Eldgjá
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Eldgjá ({{#invoke:IPA|main}}, "fire canyon") is a volcano and a canyon in Iceland. Eldgjá is part of the Katla volcano; it is a segment of a Template: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 Template:Convert of land with Template: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’s climate. The Eldgjá eruption produced a noticeable cooling of the climate, with resulting cold winters and food crises across Eurasia.
GeologyEdit
The interaction between the Mid-Atlantic Ridge and the Iceland hotspot has given rise to the stack of volcanic rocks that forms Iceland.Template: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 ZoneTemplate:Sfn where there are no large shield volcanoes but numerous long fissures, including Laki.Template:Sfn
Glaciation has influenced volcanic activity on Iceland, and the occurrence of large eruptions—such as the Template: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.Template:Sfn Eldgjá's eruption may have altered the shape of the Katla volcano and thus modified the behaviour of its glaciers.Template:Sfn Glacial meltwater drains from Katla through several subglacial "tunnels", one of which coincides with the Eldgjá lineament,Template: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.Template:Sfn Moraines from the ice cap extend to the Eldgjá lineament.Template:Sfn
The rocks erupted by Eldgjá are mainly alkali basalts, which have a uniform composition and contain phenocrysts of clinopyroxene, olivine, magnetite and plagioclase.Template:Sfn There are also a small amount of tholeiitic rocks.Template: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.Template: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.Template:Sfn
Geography and geomorphologyEdit
{{#invoke:Lang|lang}} means "fire gorge"Template:Sfn and is a reference to the fissure that makes up the volcano;Template:Sfn the term is also used with other Icelandic volcanoes.Template:Sfn It is situated between Landmannalaugar and Kirkjubæjarklaustur.Template:Sfn The Ófærufoss waterfall, a tourist attraction, lies in the main Eldgjá fissure.Template:Sfn There used to be an oft-photographed natural bridge at Ófærufoss, which collapsed during the early 1990s.Template:Sfn The northern part of Eldgjá, including Ófærufoss, and surrounding areas, have been a part of Vatnajökull National Park since 2011;Template:SfnTemplate:Sfn the entire EldgjáTemplate:Sfn is since 2010 part of the Katla Geopark.Template:Sfn There are information centres and picnic places at Eldgjá.Template:Sfn
It consists of a northeast-southwest trending graben with explosion craters, about Template:Convert long.Template:Sfn It is Template:Convert wide, Template:Convert deep and part of a larger Template:Convert long chain of offset grabens.Template:Sfn The canyon is subdivided into four segments from southwest to northeast. The northeasternmost segment is known as {{#invoke:Lang|lang}}Template:SfnTemplate:Sfn {{#invoke:IPA|main}}); the name Eldgjá is usually only applied to the Template:Convert long segmentTemplate:Sfn in the middle of the chain, but the 939 eruption also involved other segments.Template:Sfn The canyon extends between the Öldufellsjökull glacierTemplate:Sfn {{#invoke:IPA|main}} of the Myrdalsjökull Ice Cap (the ice cap covers part of the fissureTemplate:Sfn) in the southwest, stretches across mountainous terrainTemplate:Sfn and almost reaches the Vatnajökull Ice Cap to the northeast at Stakafell {{#invoke:IPA|main}} mountain.Template:Sfn It is the longest volcanic fissure in Iceland.Template:Sfn
Ground fractures, hornitos, normal faults, lava lakes, pyroclastic cones and spatter ramparts make up the Eldgjá lineament;Template:SfnTemplate:Sfn the cones form alignmentsTemplate:Sfn and have red-to-gray colours and consist of alternating layers of lava, scoria and spatter,Template:Sfn with the scoria and spatter sometimes fused together until they resemble lava flows.Template:Sfn There is evidence that the Eldgjá fissure existed before the 930s eruption.Template:Sfn Ongoing activity of the fissure can be seen in the form of ground deformation.Template: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.Template:Sfn To the northeast, the lineament runs Template:Convert away from and parallel to that of the 1783-1784 CE Laki eruption fissure,Template:SfnTemplate:Sfn which is part of the Grimsvötn volcano.Template:Sfn There are other volcanic centres in the area, some of which had large fissure-fed eruptions within historical memory.Template:Sfn
10th century eruptionEdit
The Eldgjá eruption was the largest Holocene eruption of the Katla system,Template:Sfn the largest effusive eruption on Earth during the last few millennia,Template:Sfn and the only historical eruption of this volcano outside of its caldera.Template:Sfn It involved a Template:Convert long area of the volcano, including both the central caldera and the Eldgjá lineament.Template:Sfn During the course of the eruption, about 16 episodes of Plinian or subplinian eruptions took place, producing plumes with heights of Template:Convert.Template:Sfn These episodes did not occur simultaneously across the entire length of the Eldgjá; rather the eruption commenced in the caldera and propagated northeastward.Template:Sfn Intense lava fountaining, explosive eruptions and the effusion of lava took place.Template:Sfn
The eruption has been linked to an episode of active continental rifting in the 930s,Template:Sfn during which the injection of magma into dykes led to deformation of the ground surfaceTemplate:Sfn and the evacuation of magmas from the Katla magmatic system.Template: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.Template:Sfn Other volcanoes in Iceland such as Bárðarbunga, GrimsvötnTemplate:Sfn and Reykjanes peninsula erupted at the same time as Eldgjá.Template:Sfn
DatingEdit
The Eldgjá eruption took place in the 930s, but its exact date had long been uncertain. Early research put its beginning during 934-938.Template:Sfn Later research published in 2015 indicated that it began in 939 and likely ended in 940,Template:Sfn but may have continued for several years more.Template:Sfn Further confusion had been created because the Eldgjá eruption occurred only seven years before the Millennium Eruption of Paektu Mountain on the China–Korea border.Template:Sfn Some climatic effects attributed to the Eldgjá eruption may actually have resulted from the Paektu eruption.Template:Sfn That eruption, in 946 CE, may have produced only a small amount of sulfate aerosols,Template:SfnTemplate:Sfn far less than Eldgjá.Template:SfnTemplate:Sfn A tephra layer at Katla originally attributed to a 1000 CE eruption is now considered to be part of the Eldgjá eruption.Template:Sfn
ProductsEdit
The eruption produced two fields of (mostly pahoehoeTemplate:Sfn) lava flowsTemplate:Sfn emanating from the southern and central sectors of the Eldgjá fracture.Template:Sfn Flowing through lava tubes,Template:Sfn the lava flows were channelled down river valleys and gorges and eventually reached the sea. They cover an area of Template:Convert and with a volume of Template:Convert constitute the largest lava flows of the last 1,100 years.Template:Sfn The lavas buried traces of earlier eruptionsTemplate: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.Template:Sfn Rootless cones such as {{#invoke:Lang|lang}}Template:Sfn {{#invoke:IPA|main}} and Iceland's largest complex at {{#invoke:Lang|lang}} {{#invoke:IPA|main}} are linked to lava flows attributed to Eldgjá,Template:Sfn although an older date for the latter lavas is possible.Template:Sfn Later eruptions from Laki have buried many of the northeastern Eldgjá lava flows.Template:Sfn
About Template:Convert dense rock equivalentTemplate:Sfn of mostly basaltic ejectaTemplate:Sfn became Template:Convert of tephra, which was emplaced mainly south and southeast from Eldgjá.Template:Sfn The tephra was formed through alternatingTemplate:Sfn magmatic and phreatomagmatic processes, and is more complex than common Katla tephras.Template:Sfn External water (such as from ice melt) did not play a major role in driving the explosivity of the eruption.Template:Sfn Part of the eruption occurred underneath the Katla ice cap; this part also gave rise to the Kriki {{#invoke:IPA|main}} hyaloclastite on the eastern side of the ice cap,Template:Sfn a product of an interaction between lava and ice.Template:Sfn The Eldgjá eruption was accompanied by jökulhlaups from the northern, eastern and perhaps also southern part of Myrdalsjökull Ice CapTemplate: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.Template:Sfn There is evidence that the inner structure of Katla was permanently altered by the Eldgjá eruption, as eruption rate decreased compared to the rate in the previous two millennia and there have been no meltwater floods on the southern or western side of the volcano since the event.Template:Sfn
Tephra and aerosol emissionsEdit
Both tephra layers and sulfate layers linked to the Eldgjá eruption occur in Greenland, where they have been recorded from ice coresTemplate:Sfn in the form of layers where the ice contains more acids,Template:Sfn salts and tiny glass shards.Template:Sfn Tephra layers from the eruption have been used to date lake sedimentsTemplate:Sfn and ice cores in the Northern Hemisphere,Template:Sfn volcanic eruptions at EyjafjallajökullTemplate:Sfn and other Icelandic volcanoes,Template:Sfn glacier advances on the island,Template:Sfn and events in Viking Age Iceland.Template: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.Template:Sfn Eldgjá produced about Template:Val of sulfur dioxide,Template:Sfn more than that of other well-known historical eruptions (such as Tambora in 1815 and Huaynaputina in 1600)Template:Sfn but possibly less than Laki in 1783, as phreatomagmatic activity would have scavenged sulfate from the eruption column.Template:Sfn The Eldgjá eruption is the largest volcanic atmospheric pollution event of the last several millenniaTemplate:Sfn and traces of platinum erupted by the volcano have been found across the Western Hemisphere,Template:Sfn where they have been used to date archaeological sites.Template:Sfn
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We looked at the sun, it did not have any strength, neither light nor heat. But we saw the sky and the colour [or ‘appearance’] of it changed, as though viscous. And others said that they saw the sun as though half{{#if:Annales Casinates, ItalyTemplate:Sfn|{{#if:|}}
— {{#if:|, in }}Template:Comma separated entries}}
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The climate impact of the Eldgjá has been recorded in cave deposits,Template:Sfn historical reports, ice cores, tree rings and other environmental recordsTemplate:Sfn potentially as far south as Australia.Template:Sfn Tree rings suggest a cooling of about Template: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.Template: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.Template: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.Template:Sfn Some climate impacts attributed to Eldgjá might have been caused by simultaneous eruptions of other volcanoes, such as Ceboruco in Mexico.Template:Sfn
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The sun was the colour of blood from the beginning of day to midday on the following day{{#if:Chronicon Scotorum,Template:Sfn may be a sighting of the volcanic plume from the Eldgjá eruptionTemplate:Sfn|{{#if:|}}
— {{#if:|, in }}Template:Comma separated entries}}
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Human impactsEdit
Even though Iceland was already settled at that time and the impacts of the eruption were severe,Template: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.Template:Sfn Events in the poem Völuspá may record the eruptionTemplate:Sfn or another eruption of Katla.Template:Sfn According to the Book of Settlements, lava flows forced settlers east of Katla off their land;Template:Sfn two settlements or farms belonging to at least two settlements in the Álftaver {{#invoke:IPA|main}} area southeast of Katla had to be abandoned due to damage from lava flowsTemplate:Sfn and sources of the 12th century define it a "wasteland".Template:Sfn Tephra covered an area of about Template:Convert on Iceland; of these, Template:Convert were covered with over Template:Convert of tephra and had to be abandoned, while Template:Convert received a tephra cover exceeding Template:Convert and suffered heavy damage as a result.Template:Sfn The events and impact of the eruption may have stopped the settlement of the islandTemplate:SfnTemplate:Sfn and could have played a role in stimulating the Christianization of Iceland.Template:Sfn However, it is possible that Iceland's population at the time was more resilient than during the 18th century and thus the Eldgjá event had less impact than the Laki eruption.Template:Sfn
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The settler Molda-Gnúpur took possession of land in Álftaver district between the rivers Kúðafjót and Eyjará. At that time a large lake was there and good swan hunting. He sold part of his settlement to many newcomers. The area became populated before it was overrun by jarðeldur (an earth fire), then they fled west to Höfðabrekka and set up a camp at Tjaldavellir{{#if:Landnámabók pp. 328–331; Translation in Pálsson and Edwards 1972, Chap. 86Template:Sfn|{{#if:|}}
— {{#if:|, in }}Template:Comma separated entries}}
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Unlike the local impacts on Iceland, the effects of the Eldgjá eruption on Europe appear in the historical record.Template:Sfn Darkened skies were reported from Germany, Ireland, Italy, Portugal and SpainTemplate:Sfn although the interpretation of contemporary reports as referencing atmospheric phenomena linked to the Eldgjá eruption is controversial.Template:SfnTemplate: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.Template:Sfn More tentatively, the downfall of the Later Jin DynastyTemplate:Sfn and locust plagues in China,Template:Sfn epidemics of animal diseases in EuropeTemplate:Sfn and a decrease of human activity on IrelandTemplate:Sfn and rebellions in Japan have been connected to the Eldgjá eruption.Template:Sfn
Impacts of a repeatEdit
Large fissure-fed effusive eruptions in Iceland reoccur every few centuries. The much smaller (Template:Val) 2010 eruption of Eyjafjallajökull caused worldwide disruptions of air travel, with economic losses of over $1 billion for airlines alone,Template: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.Template:Sfn
See alsoEdit
- Geography of Iceland
- Glacial lake outburst flood
- Iceland hotspot
- Iceland plume
- List of glaciers of Iceland
- List of lakes of Iceland
- Timeline of volcanism on Earth
- Volcanism of Iceland
ReferencesEdit
SourcesEdit
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