Editing Hekla (section)

==Geology==
[[File:Volcanic system of Iceland-Map-en.svg|thumb|right|A map of the volcanic systems of Iceland]]
Hekla has a morphological type between that of a [[fissure vent]] 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. The unusual form of Hekla is found on very few volcanoes around the world, notably [[Callaqui]] in [[Chile]].<ref name=callaqui>{{Citation
| last1  = Moreno Roa
| first1 = Hugo
| author-link1=Hugo Moreno Roa
| last2  = Lahsen Azar
| first2 = Alfredo
| title = Ejemplos del Volcanismo Fisural en los Andes del Sur (38°L.S.)
| journal = [[Revista de la Asociación Geológica Argentina]]
| volume  = 42
| issue   = 1–2
| year    = 1986
| pages   = 1–8
| url     = https://books.google.com/books?id=TmeTcaSm2LcC&pg=PA2
}}</ref> The {{convert|5.5|km|abbr=on}} ''Heklugjá'' fissure opens along its entire length during major eruptions and is fed by a [[magma chamber|magma reservoir]] estimated to have a top {{convert|4|km|abbr=on}} below the surface with centroid {{convert|2.5|km|abbr=on}} lower. The chamber extends to an unusual depth of more than {{convert|10|km|abbr=on}},<ref name=Vestergaard2000>{{cite journal|last1 =Vestergaard|first1 =R|last2 =Pedersen|first2 =GB|last3 =Tegner|first3 =C|title =The 1845–46 and 1766–68 eruptions at Hekla volcano: new lava volume estimates, historical accounts and emplacement dynamics|journal = Jökull| year=2020|volume =70|pages =35–56|doi =10.33799/jokull2020.70.035|doi-access =free}}</ref>{{rp|36}} and the more [[silicic]] lavas have matured at more than {{cvt|9|km}}.<ref name=Ilyinskaya2015>{{cite journal|last1 =Ilyinskaya|first1 =E.|last2 =Aiuppa|first2 =A.|last3 =Bergsson|first3 =B.|last4 =Di Napoli|first4 =R.|last5 =Fridriksson|first5 =T.|last6 =Óladóttir|first6 =A.A.|last7 =Óskarsson|first7 =F.|last8 =Grassa|first8 =F.|last9 =Pfeffer|first9 =M.|last10 =Lechner|first10 =K.|last11 =Yeo|first11 =R.|year =2015|title =Degassing regime of Hekla volcano 2012–2013|journal =Geochimica et Cosmochimica Acta|volume =159|pages =80–99|doi =10.1016/j.gca.2015.01.013|bibcode =2015GeCoA.159...80I|hdl =10447/172920|hdl-access =free}}</ref>{{rp|p=81}}

Many of the eruptions commence with thicker more explosive [[rhyolite]], [[dacite]] or [[andesite]] eruptives which create tephra and have the potential for [[pyroclastic flow]]s.<ref name=Vestergaard2000/>{{rp|36–38}}<ref name=Ilyinskaya2015/>{{rp|p=81}} Other or the later part of eruptions come from thinner [[basalt]] tending [[magma]] which forms lava fields.<ref name=Vestergaard2000/>{{rp|36–38}}

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="GVP"/><ref>
  {{cite web
  | url = http://hraun.vedur.is/ja/skyrslur/contgps/node20.html
  | title = Hekla eruption 2000
  | publisher = The Icelandic Meteorological Office
  | access-date = 19 January 2008 }}</ref>
It is the only Icelandic volcano to produce [[calc-alkaline]] lavas.<ref name="TNSC">
  {{cite web
  | url = http://www.utexas.edu/tmm/npl/mineralogy/mineral_genesis/hekla.html
  | title = Hekla
  | work = Texas Natural Science Center, Non-vertebrate Paleontology Laboratory
  | publisher = University of Texas
  | date = 24 April 2008
  | access-date = 17 August 2008 }}</ref>
[[Phenocryst]]s in Hekla's lava can contain [[plagioclase]], [[pyroxene]], [[titanomagnetite]], [[olivine]], and [[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 |author=Soosalu, Heidi |title=Hekla Seismicity |access-date=14 January 2008 |publisher=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_heklaseismicity |archive-date=12 February 2007 }}</ref> Hekla is located on the mid-ocean ridge, a [[divergent boundary|diverging plate boundary]].
Hekla is closely studied today for parameters such as [[Strain (materials science)|strain]], tilt, [[Deformation (volcanology)|deformation]] and other movement and seismic activity.<ref name="UoI_Deform">{{cite web|url=http://www.earthice.hi.is/page/ies_hekladeformation |author=Sturkell, Erik |title=Hekla Deformation |access-date=14 January 2008 |publisher=University of Iceland, Institute of Earth Sciences |url-status=dead |archive-url=https://web.archive.org/web/20070216091240/http://www.earthice.hi.is/page/ies_hekladeformation |archive-date=16 February 2007 }}</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" />