Editing Hekla (section)

==Eruption history==
[[File:Icelandic tephra.JPG|thumb|right|Tephra horizons in south-central Iceland. The thick and light coloured layer at center of the photo is rhyolitic tephra from Hekla.]]
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 varied and difficult to predict. Precursor seismic activity may only be for a couple of hours or less.<ref name=Ilyinskaya2015/>{{rp|p=80}} Some are very short (a week to ten days) whereas others can stretch into months and years (the 1947 eruption started 29 March 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 name=Thorarinsson1967/> The most recent eruption was on 26 February 2000.

===Prehistoric eruptions===
[[File:Cairns and hekla.jpg|thumb|right|Hekla beyond a snowy field of volcanic ash]]
One of the largest [[Holocene]] eruptions in Iceland was the [[Hekla 3 eruption|Hekla 3]] (or H<sub>3</sub>) eruption {{circa|1000 BC}},<ref name="GVPHEH">{{cite gvp|vn=372070|vtab=Eruptions|title=Hekla|access-date=7 July 2008}}</ref><ref name="IACIB" /> which threw about {{convert|7.3|km3|abbr=on}}<ref name="GVP"/> of [[volcanic rock]] into the atmosphere, placing its [[Volcanic Explosivity Index]] (VEI) at 5. This would have cooled temperatures in the northern parts of the globe for a few years afterwards. Traces of this eruption have been identified in 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 | isbn = 0-415-34779-3 | page = 256 | last = Cunliffe | first = Barry | year=2005 | edition = 4th | publisher = Routledge}}Pg 68</ref> The dates were recently recalibrated of the major eruptions and a table is given below as the difference in dates could cause confusion.
{| class="wikitable"
|+ Dates of major eruptions in prehistoric times:{{ref label|Historic_Eruptions|A|A}}
|-
! Eruption
! Year (2019 values)
! Year (2024 values)
|-
| H-5
| 5050 BCE
| {{dts|{{ #expr: 7053-1950 }}}} ± 260 BCE<ref name="Davis2024" />  
|-
| H-Sv
| 3900 BCE<ref name="Selsund">{{cite web
 |url=http://www.theochem.org/Raunvisindathing06/abstracts/gsv-en.pdf 
 |title=The Selsund Pumice and the old Hekla crater 
 |access-date=7 July 2008 
 |author=Guðrún Sverrisdóttir 
 |author2=Níels Óskarsson 
 |author3=Árný E. Sveinbjörnsdóttir 
 |author4=Rósa Ólafsdóttir 
 |publisher=Institute of earth sciences, Reykjavik 
 |url-status=dead 
 |archive-url=https://web.archive.org/web/20081219173906/http://www.theochem.org/Raunvisindathing06/abstracts/gsv-en.pdf 
 |archive-date=19 December 2008
}}</ref><ref>Elsa G. Vilmundardóttir og Árni Hjartarson 1985: Vikurhlaup í Heklugosum. Náttúrufræðingurinn 54, 17-30.</ref>
| 3900 BCE
|-
| H-4
| 2310 ± 20 BCE
| 2375 ± 8 BCE<ref name="Davis2024" />
|-
| [[Hekla 3 eruption|H-3]]
| 950 BCE
| {{dts|{{ #expr: 3013-1950}}}} ± 140 BCE<ref name="Davis2024" />
|}
{{note label|Historic _Eruptions|A|A}}Unless otherwise stated eruption dates in Year (2019 values) column are from Global Volcanism Program and Catalogue of Icelandic Volcanoes,<ref name="GVPHEH" /><ref name="CIV" /> As other sources can disagree,<ref name="IACIB" /><ref name="Selsund" /> there has been a recent literature update. The values and range given in the Year (2024 values) column used [[Radiocarbon dating#Calibration|IntCal20]] for H-5 and H-3 and ice core data for H-4 which were not available in 2019.<ref name="Davis2024" >{{cite journal|last1 =Davies|first1 =S.M.|last2 =Albert|first2 =P.G.|last3 =Bourne|first3 =A.J.|last4 =Owen|first4 =S.|last5 =Svensson|first5 =A.|last6 =Bolton|first6 = M.S.|last7 =Cook|first7 =E.|last8 =Jensen|first8 = B.J.|last9 =Jones|first9 =G.|last10 =Ponomareva|first10 =V.V.|last11 =Suzuki|first11 =T.|year =2024|title =Exploiting the Greenland volcanic ash repository to date caldera-forming eruptions and widespread isochrons during the Holocene|journal =Quaternary Science Reviews|volume =334|pages =108707|doi =10.1016/j.quascirev.2024.108707}}</ref>

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 |access-date=24 October 2007 |author=Guðrún Larsen |work=Natural Science Symposium in Reykjavík 2006 |date=3 March 2006 |url-status=dead |archive-url=https://web.archive.org/web/20081219173903/http://www.theochem.org/Raunvisindathing06/abstracts/gul-en.pdf |archive-date=19 December 2008}}</ref> and providing useful date markers 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 |access-date=24 October 2007|work=Orkney Landscapes |publisher=Fettes.com |archive-url = https://web.archive.org/web/20070915034132/http://www.fettes.com/Orkney/tephra.htm  |archive-date = 15 September 2007}}</ref> Scandinavia,<ref name="SI">{{cite web |url=http://www.south.is/displayer.asp?Page=222&p=ASP\Pg222.asp |archive-url=https://archive.today/20070831111627/http://www.south.is/displayer.asp?Page=222&p=ASP%5CPg222.asp |url-status=dead |archive-date=31 August 2007 |title=Hekla – The queen of the Icelandic volcanoes |access-date=24 October 2007 |author=South Iceland }}</ref> and elsewhere.<ref>{{cite web |url=http://www.tephrabase.org/ |title=A Tephrochronological Database |work=Tephrabase |publisher=School of GeoSciences, [[The University of Edinburgh]]}}</ref> H<sub>3</sub> and H<sub>4</sub> produced the largest layers of tephra in Iceland since the [[Last Glacial Period|last ice age]].<ref name="HANVp11" /> During the last 7,000 years, one third of the volcanic ash deposited in Scandinavia, Germany, Ireland, and the United Kingdom originated from Hekla.<ref name="BBC AGUKACU">{{cite news |url= https://www.bbc.co.uk/news/science-environment-14500157 |title=BBC News – Another giant UK ash cloud 'unlikely' in our lifetimes |author=Pritchard, Hamish  |work=BBC News|date=12 August 2011}}</ref>

===1104 to 1878 ===<!---could this section better be handled in a table--->
;1104 (H1)
[[File:Stöng Viking Longhouse.jpg|thumb|right|Main building of the replica of [[Þjóðveldisbærinn Stöng|Stöng]], which was buried under volcanic ash from the 1104 eruption]]
Hekla had been dormant for at least 250&nbsp;years when it erupted explosively in 1104 (probably in the autumn), covering {{convert|55000|km2|abbr=on}} which is over half of Iceland 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 |access-date=14 January 2008 |work=University of Iceland, Institute of Earth Sciences |url-status=dead |archive-url=https://web.archive.org/web/20070212095558/http://www.earthice.hi.is/page/ies_hekla |archive-date=12 February 2007 }}</ref> of [[Rhyodacite|rhyodacitic]] tephra. This was the second largest tephra eruption in the country in historical times with a VEI of 5. Farms upwind of the volcano {{convert|15|km|abbr=on}} in [[Þjórsárdalur]] valley, {{convert|50|km|abbr=on}} at Hrunamannaafréttur and {{convert|70|km|abbr=on}} at Lake [[Hvítárvatn]] were abandoned because of the damage. The eruption caused Hekla to become famous throughout Europe.<ref name="GVPHEH" /><ref name="HANVp11">Thorarinsson, p. 11</ref>

;1158
A VEI-4 eruption began on 19 January 1158 producing over {{convert|0.15|km3|abbr=on}} of [[lava]] and {{convert|0.2|km3|abbr=on}} of tephra. It is likely to be the source of the ''Efrahvolshraun'' lava on Hekla's west.<ref name="GVP" /><ref name="HANVp11" />

;1206
The VEI-3 eruption began on 4 December.

;1222
The VEI-2 eruption and the 1206 eruption distributed around {{convert|0.24|km3|abbr=on}} of tephra mainly to the northeast.<ref name="GVP" /><ref>Thorarinsson, p. 12</ref>

;1300–1301
[[File:Hekla and horse.jpg|thumb|right|Hekla in 2006 and an [[Icelandic horse]]]]
This VEI-4 eruption, which started on 11 July and lasted for a year, was the second largest tephra eruption of Hekla since Iceland was settled, covering {{convert|30000|km2|abbr=on}}
of land with {{convert|0.31|km3|abbr=on}} of tephra. Over {{convert|0.5|km3|abbr=on}} of lava was also expelled. The tephra caused significant damage to the settlements of [[Skagafjörður]] and [[Fljót]], leading to over 500&nbsp;deaths that winter.<ref name="GVP" /><ref name="HANVp14">Thorarinsson, p. 14</ref>
The material output from this eruption had SiO<sub>2</sub> levels of between 56% and 64%, and apart from a slight abundance of [[olivine]] the lava, was typical of Hekla eruptions.<ref name="GSA">{{cite conference| first = Swarr| last = Gretchen| author2 = Peter Oswald| author3 = Karen Harpp| author4 = Dennis Geist| date = 27–29 March 2008| title = THE 1300 AD ERUPTION OF HEKLA VOLCANO, ICELAND| conference = Northeastern Section, Geological Society of America, 43rd Annual Meeting| location = Buffalo| url = http://gsa.confex.com/gsa/2008NE/finalprogram/abstract_134610.htm| access-date = 17 August 2008| archive-date = 14 September 2017| archive-url = https://web.archive.org/web/20170914081538/https://gsa.confex.com/gsa/2008NE/finalprogram/abstract_134610.htm| url-status = dead}}</ref>

;1341
A small eruption (VEI-3) started on 19 May and deposited around {{convert|5E7|km3|abbr=on}} of tephra over the areas west and southwest of Hekla, leading to many cattle deaths, probably mainly from [[Skeletal fluorosis|fluorosis]].<ref name="GVP" /><ref name="HANVp14" />

;1389
In late 1389 Hekla erupted again (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 {{convert|12.5|km2|abbr=on}} ''Nordurhraun''. In total around {{convert|0.3|km3|abbr=on}} of lava and {{convert|5E7|m3|abbr=on}} of tephra were produced.<ref name="GVP" /><ref name="HANVp14" />

;1440
An eruption may have occurred 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="HANVp18">Thorarinsson, p. 18</ref><ref name="GVP" /><ref name="VW">{{cite web |url=http://volcano.oregonstate.edu/vwdocs/volc_images/europe_west_asia/eruption_history.html |title=Hekla Eruption History |access-date=7 October 2007 |work=Volcano World |archive-date=6 August 2017 |archive-url=https://web.archive.org/web/20170806082922/http://volcano.oregonstate.edu/vwdocs/volc_images/europe_west_asia/eruption_history.html |url-status=dead }}</ref>

;1510
[[Image:Volcanic bomb from Hekla.jpg|thumb|right|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 started on 25 July and was particularly violent (VEI 4), firing [[volcanic bombs]] as far as [[Vördufell]], {{convert|40|km|abbr=on}} west. Tephra was deposited over [[Oddi|Rangárvellir]], Holt and [[Landeyjar]], {{convert|0.2|km3|abbr=on}} in total. A man in Landsveit was killed.<ref name="GVP" /><ref name="HANVp14" />

;1597
A VEI-4 eruption began on 3 January and lasted for over 6&nbsp;months, with {{convert|0.15|km3|abbr=on}} of tephra being deposited to the south-southeast, damaging [[Mýrdalur]].<ref name="GVP" /><ref name="HANVp14" />

;1636–1637
A small (VEI-3) eruption began on 8 May 1636 and lasted for over a year. The {{convert|5E7|m3|abbr=on}} of tephra from the eruption damaged pasture to the northeast causing death of livestock.<ref name="GVP" /><ref name="HANVp15">Thorarinsson, p. 15</ref>

;1693
Starting 13 February and lasting for over 7&nbsp;months the eruption 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>, {{convert|0.18|km3|abbr=on}} 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 Þjórsárdalur, Land, Hreppar and [[Biskupstungur]]. Fine ash from the eruption reached Norway. There was damage to wildlife with significant numbers of [[trout]], [[salmon]], [[rock ptarmigan|ptarmigan]] and farm animals dying.<ref name="GVP" /><ref name="HANVp15" />

;1725
[[File:Hekla flank.jpg|thumb|right|The flanks of Hekla]]
A very small eruption, possibly only VEI-1, took place on 2 April 1725, producing flows of lava from locations around Hekla which have since been covered by later lava flows. These eruptions are not classed as of Hekla itself based on the SiO<sub>2</sub> content of the lava.<ref name="HANVp18" /><ref name="GVP" />

;1766–1768
The eruption of 1766 was large (VEI-4) and produced the second largest lava flow, {{convert|1.3|km3|abbr=on}} covering {{convert|65|km2|abbr=on}}, and third largest tephra volume, {{convert|0.24|km3|abbr=on}}, of any Icelandic volcano during the inhabited era. The eruption started at around 3:30 am on 5 April 1766 and ceased in 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 {{convert|0.5|m|abbr=on}} lava bombs were thrown {{convert|15-20|km|abbr=on}} away, and flooding was caused by the sudden melting of snow and ice on Hekla's slopes.<ref name="GVP" /><ref name="HANVp15" />

;1845–1846
[[File:Hecla from Westman Islands rcgl.jpg|thumb|right|Hekla {{circa|1851}}]]
Hekla was dormant for more than sixty years before 1845, when it suddenly burst forth on 2 September at 9 am:
{{Blockquote|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 had been again at work. Accordingly, tidings soon after arrived of a great eruption of the mountain. On the night of 1 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 15 September, two new openings were formed — one on the eastern, and the other on the southern slope — 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 12 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 it 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>[http://www.gutenberg.org/ebooks/6131 Wonders of Creation: A descriptive account of volcanoes and their phenomena], T. Nelson & Sons (1872)</ref>|Anonymous, 1872}}
The eruption ceased around 5 April 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 of a total amount of {{convert|0.17|km3|abbr=on}} was mainly to the east-southeast; immediately to the east of Hekla the layer was {{convert|20|-|40|cm|abbr=on}} deep. Fine ash was carried to the [[Faroes]], [[Shetland]] and Orkney. Lava flows to the west and north-west covered an area of {{convert|25|km2|abbr=on}} with a volume of {{convert|0.63|km3|abbr=on}} 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="GVP" /><ref name="HANVp17">Thorarinsson, p. 17</ref>

;1878
[[File:Iceland - Approaching Hekla.jpg|thumb|right|Hekla {{circa|1893}}]]
A small eruption (VEI-2) occurred between 27 February 1878 and April 1878, around {{convert|10|km|abbr=on}} east of Hekla, and produced {{convert|0.2|km3|abbr=on}} of lava from two parallel fissures covering {{convert|15.5|km2|abbr=on}}.

=== 1913 to 1948 ===
;1913
[[File:Image from page 30 of "Island am Beginn des 20 Jahrhunderts;" (1904).jpg|thumb|right|Hekla {{circa|1904}}]]
A small eruption (VEI-2) occurred between 25 April 1913 and 18 May 1913, around {{convert|10|km|abbr=on}} east of Hekla, and caused large fissures at [[Mundafell]] and [[Lambafit]] which produced {{convert|3.8| and|6.3|km2|abbr=on}} of lava respectively.<ref name="GVP" /><ref name="HANVp17" />

;1947–1948
The VEI-4 eruption started on 29 March 1947 and ended on 21 April 1948. 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 {{convert|0.8|km3|abbr=on}} was produced with {{convert|0.21|km3|abbr=on}} of tephra. The height of Hekla was {{convert|1447|m|abbr=on}} before the eruption, increasing to a maximum of {{convert|1503|m|abbr=on}}, before dropping to {{convert|1491|m|abbr=on}} subsequently.

The eruption occurred over a century after 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 {{convert|4|km|abbr=on}} fissure on the ridge. 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 [[Eyjafjallajökull]], turning it black. Pumice first landed on [[Fljótshlíð]] at around 7:10 am, and tephra and ash continued falling until it formed a {{convert|3|-|10|cm|abbr=on}} layer. A lava bomb that landed {{convert|32|km|abbr=on}} from Hekla was {{convert|0.5|m|abbr=on}} across and weighed {{convert|20|kg|abbr=on}}. Between [[Vatnafjöll]] and Hekla, a layer of tephra up to {{convert|1|m|abbr=on}} thick was deposited, and this included bombs with a diameter larger than {{convert|0.5|m|abbr=on}}. Bombs with surface areas of {{convert|50|m2|abbr=on}} were dropped onto the slopes of Hekla, for up to {{convert|1|km|abbr=on}}. 51&nbsp;hours after the eruption had started, ash fell on [[Helsinki]], Finland, having covered {{convert|2860|km|abbr=on}} 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 initial phase produced {{convert|0.18|km3|abbr=on}} of tephra, equating to {{convert|4.5E7|km3|abbr=on}} of [[Dense-rock equivalent]], covering {{convert|3130|km2|abbr=on}} of land and sea. 98&nbsp;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 {{convert|3|ML|abbr=on}} 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 {{convert|12|-|15|km2|abbr=on}}. On the second day, 8 distinct [[eruption column]]s were discernible. A crater formed at {{convert|860|m|abbr=on}} 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;seconds 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.

[[File:Hekla from Pæla 20090516.jpg|thumb|right|The Pæla lava field in 2009 with a lava river from the 1947 eruption]]
The [[explosive eruption]] increased in strength from 9–12 April and then from 28 April it reduced again. On 3 May, 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 2 September, the Shoulder Crater had a {{convert|960|m|abbr=on}} circumference at its top and the Summit Crater a {{convert|700|m|abbr=on}}circumference at its highest point, {{convert|90|m|abbr=on}} above the ridge. Sandy tephra and ash fell over Iceland in May and June, sometimes making it dark in the daytime near 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 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;cm·s<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;m·s<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 tubes]] before emerging again. The lava front had a height of up to {{convert|15|m|abbr=on}}. On 15 and 16 June, a branch of lava flow to the south of Melfell traveled over {{convert|1|km|abbr=on}} in 30&nbsp;hours before slowing and stopping by 21 June, {{convert|7.8|km|abbr=on}} from the Lava Crater. The longest lava stream produced was {{convert|8|km|abbr=on}} long and stopped in Stóraskógsbotnar. A scientist filming one of the lava streams on 2 November was hit by a block of lava and was killed.<ref name="Morgunblaðið">{{cite web |url= http://timarit.is/view_page_init.jsp?pageId=1265411 |title=Morgunblaðið, 04.11.1947 |work=[[Timarit.is]] |year=2012 |access-date=22 July 2012}}</ref>

The lava flow stopped after 13&nbsp;months on 21 April, having covered {{convert|40|km2|abbr=on}} and with a maximum depth of {{convert|100|m|abbr=on}}. The lava beds produced were mainly the [[ʻAʻā]] lava type with [[Pāhoehoe]] and ''lava a budella'' (lava tubes) 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 {{convert|24000|tonne}} 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, pp. 19–38</ref>

===1970 to 1991===
;1970
[[File:Hekla lava 1971.jpg|thumb|left|Lava flow from the 1970 eruption, seen in 1971]]
The 1970 eruption of Hekla started at 9:23&nbsp;pm on 5 May 1970 and lasted until 5 July. It had a VEI of 3 and produced {{convert|0.2|km3|abbr=on}} of lava covering an area of {{convert|18.5|km2|abbr=on}} and 6.6×10&nbsp;<sup>7</sup>&nbsp;m³ of tephra, deposited over an area of {{convert|40000|km2|abbr=on}}, 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 south-southwest on 10 May and in Hlídargígar on 20 May, but a new fissure opened on the same day and lava flowed from this until 5 July. The lava was andesite containing olivine, similar to the lava produced later in the eruption of 1947.<ref name="HANVp39to58">Thorarinsson, pp.&nbsp;39–58</ref>

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&nbsp;pm on the evening of the eruption; the largest had a magnitude of 4. The eruption started weakly at 9:23&nbsp;pm IMT ± 2&nbsp;min before increasing in power. The first pumice fell on [[Búrfell (Þjórsárdal)|Búrfell]] power station, {{convert|15|km|abbr=on}} away, at 9:35&nbsp;pm causing people to evacuate. The eruption seems to have started in two locations at the same time – to the Shoulder crater's south-southwest and below the Lava Crater. At 10:30&nbsp;pm a crater at {{convert|780|m|abbr=on}} was producing a lava column which reached an altitude of around {{convert|1|km|abbr=on}}. During the night a {{convert|700|m|abbr=on}} high [[lava fountain]] was thrown up from the main crater. A {{convert|500|m|abbr=on}} 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 {{convert|400|m|abbr=on}} fissure opened to the northeast, producing two main lava fountains, and shortly after another adjoining fissure opened producing lava fountains to a height of {{convert|500|m|abbr=on}}. At around midnight, another fissure opened northwest of the Lava Crater, later hurling an over {{convert|300|m|abbr=on}} long lava fountain, {{convert|200|-|300|m|abbr=on}} into the air. By midnight lava had already covered over {{convert|1|km2|abbr=on}} and this extended to {{convert|7.5|km2|abbr=on}} by next morning implying a [[Volumetric flow rate|flow rate]] of around 1500&nbsp;m³/s.

For the first two hours, tephra was produced at the rate of 10000&nbsp;m³/s. The cloud from the eruption, which had reached {{convert|53000|ft|m|0}} by 10:10&nbsp;pm, caused a [[lightning storm]]. The tephra was transported northwards by the wind, causing the sky to turn black in places – {{convert|190|km|abbr=on}} away at [[Blönduós]] tephra fell from midnight until 2&nbsp;am, and ash fell on a [[fishing trawler|trawler]] {{convert|330|km|abbr=on}} away at 2&nbsp;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&nbsp;tonnes per hectare) extending to the north coast.<ref name="GVP" /><ref name="HANVp39to58" />

[[File:Hekla and gate.jpg|thumb|right|Hekla in winter 2010]]
By 5:30 on 6 May, the lava flow measured {{convert|4|km|abbr=on}} long. Many lava bombs were found near the main crater, one had an area of {{convert|6|m2|abbr=on}} and a likely weight of 12&nbsp;tons.{{ambiguous|date=December 2023}}{{citation needed|date=December 2023}}<!--is this metric ton, long ton or short ton---> [[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 12 May, with columns of steam attaining a height of {{convert|2500|m|abbr=on}}. The eruption intensity then gradually reduced until it stopped on 20 May. The lava field then had an area of {{convert|5.8|km2|abbr=on}}. Later that day a {{convert|900|m|abbr=on}} long fissure opened {{convert|1|m2|abbr=on}}1&nbsp;km north of the main Hlídargígar crater. That night it contained 17 lava fountains, each {{convert|20|–|50|m|abbr=on}} in height. By the evening of the next day, 10–12&nbsp;craters had formed, each throwing pieces of lava {{convert|50|–|100|m|abbr=on}} 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 {{convert|100|m|abbr=on}} 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, occasionally with lightning within the tephra cloud. By 5 July, the eruption had stopped.<ref name="HANVp39to58" />

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 within 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 matter|dry weight]] content of up to 0.4%&nbsp;fluorine. 450&nbsp;farms and 95,000&nbsp;sheep were affected by the eruption. Some sheep were kept inside and fed on hay or moved, but other farmers were forced to graze their flocks outside.<ref name="HANVp39to58" />

;1980 and 1981
[[File:Hekla1980.jpg|thumb|right|Mount Hekla erupting in 1980. Seen from 4&nbsp;km NE of the summit.]]

This VEI-3 eruption started at 13:28 on 17 August 1980 and lasted until 20 August 1980. It was a mixed eruption producing a lava volume of {{convert|0.12|km3|abbr=on}} and a tephra volume of {{convert|5.8E7|m3|abbr=on}}. The fissure opened along a {{convert|7|km|abbr=on}} length. Shortly before the eruption started a steam column was produced; eventually the [[eruption column]] reached a height of {{convert|15|km|abbr=on}}. The main tephra deposits were to the north-northeast and lasted for around 2&nbsp;hours. Deposits were {{convert|20|cm|abbr=on}} thick {{convert|10|km|abbr=on}} from the summit, decreasing to less than {{convert|1|mm|abbr=on}} at the coast {{convert|230|km|abbr=on}} away.
Lava was initially produced from close to the summit, spreading to other parts of the fissure and covering an area of {{convert|22|km2|abbr=on}} in around 24&nbsp;hours. The last [[scoria]] were seen on the morning of 20 August. This was an unusual eruption both in the short time since the previous eruption – the shortest since 1104, and the length – previous eruptions had lasted from 2&nbsp;months to 2&nbsp;years rather than just 3&nbsp;days.<ref name="GVP" /><ref>{{cite journal |url=http://homepage.ntlworld.com/i.p.hutchinson/iceland/Natturu1983-175.PDF |title=Upphaf Eldgossins í Heklu, 1980 |trans-title=On the Eruption of Hekla, 1980 |access-date=1 January 2008 |author=Hutchinson, I.P. |year=1983 |journal=Náttúrufræðingurinn |volume=52 |issue=1–4 |pages=175–183 |url-status=dead |archive-url=https://web.archive.org/web/20071001050322/http://homepage.ntlworld.com/i.p.hutchinson/iceland/Natturu1983-175.PDF |archive-date=1 October 2007}}</ref>

The 1981 eruption, which is regarded as being a continuation of the previous year's eruption, began at 3&nbsp;am on 9 April 1981, had a VEI of 2 and produced {{convert|3E7|m3|abbr=on}} of lava, lasting until 16 April 1981. The eruption threw ash to a height of {{convert|6.6|km|abbr=on}}, and a new crater formed at the summit from which 3&nbsp;lava flows originated. These extended to a maximum of {{convert|4.5|km|abbr=on}} from the volcano, covering {{convert|5|-|6|km2|abbr=on}}.<ref name="GVP" /><ref name="VW" />

;1991
[[File:Hekla sideview.jpg|thumb|right|A summer 2009 view of Hekla from the side.]]
A VEI-3 eruption occurred from 17 January 1991 to 11 March 1991, producing {{convert|0.15|km3|abbr=on}} of lava and {{convert|2E7|m3|abbr=on}} of tephra. The eruption, which was preceded by sulphurous smells and earthquakes, started as a [[Plinian eruption]], producing an ash cloud reaching an altitude of {{convert|11.5|km|abbr=on}} within 10&nbsp;minutes which had travelled over {{convert|200|km|abbr=on}} north-northeast to the coast within 3&nbsp;hours. The eruption then began producing andesitic lava, the flows eventually covering an area of {{convert|23|km2|abbr=on}} to an average depth of {{convert|6|-|7|m|abbr=on}}. Initially, part of the Heklugjá fissure and other fissures erupted with lava fountains reaching {{convert|300|m|abbr=on}} in height. By the second day, the activity stopped in all but one fissure where the main crater formed. During these 2&nbsp;days, 800&nbsp;m³/s of lava were produced, slowing to between 1&nbsp;m³/s and 14&nbsp;m³/s 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.oregonstate.edu/vwdocs/volc_images/europe_west_asia/hekla_erupt.html |title=The Hekla eruption of 1991 |access-date=8 July 2008 |work=Volcano World |publisher=Oregon State University |archive-date=3 March 2016 |archive-url=https://web.archive.org/web/20160303213155/http://volcano.oregonstate.edu/vwdocs/volc_images/europe_west_asia/hekla_erupt.html |url-status=dead }}</ref>

===2000===
[[File:Iceland-Hekla2-July 2000.jpg|thumb|right|A lava field on Hekla in July 2000]]
The most recent eruption was relatively short; it started at 18:18 on 26 February 2000 and lasted until 8 March. It was a VEI-3 eruption producing a lava volume of {{convert|0.189|km3|abbr=on}},  [[Dense-rock equivalent|DRE]]<ref name="TMEOH">{{cite journal |title= The millennium eruption of Hekla in February 2000 |year= 2007 |doi=10.1007/s00445-007-0128-3|bibcode=2007BVol...70..169H|pages=169–182 |last1= Höskuldsson |first1= Ármann |last2= Óskarsson |first2= Níels |last3= Pedersen |first3= Rikke |last4= Grönvold |first4= Karl |last5= Vogfjörð |first5= Kristín |last6= Ólafsdóttir |first6= Rósa |journal= Bulletin of Volcanology |volume= 70 |issue= 2|s2cid= 129882382 }}</ref> {{convert|0.29|km3|abbr=on}} <ref name="GVP" /> and {{convert|1E7|m3|abbr=on}}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 {{convert|6|-|7|km|abbr=on}}. The steam column rose to a height of almost {{convert|15|km|abbr=on}}, and ash was transported to [[Grímsey]] on the North coast of Iceland.<ref>{{cite web |url=http://www.hi.is/~thorstur/science/hekla2000.htm |title=Hekla erupts Feb 26 – ~29, 2000|access-date=19 January 2008 |work=Modified from Daily News from Iceland}}</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.<ref name=Grindle2003/>

Up until this eruption, it had 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.
[[Image:Steaming top of Hekla volcano, Island.jpg|thumb|right|Steam at the summit of Hekla]]
=== Eruption Summary ===
{| class="wikitable sortable" width=70%
|+ Summary of known eruptions
|-
! data-sort-type="number" width=95px | Start Date<ref name="GVPHEH" />
! class="unsortable" width=95px | Years before 1950 (BP)
! width=70px | VEI<ref name="GVPHEH" />
! width=70px | Lava volume<br>(km<sup>3</sup>)<ref name="CIV">{{cite web|url =https://icelandicvolcanoes.is/?volcano=HEK|title =Catalogue of Icelandic Volcanoes:Catalogue of Icelandic Volcanoes:Hekla|access-date=30 June 2024}}</ref>
! width=70px | Tephra volume<br>(km<sup>3</sup>)<ref name="CIV" />
! class="unsortable"| Comment
|-
| align="center"|<span style="display:none">2000</span> {{dts|February 26, 2000}}
| align="center"| -
! style="background-color: #FC0;" | 3 
| align="center"| 0.19
| align="center"| 0.01
| Eruption ended {{dts|March 8, 2000}}<ref name="GVPHEH" />
|-
| align="center"|<span style="display:none">1991</span> {{dts|January 17, 1991}}
| align="center"| -
! style="background-color: #FC0;" | 3 
| align="center"| 0.15
| align="center"| 0.02
| Eruption ended {{dts|March 11, 1991}}<ref name="GVPHEH" />
|-
| align="center"|<span style="display:none">1981</span> {{dts|April 9, 1981}}
| align="center"| -
! style="background-color: #FD0;" | 2 
| align="center"| 0.03<ref name="Sonnentag2024" >{{cite thesis|url =https://skemman.is/bitstream/1946/46291/1/msthesis_kths.pdf|title =Mass eruption rates in the explosive phase of the last five Hekla eruptions, comparison between observations and models|last1 =Sonnentag|first1 =Kristín Þorsteinsdóttir|year=2024|publisher =Faculty of Earth Science, University of Iceland|access-date =1 July 2024}}</ref>
| align="center"| -
| Eruption ended {{dts|April 16, 1981}}<ref name="GVPHEH" />
|-
| align="center"|<span style="display:none">1980</span> {{dts|August 17, 1980}}
| align="center"| -
! style="background-color: #FC0;" | 3 
| align="center"| 0.12<ref name="Sonnentag2024" /> <!--smaller than 0.15 of 2019 source so preferred ---->
| align="center"| 0.06
| Eruption ended {{dts|August 20, 1980}}<ref name="GVPHEH" />
|-
| align="center"|<span style="display:none">1970</span> {{dts|May 5, 1970}}
| align="center"| 
! style="background-color: #FC0;" | 3 
| align="center"| 0.2
| align="center"| 0.07
| Eruption ended {{dts|July 5, 1970}}<ref name="GVPHEH" />
|-
| align="center"|<span style="display:none">1947</span> {{dts|March 29, 1947}}
| align="center"| 3
! style="background-color: #F90;" | 4
| align="center"| 0.8
| align="center"| 0.18
| Eruption ended {{dts|April 21, 1948}}<ref name="GVPHEH" />
|-
|-
| align="center"|<span style="display:none">1913</span> {{dts|April 25, 1913}}
| align="center"| {{ #expr: 1950-1913 }}
! style="background-color: #FD0;" | 2 
| align="center"| 0.05
| align="center"| -
| Eruption ended {{dts|May 18, 1913}}<ref name="GVPHEH" />
|-
| align="center"|<span style="display:none">1878</span> {{dts|February 27, 1878}}
| align="center"| {{ #expr: 1950-1878 }}
! style="background-color: #FD0;" | 2 
| align="center"| 0.2
| align="center"| -
| Eruption ended April 1878<ref name="GVPHEH" />
|-
| align="center"|<span style="display:none">1845</span> {{dts|September 2, 1845}}
| align="center"| {{ #expr: 1950-1854 }}
! style="background-color: #F90;" | 4 
| align="center"| 0.63
| align="center"| 0.23
| Eruption ended about {{dts|April 5, 1846}}<ref name="GVPHEH" />
|-
| align="center"|<span style="display:none">1776</span> {{dts|April 5, 1776}}
| align="center"| {{ #expr: 1950-1776 }}
! style="background-color: #F90;" | 4
| align="center"| 1.3
| align="center"| 0.4
| Eruption ended in May 1768.<ref name="GVPHEH" /> Tephra composition is rhyolite to dacite (Icelandite).<ref name="Harning2024" >{{cite journal|last1 =Harning|first1 =D.J.|last2 =Florian|first2 =C.R.|last3 =Geirsdóttir|first3 =Á.|last4 =Thordarson|first4 =T.|last5 =Miller|first5 = G.H.|last6 =Axford|first6 =Y.|last7 =Ólafsdóttir|first7 =S.|year =2024|title =High-resolution Holocene record from Torfdalsvatn, north Iceland, reveals natural and anthropogenic impacts on terrestrial and aquatic environments|journal =Climate of the Past Discussions|pages =1-41|doi =10.5194/cp-2024-26|doi-access =free}}</ref>
|-
| align="center"|<span style="display:none">1725</span> {{dts|April 2, 1725}}
| align="center"| {{ #expr: 1950-1725 }}
! style="background-color: #FE0;" | 1 
| align="center"| -
| align="center"| -
| 
|-
| align="center"|<span style="display:none">1693</span> {{dts|February 13, 1693}}
| align="center"| {{ #expr: 1950-1693 }}
! style="background-color: #F90;" | 4 
| align="center"| -
| align="center"| 0.3
| Eruption ended about {{dts|September 14, 1693}}<ref name="GVPHEH" />
|-
| align="center"|<span style="display:none">1636</span> {{dts|May 8, 1636}}
|  align="center"| {{ #expr: 1950-1636 }}
! style="background-color: #FC0;" | 3 
| align="center"| -
| align="center"| 0.18
| Eruption ended in June 1637<ref name="GVPHEH" />
|-
| align="center"|<span style="display:none">1597</span> {{dts|January 3, 1597}}
| align="center"| {{ #expr: 1950-1597 }}
! style="background-color: #F90;" | 4 
| align="center"| 
| align="center"| 0.29
| Eruption ended in or after June 1597<ref name="GVPHEH" />
|-
| align="center"|<span style="display:none">1554</span> {{dts|May 1554}}
|  align="center"|{{ #expr: 1950-1554 }}
! style="background-color: #FD0;" | 2 
| align="center"| 0.1
| align="center"| -
| Eruption ended about June 1554
|-
| align="center"|<span style="display:none">1510</span>{{dts|July 25, 1510}}
| align="center"|{{ #expr: 1950-1510 }}
! style="background-color: #F90;" | 4 
| align="center"| -
| align="center"| 0.32
| 
|-
| align="center"|<span style="display:none">1389</span> {{dts|December, 1389}}
| align="center"| {{ #expr: 1950-1389 }}
! style="background-color: #FC0;" | 3 
| align="center"| 0.2
| align="center"| 0.15
| Eruption ended in 1390
|-
| align="center"|<span style="display:none">1341</span> {{dts|May 19, 1341}}
| align="center"| {{ #expr: 1950-1341 }}
! style="background-color: #FC0;" | 3 
| align="center"| -
| align="center"| 0.18
| 
|-
| align="center"|<span style="display:none">1300</span> {{dts|July 11, 1300}}
| align="center"| {{ #expr: 1950-1300 }}
! style="background-color: #F90;" | 4 
| align="center"| 0.5
| align="center"| 0.5
| Eruption ended in July 1301. Tephra composition is rhyolite to dacite (Icelandite).<ref name="Harning2024" />
|-
| align="center"|<span style="display:none">1222</span> {{dts|1222}}
| align="center"| {{ #expr: 1950-1222 }}
! style="background-color: #F90;" | 2 
| align="center"| -
| align="center"| 0.04
| 
|-
| align="center"|<span style="display:none">1206</span> {{dts|December 4, 1206}}
|  align="center"|{{ #expr: 1950-1206 }}
! style="background-color: #FC0;" | 3
| align="center"| -
| align="center"| 0.4
| Dated using historical records.
|-
| align="center"|<span style="display:none">1158</span> {{dts|January 19, 1158}}
| align="center"| {{ #expr: 1950-1158 }}
! style="background-color: #F90;" | 4
| align="center"| 0.1
| align="center"| 0.33
| 
|-
| align="center"|<span style="display:none">1104</span> {{dts|October 15, 1104}}
| align="center"| {{ #expr: 1950-1104 }}
! style="background-color: #F60;" | 5 
| align="center"| 0
| align="center"| 2.0
| H 1 tephra, composition is rhyolite.<ref name="Harning2024" />  Erupted within 45 days of date.
|-
| align="center"|<span style="display:none">1050</span> {{dts|1050}} ± 500
| align="center"| {{ #expr: 1950-1050 }} ± 500
| align="center"| - 
| align="center"| -
| align="center"| -
| 
|-
| align="center"|<span style="display:none">781</span> {{dts|781}} ± 2
| align="center"| {{ #expr: 1950-781 }} ± 2
| align="center"| -
| align="center"| -
| align="center"| -
|Greenland ice core<ref name ="Gabriel2024" >{{cite journal|last1 =Gabriel|first1 =I.|last2 =Plunkett|first2 =G.|last3 =Abbott|first3 =P.M.|last4 =Behrens|first4 =M.|last5 =Burke|first5 =A.|last6 =Chellman|first6 = N.|last7 =Cook|first7 =E.|last8 =Fleitmann|first8 =D.|last9 =Hörhold|first9 =M.|last10 =Hutchison|first10 =W.|last11 =McConnell|first11 =J.R.|year =2024|title =Decadal-to-centennial increases of volcanic aerosols from Iceland challenge the concept of a Medieval Quiet Period|journal =Communications Earth & Environment|volume =5|issue =1|pages =194|doi =10.1038/s43247-024-01350-6|bibcode =2024ComEE...5..194G|doi-access =free|hdl =10023/29795|hdl-access =free}}</ref> 
|-
| align="center"|<span style="display:none">753</span> {{dts|753}} ± 2
| align="center"| {{ #expr: 1950-753 }} ± 2
| align="center"| -
| align="center"| -
| align="center"| -
|Greenland ice core<ref name ="Gabriel2024" />
|-
| align="center"|<span style="display:none">650</span>{{dts|650}} ± 500
| align="center"| {{ #expr: 1950-650 }} ± 500
| align="center"| -
| align="center"| -
| align="center"| -
| 
|-
| align="center"|<span style="display:none">550</span> {{dts|550}} ± 1500
| align="center"| {{ #expr: 1950-550 }} ± 1500
| align="center"| -
| align="center"| -
| align="center"| -
| 
|-
| align="center"|<span style="display:none">350</span> {{dts|350}} ± 500
| align="center"| {{ #expr: 1950-350 }} ± 500
| align="center"| -
| align="center"| -
| align="center"| -
| 
|-
| align="center"|<span style="display:none">250</span> {{dts|250}} ± 1500
| align="center"| {{ #expr: 1950-250 }} ± 1500
| align="center"| -
| align="center"| -
| align="center"| -
| 
|-
| align="center"|<span style="display:none">-150</span> {{dts|150}} ± 2500 BCE 
| align="center"| {{ #expr: 1950+150 }} ± 2500
| align="center"| -
| align="center"| -
| align="center"| -
| 
|-
| align="center"|<span style="display:none">-250</span> {{dts|250}} ± 500 BCE  
| align="center"| {{ #expr: 1950+250 }} ± 500
| align="center"| -
| align="center"| -
| align="center"| -
| 
|-
| align="center"|<span style="display:none">-650</span> {{dts|650}} ± 2500 BCE  
| align="center"| {{ #expr: 1950+650 }} ± 2500
| align="center"| -
| align="center"| -
| align="center"| -
| 
|-
| align="center"|<span style="display:none">-750</span> {{dts|750}} ± 500 BCE  
| align="center"| {{ #expr: 1950+750 }} ± 500
| align="center"| -
| align="center"| -
| align="center"| -
| 
|-
| align="center"|<span style="display:none">-850</span> {{dts|850}} ± 80 BCE  
| align="center"| {{ #expr: 1950+850 }} ± 80
| align="center"| -
| align="center"| -
| align="center"| -
|  H C dacite (Icelandite) tephra.<ref name="Harning2024" />
|-
| align="center"|<span style="display:none">{{ #expr: 1950-3013}}</span> {{dts|{{ #expr: 3013-1950}}}} ± 140 BCE  
| align="center"| 3013 ± 140
! style="background-color: #F60;" | 5
| align="center"| -
| align="center"| 10
| H 3 dacite, rhyolite tephra.<ref name="Harning2024" /> Cal. BP<ref name="Davis2024" />
|-
| align="center"|<span style="display:none">-1150</span> {{dts|1150}} ± 1500 BCE  
| align="center"| {{ #expr: 1950+1150 }} ± 1500
| align="center"| -
| align="center"| -
| align="center"| -
| 
|-
| align="center"|<span style="display:none">-1250</span> {{dts|1250}} ± 1500 BCE  
| align="center"| {{ #expr: 1950+1250 }} ± 1500
| align="center"| -
| align="center"| -
| align="center"| -
| 
|-
| align="center"|<span style="display:none">-1350</span> {{dts|1350}} ± 2500 BCE  
| align="center"| {{ #expr: 1950+1350 }} ± 2500
| align="center"| -
| align="center"| -
| align="center"| -
| 
|-
| align="center"|<span style="display:none">-1550</span> {{dts|1550}} BCE
| align="center"| {{ #expr: 1950+1550 }}
! style="background-color: #F90;" | 4 
| align="center"| -
| align="center"| -
| 
|-
| align="center"|<span style="display:none">-1650</span> {{dts|1650}} ± 2500 BCE  
| align="center"| {{ #expr: 1950+1650 }} ± 2500
| align="center"| -
| align="center"| -
| align="center"| -
| 
|-
| align="center"|<span style="display:none">-1750</span> {{dts|1750}} ± 500 BCE  
| align="center"| {{ #expr: 1950+1750 }} ± 500
| align="center"| -
| align="center"| -
| align="center"| -
| 
|-
| align="center"|<span style="display:none">-1850</span> {{dts|1850}} ± 2500 BCE  
| align="center"| {{ #expr: 1950+1850 }} ± 2500
| align="center"| -
| align="center"| -
| align="center"| 2.0
| 
|-
| align="center"|<span style="display:none">{{ #expr: 1950-4325 }}</span> {{dts|{{ #expr: 4325-1950 }}}} ± 8 BCE  
| align="center"| 4325 ± 8
! style="background-color: #F60;" | 5 
| align="center"| -
| align="center"| 10.0
| H 4 rhyolite tephra.<ref name="Harning2024" />Ice core age used.<ref name="Davis2024" />
|-
| align="center"|<span style="display:none">-2335</span> {{dts|2335}} ± 180 BCE  
| align="center"| {{ #expr: 1950+2335 }} ± 180
| align="center"| -
| align="center"| -
| align="center"| -
| H 4270 alkali basalt tephra.<ref name="Harning2024" /> Age corrected for H4 ice core age to maintain mean 10 year separation.<ref name="Davis2024" />
|-
| align="center"|<span style="display:none">-2450</span> {{dts|2450}} ± 1500 BCE  
| align="center"| {{ #expr: 1950+2450 }} ± 1500
| align="center"| -
| align="center"| -
| align="center"| -
| 
|-
| align="center"|<span style="display:none">-2750</span> {{dts|2750}} ± 2500 BCE  
| align="center"| {{ #expr: 1950+2750 }} ± 2500
| align="center"| -
| align="center"| -
| align="center"| -
| 
|-
| align="center"|<span style="display:none">-2950</span> {{dts|2950}} ± 500 BCE  
| align="center"| {{ #expr: 1950+2950 }} ± 500
| align="center"| -
| align="center"| -
| align="center"| -
| 
|-
| align="center"|<span style="display:none">-3350</span> {{dts|3350}} ± 2500 BCE  
| align="center"| {{ #expr: 1950+3350 }} ± 2500
| align="center"| -
| align="center"| -
| align="center"| -
| 
|-
| align="center"|<span style="display:none">-3450</span> {{dts|3450}} ± 1500 BCE  
| align="center"| {{ #expr: 1950+3450 }} ± 1500
| align="center"| -
| align="center"| -
| align="center"| -
| 
|-
| align="center"|<span style="display:none">-3750</span> {{dts|3750}} ± 1500 BCE  
| align="center"| {{ #expr: 1950+3750 }} ± 1500
| align="center"| -
| align="center"| -
| align="center"| -
| 
|-
| align="center"|<span style="display:none">-3950</span> {{dts|3950}} ± 500 BCE  
| align="center"| {{ #expr: 1950+3950 }} ± 500
| align="center"| -
| align="center"| -
| align="center"| -
| 
|-
| align="center"|<span style="display:none">-4050</span> {{dts|4050}} ± 500 BCE  
| align="center"| {{ #expr: 1950+4050 }} ± 500
| align="center"| -
| align="center"| -
| align="center"| -
| 
|-
| align="center"|<span style="display:none">-4110</span> {{dts|4110}} ± 100 BCE
| align="center"| {{ #expr: 1950+4110 }} ± 100
! style="background-color: #F60;" | 5 
| align="center"| 0
| align="center"| 1
|
|-
| align="center"|<span style="display:none">-4150</span> {{dts|4150}} ± 2500 BCE  
| align="center"| {{ #expr: 1950+4150 }} ± 2500
| align="center"| -
| align="center"| -
| align="center"| -
| 
|-
| align="center"|<span style="display:none">-4250</span> {{dts|4250}} ± 500 BCE  
| align="center"| {{ #expr: 1950+4250 }} ± 500
| align="center"| -
| align="center"| -
| align="center"| -
| 
|-
| align="center"|<span style="display:none">-4650</span> {{dts|4650}} ± 500 BCE  
| align="center"| {{ #expr: 1950+4650 }} ± 500
| align="center"| -
| align="center"| -
| align="center"| -
| 
|-
| align="center"|<span style="display:none">-4700</span> {{dts|4700}} BCE  
| align="center"| {{ #expr: 1950+4700 }} 
! style="background-color: #F90;" | 4 
| align="center"| -
| align="center"| -
| Date only constrained by before and after eruptions
|-
| align="center"|<span style="display:none">-4750</span> {{dts|4750}} ± 2500 BCE  
| align="center"| {{ #expr: 1950+4750 }} ± 2500
| align="center"| -
| align="center"| -
| align="center"| -
| 
|-
| align="center"|<span style="display:none">-4950</span> {{dts|4950}} ± 2500 BCE  
| align="center"| {{ #expr: 1950+4950 }} ± 2500
| align="center"| -
| align="center"| -
| align="center"| -
| 
|-
| align="center"|<span style="display:none">-5050</span> {{dts|5050}} BCE  
| align="center"| {{ #expr: 1950+5050 }}
| align="center"| -
| align="center"| -
| align="center"| -
| Date only constrained by before and after eruptions
|-
| align="center"|<span style="display:none">{{ #expr: 1950-7053 }}</span> {{dts|{{ #expr: 7053-1950 }}}} ± 260 BCE  
| align="center"| 7053 ± 260
! style="background-color: #F60;" | 5 
| align="center"| -
| align="center"| 3
| H 5 basaltic to rhyolite tephra. Cal BP age used.<ref name="Davis2024" />
|-
| align="center"|<span style="display:none">-5850</span> {{dts|5850}}  ± 2500 BCE  
| align="center"| {{ #expr: 1950+5850 }} ± 2500
| align="center"| -
| align="center"| -
| align="center"| -
|
|- 
| align="center"|<span style="display:none">{{ #expr: 1950-10550 }}</span> {{dts|{{ #expr: 10550-1950 }}}}  ± 150 BCE  
| align="center"| 10550 ± 150
| align="center"| -
| align="center"| -
| align="center"| -
|H 10550 alkali basalt tephra.<ref name="Harning2024" />
|}