Pico de Orizaba
Pico de Orizaba known as Citlaltépetl, is a stratovolcano, the highest mountain in Mexico and the third highest in North America, after Denali of Alaska in the United States and Mount Logan of Canada. It rises 5,636 metres above sea level in the eastern end of the Trans-Mexican Volcanic Belt, on the border between the states of Veracruz and Puebla; the volcano is dormant but not extinct, with the last eruption taking place during the 19th century. It is the second most prominent volcanic peak in the world after Africa's Mount Kilimanjaro. Pico de Orizaba overlooks the city of Orizaba, from which it gets its name; the name Citlaltépetl is not used by Nahuatl speakers of the Orizaba area, who instead call it Istaktepetl, or'White Mountain'. Citlaltépetl comes from the Náhuatl citlalli and tepētl and thus means "Star Mountain"; this name is thought to be based on the fact that the snow-covered peak can be seen year round for hundreds of kilometers throughout the region. During the colonial era, the volcano was known as Cerro de San Andrés due to the nearby settlement of San Andrés Chalchicomula at its base.
A third name, which means "the one that colors or illuminates", has been recorded. This name was given by the Tlaxcaltecs in memory of their lost country; the peak of Citlaltépetl rises to an elevation of 5,636 m above sea level. Regionally dominant, Pico de Orizaba is the highest peak in Mexico and the highest volcano in North America. Orizaba is ranked 7th in the world in topographic prominence, it is the second most prominent volcanic peak in the world after Africa's Mount Kilimanjaro, the volcano is ranked 16th in the world for topographic isolation. About 110 km to the west of the port of Veracruz, its peak is visible to ships approaching the port in the Gulf of Mexico, at dawn rays of sunlight strike the Pico while Veracruz still lies in shadow; the topography of Pico de Orizaba is asymmetrical from the center of the crater. The gradual slopes of the northwestern face of the volcano allows for the presence of large glaciers and is the most traveled route to take for hikers traveling to the summit.
Pico de Orizaba is one of only three volcanoes in México that continue to support glaciers and is home to the largest glacier in Mexico, Gran Glaciar Norte. Orizaba has nine known glaciers: Gran Glaciar Norte, Lengua del Chichimeco, Toro, Glaciar de la Barba, Occidental and Oriental; the equilibrium line altitude is not known for Orizaba. Snow on the south and southeast sides of the volcano melts because of solar radiation, but lower temperatures on the northwest and north sides allow for glaciers; the insolation angle and wind redeposition on the northwest and north sides allow for constant accumulation of snow providing a source for the outlet glaciers. On the north side of Orizaba, the Gran Glaciar Norte fills the elongated highland basin and is the source for seven outlet glaciers; the main glacier extends 3.5 km north of the crater rim, has a surface area of about 9.08 km2 descending from 5,650 m to about 5,000 m. It has a irregular and stepped profile, caused in part by the configuration of the bedrock.
Most crevasses show an ice thickness of 50 m. Below the 5,000 m in elevation on the north side of the volcano, the outlet glaciers Lengua del Chichimeco and Jamapa extend north and northwest another 1.5 km and 2 km, respectively. The terminal lobe of Lengua del Chichimeco at 4,740 m, having a gradient of only 140 m/km, is a low, broad ice fan that has a convex-upward profile, a front typical of all Mexican glaciers; the most distinct glacier is Glaciar de Jamapa, which leaves Gran Glaciar Norte at about 4,975 m and, after 2 km with a gradient of 145 m/km, divides into two small tongues that end at 4,650 m and 4,640 m. Both tongues terminate in broad convex-upward ice fans thinning along their edges; the retreat of these tongues prior to 1994 produced much erosion downstream and buried their edges by ablation rock debris. The west side of Gran Glaciar Norte generates five outlet glaciers. From north to south, the first two, Glaciar del Toro and Glaciar de la Barba, are hanging cliff or icefall glaciers, reaching the tops of giant lava steps at 4,930 m and 5,090 m, respectively.
They descend 200 to 300 m farther down into the heads of stream valleys as huge ice blocks but are not regenerated there. About 1 km, Glaciar Noroccidental, a small outlet glacier 300 m long, drains away from the side of Gran Glaciar Norte at about 5,100 m and draws down the ice surface a few tens of meters over a distance of 500 m, descending to 4,920 m with a gradient of 255 m/km. Another 1 km still farther south, Glaciar Occidental breaks away from Gran Glaciar Norte west of the summit crater at about 5,175 m as a steep, 1 km long glacier having a gradient of 270 m/km that ends at 4,930 m. From the southwest corner of the mountain, another outlet glacier, Glaciar Suroccidental, 1.6 km long, flows from Gran Glaciar Norte at 5,250 m with a gradient of 200 m/km, which en
In mountaineering, a first ascent is the first successful, documented attainment of the top of a mountain, or the first to follow a particular climbing route. First mountain ascents are notable because they entail genuine exploration, with greater risks and recognition than climbing a route pioneered by others; the person who performs the first ascent is called the first ascensionist. In free climbing, a first ascent of a climbing route is the first successful, documented climb of a route without using equipment such as anchors or ropes for aiding progression or resting; the details of the first ascents of many prominent mountains are scanty or unknown. Today, first ascents are carefully recorded and mentioned in guidebooks. Overwhelmingly, the idea of a "first ascent" is a modern one in places such as Africa and the Americas with a history of colonialism. There may be little or no physical evidence or documentation about the climbing activities of indigenous peoples living near the mountain.
For example, the volcano Llullaillaco on the border of Argentina and Chile is known to have been climbed in the prehistoric period due to the presence of Incan artifacts at the summit, yet credit for the first recorded ascent is given to Chilean climbers Bión González and Juan Harseim, who summited in 1952. The term is used when referring to ascents made using a specific technique or taking a specific route, such as via the North Face, without ropes or without oxygen. In rock climbing, some of the earlier first ascents for difficult routes, involved a mix of free and aid climbing; as a result, purist free climbers have developed the designation first free ascent to acknowledge ascents intentionally made more challenging by using equipment for protection only. Second ascents are noteworthy in climbing circles involving improving on a pioneering route through lessons learned from it, experience which may span from technical improvements to having a better understanding of how much gear and provisions to take.
Some other "first ascents" could be recorded for particular routes. One is the First Winter Ascent, which is, as the name suggests, the first ascent made during winter season; this is most important where the climate of winter is a factor in increasing the difficulty grade of the route. In the Northern Hemisphere conventional winter ascents are made between December 21 and March 21 and are not related to the conditions. In the Himalayan area, although Nepal and China's winter season permits start on December 1, the conventional winter ascents begin on December 21. Another is the First Solo Ascent, the first ascent made by a single climber; this is most important on high-level rock climbing, when the climber has to provide his own security or when climbing without any protection at all. Another type of ascent known as FFA is the first female ascent. While not considered as important, this designation remains significant on some difficult, limit-pushing climbs, where the first female ascent may not happen until well after the FA, due to possible difficulties encountered by female physicality.
The term last ascent has been used to refer to an ascent of a mountain or face that has subsequently changed to such an extent – because of rockfall – that the route no longer exists. It can be used facetiously to refer to a climb, so unpleasant or unaesthetic that no one would willingly repeat the first ascent party's ordeal. List of first ascents Notable first free ascents List of first ascents in the Alps List of first ascents in the Himalaya Glossary of climbing terms Alpinist Magazine – Peter Mortimer's First Ascent, Issue 17
The Smithsonian Institution, founded on August 10, 1846 "for the increase and diffusion of knowledge," is a group of museums and research centers administered by the Government of the United States. The institution is named after British scientist James Smithson. Organized as the "United States National Museum," that name ceased to exist as an administrative entity in 1967. Termed "the nation's attic" for its eclectic holdings of 154 million items, the Institution's nineteen museums, nine research centers, zoo include historical and architectural landmarks located in the District of Columbia. Additional facilities are located in Arizona, Massachusetts, New York City, Texas and Panama. More than 200 institutions and museums in 45 states, Puerto Rico, Panama are Smithsonian Affiliates; the Institution's thirty million annual visitors are admitted without charge. Its annual budget is around $1.2 billion with two-thirds coming from annual federal appropriations. Other funding comes from the Institution's endowment and corporate contributions, membership dues, earned retail and licensing revenue.
Institution publications include Air & Space magazines. The British scientist James Smithson left most of his wealth to his nephew Henry James Hungerford; when Hungerford died childless in 1835, the estate passed "to the United States of America, to found at Washington, under the name of the Smithsonian Institution, an Establishment for the increase & diffusion of knowledge among men", in accordance with Smithson's will. Congress accepted the legacy bequeathed to the nation, pledged the faith of the United States to the charitable trust on July 1, 1836; the American diplomat Richard Rush was dispatched to England by President Andrew Jackson to collect the bequest. Rush returned in August 1838 with 105 sacks containing 104,960 gold sovereigns. Once the money was in hand, eight years of Congressional haggling ensued over how to interpret Smithson's rather vague mandate "for the increase and diffusion of knowledge." The money was invested by the US Treasury in bonds issued by the state of Arkansas, which soon defaulted.
After heated debate, Massachusetts Representative John Quincy Adams persuaded Congress to restore the lost funds with interest and, despite designs on the money for other purposes, convinced his colleagues to preserve it for an institution of science and learning. On August 10, 1846, President James K. Polk signed the legislation that established the Smithsonian Institution as a trust instrumentality of the United States, to be administered by a Board of Regents and a Secretary of the Smithsonian. Though the Smithsonian's first Secretary, Joseph Henry, wanted the Institution to be a center for scientific research, it became the depository for various Washington and U. S. government collections. The United States Exploring Expedition by the U. S. Navy circumnavigated the globe between 1838 and 1842; the voyage amassed thousands of animal specimens, an herbarium of 50,000 plant specimens, diverse shells and minerals, tropical birds, jars of seawater, ethnographic artifacts from the South Pacific Ocean.
These specimens and artifacts became part of the Smithsonian collections, as did those collected by several military and civilian surveys of the American West, including the Mexican Boundary Survey and Pacific Railroad Surveys, which assembled many Native American artifacts and natural history specimens. In 1846, the regents developed a plan for weather observation; the Institution became a magnet for young scientists from 1857 to 1866, who formed a group called the Megatherium Club. The Smithsonian played a critical role as the U. S. partner institution in early bilateral scientific exchanges with the Academy of Sciences of Cuba. Construction began on the Smithsonian Institution Building in 1849. Designed by architect James Renwick Jr. its interiors were completed by general contractor Gilbert Cameron. The building opened in 1855; the Smithsonian's first expansion came with construction of the Arts and Industries Building in 1881. Congress had promised to build a new structure for the museum if the 1876 Philadelphia Centennial Exposition generated enough income.
It did, the building was designed by architects Adolf Cluss and Paul Schulze, based on original plans developed by Major General Montgomery C. Meigs of the United States Army Corps of Engineers, it opened in 1881. The National Zoological Park opened in 1889 to accommodate the Smithsonian's Department of Living Animals; the park was designed by landscape architect Frederick Law Olmsted. The National Museum of Natural History opened in June 1911 to accommodate the Smithsonian's United States National Museum, housed in the Castle and the Arts and Industries Building; this structure was designed by the D. C. architectural firm of Hornblower & Marshall. When Detroit philanthropist Charles Lang Freer donated his private collection to the Smithsonian and funds to build the museum to hold it, it was among the Smithsonian's first major donations from a private individual; the gallery opened in 1923. More than 40 years would pass before the next museum, the Museum of History and Technology, opened in 1964.
It was designed by the world-renowned firm of Mead & White. The Anacostia Community Museum, an "experimental store-front" museum created at the initiative of Smithsonian Secretary S. Dillon Ripley, opened in the Anacostia neighborhood of
Global Volcanism Program
The Smithsonian Institution's Global Volcanism Program documents Earth's volcanoes and their eruptive history over the past 10,000 years. The GVP reports on current eruptions from around the world as well as maintaining a database repository on active volcanoes and their eruptions. In this way, a global context for the planet's active volcanism is presented. Smithsonian reporting on current volcanic activity dates back to 1968, with the Center for Short-Lived Phenomena; the GVP is housed in the Department of Mineral Sciences, part of the National Museum of Natural History, on the National Mall in Washington, D. C. During the early stages of an eruption, the GVP acts as a clearing house of reports and imagery which are accumulated from a global network of contributors; the early flow of information is managed such that the right people are contacted as well as helping to sort out vague and contradictory aspects that arise during the early days of an eruption. The Weekly Volcanic Activity Report is a cooperative project between the Smithsonian's Global Volcanism Program and the United States Geological Survey's Volcano Hazards Program.
Notices of volcanic activity posted on the report website are preliminary and subject to change as events are studied in more detail. Detailed reports on various volcanoes are published monthly in the Bulletin of the Global Volcanism NetworkThe GVP documents the last 10,000 years of Earth's volcanism; the historic activity can guide perspectives on possible future events and on volcanoes showing activity. GVP's volcano and eruption databases constitute a foundation for all statistical statements concerning locations and magnitudes of Earth's volcanic eruptions during the past recent 10,000 years. Two editions of Volcanoes of the World, a regional directory... and were published based on the GVP data and interpretations. Prediction of volcanic activity Timeline of volcanism on Earth Volcanic explosivity index Volcano Number Global Volcanism Program Global Volcanism Program Facebook page
The Pleistocene is the geological epoch which lasted from about 2,588,000 to 11,700 years ago, spanning the world's most recent period of repeated glaciations. The end of the Pleistocene corresponds with the end of the last glacial period and with the end of the Paleolithic age used in archaeology; the Pleistocene is the first epoch of the Quaternary Period or sixth epoch of the Cenozoic Era. In the ICS timescale, the Pleistocene is divided into four stages or ages, the Gelasian, Middle Pleistocene and Upper Pleistocene. In addition to this international subdivision, various regional subdivisions are used. Before a change confirmed in 2009 by the International Union of Geological Sciences, the time boundary between the Pleistocene and the preceding Pliocene was regarded as being at 1.806 million years Before Present, as opposed to the accepted 2.588 million years BP: publications from the preceding years may use either definition of the period. Charles Lyell introduced the term "Pleistocene" in 1839 to describe strata in Sicily that had at least 70% of their molluscan fauna still living today.
This distinguished it from the older Pliocene epoch, which Lyell had thought to be the youngest fossil rock layer. He constructed the name "Pleistocene" from the Greek πλεῖστος, pleīstos, "most", καινός, kainós, "new"; the Pleistocene has been dated from 2.588 million to 11,700 years BP with the end date expressed in radiocarbon years as 10,000 carbon-14 years BP. It covers most of the latest period of repeated glaciation, up to and including the Younger Dryas cold spell; the end of the Younger Dryas has been dated to about 9640 BC. The end of the Younger Dryas is the official start of the current Holocene Epoch. Although it is considered an epoch, the Holocene is not different from previous interglacial intervals within the Pleistocene, it was not until after the development of radiocarbon dating, that Pleistocene archaeological excavations shifted to stratified caves and rock-shelters as opposed to open-air river-terrace sites. In 2009 the International Union of Geological Sciences confirmed a change in time period for the Pleistocene, changing the start date from 1.806 to 2.588 million years BP, accepted the base of the Gelasian as the base of the Pleistocene, namely the base of the Monte San Nicola GSSP.
The IUGS has yet to approve a type section, Global Boundary Stratotype Section and Point, for the upper Pleistocene/Holocene boundary. The proposed section is the North Greenland Ice Core Project ice core 75° 06' N 42° 18' W; the lower boundary of the Pleistocene Series is formally defined magnetostratigraphically as the base of the Matuyama chronozone, isotopic stage 103. Above this point there are notable extinctions of the calcareous nanofossils: Discoaster pentaradiatus and Discoaster surculus; the Pleistocene covers the recent period of repeated glaciations. The name Plio-Pleistocene has, in the past, been used to mean the last ice age; the revised definition of the Quaternary, by pushing back the start date of the Pleistocene to 2.58 Ma, results in the inclusion of all the recent repeated glaciations within the Pleistocene. The modern continents were at their present positions during the Pleistocene, the plates upon which they sit having moved no more than 100 km relative to each other since the beginning of the period.
According to Mark Lynas, the Pleistocene's overall climate could be characterized as a continuous El Niño with trade winds in the south Pacific weakening or heading east, warm air rising near Peru, warm water spreading from the west Pacific and the Indian Ocean to the east Pacific, other El Niño markers. Pleistocene climate was marked by repeated glacial cycles in which continental glaciers pushed to the 40th parallel in some places, it is estimated. In addition, a zone of permafrost stretched southward from the edge of the glacial sheet, a few hundred kilometres in North America, several hundred in Eurasia; the mean annual temperature at the edge of the ice was −6 °C. Each glacial advance tied up huge volumes of water in continental ice sheets 1,500 to 3,000 metres thick, resulting in temporary sea-level drops of 100 metres or more over the entire surface of the Earth. During interglacial times, such as at present, drowned coastlines were common, mitigated by isostatic or other emergent motion of some regions.
The effects of glaciation were global. Antarctica was ice-bound throughout the Pleistocene as well as the preceding Pliocene; the Andes were covered in the south by the Patagonian ice cap. There were glaciers in New Tasmania; the current decaying glaciers of Mount Kenya, Mount Kilimanjaro, the Ruwenzori Range in east and central Africa were larger. Glaciers existed to the west in the Atlas mountains. In the northern hemisphere, many glaciers fused into one; the Cordilleran ice sheet covered the North American northwest. The Fenno-Scandian ice sheet rested including much of Great Britain. Scattered domes stretched across Siberi
Tuff known as volcanic tuff, is a type of rock made of volcanic ash ejected from a vent during a volcanic eruption. Following ejection and deposition, the ash is compacted into a solid rock in a process called consolidation. Tuff is sometimes erroneously called "tufa" when used as construction material, but properly speaking, tufa is a limestone precipitated from groundwater. Rock that contains greater than 50% tuff is considered tuffaceous. Tuff is a soft rock, so it has been used for construction since ancient times. Since it is common in Italy, the Romans used it for construction; the Rapa Nui people used it to make most of the moai statues in Easter Island. Tuff can be classified as either sedimentary or igneous rock, they are studied in the context of igneous petrology, although they are sometimes described using sedimentological terms. The material, expelled in a volcanic eruption can be classified into three types: Volcanic gases, a mixture made of steam, carbon dioxide, a sulfur compound Lava, the name of magma when it emerges and flows over the surface Tephra, chunks of solid material of all shapes and sizes ejected and thrown through the airTephra is made when magma inside the volcano is blown apart by the rapid expansion of hot volcanic gases.
Magma explodes as the gas dissolved in it comes out of solution as the pressure decreases when it flows to the surface. These violent explosions produce solid chunks of material that can fly from the volcano. Chunks smaller than 2 mm in diameter are called volcanic ash. Among the loose beds of ash that cover the slopes of many volcanoes, three classes of materials are represented. In addition to true ashes of the kind described above, lumps of the old lavas and tuffs form the walls of the crater, which have been torn away by the violent outbursts of steam, pieces of sedimentary rocks from the deeper parts of the volcano that were dislodged by the rising lava and are intensely baked and recrystallized by the heat to which they have been subjected. In some great volcanic explosions, nothing but lumps of the old lavas and tuffs forming the walls of the crater etc. were emitted, as at Mount Bandai in Japan in 1888. Many eruptions have occurred in which the quantity of broken sedimentary rocks that mingled with the ash is great.
In the Scottish coalfields, some old volcanoes are plugged with masses consisting of sedimentary debris. These accessory or adventitious materials, however, as distinguished from the true ashes, tend to occur in angular fragments, when they form a large part of the mass, the rock is more properly a "volcanic breccia" than a tuff; the ashes vary in size from large blocks 20 ft or more in diameter to the minutest impalpable dust. The large masses are called "volcanic bombs". Many of them have ribbed or nodular surfaces, sometimes they have a crust intersected by many cracks like the surface of a loaf of bread. Any ash in which they are abundant is called an agglomerate. In those layers and beds of tuff that have been spread out over considerable tracts of land and which are most encountered among the sedimentary rocks, smaller fragments preponderate and bombs more than a few inches in diameter may be absent altogether. A tuff of recent origin is loose and incoherent, but the older tuffs have been, in most cases, cemented together by pressure and the action of infiltrating water, making rocks which, while not hard, are strong enough to be extensively used for building purposes.
If they have accumulated subaerially, like the ash beds found on Mt. Etna or Vesuvius at the present day, tuffs consist wholly of volcanic materials of different degrees of fineness with pieces of wood and vegetable matter, land shells, etc. but many volcanoes stand near the sea, the ashes cast out by them are mingled with the sediments that are gathering at the bottom of the waters. In this way, ashy muds, sands, or in some cases ashy limestones are being formed. Most of the tuffs found in the older formations contain admixtures of clay and sometimes fossil shells, which prove that they were beds spread out under water. During some volcanic eruptions, a layer of ashes several feet in thickness is deposited over a considerable area, but such beds thin out as the distance from the crater increases, ash deposits covering many square miles are very thin; the showers of ashes follow one another after longer or shorter intervals, hence thick masses of tuff, whether of subaerial or of marine origin, have a stratified character.
The coarsest materials or agglomerates show this least distinctly. Apart from adventitious material, such as fragments of the older rocks, pieces of trees, etc. the contents of an ash deposit may be described as consisting of more or less crystalline igneous rocks. If the lava within the crater has been at such a temperature that solidification has commenced, crystals are present, they may be of considerable size like the grey, rounded leucite crystals found on the sides of Vesuvius. Many of these are perfect and rich in faces because they grew in a medium, liquid and not viscous. Good crystals of augite and olivi
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