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Topic: Chesapeake Bay impact crater

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	Chesapeake Bay impact crater - Wikipedia, the free encyclopedia
		The Chesapeake Bay Impact Crater was formed by the impact of an extraterrestrial bolide that hit about 35.5 million years ago, in the late Eocene Epoch.
		It is one of the best-preserved 'wet-target' or marine impact craters, and the largest impact crater in the USA.
		USGS scientist David Powars, one of the impact crater's discoverers, has described the immediate aftermath: "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 tsunami engulfed the land and possibly even overtopped the Blue Ridge Mountains.
	en.wikipedia.org /wiki/Chesapeake_Bay_impact_crater (617 words)

	Chesapeake Bay - Wikipedia, the free encyclopedia
		The Chesapeake Bay Bridge-Tunnel spans a 23 mile (37 km) section of the Bay at near its mouth.
		The Chesapeake Bay was the site of the Battle of the Chesapeake in 1781, during which the French fleet defeated the Royal Navy in the decisive naval battle of the American Revolutionary War.
		In the 1970s, the Chesapeake Bay contained one of the planet's first identified marine dead zones, where hypoxic waters were so depleted in oxygen they were unable to support life, identified when massive fish kills resulted.
	en.wikipedia.org /wiki/Chesapeake_Bay (737 words)

	Chesapeake Bay impact crater -- Facts, Info, and Encyclopedia article (Site not responding. Last check: 2007-09-16)
		The bolide impacted at a speed of many kilometers per second, punching a deep hole through the sediments and into the (Plutonic igneous rock having visibly crystalline texture; generally composed of feldspar and mica and quartz) granite continental basement rock.
		The entire circular crater is about 85 km in diameter and 1.3 km deep, an area twice the size of (A state in New England; one of the original 13 colonies; the smallest state) Rhode Island, and nearly as deep as the (The enormous gorge of the Colorado River in northern Arizona) Grand Canyon.
		Until 1983, no one suspected the existence of such a crater buried 300–500 meters beneath the lower part of (A large inlet of the North Atlantic between Virginia and Maryland; fed by Susquehanna River) Chesapeake Bay and its surrounding (A large mass of land projecting into a body of water) peninsulas.
	www.absoluteastronomy.com /encyclopedia/C/Ch/Chesapeake_Bay_impact_crater.htm (649 words)

	Crater
		A crater (basin or impact crater) is a circular depression on the surface of a planet, moon, asteroid, or other celestial body.
		In the center of craters on Earth a crater lake often accumulates, and in craters formed by meteorites a central island (caused by rebounding crustal rock after the impact) is usually a prominent feature in the lake.
		Daniel Barringer was one of the first to identify a geological structure as an impact crater, the Barringer Meteorite Crater (or the "Meteor Crater") in Arizona, but at the time his ideas were not widely accepted, and when they were, there was no recognition of the fact that Earth impacts are common in geological terms.
	www.brainyencyclopedia.com /encyclopedia/c/cr/crater.html (1203 words)

	The Chesapeake Bay Impact Structure \| The Geology of Virginia (Site not responding. Last check: 2007-09-16)
		The crater is centered under the Chesapeake Bay approximately 8 km (5 miles) west of the town of Cape Charles on the Eastern Shore.
		The crater is cut into ~650 m (~2000 feet) of Early Cretaceous to late Eocene sedimentary material and at least a kilometer (~3000 feet) of the underlying granodioritic basement rocks.
		Although hidden at the surface the Chesapeake Bay impact crater is still affecting the region as briny groundwater associated with the crater is a problem for many deep water well in eastern Virginia.
	www.wm.edu /geology/virginia/cbis.html (479 words)

	USGS Professional Paper 1612
		The Chesapeake Bay impact crater is a 56-mile wide, complex peak-ring crater with an inner and outer rim, a relatively flat-floored annular trough, and an inner basin that penetrates the basement to a depth of at least 1.2 miles.
		The York-James Peninsula is bounded by the James River on the south, the York River on the north, and the Chesapeake Bay on the east (fig.
		Various structural and stratigraphic complexities related to the CBIC and its burial have altered the hydraulic characteristics of the aquifers and confining units inside and adjacent to the crater and have apparently retarded the flushing of salt water from inside the crater.
	pubs.usgs.gov /prof/p1612/powars.html (19430 words)

	Chesapeake Meteor
		Since the crater is hidden from sight, tangled clues began to emerge during a search for water for thirsty Virginians, which slowly led to this unexpected discovery far out in the Chesapeake Bay.
		Scientists now theorize that the slightly salty to brackish groundwater that occurs in the aquifers adjacent to and with the crater (beneath the lower portions of the York-James and Middle peninsulas) is due to the differential flushing of seawater related to the structure of the buried crater.
		The nature of the impact substantially affected the geology of the Atlantic continental crust and is suspected to affect the nature and quality of groundwater in southeastern Virginia.
	meteor.pwnet.org /impact_event/impact_crater.htm (3840 words)

	125th - Articles - Science - Unlocking the Secrets of the Chesapeake Bay Impact Crater and Virginia's Inland Saltwater ...
		Within minutes from the instant of impact, billions of tons of ocean water were vaporized, and millions of tons of sediment, debris, and seawater were thrown thousand of feet into the atmosphere and scattered along much of the East Coast.
		The location of the crater coincides directly with the salty ground water beneath southeastern Virginia, which chemical evidence indicates is seawater trapped within the crater fill, possibly from as far back as the impact itself.
		Through this study of one of Earth's largest known impact craters, USGS scientists and partners are increasing our scientific understanding of cratering processes, and at the same time addressing the critical issue of water availability in southeastern Virginia.
	www.usgs.gov /125/articles/craterandsaltwater.html (778 words)

	SHALLOW SEISMIC REFLECTION IMAGING ACROSS THE CHESAPEAKE BAY IMPACT INNER CRATER RIM (Site not responding. Last check: 2007-09-16)
		Since its discovery in 1993, much of the detailed work on the Chesapeake Bay Impact Crater has focused on the effects of the impact on the geologic, structural and hydrogeologic framework of the outer rim of the crater.
		Less is known about the inner crater, which is the region that was most deeply excavated by the impact and that, like the Chicxulub structure, is likely to have the most complex structure and stratigraphy.
		The primary goal of this project is to use images of the transition from the inner crater to the outer crater to study the effects of impact processes on both pre-existing shallow marine stratigraphy, and post-impact stratigraphy of the continental shelf.
	gsa.confex.com /gsa/2003AM/finalprogram/abstract_58654.htm (481 words)

	Planetary Society: Impact in the Chesapeake - Ongoing Crater Studies (Site not responding. Last check: 2007-09-16)
		The resulting impact and explosion blew a large hole in the shallow seabed, sending a jumble of rocks, soil and water flying high into the atmosphere and a tsunami rushing in to mix up whatever was left.
		Because the crater was discovered only recently (in 1994 by USGS geologist C. Wylie Poag) scientists still have much to learn about this large buried crater and its effects on the geology of the area.
		Because we believe that this ancient impact might have rendered the ground water in large areas of the crater unfavorable for development as a water source, the information we are gathering is relevant to managing ground-water resources in southeastern Virginia," said Gohn.
	www.planetary.org /html/news/articlearchive/headlines/2001/chesapeakecrater2.html (468 words)

	[No title] (Site not responding. Last check: 2007-09-16)
		The late Eocene (-35.6 Ma) Chesapeake Bay crater (85-km diameter) is filled and partly surrounded by polymictic, sediment-clast-dominated, impact breccia (Exmore breccia).
		In the case of the Chesapeake Bay impact, the entire 35.5ft and 40-ft (1 0.8 m and 12.2 m) breccia sections sampled outside the crater are matrix-dominated (WB = 2.1 and 5.2).
		Inside the crater, the next deeper section of Exmore breccia [1237-1288 ft (377-392.6 m) at Exmore; 1354-1536 ft (412.7-468.2 m) at Kiptopeke] is boulder-dominated (M/B =0.3 and 0.5, respectively).
	woodshole.er.usgs.gov /bibliographies/current2/565.html (731 words)

	The Chesapeake Bay "Bolide" That Shaped the Groundwater in Southeastern Virginia (Site not responding. Last check: 2007-09-16)
		The Chesapeake Bay "Bolide" That Shaped the Groundwater in Southeastern Virginia
		The salt and brackish water intrudes from the ocean, Chesapeake Bay, and the northern extension of Albemarle/Pamlico Sound via the porous sediments underlying Tidewater.
		The Effects of the Chesapeake Bay Impact Crater on the Geological Framework and Correlation of Hydrogeologic Units of the Lower York-James Peninsula, Virginia - Professional Paper 1612
	www.virginiaplaces.org /geology/bolide.html (285 words)

	Encyclopedia: Weaubleau-Osceola structure (Site not responding. Last check: 2007-09-16)
		These 38th parallel structures are thought to possibly be the result of a serial impact, similar to that of comet Shoemaker-Levy 9 on Jupiter, an extremely unlikely event on Earth.
		The Weaubleau-Osceola structure is one of the fifty largest known impact craters on earth and the fourth largest in the United States.
		The three larger ones in the US either have been glaciated and buried (Manson crater), are under water (Chesapeake Bay crater), or have been subjected to orogeny (Beaverhead crater).
	www.nationmaster.com /encyclopedia/Weaubleau_Osceola-structure (522 words)

	Planetary Society: Headline for 8/4/00
		There in the middle of the bay, buried by 350 meters of sediments, was a gigantic hole, 80 kilometers wide and almost a kilometer deep (50 miles wide, 0.5 miles deep).
		Moreover, it appears that the Chesapeake Bay crater was the source for a wide spread deposit of impact debris known as the North American tektite strewn field.
		The Toms Canyon crater is identical in age to the Chesapeake Bay crater and contains a similar assemblage of mixed microfossils in the crater fill.
	www.planetary.org /html/news/articlearchive/headlines/2000/bolides.html (1580 words)

	Huge, Ancient Chesapeake Impact Crater Continues To Raise Questions (Site not responding. Last check: 2007-09-16)
		Today, a rough circle of low ridges in Virginia's coastal plain, near historic Williamsburg and Jamestown, marks the outer rim of the ancient crater, which is buried under thousands of feet of sand, silt and clay.
		Other signs of the collision remain: Two million nearby residents face a shortage of fresh water, because the searing heat of the long-ago impact vaporized huge quantities of seawater, leaving the basin still filled with salt that threatens their freshwater aquifers.
		This summer, researchers from the U.S. Geological Survey are drilling holes in and around the Chesapeake Bay Impact Crater, as it is known.
	www.rense.com /general13/crater.htm (638 words)

	The Chesapeake Bay Bolide Impact: A New View of Coastal Plain Evolution
		The crater is now approximately 200 km southeast of Washington, D.C., and is buried 300-500 meters beneath the southern part of Chesapeake Bay and the peninsulas of southeastern Virginia (fig.
		Analysis of 1,200 km of profiles shows that the crater is 85 km in diameter and 1.3 km deep; an excavation twice the size of Rhode Island and as deep as the Grand Canyon.
		Evidence of accelerated land subsidence is reflected in the geology and topography of the modern land surfaces around the crater.
	marine.usgs.gov /fact-sheets/fs49-98 (1362 words)

	Team digs for scoop on huge crater - 11/02/05 (Site not responding. Last check: 2007-09-16)
		The impact vaporizes billions of tons of water, rips a hole in the sea floor six miles deep and fractures the bedrock far into the Earth.
		An impact by something a half-mile in size, and "the East Coast is in trouble," he said.
		Impact science is fairly young, the geologists said.
	www.detnews.com /2005/nation/0511/03/A12-368808.htm (791 words)

	News Release
		The Chesapeake Bay impact crater is shallower and more accessible than the much larger and older one off the coast of Mexico that most scientists believe led to the extinction of the dinosaurs."
		The impact of the comet or meteorite deformed and broke up the "layer cake" stack of aquifers (water-bearing rocks) and confining units, which restrict the flow of ground water.
		This information is gathered in every state by USGS scientists to minimize the loss of life and property from natural disasters, contribute to the sound conservation, economic and physical development of the nation's natural resources, and enhance the quality of life by monitoring water, biological, energy, and mineral resources.
	va.water.usgs.gov /NEWS_RELEASE/pp1612_pr.html (700 words)

	High-Resolution Seismic Reflection/Refraction Images Near the Outer Margin of the Chesapeake Bay Impact Crater, ... (Site not responding. Last check: 2007-09-16)
		Initial borehole and marine seismic-reflection data revealed a 90-km-diameter impact structure, referred to as the Chesapeake Bay Impact Crater (CBIC), that lies buried beneath the southern Chesapeake Bay and surrounding Virginia Coastal Plain (Powars and Bruce, Figs.
		Therefore, the CBIC affects the present-day ground-water quantity and quality in the rapidly growing Hampton Roads region of southeastern Virginia.
		However, the geographic bounds of the CBIC, its effects on the regional aquifer systems, and the distribution of impact generated faults and fractures in basement are not well determined.
	wrgis.wr.usgs.gov /open-file/of01-407 (464 words)

	"Deep Impact" In Chesapeake Bay
		The discovery of the Chesapeake Bay impact crater helps explain a number of unusual features that have been noted in the region, including salty ground water, earthquakes around the crater's perimeter, and an unusual rate of sea-level rise.
		The impact of the comet or meteorite deformed and broke up the "layer cake" stack of aquifers and confining units.
		The outer rim of the crater seems to coincide with the boundary separating salty ground water inside the outer rim from fresher, lower salinity water outside the outer rim.
	home.arcor.de /hpj/Themen/impact/DeepImpact.html (609 words)

	Earth Impact Database
		Poag, C. 1999 Secondary Craters from the Cesapeake Bay Impact LPSC XXX, Lunar and Planetary Institute, Houston, TX, Abstr.
		Powars, D.S. 1999 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 USGS Professional Paper 1622
		Powars, D.S. Bruce, T.S. The Effects of the Chesapeake Bay Impact Crater on the Geological Framework and Correlation of Hydrogeologic Units of the Lower York-James Peninsula, Virginia USGS Proffesional Paper 1612
	www.unb.ca /passc/ImpactDatabase/images/chesapeake.htm (986 words)

	SPACE.com -- Huge East Coast Impact Crater Leaves Legacy of Water Woes
		The impact created a two-tiered depression, like an inverted sombrero, in what was then a shallow part of the ocean, explains David Powars, a hydrologist with the U.S. Geological Survey.
		The crater is buried under 400 to 1,200 feet (120 to 365 meters) of sand, silt and clay.
		This site is located well within the ring-shaped trough of the impact crater, and scientists expect to penetrate the bottom of the crater at a depth between 2,000 to 2,500 feet (610 and 760 meters).
	space.com /scienceastronomy/astronomy/east_coast_asteroid_010320.html (1103 words)

	Conference Reports. The Micropalaeontological Society - TMS
		The CBIC impact occurred approximately 35 million years ago (Late Eocene) when a meteorite or comet came to earth on the U.S. Atlantic continental shelf at a location that is currently occupied by the southern part of the Chesapeake Bay and neighbouring land, within the Virginia Coastal Plain.
		The crater as currently defined is approximately 84 km (53 miles) circular structure.
		The structure of the crater has a direct and important effect on the groundwater circulation in the State of Virginia, so any research undertaken will have a strongly economic interest, as well as having an academic side.
	www.nhm.ac.uk /hosted_sites/tms/impactconf.htm (329 words)

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