Drill Explores Blast ; Research Seeks Insight into Explosion That Carved Huge Crater Under the Chesapeake
Scientists this fall will drill nearly 1.4 miles below the Eastern Shore in the latest effort to understand the catastrophic explosion that carved out a 56-mile-wide crater buried below the Chesapeake Bay.
If all goes well, the Eyreville project aims to dig more than twice the depth of previous crater drills at more than a dozen sites around Tidewater Virginia and the Eastern Shore.
The drill will look for traces of a 2-mile-wide asteroid or comet whose explosion over the Atlantic, geologists say, sent a shock wave about 7 miles underground, melted rock, briefly exposed the seafloor and vaporized water.
“It’s a world that none of us have ever seen,” said crater co- discoverer David Powars, a research geologist with the U.S. Geological Survey in Reston.
Computer simulations suggest that the devastation probably took just a few minutes, creating the largest crater in the United States and the sixth-largest in the world.
The crater — twice the size of Rhode Island and as deep as the Grand Canyon — sits below some 1,000 feet of rubble and sediment beneath the lower part of the Chesapeake Bay, its surrounding peninsulas, and the inner continental shelf of the Atlantic Ocean.
It’s “one of the largest and best preserved on Earth,” said Rutgers University geologist Ken Miller, one of four principal investigators leading the new drill. Drilling will start Sunday and continue for three months at the Buryn family farm in the Eyreville area northwest of Cheriton.
The farm is just off-center from where geologists say the fiery space rock struck, leaving an inverted sombrero-shaped crater that quickly filled with tons of water and debris.
Geologists drilling through the crater expect to learn more about the effect the prehistoric impact had on the seabed and to better estimate the space rock’s speed, size and energy as it slammed into the seafloor.
They hope to capture clues about the Earth’s primeval climate, why the impact’s effects were relatively limited and didn’t permanently wipe out life forms, and where thirsty Tidewater residents can find drinkable water.
They also hope to better calculate what will happen the next time one crosses paths with Earth.
Geological research off the coast of New Jersey and in Virginia, begun in 1983, led to the crater’s discovery a decade later. Drilling and further study of seismic data narrowed the location in the Chesapeake Bay and identified Cape Charles as “ground zero.”
Millions of tons of debris spewed 30 miles high before collapsing back into the mile-deep excavation. Towering water jets launched thousands of feet high into the upper atmosphere. A train of tsunami waves inundated the land, wiping out the tropical forests that housed ancestors to modern-day bears, crocodiles and even hippopotamus-like creatures, according to Powars.
The waves nearly overlapped the Blue Ridge Mountains before washing back into the horrible gash, then covered the superheated water beneath a thick blanket of debris, rock and sediment.
Over time, as this new geologic formation settled, it set the stage for Virginia’s baffling coastal groundwater system, with its pockets of salty groundwater.
USGS geologist Wylie Poag, another co-discoverer of the bay’s ancient depression, has called it “probably the most dramatic geological event that ever took place on the Atlantic margin of North America.”
To unlock the crater’s secrets, the USGS and an international coalition of scientists will use an 80-foot-tall drill rig.
Geologists use drill rigs because the planet’s primordial history is buried by erosion, land movement, water and organic deposits. The rig plunges a hollow tube within a pipe into the Earth and then raises the inner tube to the surface and removes the core of rock and sediment. Older material is at the bottom.
The USGS, which has spearheaded the Chesapeake Bay impact crater research, is partnering on the Eyreville drill with the International Continental Scientific Drilling Program, a coalition of the U.S. and 12 other countries. The ICDP has sunk $900,000 into the project, with the USGS providing $400,000.
Forty-nine scientists will work the site off and on through early December, according to Greg Gohn, the scientist leading the project and one of four principal investigators on the drill. More than 100 researchers from about a dozen countries have proposals to study the Eyreville cores in nearly four dozen projects.
“You’re probably only going to drill a hole like this once,” Gohn said.
Scientists and technicians working the rig in 12-hour shifts around the clock will hoist cores taken in 5- or 10-foot segments. As the rig sinks deeper, going back in time to the tail end of the Eocene epoch, it may also exhume microfossils, saltwater and perhaps even microbes that either survived the firestorm or came here as tourists from outer space.
By coring roughly 7,200 feet, the team expects to reach the crater floor and unearth traces of the space rock, according to Gohn. Telltale chemical signatures, such as the ratio of certain minerals or gases, could determine whether the Earth was pummeled by an icy comet that wandered into its path or was smacked by an incoming asteroid.
The crater has drawn attention worldwide. The project’s lead investigators include geochemist Christian Koeberl of the University of Vienna and mineralogist W. Uwe Reimold of South Africa’s University of Witwatersrand.
“We will learn about all the processes affecting the [impact] target,” Reimold said of the space ball’s melting of rock, turning the debris into rubble and then dispersing the rubble known as breccia — and compare that to other craters. The impact at Chicxulub, 65 million years ago in the Gulf of Mexico, is thought to have altered the Earth’s climate and killed off the dinosaurs.
Miller plans to study the upper portion of the Eyreville cores to glean data about the region’s subsidence and the post-impact climate changes that affected global sea levels and ice sheets.
The team hopes the drill captures not just sediment but water. Any water near the bottom of the crater is likely to be ancient brine trapped by the backwash of debris, according to Gohn. In that water, scientists might get a look at “who’s living there now,” he said.
Hints that the crater might contain microbial life came in a core taken last year below Cape Charles, said Ward Sanford of the USGS.
“High levels of methane, dissolved organic carbon and ammonia . . . tell us a lot is happening there microbially,” Sanford said. “These microbes did not come from the surface, but must have been trapped there and evolving separately for 35 million years.”
USGS paleontologist Lucy Edwards will sift the core samples for microfossils or fossil algae, which suffer certain kinds of damage depending on the temperatures and pressure they’re under.
The Eyreville project also looks to the future. Gareth Collins of the University of Arizona and colleagues will take data from the drill and apply it to computer models to learn what could happen if another asteroid were to pummel the Earth.
Although the space invader’s impact was relatively limited to the bay, it left consequences that Virginians are dealing with today. It deformed and broke up the cakelike layers of sediment and aquifers, squeezing freshwater from many of the aquifers of southeastern Virginia and filling others with briny water.
Its legacy is well-known to residents who try to drill for drinkable groundwater and encounter the saltwater “wedge,” pockets of brine nestled in an arc from the lower Eastern Shore to the Hampton Roads-Newport News area.
The crater’s third co-discoverer said understanding this cataclysm is critical because the crater continues to shape Virginia’s coastal geology and hydrology. Scott Bruce of the Virginia Department of Environmental Quality said the agency needs to understand the bizarre geology to guide water management in a region where future sources of water are controversial.
Bruce said he’s already wondering how the Eyreville cores will alter the contents of DEQ’s soon-to-be-released hydrogeologic framework for the state’s groundwater.
But for Powars, “the unknown is what’s so exciting.”
“We’re going to learn so many things about this crater that we only just kind of arm-wave about now,” he said, doing just that.
On the Internet
* For more on the Chesapeake Bay Impact Crater:
http://geology.er.usgs.gov/eespteam/crater/
Goals of the drill
* Understand the processes and products of a marine impact.
* Understand the consequences of the impact for groundwater- resource management in Virginia.
* Understand the history of the sea level after the impact, the sequences of the geologic layering and the climate variability in the area.