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102-596: A great deal of volcanic activity was occurring in the Reykjanes Peninsula in 2020 and into 2024, after nearly 800 years of inactivity. After the eruption of the Fagradalsfjall volcano on 19 March 2021, National Geographic 's experts predicted that this "may mark the start of decades of volcanic activity". The eruption was small leading to a prediction that this volcano was unlikely to threaten "any population centers". The two most important factors for

204-444: A Magazine has been determined upon as one means accomplishing these purposes. It was initially a scholarly journal sent to 165 charter members; in 2010, it reached the hands of 40 million people each month. Starting with its January 1905 publication of several full-page pictures of Tibet in 1900–01, the magazine began to transition from being a text-oriented publication to featuring extensive pictorial content. By 1908 more than half of

306-650: A balanced view of the physical and human geography of countries beyond the Iron Curtain . The magazine printed articles on Berlin, de-occupied Austria , the Soviet Union , and Communist China that deliberately downplayed politics to focus on culture. In its coverage of the Space Race , National Geographic focused on the scientific achievement while largely avoiding reference to the race's connection to nuclear arms buildup. There were also many articles in

408-486: A change in composition. Solidification into rock occurs either below the surface as intrusive rocks or on the surface as extrusive rocks. Igneous rock may form with crystallization to form granular, crystalline rocks, or without crystallization to form natural glasses . Igneous rocks occur in a wide range of geological settings: shields, platforms, orogens, basins, large igneous provinces, extended crust and oceanic crust. Igneous and metamorphic rocks make up 90–95% of

510-459: A combination of these processes. Other mechanisms, such as melting from a meteorite impact , are less important today, but impacts during the accretion of the Earth led to extensive melting, and the outer several hundred kilometres of our early Earth was probably an ocean of magma. Impacts of large meteorites in the last few hundred million years have been proposed as one mechanism responsible for

612-405: A crystalline basement formed of a great variety of metamorphic and igneous rocks, including granulite and granite. Oceanic crust is composed primarily of basalt and gabbro . Both continental and oceanic crust rest on peridotite of the mantle. Rocks may melt in response to a decrease in pressure, to a change in composition (such as an addition of water), to an increase in temperature, or to

714-698: A deal was announced for Disney to acquire 21st Century Fox , including the controlling interest in National Geographic Partners. The acquisition was completed in March 2019. NG Media publishing unit was operationally transferred into Disney Publishing Worldwide . In September 2022, the magazine laid off six of its top editors. In June 2023, the magazine laid off all of its staff writers , shifting to an entirely freelance-based writing model, and announced that beginning in 2024 it would no longer offer newsstand purchases. The magazine had

816-527: A huge mass of analytical data—over 230,000 rock analyses can be accessed on the web through a site sponsored by the U. S. National Science Foundation (see the External Link to EarthChem). The single most important component is silica, SiO 2 , whether occurring as quartz or combined with other oxides as feldspars or other minerals. Both intrusive and volcanic rocks are grouped chemically by total silica content into broad categories. This classification

918-761: A local-language logo; the other one is the Persian version published under the name Gita Nama . Following the Russian invasion of Ukraine , the Russian version of National Geographic was discontinued effective April 2022. Its publication team then launched the Russian Traveler , which is not associated with the National Geographic brand. In the United States, National Geographic

1020-554: A low-sloping lava cone surrounded by a lava apron; the older shields are made from picrite , the younger, bigger ones from olivine-tholeiite. They were probably formed in long-lived eruptions (years to decades). The best known edifices are Selvogsheiði [ˈsɛlˌvɔksˌheiːðɪ] (height 176 m, basal width 4.8 km, summit width 0.7 km, volume 0.64 km), Þráinskjöldur [ˈθrauːɪnˌscœltʏr̥] (volume 5.2 km), Heiðin há (volume 6 km) and Sandfellshæð [ˈsantˌfɛlsˌhaiːθ] (4.5 km). Sandfellshæð

1122-653: A microscope for fine-grained volcanic rock, and may be impossible for glassy volcanic rock. The rock must then be classified chemically. Mineralogical classification of an intrusive rock begins by determining if the rock is ultramafic, a carbonatite, or a lamprophyre . An ultramafic rock contains more than 90% of iron- and magnesium-rich minerals such as hornblende, pyroxene, or olivine, and such rocks have their own classification scheme. Likewise, rocks containing more than 50% carbonate minerals are classified as carbonatites, while lamprophyres are rare ultrapotassic rocks. Both are further classified based on detailed mineralogy. In

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1224-506: A part of Reykjanes volcanic system as geochemistry is similar), Fagradalsfjall volcanic system , Krýsuvík volcanic system , Brennisteinsfjöll volcanic system , and Hengill volcanic system (which stretches up to the north and into the West volcanic zone ). Only the Hengill volcanic system, the most eastern system, has an additional central volcano and this volcano is complex as it is at

1326-576: A photograph presented as a portrait of a dog with fighter jets flying over its shoulder. Lascelles had in reality created the image using photo editing software. After the annexation of Crimea by the Russian Federation in 2014, National Geographic published maps with the Crimean peninsula marked as " contested ", contrary to international norms. In March 2018, the editor of National Geographic , Susan Goldberg , said that historically

1428-553: A simplified compositional classification, igneous rock types are categorized into felsic or mafic based on the abundance of silicate minerals in the Bowen's Series. Rocks dominated by quartz, plagioclase, alkali feldspar and muscovite are felsic. Mafic rocks are primarily composed of biotite, hornblende, pyroxene and olivine. Generally, felsic rocks are light colored and mafic rocks are darker colored. For textural classification, igneous rocks that have crystals large enough to be seen by

1530-591: A single "editor" from 1888 to 1920. From 1920 to 1967, the chief editorship was held by the president of the National Geographic Society . Since 1967, the magazine has been overseen by its own "editor" and/or "editor-in-chief". The list of editors-in-chief includes three generations of the Grosvenor family between 1903 and 1980. During the Cold War , the magazine committed itself to present

1632-401: A still image. In 1915, GHG began building the group of staff photographers and providing them with advanced tools including the latest darkroom. The magazine began to feature some pages of color photography in the early 1930s, when this technology was still in its early development. During the mid-1930s, Luis Marden (1913–2003), a writer and photographer for National Geographic , convinced

1734-460: A tendency for basaltic fissure eruptions. There are tephra deposits from both offshore explosive Holocene eruptions, some of whom were from volcanoes of the Reykjanes volcanic system, and the most recent Hengill eruption. As is usual within rift zones, tectonics play an important role on Reykjanes Peninsula. Earthquakes are often registered. They may reach up to magnitude M6, but most of

1836-422: A thick square-bound glossy format with a yellow rectangular border. Map supplements from National Geographic Maps are included with subscriptions, and it is available in a traditional printed edition and an interactive online edition. As of 1995 , the magazine was circulated worldwide in nearly forty local-language editions and had a global circulation of at least 6.5 million per month including 3.5 million within

1938-617: A transtensional rift zone. The rate of spread is about 1.8 cm/year (0.71 in/year). The spreading that occurs generates NE-SE trending fissure swarm faulting and connects the area with the other surrounding rift zones. The stress that is accumulated through the volcanism is released every 800-1000 years through the fissure eruptions. The fissure swarms are the origin of underground near vertical dykes. The Reykjanes' dykes travel near vertically through Quaternary and Tertiary sediments. These dykes generate permeability in rock that would otherwise be impermeable. This increased permeability creates

2040-462: A viscosity similar to thick, cold molasses or even rubber when erupted. Felsic magma, such as rhyolite , is usually erupted at low temperature and is up to 10,000 times as viscous as basalt. Volcanoes with rhyolitic magma commonly erupt explosively, and rhyolitic lava flows are typically of limited extent and have steep margins because the magma is so viscous. Felsic and intermediate magmas that erupt often do so violently, with explosions driven by

2142-632: Is a pronounced continuation between the volcanism of Reykjanes Ridge, a part of the Mid-Atlantic Ridge, and the Reykjanes Peninsula. Famous in the area of Reykjavík is the Grágrýti ( [ˈkrauːˌkriːtɪ] , Gray Lava). These tertiary basalt lava layers cover much of the ground around and under Reykjavík, but their origin is unknown. It is thought that the small hills within the city, some of which were islands during periods of glaciation, could be small shield volcanoes from warm spells of

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2244-491: Is a very regularly constructed shield volcano and the largest in the southern part of Reykjanes Peninsula. Another important shield volcano on Reykjanes Peninsula is Leitin , formed around 5,000 years ago. Since the end of the Pleistocene glaciation (15,000–11,000 years ago in the region), Holocene volcanoes have contributed to the basaltic lava fields of the peninsula. The Reykjanes volcanic belt (previously also known as

2346-584: Is an example. The molten rock, which typically contains suspended crystals and dissolved gases, is called magma . It rises because it is less dense than the rock from which it was extracted. When magma reaches the surface, it is called lava . Eruptions of volcanoes into air are termed subaerial , whereas those occurring underneath the ocean are termed submarine . Black smokers and mid-ocean ridge basalt are examples of submarine volcanic activity. The volume of extrusive rock erupted annually by volcanoes varies with plate tectonic setting. Extrusive rock

2448-697: Is available only to subscribers beginning with the January 2024 issue. For the first 110 years of the magazine's existence, membership in the National Geographic Society was the only way to receive it. Newsstand sales, which began in 1998, ceased in 2023, following a year of layoffs and a shift in focus to digital formats amid the decline of the print media industry. Worldwide editions are sold on newsstands in addition to regular subscriptions. In several countries, such as Hungary, Slovenia, Croatia, Turkey and Ukraine, National Geographic paved

2550-566: Is basalt, though there are also some basaltic andesite or andesite volcanoes on Reykjanes, like Húsmúli [ˈhuːsˌmuːlɪ] and Stapafell [ˈstaːpaˌfɛtl̥] within the Hengill volcanic system . Examples for tuyas on Reykjanes Peninsula are Keilir (conical tuya), Geitafell [ˈceiːtaˌfɛtl̥] ( Brennisteinsfjöll ), Geitahlíð and Þorbjörn are flat-topped tuyas whereas Þorðarfell [ˈθɔrðarˌfɛtl̥] and Syllingarfell [ˈsɪtliŋkarˌfɛtl̥] are complex tuyas. The Holocene shield volcanoes represent

2652-728: Is distinguishable from the other two on the TAS diagram, being higher in total alkali oxides for a given silica content, but the tholeiitic and calc-alkaline series occupy approximately the same part of the TAS diagram. They are distinguished by comparing total alkali with iron and magnesium content. These three magma series occur in a range of plate tectonic settings. Tholeiitic magma series rocks are found, for example, at mid-ocean ridges, back-arc basins , oceanic islands formed by hotspots, island arcs and continental large igneous provinces . All three series are found in relatively close proximity to each other at subduction zones where their distribution

2754-595: Is expressed differently for major and minor elements and for trace elements. Contents of major and minor elements are conventionally expressed as weight percent oxides (e.g., 51% SiO 2 , and 1.50% TiO 2 ). Abundances of trace elements are conventionally expressed as parts per million by weight (e.g., 420 ppm Ni, and 5.1 ppm Sm). The term "trace element" is typically used for elements present in most rocks at abundances less than 100 ppm or so, but some trace elements may be present in some rocks at abundances exceeding 1,000 ppm. The diversity of rock compositions has been defined by

2856-506: Is formed by the cooling of molten magma on the earth's surface. The magma, which is brought to the surface through fissures or volcanic eruptions , rapidly solidifies. Hence such rocks are fine-grained ( aphanitic ) or even glassy. Basalt is the most common extrusive igneous rock and forms lava flows, lava sheets and lava plateaus. Some kinds of basalt solidify to form long polygonal columns . The Giant's Causeway in Antrim, Northern Ireland

2958-436: Is most often used to classify plutonic rocks. Chemical classifications are preferred to classify volcanic rocks, with phenocryst species used as a prefix, e.g. "olivine-bearing picrite" or "orthoclase-phyric rhyolite". The IUGS recommends classifying igneous rocks by their mineral composition whenever possible. This is straightforward for coarse-grained intrusive igneous rock, but may require examination of thin sections under

3060-491: Is now thought to be situated under the big glacier shield of Vatnajökull . Outcropping rocks have ages from 3.2 million years to the present. The topography of Reykjanes Peninsula was formed by glaciers and volcanism, basaltic lava fields covering a good part of the peninsula, in between volcanoes of subglacial as well as subaerial origin, namely tuyas , hyaloclastic ridges (tindars), shield volcanoes and crater rows . Some volcanic systems are submarine , so that there

3162-409: Is one of the three main rock types , the others being sedimentary and metamorphic . Igneous rocks are formed through the cooling and solidification of magma or lava . The magma can be derived from partial melts of existing rocks in either a planet 's mantle or crust . Typically, the melting is caused by one or more of three processes: an increase in temperature, a decrease in pressure , or

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3264-496: Is produced in the following proportions: The behaviour of lava depends upon its viscosity , which is determined by temperature, composition, and crystal content. High-temperature magma, most of which is basaltic in composition, behaves in a manner similar to thick oil and, as it cools, treacle . Long, thin basalt flows with pahoehoe surfaces are common. Intermediate composition magma, such as andesite , tends to form cinder cones of intermingled ash , tuff and lava, and may have

3366-402: Is related to depth and the age of the subduction zone. The tholeiitic magma series is well represented above young subduction zones formed by magma from relatively shallow depth. The calc-alkaline and alkaline series are seen in mature subduction zones, and are related to magma of greater depths. Andesite and basaltic andesite are the most abundant volcanic rock in island arc which is indicative of

3468-487: Is summarized in the following table: The percentage of alkali metal oxides ( Na 2 O plus K 2 O ) is second only to silica in its importance for chemically classifying volcanic rock. The silica and alkali metal oxide percentages are used to place volcanic rock on the TAS diagram , which is sufficient to immediately classify most volcanic rocks. Rocks in some fields, such as the trachyandesite field, are further classified by

3570-479: The IUGS , this is often impractical, and chemical classification is done instead using the TAS classification . Igneous rocks are classified according to mode of occurrence, texture, mineralogy, chemical composition, and the geometry of the igneous body. The classification of the many types of igneous rocks can provide important information about the conditions under which they formed. Two important variables used for

3672-706: The Krýsuvík system . It was followed up by over 1,000 aftershocks and is part of a series stretching over nearly one year. On 24 February 2021, a new earthquake series comprising hundreds of earthquakes and including two earthquakes over 5 were registered by the Icelandic Meteorological Office (IMO), with one registering at 5.7. The alert phase of Iceland's Civil Protection was activated, because even bigger earthquakes could not be excluded in this earthquake series. The whole region has been under close scrutiny of scientists. A magnitude 5.1 earthquake

3774-483: The Reykjanes Fires that deposited substantial amounts of lava and tephra across the peninsula. The volcanoes in the region were subsequently dormant for nearly 800 years. The second episode began in 2020 and has been dubbed the "New Reykjanes Fires" in recognition of the similarity with the previous episode. On 20 October 2020, a magnitude 5.6 volcanism-related earthquake was registered at Núpshlíðarháls within

3876-453: The convection of solid mantle, it will cool slightly as it expands in an adiabatic process , but the cooling is only about 0.3 °C per kilometre. Experimental studies of appropriate peridotite samples document that the solidus temperatures increase by 3 °C to 4 °C per kilometre. If the rock rises far enough, it will begin to melt. Melt droplets can coalesce into larger volumes and be intruded upwards. This process of melting from

3978-473: The 1640s and is derived either from French granit or Italian granito , meaning simply "granulate rock". The term rhyolite was introduced in 1860 by the German traveler and geologist Ferdinand von Richthofen The naming of new rock types accelerated in the 19th century and peaked in the early 20th century. Much of the early classification of igneous rocks was based on the geological age and occurrence of

4080-474: The 1930s, 1940s and 1950s about the individual states and their resources, along with supplementary maps of each state. Many of these articles were written by longtime staff such as Frederick Simpich . After 21st Century Fox acquired controlling interest in the magazine, articles became outspoken on topics such as environmental issues , deforestation , chemical pollution , global warming , and endangered species . Series of articles were included focusing on

4182-434: The 1960s. However, the concept of normative mineralogy has endured, and the work of Cross and his coinvestigators inspired a flurry of new classification schemes. Among these was the classification scheme of M.A. Peacock, which divided igneous rocks into four series: the alkalic, the alkali-calcic, the calc-alkali, and the calcic series. His definition of the alkali series, and the term calc-alkali, continue in use as part of

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4284-421: The 2020 Webby Award for News & Magazines in the category Apps, Mobile & Voice. National Geographic won the 2020 Webby Award and Webby People's Voice Award for Magazine in the category Web. On the magazine's February 1982 cover, the pyramids of Giza were altered, resulting in the first major scandal of the digital photography age and contributing to photography's "waning credibility". The cover of

4386-688: The Cartographic Division) became a division of the National Geographic Society in 1915. The first supplement map, which appeared in the May 1918 issue of the magazine, titled The Western Theatre of War , served as a reference for overseas military personnel and soldiers' families alike. On some occasions, the Society's map archives have been used by the United States government in instances where its own cartographic resources were limited. President Franklin D. Roosevelt 's White House map room

4488-520: The Earth's surface. Intrusive igneous rocks that form at depth within the crust are termed plutonic (or abyssal ) rocks and are usually coarse-grained. Intrusive igneous rocks that form near the surface are termed subvolcanic or hypabyssal rocks and they are usually much finer-grained, often resembling volcanic rock. Hypabyssal rocks are less common than plutonic or volcanic rocks and often form dikes, sills, laccoliths, lopoliths , or phacoliths . Extrusive igneous rock, also known as volcanic rock,

4590-623: The Magazine of the Year Award. In April 2014, National Geographic received the National Magazine Award ("Ellie") for best tablet edition for its multimedia presentation of Robert Draper's story "The Last Chase", about the final days of a tornado researcher who was killed in the line of duty. In February 2017, National Geographic received the National Magazine Award ("Ellie") for best website. National Geographic won

4692-671: The National Geographic website. In April 1995, National Geographic began publishing in Japanese, its first local language edition. The magazine is currently published in 29 local editions around the world. The following local-language editions have been discontinued. In association with Trends Publications in Beijing and IDG Asia, National Geographic has been authorized for "copyright cooperation" in China to publish

4794-568: The October 1988 issue featured a photo of a large ivory portrait of a male, whose authenticity, particularly the alleged ice age provenance, has been questioned. In 1999, the magazine was embroiled in the Archaeoraptor scandal, in which it purported to have a fossil linking birds to dinosaurs. The fossil was a forgery. In 2010, the magazine's Your Shot competition was awarded to American filmmaker and photographer William Lascelles for

4896-399: The Reykjanes Peninsula ridge, or Reykjanes Peninsula volcanic zone), one of the present day volcanic zones of Iceland , is connected to the submarine Reykjanes Ridge and consists (depending on author) of 3 to 6 or even 7 volcanic systems, arranged en echelon , i.e. more or less side by side, and in an average 40° angle to the spreading direction NE–SW over the peninsula. One of the reasons for

4998-486: The U.S., down from about 12 million in the late 1980s. As of 2015 , the magazine had won 25 National Magazine Awards . In 2023, National Geographic laid off all staff writers and announced they would stop U.S. newsstand sales in the next year. As of November 2024 , its Instagram page has 280 million followers, the third most of any account not belonging to an individual celebrity. The magazine's combined U.S. and international circulation as of June 30, 2024

5100-468: The United States, and millions more outside of the U.S. In the late 1990s, the magazine began publishing The Complete National Geographic , an electronic collection of every past issue of the magazine. It was then sued over copyright of the magazine as a collective work in Greenberg v. National Geographic and other cases, and temporarily withdrew the compilation. The magazine eventually prevailed in

5202-479: The area was imminent. The eruption began on 18 December at 10pm local time, north–east of Grindavík at the Sundhnúkur crater row. Further brief effusive eruptions with a very rapid outflow of large quantities of lava took place on 14 January and 8 February 2024, damaging the outskirts of Grindavik and other infrastructure in the area. On 16 March 2024 a fourth eruption began north–east of Hagafell. This eruption

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5304-450: The basic TAS classification include: In older terminology, silica oversaturated rocks were called silicic or acidic where the SiO 2 was greater than 66% and the family term quartzolite was applied to the most silicic. A normative feldspathoid classifies a rock as silica-undersaturated; an example is nephelinite . Magmas are further divided into three series: The alkaline series

5406-512: The calc-alkaline magmas. Some island arcs have distributed volcanic series as can be seen in the Japanese island arc system where the volcanic rocks change from tholeiite—calc-alkaline—alkaline with increasing distance from the trench. Some igneous rock names date to before the modern era of geology. For example, basalt as a description of a particular composition of lava-derived rock dates to Georgius Agricola in 1546 in his work De Natura Fossilium . The word granite goes back at least to

5508-429: The chemical composition of an igneous rock was its most fundamental characteristic, it should be elevated to prime position. Geological occurrence, structure, mineralogical constitution—the hitherto accepted criteria for the discrimination of rock species—were relegated to the background. The completed rock analysis is first to be interpreted in terms of the rock-forming minerals which might be expected to be formed when

5610-625: The classification of igneous rocks are particle size, which largely depends on the cooling history, and the mineral composition of the rock. Feldspars , quartz or feldspathoids , olivines , pyroxenes , amphiboles , and micas are all important minerals in the formation of almost all igneous rocks, and they are basic to the classification of these rocks. All other minerals present are regarded as nonessential in almost all igneous rocks and are called accessory minerals . Types of igneous rocks with other essential minerals are very rare, but include carbonatites , which contain essential carbonates . In

5712-413: The cover, while keeping its yellow border, shed its oak leaf trim and bare table of contents, to allow for a full-page photograph taken for one of the month's articles. Issues of National Geographic are often kept by subscribers for years and re-sold at thrift stores as collectibles. The standard for photography has remained high over the subsequent decades and the magazine is still illustrated with some of

5814-405: The crust of a planet. Bodies of intrusive rock are known as intrusions and are surrounded by pre-existing rock (called country rock ). The country rock is an excellent thermal insulator , so the magma cools slowly, and intrusive rocks are coarse-grained ( phaneritic ). The mineral grains in such rocks can generally be identified with the naked eye. Intrusions can be classified according to

5916-402: The different types of extrusive igneous rocks than between different types of intrusive igneous rocks. Generally, the mineral constituents of fine-grained extrusive igneous rocks can only be determined by examination of thin sections of the rock under a microscope , so only an approximate classification can usually be made in the field . Although classification by mineral makeup is preferred by

6018-521: The dispute, and in July 2009 resumed publishing all past issues through December 2008. More recent issues were later added to the collection; the archive and electronic edition of the magazine are available online to the magazine's subscribers. In September 2015, the National Geographic Society moved the magazine to a new owner, National Geographic Partners, giving 21st Century Fox a 73% controlling interest in exchange for $ 725 million. In December 2017,

6120-742: The earthquakes are small. These earthquakes often take place within the volcanic systems, but there are also many faults, fractures and fissures in the N-S direction on the peninsula. Additionally, the region is influenced by the South Iceland seismic zone. This southern transform zone of Iceland is between the West volcanic zone and the East volcanic zone . The larger earthquakes are felt and registered on Reykjanes Peninsula, and they can also trigger medium-sized quakes in this region, as last seen in 2008 and especially in 2000. The Reykjanes Peninsula lies within

6222-474: The evening of 19 March 2021. The eruption was small and effusive, from a 500–800 m long fissure; National Geographic predicted that this volcano was unlikely to threaten "any population centers". The next small fissure eruption in the Fagradalsfjall volcanic system started in the Meradalir valleys on 1 August 2022 and ceased on 22 August 2022. On 10 July 2023 at 16:40 UTC, a fissure eruption began adjacent to

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6324-526: The existence of Iceland, rifting in combination with the Iceland hotspot , were responsible for the existence of Reykjanesskagi. Reykjanes Peninsula originated in a so-called rift jump 6-7 million years ago. At this time, the Snæfellsnes - Skagi rift had drifted so far to the west and away from the presumed steady place hot spot, that activity shifted eastwards in direction of this mantle plume which

6426-484: The extensive basalt magmatism of several large igneous provinces. Decompression melting occurs because of a decrease in pressure. The solidus temperatures of most rocks (the temperatures below which they are completely solid) increase with increasing pressure in the absence of water. Peridotite at depth in the Earth's mantle may be hotter than its solidus temperature at some shallower level. If such rock rises during

6528-651: The glaciations. But it is known that during the Plio-Pleistocene (from 3.2 – 1.8 million years BP) two central volcanoes were active in the Reykjavík region, Viðey volcano and Stardals volcano . Both volcanoes partially formed Esja and the smaller mountains near Reykjavík and the hills on the islands and small peninsulas like Viðey and Kjarlarnes . Volcanic and glacial sediments outcrop at some places around Reykjavík, especially in Fossvogur . Iceland

6630-513: The great bulk of magma production in this part of Iceland and form the base of many other volcanic landforms . Olivine tholeiites constitute about 60% by volume of all post-glacial lava products on the Reykjanes Peninsula." The postglacial shield volcanoes are situated at the periphery of fissure systems . They erupted after the Weichselian glaciation. These shields are mostly circular in form, built up from pāhoehoe lavas and composed of

6732-486: The great majority of cases, the rock has a more typical mineral composition, with significant quartz, feldspars, or feldspathoids. Classification is based on the percentages of quartz, alkali feldspar, plagioclase, and feldspathoid out of the total fraction of the rock composed of these minerals, ignoring all other minerals present. These percentages place the rock somewhere on the QAPF diagram , which often immediately determines

6834-408: The highest-quality photojournalism in the world. In 2006, National Geographic began an international photography competition, with over eighteen countries participating. A map is the greatest of all epic poems. Its lines and colors show the realization of great dreams. Supplementing the articles, the magazine sometimes provides maps of the regions visited. National Geographic Maps (originally

6936-417: The history and varied uses of specific products such as a single metal, gem, food crop, or agricultural product, or an archaeological discovery. Occasionally an entire month's issue would be devoted to a single country, past civilization, a natural resource whose future is endangered, or other themes. In recent decades, the National Geographic Society has unveiled other magazines with different focuses. Whereas

7038-466: The intersection with the West volcanic zone of Iceland and South Iceland seismic zone , forming the Hengill triple junction. It has some rhyolite and andesite components. It is tectonically the current locus of accretion in the south of Iceland propagating southward at between 3.5–5 cm/year (1.4–2.0 in/year). Otherwise, the volcanic systems, because they are on top of a rift segment, show

7140-433: The larger crystals, called phenocrysts, grow to considerable size before the main mass of the magma crystallizes as finer-grained, uniform material called groundmass. Grain size in igneous rocks results from cooling time so porphyritic rocks are created when the magma has two distinct phases of cooling. Igneous rocks are classified on the basis of texture and composition. Texture refers to the size, shape, and arrangement of

7242-400: The magazine became outspoken on environmental issues . Until 2015, the magazine was completely owned and managed by the National Geographic Society . Since 2015, controlling interest has been held by National Geographic Partners. Topics of features generally concern geography , history , nature , science , and world culture . The magazine is well known for its distinctive appearance:

7344-429: The magazine featured lengthy expositions in the past, recent issues have included shorter articles. In addition to being well known for articles about scenery, history, and the most distant corners of the world, the magazine has been recognized for its book-like quality and the high standard of its photography. It was during the tenure of Society President Alexander Graham Bell and editor Gilbert H. Grosvenor (GHG) that

7446-483: The magazine has won a total of 24 National Magazine Awards. In May 2006, 2007, and 2011, National Geographic magazine won the American Society of Magazine Editors ' General Excellence Award in the over two million circulation category. In 2010, National Geographic Magazine received the top ASME awards for photojournalism and essay. In 2011, National Geographic Magazine received the top-award from ASME –

7548-460: The magazine to allow its photographers to use the so-called "miniature" 35 mm Leica cameras loaded with Kodachrome film over bulkier cameras with heavy glass plates that required the use of tripods . In 1959, the magazine started publishing small photographs on its covers, later becoming larger photographs. National Geographic photography quickly shifted to digital photography for both its printed magazine and its website. In subsequent years,

7650-559: The magazine's coverage of people around the world had been racist . Goldberg stated that the magazine ignored non-white Americans and showed different groups as exotic, thereby promoting racial clichés. This is a list of National Geographic milestones featuring turning points in the magazine's history including writing and photography assignments, design aspects, cartography and sponsored expeditions . Igneous rock Igneous rock ( igneous from Latin igneus  'fiery'), or magmatic rock ,

7752-419: The magazine's pages were photographs. The June 1985 cover portrait of a 12-year-old Afghan girl Sharbat Gula , shot by photographer Steve McCurry , became one of the magazine's most recognizable images. National Geographic Kids , the children's version of the magazine, was launched in 1975 under the name National Geographic World . At its peak in the late 1980s, the magazine had 12 million subscribers in

7854-399: The magma crystallizes, e.g., quartz feldspars, olivine , akermannite, Feldspathoids , magnetite , corundum , and so on, and the rocks are divided into groups strictly according to the relative proportion of these minerals to one another. This new classification scheme created a sensation, but was criticized for its lack of utility in fieldwork, and the classification scheme was abandoned by

7956-457: The majority of minerals will be visible to the naked eye or at least using a hand lens, magnifying glass or microscope. Plutonic rocks also tend to be less texturally varied and less prone to showing distinctive structural fabrics. Textural terms can be used to differentiate different intrusive phases of large plutons, for instance porphyritic margins to large intrusive bodies, porphyry stocks and subvolcanic dikes . Mineralogical classification

8058-697: The mineral grains or crystals of which the rock is composed. Texture is an important criterion for the naming of volcanic rocks. The texture of volcanic rocks, including the size, shape, orientation, and distribution of mineral grains and the intergrain relationships, will determine whether the rock is termed a tuff , a pyroclastic lava or a simple lava . However, the texture is only a subordinate part of classifying volcanic rocks, as most often there needs to be chemical information gleaned from rocks with extremely fine-grained groundmass or from airfall tuffs, which may be formed from volcanic ash. Textural criteria are less critical in classifying intrusive rocks where

8160-415: The naked eye are called phaneritic ; those with crystals too small to be seen are called aphanitic . Generally speaking, phaneritic implies an intrusive origin or plutonic, indicating slow cooling; aphanitic are extrusive or volcanic, indicating rapid cooling. An igneous rock with larger, clearly discernible crystals embedded in a finer-grained matrix is termed porphyry . Porphyritic texture develops when

8262-415: The potential for geothermal extraction at an economic level. The dykes underground reach up to 300 meters to the surface. Every tens of years, microearthquakes move the strike-slip plate boundaries. Since Iceland's settlement in the 9th century CE, the peninsula has undergone two periods of prolonged volcanism. The first, from 950 to 1240, culminated in the lengthy series of eruptions between 1210–1240 called

8364-752: The products of subaerial eruptions), hyaloclastite ridges (also called tindars ) which means elongated subglacially formed volcanic edifices of different sizes, and cone-like subglacial mounds (very rare). There are many hyaloclastite ridges, with most consisting of mixtures of pillow lavas , hyaloclastite and lapilli tuff . There are also elongated pillow structures, called pillow tindars . Examples on Reykjanes peninsula are Sveifluháls , Núpshlíðarháls [ˈnupsˌl̥iːðarˌhauls] , Undirhlíðar [ˈʏntɪrˌl̥iːðar̥] , Helgafell and Vífilsfell . The tuyas are often sorted according to their form (morphology) into flat-topped tuyas, elongated tuyas, conical tuyas and complex tuyas. The prominent igneous rock

8466-441: The ratio of potassium to sodium (so that potassic trachyandesites are latites and sodic trachyandesites are benmoreites). Some of the more mafic fields are further subdivided or defined by normative mineralogy , in which an idealized mineral composition is calculated for the rock based on its chemical composition. For example, basanite is distinguished from tephrite by having a high normative olivine content. Other refinements to

8568-403: The release of dissolved gases—typically water vapour, but also carbon dioxide . Explosively erupted pyroclastic material is called tephra and includes tuff , agglomerate and ignimbrite . Fine volcanic ash is also erupted and forms ash tuff deposits, which can often cover vast areas. Because volcanic rocks are mostly fine-grained or glassy, it is much more difficult to distinguish between

8670-473: The rock must be classified chemically. There are relatively few minerals that are important in the formation of common igneous rocks, because the magma from which the minerals crystallize is rich in only certain elements: silicon , oxygen , aluminium, sodium , potassium , calcium , iron, and magnesium . These are the elements that combine to form the silicate minerals , which account for over ninety percent of all igneous rocks. The chemistry of igneous rocks

8772-424: The rock type. In a few cases, such as the diorite-gabbro-anorthite field, additional mineralogical criteria must be applied to determine the final classification. Where the mineralogy of an volcanic rock can be determined, it is classified using the same procedure, but with a modified QAPF diagram whose fields correspond to volcanic rock types. When it is impractical to classify a volcanic rock by mineralogy,

8874-467: The rocks. However, in 1902, the American petrologists Charles Whitman Cross , Joseph P. Iddings , Louis V. Pirsson , and Henry Stephens Washington proposed that all existing classifications of igneous rocks should be discarded and replaced by a "quantitative" classification based on chemical analysis. They showed how vague, and often unscientific, much of the existing terminology was and argued that as

8976-435: The shape and size of the intrusive body and its relation to the bedding of the country rock into which it intrudes. Typical intrusive bodies are batholiths , stocks , laccoliths , sills and dikes . Common intrusive rocks are granite , gabbro , or diorite . The central cores of major mountain ranges consist of intrusive igneous rocks. When exposed by erosion, these cores (called batholiths ) may occupy huge areas of

9078-467: The significance of illustration was first emphasized, in spite of criticism from some of the Board of Managers who considered the many illustrations an indicator of an "unscientific" conception of geography. By 1910, photographs had become the magazine's trademark and Grosvenor was constantly on the search for "dynamical pictures" as Graham Bell called them, particularly those that provided a sense of motion in

9180-414: The summit of Litli-Hrútur and ended by the beginning of August 2023. As of June 2024, there have so far been five eruptions immediately north of Grindavík , with one partly occurring within the town's limits. Beginning in late October 2023, an intense series of earthquakes in and around Grindavík prompted the evacuation of the town, as a large underground magmatic intrusion indicated that an eruption in

9282-475: The top 16 kilometres (9.9 mi) of the Earth's crust by volume. Igneous rocks form about 15% of the Earth's current land surface. Most of the Earth's oceanic crust is made of igneous rock. Igneous rocks are also geologically important because: Igneous rocks can be either intrusive ( plutonic and hypabyssal) or extrusive ( volcanic ). Intrusive igneous rocks make up the majority of igneous rocks and are formed from magma that cools and solidifies within

9384-571: The varying number of systems in the literature is that geothermal areas, magnetic anomalies, eruptive centers, and geochemistry do not all align. Within the belt is a region of transition from the mainly extensional structure of the underwater Reykjanes Ridge of the Atlantic mid-oceanic ridge to the trans-tensional plate boundary in the Reykjanes Peninsula. These volcanic systems are: Eldey volcanic system (mostly submarine), Reykjanes volcanic system , Svartsengi volcanic system (often thought to be

9486-571: The way for a subscription model in addition to traditional newsstand sales. On May 1, 2008, National Geographic won three National Magazine Awards —an award solely for its written content—in the reporting category for an article by Peter Hessler on the Chinese economy ; an award in the photojournalism category for work by John Stanmeyer on malaria in the Third World ; and a prestigious award for general excellence. Between 1980 and 2011,

9588-586: The widely used Irvine-Barager classification, along with W.Q. Kennedy's tholeiitic series. By 1958, there were some 12 separate classification schemes and at least 1637 rock type names in use. In that year, Albert Streckeisen wrote a review article on igneous rock classification that ultimately led to the formation of the IUGG Subcommission of the Systematics of Igneous Rocks. By 1989 a single system of classification had been agreed upon, which

9690-490: The yellow-border magazine, which launched with the July 2007 issue of the magazine with an event in Beijing on July 10, 2007, and another event on December 6, 2007, in Beijing also celebrating the 29th anniversary of normalization of U.S.–China relations featuring former President Jimmy Carter . The mainland China version is one of the two local-language editions that bump the National Geographic logo off its header in favor of

9792-498: Was about 1.65 million, with its kids magazines separately achieving a circulation of about 500,000. The first issue of the National Geographic Magazine was published on September 22, 1888, nine months after the Society was founded. In the first issue, Gardiner Greene Hubbard writes, The "National Geographic Society" has been organized to "increase and defuse geographic knowledge", and the publication of

9894-445: Was expected by some by analogy to be similarly short-lived, but was only declared over on the 9th May. An eruption that started on 29th May finished on 22nd June 2024.An eruption started on 22 August 2024. National Geographic National Geographic (formerly The National Geographic Magazine , sometimes branded as Nat Geo ) is an American monthly magazine published by National Geographic Partners . The magazine

9996-656: Was filled with National Geographic maps. A National Geographic map of Europe is featured in the displays of the Winston Churchill museum in London showing Churchill's markings at the Yalta Conference where the Allied leaders divided post-war Europe. In 2001, National Geographic released an eight- CD-ROM set containing all its maps from 1888 to December 2000. Printed versions are also available from

10098-417: Was founded in 1888 as a scholarly journal, nine months after the establishment of the society, but is now a popular magazine. In 1905, it began including pictures, a style for which it became well-known. Its first color photos appeared in the 1910s. During the Cold War , the magazine committed itself to present a balanced view of the physical and human geography of countries beyond the Iron Curtain . Later,

10200-467: Was further revised in 2005. The number of recommended rock names was reduced to 316. These included a number of new names promulgated by the Subcommission. The Earth's crust averages about 35 kilometres (22 mi) thick under the continents , but averages only some 7–10 kilometres (4.3–6.2 mi) beneath the oceans . The continental crust is composed primarily of sedimentary rocks resting on

10302-471: Was heavily ice covered during the glaciations and even completely ice covered during parts of them. As a result, there are hundreds of subglacially formed volcanoes on Iceland. On Reykjanes Peninsula, glaciers were present until around 15,000 -12,000 years ago. Most subglacial edifices are thought to be Weichselian , with a few being older. The subglacial volcanoes can be identified according to type as tuyas (bigger edifices whose upper parts are covered by

10404-470: Was recorded on 1 March 2021. In addition, satellite pictures showed a pronounced uplift near the mountain Keilir . The magmatic dike to the southwest Keilir has a length of about 5 km. As of February 2024, there have so far been three eruptions on and around the mountain of Fagradalsfjall , in an uninhabited region some 15 km northeast of Grindavík . A volcanic eruption began at Fagradalsfjall on

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