Virginia Crater Research Targets Groundwater Data
Imagine something colliding with planet Earth so violently it instantly blasts a crater twice as big as Rhode Island and deeper than the Grand Canyon.
That's exactly what happened along the East Coast of what is now the United States some 35 million years ago.
An object believed to be an asteroid or comet smashed into the Earth with such awesome and lasting force its cataclysmic effects are still being seen today.
The extraterrestrial intruder, estimated by scientists to have been three to five miles in diameter, blasted into the Earth near what is now Cape Charles, VA. At impact, the object is believed to have been traveling 20 to 70 km (12.5 to 43.5 miles) per second.
Described by geologists as probably the most dramatic geological event to occur on the Atlantic margin of North America, the full scope of the immense impact is just becoming evident to researchers. The huge crater is the largest in the US and the sixth largest in the world.
When the impact occurred, according to US Geological Survey (USGS) scientist David Powars, "within minutes, millions of tons of water, sediment, and shattered rock were cast high into the atmosphere for hundreds of miles along the East Coast. An enormous seismic sea wave, or tsunami, rushed westward, engulfing the land and possibly even overtopping the Blue Ridge Mountains."
Powars, one of scientists who discovered the impact crater, said sea levels were higher at the time of the impact and most of eastern Virginia was submerged where the object smashed into the water and through thousands of feet of sediment before striking continental bedrock miles beneath the water's surface.
The huge impact crater and lasting effects of the violent collision which caused it have been the focus of special research efforts this summer by scientists from the USGS and other agencies. The researchers have gathered at NASA's Langley Research Center in Hampton, VA to study the crater and its impacts on issues such as availability of groundwater resources in the fast-growing area.
"People living in southeastern Virginia are affected by this ancient cataclysm daily," said Greg Gohn, USGS Chief of the Chesapeake Bay Impact Crater Project. "The impact severely disrupted the rock units that today are important aquifers providing drinking water to the Hampton Roads area. We believe that large areas within the crater are unsuitable for future water supply development."
As part of the project, a series of deep holes will be drilled in and around the crater site to study how the impact and the resulting crater have affected the geology and water resources in the area. Drilling of the first hole is now under way at the crater site.
"Drilling this exploratory bore hole and others in the next few years will help in understanding how to best develop and manage the region's groundwater supply," Gohn said.
Initial drilling began July 23 and the bore is expected to be 2,600 to 2,700 feet deep, said Donald Queen, chief driller for the USGS office in Reston, VA. Future plans call for drilling another 2,500 to 3,000-foot hole inside the crater area and a 6,000-foot hole near the center of the impact area, Queen said.
Queen said the drilling, which is being conducted with a Boart Longyear 44 rig and Christiansen 94mm bits, has passed the 1,400-foot level and is expected to strike bedrock at about 2,100 feet. "We don't know if it will be crystallized from the impact or shattered, no one really knows what to expect," he said.
The drilling operation is continuing 24 hours a day and Queen said core samples are being obtained along the entire length of the bore for use in the research.
"We are starting to realize there are a lot more impacts from these things than we originally thought. If we understand those impacts, we can use information gathered in this study to help supply water for the people in the area," Queen said.
Besides the research being conducted with the drilling and the core samples, Queen said a seismic reflection study will be done to map the crater's margin.
The seismic study will be conducted in an area from the Langley research facility to a site near the James River. The seismic work involves setting off quarter sticks of dynamite in patterns approximately 50 meters apart and setting off smaller shotgun shell-size charges between them. The sound waves created by the charges will be used to obtain images of the distribution of materials and structures within, outside and across the crater's margin.
Research from the drilling core samples and the seismic study will be very important in helping determine how to maintain existing groundwater resources in the crater area, said USGS Hydrologist Randy McFarland.
"The Eastern coast of Virginia in the Coastal Plains area consumes a half billion gallons of water a day and about one fourth of that is from groundwater. State and local entities are concerned about maintaining that water source," McFarland said.
He said previous studies of the aquifer system in the area were conducted before the huge crater was discovered.
"Since the crater was discovered, it has pretty profoundly affected the understanding of the aquifers and how they are structured. To understand the plumbing of the aquifers will give us some idea of the quality of the water that is available and if there are quality questions," McFarland said.
Earlier USGS research indicated the orderly stack of aquifers in the area outside the crater stops at the crater rim. A massive underground dome of water which is 1.5 times saltier than Atlantic Ocean water is also present near the crater area.
"For decades, people had known of the salt water being much farther inland than it should have been, but there was no satisfactory answer for it. When the crater was discovered, it pretty much accounted for the presence of the salt water, but it has been mostly speculation up to now as to whether the salt water came from sea water, dissolved minerals or other processes," McFarland said.
The USGS hydrologist said water demand in the area near the crater has reached the point that some cities are drilling wells into the salty water and using desalinization processes to make it usable for drinking water and other purposes.
"We don't know the effects of using the salt water, whether it will draw in more fresh water and clean up that area or whether it will make it worse," McFarland said.
The crater research project is a combined effort of the federal, state and local government agencies in the crater area. Besides NASA and USGS, other agencies cooperating in the research include the Hampton Roads, VA Planning District Commission, the Virginia Department of Environmental Quality, the Virginia Department of Mines, Minerals and Energy's Division of Mineral Resources, and the Department of Geology of the College of William and Mary.