The study, scheduled for online publication Oct. 4 in the journal AGU
Advances, presents the first global simulation of the Chicxulub impact
tsunami to be published in a peer-reviewed scientific journal. In
addition, U-M researchers reviewed the geological record at more than
100 sites worldwide and found evidence that supports their models’
predictions about the tsunami’s path and power.
“This tsunami was strong enough to disturb and erode sediments in
ocean basins halfway around the globe, leaving either a gap in the
sedimentary records or a jumble of older sediments,” said lead author
Molly Range, who conducted the modeling study for a master’s thesis
under U-M physical oceanographer and study co-author Brian Arbic and U-M
paleoceanographer and study co-author Ted Moore.
The review of the geological record focused on “boundary sections,”
marine sediments deposited just before or just after the asteroid impact
and the subsequent K-Pg mass extinction, which closed the Cretaceous Period.
“The distribution of the erosion and hiatuses that we observed in the
uppermost Cretaceous marine sediments are consistent with our model
results, which gives us more confidence in the model predictions,” said
Range, who started the project as an undergraduate in Arbic’s lab in the
Department of Earth and Environmental Sciences.
The study authors calculated that the initial energy in the impact
tsunami was up to 30,000 times larger than the energy in the December
2004 Indian Ocean earthquake tsunami, which killed more than 230,000 people and is one of the largest tsunamis in the modern record.
The team’s simulations show that the impact tsunami radiated mainly
to the east and northeast into the North Atlantic Ocean, and to the
southwest through the Central American Seaway (which used to separate
North America and South America) into the South Pacific Ocean.
In those basins and in some adjacent areas, underwater current speeds
likely exceeded 20 centimeters per second (0.4 mph), a velocity that is
strong enough to erode fine-grained sediments on the seafloor.
In contrast, the South Atlantic, the North Pacific, the Indian Ocean
and the region that is today the Mediterranean were largely shielded
from the strongest effects of the tsunami, according to the team’s
simulation. In those places, the modeled current speeds were likely less
than the 20 cm/sec threshold.
For the review of the geological record, U-M’s Moore analyzed
published records of 165 marine boundary sections and was able to obtain
usable information from 120 of them. Most of the sediments came from
cores collected during scientific ocean-drilling projects.
The North Atlantic and South Pacific had the fewest sites with
complete, uninterrupted K-Pg boundary sediments. In contrast, the
largest number of complete K-Pg boundary sections were found in the
South Atlantic, the North Pacific, the Indian Ocean and the
Mediterranean.
“We found corroboration in the geological record for the predicted
areas of maximal impact in the open ocean,” said Arbic, professor of
earth and environmental sciences who oversaw the project. “The
geological evidence definitely strengthens the paper.”
Of special significance, according to the authors, are outcrops of
the K-Pg boundary on the eastern shores of New Zealand’s north and south
islands, which are more than 12,000 kilometers (7,500 miles) from the
Yucatan impact site.
The heavily disturbed and incomplete New Zealand sediments, called
olistostromal deposits, were originally thought to be the result of
local tectonic activity. But given the age of the deposits and their
location directly in the modeled pathway of the Chicxulub impact
tsunami, the U-M-led research team suspects a different origin.
“We feel these deposits are recording the effects of the impact
tsunami, and this is perhaps the most telling confirmation of the global
significance of this event,” Range said.
The modeling portion of the study used a two-stage strategy. First, a
large computer program called a hydrocode simulated the chaotic first
10 minutes of the event, which included the impact, crater formation and
initiation of the tsunami. That work was conducted by co-author Brandon
Johnson of Purdue University.
Based on the findings of previous studies, the researchers modeled an
asteroid that was 14 kilometers (8.7 miles) in diameter, moving at 12
kilometers per second (27,000 mph). It struck granitic crust overlain by
thick sediments and shallow ocean waters, blasting a roughly
100-kilometer-wide (62-mile-wide) crater and ejecting dense clouds of
soot and dust into the atmosphere.
Two and a half minutes after the asteroid struck, a curtain of
ejected material pushed a wall of water outward from the impact site,
briefly forming a 4.5-kilometer-high (2.8-mile-high) wave that subsided
as the ejecta fell back to Earth.
Ten minutes after the projectile hit the Yucatan, and 220 kilometers
(137 miles) from the point of impact, a 1.5-kilometer-high
(0.93-mile-high) tsunami wave — ring-shaped and outward-propagating —
began sweeping across the ocean in all directions, according to the U-M
simulation.
At the 10-minute mark, the results of Johnson’s iSALE hydrocode
simulations were entered into two tsunami-propagation models, MOM6 and
MOST, to track the giant waves across the ocean. MOM6 has been used to
model tsunamis in the deep ocean, and NOAA uses the MOST model
operationally for tsunami forecasts at its Tsunami Warning Centers.
“The big result here is that two global models with differing
formulations gave almost identical results, and the geologic data on
complete and incomplete sections are consistent with those results,”
said Moore, professor emeritus of earth and environmental sciences. “The
models and the verification data match nicely.”
According to the team’s simulation:
- One hour after impact, the tsunami had spread outside the Gulf of Mexico and into the North Atlantic.
- Four hours after impact, the waves had passed through the Central American Seaway and into the Pacific.
- Twenty-four hours after impact, the waves had crossed most of the
Pacific from the east and most of the Atlantic from the west and entered
the Indian Ocean from both sides.
- By 48 hours after impact, significant tsunami waves had reached most of the world’s coastlines.
For the current study, the researchers did not attempt to estimate the extent of coastal flooding caused by the tsunami.
However, their models indicate that open-ocean wave heights in the
Gulf of Mexico would have exceeded 100 meters (328 feet), with wave
heights of more than 10 meters (32.8 feet) as the tsunami approached
North Atlantic coastal regions and parts of South America’s Pacific
coast.
As the tsunami neared those shorelines and encountered shallow bottom
waters, wave heights would have increased dramatically through a
process called shoaling. Current speeds would have exceeded the 20
centimeters per second threshold for most coastal areas worldwide.
“Depending on the geometries of the coast and the advancing waves,
most coastal regions would be inundated and eroded to some extent,”
according to the study authors. “Any historically documented tsunamis
pale in comparison with such global impact.”
Video: https://youtu.be/hy6wfjqFBE0
A follow-up study is planned to model the extent of coastal
inundation worldwide, Arbic said. That study will be led by Vasily Titov
of the National Oceanic and Atmospheric Administration’s Pacific Marine
Environmental Lab, who is a co-author of the AGU Advances paper.
In addition to Range, Arbic, Moore, Johnson and Titov, the study
authors are Alistair Adcroft of Princeton University, Joseph Ansong of
the University of Ghana, Christopher Hollis of Victoria University of
Wellington, Christopher Scotese of the PALEOMAP Project, and He Wang of
NOAA’s Geophysical Fluid Dynamics Laboratory and the University
Corporation for Atmospheric Research.
Funding was provided by the National Science Foundation and the
University of Michigan Associate Professor Support Fund, which is
supported by the Margaret and Herman Sokol Faculty Awards. The MOM6
simulations were carried out on the Flux supercomputer provided by the
University of Michigan Advanced Research Computing Technical Services.
Reference:
Molly M. Range, Brian K. Arbic, Brandon C. Johnson, Theodore C. Moore,
Vasily Titov, Alistair J. Adcroft, Joseph K. Ansong, Christopher J.
Hollis, Jeroen Ritsema, Christopher R. Scotese, He Wang. The Chicxulub
Impact Produced a Powerful Global Tsunami. AGU Advances, 2022; 3 (5) DOI: 10.1029/2021AV000627
Note: The above post is reprinted from materials provided by University of Michigan.
