Английская Википедия:Eldgjá

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Eldgjá (Шаблон:IPA-is, "fire canyon") is a volcano and a canyon in Iceland. Eldgjá is part of the Katla volcano; it is a segment of a Шаблон:Convert long chain of volcanic craters and fissure vents that extends northeast away from Katla volcano almost to the Vatnajökull ice cap. This fissure experienced a major eruption around 939 CE, which was the largest effusive eruption in recent history. It covered about Шаблон:Convert of land with Шаблон:Convert of lava from two major lava flows.

While Icelandic records about the effects of the eruption are sparse, paleoclimate proxies and historical records from China, Europe and the Islamic world describe widespread impacts on the Northern Hemisphere climate. The Eldgjá eruption produced a noticeable cooling of the climate, with resulting cold winters and food crises across Eurasia.

Geology

The interaction between the Mid-Atlantic Ridge and the Iceland hotspot has given rise to the stack of volcanic rocks that forms Iceland.Шаблон:Sfn Volcanoes on Iceland occur in four volcanic zones; the North Volcanic Zone in northeastern Iceland, the East Volcanic Zone in the southeast, the West Volcanic Zone in the southwest and the Snæfellsnes Volcanic Zone in the west. The first three of these form an upside-down Y structure, with each volcanic zone consisting of volcanic and tectonic lineaments that extend from north-northeast to south-southwest. These lineaments are dotted with volcanic edifices; Eldgjá lies in the East Volcanic ZoneШаблон:Sfn where there are no large shield volcanoes but numerous long fissures, including Laki.Шаблон:Sfn

Glaciation has influenced volcanic activity on Iceland, and the occurrence of large eruptions—such as the Шаблон:Convert Þjórsá Lava 8,600 years ago—in the early Holocene has been attributed to the unloading of the crust caused by the melting of Pleistocene ice. This process does not appear to have influenced the Eldgjá eruption.Шаблон:Sfn Eldgjá's eruption may have altered the shape of the Katla volcano and thus modified the behaviour of its glaciers.Шаблон:Sfn Glacial meltwater drains from Katla through several subglacial "tunnels", one of which coincides with the Eldgjá lineament,Шаблон:Sfn and geothermal activity on the lineament drives melting and the formation of cauldron-shaped depressions in the northeastern sector of the Myrdalsjökull Ice Cap.Шаблон:Sfn Moraines from the ice cap extend to the Eldgjá lineament.Шаблон:Sfn

The rocks erupted by Eldgjá are mainly alkali basalts, which have a uniform composition and contain phenocrysts of clinopyroxene, olivine, magnetite and plagioclase.Шаблон:Sfn There are also a small amount of tholeiitic rocks.Шаблон:Sfn The composition of Katla magmas shows evidence of long-term variations that appear to reflect a long-term cycle of its magmatic system. The Eldgjá eruption appears to be the beginning of one such cycle that continues to the present-day.Шаблон:Sfn There is evidence that eruptions of Eyjafjallajökull often precede eruptions at Katla, raising concerns after the 2010 eruption of Eyjafjallajökull that Katla may erupt again.Шаблон:Sfn

Geography and geomorphology

Файл:Eldgjá Volcanic Canyon Iceland (176657459).jpeg
Eldgjá

Шаблон:Lang means "fire gorge"Шаблон:Sfn and is a reference to the fissure that makes up the volcano;Шаблон:Sfn the term is also used with other Icelandic volcanoes.Шаблон:Sfn It is situated between Landmannalaugar and Kirkjubæjarklaustur.Шаблон:Sfn The Ófærufoss waterfall, a tourist attraction, lies in the main Eldgjá fissure.Шаблон:Sfn There used to be an oft-photographed natural bridge at Ófærufoss, which collapsed during the early 1990s.Шаблон:Sfn The northern part of Eldgjá, including Ófærufoss, and surrounding areas, have been a part of Vatnajökull National Park since 2011;Шаблон:SfnШаблон:Sfn the entire EldgjáШаблон:Sfn is since 2010 part of the Katla Geopark.Шаблон:Sfn There are information centres and picnic places at Eldgjá.Шаблон:Sfn

It consists of a northeast-southwest trending graben with explosion craters, about Шаблон:Convert long.Шаблон:Sfn It is Шаблон:Convert wide, Шаблон:Convert deep and part of a larger Шаблон:Convert long chain of offset grabens.Шаблон:Sfn The canyon is subdivided into four segments from southwest to northeast. The northeasternmost segment is known as Шаблон:LangШаблон:SfnШаблон:Sfn Шаблон:IPA-is); the name Eldgjá is usually only applied to the Шаблон:Convert long segmentШаблон:Sfn in the middle of the chain, but the 939 eruption also involved other segments.Шаблон:Sfn The canyon extends between the Öldufellsjökull glacierШаблон:Sfn Шаблон:IPA-is of the Myrdalsjökull Ice Cap (the ice cap covers part of the fissureШаблон:Sfn) in the southwest, stretches across mountainous terrainШаблон:Sfn and almost reaches the Vatnajökull Ice Cap to the northeast at Stakafell Шаблон:IPA-is mountain.Шаблон:Sfn It is the longest volcanic fissure in Iceland.Шаблон:Sfn

Ground fractures, hornitos, normal faults, lava lakes, pyroclastic cones and spatter ramparts make up the Eldgjá lineament;Шаблон:SfnШаблон:Sfn the cones form alignmentsШаблон:Sfn and have red-to-gray colours and consist of alternating layers of lava, scoria and spatter,Шаблон:Sfn with the scoria and spatter sometimes fused together until they resemble lava flows.Шаблон:Sfn There is evidence that the Eldgjá fissure existed before the 930s eruption.Шаблон:Sfn Ongoing activity of the fissure can be seen in the form of ground deformation.Шаблон:Sfn

The Eldgjá is part of the wider Katla volcano, which features a series of fissures, as well as a caldera covered by the Myrdalsjökull Ice Cap.Шаблон:Sfn To the northeast, the lineament runs Шаблон:Convert away from and parallel to that of the 1783-1784 CE Laki eruption fissure,Шаблон:SfnШаблон:Sfn which is part of the Grimsvötn volcano.Шаблон:Sfn There are other volcanic centres in the area, some of which had large fissure-fed eruptions within historical memory.Шаблон:Sfn

10th century eruption

The Eldgjá eruption was the largest Holocene eruption of the Katla system,Шаблон:Sfn the largest effusive eruption on Earth during the last few millennia,Шаблон:Sfn and the only historical eruption of this volcano outside of its caldera.Шаблон:Sfn It involved a Шаблон:Convert long area of the volcano, including both the central caldera and the Eldgjá lineament.Шаблон:Sfn During the course of the eruption, about 16 episodes of Plinian or subplinian eruptions took place, producing plumes with heights of Шаблон:Convert.Шаблон:Sfn These episodes did not occur simultaneously across the entire length of the Eldgjá; rather the eruption commenced in the caldera and propagated northeastward.Шаблон:Sfn Intense lava fountaining, explosive eruptions and the effusion of lava took place.Шаблон:Sfn

The eruption has been linked to an episode of active continental rifting in the 930s,Шаблон:Sfn during which the injection of magma into dykes led to deformation of the ground surfaceШаблон:Sfn and the evacuation of magmas from the Katla magmatic system.Шаблон:Sfn Part of this magma entered into the Katla magma chamber, triggering the release of silicic magmas that form part of the tephra and were at least for some time erupted simultaneously with basaltic magmas.Шаблон:Sfn

Dating

The Eldgjá eruption took place in the 930s, but its exact date has long been uncertain. Early research put its beginning during 934-938.Шаблон:Sfn Later research published in 2015 indicated that it began in 939 and likely ended in 940,Шаблон:Sfn but may have continued for several years more.Шаблон:Sfn Further confusion is created by the fact that the Eldgjá eruption occurred only seven years before the Millennium Eruption of Paektu Mountain on the China–Korea border.Шаблон:Sfn Some climatic effects attributed to the Eldgjá eruption may actually have resulted from the Paektu eruption.Шаблон:Sfn That eruption, in 946 CE, may have produced only a small amount of sulfate aerosols,Шаблон:SfnШаблон:Sfn far less than Eldgjá.Шаблон:SfnШаблон:Sfn A tephra layer at Katla originally attributed to a 1000 CE eruption is now considered to be part of the Eldgjá eruption.Шаблон:Sfn

Products

The eruption produced two fields of (mostly pahoehoeШаблон:Sfn) lava flowsШаблон:Sfn emanating from the southern and central sectors of the Eldgjá fracture.Шаблон:Sfn Flowing through lava tubes,Шаблон:Sfn the lava flows were channelled down river valleys and gorges and eventually reached the sea. They cover an area of Шаблон:Convert and with a volume of Шаблон:Convert constitute the largest lava flows of the last 1,100 years.Шаблон:Sfn The lavas buried traces of earlier eruptionsШаблон:Sfn and obstructed river valleys, forcing the rivers to change their course, and altered the terrain so that large parts of the plains east of Katla can no longer be reached by jökulhlaups (glacier meltwater flood) from the volcano.Шаблон:Sfn Rootless cones such as Шаблон:LangШаблон:Sfn Шаблон:IPA-is and Iceland's largest complex at Шаблон:Lang Шаблон:IPA-is are linked to lava flows attributed to Eldgjá,Шаблон:Sfn although an older date for the latter lavas is possible.Шаблон:Sfn Later eruptions from Laki have buried many of the northeastern Eldgjá lava flows.Шаблон:Sfn

About Шаблон:Convert dense rock equivalentШаблон:Sfn of mostly basaltic ejectaШаблон:Sfn became Шаблон:Convert of tephra, which was emplaced mainly south and southeast from Eldgjá.Шаблон:Sfn The tephra was formed through alternatingШаблон:Sfn magmatic and phreatomagmatic processes, and is more complex than common Katla tephras.Шаблон:Sfn External water (such as from ice melt) did not play a major role in driving the explosivity of the eruption.Шаблон:Sfn Part of the eruption occurred underneath the Katla ice cap; this part also gave rise to the Kriki Шаблон:IPA-is hyaloclastite on the eastern side of the ice cap,Шаблон:Sfn a product of an interaction between lava and ice.Шаблон:Sfn The Eldgjá eruption was accompanied by jökulhlaups from the northern, eastern and perhaps also southern part of Myrdalsjökull Ice CapШаблон:Sfn but the burial of its deposits by later glacier meltwater floods and lavas make it difficult to trace the precise extent of the flood.Шаблон:Sfn

Tephra and aerosol emissions

Both tephra layers and sulfate layers linked to the Eldgjá eruption occur in Greenland, where they have been recorded from ice coresШаблон:Sfn in the form of layers where the ice contains more acids,Шаблон:Sfn salts and tiny glass shards.Шаблон:Sfn Tephra layers from the eruption have been used to date lake sedimentsШаблон:Sfn and ice cores in the Northern Hemisphere,Шаблон:Sfn volcanic eruptions at EyjafjallajökullШаблон:Sfn and other Icelandic volcanoes,Шаблон:Sfn glacier advances on the island,Шаблон:Sfn and events in Viking Age Iceland.Шаблон:Sfn

Large volcanic eruptions can produce veils of aerosols in the atmosphere from sulfur dioxide, which reduce the amount of sunlight reaching Earth's surface and alter its climate.Шаблон:Sfn Eldgjá produced about Шаблон:Val of sulfur dioxide,Шаблон:Sfn more than that of other well-known historical eruptions (such as Laki in 1783, Tambora in 1815 and Huaynaputina in 1600).Шаблон:Sfn The Eldgjá eruption is the largest volcanic atmospheric pollution event of the last several millenniaШаблон:Sfn and traces of platinum erupted by the volcano have been found across the Western Hemisphere,Шаблон:Sfn where they have been used to date archaeological sites.Шаблон:Sfn

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The climate impact of the Eldgjá has been recorded in cave deposits,Шаблон:Sfn historical reports, ice cores, tree rings and other environmental recordsШаблон:Sfn potentially as far south as Australia.Шаблон:Sfn Tree rings suggest a cooling of about Шаблон:Convert in the Northern Hemisphere during 940 CE, most pronounced in Alaska, the Canadian Rocky Mountains, Central Asia, Central Europe and Scandinavia; in Canada and Central Asia it lasted until 941 CE.Шаблон:Sfn Volcanic aerosols often weaken the monsoons that feed the Nile River in Africa; during 939 the water levels of the river were unusually low.Шаблон:Sfn Conversely, increased flooding in Europe after the Eldgjá and other volcanic eruptions during the 10th century have been correlated to declines in Poland's Alnus trees.Шаблон:Sfn

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Human impacts

Even though Iceland was already settled at that time and the impacts of the eruption were severe,Шаблон:Sfn there are no contemporary historical records of the eruption. Anecdotal reports are recorded in the Book of Settlements, which was written about 200 years later.Шаблон:Sfn Events in the poem Völuspá may record the eruptionШаблон:Sfn or another eruption of Katla.Шаблон:Sfn According to the Book of Settlements, lava flows forced settlers east of Katla off their land;Шаблон:Sfn two settlements or farms belonging to at least two settlements in the Álftaver Шаблон:IPA-is area southeast of Katla had to be abandoned due to damage from lava flowsШаблон:Sfn and sources of the 12th century define it a "wasteland".Шаблон:Sfn Tephra covered an area of about Шаблон:Convert on Iceland; of these, Шаблон:Convert were covered with over Шаблон:Convert of tephra and had to be abandoned, while Шаблон:Convert received a tephra cover exceeding Шаблон:Convert and suffered heavy damage as a result.Шаблон:Sfn The events and impact of the eruption may have stopped the settlement of the islandШаблон:SfnШаблон:Sfn and could have played a role in stimulating the Christianization of Iceland.Шаблон:Sfn

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Unlike the local impacts on Iceland, the effects of the Eldgjá eruption on Europe appear in the historical record.Шаблон:Sfn Darkened skies were reported from Germany, Ireland, Italy, Portugal and SpainШаблон:Sfn although the interpretation of contemporary reports as referencing atmospheric phenomena linked to the Eldgjá eruption is controversial.Шаблон:SfnШаблон:Sfn Reportedly, winters in Europe and China between 939-942 were severe, with the sea and canals freezing, while droughts occurred during the summer months. Food crises reported in China, the Maghreb, the Levant and Western Europe at that time have been linked to the Eldgjá eruption.Шаблон:Sfn More tentatively, the downfall of the Later Jin DynastyШаблон:Sfn and locust plagues in China,Шаблон:Sfn a decrease of human activity on IrelandШаблон:Sfn and rebellions in Japan have been connected to the Eldgjá eruption.Шаблон:Sfn

Impacts of a repeat

Large fissure-fed effusive eruptions in Iceland reoccur every few centuries. The much smaller (Шаблон:Val) 2010 eruption of Eyjafjallajökull caused worldwide disruptions of air travel, with economic losses of over $1 billion for airlines alone,Шаблон:Sfn because volcanic ash can interfere with the operation of airplane engines. Additional hazards of a widespread aerosol layer are its corrosive effects on equipment, decreased visibility leading to accidents on the sea, as well as health hazards resulting from the aerosols. The impact could extend to North Africa.Шаблон:Sfn

See also

References

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Sources

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External links

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