Approximately 35 million years ago, an asteroid or comet crashed into the then shallow marine environment of the North American Atlantic Coast near present day Hampton Beach, Virginia. The estimated 3km bolide excavated an 85km depression believed to be 1.3km deep. To put this in perspective, the crater would be twice the size of Rhode Island and as deep as the Grand Canyon.
graphic by Michael Hall, The Virginian-Pilot, June 25,2001
The location of the Chesapeake Bay Impact Crater
The immediate result was the displacement or vaporization of the water where the bolide impacted. Tsunamis crashed into the Blue Ridge Mountains and even into Europe. The returning seawater carried with it saturated plant, animal and rock debris, which filled in the crater nearly as quickly as it was created.
modified from Koeberl, 1993, by Hugh, Snyder and Miller, 1998
The North American tektite strewn field
The crater has remained buried under 35 million years worth of sediment, making conclusive identification difficult. The correlated composition, age and radial distribution of the North American tektite strewn field, abundant shocked minerals in core samples, related iridium anomalies, concurrent extinction events, and seismic profiles have allowed for the positive identification of the site as a recognized extraterrestrial impact structure.
from USGS Fact Sheet 49-98, C. Wylie Poag, 1998
Present day subsidence of the infilling crater breccia, and associated faulting has been a cause of concern regarding the risk of contamination of the drinking water supply in the Norfolk area. The truncated coastal aquifers and fractured basement rock, estimated to be disrupted to a depth of 11.43km, may provide the means by which the highly saline brine solution of crater debris could be channeled into the aquifers in the event of excessive well pumping.
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McHugh, Cecilia M. G., Snyder, Scott W., and Miller, Kenneth G., 1998, Upper Eocene Ejecta of the New Jersey Continental Margin Reveal Dynamics of Chesapeake Bay Impact, Elsevier, Earth and Planetary Science Letters, vol. 160, issues 3-4, p. 353-367, http://www.sciencedirect.com
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Poag, C. Wylie, 1998, The Chesapeake Bay Bolide Impact: A New View of Coastal Plain Evolution, United State Geological Survey, Fact Sheet fs49-98
Powars, David S., and Bruce, T. Scott, 1999, The Effects of the Chesapeake Bay Impact Crater on the Geologic Framework and Correlation of Hydrogeologic Units of the Lower York-James Peninsula, Virginia, United States Geological Survey, Professional Paper 1612
Powars, David S., 2000, The Effects of the Chesapeake Bay Impact Crater on the Geologic Framework and the Correlation of Hydrogeologic Units of Southeastern Virginia, South of the James River, United States Geological Survey, Professional Paper 1622
Stothers, Richard B., and Rampino, Michael R., 1990, Periodicity in Flood Basalts, Mass Extinctions, and Impacts: A Statistical View and a Model, The Geologic Society of America, Special Paper 247, p. 9-17
Terrestrial Impact Craters, http://www.star.le.ac.uk
United State Geological Survey, 1998, Chesapeake Bay Bolide homepage, http://woodshole.er.usgs.gov
The Virginian-Pilot, 2001, A Cosmic Tale, parts 1-7, http://www.pilotonline.com