[meteorite-list] Seismic Blasts Aim To Get 'Hole' Story of Chesapeake Bay's Creation

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Wed Nov 24 17:29:34 2004
Message-ID: <200411242229.OAA13476_at_zagami.jpl.nasa.gov>

http://www.bayjournal.com/article.cfm?article=2413

Seismic blasts aim to get 'hole' story of Bay's creation
By Joanne Kimberlin
Virginian-Pilot
November 2004

Crickets thrummed in the dark mist. A harvest moon glowed orange in the
heavens. The earth moved.

Thirty-five times.

It shuddered repeatedly as scientists detonated a 20-mile string of
underground explosives along Virginia's Eastern Shore this October. The
concussions, bouncing back from far below, will help to map the most
detailed profile yet of an ancient wound in the planet's crust: the
35-million-year-old Chesapeake Bay impact crater.

Pushing the button was the easy part; reaching countdown required a
diplomatic endeavor worthy of the United Nations.

Scores of local landowners had to open their gates to dozens of
scholarly visitors - a remarkable consensus in a community that doesn't
cotton much to intrusion.

One by one, residents yielded to the common good - and to the long-winded,
high-wattage, caffeine-powered zeal of a wiry scientist from the
Shenandoah Valley, the man who loves the crater the most.

David Powars was one of the first scientists convinced of its
existence - a notion many of his colleagues had scoffed at for years. Now
confirmed by a battery of drill samples and other tests, the crater will
be investigated deeper than ever next fall, when a $1.5 million core
hole punches 7,000 feet into its mysteries.

No one knows whether an asteroid or a comet gouged the one-mile-deep,
56-mile-wide crater beneath the Bay. But judging by the damage it
caused, the meteorite slammed into the planet at about 76,000 mph. The
explosion, equal to 10 trillion tons of TNT, wiped out life for miles
around, creating the largest impact crater in the United States and the
sixth-largest in the world.

Thousand-foot-tall tidal waves likely topped parts of the Blue Ridge
Mountains.

Concealed by the Bay and filled in the passing eons with rock and
sediment, the crater wasn't discovered until the mid-1980s.

Scientists now suspect it is the culprit behind a host of modern-day
concerns, from the region's shortage of fresh groundwater to its slow
sink into the sea. Answers could lie inside layers brought up in the
drill tube. A sort of seismic ultrasound, created by the recent blasts,
will determine the bull's-eye for the drill bit.

To get the best picture, an alphabet soup of about two dozen
'ologists'-experts in rocks, fossils, atmosphere, outer space and
more - descended on the Shore.

The team laid a line of 70-foot-deep shot holes that stretches from the
center of the crater, located beneath the town of Cape Charles, VA, to
its northeastern rim, near Nassawadox, VA. About 700 seismographs, tuned
to record the results, had to be poked into the soil every 50 yards
along the line. All were on private property - often co-owned by a web of
relatives.

Powars, as the point man of the operation, began knocking on doors in
March, spinning his spiel, trying to win access to the land he needed.
"I'd get one person's OK and then find out I also had to get it from
their cousins or their brothers or their in-laws," Powars said. "I bet I
wound up talking to 150 people. Some of them were scattered across the
country. One was in a mental institution. Let's just say that one was
interesting."

Fortunately for Powars, talking is among the things he does best. When
he's excited, as he is about the crater, his words gush in a nonstop
stream that's almost legendary.

"We all love David," said Greg Gohn, Powar's boss at the U.S. Geological
Survey. "But you just have to walk away sometimes."

His chatter proved effective with landowners. Many nodded immediately
while others required some courting. Powars put in plenty of hours
perched on living room sofas, answering questions. "By the time it was
done, I was adopted," Powars said. "People were feeding me meals."

In the end, only one family resisted his enthusiasm - a rejection that
will leave a mile-long gap in the seismic profile.

For the most part, though, meteor mania blossomed as word spread. Almost
100 people attended a September meeting Powars held in Cape Charles.

Tom Saunders, a project manager at the town's new Bay Creek development,
was impressed. "You can't get 100 people to come to a meeting in Cape
Charles if you're giving away money," he said.

Saunders would like to see sleepy Cape Charles benefit from its status
as the crater's ground zero. There has been talk of building an
interpretive center to draw tourists.

Mayor Frank Lewis isn't convinced that an underwater hole is marketable.
"Seems like it'd be hard to start an industry around something no one
can see," he said.

As for the scientists, they're delighted to be the first to explore the
anatomy of a crater so well-preserved by the blanket of the Bay.
Exhausted by weeks spent tromping through farm fields and bug-swarmed
swamps, scientists were thrilled to finally close in on October's
detonation.

Powars, functioning on too little sleep and too much coffee and candy,
was a verbal shock wave. An unexpected surplus of explosives and
seismographs had prompted a last-minute decision to add a short
east-west cross line of extra shot holes.

Dashing up and down the line in his pickup, Powars veered off to soothe
a jittery landowner here, an overworked team member there. "This is just
so exciting," he jabbered, with no apparent need for a breath. "We've
waited so long. I can't wait to see what this thing looks like. Everyone
thought an impact this big would wipe out the planet. Now, we know they
were wrong. We're all so tired. No one knows what's under there, you know."

By that night, even Powars was silenced by the explosions. Synchronized
by satellite-set timers, the blasts went off between 10:30 p.m. and
sunrise to minimize vibrations from traffic that might be picked up by
the sensitive seismographs. Gravel and sandbags capped the shot holes,
directing the explosions downward to reveal the topography up to 9 miles
beneath the surface. As they went off, a wave of mini-earthquakes rocked
the area.

Under foot, they rippled by with a rubbery jolt. Inside homes, they
rocked beds and rattled dishes.

After a series of shallower, less-powerful explosions were wrapped up,
the recordings were to be entered into a computer and analyzed. Powars
hopes to have a sketch of his crater by December.

His hunch says the data will pinpoint Eyre Hall as the best spot for
next year's deep-hole project. The colonial-era plantation, located just
south of Eastville, VA, belongs to Furlong Baldwin. Shot holes already
dot the property. The deep hole could bring an international circus of
science types to a place Baldwin treasures for its peace.

"I've already told David that we'll cross that bridge when we come to
it," Baldwin said. "If I can just get him to stop talking, I'll probably
agree to anything."
Received on Wed 24 Nov 2004 05:29:30 PM PST