View source for Hengill

{{Short description|Mountain range in Iceland}}
{{Infobox mountain
| name = Hengill
| photo = Þingvellir_Iceland_034.JPG
| photo_caption = Hengill, 2004
| elevation_m = 803
| elevation_ref = <ref name="LI">{{cite web|url=https://kortasja.lmi.is/mapview/|title=National Land Survey of Iceland: Sýrfell|publisher =Landmælingar Íslands|date=30 December 2023}}</ref><ref name=gvp>{{harvnb|Venzke|2023}} {{cite gvp|vn=371050|vtab=Eruptions|title=Hengill}}</ref>
| prominence = 
| listing = [[List of volcanoes in Iceland]]
| location = [[Iceland]]
| range = 
| map = Iceland |relief=1
| range_coordinates = 
| map_caption = 
| map_size = 200
| label_position = right
| coordinates = {{coord|64|05|08|N|21|18|48|W|type:mountain_region:IS_scale:100000|format=dms|display=inline,title}}
| coordinates_ref = 
| type = [[Shield volcano]], [[fissure vent]]s
| age = 200,000 years ago{{snf|Sæmundsson|2019|loc=4. Eruption history and pattern}}
| last_eruption = 150 CE ± 75 years <ref name=gvp/>
| first_ascent = 
| easiest_route = Hike
| map_image = {{maplink|frame=yes|frame-align=center|frame-width=280|frame-height=300|frame-long=-21.5|frame-lat=64.1|zoom=8|raw=[{{Wikipedia:Map data/Askja}},{{Wikipedia:Map data/Grímsvötn}},{{Wikipedia:Map data/Öræfi volcanic belt}},{{Wikipedia:Map data/Hofsjökull}},{{Wikipedia:Map data/Katla}},{{Wikipedia:Map data/Hengill}},{{Wikipedia:Map data/Snæfellsnes volcanic belt}}]
|text=Selected geological features near Hengill (red outline). {{Wikipedia:Map data/Askja/key}}
}} 
}}
'''Hengill''' ({{IPA|is|ˈheiɲcɪtl̥|audio=Hengill pronunciation.ogg}}) is a [[volcano|volcanic]] table mountain situated in the south-west of [[Iceland]], to the south of [[Þingvellir]]. <!-- The mountain range covers an area of about 4 by 7 km². REMOVED FROM LEAD as although about right is currently unreferenced -mention 20km2 size later-->

The volcano is still active, as evidenced by its numerous [[hot springs]] and [[fumarole]]s, but the last [[eruption]] occurred approximately 2,000&nbsp;years ago, before the [[settlement of Iceland]].

==Geography==
The mountain is south of Lake Thingvallavatn ([[Þingvallavatn]] in Icelandic), south-west of the Nesjavellir geothermal area, south of Þingvellir National Park and is the most prominent part of a volcanic region that extends to the coast.<ref name="LI"/> South of the mountain towards the coast is the Hellisheiði geothermal area to its south-west, and the town of [[Hveragerði]] on Iceland's main ringroad, [[Route 1 (Iceland)|Route 1]] about {{cvt|45|km|abbr=on}} east of [[Reykjavík]].<ref name="LI"/> At the coast is the port of [[Þorlákshöfn]].<ref name="LI"/>
<!--[[File:Reykjanes volcanic systems.png|thumb|290px|Map of the Reykjanes volcanic belt with 6) Hengill volcanic system]]--->
[[File:Hengladir.jpg|right|thumb|290px|Overlooking the Hengladalir {{IPA|is|ˈheiŋlaˌtaːlɪr̥|}} valleys to the east of Hengill]]
[[File:Spring in Hengill, Iceland.jpg|right|thumb|290px|A hot spring at the base of the Hengladalir valleys]]
[[File:Spring in Henfill.jpg|right|290px|A hot spring at the base of the Hengladalir valleys]]

==Geology==
The mountain is part of the {{cvt|60|km|abbr=on}} long Hengill volcanic system,{{snf|Sæmundsson|2019|loc=Short Description}}{{snf|Hernández|Pérez|Fridriksson|Egbert|2012|p=2437}} which is part of the [[Reykjanes volcanic belt]], and is a [[hyaloclastite]] massif of [[tuya]]s and [[Tindar (landform)|tindar]]s.{{snf|Sæmundsson|2019|loc=2. Morphology and topography}} The dominant lava in the Hengill volcanic system is [[Tholeiitic magma series|tholeiitic basalt]],{{snf|Sæmundsson|2019|loc=
1. Geological setting and tectonic context}} but [[andesite]] and about {{cvt|20|km2|abbr=on}} rhyolite occur within the central mountain.{{snf|Sæmundsson|2019|loc=2. Morphology and topography}} The largest lava shield covers about {{cvt|50|km2|abbr=on}}.{{snf|Sæmundsson|2019|loc=7. Erupted material & Grain size distribution:Basaltic lava flows}} Four small lava shields are [[picrite]] [[basalt]] and one lava shield contains about {{cvt|3|km3|abbr=on}}of [[olivine]] tholeiite.{{snf|Sæmundsson|2019|loc=4. Eruption history and pattern:Fissure swarm}} It is located at the intersection with two other tectonic volcanic systems, the [[West volcanic zone of Iceland]] and [[South Iceland seismic zone]],{{snf|Zakharova|Spichak|2012|p=5}}{{snf|Sæmundsson|2019|loc=Short Description}} and is co-located to the plate boundary between the [[North American Plate|North American]], [[Eurasian Plate|Eurasian]] and [[Geological deformation of Iceland#Hreppar microplate|Hreppar]] plates. This intersection is called the Hengill triple junction.{{snf|Decriem|Árnadóttir|Hooper|Geirsson|2010|p=1128}}
 
Hveragerdi to the south is a volcano in the volcanic system that became extinct 300,000 years ago, but still has significant seismic activity.{{snf|Zakharova|Spichak|2012|p=5}} It can be regarded as a predecessor volcano.{{snf|Hernández|Pérez|Fridriksson|Egbert|2012|p=2437}}  This seismic activity is significant not only because of human impact but also because the earthquakes are grouped along faults striking north–south or east–west, but not north to north-east, as might be supposed based on the surface geological structure and that the rift zone is deep as {{cvt|3|–|9|km|abbr=on}} locally.{{snf|Zakharova|Spichak|2012|p=5}} The earthquake distribution has been interpreted to have defined the heat source of the Hengill volcano.{{snf|Hernández|Pérez|Fridriksson|Egbert|2012|p=2437}}

Extending to the north-east from the central volcano is a fissure swarm with a number of tindars associated with an asymmetrical [[graben]].{{snf|Sæmundsson|2019|loc=2. Morphology and topography}} Lake Thingvallavatn, occupies the proximal graben, and has at its southern end lava flows from the mountain and has hosted explosive eruptions historically. Amongst the faults on the north-west side of the graben is the Almannagjá chasm which extends from the northern shore of Lake Thingvallavatn.{{snf|Sæmundsson|2019|loc=2. Morphology and topography}}

Towards the south-east from the mountain towards the sea is a lava covered plateau whose height is about {{cvt|300|-|400|m|abbr=on}} with scattered higher tindars and tuyas.{{snf|Sæmundsson|2019|loc=2. Morphology and topography}}

During the [[Holocene]] volcanic eruptions in the zone have been predominantly effusive and [[basalt]]ic with minor tephra production. Erupted lava volumes have ranged from {{cvt|0.05|-|3|km3|abbr=on}}.{{snf|Sæmundsson|2019|loc=Short Description}}
{| class="wikitable sortable"
|+ Hengill area recent tectonic history
|-
! Date !! Event !! Comment
|-
| 2008&nbsp;CE || [[2008 Iceland earthquake|Earthquake]]  ||No loss of life but 50% property damage in Ölfus region{{snf|Bessason|Sólnes|Bjarnason|Guðmundsson|2012|loc=5. Summary and Conclusions}}
|-
| 1789&nbsp;CE ||Subsurface [[Dike (geology)|dyke]] intrusion || Dyke injection later identified{{snf|Hernández|Pérez|Fridriksson|Egbert|2012|p=2437}}
|-
| 1000&nbsp;CE ||Adjacent volcanic system eruption ||Fissure west of Hengill, in the [[Brennisteinsfjöll]] volcanic system.{{snf|Hernández|Pérez|Fridriksson|Egbert|2012|p=2437}}<!--note can not find more than two references to the name Svínafellsbruni used in this reference in English literature and it is not an officially recognised Icelandic geographical name. There are hints that it is (was) a recognised Iceland area related to this eruption --> This eruption was at the time of a meeting of the Icelandic parliament at Thingvellir.<ref name=gvp/>  
|-
| 150±75&nbsp;CE || Eruption ||Along a fissure length of {{cvt|27|km|abbr=on}} and about {{cvt|30|km2|abbr=on}} lava erupted{{snf|Sæmundsson|2019|loc=Short Description}}. Included phreatomagmatic eruption from lake Thingvallavatn.{{snf|Sæmundsson|2019|loc=4. Eruption history and pattern:Fissure swarm}}<ref name=gvp/>
|-
| 80±75&nbsp;BCE || Eruption ||<ref name=gvp/>
|-
| 1730±50&nbsp;BCE || Eruption ||<ref name=gvp/>
|-
| ~3250&nbsp;BCE || Eruption ||<ref name=gvp/>
|-
| ~3750&nbsp;BCE || Eruption ||Along a fissure length of {{cvt|20|km|abbr=on}} and about {{cvt|30|km2|abbr=on}} lava erupted{{snf|Sæmundsson|2019|loc=Short Description}}<ref name=gvp/>
|-
| ~5000&nbsp;BCE || Eruption ||<ref name=gvp/>
|-
| ~5550±500&nbsp;BCE || Eruption ||Not well dated{{snf|Sæmundsson|2019|loc=4. Eruption history and pattern:Fissure swarm}}<ref name=gvp/>
|-
| ~7100&nbsp;BCE || Eruption ||<ref name=gvp/>
|-
| ~7300&nbsp;BCE || Eruption ||<ref name=gvp/>
|-
| ~7550&nbsp;BCE || Eruption ||<ref name=gvp/>
|-
| ~8200&nbsp;BCE || Eruption ||{{snf|Sæmundsson|2019|loc=4. Eruption history and pattern:Fissure swarm}}<ref name=gvp/>
|-
| ~8250&nbsp;BCE || Eruption ||<ref name=gvp/>
|-
| ~8350&nbsp;BCE || Eruption ||<ref name=gvp/>
|}
===Risk===
The official view of the volcanic hazard is that it is confined to a radius of {{cvt|30|km|abbr=on}} and is related to lava flows, plugging of geothermal boreholes by lava, volcano-tectonic faulting and volcanic gas pollution.{{snf|Sæmundsson|2019|loc=8. Volcanic hazards}}
<ref Group="lower-alpha">It is unclear why the known previous risks of either a phreatomagmatic eruption and/or of a rhyolitic eruption are not mentioned in this official hazard analysis. There is recent work suggesting the magma chamber may extend further in depth than past work suggested and this may or may not have been taken into account.</ref>

There was either hydrothermal fluid or magma increase at a depth of approximately {{cvt|5|–|7|km}} within the inferred brittle-ductile transition zone of the area centred at Ölkelduháls, between Hengill and [[Hrómundartindur]] to its east during 2017 and 2018. This volume had had  been contracting between 2006–2017, and was about {{cvt|3|km}} north-west from an area of uplift between 1993 and 1999.{{snf|Ducrocq|Geirsson|Árnadóttir|Juncu|2021|loc=4.2 Ölkelduháls, 5 Conclusion}}

==Geothermal resources==
There are three associated geothermal areas related to the high amount of fissuring in the Hengill volcanic
system producing high water subsurface permeability.{{snf|Zakharova|Spichak|2012|pp=5-6}} These areas include Iceland's second largest geothermal field which now is an important source of [[energy]] for the south of the country.{{snf|Sæmundsson|2019|loc=Short Description}} The three areas are:
#Nesjavellir [[Geothermal activity|geothermal system]], which is captured at the [[Nesjavellir power station]] near the western shore of the lake Þingvallavatn 
#Hellisheiði, which has the largest power station in Iceland, [[Hellisheiði power station]], approximately {{cvt|11|km|abbr=on}} south-west of Nesjavelli.  Both stations are operated by [[Orkuveita Reykjavíkur]] (Reykjavik Energy).
#Hveragerdi, whose hydrothermal waters have been used for greenhouse heating.

The area with its mountains and [[hot springs]] is well suited for [[hiking]] and there are a lot of hiking trails.
The town of Hveragerði with its multitude of hot springs is also part of the Hengill area.

==Culture==
Some [[Folklore|folk tale]]s are connected to the region.<ref>{{Cite web |title=Ísmús - íslenskur músík- og menningararfur |url=https://www.ismus.is/ |access-date=2023-12-31 |website=www.ismus.is |language=en}}</ref> For example, in a folk tale collected and published by [[Jón Árnason (author)|Jón Árnason]] in 1862, a young farmer is said to have killed the sleeping [[troll]] woman Jóra {{IPA|is|ˈjouːra|}} while she lay in wait for innocent wanderers or horsemen on the trail over Dyrafjöll {{IPA|is|ˈtɪːraˌfjœtl̥|}} north of Hengill.<ref name=":0">{{Cite book |last=Árnason |first=Jón |title=Íslenzkar Þjóðsögur og Æfintýri |publisher=J.C. Hinrichs |year=1862–1864 |location=Leipzig |pages=II: 251}}</ref> In another folk tale, according to some people, a woman's body found in the area was believed to be that of Halla, the wife of the famous Icelandic outlaw [[Fjalla-Eyvindur]].<ref name=":0" />

==See also==
* [[Geography of Iceland]]
* [[List of lakes of Iceland]]
* [[Volcanism of Iceland]]
** [[List of volcanic eruptions in Iceland]]
** [[List of volcanoes in Iceland]]

==Notes==
{{reflist|group=lower-alpha}}
==References==
{{Reflist}}
===Sources===
*{{cite web|title= Global Volcanism Program, 2023. Hengill (371050) in [Database] Volcanoes of the World (v. 5.1.5; 15 Dec 2023)|date =15 December 2023|publisher=Smithsonian Institution |editor-first1 =Edward|editor-last1 =Venzke| doi=10.5479/si.GVP.VOTW5-2023.5.1|url =https://volcano.si.edu/volcano.cfm?vn=371050}}<!--{{snf|Venzke|2023}}--->
*{{cite journal|last1 =Zakharova|first1 =O.K.|last2 =Spichak|first2 =V.V.|year =2012|title =Geothermal fields of Hengill volcano, Iceland|journal =Journal of Volcanology and Seismology|volume =6|issue =1|pages=1–14|doi =10.1134/S074204631201006X|bibcode =2012JVolS...6....1Z|s2cid =129031347| url=https://www.researchgate.net/publication/257847359 |access-date=30 December 2023}}
*{{cite web|url =https://icelandicvolcanoes.is/?volcano=HEN|title =Catalogue of Icelandic Volcanoes - Hengill|access-date =30 December 2023| publisher =Icelandic Meteorological Office, Institute of Earth Sciences at the University of Iceland, Civil Protection Department of the National Commissioner of the Iceland Police|year=2019|first1 =Kristján|last1 =Sæmundsson}}
* {{Cite journal|first1= J. |last1= Decriem|first2= T. |last2= Árnadóttir|first3= A. |last3= Hooper|first4= H. |last4= Geirsson|first5= F. |last5= Sigmundsson|first6= M. |last6= Keiding|first7= B. G. |last7= Ófeigsson|first8= S. |last8= Hreinsdóttir|first9= P. |last9= Einarsson|first10= P. |last10= LaFemina|first11= R. A. |last11= Bennett|date= 2010|title= The 2008 May 29 earthquake doublet in SW Iceland|journal= [[Geophysical Journal International]]|volume= 181 | issue= 2 | pages= 1128–1146 |doi= 10.1111/j.1365-246x.2010.04565.x|bibcode= 2010GeoJI.181.1128D|doi-access= free}}
* {{cite book|last1 =Bessason|first1 =B.|last2 =Sólnes|first2 =J.|last3 =Bjarnason|first3 =J.Ö.|last4 =Guðmundsson|first4 =A.|last5 =Steedman|first5 =S.|year =2012 |chapter =Comprehensive damage analysis of buildings affected by the 2008 South Iceland earthquake|title =Proceedings of the 15th World Conference of Earthquake Engineering|isbn=978-1-63439-651-6|publisher=Sociedade Portuguesa de Engenharia Sismica (SPES)|chapter-url =https://www.iitk.ac.in/nicee/wcee/article/WCEE2012_2384.pdf |access-date=30 December 2023}}
* {{cite journal|last1 =Hernández|first1 =P.A.|last2 =Pérez|first2 =N.M.|last3 =Fridriksson|first3 =T.|last4 =Egbert|first4 =J.|last5 =Ilyinskaya|first5 =E.|last6 =Thárhallsson|first6 =A.|last7 =Ívarsson|first7 =G.|last8 = Gíslason|first8 =G.|last9 =Gunnarsson|first9 =I.|last10 =Jónsson|first10 =B.|last11 =Padrón|first11 =E.|year =2012|title =Diffuse volcanic degassing and thermal energy release from Hengill volcanic system, Iceland|journal =Bulletin of Volcanology|volume =74|issue =10|pages =2435–2448|doi =10.1007/s00445-012-0673-2|bibcode =2012BVol...74.2435H|s2cid =128693606|url =https://www.academia.edu/download/49735231/s00445-012-0673-220161020-6526-s2jftb.pdf|access-date =30 December 2023}}
* {{cite journal|last1 =Ducrocq|first1 =C.|last2 =Geirsson|first2 =H.|last3 =Árnadóttir|first3 =T.|last4 =Juncu|first4 =D.|last5 =Drouin|first5 =V.|last6 =Gunnarsson|first6 =G.|last7 =Kristjansson|first7 =B.R.|last8 =Sigmundsson|first8 =F.|last9 =Hreinsdottir|first9 =S.|last10 =Tómasdóttir|first10 =S.|last11=Blanck|first11 =H.|year =2021|title =Inflation-deflation episodes in the Hengill and Hrómundartindur volcanic complexes, SW Iceland|journal =Frontiers in Earth Science|volume =9|article-number =725109|doi =10.3389/feart.2021.725109|bibcode=2021FrEaS...9..915D|doi-access=free}}

== External links ==
* [https://icelandicvolcanoes.is/?volcano=HEN Hengill] in the [[Catalogue of Icelandic Volcanoes]]
* [https://web.archive.org/web/20160413195148/https://www.or.is/sites/default/files/welcome_to_the_hengill_area_hiking_map.pdf Map]
* [https://arcgisserver.isor.is/?lon=-20.03821&lat=64.10749&zoom=8&layers%5B%5D=elevationModel&layers%5B%5D=heatFlow&layers%5B%5D=highTemperatureAreas&layers%5B%5D=miscellaneousLocations&layers%5B%5D=geothermalAreas&layers%5B%5D=highTemperaturePoints ÍSOR Interactive map of geothermal areas in Iceland (in Icelandic)]
{{Volcanoes of Iceland|state=collapsed}}
{{Authority control}}
[[Category:Active volcanoes]]
[[Category:Fissure vents]]
[[Category:West Volcanic Zone of Iceland]]
[[Category:Mountains of Iceland]]
[[Category:Polygenetic shield volcanoes]]
[[Category:Central volcanoes of Iceland]]
[[Category:Volcanic systems of Iceland]]
[[Category:Reykjanes Volcanic Belt]]
[[Category:South Iceland Seismic Zone]]