Editing Hekla (section)

===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>