[meteorite-list] Tsunami Risk of Asteroid Strikes Revealed

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Mon May 15 00:24:05 2006
Message-ID: <200605150401.VAA26426_at_zagami.jpl.nasa.gov>

http://www.newscientistspace.com/article/dn9160-tsunami-risk-of-asteroid-strikes-revealed.html

Tsunami risk of asteroid strikes revealed
Jeff Hecht
New Scientist
12 May 2006

Tsunamis triggered by asteroid impacts cause a disaster similar to the
2004 Asian tsunami once every 6000 years on average, according to the
first detailed analysis of their effects.

Researchers have assumed that tsunamis would make ocean impacts more
deadly than those on land. But Steve Chesley at the Jet Propulsion
Laboratory in Pasadena, and Steve Ward at the University of California
at Santa Cruz, both in the US, are the first to quantify the risks.

The pair first calculated the chance of various size asteroids reaching
the Earth's surface, and then modelled the tsunamis that would result
for asteroids that hit the oceans.

For example, the model shows that waves radiating from the impact of a
300-metre-wide asteroid would carry 300 times more energy than the 2004
Asian tsunami. You can view movies of impact simulations in the North
Atlantic <http://es.ucsc.edu/~ward/1950-DA(5).mov>, South Atlantic
<http://es.ucsc.edu/~ward/eltanin_small.mov>, Gulf of Mexico
<http://es.ucsc.edu/~ward/2004MN4(b).mov> and Pacific
<http://es.ucsc.edu/~ward/2004MN4(a).mov> (all in .mov format).

Fifty million people

To accurately assess the overall impact-tsunami risks, the analysis
included the full range of asteroid sizes, including the smallest
asteroids capable of penetrating the Earth's atmosphere. These are
between 60 and 100 metres, depending on their composition.

The most common asteroids, between 100 m and 400 m, would yield tsunami
waves up to 10 m when they arrived at the coast. A total of about 50
million coastal residents are vulnerable to such waves, though no single
impact would affect them all. The researchers predict a
tsunami-generating impact should occur about once every 6000 years, and
would on average affect over one million people and cause $110 billion
in property damage.

The study also showed that asteroid impacts in the 300-metre class might
be similar to the huge tsunamis thrown up when massive chunks of rock
break from the sides of volcanoes and fall into the ocean. These events
are also thought to occur roughly once every 6000 years.

The analysis confirms suspicions that tsunamis are the biggest risk
posed by asteroid impacts. The risks from climate effects of big impacts
- through dust and smoke that blocks out the Sun - are about two-thirds
that of tsunamis, while those of land impacts are about one-third of the
tsunami risk.

Hurricane aspects

"There still are a lot of uncertainties," Chesley cautions. The solar
system's population of 100 m to 400 m asteroids is poorly known, as are
coastal population distributions. A big question is how the waves would
behave when they reach the shore; successive wave peaks are much closer
together in asteroid tsunamis than in earthquake tsunamis (see a
simulation of an asteroid hitting the water, here
<http://es.ucsc.edu/~ward/splash_250m.mov>).

But the ultimate uncertainty is when and where an asteroid might hit.
"Asteroids sprinkle down pretty much at random," says Ward, "They don't
pick out California or Florida."

And, like hurricanes, location is the key. Hurricane Katrina became
America's worst natural disaster in living memory not because it was the
biggest storm, but because it made a direct hit on vulnerable New Orleans.

But while hurricanes are difficult to predict, they do follow the same
general paths. Asteroids come out of the blue - literally.

Journal reference: Natural Hazards (vol 38 p 355)
Received on Mon 15 May 2006 12:01:48 AM PDT