came from previous scientific ocean-drilling projects. There were more intact sediment layers in the waters protected from the tsunami’s wrath. Meanwhile, there were gaps in the sediment record for the North Atlantic and South Pacific oceans.

The researchers were surprised to find that sediment on the eastern shores of New Zealand’s north and south islands had been heavily disturbed with multiple gaps. Initially, scientists thought this was because of the activity of tectonic plates.

But the new model shows the sediments being directly in the pathway of the Chicxulub tsunami, despite being 7,500 miles (12,000 kilometers) away.

“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.

While the team didn’t estimate the tsunami’s impact on coastal flooding, the model shows that the North Atlantic coastal regions and South America’s Pacific coast were likely hit with waves taller than 32.8 feet (20 meters). The waves only grew as they neared the shore, causing flooding and erosion.

Future research will model the extent of global flooding after the impact and how far inland the tsunami’s effects could be felt, according to study coauthor and University of Michigan professor and physical oceanographer Brian Arbic.

“Obviously the greatest inundations would have been closest to the impact site, but even far away the waves were likely to be very large,” Arbic said.

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