[meteorite-list] Chesapeake Bay Impact Crater (Part 3 of 7)

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Thu Apr 22 09:44:14 2004
Message-ID: <200106261707.KAA22255_at_zagami.jpl.nasa.gov>

http://www.pilotonline.com/special/meteor/part3.html

Elusive proof to satisfy the skeptics
By DIANE TENNANT
The Virginian-Pilot
June 26, 2001

Part 3 of 7

Coon Butte was an enigma to folks in Arizona.

Three-quarters of a mile in diameter, it had a rim about 160 feet high and
dipped about 600 feet inside.

In 1891, a mineral dealer from Philadelphia went there looking for
meteorites and picked up 137 iron rocks around the edges. He was pretty sure
Coon Butte wasn't a volcanic crater, and he published his opinion.

One of the chief geologists from the U.S. Geological Survey came to take a
look. Grove Karl Gilbert, who had been studying the moon, would soon publish
a report claiming that its craters were caused by impacts, not volcanoes. He
thought that Coon Butte might have a similar origin.

He was disappointed. The huge iron meteorite he expected to find in the
depression was just not there. In his report, published in 1896, Gilbert
wrote that the formation was volcanic, despite its lack of volcanic
features. A new word was coined to describe such hidden elements:
cryptovolcanic, in which ``crypto'' stood for ``hidden.''

He was wrong, of course.

Now it's a major tourist attraction. They call it Meteor Crater.

But David Powars avoided disappointment in Virginia. When he went looking,
he saw what wasn't right before his eyes.

Powars knew the oil companies had the information he needed.

It was buried beneath layers of bureaucracy and suspicion.

The companies were loath to reveal seismic surveys, fearing that competitors
would profit. Powars inched his way through the maze of buck passing.

``I basically said, `I have no money, this is what I'm doing, I have this
core hole, I don't know what it is,' '' Powars recalls. ``Everybody couldn't
be nicer, but when you get down to the reality of what you're asking, it's
like, `You've got to be kidding me.' ''

He was desperate to know what the seismic profiles showed. Perhaps they
would shed light on an intriguing new puzzle from the Kiptopeke core hole.

When Scott Bruce got his water sample, it was an undrinkable brine, 1.5
times saltier than the sea. Could the boulder bed be somehow responsible?
Bruce, remembering the mixed fossils that had turned up in the well at
Newport News Park, returned there to drill a continuous core sample that
could not possibly be accused of contamination. Again, the fossils came up
with ancient ones lying above or alongside those from younger eras.

Seeking answers, the USGS drilled a core sample in 1992 at Windmill Point on
the tip of the Northern Neck and again turned up the puzzling layer. To
Powars, the evidence seemed unmistakable, but the seismic information was
crucial. He kept dialing.

``From '89 to '93, that's how long it took me to get that oil company
data,'' he says now. ``Man, I called for four years, begging. People laughed
at me for wasting my time.''

During the years, Powars had fine-tuned his request. The oil companies were
interested only in deep, deep geologic structures, so the first second of
the sound wave, and the objects it reflected off, were waste material. But
that was all Powars needed to show the definite outline of a crater.

``See how you're rolling along there and then, bang, it just breaks out, all
those normal layers and then look at this thing coming down and changing,''
Powars says, tracing the seismic reflection with one finger. ``To me, this
was good seismic data. I'd done enough schooling in advanced geophysics and
had gotten my own books and studying that I didn't need to be a rocket
scientist to interpret this stuff.''

Rubble over thousands of square miles, briny water in freshwater aquifers, a
seismic outline. Still, his critics didn't believe.

So again he turned to C. Wylie Poag, in Woods Hole, Mass. Poag had been
working on what he thought might be an undersea impact crater at Toms
Canyon, 90 miles east of Atlantic City, N.J. Poag confirmed the seismic
analysis, and Powars was suddenly vindicated for years of work.

Much of it had taken place between 10 p.m. and 3 a.m., hours in which
neither his family, his elderly father nor his horses required anything of
him. The home office was quiet except for the dog's snoring, the papers
rustling and Powars' conversations with himself. The crater was all he
thought about. His dreams, in the short hours of sleep, were often of fault
lines and geothermal gradients.

In 1994, Poag, Powars and Bruce cowrote an announcement article in the
professional journal Geology. Their report made headlines around the world.

But the next year, when the USGS cut its staff, Powars, like Cederstrom
before him, lost his job.

The day before he was to leave the geologic division, Powars was hired as a
temporary employee in the USGS water resources section. He tried not to
break stride on his crater work. His critics certainly hadn't.

For some people, a large hole in the ground was not enough to prove a
prehistoric meteorite strike, even one with a megaton blast and devastating
tsunamis. The ultimate proof, the evidence that without a doubt would show
extraterrestrial origin, were tektites, and Powars didn't have any.

Poag did.

Beneath 4,500 feet of ocean water off New Jersey, Poag and his colleagues
had retrieved core samples containing tektites and shocked quartz.

Quartz develops naturally from sand under heat or pressure, but it cracks
into dark lines along crystal planes when subjected to the astronomical
shock of a meteorite impact. Traces of shocked quartz had turned up in
Virginia core samples, but not enough to convince skeptics.

Tektites form when melted sand splatters into the air and cools into tears
and spheres and dumbbells of glass as it rides atmospheric winds around the
globe. Tektites had been found over 3.6 million square miles of the East
Coast, each bead with the same composition, suggesting the same point of
origin. But no one knew where the crater was. The North American Tektite
Strewn Field stretches from New England to Texas to Cuba and Barbados.
Tektites from a point off the tip of South America also may be part of the
field.

Poag and his colleagues estimated that the tektites had come from a crater
within a few hundred miles of their core hole. Toms Canyon was only 12 miles
away, but Poag wasn't sure that it was the one. The Exmore core gave him
another possibility.

In 1996, Poag sent samples of that core to experts in Austria and South
Africa, who found abundant shocked quartz in the jumbled layers. Then no one
could deny the evidence: The Chesapeake Bay and its surrounding land lay
over an impact crater, formed by the enormous explosion of a meteorite, a
comet or an asteroid, about 35 million years ago.

In recognition of their discovery, Poag, Powars and Bruce were presented in
2000 with Virginia's highest scientific honor, the Thomas Jefferson Award.
It was named for a man with great interest in science, but a critic who had
denied that rocks could come from outer space.

Even he would have been convinced.

The Chesapeake Bay impact crater is said to look like an upside-down
sombrero, with an upturned outer rim, a trough, then a high peak in the
center.

It is a complex crater, as opposed to a simple, bowl-shaped crater, because
the object that created it hit hard and fast enough to melt the rock and
splash it tall in the center like a skyscraper, where it hardened. A deep
inner ring circles the peak like a small moat before the flat, annular
trough falls away for about 25 miles on either side. The high peak, nearly a
mile tall, juts up directly under the quiet town of Cape Charles on the
Eastern Shore. In the late Eocene, part of the Cenozoic era, Cape Charles
was ground zero.

No sign of the massive destruction is visible from the sidewalk of Bay
Avenue, or indeed from anywhere in town. The deserted waterfront gazebo with
the partial message ``ur Own Risk'' was built 35 million years too late for
the warning. It looks out on a serene landscape of small dunes, tidal flats
and waves not 6 inches high.

Underneath, far and deep and forgotten, is the jumbled mass of boulders and
grit that was blasted out of the sea floor, then dropped back to fill a
mile-deep void in the earth. Bits of the Blue Ridge Mountains lie there,
too, torn from their roots by tsunamis and tumbled into the pit. The edges
of the hole crumbled and slumped in, widening the crater and adding to the
loose rocky clutter that geologists call breccia (BREH-chee-uh).

But even about this there is disagreement. Some geologists insist that true
breccia is sharp and angular, while the Chesapeake Bay crater contains
rounded, smooth rocks. Powars, in presenting his material to the layman, has
no patience with nits. ``They just want to play definition-a-go-go,'' he
says. ``Just call them breccias. The bottom line is, this is a pile of
debris. I just call it `crater fill.' ''

And what it filled was an area the size of Delaware, smack dab on top of
Virginia.

The mystery solved led only to a bigger puzzle, with more pieces missing.
What was in the breccia? How thick was it? And, more importantly, what was
it doing to the groundwater?

Bruce had achieved his goal at Kiptopeke, sinking test wells into aquifers
at various depths. But the well in the breccia produced undrinkable water.
At depths of only 1,330 feet, the groundwater was 1.3 times saltier than the
sea.

For the State Water Control Board, the results were troubling. With Hampton
Roads and the Eastern Shore already scrambling for water, and with
developers lined up to build houses and schools and industry, water was the
biggest, and most basic, need.

Did the nine aquifers on state groundwater maps flow into the crater or
around it? Was the water any good? In places like Mathews County, which lie
entirely above the crater, would pumping draw salt water into fresh? Would a
well in the breccia be reliable or peter out?

And what did it mean for cities on the crater rim, like Norfolk and Virginia
Beach? A well in Norfolk, at Moores Bridges, has already produced water 1.4
times saltier than the sea. Was it a fluke? Or a problem?

The seismic profiles proved more revealing than anyone expected. The
prehistoric impact had possibly fractured bedrock seven miles deep into the
Earth and as far as 84 miles in diameter. The crater was affecting the land
from the shoreline to West Point, and the ocean floor halfway to the
continental shelf.

Intrigued by the science and worried by the economics, four different
agencies drew up a five-year plan to study the Chesapeake Bay impact crater.
The work, at about $1 million a year, began in October 1999 with the
drilling of a core hole at NASA Langley Research Center, which lay inside
the crater's outer rim.

NASA has sent satellites and orbiters into space to study impact craters,
but now it could look in its own back yard for information. The USGS and the
Water Control Board (by this time, renamed the Virginia Department of
Environmental Quality) would examine geology and aquifers. And the Hampton
Roads Planning District Commission would hope for an answer to the big
question: Is the region's water supply in trouble?

Finally, the scientific community was as engaged as Powars had been all
along.

Reach Diane Tennant at 446-2478 or dianet_at_pilotonline.com
Received on Tue 26 Jun 2001 01:07:54 PM PDT