The Chesapeake Bay Impact Crater

Rhonda Olson

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.

Resources

Alvarez, W., Asaro, F., Michel, H., and Alvarez, L., 1982, Iridium Anomaly Approximately Synchronous with Terminal Eocene Extinctions, AAAS, Science, vol. 216, p. 886-888

Geotimes, 1995, Chesapeake Bay Impact Crater Confirmed, p. 10-11, contributed by Richard A. Kerr, reprinted with permission from Science, vol. 269, Sept. 22, 1995, p. 1672, AAAS

Gilmore, J., Knight, J., Pillmore, C., Tschudy, R., and Fasset, J. E., 1981, Nonmarine Iridium Anomaly Linked to Extinctions, AAAS, Science, vol. 212, p. 1376

Grieve, R., Rupert, J., Smith J., and Therriault A., 1995, The Record of Terrestrial Impact Cratering, The Geologic Society of America, GSA Today, vol. 5, No. 10, October

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

Montanari, Alessandro, 1990, Geochronology of the Terminal Eocene Impacts: An Update, The Geologic Society of America, Special Paper 247, p. 607-614

Orth, C. J., Attrep, M., and Quintana, L. R., 1990, Iridium Abundance Patterns Across Bio-event Horizons in the Fossil Record, The Geologic Society of America, Special Paper 247, p. 45-58

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