Hekla 113726 226057795 2008-07-16T17:14:43Z Ben MacDui 2259739 Reverted 1 edit by [[Special:Contributions/92.237.109.4|92.237.109.4]]. ([[WP:TW|TW]]) {{Infobox Mountain | Name = Hekla | Photo = Hekla and horse.jpg | Caption = Hekla and an [[Icelandic Horse]] | Elevation = {{convert|1488|m|ft|0}} | Location = [[Iceland]] | Range = | Prominence = | Coordinates = {{coord|63|59|N|19|42|W|type:mountain|display=inline,title}} | Type=[[Stratovolcano]] | Age= | Last eruption=[[February 28]] [[2000]] | First ascent = Eggert Ólafsson, Bjarni Pálsson, [[June 20]] [[1750]]<ref name="HANVp19">Thorarinsson, ''Hekla, A Notorious Volcano'', p. 19</ref> | Easiest route = | Translation = Hooded | Language = English | Pronunciation = }} {{Location map|Iceland|label=Hekla |lon_dir=W|lat_dir=N|lat_deg=63|lat_min= 59|lon_deg= 19|lon_min = 42|position=right|width=300|float=right|caption=Hekla on the map of Iceland}} '''Hekla''' is a [[stratovolcano]] located in the south of [[Iceland]] with a height of {{convert|1488|m|ft|0}}. Hekla is Iceland's most active [[volcano]]; over 20 eruptions have occurred in and around the volcano since [[874]]. During the [[Middle Ages]], Icelanders called the volcano the "Gateway to [[Hell]]." Hekla is part of a volcanic ridge, {{convert|40|km|mi|0|abbr=off}} long. However, the most active part of this ridge, a fissure about {{convert|5.5|km|mi|1|abbr=on}} long named ''Heklugjá'', is considered to be the volcano Hekla proper. Hekla looks rather like an overturned boat, with its keel being in fact a series of craters, two of which are generally the most active. The volcano's frequent large eruptions have covered much of Iceland with [[tephra]] and these layers can be used to date eruptions of Iceland's other volcanos. 10% of the tephra produced in Iceland in the last thousand years has come from Hekla, amounting to 5&nbsp;km<sup>3</sup>. The volcano has produced one of the largest volumes of lava of any in the world in the last millennium, around 8&nbsp;km<sup>3</sup>. ==Reputation== After the eruption of 1104 stories, which were probably spread deliberately through Europe by [[Cistercian]] monks, told that Hekla was the gateway to Hell. The Cistercian monk Herbert of [[Clairvaux]] wrote in his ''De Miraculis'' without naming Hekla {{Quote|The renowned fiery cauldron of [[Sicily]], which men call Hell's chimney... that cauldron is affirmed to be like a small furnace compared to this enormous inferno.<ref name="HANVp5">Thorarinsson, ''Hekla, A Notorious Volcano'', p. 5</ref>|Herbert of Clairvaux|''Liber De Miraculis'', 1180}} A poem by the monk Benedeit from circa 1120 about the voyages of [[Saint Brendan]] mentions Hekla as the prison of [[Judas Iscariot|Judas]]. The ''Flatey Book Annal'' wrote of the 1341 eruption that people saw large and small birds flying in the mountain's fire which were taken to be souls.<ref name="HANVp6">Thorarinsson, ''Hekla, A Notorious Volcano'', p. 6</ref> In the 16th century [[Caspar Peucer]] wrote that the Gates of Hell could be found in "the bottomless abyss of Hekla Fell". The belief that Hekla was the gate to Hell persisted until the 1800s.<ref name="HANVp5" /> There is still a legend that witches gather on Hekla for [[Easter]].<ref name="SI" /> ==Name== In [[Icelandic language|Icelandic]] ''Hekla'' is the word for a short hooded cloak which may relate to the frequent cloud cover on the summit. An early [[Latin]] source refers to the mountain as ''Mons [[chasuble|Casule]]''.<ref name="HANVp7">Thorarinsson, ''Hekla, A Notorious Volcano'', p. 7</ref> ==Geology== Hekla has a morphological type between that of a [[fissure vent|crater row]] and [[stratovolcano]] (built from mixed lava and tephra eruptions) sited at a rift-[[Transform fault|transform]] junction in the area where the south Iceland seismic zone and eastern volcanic zone meet. Hekla is situated on a long volcanic ridge of which the 5.5&nbsp;km ''Heklugjá'' fissure is considered Hekla proper. This fissure opens along its entire length during major eruptions and is fed by a [[magma chamber|magma reservoir]] estimated to have a top 4&nbsp;km below the surface with [[centroid]] 2.5&nbsp;km lower. The tephra produced by its eruptions is high in [[fluorine]] which is poisonous to animals. Hekla's basaltic [[andesite]] [[lava]] generally has a [[Silicon dioxide|SiO<sub>2</sub>]] content of over 54%, compared to the 45-50% of other nearby [[Tholeiitic basalt|transitional alkaline basalt]] eruptions (see [[TAS classification]]).<ref name="HANVp18" /><ref name="UoI_Deform" /><ref name="GVPHS">{{cite web |url=http://www.volcano.si.edu/world/volcano.cfm?vnum=1702-07= |title=Hekla » Summary |accessdate=2007-10-07 |format=HTML |work=Global Volcanism Project }}</ref><ref>{{cite web |url=http://hraun.vedur.is/ja/skyrslur/contgps/node20.html |title=Hekla eruption 2000 |accessdate=2008-01-19 |publisher=The Icelandic Meteorological Office}}</ref> [[Phenocryst]]s in Hekla's lava can contain [[plagioclase]], [[pyroxene]], [[titanomagnetite]], [[olivine]] & [[apatite]].<ref name="HANVp39to58" />. When not erupting Hekla is often covered with snow and small [[glacier]]s, it is also unusually aseismic with [[Earthquake|activity]] only starting 30-80&nbsp;minutes before an eruption.<ref name="UoI_Seismo">{{cite web |url=http://www.earthice.hi.is/page/ies_heklaseismicity |title=Hekla Seismicity |accessdate=2008-01-14 |format=html |publisher=University of Iceland, Institute of Earth Sciences}}</ref> Hekla is closely studied today for parameters such as [[Strain (materials science)|strain]], tilt, [[deformation]] and other movement and seismic activity.<ref name="UoI_Deform">{{cite web |url=http://www.earthice.hi.is/page/ies_hekladeformation |title=Hekla Deformation |accessdate=2008-01-14 |format=html |publisher=University of Iceland, Institute of Earth Sciences}}</ref> Earthquakes in the volcano's vicinity are generally below [[moment magnitude scale|magnitude]] 2 while it is dormant and magnitude 3 when erupting.<ref name="UoI_Seismo" /> == Eruption History == [[Image:Hekla hraun.jpg|thumb|right|300px|Hekla beyond a field of volcanic ash]] The earliest recorded eruption of Hekla took place in [[1104]], since then there have been between twenty and thirty considerable eruptions, with the mountain sometimes remaining active for periods of six years with little pause. Eruptions in Hekla are extremely varied and difficult to predict. Some are very short (a week to ten days) whereas others can stretch into months and years (the 1947 eruption started [[March 29]] [[1947]] and ended April 1948). But there is a general correlation: the longer Hekla goes dormant, the larger and more catastrophic its opening eruption will be.<ref>{{cite journal | author = Sigurdur Þórarinsson | authorlink = Sigurdur Thorarinsson | title = The eruption of Hekla in historical times. Vol. I: The eruption of Hekla 1947–48 | year = 1967 | journal = Soc. Sci. Islandica| volume = 38 | pages = p. 1–183 | publisher = }}</ref> The most recent eruption was on [[February 26]] [[2000]]. == Historical and prehistoric eruptions == [[Image:362839380 4fa8923421 o.jpg|thumb|right|300px|Steam at the summit of Hekla]] One of the largest [[Holocene]] eruptions was the [[Hekla 3 eruption|Hekla 3]] (or H<sub>3</sub>) eruption of ([[950 BC]]<ref name="GVPHEH">{{cite web | title = Hekla - Eruptive History | work = Global Volcanism Program | publisher = [[Smithsonian Institution]] | url = http://www.volcano.si.edu/world/volcano.cfm?vnum=1702-07=&volpage=erupt | accessdate = 2008-07-07}}</ref>) ([[1159 BC]]<ref name="IACIB" />) which threw about 7.3&nbsp;km<sup>3</sup><ref name="gvp">{{VNUM|1=1702-07=}}</ref> of [[volcanic rock]] into the atmosphere and very likely caused cooling of global temperatures for a few years afterwards. Traces of this eruption have been identified in [[Scotland|Scottish]] [[peat bog]]s, and in [[Ireland]] a study of [[dendrochronology|tree rings dating]] from this period has shown negligible [[Growth ring|tree ring]] growth for a decade.<ref name="IACIB">{{cite book | title = Iron Age Communities in Britain | id = ISBN 0415347793 | pages = 256 | last = Cunliffe | first = Barry | date=2005 | Edition = 4th | publisher = Routledge}}Pg 68</ref> {| class="wikitable" |+ Main eruptions in prehistoric times:{{ref label|Historic_Eruptions|A|A}} |- ! Eruption ! Year |- | H-5 | 5050 BC |- | H-Sv | 3900 BC<ref name="Selsund">{{cite web |url=http://www.theochem.org/Raunvisindathing06/abstracts/gsv-en.pdf |title=The Selsund Pumice and the old Hekla crater |accessdate=2008-07-07 |author=Guðrún Sverrisdóttir |coauthors=Níels Óskarsson, Árný E. Sveinbjörnsdóttir, Rósa Ólafsdóttir |publisher=Institute of earth sciences, Reykjavik}}</ref> |- | H-4 | 2310±20 BC |- | H-3 | 950 BC |} {{note label|Historic _Eruptions|A|A}}Unless otherwise stated eruption dates are from Global Volcanism Program<ref name="GVPHEH" />, other sources disagree.<ref name="VAAEC">{{cite web |url=http://www.barry.warmkessel.com/barry/7910.html |title=Lecture two: Climatic responses to volcanic eruptions |accessdate=2007-10-24 |date= |work=Volcanic Activity and Environmental Change |publisher=(orig.) University Of Wales}}</ref><ref name="IACIB" /><ref name="Selsund" /> Hekla 3,4 and 5 produced huge amounts of rhyolitic ash and tephra, covering 80% of Iceland<ref>{{cite web |url=http://www.theochem.org/Raunvisindathing06/abstracts/gul-en.pdf |title=Tephra layers as part of Holocene volcanic history |accessdate=2007-10-24 |author=Guðrún Larsen |work=Natural Science Symposium in Reykjavík 2006 |date=March 3,4 2006}}</ref> and providing a useful date marker in soil profiles in other parts of Europe such as [[Orkney]],<ref>{{cite web |url=http://www.fettes.com/Orkney/tephra.htm |title=Tephra on Orkney |accessdate=2007-10-24}}</ref> [[Scandinavia]]<ref name="SI">{{cite web |url=http://www.south.is/displayer.asp?Page=222&p=ASP\Pg222.asp |title=Hekla - The queen of the Icelandic volcanoes |accessdate=2007-10-24 |author=South Iceland}}</ref> and elsewhere.<ref>{{cite web |url=http://www.tephrabase.org/ |title=Tephrabase}}</ref> H<sub>3</sub> and H<sub>4</sub> produced the largest layers of tephra in Iceland since the last [[Ice Age]].<ref name="HANVp11" /> ===1104 (H1)=== Hekla had been dormant for at least 250 years when it erupted explosively in 1104 (probably in the autumn), covering over half of Iceland (55,000&nbsp;km<sup>2</sup>) with 1.2&nbsp;km<sup>3</sup><ref name="HANVp11" /> / 2.5&nbsp;km<sup>3</sup><ref name="UoI_Hekla">{{cite web |url=http://www.earthice.hi.is/page/ies_hekla |title=Hekla Volcano |accessdate=2008-01-14 |format=HTML |work=University of Iceland, Institute of Earth Sciences}}</ref> of [[Rhyodacite|rhyodacitic]] [[tephra]]. This was the second largest tephra eruption in the country in historical times with a [[Volcanic Explosivity Index]] (VEI) of 5. Farms upwind of the volcano in Þjórsárdalur valley (15&nbsp;km away), Hrunamannaafréttur (50&nbsp;km away) and Lake [[Hvítárvatn]] (70&nbsp;km away) were abandoned due to the damage. The eruption caused Hekla to become famous throughout Europe.<ref name="HANVp11">Thorarinsson, ''Hekla, A Notorious Volcano'', p. 11</ref><ref name="GVP">{{cite web |url=http://www.volcano.si.edu/world/volcano.cfm?vnum=1702-07=&volpage=erupt |title=Hekla » Eruptive History |accessdate=2007-10-07 |format=HTML |work=Global Volcanism Project }}</ref> ===1158=== A VEI of 4 eruption commenced on [[January 19]] producing over 0.15&nbsp;km<sup>3</sup> of [[lava]] and 0.2&nbsp;km<sup>3</sup> of tephra. It is likely to be the source of the ''Efrahvolshraun'' lava on the volcano's west.<ref name="HANVp11" /><ref name="GVP" /> ===1206 and 1222=== These eruptions, the first of which began on [[December 4]], were not large (VEIs of 3 and 2 respectively) and distributed around 0.24&nbsp;km<sup>3</sup> of tephra mainy to the northeast.<ref>Thorarinsson, ''Hekla, A Notorious Volcano'', p. 12</ref><ref name="GVP" /> ===1300-1301=== This VEI 4 eruption which started on [[July 11]] and lasted for a year was the second largest tephra eruption of Hekla since Iceland was settled, covering 30,000&nbsp;km<sup>2</sup> of land with 0.31&nbsp;km<sup>3</sup> of tephra. Over 0.5&nbsp;km<sup>3</sup> of lava was also expelled. The tephra caused significant damage to the settlements of Skagafjördur and Fljót leading to over 500 deaths that winter.<ref name="HANVp14">Thorarinsson, ''Hekla, A Notorious Volcano'', p. 14</ref><ref name="GVP" /> ===1341=== A small eruption (VEI 3) that started on [[May 19]] and deposited around 5x10<sup>7</sup>&nbsp;m<sup>3</sup> of tephra over the areas west and southwest of Hekla leading to many cattle deaths, probably mainly from [[Skeletal fluorosis|fluorosis]].<ref name="HANVp14" /><ref name="GVP" />. ===1389 and 1440=== In late 1389 Hekla erupted (VEI 3), starting with a large ejection of tephra to the southeast. Later "the eruption fissure moved itself out of the mountain proper and into the woods a little above Skard". Skard and another nearby farm were destroyed by a large lava flow that now forms the 12.5&nbsp;km<sup>2</sup> ''Nordurhraun''. In total around 0.3&nbsp;km<sup>3</sup> of lava and 5x10<sup>7</sup>&nbsp;m<sup>3</sup> of tephra were produced.<ref name="HANVp14" /><ref name="GVP" /> Another eruption may have occurred in around 1440 at Raudölder, despite being close to Hekla this is not classed as an eruption of Hekla based on the [[Silicon dioxide|SiO<sub>2</sub>]] content of the lava.<ref name="GVP" /><ref name="VW">{{cite web |url=http://volcano.und.edu/vwdocs/volc_images/europe_west_asia/eruption_history.html |title=Hekla Eruption History |accessdate=2007-10-07 |format=HTML |work=Volcano World }}</ref><ref name="HANVp18">Thorarinsson, ''Hekla, A Notorious Volcano'', p. 18</ref> ===1510 and 1597=== [[Image:Volcanic bomb from Hekla.jpg|thumb|right|300px|17&nbsp;cm long volcanic bomb found in the lava-fields of Hekla]] Details of the 1510 eruption were not recorded until a century later. It that started on [[July 25]] was particularly violent (VEI 4) and fired [[volcanic bombs]] as far as [[Vördufell]], 40&nbsp;km west. Tephra was deposited over Rangárvellir, Holt and Landeyjar, 0.2&nbsp;km<sup>3</sup> in total. A man in Landsveit was killed.<ref name="HANVp14" /><ref name="GVP" /> The 1597 (VEI 4) eruption commenced on [[January 3]] and lasted for over 6 months. 0.15&nbsp;km<sup>3</sup> of tephra was deposited to the south-southeast, damaging Mýrdalur.<ref name="HANVp14" /><ref name="GVP" /> ===1636-1637=== A small eruption (VEI 3), starting on [[May 8]] that nevertheless lasted for over a year. The 5x10<sup>7</sup>&nbsp;m<sup>3</sup> of tephra from the eruption damaged pasture to the northeast causing deaths amongst livestock.<ref name="HANVp15">Thorarinsson, ''Hekla, A Notorious Volcano'', p. 15</ref><ref name="GVP" /> ===1693=== This eruption, which started on [[January 13]] and lasted for over 7 months, was one of Hekla's most destructive (VEI 4). Initially tephra was produced at 60,000&nbsp;m<sup>3</sup>s<sup>-1</sup>, 0.18&nbsp;km<sup>3</sup> during the entire eruption, which also caused [[lahar]]s and [[tsunami]]. The tephra was deposited to the northwest, destroying and damaging farms and woodland in Thjórsárdalur, Land, Hreppar and Biskupstungur. Fine ash from the eruption reached [[Norway]]. There was also damage to wildlife with significant numbers of [[trout]], [[salmon]], [[ptarmigan]] and farm animals dying.<ref name="HANVp15" /><ref name="GVP" /> ===1725 and 1766-1768=== A very small eruption, possibly only VEI 1, took place on [[April 2]] [[1725]] producing flows of lava from locations around Hekla which have since been covered by later lava flows, again these eruptions are not classed as of Hekla itself based on the SiO<sub>2</sub> content of the lava.<ref name="GVP" /><ref name="HANVp18" /> The eruption of 1766 was much larger (VEI 4) and produced the second largest lava flow, 1.3&nbsp;km<sup>3</sup> covering 65&nbsp;km<sup>2</sup>, and third largest tephra volume, 0.24&nbsp;km<sup>3</sup>, of any Icelandic volcano during the inhabited era. The eruption started at around 3:30 am on [[April 5]] [[1766]] and did not stop until May 1768. Initially a 2-4&nbsp;cm layer of tephra was deposited over Austur-Húnavatnssýsla and Skagafjördur, resulting in the deaths of both fish and livestock. Rangárvellir, Land and Hreppar also suffered damage. During the eruption up to 0.5&nbsp;m lava bombs were thrown 15-20&nbsp;km away and a flooding was caused by the sudden melting of snow and ice on Hekla's slopes.<ref name="HANVp15" /><ref name="GVP" /> ===1845-1846, 1878 and 1913=== Hekla took was dormant for more than sixty years prior to 1845, when it suddenly burst forth on [[September 2]] at 9 am: {{Quote|After a violent storm on the night of the 2nd of September in that year, the surface of the ground in the [[Orkney Islands]] was found strown with volcanic dust. There was thus conveyed to the inhabitants of [[Great Britain]] an intimation that Hecla'' <nowiki>[sic]</nowiki> ''had been again at work. Accordingly, tidings soon after arrived of a great eruption of the mountain. On the night of the 1st of September, the dwellers in its neighbourhood were terrified by a fearful underground groaning, which continued till mid-day on the 2nd. Then, with a tremendous crash, there were formed in the sides of the cone two large openings, whence there gushed torrents of lava, which flowed down two gorges on the flanks of the mountain. The whole summit was enveloped in clouds of vapour and volcanic dust. The neighbouring rivers became so hot as to kill the fish, and the sheep fled in terror from the adjoining heaths, some being burnt before they could escape. On the night of the 15th of September, two new openings were formed &mdash; one on the eastern, and the other on the southern slope &mdash; from both of which lava was discharged for twenty-two hours. It flowed to a distance of upwards of twenty miles, killing many cattle and destroying a large tract of pasturage. Twelve miles from the crater, the lava-stream was between forty and fifty feet deep and nearly a mile in width. On the 12th of October a fresh torrent of lava burst forth, and heaped up another similar mass. The mountain continued in a state of activity up to April 1846; then it rested for a while, and began again in the following month of October. Since then, however, it has enjoyed repose. The effects of these eruptions were disastrous. The whole island was strewn with volcanic ash, which, where they did not smother the grass outright, gave it a poisonous taint. The cattle that ate of it were attacked by a [[murrain]], of which great numbers died. The ice and snow, which had gathered about the mountain for a long period of time, were wholly melted by the heat. Masses of [[pumice]] weighing nearly half a ton were thrown to a distance of between four and five miles.<ref>{{cite gutenberg|Anonymous|Wonders of Creation: A descriptive account of volcanoes and their phenomena|6131}}</ref>|Anonymous, 1872}} The eruption did not finish until around [[April 5]] [[1846]]. Initially in this VEI 4 eruption tephra was produced at 20,000&nbsp;m<sup>3</sup>s<sup>-1</sup>. The tephra deposition (0.17&nbsp;km<sup>3</sup>) was mainly to the east-southeast, immediately to the east of Hekla the layer was 20-40&nbsp;cm deep. Fine ash was carried to the [[Faroes]], [[Shetlands]] and Orkneys. Lava flows to the west and northwest covered an area of 25&nbsp;km<sup>2</sup> with 0.63&nbsp;km<sup>3</sup> of lava. Large quantities of dark ash were deposited over pasture in the same directions leading to many livestock deaths through fluorosis for the next two years.<ref name="HANVp17">Thorarinsson, ''Hekla, A Notorious Volcano'', p. 17</ref><ref name="GVP" /> Small eruptions (VEI 2) occurred between [[February 27]] [[1878]] and April 1878 and then [[April 25]] [[1913]] and [[May 18]] [[1913]]. These were around 10&nbsp;km east of Hekla, the first produced 0.2&nbsp;km<sup>3</sup> of lava from two parallel fissures covering 15.5&nbsp;km<sup>2</sup>. The second caused large fissures at Mundafell and Lambafit which produced 3.8 and 6.3&nbsp;km<sup>2</sup> of lava respectively.<ref name="GVP" /><ref name="HANVp17" /> ===1947-1948=== [[Image:Hekla winter.jpg|thumb|right|300px|Hekla in winter]] The 1947 eruption started on [[March 29]] [[1947]] and ended on [[April 21]] [[1948]] it had a VEI of 4. It is likely that this was both the second greatest lava eruption of Hekla whilst Iceland was inhabited and the second greatest lava eruption in the world in the period 1900-1970. A total lava volume 0.8&nbsp;km<sup>3</sup> was produced with 0.21&nbsp;km<sup>3</sup> of tephra. The height of Hekla was 1447&nbsp;m before the eruption, increasing to a maximum of 1503&nbsp;m, before dropping to 1491&nbsp;m subsequently. ====Initial eruption==== The 1947 eruption occurred over a century since the last eruption of Hekla proper, the longest dormant period since 1104. Before the eruption the volcano had been visible from the surrounding area but nothing remarkable was noticed. The eruption occurred at 6:41 am ± 3&nbsp;min with a loud roar, later eruptions could be heard throughout Iceland. An earthquake at 6:50 am measured 6 on the [[Mercalli intensity scale]] and increased the eruption intensity until it covered a 4&nbsp;km fissure on the ridge. For the first hours the eruption was [[Plinian]], after that it became [[Vesuvian]]. The cloud from the eruption had ascended to a height of 30&nbsp;km by 7:08 am, the wind then carried it southwards towards the [[Eyjafjallajökull]] glacier, turning it black. Pumice first landed on Fljótshlíd at around 7:10 am and tephra and ash continued falling until it formed a 3-10&nbsp;cm layer. A lava bomb that landed 32&nbsp;km from Hekla was 0.5&nbsp;m across and weighed 20&nbsp;kg. Between Vatnafjöll and Hekla a layer of tephra up to a metre thick was deposited including bombs with a diameter larger than this. Bombs with areas of 50&nbsp;m<sup>2</sup> were dropped onto the slopes of Hekla, up to 1&nbsp;km away. 51&nbsp;hours after the eruption had started ash fell on [[Helsinki]], [[Finland]] having covered 2860&nbsp;km in this time. The initial tephra production rate in the first 30&nbsp;minutes of the eruption was 75,000&nbsp;m<sup>3</sup>s<sup>-1</sup>, dropping to 22,000&nbsp;m<sup>3</sup>s<sup>-1</sup> for the next half hour. The inital phase produced 0.18&nbsp;km<sup>3</sup> of tephra, equating to 4.5x10<sup>7</sup>m<sup>3</sup> of solid rock, covering 3,130&nbsp;km<sup>2</sup> of land and sea. 98 farms were damaged by the eruption but only 2 were no longer farmed in 1970. A large volunteer effort was mobilized to clear the tephra - around 1000&nbsp;man-days by the end of July. The eruption produced around 3&nbsp;Ml of water (snowmelt and directly from the fissure) which caused flooding of the Ytri Rangá river. In the first 20&nbsp;hours of the eruption approximately 3,500&nbsp;m<sup>3</sup>s<sup>-1</sup> of lava was produced from the fissure dividing into various branches and covering 12-15&nbsp;km<sup>2</sup>. On the second day 8 distinct eruption columns were discernable. A crater formed at 860&nbsp;m called the Lava Crater (''Hraungígur'') producing a constant flow of lava. Another crater named the Shoulder Crater (''Axlargígur'') produced a column of smoke every 10&nbsp;s together with loud explosions that created visible compression waves in the smoke. By the fourth, fifth and sixth days the eruption was greatly diminished and only the shoulder and summit craters were erupting explosively. ====Later eruption==== [[Image:Islande volcan Hekla.jpg|thumb|right|300px|View of Hekla]] The [[explosive eruption]] increased in strength from 9-12 April and then from [[April 28]] reduced again. On [[May 3]] the volcano stopped throwing out lava in sudden explosions from its craters and changed to continuously ejecting tephra and ash for long periods, until early June when this reduced. On [[September 2]] the Shoulder Crater had a 960&nbsp;m circumference at its top and the Summit Crater a 700&nbsp;m circumference at its highest point, 90&nbsp;m above the ridge. Sandy tephra and ash fell over Iceland in May and June, sometimes making it dark in the daytime near to Hekla. The tephra caused fluorine poisoning of grazing sheep, making them unable to walk. That winter more craters formed, building up cones. Explosive activity had ceased six months after the first eruption. Lava flowed from the the Lava Crater continuously during the eruption, starting at a rate of over 100&nbsp;m<sup>3</sup>s<sup>-1</sup>, dropping to 5-10&nbsp;m<sup>3</sup>s<sup>-1</sup> in April and early May at a speed of around 20&nbsp;cms<sup>-1</sup> before increasing, eventually reaching 150&nbsp;m<sup>3</sup>s<sup>-1</sup> at the end of June and at similar levels until mid-July with a peak flow speed of 2-2.5&nbsp;ms<sup>-1</sup>. From there it gradually decreased to under 10&nbsp;m<sup>3</sup>s<sup>-1</sup> in November. Initially the lava comprised 57-58% SiO<sub>2</sub> and 11% Fe<sub>2</sub>O<sub>3</sub>, from the time of peak flow onwards this changed to 54% SiO<sub>2</sub> and 13.5% Fe<sub>2</sub>O<sub>3</sub>. The lava river sometimes ran through [[Lava tube|tunnels]] before emerging again. The lava front had a height of up to 15&nbsp;m. On [[June 15]] and 16 a branch of lava flow to the south of Melfell travelled over 1&nbsp;km in 30&nbsp;hours before slowing and stopping by [[June 21]], 7.8&nbsp;km from the Lava Crater. The longest lava stream produced was 8&nbsp;km long and stopped in Stóraskógsbotnar. A scientist filming one of the lava streams on [[November 2]] was hit by a block of lava and killed. The lava flow stopped after 13 months on [[April 21]] having covered 40&nbsp;km<sup>2</sup> and with a maximum depth of 100&nbsp;m. The lava beds produced were mainly the [[Lava#ʻAʻā|ʻAʻā]] lava type with [[Lava#Pāhoehoe|Pāhoehoe]] and ''lava a budella'' areas. In April and May 1948 [[CO2|CO<sub>2</sub>]] emitted from cracks in the ground pooled in hollows near to Hekla killing 15 sheep and some wild animals and birds. In total 24,000 tonnes of CO<sub>2</sub> was emitted. Ditches were dug by farmers to drain these hollows and the CO<sub>2</sub> emission had stopped by the end of the year.<ref name="GVP" /><ref name="HANVp19-38">Thorarinsson, ''Hekla, A Notorious Volcano'', p. 19-38</ref> ===1970=== [[Image:Islande volcan Hekla nord-ouest.jpg|thumb|right|300px|The north-west side of Hekla]] The 1970 eruption of Hekla started at 9:23 pm on [[May 5]] [[1970]] and lasted until [[July 5]]. It had a VEI of 3 and produced 0.2&nbsp;km<sup>3</sup> of lava covering an area of 18.5&nbsp;km<sup>2</sup> and 6.6x10&nbsp;<sup>7</sup>m<sup>3</sup> of tephra, deposited over an area of 40,000&nbsp;km<sup>2</sup>, mainly to the northwest of the volcano.<ref name="GVP" /> The main Hekla fissure only erupted at its far southwest end, most of the eruption was from other fissures nearby. The eruption stopped in the SSW on [[May 10]] and in Hlídargígar on [[May 20]] but a new fissure opened on the same day and lava flowed from this until [[July 5]]. The lava was andesite containing olivine, similar to the lava produced later in the eruption of 1947.<ref name="HANVp39to58">Thorarinsson, ''Hekla, A Notorious Volcano'', p. 39-58</ref> ====Initial eruption==== Before the eruption a greater than normal amount of snow melting had occurred, indicating the volcano was heating up. Earth tremors began at 8:48 pm on the evening of the eruption, the largest had a magnitude of 4. The eruption started weakly at 9:23 pm IMT ± 2&nbsp;min before increasing in power.The first pumice fell on Búrfell [[power station]], 15&nbsp;km away, at 9:35 pm causing people to evacuate. The eruption seems to have started in 2 locations at the same time - to the Shoulder crater's SSW and below the Lava Crater. At 10:30 pm a crater at 780&nbsp;m was producing a lava column which reached an altitude of around 1000&nbsp;m. During the night a 700&nbsp;m high [[lava fountain]] was thrown up from the main crater. A 500&nbsp;m long fissure starting below the Lava Crater opened and lava fountains and other lava flows emanated from it. One hour into the eruption a new 400&nbsp;m fissure opened to the NE producing two main lava fountains and shortly after another adjoining fissure opened producing lava fountains to a height of 500&nbsp;m. At around midnight another fissure opened NW of the Lava Crater, later hurling an over 300&nbsp;m long lava fountain, 200-300&nbsp;m into the air. By midnight lava had already covered over 1&nbsp;km<sup>2</sup> and this extended to 7.5&nbsp;km<sup>2</sup> by next morning implying a [[Volumetric flow rate|flow rate]] of around 1500&nbsp;m<sup>3</sup>s<sup>-1</sup>. For the first two hours tephra was produced at the rate of 10,000&nbsp;m<sup>3</sup>s<sup>-1</sup>. The cloud from the eruption, which had reached {{convert|53000|ft|m|0|lk=off}} by 10:10 pm caused a noisy [[lightning storm]]. The tephra was transported northwards by the wind causing the sky to turn black in places - 190&nbsp;km away at Blönduós tephra fell from midnight until 2 am and ash fell on a [[trawler]] 330&nbsp;km away at 2 am. Icelanders sampled the tephra fall in their locality by putting a plate outside to capture everything that fell onto it. This, and other measurements, showed the area covered was long and narrow with the 1&nbsp;mm contour (an equivalent of 8 tonnes per hectare) extending to the north coast.<ref name="HANVp39to58" /><ref name="GVP" /> ====Later eruption==== By 5:30 on [[May 6]] the lava flow measured 4&nbsp;km long. Many lava bombs were found near the main crater, one had an area of 6&nbsp;m<sup>2</sup> and a likely weight of 12&nbsp;tons. [[Xenolith]]s formed around 2% of the material produced by the craters. These were of rock types including basalt, andesite, [[ignimbrite]] and [[sedimentary rock]]. The eruption became stronger at Skjólkvíar on [[May 12]] with columns of steam attaining a height of 2500&nbsp;m. The eruption intensity then gradually reduced until it stopped on [[May 20]]. The lava field then had an area of 5.8&nbsp;km<sup>2</sup>. Later that day a 900&nbsp;m long fissure opened 1&nbsp;km north of the main Hlídargígar crater. That night it contained 17 lava fountains, each 20-50&nbsp;m in height. By the evening of the next day 10-12 craters had formed, each throwing pieces of lava 50-100&nbsp;m in the air. This row of craters was named Öldugígar. Gradually the number of active craters decreased, the most active of these built a cone 100&nbsp;m higher than the level of the ridge. Lava flowed from its base until mid-June when the lava cut through the north crater wall. The larger cones produced more tephra, occasonally with lightning within the tephra cloud. By [[July 5]] the eruption had stopped.<ref name="HANVp39to58" /> ====Effects==== During eruptions of Hekla fluorine is produced and sticks to the surfaces of the grains of tephra. Fine grains can have a fluorine content of 350&nbsp;ppm and [[Skeletal fluorosis|fluorine poisoning]] can start in sheep at a diet with fluorine content of 25&nbsp;ppm. At 250&nbsp;ppm death can occur wthin a few days. In 1783, 79% of the [[Icelandic sheep]] stock were killed, probably as a result of fluorosis caused by the eruption of [[Lakagígar]]. Some of the ash produced in this eruption had a fluorine content of 0.2% and two days after the eruption contaminated grass had a [[dry weight]] content of up to 0.4%. 450 farms and 95,000 sheep were affected by the eruption. Some were kept inside and fed on hay or moved but other farmers were forced to graze their flocks outside. Fluorine poisoning killed over 1500 ewes, 6000 lambs and some horses.<ref name="HANVp39to58" /> ===1980=== [[Image:Hekla1980.jpg|thumb|right|300px|Mount Hekla erupting in 1980. Seen from 4&nbsp;km NE of the summit.]] This VEI3 eruption started at 13:28 on [[August 17]] [[1980]] and lasted until [[August 20]] [[1980]]. It was a mixed eruption producing a lava volume of 0.12&nbsp;km<sup>3</sup> and a tephra volume of 5.8x10<sup>7</sup>&nbsp;m<sup>3</sup>. The fissure opened along a 7&nbsp;km length. Shortly before the eruption started a steam column was produced, eventually the [[eruption column]] reached a height of 15&nbsp;km. The main tephra deposits were to the NNE and lasted for around 2&nbsp;hours. Deposits were 20&nbsp;cm thick 10&nbsp;km from the summit, decreasing to <1&nbsp;mm at the coast 230&nbsp;km away. Lava was initially produced from close to the summit, spreading to other parts of the fissure and coverng an area of 22&nbsp;km<sup>2</sup> in around 24&nbsp;hours. The last [[scoria]] were seen on the morning of [[August 20]]. This was an unusual eruption both in the short time since the previous eruption - the shortest since 1104, and the length - previous eruptions have lasted from 2 months to 2 years rather than just 3 days.<ref name="GVP" /><ref>{{cite web |url=http://homepage.ntlworld.com/i.p.hutchinson/iceland/Natturu1983-175.PDF |title=''Upphaf Eldgossins í Heklu, 1980'' (On the Eruption of Hekla, 1980)|accessdate=2008-01-01 |author=Hutchinson, I.P. |year=1983 |format=PDF |work=Náttúrufræðingurinn '''52''' (1–4) |pages=175–183 |language=Icelandic and English}}</ref> ===1981=== [[Image:Hekla 2004.jpg|thumb|300px|Mount Hekla seen from the Þjórsárdalur]] The eruption, which is regarded as being a continuation of the previous year's eruption, began at 3 am on [[April 9]] [[1981]], had a VEI of 2 and produced 3x10<sup>7</sup>&nbsp;m<sup>3</sup> of lava, lasting until [[April 16]] [[1981]]. The eruption threw ash to a height of 6.6&nbsp;km and a new crater formed at the summit from which 3 lava flows originated. These extended to a maximum of 4.5&nbsp;km from the volcano, covering 5-6&nbsp;km<sup>2</sup>.<ref name="GVP" /><ref name="VW" /> ===1991=== A larger eruption (VEI 3) occurred from [[January 17]] [[1991]] to [[March 11]] [[1991]], producing 0.15&nbsp;km<sup>3</sup> of lava and 2x10<sup>7</sup>&nbsp;m<sup>3</sup> of tephra. The eruption, which was preceded by sulpherous smells and earthquakes, started as a [[Plinian eruption]], producing an ash cloud reaching an altitude of 11.5&nbsp;km within 10&nbsp;minutes which had travelled over 200&nbsp;km to the coast within 3&nbsp;hours. The eruption then moved quickly to producing andesitic lava, the flows eventually covering an area of 23&nbsp;km<sup>2</sup> to an average depth of 6-7&nbsp;m. Initially part of the Heklugja fissure and other fissures erupted with lava fountains reaching 300&nbsp;m in height. By the second day the activity stopped in all but one fissure where the main crater formed. During these 2 days 800&nbsp;m<sup>3</sup>s<sup>-1</sup> of lava were produced, slowing to 800&nbsp;m<sup>3</sup>s<sup>-1</sup> for most of the eruption. This low [[viscosity]] lava had a SiO<sub>2</sub> content of approximately 54%.<ref name="GVP" /><ref name="VW_H1991">{{cite web |url=http://volcano.und.edu/vwdocs/volc_images/europe_west_asia/hekla_erupt.html |title=The Hekla Eruption of 1991 |accessdate=2008-07-08 |work=Volcano World}}</ref> ===2000=== [[Image:Iceland-Hekla2-July 2000.jpg|thumb|300px|right|A lava field on Hekla in July 2000]] The most recent eruption was relatively short, it started at 18:18 on [[February 26]] [[2000]] and lasted until [[March 8]]. It was a VEI3 eruption producing a lava volume of 0.189&nbsp;km<sup>3</sup> [[Dense-rock equivalent|DRE]]<ref name="TMEOH">{{cite web |url=http://www.springerlink.com/content/p25157781v031261/ |title= The millennium eruption of Hekla in February 2000 |accessdate=2008-01-19 |author=Ármann Höskuldsson |coauthors=Níels Óskarsson, Rikke Pedersen, Karl Grönvold, Kristín Vogfjörð, Rósa Ólafsdóttir |date=2007-04-11 |work=Bulletin of Volcanology |publisher=Springer Berlin / Heidelberg |pages=169-182}}</ref> / 0.29&nbsp;km<sup>3</sup><ref name="GVP" /> and 10<sup>7</sup>&nbsp;m<sup>3</sup> of tephra.<ref name="GVP" /> The eruption went through four phases: #initial explosive stage #fire fountains #bursts of [[Strombolian eruption]] #effusion of lava<ref name="TMEOH" /> Eruption activity was at a maximum in the first hour and by the first night the fissure on Hekla had opened to a length of 6-7&nbsp;km. The steam column rose to a height of almost 15&nbsp;km and ash was transported to [[Grímsey]].<ref>{{cite web |url=http://www.hi.is/~thorstur/science/hekla2000.htm |title=Hekla erupts Feb 26 - ~29, 2000 |accessdate=2008-01-19 |format=html |work=turdus.net}}</ref> During this eruption, a [[NASA]] [[DC-8]] aeroplane accidentally flew through the plume with all instruments switched on, resulting in unprecedented measurement of a young volcanic plume. Up until this eruption, it had always been assumed that Hekla was incapable of producing the most dangerous of volcanic phenomena, the [[pyroclastic flow]]. In January 2003, however, a team from the Norvol Institute in [[Reykjavík]], under the leadership of Dr. Ármann Höskuldsson, reported that they found traces of a pyroclastic flow, roughly 5&nbsp;km long, stretching down the side of the mountain. This will call for a reappraisal of volcanic eruptions of the [[Mafic|basic]] rock type, which up to now were generally thought not to produce large pyroclastic flows. It will also require that the public and curious spectators who always rush to the scene at the start of a new outbreak, be kept much further away from the volcanic activity than was thought necessary during previous outbreaks. ==Flora & Fauna== The Hekla area was once forested. Forest and some grasses are much more resiliant to ash and pumice fall than low vegetation, but the combined effect of human habitation and the volcanic activity has left an unstable surface very susceptible to erosion. A 90,000&nbsp;ha [[reforesting]] project is running to restore the previously present [[birch]] and [[willow]] woodland to the slopes of Hekla, starting with soil fertilisation and grass sowing. This would stabilize the large areas of [[volcanic ash]], help to reduce erosion by the wind of the [[frost heave]]d surface, slow drainage rates and hence [[water erosion]], and ultimately increase [[biodiversity]]. It is the largest reforestation of its type in Europe.<ref>{{cite web |url=http://hekluskogar.is/index_ensk.html |title=The Hekluskogar idea |accessdate=2008-01-14 |format=html|work=Heklaforests}}</ref><ref>{{cite web |url=http://hekluskogar.is/Skjol/Heklubaekl%20enska2.pdf |title=The Hekla Forest Project |accessdate=2008-01-14 |format=pdf |work=Heklaforests }}</ref> ==Sport and Recreation== [[Image:Hekla slopes june 2005.jpg|thumb|right|300px|Walkers on the slopes of Hekla]] Hekla is a popular destination for hiking, following the most recent eruption the path goes most of the way to the summit<ref>{{cite web |url=http://www.summitpost.org/mountain/rock/152891/hekla.html |title=Hekla |accessdate=2007-10-23 |author=Brian Jenkins |date=May 2, 2007 |work=SummitPost.org}}</ref> the walk takes 3 to 4&nbsp;hours.<ref name="SI" /> In spring [[skiing]] is possible on short routes around the rim of the crater, in summer there are easy ([[Grade (climbing)#Grade systems for mountaineering|F]]) [[mountaineering]] routes also around the crater rim.<ref>{{cite book | last = Escritt | first = Tony | title = Iceland, The Travellers Guide | year = 1990 | publisher = Iceland Information Centre | location = London | isbn = 0 948192 04 6 |pages = p321,325}}</ref> and it is possible to [[snowcat]] to the top in winter. The volcano can be reached using the buses to [[Landmannalaugar]] 30&nbsp;km further east and it is possible to stay or camp at farms in the area.<ref> {{cite book| last = Leffman | first = David | coauthors = James Proctor | title = The Rough Guide to Iceland | series = Rough Guides | year = 2007 | pages = 130 | isbn = 978-1-84353-767-0 }}</ref> == In popular culture == *''Hekla'', Op 52 (1964) by Icelandic composer [[Jón Leifs]] has been called the "loudest [[classical music]] of all time". The requirements for a performance of ''Hekla'' include four sets of rocks hit with hammers, steel plates, anvils, sirens, cannons, metal chains, choir, a [[Orchestra|large orchestra]], and organ.<ref>Booklet of CD: "Earquake" (sic), [[Helsinki Philharmonic Orchestra]], [[Leif Segerstam]]. [[Ondine (record label)|Ondine]] ODE 894-2</ref> *In the Boston area, Hekla pastries can be found - large, upside-down [[cinnamon roll]]s with white sugar icing spooned over the top to look like the snow-topped volcano.<ref>{{cite web |url=http://bikenerd.blogspot.com/2006/02/behold-hekla.html |title=Behold! Hekla |accessdate=2007-12-31 |author= |date=2006-02-22 |work=bikenerd |publisher=www.blogger.com}}</ref> *The poet [[William Blake]] shows Winter being banished to Hecla in ''To Winter,'' one of the works from his ''Poetical Sketches''. == See also == * [[Geography of Iceland]] * [[Iceland plume]] * [[Iceland hotspot]] * [[List of volcanoes in Iceland]] * [[Volcanoes of Iceland]] ==References== {{reflist|2}} ==Bibliography== *{{cite book | last = Thorarinsson | first = Sigurdur | authorlink = Sigurdur Thorarinsson | others = trans. Jóhann Hannesson, Pétur Karlsson | title = Hekla, A Notorious Volcano | year = 1970 | publisher = Almenna bókafélagið | location = Reykjavík | language = English | isbn = }} == External links == * [http://www.arctic-images.com/picture_gallery/Hot/hot_pages/pages/Heklugos.htm Photo of 2000 eruption] * [http://antwrp.gsfc.nasa.gov/apod/ap060129.html Night time photo of eruption with Aurora] * [http://www.earthice.hi.is/page/ies_hekla Institute of Earth Sciences, University of Iceland, Hekla pages] [[Category:Mountains of Iceland]] [[Category:Volcanoes of Iceland]] [[Category:Active volcanoes]] [[Category:VEI-5 volcanoes]] [[af:Hekla]] [[cs:Hekla]] [[da:Hekla]] [[de:Hekla]] [[et:Hekla]] [[es:Hekla]] [[eo:Hekla]] [[fr:Hekla]] [[fy:Hekla]] [[gl:Hekla]] [[is:Hekla]] [[it:Hekla]] [[ja:ヘクラ山]] [[lt:Hekla]] [[hu:Hekla]] [[nl:Hekla]] [[nn:Hekla]] [[no:Hekla]] [[pl:Hekla]] [[ro:Hekla]] [[sk:Hekla]] [[sl:Hekla]] [[sh:Hekla]] [[fi:Hekla]] [[sv:Hekla]] [[uk:Гекла]]