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 likely exposed by drops in sea level during glacial periods. The shelf surrounding an island is known as an insular shelf.

The shelf usually ends at a point of increasing slope gradient, called the shelf break. The sea floor below the break is called the continental slope. Below the continental slope is the continental rise, which finally merges into the part of the deep ocean floor region called the abyssal plain. In the deep ocean floor region the abyssal plains break away into the much deeper oceanic trenches.

The continental margin, also known as the Continental Shelf Region is the area between the Coastal Plain Region and the Deep Ocean Floor Region. The continental margin comprises (1) the shallow water Continental Shelf, (2) a steeper Continental Slope, and (3) the flatter Continental Rise.

The continental shelf area is commonly subdivided into the (1) inner continental shelf, (2) mid continental shelf, and (3) outer continental shelf; each division with their specific geomorphology and marine biology.

The character of the continental shelf changes dramatically at the shelf break, below which the continental slope begins. With a few exceptions, the shelf break is located at a remarkably uniform depth of roughly 460 feet (140 m).

From the Shelf Break, the Continental Slope continues downward at an average angle of 3° but it can be as low as 1° or as high as 10°. The continental slope is often cut with submarine canyons. The physical mechanisms involved in forming these canyons were not well understood until the 1960s.

The continental rise normally has sediment from the parts of the above continent margin which cascades down the slope and accumulates as a pile at the base of the slope.

Extending as far as 310 miles (500 km) from the slope, it consists of thick sediments deposited by turbidity currents from the shelf and slope. The degree of angle (gradient) in the continental rise is intermediate between the gradients of the continental shelf and the continental slope.

Earth wide, Continental Shelves cover an area of about 10 million square miles, (27 million square km), which is equal to about seven percent of the total surface area of all the oceans.

The average width of continental shelves, as measured out from dry land to the shelf break, is about 80 km (50 mi). The depth of the shelf also varies, but is generally limited to water shallower than 100 m (330 ft). The slope of the shelf is usually quite low, on the order of 0.5°; vertical relief is also minimal, at less than 20 m (66 ft),

The width of the continental shelf varies considerably, and it is not uncommon for some coastal areas to have virtually no shelf whatsoever, which normally occurs where the forward edge of an advancing oceanic plate dives beneath continental crust in an offshore subduction zone. Two good example of this are (1) the west coast of Chile and (2) the west coast of Sumatra.

In both cases, the advancing oceanic plate that dives beneath the continental crust cause a deep ocean trench relatively near to the coast line in which areas are active seismic zones with frequent earthquakes and volcanoes. (See Volcanoes)

The largest shelf is the Siberian Shelf in the Arctic Ocean, which stretches out from dry land as far as 930 miles (1,500 kilometers) to the self break. Also, The South China Sea lies over another extensive area of continental shelf, called the Sunda Shelf, and which joins Borneo, Sumatra, and Java to the Asian mainland. Other familiar bodies of water that overlie large continental shelves are the North Sea and the Persian Gulf.

Although the continental shelf is treated as a physiographic province of the ocean, it is not part of the deep ocean basin proper, but is considered to be the flooded margins of the continent in which it surrounds.

Passive continental margins such as most of the Atlantic coasts have wide and shallow shelves, made of thick sedimentary wedges derived from long erosion of a neighboring continent, which in some reconing were once joined previously as a supercontinent known as Pangaea.

Active continental margins have narrow, relatively steep shelves, due to frequent earthquakes that move sediment to the deep sea, such as those in the areas of the Ring of Fire.

In 2023, the United States increased in land area by 386,000 square mile. It is true that the fiftieth state that joined the union was Hawaii in 1959. However, this new land area increase is not by the addition of another state.

Instead, this land area increase has been made by a shift in geographical coordinates that has resulted in the annexation of thousand of miles of extended underwater continental shelf (ECS).

To help understand how big this ECS addition actully is, below is a list of the land area of the four largest states in the United States.

Essentially, around every mass of continental land lies a large area of underwater land known as the continental shelf. This continental shelf slowly deepens in the ocean as it extends outward from the dry land until it arrives at where the shelf breaks away and becomes the continental slope. Previously, most countries knew that the continental shelf was part of their territorial land.

At the break of the continental shelf, the continental slope drops rapidly in depth until it bottoms out at the continental rise. (see attached diagram) The extended continental shelf (ECS) thus begins at that point where the continental shelf breaks and then continues down to the bottom of the continental slope. The ECS next continues along the continental rise until the continental rise arrives at the point where the Deep Ocean Floor Region begins. This is the area of the ECS that amounts to the 386,000 square miles for the United States and this land area is in addition to all of the land area of the continental shelf.

According to the "Law of the Sea Convention," also known as the United Nations Convention on the Law of the Sea (UNCLOS) which occurred in 1982, the ECS belongs to the country from which they extend. Thus, the ECS is now connected to the Continental Shelf as part of the territorial land that belongs to the country that has the dry land. This entire underwater area that is thus the property of the adjacent country is called the Continental Margin. The idea behind this law was to ensure the oceans directly surrounding the continents were protected for both their natural and cultural resources.

The idea behind this law was to ensure the oceans directly surrounding the continents were protected for both natural and cultural resources.

Not surprising to some, the largest ECS holding of the US is in the Arctic Ocean around the state of Alaska and the Bering Straight. However, this region sits so close to the easternmost shorelines of the country of Russia that a long-time debate has arisen over where the actual ECS borders are actually located.

Thus, since 2003, the United States together with the help of the National Oceanic and Atmospheric Administration (NOAA) and the U.S Geological Survey (USGS) has been on the job collecting masses of date from the areas around the Bering Strait.

In fact, for at least three decades, the NOAA has been using several types of data including that from: bathymetric, sub bottom, gravity, magnetic, seismic, and geologic samples to create an extremely detailed map of the below the water line region, including the ECS of the entire United States.

On 19 December 2023, the US made the long-awaited announcement with regards to the new ECS borders and the results made it clear that the United States has a total of 386,000 square miles of extended underwater continental shelf.

This new border was analyzed and confirmed by the Wilson Center, which was chartered by Congress to provide nonpartisan counsel and insight on global affairs to policy makers. They do this by extensive analysis and research.

The conclusion of the Wilson Center is, and I quote: "There is no need for a future negotiation with Russia because each country has delineated the outer limit of its continental shelf consistent with the boundary established in 1990 in the Agreement between the United States of America and the Union of Soviet Socialist Republics on the Maritime Boundary"

The underwater region known as the ECS is believed to be a treasure trove of oil, natural gas, minerals, sea life and even pirate treasure. Too, whatever is found in this new territorial region belongs to the country where it is located, and often that country must provide efforts to protect those treasures.

Often, the ECS is home to an abundance of wildlife, as well as entire ecosystems. But with this windfall comes the responsibility not to ruin the natural ecosystem nor over reap the treasures. Time will tell what the government of the United States will do, but most likely, like most all past endeavors, greed will play a crucial role.