In addition to helping to piece together details about the end of the dinosaurs, the researchers said the findings provided insight into the geology of the end of the Cretaceous period.
“This was a global tsunami,” said Molly Ring, a scientist at the University of Michigan and corresponding researcher on the study. “All the world saw this.”
After the asteroid impact, there will be extreme water-level rises in two phases, the team found: the rim wave and subsequent tsunami waves.
“If you just drop a stone in a puddle of water, there’s that initial spot,” said Rang.
These edge waves may reach an unimaginable height of one mile – and that’s before the tsunami really begins, the paper estimates.
“Then you see a wedge effect with the water being pushed out symmetrically [from the impact site],” said Ring, noting that the Chicxulub asteroid hit the Gulf of Mexico north of what is now the Yucatan Peninsula.
After the first 10 minutes after the collision, all airborne debris associated with the asteroid had stopped falling into the bay and displacing the water.
“It calmed down enough and the crater formed,” Rang said. This was at the time when the tsunami began racing across the ocean at the speed of a commercial jet.
“The continents looked a little different,” Rang said. “Most of the eastern coast of North America and the northern coast of Africa saw waves over 8 meters high easily. There was no land between North and South America, so the wave went to the Pacific Ocean.”
Ring compared the episode with the infamous Sumatra tsunami in 2004 that followed a 9.2-magnitude earthquake off the west coast of North Sumatra. More than 200,000 people died.
More than 60 million years ago, Ring said, a megatsunami had 30,000 times more energy than it did in 2004.
To simulate the megatsunami, the team of scientists used hydraulic code – a 3D computer program that models the behavior of fluids. Hydrocode programs work by digitally dividing the system into a series of small, Lego-like blocks, and then calculating the forces acting on it in three dimensions.
The researchers built on previous research and assumed the meteorite had a diameter of 8.7 miles and a density of about 165 pounds per cubic foot — roughly the weight of an average male stuffed inside a volume the size of a milk crate. This means that the entire asteroid probably weighed about 2 quadrillion pounds – that’s 2 followed by 15 zeros.
After the hydraulic code produced a simulation of the initial stages of the impact and the first 10 minutes of a tsunami, the modeling was converted into a pair of models developed by the National Oceanic and Atmospheric Administration (NOAA) to deal with the spread of the tsunami throughout the global oceans. The first was called MOM6.
“Initially we started using the MOM6 model which is an all-purpose ocean model, not just a tsunami model,” Ring said. The team was forced to make assumptions about the bathymetry, or the shape and slope of the sea floor, as well as the depth of the ocean and the structure of the asteroid’s crater. This information, along with the tsunami waveform from the water blade model, was injected into MOM6.
In addition to building a model, study researchers reviewed geological evidence to study the course and strength of the tsunami.
Range co-author Ted Moore has found evidence of significant disturbances in sediment layers in ocean plateaus and coasts at more than 100 sites, supporting the study model simulation results.
Modeling predicted tsunami flow velocities of 20 cm per second along most beaches worldwide, more than enough to disturb and erode sediments.
The researchers said the geological findings added confidence to their model simulations.
Going forward, the team hopes to learn more about the amount of flooding that accompanied the tsunami.
“We would like to look at the flood, which we haven’t done with just this current work,” Ring said. “You really need to know bathymetry and topography.”
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