The findings help piece together details about the end of the dinosaurs and provide insight into the geography of the end of the Cretaceous period, the researchers said.
“It’s a global tsunami,” said Molly Range, a scientist at the University of Michigan and the study’s corresponding researcher. “The whole world saw it.”
Following an asteroid impact, there would be two phases of intense rise in water levels, the team found: the marginal wave and subsequent tsunami waves.
“If you drop a rock in a puddle, there’s that initial splash; that’s the rim wave,” Range said.
These fringe waves could reach an unimaginable height of a mile — and that’s before the tsunami actually hits, the paper estimates.
“Then you see a wedge effect with the water being pushed out symmetrically [from the impact site],” Range said, adding that the Chicxulub asteroid hit the Gulf of Mexico just north of the Yucatan Peninsula.
After the first 10 minutes post-impact, all the airborne debris associated with the asteroid fell into the bay and stopped the water migration.
“It calmed down enough that the crater formed,” Range said. That’s when the tsunami started racing across the ocean at the speed of a commercial jetliner.
“The continents looked a little different,” Range said. “Most of the east coast of North America and the northern coast of Africa easily saw waves over 8 meters. There was no land between North America and South America, so the wave went into the Pacific.
Range compared the episode to the infamous Sumatran tsunami in 2004, which followed a magnitude 9.2 earthquake off the west coast of North Sumatra. More than 200,000 people died.
A megatsunami that occurred 60 million years ago was 30,000 times more powerful than the one in 2004, Range said.
To simulate the megatsunami, the team of scientists used Hydrocode – a three-dimensional computer program that models the behavior of fluids. Hydrocode programs digitally break the system into small Lego-like blocks and calculate the forces acting on them in three dimensions.
The researchers drew on previous research and found that the meteorite was 8.7 miles in diameter and had a density of about 165 pounds per cubic foot — roughly the weight of an average adult male crammed into a milk crate. That means the entire asteroid weighs two quadrillion pounds — that’s 2s followed by 15 zeros.
After creating a simulation of the initial stages of hydrocode impact and the first 10 minutes of the tsunami, the modeling was transferred to a pair of NOAA-developed models to handle tsunami propagation across the world’s oceans. Originally called MOM6.
“Initially we started using the MOM6 model, which is not just a tsunami model, but an all-purpose ocean model,” Range said. The group was forced to make assumptions about bathymetry, or the shape and slope of the ocean floor, the depth of the ocean, and the structure of the asteroid crater. That information, along with the tsunami waveform from the hydrocode model, was fed into MOM6.
In addition to developing a model, study researchers reviewed geological evidence to study the path and power of the tsunami.
RANGE co-author Ted Moore found evidence of large disturbances in sedimentary layers on offshore plateaus and along coastlines at more than 100 sites, supporting the results of the study’s model simulations.
Modeling predicts a tsunami runoff of 20 centimeters per second along most coastlines around the world, enough to disturb and erode sediment.
The researchers said the geological findings added confidence to their model simulations.
Going forward, the team hopes to learn more about how much flooding accompanied the tsunami.
“We’d love to see flooding, which we’re not doing in this current work,” Range said. “You really have to know the bathymetry and the topography.”
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