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34-712: Timpanogos Glacier is a rock glacier located on Mount Timpanogos in the Wasatch Range within the Mount Timpanogos Wilderness (in the Uinta-Wasatch-Cache National Forest ) in northeastern Utah County , Utah , United States. The glacier is situated in a north-facing cirque on the east slope of Mount Timpanogos (11,749 feet or 3,581 metres). The best evidence indicates that the Timpanogos Glacier

68-459: A basaltic magma must crystallize specific minerals that are then removed from the melt. This removal can take place in a variety of ways, but most commonly this occurs by crystal settling. The first minerals to crystallize and be removed from a basaltic parent are olivines and amphiboles . These mafic minerals settle out of the magma, forming mafic cumulates. There is geophysical evidence from several arcs that large layers of mafic cumulates lie at

102-557: A common rule of thumb , used away from the laboratory, is that andesite has a color index less than 35. The plagioclase in andesite varies widely in sodium content, from anorthite to oligoclase , but is typically andesine , in which anorthite makes up about 40 mol% of the plagioclase. The pyroxene minerals that may be present include augite , pigeonite , or orthopyroxene . Magnetite , zircon , apatite , ilmenite , biotite , and garnet are common accessory minerals. Alkali feldspar may be present in minor amounts. Andesite

136-446: A single day, apparently due to climate change . Andesite Andesite ( / ˈ æ n d ə z aɪ t / ) is a volcanic rock of intermediate composition . In a general sense, it is the intermediate type between silica -poor basalt and silica-rich rhyolite . It is fine-grained ( aphanitic ) to porphyritic in texture, and is composed predominantly of sodium-rich plagioclase plus pyroxene or hornblende . Andesite

170-534: A subducting slab generates magma resembling high-magnesium andesites. Notable stonemasonry structures built with andesite include: In 2009, researchers revealed that andesite was found in two meteorites (numbered GRA 06128 and GRA 06129) that were discovered in the Graves Nunataks icefield during the US Antarctic Search for Meteorites 2006/2007 field season. This possibly points to

204-731: A talus lobe. Periglacial rock glaciers can form from the alternation of rock debris incoming with autumn firn or avalanche snow. Nearby cliffs are in many cases a requirement for the formation of rock glaciers, and as such many rock glaciers form in valleys steepened by glacier erosion . Rock masses of rock glaciers have been found to make up different rock types depending on the local geology. These rock types include andesite , basalt , granite , porphyry , quartzite , and sandstone . Ordinary glaciers can override rock glaciers, acquiring some of its material and properties. Likewise, rock glaciers can originate from debris-rich remnants of glaciers. Rock glaciers move downslope by deformation of

238-420: A very slow rate, in part dependent on the amount of ice present. According to recent studies, rock glaciers positively influence the streams around them. Subject to climate variation, rock glaciers in proximity tend to have a highly synchronous movement pattern over a short time scale; over long term, however, the relationship between rock glacier velocity and climate difference may not be as pronounced, due to

272-518: Is so characteristic of the Earth's unique plate tectonics that the Earth has been described as an "andesite planet". During subduction, the subducted oceanic crust is subjected to increasing pressure and temperature, leading to metamorphism . Hydrous minerals such as amphibole , zeolites , or chlorite (which are present in the oceanic lithosphere ) dehydrate as they change to more stable, anhydrous forms, releasing water and soluble elements into

306-506: Is 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, andesites are a component of the Martian crust . The name andesite is derived from the Andes mountain range, where this rock type is found in abundance. It

340-472: Is usually porphyritic , containing larger crystals ( phenocrysts ) of plagioclase formed prior to the extrusion that brought the magma to the surface, embedded in a finer-grained matrix . Phenocrysts of pyroxene or hornblende are also common. These minerals have the highest melting temperatures of the typical minerals that can crystallize from the melt and are therefore the first to form solid crystals. Classification of andesites may be refined according to

374-453: The Andes , magma often pools in the shallow crust creating magma chambers. Magmas in these reservoirs become evolved in composition (dacitic to rhyolitic) 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

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408-487: The Mars Orbiter spacecraft. A rock glacier, especially if its origin is unclear, can be considered as a discrete debris accumulation . The two known factors that must be present in order to create rock glaciers are low ice velocity and permafrost . Most glacial rock glaciers are created by the recession of debris covered glaciers. Glacial rock glaciers are often found in cirque basins where rocky debris falls off

442-512: The QAPF diagram . Andesite is further distinguished from basalt by its silica content of over 52%. However, it is often not possible to determine the mineral composition of volcanic rocks, due to their very fine grain size, and andesite is then defined chemically as volcanic rock with a content of 57% to 63% silica and not more than about 6% alkali metal oxides. This places the andesite in the O2 field of

476-617: The TAS classification . Basaltic andesite , with a content of 52% to 57% silica, is represented by the O1 field of the TAS classification but is not a distinct rock type in the QAPF classification. Andesite is usually light to dark grey in colour, due to its content of hornblende or pyroxene minerals. but can exhibit a wide range of shading. Darker andesite can be challenging to distinguish from basalt, but

510-442: The shield volcanoes characteristic of basalt, with its much lower viscosity resulting from its lower silica content and higher eruption temperature. Block lava flows are typical of andesitic lavas from composite volcanoes. They behave in a similar manner to ʻaʻā flows but their more viscous nature causes the surface to be covered in smooth-sided angular fragments (blocks) of solidified lava instead of clinkers. As with ʻaʻā flows,

544-408: 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 eventually becoming andesitic. Without continued addition of mafic material, however,

578-474: The ice contained within them, causing their surface to resemble those of glaciers. Some rock glaciers can reach lengths of three kilometres (2 mi) and can have terminal embankments 60 m (200 ft) high. Blocks on the surface can be up to 8 m (26 ft) in diameter. Flow features on the surface of rock glaciers may develop from: Their growth and formation is subject to some debate, with three main theories: Rock glaciers may move or creep at

612-566: The influences of topographic factors and lack of ice or debris budget within the glacier body. Rock glaciers in the Chilean Andes help supply the water for much of Chile, including the capital of Santiago. Mining operations in the high mountains have led to the degradation and destruction of more than two rock glaciers. Several copper mines dump their waste rock onto rock glaciers, which results in faster melting and higher velocity movement of these rock glaciers. The dumping of waste rock on

646-420: The late 1990s or early 2000s. One witness threw a stone in and from the fall time calculated that it was over 100 feet (30 m) deep. Around this time Brigham Young University dug three to five feet (0.91–1.52 m) down to the ice and attempted to obtain a core sample and study the ice crystal morphology. The core sample was reportedly contaminated and crystal morphology study was unsuccessful. Today,

680-573: The main flow lobe of the glacier which touches the lake may now be inactive. [REDACTED] Media related to Timpanogos Glacier at Wikimedia Commons Rock glacier There are two types of rock glaciers: periglacial glaciers (or talus-derived glaciers), and glacial rock glaciers, such as the Timpanogos Glacier in Utah , which are often found where glaciers once existed. Possible Martian rock glacier features have been identified by

714-437: The melt will eventually reach a rhyolitic composition. This produces the characteristic basalt-andesite-rhyolite association of island arcs, with andesite the most distinctive rock type. Partially 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

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748-523: The molten interior of the flow, which is kept insulated by the solidified blocky surface, advances over the rubble that falls off the flow front. They also move much more slowly downhill and are thicker in depth than ʻaʻā flows. Though andesite is common in other tectonic settings, it is particularly characteristic of convergent plate margins . Even before the Plate Tectonics Revolution , geologists had defined an andesite line in

782-492: The most abundant phenocryst . For example, if hornblende is the principal phenocryst mineral, the andesite will be described as a hornblende andesite . Andesite lava typically has a viscosity of 3.5 × 10 cP (3.5 × 10 Pa⋅s) at 1,200 °C (2,190 °F). This is slightly greater than the viscosity of smooth peanut butter . As a result, andesitic volcanism is often explosive, forming tuffs and agglomerates . Andesite vents tend to build up composite volcanoes rather than

816-510: 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 partially 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 (e.g. potassium (K), barium (Ba), and lead (Pb)) which are contributed from sediment that lies at

850-441: The overriding plate in the form of dykes . If it underplates the crust, the basalt can (in theory) cause partial melting of the lower crust due to the transfer of heat and volatiles. Models of heat transfer, however, show that arc basalts emplaced at temperatures 1100–1240 °C cannot provide enough heat to melt lower crustal amphibolite . Basalt can, however, melt pelitic upper crustal material. In continental arcs, such as

884-458: The rock glacier consists of three flow lobes. The main one may be inactive, the uppermost one is probably active, and the one in-between is probably extinct. On September 3, 2016, an amateur geologist found a meltwater pit in the uppermost flow lobe full of opaque glacial runoff and a small amount of exposed glacial ice. He dug through the rocks in the slope of the pit and found blue ice about three feet (0.91 m) down. The ice contained bubbles and

918-582: The rock glaciers may lead to their destabilization. In 2004, protesting irrigation farmers and environmentalists changed rules so new mining projects can no longer damage or alter rock glaciers in Chile. Parts of the only road into Denali National Park and Preserve in Alaska are built on a rock glacier known as "Pretty Rocks". In late summer 2021 the road had to be closed due to accelerating rockslides in that area, sometimes sliding up to 10 inches (250 mm) in

952-581: The steep sides and accumulates on ice glaciers. As the glaciers shrink, their composition changes as they become increasingly covered with debris. Eventually, the glacial ice is replaced by ice cored rocks. With the exception of ice-cored rock glaciers, rock glaciers are a periglacial process. This means that they are a nonglacial landform associated with cold climates, particularly with various aspects of frozen ground. Periglacial rock glaciers require permafrost instead of glacial ice in order to form. Instead, they are caused by continuous freezing occurring within

986-541: The system. When this basaltic material mixes with the evolved rhyolitic magma, the composition is returned to andesite, its intermediate phase. Evidence of magma mixing is provided by the presence of phenocrysts in some andesites that are not in chemical equilibrium with the melt in which they are found. High-magnesium andesites ( boninites ) in island arcs may be primitive andesites, generated from metasomatized mantle. Experimental evidence shows that depleted mantle rock exposed to alkali fluids such as might be given off by

1020-585: The top of the subducting plate. Although there is evidence to suggest that the subducting oceanic crust may also melt during this process, the relative contribution of the three components (crust, sediment, and wedge) 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. Intermediate volcanic rocks are created via several processes: To achieve andesitic composition via fractional crystallization ,

1054-488: The western Pacific that separated basalt of the central Pacific from andesite further west. This coincides with the subduction zones at the western boundary of the Pacific Plate . 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. The presence of convergent margins dominated by andesite

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1088-420: Was first applied by Christian Leopold von Buch in 1826. Andesite is an aphanitic (fine-grained) to porphyritic (coarse-grained) igneous rock that is intermediate in its content of silica and low in alkali metals . It has less than 20% quartz and 10% feldspathoid by volume, with at least 65% of the feldspar in the rock consisting of plagioclase . This places andesite in the basalt /andesite field of

1122-560: Was once a "true" glacier with crevasses present in the early 20th century, but that the surface portion was lost during the Dust Bowl drought of the 1930s and reduced to a permanent snowfield. The glacier is considered to be a rock glacier, since the remaining ice is buried in the talus. However, in 1994 the rocks parted, revealing a crevasse or meltwater channel in the buried ice. One witness described it as being "40 feet [12 m] thick at least." Another crevasse reportedly opened up in

1156-427: Was therefore probably glacial in origin. Over the years, the glacier has been the site of multiple injuries and several fatalities. Emerald Lake is a small proglacial lake which lies at the terminal moraine left behind by the now mostly vanished Timpanogos Glacier. The occasional blue color of Emerald Lake is an indicator of the buried glacial ice. Since this color did not appear in 2016 despite low water levels,

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