In addition to helping piece together details about the end of the dinosaurs, the researchers said the findings offer insights into the geology of the late Cretaceous period.
“It was a global tsunami,” said Molly Range, a University of Michigan scientist and the study’s corresponding researcher. “The whole world saw it.”
After an asteroid impact, there would be extreme rises in water levels in two phases, the team found: the edge wave and subsequent tsunami waves.
“If you’ve just thrown a stone into a pond, there’s an initial splash; it’s a ring wave,” Range said.
The paper estimates that these waves could have reached an incredible height of a mile – and that’s before the tsunami actually started.
“Then you see a wedge effect with the water moving away symmetrically [from the impact site]”,” Range noted that the Chicxulub asteroid is currently falling into the Gulf of Mexico, north of the Yucatan Peninsula.
After the first 10 minutes after the impact, all the airborne debris associated with the asteroid stopped falling into the bay and displacing the water.
“It got pretty quiet there and the crater formed,” Range said. This is when the tsunami begins to cross the ocean at the speed of a commercial airliner.
“The continents looked a little different,” Range said. “Most of the east coast of North America and the northern coast of Africa saw waves of easily 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 Sumatran tsunami in 2004, which followed a 9.2-magnitude earthquake off the west coast of northern Sumatra. More than 200 thousand people died.
A megatsunami more than 60 million years ago had 30,000 times the energy of the one in 2004, Range said.
To simulate a megatsunami, the team of scientists used hydrocode, a three-dimensional computer program that models the behavior of fluids. Hydrocode programs work by digitally dividing a system into a series of small Lego-like blocks and then calculating the forces acting on it in three dimensions.
Based on previous studies, the researchers hypothesized that the meteor had a diameter of 8.7 miles and a density of about 165 pounds per cubic foot—the weight of an average adult man, roughly the size of a milk carton. That means the entire asteroid weighed about two quadrillion pounds—that’s 2 followed by 15 zeros.
After Hydrocode created a simulation of the early stages of a tsunami and the first 10 minutes of a tsunami, the modeling evolved into a pair of models developed by NOAA to manage tsunami propagation in the global oceans. The first was called MOM6.
“At first we started using the MOM6 model, which is a comprehensive ocean model, not just a tsunami model,” Range said. The team had to make assumptions about bathymetry, or the shape and slope of the sea floor, as well as the depth of the ocean and the structure of the asteroid crater. This information was injected into MOM6 along with the tsunami waveform from the hydrocode model.
In addition to building a model, the researchers reviewed geological evidence to study the tsunami’s path and strength.
Range co-author Ted Moore found evidence of major disruptions in the folding of sediments on oceanic plateaus and coastlines at more than 100 sites, supporting the results of the study’s model simulations.
Modeling predicted tsunami runoff speeds of 20 centimeters per second along most coasts around the world, enough to disrupt and erode sediments.
The geological findings add confidence to their model simulations, the researchers said.
In the future, the team hopes to learn more about how often tsunamis are accompanied by flooding.
“We’d like to look at flooding, which we just haven’t done with this current work,” Range said. “You really have to know the bathymetry and the topography.”
