Comment Sixty-six million years ago, an asteroid nearly nine miles across collided with Earth, triggering a mass extinction that wiped out most of the dinosaurs and three-quarters of the planet’s plant and animal species. Now we learn that the so-called Chicxulub asteroid also created a massive “megatsunami” with waves over a mile high. A study, published in AGU Advances, recently allowed scientists to reconstruct the impact of the asteroid. Scientists were able to estimate the extreme effects of the conflict, which included a global tsunami that caused flooding around the world. In addition to helping piece together details about the end of the dinosaurs, the 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. “The whole world saw that.” NASA reports huge success with asteroid redirection test After the asteroid hit, there would have been extreme rises in water levels in two phases, the team found: the rim wave and subsequent tsunami waves. “If you just drop a rock into a puddle, there’s that initial splash. that’s the lip wave,” Range said. Those waves could have reached an unimaginable height of a mile — and that’s before the tsunami actually started, the paper estimates. “Then you see a wedge effect with the water moving away symmetrically [from the impact site]Range said, noting that the Chicxulub asteroid hit the Gulf of Mexico just north of what is now the Yucatan Peninsula. After the first 10 minutes after impact, all airborne debris associated with the asteroid stopped falling into the Gulf and displacing the water. “It had calmed down enough and the crater had formed,” Range said. At that moment the tsunami began to race across 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 north coast of Africa saw easily 8m waves. There was no land between North and South America, so the wave went into the Pacific.” Range compared the episode to the infamous 2004 Sumatra tsunami that followed a magnitude 9.2 earthquake off the west coast of northern Sumatra. Over 200,000 people perished. The megatsunami more than 60 million years ago had 30,000 times more energy than what happened in 2004, Range said. To simulate the megatsunami, the team of scientists used a hydrocode – a 3D 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 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 — about the weight of an average adult male crammed into a volume the size of a milk crate. That means the entire asteroid probably weighed about two four billion pounds—that’s a 2 followed by 15 zeros. After the hydrocode produced a simulation of the initial stages of impact and the first 10 minutes of the tsunami, the modeling was turned over to a pair of models developed by NOAA to handle tsunami propagation throughout the world’s oceans. The first was called MOM6. “We originally started out using the MOM6 model which is an all-purpose 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’s crater. This information, along with the tsunami waveform from the hydrocode model, was pulled into MOM6. In addition to building a model, the study’s researchers examined geological evidence to study the path and strength of the tsunami. Range co-author Ted Moore found evidence of major disruptions in sediment stratification on oceanic and coastal plateaus at more than 100 sites, supporting results from the study’s model simulations. Modeling predicted tsunami flow speeds of 20 centimeters per second along most coastlines worldwide, more than enough to disturb and erode sediments. The researchers said the geological findings added confidence to their model simulations. In the future, the team hopes to learn more about how much flooding accompanied the tsunami. “We’d like to see the flood, which we haven’t done with just this current work,” Range said. “You really have to know bathymetry and topography.”
