United States Navy
The United States Navy is the naval warfare service branch of the United States Armed Forces and one of the seven uniformed services of the United States. It is the largest and most capable navy in the world and it has been estimated that in terms of tonnage of its active battle fleet alone, it is larger than the next 13 navies combined, which includes 11 U. S. allies or partner nations. With the highest combined battle fleet tonnage and the world's largest aircraft carrier fleet, with eleven in service, two new carriers under construction. With 319,421 personnel on active duty and 99,616 in the Ready Reserve, the Navy is the third largest of the service branches, it has 282 deployable combat vessels and more than 3,700 operational aircraft as of March 2018, making it the second-largest air force in the world, after the United States Air Force. The U. S. Navy traces its origins to the Continental Navy, established during the American Revolutionary War and was disbanded as a separate entity shortly thereafter.
The U. S. Navy played a major role in the American Civil War by blockading the Confederacy and seizing control of its rivers, it played the central role in the World War II defeat of Imperial Japan. The US Navy emerged from World War II as the most powerful navy in the world; the 21st century U. S. Navy maintains a sizable global presence, deploying in strength in such areas as the Western Pacific, the Mediterranean, the Indian Ocean, it is a blue-water navy with the ability to project force onto the littoral regions of the world, engage in forward deployments during peacetime and respond to regional crises, making it a frequent actor in U. S. foreign and military policy. The Navy is administratively managed by the Department of the Navy, headed by the civilian Secretary of the Navy; the Department of the Navy is itself a division of the Department of Defense, headed by the Secretary of Defense. The Chief of Naval Operations is the most senior naval officer serving in the Department of the Navy.
The mission of the Navy is to maintain and equip combat-ready Naval forces capable of winning wars, deterring aggression and maintaining freedom of the seas. The U. S. Navy is a seaborne branch of the military of the United States; the Navy's three primary areas of responsibility: The preparation of naval forces necessary for the effective prosecution of war. The maintenance of naval aviation, including land-based naval aviation, air transport essential for naval operations, all air weapons and air techniques involved in the operations and activities of the Navy; the development of aircraft, tactics, technique and equipment of naval combat and service elements. U. S. Navy training manuals state that the mission of the U. S. Armed Forces is "to be prepared to conduct prompt and sustained combat operations in support of the national interest." As part of that establishment, the U. S. Navy's functions comprise sea control, power projection and nuclear deterrence, in addition to "sealift" duties, it follows as certain as that night succeeds the day, that without a decisive naval force we can do nothing definitive, with it, everything honorable and glorious.
Naval power... is the natural defense of the United States The Navy was rooted in the colonial seafaring tradition, which produced a large community of sailors and shipbuilders. In the early stages of the American Revolutionary War, Massachusetts had its own Massachusetts Naval Militia; the rationale for establishing a national navy was debated in the Second Continental Congress. Supporters argued that a navy would protect shipping, defend the coast, make it easier to seek out support from foreign countries. Detractors countered that challenging the British Royal Navy the world's preeminent naval power, was a foolish undertaking. Commander in Chief George Washington resolved the debate when he commissioned the ocean-going schooner USS Hannah to interdict British merchant ships and reported the captures to the Congress. On 13 October 1775, the Continental Congress authorized the purchase of two vessels to be armed for a cruise against British merchant ships. S. Navy; the Continental Navy achieved mixed results.
In August 1785, after the Revolutionary War had drawn to a close, Congress had sold Alliance, the last ship remaining in the Continental Navy due to a lack of funds to maintain the ship or support a navy. In 1972, the Chief of Naval Operations, Admiral Elmo Zumwalt, authorized the Navy to celebrate its birthday on 13 October to honor the establishment of the Continental Navy in 1775; the United States was without a navy for nearly a decade, a state of affairs that exposed U. S. maritime merchant ships to a series of attacks by the Barbary pirates. The sole armed maritime presence between 1790 and the launching of the U. S. Navy's first warships in 1797 was the U. S. Revenue-Marine, the primary predecessor of the U. S. Coast Guard. Although the USRCS conducted operations against the pirates, their depredations far outstripped its abilities and Congress passed the Naval Act of 1794 that established a permanent standing navy on 27 March 1794; the Naval Act ordered the construction and manning of six frigates and, by October 1797, the first three were brought into service: USS United States, USS Constellation, USS Constitution.
Due to his strong posture on having a strong standing Navy during this period, John Adams is "often called the father of the American Navy". In 1798–99 the Navy was involved in an undeclared Quasi-War with France. From 18
The World Ocean or Global Ocean is the interconnected system of Earth's oceanic waters, comprises the bulk of the hydrosphere, covering 361,132,000 square kilometres of Earth's surface, with a total volume of 1,332,000,000 cubic kilometres. The unity and continuity of the World Ocean, with free interchange among its parts, is of fundamental importance to oceanography, it is divided into a number of principal oceanic areas that are delimited by the continents and various oceanographic features: these divisions are the Atlantic Ocean, Arctic Ocean, Indian Ocean, Pacific Ocean, Southern Ocean, defined by the International Hydrographic Organization in 2000, based on evidence that this region of the World Ocean has a distinct ecosystem and a unique impact on global climate. In turn, oceanic waters are interspersed by many smaller seas and bays. A global ocean has existed in one form or another on Earth for eons, the notion dates back to classical antiquity in the form of Oceanus; the contemporary concept of the World Ocean was coined in the early 20th century by the Russian oceanographer Yuly Shokalsky to refer to the continuous ocean that covers and encircles most of Earth.
If viewed from the southern pole of Earth, the Atlantic and Pacific Oceans can be seen as lobes extending northward from the Southern Ocean. Farther north, the Atlantic opens into the Arctic Ocean, connected to the Pacific by the Bering Strait, forming a continuous expanse of water; the Pacific Ocean, the largest of the oceans reaches northward from the Southern Ocean to the Arctic Ocean. It spans the gap between Australia and Asia, the Americas; the Pacific Ocean meets the Atlantic Ocean south of South America at Cape Horn. The Atlantic Ocean, the second largest, extends from the Southern Ocean between the Americas, Africa and Europe, to the Arctic Ocean; the Atlantic Ocean meets the Indian Ocean south of Africa at Cape Agulhas. The Indian Ocean, the third largest, extends northward from the Southern Ocean to India, the Arabian Peninsula, Southeast Asia in Asia, between Africa in the west and Australia in the east; the Indian Ocean joins the Pacific Ocean to the near Australia. The Arctic Ocean is the smallest of the five.
It joins the Atlantic Ocean near Greenland and Iceland and joins the Pacific Ocean at the Bering Strait. It overlies the North Pole, touching North America in the Western Hemisphere and Scandinavia and Siberia in the Eastern Hemisphere; the Arctic Ocean is covered in sea ice, the extent of which varies according to the season. The Southern Ocean is a proposed ocean surrounding Antarctica, dominated by the Antarctic Circumpolar Current the ocean south of 60 degrees south latitude; the Southern Ocean is covered in sea ice, the extent of which varies according to the season. The Southern Ocean is the second smallest of the five named oceans. Plate tectonics, post-glacial rebound, sea level rise continually change the coastline and structure of the world ocean. World Ocean portal Superocean World Ocean Atlas Panthalassa Oceans portal Chekin, L. 2002. "The world ocean in medieval cartography". Moscow: S. I. Vavilov Institute of the History of Science and Technology of the Russian Academy of Sciences.
"Ocean". The Columbia Encyclopedia, 6th ed. 2003. New York: Columbia University Press. "The role of mesoscale tracer transports in the global ocean circulation". Science: vol. 264. Pp. 1123–1126. Levitus, Sydney. 2000. "Warming of the world ocean": abstract, article. Science: vol. 287. Pp. 2225–2229. Spilhaus, Athelstan F. 1942. "Maps of the whole world ocean." Geographical Review: vol. 32, pp. 431–5. UN Atlas of the Oceans: "Distribution of land and water on the planet", "Origins of the oceans and continents" Global Ocean Commission Pew Charitable Global Ocean Legacy
Whales are a distributed and diverse group of aquatic placental marine mammals. They are an informal grouping within the infraorder Cetacea excluding dolphins and porpoises. Whales and porpoises belong to the order Cetartiodactyla with even-toed ungulates and their closest living relatives are the hippopotamuses, having diverged about 40 million years ago; the two parvorders of whales, baleen whales and toothed whales, are thought to have split apart around 34 million years ago. The whales comprise eight extant families: Balaenopteridae, Cetotheriidae, Monodontidae, Physeteridae and Ziphiidae. Whales are creatures of the open ocean. So extreme is their adaptation to life underwater. Whales range in size from the 2.6 metres and 135 kilograms dwarf sperm whale to the 29.9 metres and 190 metric tons blue whale, the largest creature that has lived. The sperm whale is the largest toothed predator on earth. Several species exhibit sexual dimorphism. Baleen whales have no teeth, they use their throat pleats to expand the mouth to take in huge gulps of water.
Balaenids have heads. Toothed whales, on the other hand, have conical teeth adapted to catching squid. Baleen whales have a well developed sense of "smell", whereas toothed whales have well-developed hearing − their hearing, adapted for both air and water, is so well developed that some can survive if they are blind; some species, such as sperm whales, are well adapted for diving to great depths to catch squid and other favoured prey. Whales have evolved from land-living mammals; as such whales must breathe air although they can remain submerged under water for long periods of time. Some species such as the sperm whale are able to stay submerged for as much as 90 minutes, they have blowholes located on top of their heads, through which air is expelled. They are warm-blooded, have a layer of fat, or blubber, under the skin. With streamlined fusiform bodies and two limbs that are modified into flippers, whales can travel at up to 20 knots, though they are not as flexible or agile as seals. Whales produce a great variety of notably the extended songs of the humpback whale.
Although whales are widespread, most species prefer the colder waters of the Northern and Southern Hemispheres, migrate to the equator to give birth. Species such as humpbacks and blue whales are capable of travelling thousands of miles without feeding. Males mate with multiple females every year, but females only mate every two to three years. Calves are born in the spring and summer months and females bear all the responsibility for raising them. Mothers of some species nurse their young for one to two years. Once relentlessly hunted for their products, whales are now protected by international law; the North Atlantic right whales nearly became extinct in the twentieth century, with a population low of 450, the North Pacific grey whale population is ranked Critically Endangered by the IUCN. Besides whaling, they face threats from bycatch and marine pollution; the meat and baleen of whales have traditionally been used by indigenous peoples of the Arctic. Whales have been depicted in various cultures worldwide, notably by the Inuit and the coastal peoples of Vietnam and Ghana, who sometimes hold whale funerals.
Whales feature in literature and film, as in the great white whale of Herman Melville's Moby Dick. Small whales, such as belugas, are sometimes kept in captivity and trained to perform tricks, but breeding success has been poor and the animals die within a few months of capture. Whale watching has become a form of tourism around the world; the word "whale" comes from the Old English whæl, from Proto-Germanic *hwalaz, from Proto Indo European *kwal-o-, meaning "large sea fish". The Proto-Germanic *hwalaz is the source of Old Saxon hwal, Old Norse hvalr, Swedish val, Middle Dutch wal, Dutch walvis, Old High German wal, German Wal; the obsolete "whalefish" has a similar derivation, indicating a time when whales were thought to be fish. Other archaic English forms include wal, whal, whaille, etc; the term "whale" is sometimes used interchangeably with dolphins and porpoises, acting as a synonym for Cetacea. Six species of dolphins have the word "whale" in their name, collectively known as blackfish: the killer whale, the melon-headed whale, the pygmy killer whale, the false killer whale, the two species of pilot whales, all of which are classified under the family Delphinidae.
Each species has a different reason for it, for example, the killer whale was named "Ballena asesina"'killer whale' by Spanish sailors. The term "Great Whales" covers those regulated by the International Whaling Commission: the Odontoceti family Physeteridae; the whales are part of the terrestrial mammalian clade Laurasiatheria. Whales do not form a order.
Roald Engelbregt Gravning Amundsen was a Norwegian explorer of polar regions and a key figure of the Heroic Age of Antarctic Exploration. He led the first expedition to traverse the Northwest Passage in 1906 and the first expedition to the South Pole in 1911, he led the first expedition to reach the North Pole in 1926. He disappeared while taking part in a rescue mission for the airship Italia in 1928. Amundsen was born to a family of Norwegian shipowners and captains in Borge, between the towns Fredrikstad and Sarpsborg, his parents were Hanna Sahlqvist. Roald was the fourth son in the family, his mother wanted him to avoid the family maritime trade and encouraged him to become a doctor, a promise that Amundsen kept until his mother died when he was aged 21. He promptly quit university for a life at sea. Amundsen had hidden a lifelong desire inspired by Fridtjof Nansen's crossing of Greenland in 1888 and Franklin's lost expedition, he decided on a life of intense exploration of wilderness places.
Amundsen joined the Belgian Antarctic Expedition as first mate. This expedition, led by Adrien de Gerlache using the ship the RV Belgica, became the first expedition to overwinter in Antarctica; the Belgica, whether by mistake or design, became locked in the sea ice at 70°30′S off Alexander Island, west of the Antarctic Peninsula. The crew endured a winter. By Amundsen's own estimation, the doctor for the expedition, the American Frederick Cook saved the crew from scurvy by hunting for animals and feeding the crew fresh meat. In cases where citrus fruits are lacking, fresh meat from animals that make their own vitamin C contains enough of the vitamin to prevent scurvy, partly treat it; this was an important lesson for Amundsen's future expeditions. In 1903, Amundsen led the first expedition to traverse Canada's Northwest Passage between the Atlantic and Pacific oceans, he planned a small expedition of six men in a 45-ton fishing vessel, Gjøa, in order to have flexibility. His ship had shallow draft.
His technique was to hug the coast. Amundsen had the ship outfitted with a small 13 horsepower single-screw paraffin engine, they traveled via Baffin Bay, the Parry Channel and south through Peel Sound, James Ross Strait, Simpson Strait and Rae Strait. They spent two winters in the harbor of what is today Gjoa Haven. During this time and the crew learned from the local Netsilik Inuit people about Arctic survival skills, which he found invaluable in his expedition to the South Pole. For example, he learned to use sled dogs for transportation of goods and to wear animal skins in lieu of heavy, woolen parkas, which could not keep out the cold when wet. Leaving Gjoa Haven, he sailed west and passed Cambridge Bay, reached from the west by Richard Collinson in 1852. Continuing to the south of Victoria Island, the ship cleared the Canadian Arctic Archipelago on 17 August 1905, it had to stop for the winter before going on to Nome on Alaska's Pacific coast. The nearest telegraph station was 500 miles away in Eagle.
Amundsen traveled there overland to wire a success message on 5 December returned to Nome in 1906. That year he was elected to the American Antiquarian Society. At this time, Amundsen learned of the dissolution of the union between Norway and Sweden and had a new king; the explorer sent the new king, Haakon VII, news that his traversing the Northwest Passage "was a great achievement for Norway". He said he hoped to do more and signed it "Your loyal subject, Roald Amundsen." The crew returned to Oslo in November 1906, after three-and-a-half years abroad. Gjøa was returned to Norway in 1972. After a 45-day trip from San Francisco on a bulk carrier, she was placed in her current location on land, outside the Fram Museum in Oslo. Amundsen next planned to explore the Arctic Basin. Finding it difficult to raise funds, when he heard in 1909 that the Americans Frederick Cook and Robert Peary had claimed to reach the North Pole as a result of two different expeditions, he decided to reroute to Antarctica.
He was not clear about his intentions, Robert F. Scott and the Norwegian supporters felt misled. Scott was planning his own expedition to the South Pole that year. Using the ship Fram, earlier used by Fridtjof Nansen, Amundsen left Oslo for the south on 3 June 1910. At Madeira, Amundsen alerted his men that they would be heading to Antarctica, sent a telegram to Scott: "Beg to inform you Fram proceeding Antarctic—Amundsen."Nearly six months the expedition arrived at the eastern edge of the Ross Ice Shelf, at a large inlet called the Bay of Whales, on 14 January 1911. Amundsen established his base camp there. Amundsen eschewed the heavy wool clothing worn on earlier Antarctic attempts in favour of adopting Inuit-style furred skins. Using skis and dog sleds for transportation and his men created supply depots at 80°, 81° and 82° South on the Barrier, along a line directly south to the Pole. Amundsen planned to kill some of his dogs on the way and use them as a source for fresh meat. A small group, including Hjalmar Johansen, Kristian Prestrud and Jørgen Stubberud, set out on 8 September, but had to abandon their trek due to extreme temperatures.
The painful retreat caused a quarrel within the group, Amundsen sent Johansen and the other two men to explore King Edward VII Land. A second attempt, with a team of five made up of Olav Bjaaland, Helmer Hanssen, Sverre Hassel, Oscar Wisting, Amundsen, departed base camp on 19 October. The
United States Geological Survey
The United States 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, the natural hazards that threaten it; the organization has four major science disciplines, concerning biology, geography and hydrology. The USGS is a fact-finding research organization with no regulatory responsibility; the USGS is a bureau of the United States Department of the Interior. The USGS employs 8,670 people and is headquartered in Reston, Virginia; the USGS has major offices near Lakewood, Colorado, at the Denver Federal Center, Menlo Park, California. The current motto of the USGS, in use since August 1997, is "science for a changing world." The agency's previous slogan, adopted on the occasion of its hundredth anniversary, was "Earth Science in the Public Service." Since 2012, the USGS science focus is directed at six topical "Mission Areas", namely Climate and Land Use Change, Core Science Systems, Ecosystems and Minerals and Environmental Health, Natural Hazards, Water.
In December 2012, the USGS split the Energy and Minerals and Environmental Health Mission Area resulting in seven topical Mission Areas, with the two new areas being: Energy and Minerals and Environmental Health. Administratively, it is divided into six Regional Units. Other specific programs include: Earthquake Hazards Program monitors earthquake activity worldwide; the National Earthquake Information Center in Golden, Colorado on the campus of the Colorado School of Mines detects the location and magnitude of global earthquakes. The USGS runs or supports several regional monitoring networks in the United States under the umbrella of the Advanced National Seismic System; the USGS informs authorities, emergency responders, the media, the public, both domestic and worldwide, about significant earthquakes. It maintains long-term archives of earthquake data for scientific and engineering research, it conducts and supports research on long-term seismic hazards. USGS has released the UCERF California earthquake forecast.
As of 2005, the agency is working to create a National Volcano Early Warning System by improving the instrumentation monitoring the 169 volcanoes in U. S. territory and by establishing methods for measuring the relative threats posed at each site. The USGS National Geomagnetism Program monitors the magnetic field at magnetic observatories and distributes magnetometer data in real time; the USGS collaborates with Canadian and Mexican government scientists, along with the Commission for Environmental Cooperation, to produce the North American Environmental Atlas, used to depict and track environmental issues for a continental perspective. The USGS operates the streamgaging network for the United States, with over 7400 streamgages. Real-time streamflow data are available online. National Climate Change and Wildlife Science Center implements partner-driven science to improve understanding of past and present land use change, develops relevant climate and land use forecasts, identifies lands and communities that are most vulnerable to adverse impacts of change from the local to global scale.
Since 1962, the Astrogeology Research Program has been involved in global and planetary exploration and mapping. In collaboration with Stanford University, the USGS operates the USGS-Stanford Ion Microprobe Laboratory, a world-class analytical facility for U--Pb geochronology and trace element analyses of minerals and other earth materials. USGS operates a number of water related programs, notably the National Streamflow Information Program and National Water-Quality Assessment Program. USGS Water data is publicly available from their National Water Information System database; the USGS operates the National Wildlife Health Center, whose mission is "to serve the nation and its natural resources by providing sound science and technical support, to disseminate information to promote science-based decisions affecting wildlife and ecosystem health. The NWHC provides information, technical assistance, research and leadership on national and international wildlife health issues." It is the agency responsible for surveillance of H5N1 avian influenza outbreaks in the United States.
The USGS runs 17 biological research centers in the United States, including the Patuxent Wildlife Research Center. The USGS is investigating collaboration with the social networking site Twitter to allow for more rapid construction of ShakeMaps; the USGS produces several national series of topographic maps which vary in scale and extent, with some wide gaps in coverage, notably the complete absence of 1:50,000 scale topographic maps or their equivalent. The largest and best-known topographic series is the 7.5-minute, 1:24,000 scale, quadrangle, a non-metric scale unique to the United States. Each of these maps covers an area bounded by two lines of latitude and two lines of longitude spaced 7.5 minutes apart. Nearly 57,000 individual maps in this series cover the 48 contiguous states, Hawaii, U. S. territories, areas of Alaska near Anchorage and Prudhoe Bay. The area covered by each map varies with the latitude of its represented location due to convergence of the meridians. At lower latitudes, near 30° north, a 7.5-minute quadrangle contains an area of about 64 square miles.
At 49° north latitude, 49 square miles are contained within a quadrangle of that size. As a unique non-metric map scale, the 1:24,000 scale requires a separate and specialized romer scale for pl
Ice calving known as glacier calving or iceberg calving, is the breaking of ice chunks from the edge of a glacier. It is a form of ice ablation or ice disruption and is caused by the glacier expanding, it is the sudden release and breaking away of a mass of ice from a glacier, ice front, ice shelf, or crevasse. The ice that breaks away can be classified as an iceberg, but may be a growler, bergy bit, or a crevasse wall breakaway. Calving of glaciers is accompanied by a loud cracking or booming sound before blocks of ice up to 60 metres high break loose and crash into the water; the entry of the ice into the water causes large, hazardous waves. The waves formed in locations like Johns Hopkins Glacier can be so large that boats cannot approach closer than 3 kilometres; these events have become major tourist attractions in locations such as Alaska. Many glaciers terminate at oceans or freshwater lakes which results with the calving of large numbers of icebergs. Calving of Greenland's glaciers produce 12,000 to 15,000 icebergs each year alone.
Calving of ice shelves is preceded by a rift. These events are not observed. Etymologically, calving is cognatic with calving as in bearing a calf, it is useful to classify causes of calving into first and third order processes. First order processes are responsible for the overall rate of calving at the glacier scale; the first order cause of calving is longitudinal stretching, which controls the formation of crevasses. When crevasses penetrate the full thickness of the ice, calving will occur. Longitudinal stretching is controlled by friction at the base and edges of the glacier, glacier geometry and water pressure at the bed; these factors, exert the primary control on calving rate. Second and third order calving processes can be considered to be superimposed on the first order process above, control the occurrence of individual calving events, rather than the overall rate. Melting at the waterline is an important second order calving process as it undercuts the subaerial ice, leading to collapse.
Other second order processes include tidal and seismic events, buoyant forces and melt water wedging. When calving occurs due to waterline melting, only the subaerial part of the glacier will calve, leaving a submerged'foot'. Thus, a third order process is defined, whereby upward buoyant forces cause this ice foot to break off and emerge at the surface; this process is dangerous, as it has been known to occur, without warning, up to 300m from the glacier terminus. Though many factors that contribute to calving have been identified, a reliable predictive mathematical formula is still under development. Data is being assembled from ice shelves in Antarctica and Greenland to help establish a'calving law'. Variables used in models include properties of the ice such as thickness, temperature, c-axis fabric, impurity loading, though'ice front normal spreading stress', is the most important variable, however it is not measured. There are several concepts upon which to base a predictive law. One theory states that the calving rate is a function of the ratio of tensile stress to vertical compressive stress, i.e. the calving rate is a function of the ratio of the largest to smallest principle stress.
Another theory, based on preliminary research, shows that the calving rate increases as a power of the spreading rate near the calving front. In October, 1988, the A-38 iceberg broke away from the Filchner-Ronne Ice Shelf, it was about 150 km x 50 km. A second calving created an iceberg 167 km x 32 km. A major calving event occurred in 1962 to 1963. There is a section at the front of the shelf referred to as the'loose tooth'; this section, about 30 km by 30 km is moving at about 12 meters per day and is expected to calve away. The largest observed calving of an ice island happened at Ward Hunt Ice Shelf. Sometime between August 1961 and April 1962 600 km2 of ice broke away. In 2005, nearly the entire shelf calved from the northern edge of Ellesmere Island. Since 1900, about 90 % of Ellesmere Island's ice shelves have floated away; this event was the biggest of its kind for at least the past 25 years. A total of 87.1 km2 of ice was lost in this event. The largest piece was 66.4 km2 in area, This large ice shelf, located in the Weddell Sea, extending along the east coast of Antarctic Peninsula, consists of three segments, two of which have calved.
In January 1995, the Larsen A Ice Shelf containing 3,250 km² of ice 220 m thick calved and disintegrated. The Larsen B Ice Shelf calved and disintegrated in February 2002. Known as the Ilulissat Glacier or Sermeq Kujalleq in western Greenland, in an ongoing event, 35 billion tonnes of icebergs calve off and pass out of the fjord every year. Photographer James Balog and his team were examining this glacier in 2008 when their cameras caught a piece of glacier the size of the Lower Manhattan fall into the ocean; the calving event lasted for 75 minutes, during which time the glacier retreated a full mile across a calving face three miles wide. Adam LeWinter and Jeff Orlowski captured this footage, featured in the film Chasing Ice. First conceived in 1995 by Ryan Casey while filming for IMAX, this sport involves a surfer being towed into range by a jet ski and waiting for a mass of ice to calve from a glacier. Surfers can wait for several hours in the icy water for an event; when a glacier calves, the mass of ice can produce 8 metre waves.
Rides of 300 metres lasting for one minute can be achieved. Ice sheet dynamics Ice shelf Glacier Ablation Holdsworth, G. 1971. Calving From Wa
A continental shelf is a portion of a continent, submerged under an area of shallow water known as a shelf sea. Much of the shelves were exposed during interglacial periods; the shelf surrounding an island is known as an insular shelf. The continental margin, between the continental shelf and the abyssal plain, comprises a steep continental slope followed by the flatter continental rise. Sediment from the continent above cascades down the slope and accumulates as a pile of sediment at the base of the slope, called the continental rise. Extending as far as 500 km from the slope, it consists of thick sediments deposited by turbidity currents from the shelf and slope; the continental rise's gradient is intermediate between the shelf. Under the United Nations Convention on the Law of the Sea, the name continental shelf was given a legal definition as the stretch of the seabed adjacent to the shores of a particular country to which it belongs. Width of the continental shelf varies – it is not uncommon for an area to have no shelf at all where the forward edge of an advancing oceanic plate dives beneath continental crust in an offshore subduction zone such as off the coast of Chile or the west coast of Sumatra.
The largest shelf – the Siberian Shelf in the Arctic Ocean – stretches to 1,500 kilometers in width. The South China Sea lies over another extensive area of continental shelf, the Sunda Shelf, which joins Borneo and Java to the Asian mainland. Other familiar bodies of water that overlie continental shelves are the North Sea and the Persian Gulf; the average width of continental shelves is about 80 km. The depth of the shelf varies, but is limited to water shallower than 100 m; the slope of the shelf is quite low, on the order of 0.5°. Though the continental shelf is treated as a physiographic province of the ocean, it is not part of the deep ocean basin proper, but the flooded margins of the continent. 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. Active continental margins have narrow steep shelves, due to frequent earthquakes that move sediment to the deep sea.
The shelf ends at a point of increasing slope. The sea floor below the break is the continental slope. Below the slope is the continental rise, which merges into the deep ocean floor, the abyssal plain; the continental shelf and the slope are part of the continental margin. The shelf area is subdivided into the inner continental shelf, mid continental shelf, outer continental shelf, each with their specific geomorphology and marine biology; the character of the shelf changes at the shelf break, where the continental slope begins. With a few exceptions, the shelf break is located at a remarkably uniform depth of 140 m; the continental slope is much steeper than the shelf. The slope is cut with submarine canyons; the physical mechanisms involved in forming these canyons were not well understood until the 1960s. The continental shelves are covered by terrigenous sediments. However, little of the sediment is from current rivers. Sediments become fine with distance from the coast; these accumulate 15–40 cm every millennium, much faster than deep-sea pelagic sediments.
Continental shelves teem with life because of the sunlight available in shallow waters, in contrast to the biotic desert of the oceans' abyssal plain. The pelagic environment of the continental shelf constitutes the neritic zone, the benthic province of the shelf is the sublittoral zone. Though the shelves are fertile, if anoxic conditions prevail during sedimentation, the deposits may over geologic time become sources for fossil fuels; the accessible continental shelf is the best understood part of the ocean floor. Most commercial exploitation from the sea, such as metallic-ore, non-metallic ore, hydrocarbon extraction, takes place on the continental shelf. Sovereign rights over their continental shelves up to a depth of 100 m or to a distance where the depth of waters admitted of resource exploitation were claimed by the marine nations that signed the Convention on the Continental Shelf drawn up by the UN's International Law Commission in 1958; this was superseded by the 1982 United Nations Convention on the Law of the Sea.
Which created the 200 nautical miles exclusive economic zone, plus continental shelf rights for states with physical continental shelves that extend beyond that distance. The legal definition of a continental shelf differs from the geological definition. UNCLOS states that the shelf extends to the limit of the continental margin, but no less than 200 nmi and no more than 350 nmi from the baseline, thus inhabited volcanic islands such as the Canaries, which have no actual continental shelf, nonetheless have a legal continental shelf, whereas uninhabitable islands have no shelf. Baseline Continental Island Continental shelf pump Continental shelf of Russia Exclusive ec