In addition to helping piece together details about the end of the dinosaurs, researchers said the findings offered insight into the geology of the end of the Cretaceous period.
“This was a global tsunami,” said Molly Range, a scientist at the University of Michigan and the study’s corresponding researcher. “All of the world did see this.”
Following the asteroid’s impact, there would be extreme rises in water level in two phases, the team found: the rim wave and subsequent tsunami waves.
“If you just dropped a rock in a puddle, there’s that initial splash; that’s the rim wave,” Range said.
These rim waves could have reached an inconceivable height of one mile — and that’s before the tsunami really gets going, the paper estimates.
“Then you see a wedge effect with the water being pushed symmetrically away [from the impact site],” Range said, noting that the Chicxulub asteroid struck in the Gulf of Mexico just north of what’s presently the Yucatán Peninsula.
After the first 10 minutes post-impact, all of the airborne debris associated with the asteroid stopped falling into the Gulf and displacing water.
“It had calmed down enough and the crater had formed,” Range said. That’s around the time the tsunami began racing across the ocean at the speed of a commercial jetliner.
“The continents looked a little bit different,” Range said. “Most of the East Coast of North America and the north coast of Africa easily saw 8 meter-plus waves. There was no land between North and South America, so the wave went into the Pacific.”
Range compared the episode to the infamous Sumatra Tsunami in 2004 that followed a magnitude 9.2 earthquake on the west coast of northern Sumatra. More than 200,000 people perished.
The megatsunami more than 60 million years ago had 30,000 times more energy than what occurred in 2004, Range said.
To simulate the megatsunami, the team of scientists used a hydrocode — a three-dimensional computer program that models the behavior of fluids. Hydrocode programs work by digitally breaking the system into a series of small Lego-like blocks, and then calculating forces acting on it in three dimensions.
The researchers drew on previous research and assumed the meteor had a diameter of 8.7 miles and a density of about 165 pounds per cubic foot — roughly the weight of an average adult male crammed within a volume the size of a milk crate. That means the entire asteroid probably weighed about two quadrillion pounds — that’s a 2 followed by 15 zeros.
After the hydrocode produced a simulation of the initial stages of impact and first 10 minutes of the tsunami, the modeling was turned over to a pair of NOAA-developed models to handle tsunami propagation throughout the global oceans. The first was called MOM6.
“Initially we started using the MOM6 model that is an all-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 sea floor, as well as the ocean’s depth and the structure of the asteroid crater. That information, along with the tsunami waveform from the hydrocode model, were pumped into MOM6.
In addition to building a model, the study researchers reviewed geologic evidence to study the tsunami’s path and power.
Range’s co-author, Ted Moore, found evidence of major disruptions in the layering of sediment at plateaus in the ocean and coastlines at more than 100 sites, supporting results from the study’s model simulations.
The modeling predicted tsunami flow velocities of 20 centimeters per second along most shorelines worldwide, more than sufficient to disturb and erode sediment.
The researchers said the geologic findings added confidence to their model simulations.
Going forward, the team hopes to learn more about how much flooding accompanied the tsunami.
“We’d like to look at inundation, which we didn’t do with just this current work,” Range said. “You really need to know the bathymetry and the topography.”
