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(meteorobs) Asteroid Waves

Since it is a little slow here, thought I'd copy this for our reading 
pleasure

Wayne


Los Alamos National Laboratory
Los Alamos, New Mexico

Contact:
Gary Kliewer, (505) 665-2085 garyk@lanldot gov

RESEARCHERS MAKING WAVES AT LOS ALAMOS

WASHINGTON, D.C., Jan. 7, 1998 -- Los Alamos National Laboratory
researchers are demonstrating the enormous damage of an asteroid
strike -- not from an impact on land but from tsunamis caused by an
asteroid hitting Earth's oceans. Computer models show how impacts of
various sizes will generate waves that could devastate entire coastlines
on several continents. A surveillance and defense system could prevent
such a disaster.

Astrophysicist Jack Hills of the U.S. Department of Energy's Los Alamos
National Laboratory presented his findings today at a news conference
and a scientific session at the Washington, D.C., meeting of the American
Astronomical Society.

A tsunami is a fast-moving ocean wave, usually caused by underwater
earthquakes or volcanic eruptions, that runs up on a coastline, causing
widespread damage. A tsunami retains its destructive energy while it
travels enormous distances. When the wave strikes a continental shelf,
its speed decreases and its height increases. An asteroid impact would
induce a series of waves that could scour thousands of miles of coastline
with walls of water and roiling debris.

Hills and his colleague Charles Mader use a detailed numerical
simulation with a one kilometer spatial resolution and comparative data
from historical tsunami events.

The Los Alamos model estimates that an asteroid three miles across
hitting the mid-Atlantic would produce a tsunami that would swamp the
entire upper East Coast of the United States to the Appalachian
Mountains. Delaware, Maryland and Virginia would be inundated,
including Long Island and all the coastal cities in this region. It would 
also
drown the coasts of France and Portugal.

Alternately, Hills' model shows how much of Los Angeles and Waikiki
would be lost if the same rock cratered the ocean between Hawaii and
the West Coast.

Fortunately, Earth is likely to take a hit from an object that large only
once every 10 million years. However, the chance of a strike by a
relatively small asteroid is two or three thousand times more likely, or
once every few thousand years.

Objects larger than about 600 feet across are virtually unaffected by the
atmosphere and will reach Earth's surface at nearly full velocity to cause
a crater on land or sea. Most of the damage from such an impact would
come from a tsunami.

For example, the Los Alamos model shows that an asteroid about 1,300
feet in diameter would devastate the coasts on both sides of the ocean
with a tsunami more than 300 feet high.

Asteroids smaller than the threshold 600 feet across lose most of their
energy in the atmosphere but can still cause unprecedented damage. A
"small" impactor hit near the Tunguska River in central Siberia in 1908.
Though it never hit the ground, the shock wave flattened 800 square
miles of forest.

An impact like Tunguska, which hit with a force a thousand times greater
than the Hiroshima bomb, occurs over land every 300 years on average.
Hills and Mader have received Laboratory funding for an additional three
years of model development. They expect increasingly sophisticated
models to predict more extensive coastal damage than previously
calculated. And Hills would like to see the research yield a practical plan
of defense. "An impact from the smaller asteroids is one disaster that is
preventable," Hills said.

But to deflect an asteroid on a collision course, first it must be seen
ahead of time. Then a nuclear-armed rocket must be ready to intercept it.
A nuclear blast in space could either shatter or re-direct the incoming
asteroid, Hills said. Currently, there is no such surveillance or defense
capability in place.

"It's a problem that could be solved for much less than the cost of one
hurricane. We could just set it up and be done with it," said Hills.

Los Alamos National Laboratory is operated by the University of California
for the U.S. Department of Energy.