Many of the giant sea waves known as tsunamis are caused by
underwater earthquakes and volcanoes -- for example, the devastating 2004
Indian Ocean tsunami was triggered by a quake off the northwestern coast of
Sumatra. Still, the causes of nearly 10 percent of all tsunamis nowadays remain
Cosmic impacts have been known to cause tsunamis in the
past. For instance, scientists have found evidence that the Chicxulub
impact in Mexico, which may have ended the age of dinosaurs, triggered
Now researchers have evidence suggesting that an asteroid
roughly 200 yards (183 meters) wide crashed off the coast of New Jersey and
sent tsunamis surging toward what is now New York City some 2,300 years ago. [Video
- Recreating an Ancient Tsunami]
"Our models suggest the tsunamis were up to 20 meters (66
feet) high when they entered the Hudson River," said researcher Dallas
Abbott, a geologist at Columbia University's Lamont-Doherty Earth Observatory
in New York.
New York City lies at the mouth of the Hudson. When the
scientists drilled out tubes of sediment from the New York and New Jersey area,
they discovered layers of unusual debris that, they suggest, were laid down by
"We have layers up to maybe 30 centimeters (11.8 inches)
thick," Abbott said. "They get thinner upriver, where they're more
like 6 centimeters (2.3 inches) thick."
Within these potential tsunami layers is evidence of a cosmic
impact, including shocked minerals and microscopic carbon beads loaded with
"nano-diamonds," which are "all things only impacts can
do," Abbott said. One candidate for the crater that was produced by this
impact, she said, lies in the undersea Carteret Canyon, located roughly 90
miles (150 km) off the coast of New Jersey.
Other scientists have raised alternate explanations for
these layers. For instance, volcanic eruptions or gigantic landslides on the
other side of the Atlantic might have caused the giant waves. Or these
anomalous layers of sediment that Abbott and her colleagues are investigating may
not have been caused by tsunamis at all -- hurricanes can generate huge pulses
of water known as storm surges, whose effects on sediment could resemble those
"Of course, that doesn't explain the evidence of impact
that we've found," Abbott said.
For a cosmic impact, one smoking gun would be a specific
form of deformed rock known as shocked quartz. The rock is generated by the
intense heat and pressure of a collision
with an extraterrestrial object. "But if there was an oceanic impact,
the oceanic crust doesn't really have quartz to shock," Abbott said.
It there were tsunamis, it remains unclear if ancient Native
Americans witnessed them.
"One possible reason why Indian tribes only moved into
the area relatively recently is that the people who were once there were all
wiped out," Abbott said. "If you look at the predicted wave heights,
there would have been few places to hide."
Abbott and her colleagues plan to detail their most recent
findings Nov. 3 in Denver, at the annual meeting of the Geological Society of