When the Chicxulub asteroid hurtled to Earth 66 million years ago, dead dinosaurs were not the only things it left in its wake. Besides setting off epic volcanic eruptions and wildfires, which led to a subsequent nuclear winter when all the ash and smoke that were released blocked out sunlight, the space rock triggered tsunamis that left behind enormous ripples right under Louisiana.
These ripples are as high as five-story buildings, and formed so deep underwater that they survived for tens of millions of years. You could be standing above them right now and not even know it.
As geoscientist Gary Kinsland of the University of Louisiana found out, after the tsunamis were done wreaking havoc, there were no other storms whose effects could reach the mega-ripples in the sediment 5,000 feet beneath what is now central Louisiana. Kinsland realized something previously unknown was there when he analyzed what lay beneath. He led a study published recently in Earth and Planetary Science Letters.
“We had to flatten the horizon,” he told SYFY WIRE. “Since the mega-ripples really exist within the part of the horizon chosen for flattening, the nearby layers above the horizon were distorted during flattening. We could then see the wavelength and orientation of the ripples.”
To find out exactly how huge these ripples were, the researchers again observed the flattened image of the horizon, which revealed that the subsurface was rippled. Horizon flattening helps with understanding what happened seismically during the time the highest part, or horizon of any one layer formed as material was being deposited into that layer. The difference in how the monster tsunami waves traveled to and from the horizon (also known as two-way travel time or TWTT) was one factor. Another was the waves generated by the asteroid.
If you throw a stone in the ocean, ripples will be visible on the water’s surface. They might even form temporarily in the sand that stone sinks to. Now think of this happening with a gargantuan object from space. Taking velocity of the seismic wave from the tsunami and adding that to the difference between TWTT at the highest and lowest points of the mega-ripples gave the team an idea of ripple height. The tsunamis that caused them are thought to have been powerful enough to leave a path of destruction throughout the planet.
“I have seen computer models which show the tsunami traveling both ways, east and west, as Central America was not there during that time period, and all around Earth,” Kinsland said. “Tsunamis that traveled north and south soon ran into North and South America.”
Besides being too deep to be disturbed was one thing that saved the ripples. They also remained where they were after being fossilized in deep water shale during the subsequent Paleocene era. Unlike dinosaur bones that go through chemical processes of fossilization when they are buried, the mega-ripples were preserved by particles of shale that still had a claylike texture when they fell through the water. As more and more of these particles accumulated on the ripples, they formed a layer of mud that turned into shale as it was compacted after burial.
Even more eerie was Kinsland’s realization that going directly backwards from that site would lead to the Chicxulub crater near what is now the Yucatan peninsula of Mexico. The mega-ripples occurred on top of a massive deposit of debris kicked up by the asteroid or dumped there by the tsunamis that followed. There is no way they could have been formed by any other phenomenon. Just in case anyone doesn’t believe the overwhelming evidence for this asteroid ending the dinosaurs, this is more proof.
“We still know very little about the deposits formed by the tsunami,” Kinsland said. “I know where other 3D seismic data with evidence of mega-ripples exist. This has really opened up a large field of research, and I hope to get a lot more done in the next few years.”