[meteorite-list] Scientists Piecing Together Mystery Of Crater

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Thu Apr 22 10:08:26 2004
Message-ID: <200209161542.IAA11965_at_zagami.jpl.nasa.gov>

http://www.pilotonline.com/news/nw0916cra.html

Scientists piecing together mystery of crater
By DIANE TENNANT
The Virginian-Pilot
September 16, 2002

Thirty-five million years ago, a meteorite hurtled out of the sky and
blasted a mile-deep hole in what is now the coast of Virginia. Or did it?

Whatever the object, asteroid or ice ball, it was two miles wide. Or was it?

>From samples of earth drilled out of the crater came particles of shocked
quartz, the only positive proof that the hole was created by an
extraterrestrial impact. Or is it?

In the past year, scientists from around the world have continued their
studies of the Chesapeake Bay impact crater, the sixth-largest on Earth and
one of the best preserved. From South Africa to Arizona to Illinois to
Hampton Roads, scientists are trying to reconstruct what happened, when it
happened and what the lasting effects are, from earthquakes to salty
groundwater.

New studies are constantly being proposed; old ones are continuing.

So much has been learned. And so much more remains to be discovered.

Much of what is known about the crater came from cores, long cylinders of
sand, clay and rock pulled from thousands of feet underground. Drilling a
new core hole began in July on the grounds of Watkins Elementary School in
Newport News.

Cores already had been collected from the Eastern Shore, from NASA Langley
in Hampton and from two sites in Mathews County, all within the crater. This
one would be taken from just outside the crater rim.

The cores show clearly that the sediment layers on top of the crater are in
perfect order, youngest on top and aging as they go deeper. Once into the
layer of rubble that fills the crater, all order disappears. Rocks and
fossils of various ages are jumbled together, where the enormous blast of
the comet or meteorite hurled them into the air, then collected them
randomly as seawater rushed to fill the void.

Evidence seems to be pointing toward a comet. At the upcoming Geological
Society of America meeting in Denver, U.S. Geological Survey scientist C.
Wylie Poag will present information on that topic, citing evidence of three
craters that date from the same time period: Chesapeake Bay, a smaller
crater called Tom's Canyon off New Jersey and a crater at Popigai in
northern Siberia.

David Powars, the USGS geologist who first proposed the existence of a
Chesapeake Bay crater, now thinks that the object was smaller than first
believed. He will discuss his reasoning at the October meeting.

Other subjects to be presented include fossil findings. Previously, the one
definite indicator of an impact crater was shocked minerals: quartz and
other minerals fractured in distinctive ways. Paleontologists will propose
that the Chesapeake Bay crater has produced objects so indicative of
extraterrestrial impact that they could be used to identify other buried
craters. Those objects are burned and deformed shells of microscopic
creatures, showing damage that could only be caused by high-speed,
high-temperature impacts.

And all of this research begins at the core holes.

In the sweltering heat of July, Powars sat outside a tent and wrote
descriptions of cores in a log book. ``It's just loaded with fossils,'' he
said. ``See, they look like a Pop Tart. There's two parts to it.''

Three residents of a nearby subdivision wandered over to see what was going
on. ``What is that?'' asked the grandmother. ``Dirt?''

``This is the typical matrix,'' Powars told her. ``It's got bugs in it that
are 35 million years old.''

``Wait a minute,'' interjected T. Scott Bruce of the state Department of
Environmental Quality. ``They think bugs are insects.''

``Oh,'' Powars said. ``Fossils. Critters.''

``What do you do with all this information?'' asked the mother.

``In the coastal plain of Virginia, there are aquifers stacked one of top of
the other, under the ground,'' Bruce said. ``The aquifers are controlled by
the geology. We need to know, from spot to spot, what the geology is so we
know about the aquifers. We're in the process of constructing a mathematical
groundwater flow model.''

Just then, another core came up out of the ground. ``Just think,'' said the
driller. ``No human ever saw that.''

Watkins Elementary School sits right where the crater scientists shot a
seismic line a couple years ago. The line, from the NASA core hole to near
the James River, took an underground reflection picture of ground layers
across the Peninsula, sort of like an ultrasound. In mid-September,
scientists will shoot a seismic line across the crater rim in Mathews
County.

The core hole had turned up no good water sources, not exactly what Newport
News wanted to hear. Information on the ability of the ground to transport
water will come later, after hydrologists analyze the permeability of the
core and study its salt content.

``Have you come up with any surprises?'' the grandmother asked, and Bruce
said, ``There are always surprises.''

``Ready?'' asked Karl Dydak, tube in hand. ``Set, go.''

Roger Moberg eyed his wristwatch, while Dydak kept an eye on the gallon jug
that was filling with water.

``Ready, stop,'' Dydak said, pulling the tube out of the jug.

``Thirty-five point three two,'' Moberg said, and Dydak punched the numbers
on a calculator.

``One seven,'' he said.

``Still?'' Moberg asked.

``Yeah.'' And Dydak poured the water out of the jug onto the ground.

For three days in August, the two hydrologic technicians had been watching
water trickle out of a deep well into a tube, into a five-gallon bucket,
then onto the ground at the Eastern Shore of Virginia National Wildlife
Refuge at Kiptopeake. It had been running steady at 1.7 gallons a minute,
running out of the crater, buried deep under the ground. They had to purge
2,106 gallons before taking samples.

The water had stained the white bucket orange. It was slowly killing the
plants on the ground. It fizzed like soda pop.

The samples will help scientists figure out why the water from the
1,300-foot well is so salty, where the salt came from, where it is going,
how long it has been there.

``So this is the one that's saltier than seawater, that's got everybody
speculating,'' said Ward Sanford, a hydrogeologist from the U.S. Geological
Survey in Reston.

``That's the stuff,'' said Randy McFarland, a USGS hydrologist from
Richmond. ``It's pretty bubbly, isn't it?''

``But it doesn't smell bad,'' Dydak said.

``I guess,'' McFarland said, ``methane doesn't have a smell.''

Of all the oddities the buried crater has produced -- earthquakes, land
subsidence, salty groundwater -- this is one of the strangest. Trapped in
the water underground is methane, a colorless, odorless gas that seeps into
basements on the western edge of the crater, and effervesces out of the
water like Perrier near the crater's center. Methane is formed by the
decomposition of organic matter. It came, possibly, from the prehistoric
sharks and camels and plants that were swept into the crater by tsunamis
that scoured as far as the Blue Ridge Mountains and then rushed back into
the great empty hole in the sea floor.

Methane was found in a research well in Mathews County at 8 parts per
million. It may be higher at Kiptopeake. In the mornings, after the well had
built up pressure overnight, the fizz was like steam coming off the water,
Moberg said.

The water coming out of the well may have been trapped in the crater for 35
million years, through warm periods when it was undersea and the shoreline
was at present-day Richmond, and through ice ages when sea level dropped and
left the impact site dry.

The implications for Hampton Roads are great. The crater lies under the
Chesapeake Bay, centered on Cape Charles at the tip of the Eastern Shore.
The land for miles around it -- under the major cities -- was faulted and
disrupted. The underground aquifers that carry fresh water from the fall
line at Richmond to the sea were destroyed by the impact.

The water comes out at 76 degrees, warmer at the bottom of the well than at
the top, because it is closer to the center of the Earth. It has enough salt
to be called a brine. And it has something else.

``This has sort of a strange odor to it, almost a petroleum smell,''
McFarland said.

Sanford peered into the bucket. ``We could light a match and find out,'' he
said, and everyone laughed, but no one lit a match.

Labs around the country were waiting for water samples from Kiptopeake,
ready to test for helium, argon, neon, sulfur hexafloride, hydrogen, oxygen,
sulfate isotopes and more.

The goal in the sampling was to capture the well water in the condition it
was in underground, without it touching the atmosphere. Some of the samples
had to be sealed in bottles with absolutely no air bubbles inside. Air
bubbles would allow dissolved gases, released from underground pressure, to
escape, as they were doing in the effervescence. But as they fizzed out,
they created their own bubbles.

Bottles broke, bubbles formed, stoppers popped. But finally, after four
hours, the sampling was done.

``Surprising that it took this long,'' Dydak said. ``But after 35 million
years, I guess an hour longer doesn't matter.''

The ultimate goal of the USGS is to core 4,000 to 5,000 feet deep in the
center of the crater, near Cape Charles. Drilling alone would cost $1.5
million, said project chief Greg S. Gohn, so a consortium of agencies and
funding sources would be needed.

Virginia Tech is already working on a jointly funded proposal that would go
hand-in-hand with the deep hole. John Hole, an associate professor of
geological sciences, and three colleagues from around the country want to do
three-dimensional seismic imaging of the bedrock underneath the crater, to
see how the impact affected Earth's crust.

Ideally, the study would go down the Eastern Shore and cross to the
Peninsula, he said, using special trucks that lift off the ground on
hydraulic pads and then send vibrations deep into the Earth. The proposal
has not been funded, he cautioned, and any work would be at least two years
away.

The crater has generated so much interest that a live television broadcast,
sent to public TV stations around the country, will take place on Oct. 9.
Scientists involved in the crater research will gather in Mathews County for
the educational presentation.

``People are very interested in this, not only because it's a very cool
thing that happened but because it relates to their groundwater,'' Powars
said. ``You know, what I'm having more fun with is the bottom line: Is it
going to happen again? Yes. The only thing we don't know is when. We'd
better start learning about the effects. What's covering the planet?
Two-thirds water. So it's going to be an oceanic impact. Over half the
population of the world lives in harm's way, on lowland coastal regions. And
where are you going to study that? Right here.''

Scientists are already watching the skies for asteroids that could cross
Earth's orbit. Some have suggested that explosives could nudge those on a
collision course out of the way.

``It's pretty wild to think we're worried now about space debris,'' Powars
said, ``but just a few years ago we didn't think anything ever hit the
planet at all. You go, wow. Wow!''

Reach Diane Tennant at 446-2478 or dianet_at_pilotonline.com</i
Received on Mon 16 Sep 2002 11:42:09 AM PDT