[meteorite-list] Dino-Killer Asteroid Triggered Huge Tsunamis

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Thu Apr 22 09:52:19 2004
Message-ID: <200208211545.IAA12028_at_zagami.jpl.nasa.gov>

http://dsc.discovery.com/news/briefs/20020819/tsunami.html

Dino-Killer Asteroid Triggered Huge Tsunamis
By Larry O'Hanlon
Discovery News
August 20, 2002

Evidence of huge ancient landslides along the Pacific Coast could
mean that the cosmic collision that killed the dinosaurs also triggered
avalanches far and wide that turned Earth into a world of tsunamis.

Landslide deposits found in a coastal canyon near San Rosario, Baja
California Norte, Mexico, are the first evidence that the magnitude 13
seismic shock of the Chicxulub impact 65 million years ago also set off huge
tsunami-making landslides far beyond the Atlantic Ocean.

There are two ways tsunamis can be created during an asteroid impact: if the
asteroid itself hits the ocean; and if submarine slopes give way, pushing
huge amounts of water at the coast.

For years geologists have known that massive offshore landslides occurred in
the western Atlantic as far north as Newfoundland, because of evidence found
in cores drilled out of the seafloor sediments.

But the Chicxulub impact didn't happen in the Pacific Ocean, and the
tsunamis there would have been caused by quake-induced landslides like that
seen in San Rosario.

"Here (at San Rosario) we have an outcrop where you can walk and see the
huge landslide sheets," said Grant Yip, a geology graduate student at the
University of California at San Diego.

Besides being on land and easy to see, the sediments of the Pacific
landslides are unlike those discovered in the Atlantic because they are most
likely the direct result of the gargantuan earthquake that the Chicxulub
impact sent shivering through the planet. The Atlantic landslides, on the
other hand, could have been caused by either the quake or the churning of an
initial monster tsunami created by the gigantic asteroid impact itself. Or
both.

Yip and his advisor, geologist Cathy Busby, and two other researchers
published their discovery in the August issue of the journal Geology.

Busby and her team have been studying the San Rosario sediments for years,
but it was the discovery of volcanic layers within them that connected them
to the Chicxulub impact. Unlike the other sediments, volcanic rocks can be
accurately dated to the time they cooled and solidified using naturally
occurring isotopes of Argon.

The isotopes in the San Rosario volcanic tested out to about 65 million
years old, meaning the jumbled rocks around them are of similar ages and
likely a result of the cosmic collision.

There's also a third reason the San Rosario discovery is different, said
geologist Richard Norris of the U.C. San Diego's Scripps Institution of
Oceanography.

"This is a very shallow water deposit, which is rare," he said.

The Atlantic deposits are all in deeper water and tell less about what
happened right at the coast, where sea life tends to be most concentrated
and where a lot of species were probably wiped out by horrendous landslides,
as well as a spider's web of tsunamis that were crisscrossing the oceans.

Getting to the bottom of what happened 65 million years ago is important,
said Norris, because we'd like to know the details about how an asteroid
impact can cause 70 percent of species to disappear.

"The lurking issue that hides behind all this is what happens if one hits
tomorrow," Norris said.
Received on Wed 21 Aug 2002 11:45:59 AM PDT