The Chesapeake Bay impact crater is a buried impact crater, located beneath the mouth of

Chesapeake Bay The Chesapeake Bay ( ) is the largest estuary in the United States. The Bay is located in the Mid-Atlantic region and is primarily separated from the Atlantic Ocean by the Delmarva Peninsula (including the parts: the Eastern Shore of Maryland / ...

, United States. It was formed by a

bolide A bolide is normally taken to mean an exceptionally bright meteor, but the term is subject to more than one definition, according to context. It may refer to any large crater-forming body, or to one that explodes in the atmosphere. It can be a ...

that

struck Struck is a surname. Notable people with the surname include: * Adolf Struck (1877–1911), German author *Hermann Struck (1876–1944), German artist *Karin Struck (1947–2006), German author *Paul Struck (1776-1820), German composer *Peter Stru ...

the eastern shore of North America about 35.5 ± 0.3 million years ago, in the late

Eocene The Eocene ( ) Epoch is a geological epoch that lasted from about 56 to 33.9 million years ago (mya). It is the second epoch of the Paleogene Period in the modern Cenozoic Era. The name ''Eocene'' comes from the Ancient Greek (''ēṓs'', ...

epoch. It is one of the best-preserved "wet-target"

impact crater An impact crater is a circular depression in the surface of a solid astronomical object formed by the hypervelocity impact of a smaller object. In contrast to volcanic craters, which result from explosion or internal collapse, impact crater ...

s in the world. Continued slumping of

sediment Sediment is a naturally occurring material that is broken down by processes of weathering and erosion, and is subsequently transported by the action of wind, water, or ice or by the force of gravity acting on the particles. For example, sand ...

s over the rubble of the crater has helped shape the Chesapeake Bay.

Formation and aftermath

During the warm late

sea level Mean sea level (MSL, often shortened to sea level) is an average surface level of one or more among Earth's coastal bodies of water from which heights such as elevation may be measured. The global MSL is a type of vertical datuma standardis ...

s were high, and the

tidewater region Tidewater refers to the north Atlantic coastal plain region of the United States of America. Definition Culturally, the Tidewater region usually includes the low-lying plains of southeast Virginia, northeastern North Carolina, southern Mary ...

of Virginia lay in the

coast The coast, also known as the coastline or seashore, is defined as the area where land meets the ocean, or as a line that forms the boundary between the land and the coastline. The Earth has around of coastline. Coasts are important zones in n ...

al shallows. The shore of eastern North America, about where

Richmond, Virginia (Thus do we reach the stars) , image_map = , mapsize = 250 px , map_caption = Location within Virginia , pushpin_map = Virginia#USA , pushpin_label = Richmond , pushpin_m ...

is today, was covered with thick

tropical rainforest Tropical rainforests are rainforests that occur in areas of tropical rainforest climate in which there is no dry season – all months have an average precipitation of at least 60 mm – and may also be referred to as ''lowland equator ...

, and the waters of the gently sloping

continental shelf A continental shelf is a portion of a continent that is submerged under an area of relatively shallow water, known as a shelf sea. Much of these shelves were exposed by drops in sea level during glacial periods. The shelf surrounding an island ...

were rich with marine life that was depositing dense layers of lime from their microscopic shells. The bolide made impact at a speed of approximately per second, punching a deep hole through the sediments and into the

granite Granite () is a coarse-grained ( phaneritic) intrusive igneous rock composed mostly of quartz, alkali feldspar, and plagioclase. It forms from magma with a high content of silica and alkali metal oxides that slowly cools and solidifies un ...

continental

basement rock In geology, basement and crystalline basement are crystalline rocks lying above the mantle and beneath all other rocks and sediments. They are sometimes exposed at the surface, but often they are buried under miles of rock and sediment. The baseme ...

. The bolide itself was completely vaporized, with the basement rock being fractured to depths of , and a

peak ring A peak ring crater is a type of complex crater, which is different from a multi-ringed basin or central-peak crater. A central peak is not seen; instead, a roughly circular ring or plateau, possibly discontinuous, surrounds the crater's center, ...

being raised around it. The deep crater, across, is surrounded by a flat-floored terrace-like ring trough with an outer edge of collapsed blocks forming ring faults. The entire circular crater is about in diameter and deep, an area twice the size of

Rhode Island Rhode Island (, like ''road'') is a U.S. state, state in the New England region of the Northeastern United States. It is the List of U.S. states by area, smallest U.S. state by area and the List of states and territories of the United States ...

, and nearly as deep as the

Grand Canyon The Grand Canyon (, yuf-x-yav, Wi:kaʼi:la, , Southern Paiute language: Paxa’uipi, ) is a steep-sided canyon carved by the Colorado River in Arizona, United States. The Grand Canyon is long, up to wide and attains a depth of over a m ...

. However, numerical modeling techniques by Collins et al. indicate that the post-impact diameter was likely to have been around , rather than the observed . The surrounding region suffered massive devastation.

USGS The United States Geological Survey (USGS), formerly simply known as the Geological Survey, is a scientific agency of the United States government. The scientists of the USGS study the landscape of the United States, its natural resources, ...

scientist David Powars, one of the impact crater's discoverers, described the immediate aftermath: "Within minutes, millions of tons of water, sediment, and shattered rock were cast high into the

atmosphere An atmosphere () is a layer of gas or layers of gases that envelop a planet, and is held in place by the gravity of the planetary body. A planet retains an atmosphere when the gravity is great and the temperature of the atmosphere is low. A ...

for hundreds of miles along the East Coast." An enormous megatsunami engulfed the land and possibly even reached the

Blue Ridge Mountains The Blue Ridge Mountains are a physiographic province of the larger Appalachian Mountains range. The mountain range is located in the Eastern United States, and extends 550 miles southwest from southern Pennsylvania through Maryland, West Virg ...

. The sedimentary walls of the crater progressively slumped in, widened the crater, and formed a layer of huge blocks on the floor of the ring-like trough. The slump blocks were then covered with the rubble or ''

breccia Breccia () is a rock composed of large angular broken fragments of minerals or rocks cemented together by a fine-grained matrix. The word has its origins in the Italian language, in which it means "rubble". A breccia may have a variety of ...

''. The entire bolide event, from initial impact to the termination of breccia deposition, lasted only a few hours or days. In the perspective of geological time, the breccia is an instantaneous deposit. The crater was then buried by additional sedimentary beds that have accumulated during the 35 million years following the impact. The impact has been identified as the source of the North American tektite field, namely the Georgiaite and Bediasite fields.

Discovery

Until 1983 there was no evidence of a large impact crater buried beneath the lower part of the

and its surrounding

peninsula A peninsula (; ) is a landform that extends from a mainland and is surrounded by water on most, but not all of its borders. A peninsula is also sometimes defined as a piece of land bordered by water on three of its sides. Peninsulas exist on a ...

s. The first hint was a layer of

ejecta Ejecta (from the Latin: "things thrown out", singular ejectum) are particles ejected from an area. In volcanology, in particular, the term refers to particles including pyroclastic materials (tephra) that came out of a volcanic explosion and magma ...

found in a drilling core taken off

Atlantic City, New Jersey Atlantic City, often known by its initials A.C., is a coastal resort city in Atlantic County, New Jersey, United States. The city is known for its casinos, boardwalk, and beaches. In 2020, the city had a population of 38,497.

, about to the north. The layer contained the fused

glass Glass is a non- crystalline, often transparent, amorphous solid that has widespread practical, technological, and decorative use in, for example, window panes, tableware, and optics. Glass is most often formed by rapid cooling (quenchin ...

beads called tektites and shocked quartz grains that are unmistakable signs of a bolide impact. In 1993, data from

oil exploration Hydrocarbon exploration (or oil and gas exploration) is the search by petroleum geologists and geophysicists for deposits of hydrocarbons, particularly petroleum and natural gas, in the Earth using petroleum geology. Exploration methods Vis ...

revealed the extent of the crater.

Effects on local rivers

The continual slumping of the rubble within the crater has affected the flow of the

river A river is a natural flowing watercourse, usually freshwater, flowing towards an ocean, sea, lake or another river. In some cases, a river flows into the ground and becomes dry at the end of its course without reaching another body of ...

s and shaped the Chesapeake Bay. The impact crater created a long-lasting topographic depression which helped predetermine the course of local rivers and the eventual location of the Chesapeake Bay. Most important for present-day inhabitants of the area, the impact disrupted

aquifer An aquifer is an underground layer of water-bearing, permeable rock, rock fractures, or unconsolidated materials ( gravel, sand, or silt). Groundwater from aquifers can be extracted using a water well. Aquifers vary greatly in their characte ...

s. The present freshwater aquifers lie above a deep salty

brine Brine is a high-concentration solution of salt (NaCl) in water (H2O). In diverse contexts, ''brine'' may refer to the salt solutions ranging from about 3.5% (a typical concentration of seawater, on the lower end of that of solutions used for ...

, remnants of 100- to 145-million-year-old

Early Cretaceous The Early Cretaceous (geochronology, geochronological name) or the Lower Cretaceous (chronostratigraphy, chronostratigraphic name), is the earlier or lower of the two major divisions of the Cretaceous. It is usually considered to stretch from 145& ...

North Atlantic The Atlantic Ocean is the second-largest of the world's five oceans, with an area of about . It covers approximately 20% of Earth's surface and about 29% of its water surface area. It is known to separate the " Old World" of Africa, Europe a ...

seawater, making the entire lower Chesapeake Bay area susceptible to

groundwater contamination Groundwater pollution (also called groundwater contamination) occurs when pollutants are released to the ground and make their way into groundwater. This type of water pollution can also occur naturally due to the presence of a minor and unwante ...

References

Bibliography

*Poag, C. Wiley. ''Chesapeake Invader: Discovering America's Giant Meteorite Crater.'' Princeton, NJ: Princeton University Press, 1999. *''Post-impact Effects of the Eocene Chesapeake Bay Impact, Lower York-James Peninsula, Virginia'', 31st Annual Meeting
Virginia Geological Field Conference
Williamsburg, Virginia, Oct. 19 and 20, 2001, G.H. Johnson et al. (fieldtrip guidebook)

External links