Some 66 million years ago, a huge space rock about the size of Manhattan slammed into Earth near the Yucatan peninsula. The enormous asteroid sent huge blasts of dust and waves rippling across the planet and wiped out up to 75 percent of life, including dinosaurs.
Now, scientist say they have found evidence of the resulting giant tsunami that swamped much of the Earth. In a study published in the journal Earth & Planetary Science Letters, researchers report how they discovered 52-foot-tall “megaripples” nearly a mile below the surface of what is now central Louisiana.
According to the paper:
“These megaripple features have average wavelengths of 600 meters (1,968.5 feet) and average wave heights of 16 meters (almost 52.5 feet) making them the largest ripples documented on Earth.”
Led by Gary Kinsland, a geoscientist at the University of Louisiana, the research team found fossil records of the huge waves in sediment 5,000 feet below the surface. They used seismic imaging data provided by oil and gas exploration companies to locate the geological features.
Kinsland is convinced these fossilized remains were left behind by the megaripples as they neared what was then the coastline. At the time, the area was about 200 feet below the surface of the ocean, he tells Akila Raghavan of Science Magazine.
“The water was so deep that once the tsunami had quit, regular storm waves couldn’t disturb what was down there,” Kinsland says.
The researchers found a series of megaripples spaced about a half-mile apart preserved in sediment, including shale formations, that settled on the site, reports geologist David Bressan in Forbes Magazine.
“The researchers argue that the megaripples are the results of a series of impact-induced tsunami washing up an ancient seashore. The thick sand-layers deposited by the uprush and backwash currents of the tsunami waves formed symmetrical ripples on the seafloor.”
Kinsland and his colleagues selected central Louisiana as a search site because that’s where they suspected the shoreline was 66 million years ago, a time when water levels were much higher. The dinosaur-killing asteroid left a nearly 100-mile wide crater on the floor of the Gulf of Mexico, near the modern community of Chicxulub on the Yucatan peninsula, reports Tessa Koumoundouros for ScienceAlert.
The researchers determined the megaripples corresponded accurately to the crater in the Gulf of Mexico. The circumferences of the geologic features in Louisiana match up with the impact site, Kinsland tells Raghavan.
The study builds on past research about the impact of the asteroid near Chicxulub. In 2016, cores from a drilling expedition determined how the crater was formed. Two years ago, scientists located a fossil site in North Dakota that included debris swept inland by the tsunami.
“We have small pieces of the puzzle that keep getting added in,” Alfio Alessandro Chiarenza, a paleontologist at the University of Vigo, tells Raghavan. “Now this research is another one, giving more evidence of a cataclysmic tsunami that probably inundated [everything] for thousands of miles.”