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
A hairpin turn, named for its resemblance to a hairpin/bobby pin, is a bend in a road with a acute inner angle, making it necessary for an oncoming vehicle to turn about 180° to continue on the road. Such turns in ramps and trails may be called switchbacks in American English, by analogy with switchback railways. In British English "switchback" is more to refer to a undulating road—a use extended from the rollercoaster and the other type of switchback railway. Hairpin turns are built when a route climbs up or down a steep slope, so that it can travel across the slope with only moderate steepness, are arrayed in a zigzag pattern. Highways with repeating hairpin turns allow easier, safer ascents and descents of mountainous terrain than a direct, steep climb and descent, at the price of greater distances of travel and lower speed limits, due to the sharpness of the turn. Highways of this style are generally less costly to build and maintain than highways with tunnels. On occasion, the road may loop using a tunnel or bridge to cross itself at a different elevation.
When this routing geometry is used for a rail line, it is called spiral loop. In trail building, an alternative to switchbacks is the stairway; some roads with switchbacks include: Alpe d'Huez in the French Alps, famous for its 21 hairpin bends Stelvio Pass with its 48 hairpin bends on the northern ramp is one of the most famous Alpine Mountain passes Transfăgărăşan in the Romanian Carpathians, famous for its hairpin bends In rallying, the cars slide sideways around hairpins in spectacular style, such as at the Col de Turini of the Monte Carlo Rally Hillclimbing is a special kind of automobile racing held of mountain roads with hairpins, which keeps average speeds lower than on tracks In bicycle racing, climbs up mountains roads with many U-turns are considered the most difficult, feature in Tour de France, Giro d'Italia, Tour de Suisse and Vuelta a España The roads above Monaco, on the foothills of the Alps. The Geiranger road from Geirangerfjord to the mountain pass won the gold medal on the world exhibition, Paris 1900, the original design included a 270° spiral.
Norwegian National Road 7 through Måbødalen has a spiral within tunnels. The road from Frangokastello to Kallikratis in Crete has 27 tight bends. Due to mountainous profile of the country are many public streets in Greece having tight bends, the asphalt is little slippery, making the traction loosen; the situation worsens with the first rains after the long dry summer asphalt slips more than usual The Veleta access road in Granada, Spain is the highest paved road in Europe City streets: Winters Street Vermont Street Lombard Street Snake Alley Mountain Road Shippen Street US Highways: US 6 through Loveland Pass over the Continental Divide in Colorado US 44/NY 55 on the east face of the Shawangunk Ridge in Gardiner. US 93 used to be on both the Nevada and Arizona sides of Hoover Dam, though these sections were bypassed by a new highway alignment and bridge south of the dam that opened in 2010 US 250 between the West Virginia border and West Augusta, Virginia US 129 around the Tennessee/North Carolina border, 318 curves in 11 miles US 191 in Arizona between Morenci and Alpine), has a few switchbacks and about 460 curves.
US 441 through Great Smoky Mountains National Park on the Tennessee/North Carolina border. US 212 contains 19 switchbacks in the Beartooth Mountains; this section is known as Beartooth Highway. US 40 over Berthoud Pass in Colorado. US 550 in Colorado between Silverton and Ouray, nicknamed the "Million Dollar Highway" US 34 in Colorado in Rocky Mountain National Park has 10 switchbacks on Trail Ridge Road State Highways: AZ 89A as it enters Oak Creek Canyon in Arizona. AR 7 in various places in Arkansas CA 1 south of Bodega Bay, California. CA 130 Originally built as a wagon trail to aid in the construction of Lick Observatory, "Mt. Hamilton Road" travels east out of San Jose, CA and rises over the foothills, only to ascend again up the summit of Mt. Hamilton, it has a total of 365 curves and switchbacks: "...one for every day of the year" CA 152 east of Watsonville, California is known as Hwy 152 or Hecker Pass.
Pinus contorta, with the common names lodgepole pine and shore pine, known as twisted pine, contorta pine, is a common tree in western North America. It is common near the ocean shore and in dry montane forests to the subalpine, but is rare in lowland rain forests. Like all pines, it is an evergreen conifer. There are four subspecies of Pinus contorta, one of them is sometimes considered to have two varieties; the subspecies are sometimes treated at the rank of variety. Pinus contorta subsp. Bolanderi: Bolander's beach pine, Bolander pine. Contorta: shore pine. Pinus contorta subsp. Murrayana: tamarack pine, or Sierra lodgepole pine. Pinus contorta subsp. Latifolia: lodgepole pine. Depending on subspecies, Pinus contorta grows as tree; the shrub form is krummholz and is 1 to 3 m high. The thin and narrow-crowned tree is 40 to 50 m high and can achieve up to 2 m in diameter at chest height; the murrayana subspecies is the tallest. The crown is rounded and the top of the tree is flattened. In dense forests, the tree has a conical crown.
The formation of twin trees is common in some populations in British Columbia. The elastic branches are difficult to break; the branches are covered with short shoots. The species name is contorta because of the twisted, bent pines found at coastal areas and the tree's twisted needles. Pinus contorta is known under several English names: black pine, scrub pine, coast pine. P. contorta subsp. Latifolia will hybridise with the related jack pine; the egg-shaped growth buds are between 20 and 30 mm long. They are short pointed rotated, resinous. Spring growth starts in beginning of April and the annual growth is completed by early July; the dark and shiny needles are pointed and 4 to 8 cm long and 0.9 to 2 mm wide. The needle edge is weak to serrated; the needles rotated about the shoots' longitudinal axes. In Alberta above 2,000 m, 1 to 5 needles occur per short shoot. A population with a high proportion of three-needled short shoots occurs in the Yukon. Needles live an average of four to six years, with a maximum of 13 years.
The cones are 3–7 centimetres long. The cones have prickles on the scales. Many populations of the Rocky Mountain subspecies, P. contorta subsp. Latifolia, have serotinous cones; this means that the cones are closed and must be exposed to high temperatures, such as from forest fires, in order to open and release their seeds. The variation in their serotiny has been correlated with mountain pine beetle attacks; the cones of the coastal Pacific subspecies, P. contorta subsp. Contorta, are non-serotinous, those of the inland Pacific subspecies, P. contorta subsp. Murrayana, are non-serotinous. Pinus contorta is a fire-dependent species, requiring wildfires to maintain healthy populations of diverse ages; the bark of the lodgepole pine is thin, minimizing the tree's defense to fire. This allows the species to maintain its place in the forest habitat. One plant community in which Pinus contorta is found is the closed-cone pine forest of coastal California. Excessive wildfire prevention disrupts the fire ecology.
The stands are so densely populated that the trees self-thin, or out-compete each other, leaving dead trees standing. These become a dry ladder fuel; when the fire reaches the crowns of the trees, it can jump from tree to tree and becomes unstoppable. The natural fire regime for this species is driven by climate; the fires occur most after years of drought. Pinus contorta occurs from the upper montane to the subalpine region; these types of forests experience a lot of moisture in the form of snow in the winter due to their altitude. The density of the tree stand prohibits the establishment of an understory. With all of that being said, the likelihood of a surface fire occurring is rare. Thus, infrequent but severe fires dominate this species. An example of the climate that plays a huge role in the fire regime of Pinus contorta is quite complex. There are three different oscillations; these are Atlantic Multi-decadal Oscillation and El Nino. A combination of these oscillations being in effect or not in effect have a global effect on the water available to these forests.
So when the AMO +, ENSO – and PDO –, there is going to be a drought and a severe subalpine fire. Suillus tomentosus, a fungus, produces specialized structures called tuberculate ectomycorrhizae with the roots of lodgepole pine; these structures have been shown to be the location of concentrations of nitrogen-fixing bacteria which contribute a significant amount of nitrogen to tree growth and allow the pines to colonize nutrient-poor sites. This species is attacked by blue stain fungus, distributed
The onion known as the bulb onion or common onion, is a vegetable, the most cultivated species of the genus Allium. Its close relatives include the garlic, leek and Chinese onion; this genus contains several other species variously referred to as onions and cultivated for food, such as the Japanese bunching onion, the tree onion, the Canada onion. The name "wild onion" is applied to a number of Allium species, but A. cepa is known from cultivation. Its ancestral wild original form is not known, although escapes from cultivation have become established in some regions; the onion is most a biennial or a perennial plant, but is treated as an annual and harvested in its first growing season. The onion plant has a fan of hollow, bluish-green leaves and its bulb at the base of the plant begins to swell when a certain day-length is reached; the bulbs are composed of shortened, underground stems surrounded by fleshy modified scale that envelop a central bud at the tip of the stem. In the autumn, the foliage dies down and the outer layers of the bulb become dry and brittle.
The crop is harvested and dried and the onions are ready for use or storage. The crop is prone to attack by a number of pests and diseases the onion fly, the onion eelworm, various fungi cause rotting; some varieties of A. cepa, such as shallots and potato onions, produce multiple bulbs. Onions are used around the world; as a food item, they are served cooked, as a vegetable or part of a prepared savoury dish, but can be eaten raw or used to make pickles or chutneys. They are pungent when contain certain chemical substances which irritate the eyes; the onion plant known as the bulb onion or common onion, is the most cultivated species of the genus Allium. It was first described by Carl Linnaeus in his 1753 work Species Plantarum. A number of synonyms have appeared in its taxonomic history: Allium cepa var. aggregatum – G. Don Allium cepa var. bulbiferum – Regel Allium cepa var. cepa – Linnaeus Allium cepa var. multiplicans – L. H. Bailey Allium cepa var. proliferum – Regel Allium cepa var. solaninum – Alef Allium cepa var. viviparum – Mansf.
A. Cepa is known from cultivation, but related wild species occur in Central Asia; the most related species include A. vavilovii and A. asarense from Iran. However and Hopf state that "there are doubts whether the A. vavilovii collections tested represent genuine wild material or only feral derivatives of the crop."The vast majority of cultivars of A. cepa belong to the "common onion group" and are referred to as "onions". The Aggregatum group of cultivars includes both shallots and potato onions; the genus Allium contains a number of other species variously referred to as onions and cultivated for food, such as the Japanese bunching onion, Egyptian onion, Canada onion. Cepa is accepted as Latin for "onion" and has an affinity with Ancient Greek: κάπια and Albanian: qepë and is ancestral to Aromanian: tseapã, Catalan: ceba, Occitan: ceba, Spanish: cebolla, Romanian: ceapă; the English word chive is derived from the Old French cive, which derived from cepa. The onion plant has been selectively bred in cultivation for at least 7,000 years.
It is a biennial plant, but is grown as an annual. Modern varieties grow to a height of 15 to 45 cm; the leaves are yellowish - to bluish green and grow alternately in a fan-shaped swathe. They are fleshy and cylindrical, with one flattened side, they are at their broadest about a quarter of the way up, beyond which they taper towards a blunt tip. The base of each leaf is a flattened white sheath that grows out of a basal disc. From the underside of the disc, a bundle of fibrous roots extends for a short way into the soil; as the onion matures, food reserves begin to accumulate in the leaf bases and the bulb of the onion swells. In the autumn, the leaves die back and the outer scales of the bulb become dry and brittle, so the crop is normally harvested. If left in the soil over winter, the growing point in the middle of the bulb begins to develop in the spring. New leaves appear and a long, hollow stem expands, topped by a bract protecting a developing inflorescence; the inflorescence takes the form of a globular umbel of white flowers with parts in sixes.
The seeds are glossy triangular in cross section. The average pH of an onion is around 5.5 Because the wild onion is extinct and ancient records of using onions span western and eastern Asia, the geographic origin of the onion is uncertain, with domestication worldwide. Food uses of onions date back thousands of years in China and Persia. Traces of onions recovered from Bronze Age settlements in China suggest that onions were used as far back as 5000 BCE, not only for their flavour, but the bulb's durability in storage and transport. Ancient Egyptians revered the onion bulb, viewing its spherical shape and concentric rings as symbols of eternal life. Onions were used in Egyptian burials, as evidenced by onion traces found in the eye sockets of Ramesses IV. Pliny the Elder of the first century CE wrote about the use of onions and cabbage in Pompeii, he documented Roman beliefs about the onion's ability to improve ocular ailments, aid in sleep, heal everything from oral sores and toothaches to dog bites and dysentery.
For the extinct cephalopod genus, see Andesites. Andesite is an extrusive igneous, volcanic rock, of intermediate composition, with aphanitic to porphyritic texture. In a general sense, it is the intermediate type between basalt and rhyolite, ranges from 57 to 63% silicon dioxide as illustrated in TAS diagrams; the mineral assemblage is dominated by plagioclase plus pyroxene or hornblende. Magnetite, apatite, ilmenite and garnet are common accessory minerals. Alkali feldspar may be present in minor amounts; the quartz-feldspar abundances in andesite and other volcanic rocks are illustrated in QAPF diagrams. Classification of andesites may be refined according to the most abundant phenocryst. Example: hornblende-phyric andesite, if hornblende is the principal accessory mineral. Andesite can be considered as the extrusive equivalent of plutonic diorite. Characteristic of subduction zones, andesite represents the dominant rock type in island arcs; the average composition of the continental crust is andesitic.
Along with basalts they are a major component of the Martian crust. The name andesite is derived from the Andes mountain range. Magmatism in island arc regions comes from the interplay of the subducting plate and the mantle wedge, the wedge-shaped region between the subducting and overriding plates. During subduction, the subducted oceanic crust is submitted to increasing pressure and temperature, leading to metamorphism. Hydrous minerals such as amphibole, chlorite etc. dehydrate as they change to more stable, anhydrous forms, releasing water and soluble elements into the overlying wedge of mantle. Fluxing water into the wedge lowers the solidus of the mantle material and causes partial melting. Due to the lower density of the molten material, it rises through the wedge until it reaches the lower boundary of the overriding plate. Melts generated in the mantle wedge are of basaltic composition, but they have a distinctive enrichment of soluble elements which are contributed from sediment that lies at the top of the subducting plate.
Although there is evidence to suggest that the subducting oceanic crust may melt during this process, the relative contribution of the three components to the generated basalts is still a matter of debate. Basalt thus formed can contribute to the formation of andesite through fractional crystallization, partial melting of crust, or magma mixing, all of which are discussed next. Andesite is formed at convergent plate margins but may occur in other tectonic settings. Intermediate volcanic rocks are created via several processes: Fractional crystallization of a mafic parent magma. Partial melting of crustal material. Magma mixing between felsic rhyolitic and mafic basaltic magmas in a magma reservoir To achieve andesitic composition via fractional crystallization, a basaltic magma must crystallize specific minerals that are removed from the melt; this removal can take place in a variety of ways, but most this occurs by crystal settling. The first minerals to crystallize and be removed from a basaltic parent are amphiboles.
These mafic minerals settle out of the magma. There is geophysical evidence from several arcs that large layers of mafic cumulates lie at the base of the crust. Once these mafic minerals have been removed, the melt no longer has a basaltic composition; the silica content of the residual melt is enriched relative to the starting composition. The iron and magnesium contents are depleted; as this process continues, the melt becomes more and more evolved becoming andesitic. Without continued addition of mafic material, the melt will reach a rhyolitic composition. Molten basalt in the mantle wedge moves upwards until it reaches the base of the overriding crust. Once there, the basaltic melt can either underplate the crust, creating a layer of molten material at its base, or it can move into the overriding plate in the form of dykes. If it underplates the crust, the basalt can cause partial melting of the lower crust due to the transfer of heat and volatiles. Models of heat transfer, show that arc basalts emplaced at temperatures 1100–1240 °C cannot provide enough heat to melt lower crustal amphibolite.
Basalt can, melt pelitic upper crustal material. Andesitic magmas generated in island arcs, are the result of partial melting of the crust. In continental arcs, such as the Andes, magma pools in the shallow crust creating magma chambers. Magmas in these reservoirs become evolved in composition through both the process of fractional crystallization and partial melting of the surrounding country rock. Over time as crystallization continues and the system loses heat, these reservoirs cool. In order to remain active, magma chambers must have continued recharge of hot basaltic melt into the system; when this basaltic material mixes with the evolved rhyolitic magma, the composition is returned to andesite, its intermediate phase. In 2009, researchers revealed that andesite was found in two meteorites that were discovered in the Graves Nunataks icefield during the US Antarctic Search for Meteorites 2006/2007 field season; this points to a new mechanism to generate andesite crust. Andesite line Basaltic andesite Continental crust – Layer of rock that forms the continents and continental shelves Fractional crystallization – One of the main processes of magmatic differentiation List of rock types – A list of rock types recognized by geologists Metamorphism – The change of minerals in pre-existing rocks w
Scoria is a vesicular, dark colored volcanic rock that may or may not contain crystals. It is dark in color, basaltic or andesitic in composition. Scoria is low in density as a result of its numerous macroscopic ellipsoidal vesicles, but in contrast to pumice, all scoria has a specific gravity greater than 1, sinks in water; the holes or vesicles form when gases that were dissolved in the magma come out of solution as it erupts, creating bubbles in the molten rock, some of which are frozen in place as the rock cools and solidifies. Scoria may form as part of a lava flow near its surface, or as fragmental ejecta, for instance in Strombolian eruptions that form steep-sided scoria cones. Most scoria is composed of glassy fragments, may contain phenocrysts; the word scoria comes from the Greek skōria, rust. A colloquial term for scoria is cinder. Scoria differs from pumice, another vesicular volcanic rock, in having larger vesicles and thicker vesicle walls, hence is denser; the difference is the result of lower magma viscosity, allowing rapid volatile diffusion, bubble growth and bursting.
As rising magma encounters lower pressures, dissolved gases are able to form vesicles. Some of the vesicles are trapped when the magma solidifies. Vesicles are small, spheroidal and do not impinge upon one another. Volcanic cones of scoria can be left behind after eruptions forming mountains with a crater at the summit. An example is Maungarei in New Zealand, which like Te Tatua-a-Riukiuta in the south of the same city has been extensively quarried. Quincan, a unique form of Scoria, is quarried at Mount Quincan in Australia. Scoria has several useful characteristics, it is somewhat porous, has high surface area and strength for its weight, has striking colours. Scoria is used in landscaping and drainage works, it is commonly used in gas barbecue grills. Scoria can be used for high-temperature insulation. Scoria is used on oil well sites to limit mud issues with heavy truck traffic; the quarry of Puna Pau on Rapa Nui/Easter Island was the source of a red-coloured scoria which the Rapanui people used to carve the pukao for their distinctive moai statues, to carve some moai from.
It is used as a traction aid on ice- and snow-covered roads. Cinder – Pyroclastic vesicular rock Tuff – Rock consolidated from volcanic ash Pumice – Light coloured vesicular volcanic glass Volcano – A rupture in the crust of a planetary-mass object that allows hot lava, volcanic ash, gases to escape from a magma chamber below the surface List of rock types – A list of rock types recognized by geologists Rock – A occurring solid aggregate of one or more minerals or mineraloids
Types of volcanic eruptions
Several types of volcanic eruptions—during which lava and assorted gases are expelled from a volcanic vent or fissure—have been distinguished by volcanologists. These are named after famous volcanoes where that type of behavior has been observed; some volcanoes may exhibit only one characteristic type of eruption during a period of activity, while others may display an entire sequence of types all in one eruptive series. There are three different types of eruptions; the most well-observed are magmatic eruptions, which involve the decompression of gas within magma that propels it forward. Phreatomagmatic eruptions are another type of volcanic eruption, driven by the compression of gas within magma, the direct opposite of the process powering magmatic activity; the third eruptive type is the phreatic eruption, driven by the superheating of steam via contact with magma. Within these wide-defining eruptive types are several subtypes; the weakest are Hawaiian and submarine Strombolian, followed by Vulcanian and Surtseyan.
The stronger eruptive types are Pelean eruptions, followed by Plinian eruptions. Subglacial and phreatic eruptions are defined by their eruptive mechanism, vary in strength. An important measure of eruptive strength is Volcanic Explosivity Index, an order of magnitude scale ranging from 0 to 8 that correlates to eruptive types. Volcanic eruptions arise through three main mechanisms: Gas release under decompression causing magmatic eruptions Thermal contraction from chilling on contact with water causing phreatomagmatic eruptions Ejection of entrained particles during steam eruptions causing phreatic eruptionsThere are two types of eruptions in terms of activity, explosive eruptions and effusive eruptions. Explosive eruptions are characterized by gas-driven explosions that propels tephra. Effusive eruptions, are characterized by the outpouring of lava without significant explosive eruption. Volcanic eruptions vary in strength. On the one extreme there are effusive Hawaiian eruptions, which are characterized by lava fountains and fluid lava flows, which are not dangerous.
On the other extreme, Plinian eruptions are large and dangerous explosive events. Volcanoes are not bound to one eruptive style, display many different types, both passive and explosive in the span of a single eruptive cycle. Volcanoes do not always erupt vertically from a single crater near their peak, either; some volcanoes exhibit lateral and fissure eruptions. Notably, many Hawaiian eruptions start from rift zones, some of the strongest Surtseyan eruptions develop along fracture zones. Scientists believed that pulses of magma mixed together in the chamber before climbing upward—a process estimated to take several thousands of years, but Columbia University volcanologists found that the eruption of Costa Rica’s Irazú Volcano in 1963 was triggered by magma that took a nonstop route from the mantle over just a few months. The Volcanic Explosivity Index is a scale, for measuring the strength of eruptions, it is used by the Smithsonian Institution's Global Volcanism Program in assessing the impact of historic and prehistoric lava flows.
It operates in a way similar to the Richter scale for earthquakes, in that each interval in value represents a tenfold increasing in magnitude. The vast majority of volcanic eruptions are of VEIs between 0 and 2. Volcanic eruptions by VEI index Magmatic eruptions produce juvenile clasts during explosive decompression from gas release, they range in intensity from the small lava fountains on Hawaii to catastrophic Ultra-Plinian eruption columns more than 30 km high, bigger than the eruption of Mount Vesuvius in 79 that buried Pompeii. Hawaiian eruptions are a type of volcanic eruption, named after the Hawaiian volcanoes with which this eruptive type is hallmark. Hawaiian eruptions are the calmest types of volcanic events, characterized by the effusive eruption of fluid basalt-type lavas with low gaseous content; the volume of ejected material from Hawaiian eruptions is less than half of that found in other eruptive types. Steady production of small amounts of lava builds up the broad form of a shield volcano.
Eruptions are not centralized at the main summit as with other volcanic types, occur at vents around the summit and from fissure vents radiating out of the center. Hawaiian eruptions begin as a line of vent eruptions along a fissure vent, a so-called "curtain of fire." These die down. Central-vent eruptions, meanwhile take the form of large lava fountains, which can reach heights of hundreds of meters or more; the particles from lava fountains cool in the air before hitting the ground, resulting in the accumulation of cindery scoria fragments. If eruptive rates are high enough, they may form splatter-fed lava flows. Hawaiian eruptions are extremely long lived. Another Hawaiian volcanic feature is the formation of active lava lakes, self-maintaining pools of raw lava with a thin crust of semi-cooled rock. Flows from Hawaiian eruptions are basal