Alaska is a U. S. state in the northwest extremity of North America, just across the Bering Strait from Asia. The Canadian province of British Columbia and territory of Yukon border the state to the east and southeast, its most extreme western part is Attu Island, it has a maritime border with Russia to the west across the Bering Strait. To the north are the Chukchi and Beaufort seas—southern parts of the Arctic Ocean; the Pacific Ocean lies to southwest. It is the largest U. S. state by the seventh largest subnational division in the world. In addition, it is the most sparsely populated of the 50 United States. Half of Alaska's residents live within the Anchorage metropolitan area. Alaska's economy is dominated by the fishing, natural gas, oil industries, resources which it has in abundance. Military bases and tourism are a significant part of the economy; the United States purchased Alaska from the Russian Empire on March 30, 1867, for 7.2 million U. S. dollars at two cents per acre. The area went through several administrative changes before becoming organized as a territory on May 11, 1912.
It was admitted as the 49th state of the U. S. on January 3, 1959. The name "Alaska" was introduced in the Russian colonial period when it was used to refer to the Alaska Peninsula, it was derived from an Aleut-language idiom. It means object to which the action of the sea is directed. Alaska is the northernmost and westernmost state in the United States and has the most easterly longitude in the United States because the Aleutian Islands extend into the Eastern Hemisphere. Alaska is the only non-contiguous U. S. state on continental North America. It is technically part of the continental U. S. but is sometimes not included in colloquial use. S. called "the Lower 48". The capital city, Juneau, is situated on the mainland of the North American continent but is not connected by road to the rest of the North American highway system; the state is bordered by Yukon and British Columbia in Canada, to the east, the Gulf of Alaska and the Pacific Ocean to the south and southwest, the Bering Sea, Bering Strait, Chukchi Sea to the west and the Arctic Ocean to the north.
Alaska's territorial waters touch Russia's territorial waters in the Bering Strait, as the Russian Big Diomede Island and Alaskan Little Diomede Island are only 3 miles apart. Alaska has a longer coastline than all the other U. S. states combined. Alaska is the largest state in the United States by total area at 663,268 square miles, over twice the size of Texas, the next largest state. Alaska is larger than all but 18 sovereign countries. Counting territorial waters, Alaska is larger than the combined area of the next three largest states: Texas and Montana, it is larger than the combined area of the 22 smallest U. S. states. There are no defined borders demarcating the various regions of Alaska, but there are six accepted regions: The most populous region of Alaska, containing Anchorage, the Matanuska-Susitna Valley and the Kenai Peninsula. Rural unpopulated areas south of the Alaska Range and west of the Wrangell Mountains fall within the definition of South Central, as do the Prince William Sound area and the communities of Cordova and Valdez.
Referred to as the Panhandle or Inside Passage, this is the region of Alaska closest to the rest of the United States. As such, this was where most of the initial non-indigenous settlement occurred in the years following the Alaska Purchase; the region is dominated by the Alexander Archipelago as well as the Tongass National Forest, the largest national forest in the United States. It contains the state capital Juneau, the former capital Sitka, Ketchikan, at one time Alaska's largest city; the Alaska Marine Highway provides a vital surface transportation link throughout the area, as only three communities enjoy direct connections to the contiguous North American road system. Designated in 1963; the Interior is the largest region of Alaska. Fairbanks is the only large city in the region. Denali National Park and Preserve is located here. Denali is the highest mountain in North America. Southwest Alaska is a sparsely inhabited region stretching some 500 miles inland from the Bering Sea. Most of the population lives along the coast.
Kodiak Island is located in Southwest. The massive Yukon–Kuskokwim Delta, one of the largest river deltas in the world, is here. Portions of the Alaska Peninsula are considered part of Southwest, with the remaining portions included with the Aleutian Islands; the North Slope is tundra peppered with small villages. The area is known for its massive reserves of crude oil, contains both the National Petroleum Reserve–Alaska and the Prudhoe Bay Oil Field; the city of Utqiagvik known as Barrow, is the northernmost city in the United States and is located here. The Northwest Arctic area, anchored by Kotzebue and containing the Kobuk River valley, is regarded as being part of this region. However, the respective Inupiat of the No
Denali Borough, Alaska
The Denali Borough is a borough located in the U. S. state of Alaska. As of the 2010 census the population of the borough was 1,826; the borough seat is Healy, its only incorporated place is Anderson. The borough was incorporated in 1990; the area was a part of the Unorganized Borough, with the Upper Railbelt School District serving as the region's rural education attendance area. The borough has a total area of 12,777 square miles, of which 12,751 square miles is land and 26 square miles is water; the borough contains North America's highest point: Denali, from which it derives its name, at 6190.5 m. Denali National Park and Preserve Denali Wilderness Yukon-Koyukuk Census Area - west/north Fairbanks North Star Borough - northeast Southeast Fairbanks Census Area - east Matanuska-Susitna Borough - south As of the census of 2000, there were 1,893 people, 785 households, 452 families residing in the borough; the population density was 0.148 people per square mile. There were 1,351 housing units at an average density of 0.106 per square mile.
The racial makeup of the borough was 85.74% White, 1.43% Black or African American, 4.75% Native American, 1.53% Asian, 0.37% Pacific Islander, 0.95% from other races, 5.23% from two or more races. 2.48% of the population were Hispanic or Latino of any race. There were 785 households out of which 31.00% had children under the age of 18 living with them, 48.40% were married couples living together, 4.50% had a female householder with no husband present, 42.30% were non-families. 35.00% of all households were made up of individuals and 1.40% had someone living alone, 65 years of age or older. The average household size was 2.28 and the average family size was 3.03. In the borough the population was spread out with 23.80% under the age of 18, 6.70% from 18 to 24, 36.80% from 25 to 44, 29.70% from 45 to 64, 3.10% who were 65 years of age or older. The median age was 38 years. For every 100 females, there were 139.00 males. For every 100 females age 18 and over, there were 147.10 males. Denali Borough is the 63rd highest-income county in the United States, highest-income county in Alaska, by personal per capita income as of 2009.
Anderson Clear Clear AFS Cantwell Denali Park Ferry Healy Kantishna Suntrana Usibelli Diamond In the Twilight Saga by Stephenie Meyer, the Denali vampire coven lives in Denali because of the lack of sunlight. List of airports in the Denali Borough National Register of Historic Places listings in Denali Borough, Alaska Media related to Denali Borough, Alaska at Wikimedia Commons Official website
Denali National Park and Preserve
Denali National Park and Preserve is an American national park and preserve located in Interior Alaska, centered on Denali, the highest mountain in North America. The park and contiguous preserve encompass 6,045,153 acres, larger than the state of New Hampshire. On December 2, 1980, 2,146,580-acre Denali Wilderness was established within the park. Denali's landscape is a mix of forest at the lowest elevations, including deciduous taiga, with tundra at middle elevations, glaciers and bare rock at the highest elevations; the longest glacier is the Kahiltna Glacier. Wintertime activities include dog sledding, cross-country skiing, snowmobiling; the park received 594,660 recreational visitors in 2018. Human habitation in the Denali Region extends to more than 11,000 years before the present, with documented sites just outside park boundaries dated to more than 8,000 years before present; however few archaeological sites have been documented within the park boundaries, owing to the region's high elevation, with harsh winter conditions and scarce resources compared to lower elevations in the area.
The oldest site within park boundaries is the Teklanika River site, dated to about 7130 BC. More than 84 archaeological sites have been documented within the park; the sites are characterized as hunting camps rather than settlements, provide little cultural context. The presence of Athabaskan peoples in the region is dated to 1,500 - 1,000 years before present on linguistic and archaeological evidence, while researchers have proposed that Athabaskans may have inhabited the area for thousands of years before then; the principal groups in the park area in the last 500 years include the Koyukon and Dena'ina people. Other prehistoric finds include Mesozoic fossils from the Denali Region. Studies of fossil plants from the same formation indicate the area was wet, with marshes and ponds throughout the region. In 1906, conservationist Charles Alexander Sheldon conceived the idea of preserving the Denali region as a national park, he presented the plan to his co-members of the Crockett Club. They decided that the political climate at the time was unfavorable for congressional action, that the best hope of success rested on the approval and support from the Alaskans themselves.
Sheldon wrote, "The first step was to secure the approval and cooperation of the delegate who represented Alaska in Congress."In October 1915, Sheldon took up the matter with Dr. E. W. Nelson of the Biological Survey at Washington, D. C. and with George Bird Grinnell, with a purpose to introduce a suitable bill in the coming session of Congress. The matter was taken to the Game Committee of the Boone and Crockett Club and, after a full discussion, it received the committee's full endorsement. On December 3, 1915, the plan was presented to Alaska's delegate, James Wickersham, who after some deliberation gave his approval; the plan went to the Executive Committee of the Boone and Crockett Club and, on December 15, 1915, it was unanimously accepted. The plan was thereupon endorsed by the Club and presented to Stephen Mather, Assistant Secretary of the Interior in Washington, D. C. who approved it. The bill was introduced in April, 1916, by Delegate Wickersham in the House and by Senator Key Pittman of Nevada in the Senate.
Much lobbying took place over the following year, on February 19, 1917, the bill passed. On February 26, 1917, 11 years from its conception, the bill was signed in legislation by the President of the United States, Woodrow Wilson, thereby creating Mount McKinley National Park. A portion of Denali, excluding the summit, was included the original park boundary. On Thanksgiving Day in 1921, the Mount McKinley Park Hotel opened. In July 1923, President Warren Harding stopped at the hotel, on a tour of the length of the Alaska Railroad, during which he drove a golden spike signaling its completion at Nenana; the hotel was the first thing. The flat-roofed, two-story log building featured exposed balconies, glass windows, electric lights. Inside were two dozen guest rooms, a shop, lunch counter and storeroom. By the 1930s, there were reports of lice, dirty linen, drafty rooms, marginal food, which led to the hotel's closing. In 1947, the park boundaries expanded to include the area of the railroad. After being abandoned for many years, the hotel was destroyed in 1950 by a fire.
There was no road access to the park entrance until 1957. Now with a highway connection to Anchorage and Fairbanks, park attendance expanded: there were 5,000 visitors in 1956 and 25,000 visitors by 1958; the park was designated an international biosphere reserve in 1976. A separate Denali National Monument was proclaimed by President Jimmy Carter on December 1, 1978; the name of Mount McKinley National Park was subject to local criticism from the beginning of the park. The word Denali means "the high one" in the native Athabaskan language and refers to the mountain itself; the mountain was named after newly elected US president William McKinley in 1897 by local prospector William A. Dickey; the United States government formally adopted the name Mount McKinley after President Wilson signed the bill creating Mount McKinley National Park into effect in 1917. In 1980, Mount McKinley National Park was combined with Denali National Monument, the Alaska National Interest Lands Conservation Act named the combined unit the Denali National Park and Preserve.
At that time the Alaska state Board of Geographic Names changed
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
Denali is the highest mountain peak in North America, with a summit elevation of 20,310 feet above sea level. With a topographic prominence of 20,156 feet and a topographic isolation of 4,629 miles, Denali is the third most prominent and third most isolated peak on Earth, after Mount Everest and Aconcagua. Located in the Alaska Range in the interior of the U. S. state of Alaska, Denali is the centerpiece of Preserve. The Koyukon people who inhabit the area around the mountain have referred to the peak as "Denali" for centuries. In 1896, a gold prospector named it "Mount McKinley" in support of then-presidential candidate William McKinley. In August 2015, following the 1975 lead of the State of Alaska, the United States Department of the Interior announced the change of the official name of the mountain to Denali. In 1903, James Wickersham recorded the first attempt at climbing Denali, unsuccessful. In 1906, Frederick Cook claimed the first ascent, proven to be false; the first verifiable ascent to Denali's summit was achieved on June 7, 1913, by climbers Hudson Stuck, Harry Karstens, Walter Harper, Robert Tatum, who went by the South Summit.
In 1951, Bradford Washburn pioneered the West Buttress route, considered to be the safest and easiest route, therefore the most popular in use. On September 2, 2015, the U. S. Geological Survey announced that the mountain is 20,310 feet high, not 20,320 feet, as measured in 1952 using photogrammetry. Denali is a granitic pluton lifted by tectonic pressure from the subduction of the Pacific Plate beneath the North American Plate; the forces that lifted Denali cause many deep earthquakes in Alaska and the Aleutian Islands. The Pacific Plate is seismically active beneath Denali, a tectonic region, known as the "McKinley cluster". Denali has a summit elevation of 20,310 feet above sea level, making it the highest peak in North America and the northernmost mountain above 6,000 meters elevation in the world. Measured from base to peak at some 18,000 ft, it is among the largest mountains situated above sea level. Denali rises from a sloping plain with elevations from 1,000 to 3,000 ft, for a base-to-peak height of 17,000 to 19,000 ft.
By comparison, Mount Everest rises from the Tibetan Plateau at a much higher base elevation. Base elevations for Everest range from 13,800 ft on the south side to 17,100 ft on the Tibetan Plateau, for a base-to-peak height in the range of 12,000 to 15,300 ft. Denali's base-to-peak height is little more than half the 33,500 ft of the volcano Mauna Kea, which lies under water. Denali has two significant summits: the South Summit is the higher one, while the North Summit has an elevation of 19,470 ft and a prominence of 1,270 ft; the North Summit is sometimes counted as sometimes not. Five large glaciers flow off the slopes of the mountain; the Peters Glacier lies on the northwest side of the massif, while the Muldrow Glacier falls from its northeast slopes. Just to the east of the Muldrow, abutting the eastern side of the massif, is the Traleika Glacier; the Ruth Glacier lies to the southeast of the mountain, the Kahiltna Glacier leads up to the southwest side of the mountain. With a length of 44 mi, the Kahiltna Glacier is the longest glacier in the Alaska Range.
The Koyukon Athabaskans who inhabit the area around the mountain have for centuries referred to the peak as Dinale or Denali. The name is based on a Koyukon word for "high" or "tall". During the Russian ownership of Alaska, the common name for the mountain was Bolshaya Gora, the Russian translation of Denali, it was called Densmore's Mountain in the late 1880s and early 1890s after Frank Densmore, an Alaskan prospector, the first European to reach the base of the mountain. In 1896, a gold prospector named it McKinley as political support for then-presidential candidate William McKinley, who became president the following year; the United States formally recognized the name Mount McKinley after President Wilson signed the Mount McKinley National Park Act of February 26, 1917. In 1965, Lyndon B. Johnson declared the north and south peaks of the mountain the "Churchill Peaks", in honor of British statesman Winston Churchill; the Alaska Board of Geographic Names changed the name of the mountain to Denali in 1975, how it is called locally.
However, a request in 1975 from the Alaska state legislature to the United States Board on Geographic Names to do the same at the federal level was blocked by Ohio congressman Ralph Regula, whose district included McKinley's hometown of Canton. On August 30, 2015, just ahead of a presidential visit to Alaska, the Barack Obama administration announced the name Denali would be restored in line with the Alaska Geographic Board's designation. U. S. Secretary of the Interior Sally Jewell issued the order changing the name to Denali on August 28, 2015, effective immediately. Jewell said the change had been "a long time coming"; the renaming of the mountain received praise from Alaska's senior U. S. senator, Lisa Murkowski, who had introduced legislation to accomplish the name change, but it drew criticism from several politicians from Pres
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
A glacier is a persistent body of dense ice, moving under its own weight. Glaciers deform and flow due to stresses induced by their weight, creating crevasses and other distinguishing features, they abrade rock and debris from their substrate to create landforms such as cirques and moraines. Glaciers form only on land and are distinct from the much thinner sea ice and lake ice that form on the surface of bodies of water. On Earth, 99% of glacial ice is contained within vast ice sheets in the polar regions, but glaciers may be found in mountain ranges on every continent including Oceania's high-latitude oceanic island countries such as New Zealand and Papua New Guinea. Between 35°N and 35°S, glaciers occur only in the Himalayas, Rocky Mountains, a few high mountains in East Africa, New Guinea and on Zard Kuh in Iran. Glaciers cover about 10 percent of Earth's land surface. Continental glaciers cover nearly 13 million km2 or about 98 percent of Antarctica's 13.2 million km2, with an average thickness of 2,100 m.
Greenland and Patagonia have huge expanses of continental glaciers. Glacial ice is the largest reservoir of fresh water on Earth. Many glaciers from temperate and seasonal polar climates store water as ice during the colder seasons and release it in the form of meltwater as warmer summer temperatures cause the glacier to melt, creating a water source, important for plants and human uses when other sources may be scant. Within high-altitude and Antarctic environments, the seasonal temperature difference is not sufficient to release meltwater. Since glacial mass is affected by long-term climatic changes, e.g. precipitation, mean temperature, cloud cover, glacial mass changes are considered among the most sensitive indicators of climate change and are a major source of variations in sea level. A large piece of compressed ice, or a glacier, appears blue, as large quantities of water appear blue; this is. The other reason for the blue color of glaciers is the lack of air bubbles. Air bubbles, which give a white color to ice, are squeezed out by pressure increasing the density of the created ice.
The word glacier is a loanword from French and goes back, via Franco-Provençal, to the Vulgar Latin glaciārium, derived from the Late Latin glacia, Latin glaciēs, meaning "ice". The processes and features caused by or related to glaciers are referred to as glacial; the process of glacier establishment and flow is called glaciation. The corresponding area of study is called glaciology. Glaciers are important components of the global cryosphere. Glaciers are categorized by their morphology, thermal characteristics, behavior. Cirque glaciers form on the slopes of mountains. A glacier that fills a valley is called a valley glacier, or alternatively an alpine glacier or mountain glacier. A large body of glacial ice astride a mountain, mountain range, or volcano is termed an ice cap or ice field. Ice caps have an area less than 50,000 km2 by definition. Glacial bodies larger than 50,000 km2 are called continental glaciers. Several kilometers deep, they obscure the underlying topography. Only nunataks protrude from their surfaces.
The only extant ice sheets are the two that cover most of Greenland. They contain vast quantities of fresh water, enough that if both melted, global sea levels would rise by over 70 m. Portions of an ice sheet or cap that extend into water are called ice shelves. Narrow, fast-moving sections of an ice sheet are called ice streams. In Antarctica, many ice streams drain into large ice shelves; some drain directly into the sea with an ice tongue, like Mertz Glacier. Tidewater glaciers are glaciers that terminate in the sea, including most glaciers flowing from Greenland, Antarctica and Ellesmere Islands in Canada, Southeast Alaska, the Northern and Southern Patagonian Ice Fields; as the ice reaches the sea, pieces break off, or calve. Most tidewater glaciers calve above sea level, which results in a tremendous impact as the iceberg strikes the water. Tidewater glaciers undergo centuries-long cycles of advance and retreat that are much less affected by the climate change than those of other glaciers.
Thermally, a temperate glacier is at melting point throughout the year, from its surface to its base. The ice of a polar glacier is always below the freezing point from the surface to its base, although the surface snowpack may experience seasonal melting. A sub-polar glacier includes both temperate and polar ice, depending on depth beneath the surface and position along the length of the glacier. In a similar way, the thermal regime of a glacier is described by its basal temperature. A cold-based glacier is below freezing at the ice-ground interface, is thus frozen to the underlying substrate. A warm-based glacier is above or at freezing at the interface, is able to slide at this contact; this contrast is thought to a large extent to govern the ability of a glacier to erode its bed, as sliding ice promotes plucking at rock from the surface below. Glaciers which are cold-based and warm-based are known as polythermal. Glaciers form where the accumulation of ice exceeds ablation. A glacier originates from a landform called'cirque' – a armchair-shaped geological feature (such as a depressio