Lava is molten rock generated by geothermal energy and expelled through fractures in planetary crust or in an eruption at temperatures from 700 to 1,200 °C. The structures resulting from subsequent solidification and cooling are sometimes described as lava; the molten rock is formed in the interior of some planets, including Earth, some of their satellites, though such material located below the crust is referred to by other terms. A lava flow is a moving outpouring of lava created during a non-explosive effusive eruption; when it has stopped moving, lava solidifies to form igneous rock. The term lava flow is shortened to lava. Although lava can be up to 100,000 times more viscous than water, lava can flow great distances before cooling and solidifying because of its thixotropic and shear thinning properties. Explosive eruptions produce a mixture of volcanic ash and other fragments called tephra, rather than lava flows; the word lava comes from Italian, is derived from the Latin word labes which means a fall or slide.
The first use in connection with extruded magma was in a short account written by Francesco Serao on the eruption of Vesuvius in 1737. Serao described "a flow of fiery lava" as an analogy to the flow of water and mud down the flanks of the volcano following heavy rain; the composition of all lava of the Earth's crust is dominated by silicate minerals feldspars, pyroxenes, amphiboles and quartz. Igneous rocks, which form lava flows when erupted, can be classified into three chemical types: felsic and mafic; these classes are chemical, the chemistry of lava tends to correlate with the magma temperature, its viscosity and its mode of eruption. Felsic or silicic lavas such as rhyolite and dacite form lava spines, lava domes or "coulees" and are associated with pyroclastic deposits. Most silicic lava flows are viscous, fragment as they extrude, producing blocky autobreccias; the high viscosity and strength are the result of their chemistry, high in silica, potassium and calcium, forming a polymerized liquid rich in feldspar and quartz, thus has a higher viscosity than other magma types.
Felsic magmas can erupt at temperatures as low as 650 to 750 °C. Unusually hot rhyolite lavas, may flow for distances of many tens of kilometres, such as in the Snake River Plain of the northwestern United States. Intermediate or andesitic lavas are lower in aluminium and silica, somewhat richer in magnesium and iron. Intermediate lavas form andesite domes and block lavas, may occur on steep composite volcanoes, such as in the Andes. Poorer in aluminium and silica than felsic lavas, commonly hotter, they tend to be less viscous. Greater temperatures tend to destroy polymerized bonds within the magma, promoting more fluid behaviour and a greater tendency to form phenocrysts. Higher iron and magnesium tends to manifest as a darker groundmass, occasionally amphibole or pyroxene phenocrysts. Mafic or basaltic lavas are typified by their high ferromagnesian content, erupt at temperatures in excess of 950 °C. Basaltic magma is high in iron and magnesium, has lower aluminium and silica, which taken together reduces the degree of polymerization within the melt.
Owing to the higher temperatures, viscosities can be low, although still thousands of times higher than water. The low degree of polymerization and high temperature favors chemical diffusion, so it is common to see large, well-formed phenocrysts within mafic lavas. Basalt lavas tend to produce low-profile shield volcanoes or "flood basalt fields", because the fluidal lava flows for long distances from the vent; the thickness of a basalt lava on a low slope, may be much greater than the thickness of the moving lava flow at any one time, because basalt lavas may "inflate" by supply of lava beneath a solidified crust. Most basalt lavas are of pāhoehoe types, rather than block lavas. Underwater, they can form pillow lavas, which are rather similar to entrail-type pahoehoe lavas on land. Ultramafic lavas such as komatiite and magnesian magmas that form boninite take the composition and temperatures of eruptions to the extreme. Komatiites contain over 18% magnesium oxide, are thought to have erupted at temperatures of 1,600 °C.
At this temperature there is no polymerization of the mineral compounds, creating a mobile liquid. Most if not all ultramafic lavas are no younger than the Proterozoic, with a few ultramafic magmas known from the Phanerozoic. No modern komatiite lavas are known, as the Earth's mantle has cooled too much to produce magnesian magmas; some lavas of unusual composition have erupted onto the surface of the Earth. These include: Carbonatite and natrocarbonatite lavas are known from Ol Doinyo Lengai volcano in Tanzania, the sole example of an active carbonatite volcano. Iron oxide lavas are thought to be the source of the iron ore at Kiruna, Sweden which formed during the Proterozoic. Iron oxide lavas of Pliocene age occur at the El Laco volcanic complex on the Chile-Argentina border. Iron oxide lavas are thought to be the result of immiscible separation of iron oxide magma from a parental magma of calc-alkaline or alkaline composition. Sulfur lava flows up to 250 metres 10 metres wide occur at Lastarria volcano, Chile.
They were formed by the melting of sulfur deposits at temperatures as low as 113 °C
Mount St. Helens National Volcanic Monument
Mount St. Helens National Volcanic Monument is a U. S. National Monument that includes the area around Mount St. Helens in Washington, it was established on August 27, 1982 by U. S. President Ronald Reagan following the 1980 eruption; the 110,000 acre National Volcanic Monument was set aside for research and education. Inside the Monument, the environment is left to respond to the disturbance. Mount St. Helens National Volcanic Monument was the United States' first such monument managed by the U. S. Forest Service. At dedication ceremonies on May 18, 1983, Max Peterson, head of the USFS, said, "we can take pride in having preserved the unique episode of natural history for future generations." Since many trails, information stations and picnic areas have been established to accommodate the increasing number of visitors each year. Beginning in 1983, visitors have been able to drive to Windy Ridge, only 4 miles northeast of the crater. Mountain climbing to the summit of the volcano has been allowed since 1986.
The Mount St. Helens Visitor Center at Silver Lake, about 30 miles west of Mount St. Helens and five miles east of Interstate 5, opened in 1987 and has been operated by the Washington State Park System since October 2000. Exhibits include the area's culture and history, the natural history and geology of the volcano and the eruption, including the recovery of the area's vegetation and animal life; the Center includes a gift shop and outdoor trails. By the end of 1989, the Center had hosted more than 1.5 million visitors. A small admission fee is charged; the Center was operated by the U. S. Forest Service; the Johnston Ridge Observatory is located 52 miles east of Castle Rock, Washington, at the end of Washington State Route 504, four miles from the mountain. Exhibits focus on the geologic history of the volcano, eyewitness accounts of the explosion, the science of monitoring volcanic activity. Two movies and ranger-led programs are available every hour. A half-mile paved trail provides views of the lava dome, pumice plain, landslide deposit, with access to hiking trails in the restricted area.
The observatory is located near the site of volcanologist David A. Johnston's camp on the morning of May 18, 1980, opened in 1993; the Coldwater Ridge Visitor Center in the Coldwater Lake area opened in 1993, operated by the Forest Service, but closed in November 2007 due to a lack of funding. The center reopened as the Science and Learning Center at Coldwater in May 2013, operating as an educational facility and conference center in cooperation with the Mount St. Helens Institute, it is open to the public on weekends from 10am to 6pm. Many of the exhibits have been removed, but the gift shop and some signage still exist; the Winds of Change Trail #232, a short, barrier-free interpretive trail, departs from the Science and Learning Center. The southern and eastern sides of Mount St. Helens are accessible only by U. S. Forest Service roads; the main roads are: U. S. Forest Service Road 25 – Monument entrance from U. S. Route 12 to Road 90. U. S. Forest Service Road 26 – Road 99 to Norway Pass to Road 25.
U. S. Forest Service Road 81 – SR 503/Road 90 to Merrill Lake, Kalama Horse Camp, Climber's Bivouac. U. S. Forest Service Road 83 – Road 90 to Ape Cave, Ape Canyon, Lava Canyon lahar, Smith Creek. U. S. Forest Service Road 90 – Monument entrance from State Route 503. U. S. Forest Service Road 99 – Road 25 to Bear Meadows, Meta Lake and Miner's Car, Windy Ridge. Bear Meadows is an alpine viewpoint northeast of Mt. St. Helens, it is located on U. S. Forest Service Road 99. Gary Rosenquist camped here with friends on May 17–18, 1980, he started taking his famous eruption photographs from this location. The sequence of eruption photos show give a time lapse view of the developing eruption; as the lateral blast developed, he and his friends abandoned their campsite fearing for their lives. He continued taking photos; the eruption's lateral blast narrowly missed the site as it was deflected by a ridge just west of the meadow. In an interview with KIRO-TV in 1990, a friend called that ridge "the line of death."
Windy Ridge is the closest view point accessible to the general public. Beginning in the summer of 1983, visitors have been able to drive to Windy Ridge, on U. S. Forest Service Road 99, only 4 miles northeast of the crater. From this vantage point overlooking Spirit Lake, people see not only the evidence of a volcano's destruction, but the remarkable, gradual recovery of the land as revegetation proceeds and wildlife returns. Ape Cave is a lava tube located in Gifford Pinchot National Forest just to the south of Mount St. Helens in Washington state, its passageway is the longest continuous lava tube in the continental United States and the third longest lava tube in North America at 2.5 miles. Ape Cave is a popular hiking destination with beautiful views of the Mount St. Helens lahar region. Lava tubes are an unusual formation in this region, as volcanoes of the Cascade Range are stratovolcanos and do not erupt with pahoehoe; the cave was discovered circa 1951 by Lawrence Johnson, a logger, when he noticed a tree that "looked wrong."
After investigating the tree, he discovered. A few days Johnson brought the Reese family back to the cave, Harry Reese was lowered to the floor and became the first person to explore the interior. Subsequent explorations were conducted by members of the Mount St. Helens Apes, a local Boy Scout troop. Ape Cave Trail No. 239, which runs along the interior of the cave, is a National Recreatio
Manhattan Project National Historical Park
Manhattan Project National Historical Park is a United States National Historical Park commemorating the Manhattan Project, run jointly by the National Park Service and Department of Energy. The park consists of three units: one in Oak Ridge, one in Los Alamos, New Mexico and one in Hanford, Washington, it was established on November 10, 2015 when Secretary of the Interior Sally Jewell and Secretary of Energy Ernest Moniz signed the memorandum of agreement that defined the roles that the two agencies had when managing the park. The Department of Energy had owned and managed most of the properties located within the three different sites. For over ten years, the DoE worked with the National Park Service and federal and local governments and agencies with the intention of turning places of importance into a National Historical Park. After several years of surveying the three sites and five other possible alternatives, the two agencies recommended a historical park be established in Hanford, Los Alamos and Oak Ridge.
The Department of Energy would continue to manage and own the sites while the National Park Service would provide interpretive services, visitor centers and park rangers. After two unsuccessful attempts at passing a bill in Congress authorizing the park in 2012 and 2013, the House and Senate passed the bill in December 2014, with President Obama signing the National Defense Authorization Act shortly thereafter which authorized the Manhattan Project National Historical Park; the Manhattan Project National Historical Park protects many structures associated with the Manhattan Project, but only some are open for touring. B Reactor National Historic Landmark – bus tours are available by advance reservation the previous Hanford High School in the former Town of Hanford and Hanford Construction Camp Historic District Bruggemann's Agricultural Warehouse Complex White Bluffs Bank and Hanford Irrigation District Pump House The Los Alamos visitor center for the Manhattan Project NHP is located at 475 20th Street in downtown Los Alamos.
This location is open daily 9-4 staffing permitting. It is in the Los Alamos Community Building on the front left as you face the building from the street. At the visitor center, visitors can learn about the Manhattan Project and related sites in the vicinity. There are 3 locations of park; these locations are not open to the public: Gun Site Facilities: three bunkered buildings, a portable guard shack. V-Site Facilities: TA-16-516 and TA-16-517 V-Site Assembly Building Pajarito Site: TA-18-1 Slotin Building, TA-8-2 Battleship Control Building, the TA-18-29 Pond Cabin; the American Museum of Science and Energy provides bus tours of several buildings in the Clinton Engineer Works including the: X-10 Graphite Reactor Buildings 9731 and 9204-3 at the Y-12 complex East Tennessee Technology Park, located on the site of the K-25 Building Official National Park Service website: Manhattan Project National Historical Park Official Department of Energy website: Manhattan Project National Historical Park
United States Forest Service
The United States Forest Service is an agency of the U. S. Department of Agriculture that administers the nation's 154 national forests and 20 national grasslands, which encompass 193 million acres. Major divisions of the agency include the National Forest System and Private Forestry, Business Operations, the Research and Development branch. Managing 25% of federal lands, it is the only major national land agency, outside the U. S. Department of the Interior; the concept of the National Forests was born from Theodore Roosevelt’s conservation group and Crockett Club, due to concerns regarding Yellowstone National Park beginning as early as 1875. In 1876, Congress formed the office of Special Agent in the Department of Agriculture to assess the quality and conditions of forests in the United States. Franklin B. Hough was appointed the head of the office. In 1881, the office was expanded into the newly formed Division of Forestry; the Forest Reserve Act of 1891 authorized withdrawing land from the public domain as "forest reserves," managed by the Department of the Interior.
In 1901, the Division of Forestry was renamed the Bureau of Forestry. The Transfer Act of 1905 transferred the management of forest reserves from the General Land Office of the Interior Department to the Bureau of Forestry, henceforth known as the United States Forest Service. Gifford Pinchot was the first United States Chief Forester in the Presidency of Theodore Roosevelt. Significant federal legislation affecting the Forest Service includes the Weeks Act of 1911, the Multiple Use – Sustained Yield Act of 1960, P. L. 86-517. L. 88-577. L. 94-588. L. 91-190. L. 95-313. L. 95-307. In February 2009, the Government Accountability Office evaluated whether the Forest Service should be moved from the Department of Agriculture to the Department of the Interior, which includes the National Park Service, the Fish and Wildlife Service, the Bureau of Land Management, managing some 438,000,000 acres of public land; as of 2009, the Forest Service has a total budget authority of $5.5 billion, of which 42% is spent fighting fires.
The Forest Service employs 34,250 employees in 750 locations, including 10,050 firefighters, 737 law enforcement personnel, 500 scientists. The mission of the Forest Service is "To sustain the health and productivity of the Nation's forests and grasslands to meet the needs of present and future generations." Its motto is "Caring for the land and serving people." As the lead federal agency in natural resource conservation, the US Forest Service provides leadership in the protection and use of the nation's forest and aquatic ecosystems. The agency's ecosystem approach to management integrates ecological and social factors to maintain and enhance the quality of the environment to meet current and future needs. Through implementation of land and resource management plans, the agency ensures sustainable ecosystems by restoring and maintaining species diversity and ecological productivity that helps provide recreation, timber, fish, wildlife and aesthetic values for current and future generations of people.
The everyday work of the Forest Service balances resource extraction, resource protection, providing recreation. The work includes managing 193,000,000 acres of national forest and grasslands, including 59,000,000 acres of roadless areas. Further, the Forest Service fought fires on 2,996,000 acres of land in 2007; the Forest Service organization includes ranger districts, national forests, research stations and research work units and the Northeastern Area Office for State and Private Forestry. Each level has responsibility for a variety of functions; the Chief of the Forest Service is a career federal employee. The Chief reports to the Under Secretary for Natural Resources and Environment in the U. S. Department of Agriculture, an appointee of the President confirmed by the Senate; the Chief's staff provides broad policy and direction for the agency, works with the Administration to develop a budget to submit to Congress, provides information to Congress on accomplishments, monitors activities of the agency.
There are five deputy chiefs for the following areas: National Forest System and Private Forestry and Development, Business Operations, Finance. The Forest Service Research and Development deputy area includes five research stations, the Forest Products Laboratory, the International Institute of Tropical Forestry, in Puerto Rico. Station directors, like regional foresters, report to the Chief. Research stations include Northern, Pacific Northwest, Pacific Southwest, Rocky Mountain, Southern. There are 92 research work units located at 67 sites throughout the United States. There are 80 Experimental Forests and Ranges that have been established progressively since 1908; the system provides places for long-term science and management studies in major vegetation types of the 195 million acres of public land administered by the Forest Service. Individual sites range from 47 to 22,500 ha in size. Operations of Experimental Forests and Ranges are directed by local research teams for the individual sites, by Research Stations for the regions in which they are located, at the level of the Forest Service.
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Bureau of Land Management
The Bureau of Land Management is an agency within the United States Department of the Interior that administers more than 247.3 million acres of public lands in the United States which constitutes one eighth of the landmass of the country. President Harry S. Truman created the BLM in 1946 by combining two existing agencies: the General Land Office and the Grazing Service; the agency manages the federal government's nearly 700 million acres of subsurface mineral estate located beneath federal and private lands severed from their surface rights by the Homestead Act of 1862. Most BLM public lands are located in these 12 western states: Alaska, California, Idaho, Nevada, New Mexico, Utah and Wyoming; the mission of the BLM is "to sustain the health and productivity of the public lands for the use and enjoyment of present and future generations." BLM holdings were described as "land nobody wanted" because homesteaders had passed them by. All the same, ranchers hold nearly 18,000 permits and leases for livestock grazing on 155 million acres of BLM public lands.
The agency manages 221 wilderness areas, 27 national monuments and some 636 other protected areas as part of the National Conservation Lands, totaling about 36 million acres. In addition the National Conservation Lands include nearly 2,400 miles of Wild and Scenic Rivers, nearly 6,000 miles of National Scenic and Historic Trails. There are more than 63,000 gas wells on BLM public lands. Total energy leases generated $5.4 billion in 2013, an amount divided among the Treasury, the states, Native American groups. The BLM's roots go back to the Land Ordinance of 1785 and the Northwest Ordinance of 1787; these laws provided for the survey and settlement of the lands that the original 13 colonies ceded to the federal government after the American Revolution. As additional lands were acquired by the United States from Spain and other countries, the United States Congress directed that they be explored and made available for settlement. During the Revolutionary War, military bounty land was promised to soldiers who fought for the colonies.
After the war, the Treaty of Paris of 1783, signed by the United States, England and Spain, ceded territory to the United States. In the 1780s, other states relinquished their own claims to land in modern-day Ohio. By this time, the United States needed revenue to function. Land was sold. In order to sell the land, surveys needed to be conducted; the Land Ordinance of 1785 instructed a geographer to oversee this work as undertaken by a group of surveyors. The first years of surveying were completed by error. In 1812, Congress established the General Land Office as part of the Department of the Treasury to oversee the disposition of these federal lands. By the early 1800s, promised bounty land claims were fulfilled. Over the years, other bounty land and homestead laws were enacted to dispose of federal land. Several different types of patents existed; these include cash entry, homestead, military warrants, mineral certificates, private land claims, state selections, town sites, town lots. A system of local land offices spread throughout the territories, patenting land, surveyed via the corresponding Office of the Surveyor General of a particular territory.
This pattern spread across the entire United States. The laws that spurred this system with the exception of the General Mining Law of 1872 and the Desert Land Act of 1877 have since been repealed or superseded. In the early 20th century, Congress took additional steps toward recognizing the value of the assets on public lands and directed the Executive Branch to manage activities on the remaining public lands; the Mineral Leasing Act of 1920 allowed leasing and production of selected commodities, such as coal, oil and sodium to take place on public lands. The Taylor Grazing Act of 1934 established the United States Grazing Service to manage the public rangelands by establishment of advisory boards that set grazing fees; the Oregon and California Revested Lands Sustained Yield Management Act of 1937 referred as the O&C Act, required sustained yield management of the timberlands in western Oregon. In 1946, the Grazing Service was merged with the General Land Office to form the Bureau of Land Management within the Department of the Interior.
It took several years for this new agency to reorganize. In the end, the Bureau of Land Management became less focused on land disposal and more focused on the long term management and preservation of the land; the agency achieved its current form by combining offices in the western states and creating a corresponding office for lands both east of and alongside the Mississippi River. As a matter of course, the BLM's emphasis fell on activities in the western states as most of the mining, land sales, federally owned areas are located west of the Mississippi. BLM personnel on the ground have been oriented toward local interests, while bureau management in Washington are led by presidential guidance. By means of the Federal Land Policy and Management Act of 1976, Congress created a more unified bureau mission and recognized the value of the remaining public lands by declaring that these lands would remain in public ownership; the law directed that these lands be managed with a view toward "multiple use" defined as "management of the public lands and their various resource values so that th
National Wilderness Preservation System
The National Wilderness Preservation System of the United States protects federally managed wilderness areas designated for preservation in their natural condition. Activity on formally designated wilderness areas is coordinated by the National Wilderness Preservation System. Wilderness areas are managed by four federal land management agencies: the National Park Service, the U. S. Forest Service, the U. S. Fish and Wildlife Service, the Bureau of Land Management; the term "wilderness" is defined as "an area where the earth and community of life are untrammeled by man, where man himself is a visitor who does not remain" and "an area of undeveloped Federal land retaining its primeval character and influence, without permanent improvements or human habitation, protected and managed so as to preserve its natural conditions." As of 2016, there are 765 designated wilderness areas, totaling 109,129,657 acres, or about 4.5% of the area of the United States. During the 1950s and 1960s, as the American transportation system was on the rise, concern for clean air and water quality began to grow.
A conservation movement began to take place with the intent of establishing designated wilderness areas. Howard Zahniser created the first draft of the Wilderness Act in 1956, it took nine years and 65 rewrites before the Wilderness Act was passed in 1964. The Wilderness Act of 1964, which established the NWPS, was signed into law by President Lyndon B. Johnson on September 3, 1964; the Wilderness Act mandated that the National Park Service, U. S. Forest Service, U. S. Fish and Wildlife Service review all federal lands under their jurisdiction for wilderness areas to include in the NWPS; the first national forest wilderness areas were established by the Wilderness Act itself. The Great Swamp in New Jersey became the first National Wildlife Refuge with formally designated wilderness in 1968. Wilderness areas in national parks followed, beginning with the designation of wilderness in part of Craters of the Moon National Monument in Idaho in 1970. A dramatic spike in acreage added to the wilderness system in 1980 was due in large part to the Alaska National Interest Lands Conservation Act, signed into law by President Jimmy Carter on December 2, 1980.
A smaller spike in 1984 came with the passage of many bills establishing national forest wilderness areas identified by the Forest Service's Roadless Area Review and Evaluation process. The Bureau of Land Management was not required to review its lands for inclusion in the NWPS until after October 21, 1976, when the Federal Land Policy and Management Act of 1976 was signed into law. Over 200 wilderness areas have been created within Bureau of Land Management administered lands since consisting of 8.71 million acres in September 2015. As of August 2008, a total of 704 separate wilderness areas, encompassing 107,514,938 acres, had become part of the National Wilderness Preservation System. With the passage of the Omnibus Public Lands Act in March 2009, there were 756 wilderness areas; as of September 2015, the system includes 765 wilderness areas totaling 109,129,657 acres. On federal lands in the United States, Congress may designate an area as wilderness under the provisions of the Wilderness Act of 1964.
Multiple agencies, including the Bureau of Land Management, the National Park Service, the Fish and Wildlife Service, the U. S. Forest Service, are responsible for the submission of new areas that fit the criteria to become wilderness to congress. Congress reviews these cases on a state by state basis and determines which areas and how much land in each area will become part of the WPS. There have been multiple occasions in which congress designated more federal land than had been recommended by the nominating agency. Whereas the Wilderness Act stipulated that a wilderness area must be "administered for the use and enjoyment of the American people in such a manner as will leave them unimpaired for future use and enjoyment as wilderness", the Eastern Wilderness Act, which added 16 National Forest areas to the NWPS, allowed for the inclusion of areas, modified by human interference; the Wilderness Act provides criteria for lands being considered for wilderness designation. Though there are some exceptions, the following conditions must be present for an area to be included in the NWPS: the land is under federal ownership and management, the area consists of at least five thousand acres of land, human influence is "substantially unnoticeable," there are opportunities for solitude and recreation, the area possesses "ecological, geological, or other features of scientific, scenic, or historical value."
Wilderness areas are subject to specific management restrictions. During these activities, patrons are asked to abide by the "Leave No Trace" policy; this policy sets guidelines for using the wilderness responsibly, leaving the area as it was before usage. These guidelines include: Packing all trash out of the wilderness, using a stove as opposed to a fire, camping at least 200 feet from trails or water sources, staying on marked trails, keeping group size small; when observed, the "Leave No Trace" ethos ensures that wilderness areas remain untainted by human interaction. In general, the law prohibits logging, mechanized vehicles, road-building, other forms of development in wilderness areas, though pre-existing mining claims and grazing ranges are permitted through grandf
The United States of America known as the United States or America, is a country composed of 50 states, a federal district, five major self-governing territories, various possessions. At 3.8 million square miles, the United States is the world's third or fourth largest country by total area and is smaller than the entire continent of Europe's 3.9 million square miles. With a population of over 327 million people, the U. S. is the third most populous country. The capital is Washington, D. C. and the largest city by population is New York City. Forty-eight states and the capital's federal district are contiguous in North America between Canada and Mexico; the State of Alaska is in the northwest corner of North America, bordered by Canada to the east and across the Bering Strait from Russia to the west. The State of Hawaii is an archipelago in the mid-Pacific Ocean; the U. S. territories are scattered about the Pacific Ocean and the Caribbean Sea, stretching across nine official time zones. The diverse geography and wildlife of the United States make it one of the world's 17 megadiverse countries.
Paleo-Indians migrated from Siberia to the North American mainland at least 12,000 years ago. European colonization began in the 16th century; the United States emerged from the thirteen British colonies established along the East Coast. Numerous disputes between Great Britain and the colonies following the French and Indian War led to the American Revolution, which began in 1775, the subsequent Declaration of Independence in 1776; the war ended in 1783 with the United States becoming the first country to gain independence from a European power. The current constitution was adopted in 1788, with the first ten amendments, collectively named the Bill of Rights, being ratified in 1791 to guarantee many fundamental civil liberties; the United States embarked on a vigorous expansion across North America throughout the 19th century, acquiring new territories, displacing Native American tribes, admitting new states until it spanned the continent by 1848. During the second half of the 19th century, the Civil War led to the abolition of slavery.
By the end of the century, the United States had extended into the Pacific Ocean, its economy, driven in large part by the Industrial Revolution, began to soar. The Spanish–American War and World War I confirmed the country's status as a global military power; the United States emerged from World War II as a global superpower, the first country to develop nuclear weapons, the only country to use them in warfare, a permanent member of the United Nations Security Council. Sweeping civil rights legislation, notably the Civil Rights Act of 1964, the Voting Rights Act of 1965 and the Fair Housing Act of 1968, outlawed discrimination based on race or color. During the Cold War, the United States and the Soviet Union competed in the Space Race, culminating with the 1969 U. S. Moon landing; the end of the Cold War and the collapse of the Soviet Union in 1991 left the United States as the world's sole superpower. The United States is the world's oldest surviving federation, it is a representative democracy.
The United States is a founding member of the United Nations, World Bank, International Monetary Fund, Organization of American States, other international organizations. The United States is a developed country, with the world's largest economy by nominal GDP and second-largest economy by PPP, accounting for a quarter of global GDP; the U. S. economy is post-industrial, characterized by the dominance of services and knowledge-based activities, although the manufacturing sector remains the second-largest in the world. The United States is the world's largest importer and the second largest exporter of goods, by value. Although its population is only 4.3% of the world total, the U. S. holds 31% of the total wealth in the world, the largest share of global wealth concentrated in a single country. Despite wide income and wealth disparities, the United States continues to rank high in measures of socioeconomic performance, including average wage, human development, per capita GDP, worker productivity.
The United States is the foremost military power in the world, making up a third of global military spending, is a leading political and scientific force internationally. In 1507, the German cartographer Martin Waldseemüller produced a world map on which he named the lands of the Western Hemisphere America in honor of the Italian explorer and cartographer Amerigo Vespucci; the first documentary evidence of the phrase "United States of America" is from a letter dated January 2, 1776, written by Stephen Moylan, Esq. to George Washington's aide-de-camp and Muster-Master General of the Continental Army, Lt. Col. Joseph Reed. Moylan expressed his wish to go "with full and ample powers from the United States of America to Spain" to seek assistance in the revolutionary war effort; the first known publication of the phrase "United States of America" was in an anonymous essay in The Virginia Gazette newspaper in Williamsburg, Virginia, on April 6, 1776. The second draft of the Articles of Confederation, prepared by John Dickinson and completed by June 17, 1776, at the latest, declared "The name of this Confederation shall be the'United States of America'".
The final version of the Articles sent to the states for ratification in late 1777 contains the sentence "The Stile of this Confederacy shall be'The United States of America'". In June 1776, Thomas Jefferson wrote the phrase "UNITED STATES OF AMERICA" in all capitalized letters in the headline of his "original Rough draught" of the Declaration of Independence; this draft of the document did not surface unti