[meteorite-list] Scientists Seek Chesapeake Bay Crater's Boundary

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Thu Apr 22 10:08:24 2004
Message-ID: <200209131601.JAA08435_at_zagami.jpl.nasa.gov>

Scientists seek crater's boundary
Gloucester, Mathews sites being probed

By Tina McCloud
Daily Press (Hampton, Virginia)
September 10, 2002

Scientists are in Gloucester and Mathews for the next couple of
weeks to dig holes, make noise and tell us more about what lies
beneath our feet.

"Ultrasound of the underground" is what one scientist, Rufus
Catchings, a seismologist with the U.S. Geological Survey,
calls the research.

This is the latest phase of an ongoing study of how a collision with
a huge meteor 35 million years ago affected the Chesapeake Bay region.

The big crash left a crater about 56 miles wide and one mile deep that is
now known as the Chesapeake Bay Impact Crater.

At impact, chunks of debris were blown into the air. Some settled back
into the crater in a jumble, and the rest formed two concentric, uneven
ridges like a bull's eye target.

As a result, the jumble of sediment and rocks displaced the aquifers, the
underground water supplies that now provide water for thousands of
people and businesses in Southeastern Virginia. Much of the water in the
vicinity of the crater is too salty to drink.

The outer rim is extremely variable - it's a zone, not a clearly defined
circle, said Scott Bruce, a groundwater geologist with the Department of
Environmental Quality. If scientists can locate the outer rim more
precisely, it should be easier to go outside the rim to where the geologic
formations and aquifers have not been disturbed, and find fresh water
underground, said Bruce.

Gloucester and Mathews are prime study areas because they lie near the
outer rim.

The outer rim runs close to the James Store area of Gloucester, near
the Mathews line. (The inner rim is in the bay, several miles off
the shoreline.)

Last year, researchers from the U.S.G.S. and the D.E.Q. bored two
deep holes in Mathews. They extracted core samples to analyze the
materials that form the rim.

The data that will be collected in the new few weeks, and analyzed
over coming months, will provide more information about the shape
of the rim, said Bruce.

For the next few days, people will be putting out flag markers along
roads in five areas. The routes will be one to two miles long.

After the mapping, they'll bore a 10-inch hole every 15 feet or so
along each route.

Next week, the scientists will begin dropping a "geophone," a
device to record energy waves, into the holes. Then they'll fire a
noise-making projectile into the ground. A computer will analyze
the resulting energy waves, which will reveal the density of
surrounding soil - the jumbled pieces of the outer rim.

Bruce said that above ground the noise would sound like a thump.
It won't be loud enough to scare people or animals, he said.

Three U.S.G.S. scientists are leading the new phase of the study:
Catchings, a seismologist; David Powars, co-discoverer of the
Chesapeake Bay Impact Crater; and Greg Gohn, project chief.

Tina McCloud can be reached at (804) 642-1746 or by e-mail at
tmccloud_at_dailypress.com
Received on Fri 13 Sep 2002 12:01:10 PM PDT