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United States. Final Report". Other availability.
Please see Document Availability for additional information on obtaining the full-text document. Library patrons may search WorldCat to identify libraries that may hold this item. Keep in mind that many technical reports are not cataloged in WorldCat. At times the process reversed and sea level rose briefly to drown the land again, with one such "transgression" occurring 35, years ago.
About 30, years ago, the last step was a rapid expansion of the ice sheet and equally-rapid drop in sea level, exposing the last wedge of sediments that had been deposited on the outer edge of the Continental Shelf.
Estuarine, Coastal and Shelf Science
When the first Virginian's arrived perhaps 15, years ago, sea levels were feet lower because so much water was locked up in the glaciers and continental ice sheets. The Coastal Plain of Virginia extended much further to the east, where sloping hills and cliffs marked the edge of the land and ocean. Discovery of the original campsites of the first Virginians may require using submersibles to support underwater explorations and excavations. The Cinmar bipoint was dredged up from the Outer Continental Shelf, feet deep off the coast of Virginia, in That point had been flaked skillfully from a chunk of volcanic rock rhyolite whose original source was South Mountain in modern-day Pennsylvania.
The Cinmar bipoint could be dated because it was dredged up together with a mastodon skull that was roughly 25, years old. If that date is accurate the point was not directly lodged in the skull when the scallop dredger pulled the items from the haul Those humans were crafting bipoints long before the Clovis style was adopted.
Rivers flowing off the Appalachian Mountains dug paths into the newly-exposed Continental Shelf as water levels in the ocean dropped from its last peak, at the start of the Wisconsin Ice Age. The Potomac and James rivers carved separate valleys across the wide Coastal Plain to the salt water, and there was no Chesapeake Bay.
The most powerful rivers carved channels even through the Continental Rise, and massive landslides reshaped the cliffs between the canyons. The ancient, separate river valleys of the Susquehanna and James rivers remain today. Those driving across the Chesapeake Bay Bridge-Tunnel dip underwater at two locations shaped by those rivers, in a tunnel under the James River channel Thimble Shoals and further north under the old path of the Susquehanna River Chesapeake Channel.
Much of the Coastal Plain that existed 18, years ago has been drowned by the rising Atlantic Ocean. The first people who arrived in Virginia witnessed rising sea levels drowning the eastern edge of the Coastal Plain, creating today's Continental Shelf between the current Atlantic Ocean shoreline and the cliffs of the Continental Slope. We still witness sea level rise today, gradually altering the outline of the Chesapeake Bay and continuing to widen the extent of the Continental Shelf.
The development of submarines, starting in World War I, increased our capacity to map the seafloor. Today we know: 4. The continental shelf is the submarine extension of the coastal plain deposits from the shoreline to about the m water depth, characterized by a gentle slope of a few meters per kilometer i. During the last low stand of sea level, ice-fed streams carried glacial outwash gravels and sands onto the shelf.
Major rivers flowed across the shelf to submarine canyons on the shelf edge and deposited further sediment. As the glacial ice melted during later periods of geologic time, the rivers receded across the shelf, leaving behind their shoreline sediment complexes and associated stream valley features The mid-Atlantic Continental Slope is a steep, narrow area paralleling the shelf and extending from the shelf break to depths of about 2, m 6, feet.
The upper slope has gradients ranging from feet per mile to feet per mile, and is incised by numerous submarine canyons.
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These topographic canyons are primarily features of the northern mid-Atlantic slope. Topographically, the mid-Atlantic Continental Slope appears to be much more complex than previously thought. Long-range sidescan-sonar surveys of the slope reveal extensive and rugged terrains of valleys and gullies within the intercanyon areas. In addition, the surveys have revealed many more submarine canyons than are presently shown on bathymetric diagrams. The continental rise is a gently sloping, wide sedimentary apron extending from the base of the continental slope Turbidity currents flow down the submarine canyons and form channel systems on the rise, contributing to the accumulation of sediment.
Developing the mineral resources below the ocean became technologically feasible in the middle of the 20th Century, greatly increasing interest in the Continental Shelf. Geological investigations revealed that onshore oil fields clearly extended past the coastline, and oil companies sought to build platforms for offshore oil wells. In , the Supreme Court ruled that the Federal government could control development of offshore mineral resources. According to the Supreme Court, the first 13 colonial governments had not acquired ownership of the seabed through their charters from the king in England, so at the start of the American Revolution the 13 original states did not inherit control over the seabed.
To resolve the controversy over control of oil underneath the tidelands i. That law granted coastal states control over the bottom of the ocean for three nautical miles offshore, with the exception of 9 nautical miles for Texas and the west coast of Florida. The law also confirmed state ownership of " all lands permanently or periodically covered by tidal waters up to but not above the line of mean high tide.
Defining the boundary three miles offshore requires defining the shoreline itself. However, the ocean-land interface is constantly shifting; the shoreline is not a static line. International claims of rights to control navigation, fishing, and economic development of mineral resources led to the United Nations Convention on the Law of the Sea. Because the boundary changes as storms, currents, or even construction projects reshape the shoreline, the Federal government is partnering with the states to adopt a fixed set of geographic coordinates to "immobilize" the boundary, eliminating future changes and minimizing confusion regarding jurisdiction.
In United States v. Maine , Virginia claimed that its colonial charters granted the state exclusive jurisdiction of Atlantic Ocean resources for miles beyond the coastline. International standards for ocean boundaries are established in an international treaty. However, Senate approval is required to finalize the US commitment to the treaty.
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Congress has never ratified it, declining once again in due in part to concerns that the International Seabed Authority could limit US sovereignty. Consistent with the treaty even though Congress has not ratified it , the United States claims a Territorial Sea for 12 nautical miles offshore.
The starting point for defining offshore vs. The US exercises sovereignty over its Territorial Sea, the air space above it, and the seabed and subsoil beneath it, but foreign-flag ships enjoy the right of innocent passage. The Federal government also claims a Contiguous Zone out to 24 miles 12 miles further than the Territorial Sea , allowing enforcement of federal customs, fiscal, immigration, and sanitary laws but otherwise the US does not exercise sovereignty in the Contiguous Zone.
While the Federal government claims full ownership of lands outside the state claims, in Congress created the Revenue Sharing Boundary in section 8 g of the OCS Lands Act amendments so the Federal government will share a "fair and equitable" portion of offshore revenues. NOAA has rules with complicated mathematics involving equidistant arcs that guide how to map the baseline between headlands and across the mouths of rivers, bays, and estuaries.
The baseline is dynamic "ambulatory" , subject to change due to accretion and erosion of the shore. Permanent structures built on the shoreline, such as jetties, groins, and breakwaters, can alter the baseline. Beyond 6 miles, however, the Federal government would receive all revenues associated with easing submerged lands on the Outer Continental Shelf.
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The various ownership boundaries migrate as the shoreline changes. Maritime limits and boundaries for the United States are measured from the official U. Because U. Baseline Committee, continually maintains the dataset. When NOAA releases a new nautical chart the maritime limits and boundaries are updated as needed.
Since "low-water line" does not reference a specific tidal datum, the U. The United States is considering extending its claim beyond the nautical mile limit, to encompass the entire Outer Continental Shelf. Article 76 of the United Nations Convention on the Law of the Sea would allow extending American claims from nautical miles to as much as nautical miles east of the shoreline, based on the location of the foot bottom of the Continental Slope.
Most effort is focused now on defining the edge of the continental shelf in the Arctic Ocean, as the basis for clarifying boundaries between Russia, Canada, and the US, but the US government is exploring the potential for an extension of the EEZ in the Atlantic as well. Responsibility for the land and water off the Virginia coast is split between the state and Federal government. Satellite Remote Sensing Helps Monitor Live Vegetation in Kenya A newly developed, user-friendly mapping system will assist resource managers of arid and semiarid rangelands Read more. Happy World Wetlands Day!
We celebrate wetlands around the world on February 2, but USGS scientists study these amazing ecosystems all year long. Learn more. Learn More. Science for Detection, Containment, and Control of Invasive Species USGS scientists focus on the development of innovative prevention, prediction, early detection, containment, and control tools. Let us help. Date published: July 3, Date published: July 2, Date published: June 30, View All News. Year Published: Reporting the limits of detection and quantification for environmental DNA assays BackgroundEnvironmental DNA eDNA analysis is increasingly being used to detect the presence and relative abundance of rare species, especially invasive or imperiled aquatic species.