The researchers said the findings not only helped piece together details about the end of the dinosaurs, but also offered insight into the geology of the end of the Cretaceous.
“It was a global tsunami,” said Molly Range, a University of Michigan scientist and lead investigator on the study. “The whole world saw that.”
NASA reports overwhelming success with asteroid redirection test
After the impact of the asteroid, there would be two phases to an extreme rise in the water level, the team determined: the edge wave and the subsequent tsunami waves.
“If you’re about to drop a rock in a puddle, there’s that first splash; that’s the rim shaft,” said Range.
Those rim waves could have reached an unimaginable height of a mile — and that’s before the tsunami really hits, the paper estimates.
“Then you see a wedge effect where the water is pushed away symmetrically [from the impact site]’ said Range, noting that the Chicxulub asteroid impacted in the Gulf of Mexico north of what is now the Yucatán Peninsula.
After the first 10 minutes after impact, any debris suspended in the air with the asteroid stopped falling into the Gulf, displacing water.
“It had settled enough and the crater had formed,” Range said. That was around the time the tsunami sped across the ocean at the speed of an airliner.
“The continents looked a bit different,” Range said. “Most of the east coast of North America and the north coast of Africa easily saw waves over 8 meters. There was no land between North and South America, so the wave went into the Pacific.”
Range compared the episode to the infamous 2004 Sumatran tsunami, which followed a magnitude 9.2 earthquake on the west coast of North Sumatra. More than 200,000 people died.
The megatsunami more than 60 million years ago was 30,000 times more energetic than in 2004, Range said.
To simulate the megatsunami, the team of scientists used hydrocode – a three-dimensional computer program that models the behavior of liquids. Hydrocode programs digitally break down the system into a series of small Lego-like blocks and then calculate the forces acting on them in three dimensions.
Relying on previous research, the researchers estimated that the meteor was 8.7 miles in diameter and had a density of about 165 pounds per cubic foot – about the weight of an average adult man packed in a volume the size of a milk crate is crammed together. That means the entire asteroid probably weighed about two quadrillion pounds – that’s a 2 followed by 15 zeros.
After the hydrocode created a simulation of the initial stages of impact and the first 10 minutes of the tsunami, modeling was turned off to a pair of NOAA-developed models to handle tsunami propagation in the global oceans. The first was called MOM6.
“Initially, we started using the MOM6 model, which is a general-purpose ocean model, not just a tsunami model,” Range said. The team was forced to make assumptions about the bathymetry, or shape and slope, of the seafloor, as well as the depth of the ocean and the structure of the asteroid crater. This information was pumped into MOM6 along with the tsunami waveform from the Hydrocode model.
In addition to building a model, the study researchers reviewed geological evidence to examine the path and power of the tsunami.
Range co-author Ted Moore found evidence of major disturbances in sediment stratification on ocean plateaux and coasts at more than 100 sites, supporting the results of the study’s model simulations.
The modeling predicted tsunami flow rates of 20 centimeters per second along most coastlines around the world, more than sufficient to disturb and erode sediments.
The researchers said the geological findings have increased confidence in their model simulations.
In the future, the team hopes to learn more about how much flooding accompanied the tsunami.
“We’d like to address flooding, which we haven’t done with this current work,” Range said. “You really need to know the bathymetry and the topography.”
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