[meteorite-list] Chesapeake Bay Impact Crater (Part 5 of 7)

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Thu Apr 22 09:44:14 2004
Message-ID: <200106281514.IAA16476_at_zagami.jpl.nasa.gov>

http://www.pilotonline.com/special/meteor/part5.html

Rumblings from the Earth
By DIANE TENNANT
The Virginian-Pilot
June 28, 2001

Part 5 of 7

The Earth is a shifting planet, continents drifting over liquid lava, rocks
refusing to lie still under the soil.

Where they slip and grind together, the planet shivers, sometimes
dramatically, like in Turkey and California and Seattle.

Smaller earthquakes have been recorded around Hampton Roads since 1775.
Doubtless, they also occurred earlier, but no one knew how to measure them
or to tell where they originated.

Now they do.

The meteorite hit with tremendous energy, and that energy had to go
someplace. It went into heat and light, into melting the rocks and blasting
a hole. And what was left over rippled through the ground itself, creating
swells and waves and, finally, cracks.

The cracks, or faults, broke in concentric circles around the crater,
intersected by other faults that began at the center and radiated outward
until they lay in the delicate symmetry of a spider web -- rings within
rings, connected with spokes -- over southeastern Virginia.

The fractured earth never healed. Small movements attest to that.

In York River State Park, in 1995, the temblor felt like a heavy truck
rumbling past. Some people didn't even notice. At 2.6 on the Richter scale,
the earthquake was too small to do any damage but was felt at Camp Peary and
detected on instruments in Blacksburg and Goochland County.

Three other earthquakes with known points of origin were plotted by Gerald
Johnson, a geology professor recently retired from the College of William
and Mary. They were felt in Painter, on the Eastern Shore, in 1884; in
Norfolk in 1899; and Chesapeake in 1918. Their strength is unknown, but one
thing is certain: They plot on a large circle that overlies the rim of the
buried crater.

York River State Park is not within the crater. But it does lie over an area
where rock was cracked by shock waves from the meteorite impact. If a line
were drawn connecting the ends of tidal rivers like the Chickahominy and
Elizabeth and Piankatank, it would form a rough circle around the crater, on
the boundary of this fracture zone.

``We think that where we've been defining the outer rim is not really the
outer rim,'' David Powars says. ``I mean it is, it's an escarpment, but
there's still all sorts of things messed up and we may have some real
jumbled-up piles of sediment outside the escarpment for quite a ways in what
we've been calling this outer fracture zone. That's why, instead of coming
up with a roughly 90-kilometer crater, we come up with a 135-kilometer
(90-mile) structure.''

The seismic reflections taken by the oil companies show small faults webbing
through the rock from the crater almost to the bottom of the Bay. They look
misleadingly small on the roll of paper spread out on Powars' couch.

``At that depth, even seeing that little teeny bit, that's a couple hundred
feet,'' he says. ``That's what's really scary. So when you see one that
really steps up, like we saw in the raw data, there might be 700 feet of
offset there. This is still nothing compared to California. They have faults
tens of thousands of feet offset. California's a mess.''

The U.S. Geological Survey ran its own seismic study last summer, from the
NASA Langley Research Center to the north edge of the James River.
Approximately every 5 feet, a small charge was detonated about 2 feet
underground. Powars has just received the results and, when analyzed, the
reflections should give more precise information about fault lines and the
fracture zone.

The researchers hope to run another seismic line later this year, perhaps
across Mathews County from the core hole drilled this spring near the
village of North. Powars would love to see it cross a strange ridge called
the Suffolk Scarp.

Along Va. 14, just after leaving the town of Gloucester Court House on the
way to Mathews, the Mount Zion United Methodist Church perches on the scarp
about 85 feet above sea level. The scarp juts abruptly from flat soybean
fields only 12 feet in elevation and extends just a short distance before
sinking back down.

The William and Mary professor had puzzled over the ridge since the 1960s.
He had mapped the layers of earth that were exposed in the cliffs of
Cornwallis Cave in Yorktown and examined the fossil shells of different ages
that lay side by side in a borrow pit at Mobjack. It was a splendid riddle,
but he could not explain it. The layers of dirt, instead of sloping seaward,
tilted back toward land. That they had tilted this way for eons was obvious
to Johnson: A fairy shrimp had tunneled into the sediment millions of years
before, a shrimp that digs a vertical burrow. The fairy shrimp's hole was
not tilted; the sediments around it were.

``I gave a fantastic paper in 1968, described everything beautifully, but
couldn't explain it,'' Johnson says now. ``Now things that were
unexplainable are explainable. We've discovered that, really, this area of
Virginia is not the most stable, it's moving and things are changing, and
it's all because of what took place 35 million years ago.''

The ridge along Va. 14 apparently mimics the outer rim of the crater far
below it. Another ridge northwest of U.S. 13 near Painter, where the
earthquake was, also appears to follow the crater rim. The Big Bethel Scarp
and the Diamond Springs Scarp, low terraces in Hampton and Virginia Beach,
also are on the crater rim, buried several thousand feet below but still
influencing the surface of the volatile land.

``Anywhere from I-64 to Big Bethel Road behind the landfill, right in there
seems to be some good faulting,'' Powars says. ``The other interesting point
from that seismic data was when we got outside (the crater), we were well
over near the James River, the basement was noticeably higher up.

``I'm pushing very hard for the project to study more of this aspect. It may
give an idea of what may happen in the future as we continue to pump on the
south side of the crater. You've got this real high salinity in here. It
could be that it's just a natural phenomenon; it's never been flushed
because there's a natural barrier here with the basement up high.''

Much of Hampton Roads and even beyond is settling slowly over faults and
cracks and the loose breccia filling the crater.

Picture the cover over a swimming pool. Every time it rains, water puddles
in the center. The weight of the puddle makes the cover sink lower, making
room for more water to collect, which makes the cover sink lower, which
makes more room, and so on.

Scientists concerned about global warming and melting polar ice set up a
network of monitors to track the rise in relative sea level around the
world: in other words, how fast the water is rising in relation to the land.
The monitor in Hampton Roads, in the lower James River near its sharp
northeast turn, shows one of the highest relative rises in sea level of
anywhere on Earth. Melting ice is not the sole cause. More likely, the land
is sinking.

But the crater's presence is not all negative. Scientist C. Wylie Poag has
suggested that the Chesapeake Bay crater, like 35 others around the world,
may contain mineral deposits such as oil or gas or gold or nickel, valued at
billions of dollars.

He says that crystalline basement rocks, like those under the crater,
usually form enormous melt sheets when impacted, up to 2,500 cubic miles in
size. Mineral deposits in such a melt sheet could be valuable, but the core
hole needed to sample them, perhaps 5,000 feet deep, would cost at least
half a million dollars.

It is possible that the Chesapeake Bay crater was formed by an object that
broke apart before impact, or that several celestial objects hit Earth
around the same time, leaving craters strewn around the world. Two other
craters -- Toms Canyon off New Jersey and Popigai in Russia -- also are
around 35 million years old.

``We're constantly thinking . . . it should be a mile or two-mile diameter
impactor,'' Powars says. ``I'm thinking that our impactor may be smaller.
There's a theory that says this large an impactor ought to cause global
extinction. Well, it may be that this one wasn't that big, or that it broke
up. I still think this may be one of a whole bunch, like a comet like
Shoemaker-Levy that broke up.''

One of the discoverers of that comet, which smashed into Jupiter in 1994,
was Eugene Shoemaker. Shortly before his death, Shoemaker looked at the
Exmore cores and said they were unquestionably of extraterrestrial
formation, the stamp of approval from the world's most renowned impact
scientist.

In 1997, Scott Bruce placed a call to John Cederstrom, long since retired
from the USGS and living in southwest Virginia. You were right, Bruce told
him. There really is a jumbled layer of rock and sediment, what you called
the Mattaponi Formation back in the 1940s. We think it was caused by a
meteorite, or a comet, or an asteroid, because there's a crater there, too.

He was thrilled, Bruce recalled. Just a few months later, Cederstrom died,
absolved, after 50 years, of bad science and bad image and bad work.

His legacy continues. In a NASA lab at Langley, Joel Levine is prepared to
go out on a scientific limb with a piece of Cederstrom's Mattaponi.

Reach Diane Tennant at 446-2478 or dianet_at_pilotonline.com
Received on Thu 28 Jun 2001 11:14:28 AM PDT