“Megaripples” in the seafloor that were created in the aftermath of the dinosaur-killing asteroid impact extend much farther than scientists originally thought, new research shows.
The findings offer a new insight into the extreme forces unleashed by the tsunami that followed the Chicxulub asteroid impact at the end of the Cretaceous period 66 million years ago.
In the new study, published online Jan. 19 in the journal Marine Geology, researchers analyzed an extensive set of petroleum industry 3D seismic data and found that these tsunami-driven ripples extend across a far larger area than previously documented.
In a 2021 study, University of Louisiana at Lafayette geoscientist Gary Kinsland and colleagues first identified a 77-square-mile (200 square kilometers) region of seismically imaged megaripples on the shelf of what is now central Louisiana. This relatively shallow part of the landmass was once submerged and extended from the coastline before dropping off into deeper ocean waters.
Related: What happened when the dinosaur-killing asteroid slammed into Earth?
In that 2021 study, the research team suggested that the megaripples, which have an average height of 52 feet (16 meters) and an average wavelength (from one crest of a wave to the next) of 1,970 feet (600 m), were sculpted by tsunami waves as they surged across the sediment-laden seafloor following the asteroid’s impact.
To build on that research, the team analyzed 900 square miles (2,400 square km) of 3D seismic data encompassing regions farther up the shelf and down into deeper waters. The results show that megaripples are present across the entire study area, revealing the widespread impact of the tsunami.
However, the researchers also found significant variations in the ripples’ shapes and orientations depending on their location.
“The megaripples are different on the slope, at the shelf break and further up the shelf,” Kinsland, who is the lead author of the new study, told Live Science in an email. “This is important information in modeling of tsunami, in prediction of future tsunami interactions with shelves and in the understanding of the Chicxulub tsunami.”
Near the shelf break — the point where the continental shelf suddenly drops off — for example, the megaripples are strongly asymmetric, likely due to the tsunami’s surge onto the shelf. This asymmetry is what allowed Kinsland and the authors of the 2021 study to determine the direction the water was flowing when the ripples were made. The long, asymmetrical sides of the ripples slope south-southeast, pointing back to their source in the Chicxulub impact crater at the tip of Mexico’s Yucatán Peninsula.
About 30 miles (45 km) further inland, the megaripples are more weakly asymmetric, suggesting differences in the behavior of the tsunami as it moved into shallower waters. Meanwhile, in the deeper slope sections the team analyzed, the ripples have a much more varied shape — likely a result of the tsunami’s interaction with features such as faults and collapses.
The researchers propose that the megaripples were not formed in the same way as ordinary sand ripples on a beach, which develop from the movement of individual grains. Instead, they suggest that the massive earthquake following the impact fluidized a layer of sediment, which the high-speed tsunami waves then shaped into standing waveforms.
“The ripples must be formed by deformation of the mass of the material,” Kinsland said. “An analogy is the ripples formed in the process of making whipped cream, which produces ripples which stand after having been pushed into ripple shapes.” The exact mechanism for the megaripples’ formation, however, remains an open question, the authors wrote in the paper.
Understanding these ancient tsunami dynamics is not just about reconstructing the past. With modern asteroid-tracking programs in place, scientists are keenly aware of the potential for future impacts.
“We track asteroids now and should be able to predict future impacts,” Kinsland said. “Understanding the worldwide impact effects will help us prepare if we see one coming which we cannot deflect.”
With more studies underway to examine the global impact of the Chicxulub tsunami, researchers will continue to uncover new details about one of the most devastating events in Earth’s history — one that reshaped both the planet’s surface and the course of life itself.
