Hengill
Template:Short description Template:Infobox mountain Hengill ({{#invoke:IPA|main}}) is a volcanic table mountain situated in the south-west of Iceland, to the south of Þingvellir.
The volcano is still active, as evidenced by its numerous hot springs and fumaroles, but the last eruption occurred approximately 2,000 years ago, before the settlement of Iceland.
GeographyEdit
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 about Template:Cvt east of Reykjavík.<ref name="LI"/> At the coast is the port of Þorlákshöfn.<ref name="LI"/>
GeologyEdit
The mountain is part of the Template:Cvt long Hengill volcanic system,Template:SnfTemplate:Snf which is part of the Reykjanes volcanic belt, and is a hyaloclastite massif of tuyas and tindars.Template:Snf The dominant lava in the Hengill volcanic system is tholeiitic basalt,Template:Snf but andesite and about Template:Cvt rhyolite occur within the central mountain.Template:Snf The largest lava shield covers about Template:Cvt.Template:Snf Four small lava shields are picrite basalt and one lava shield contains about Template:Cvtof olivine tholeiite.Template:Snf It is located at the intersection with two other tectonic volcanic systems, the West volcanic zone of Iceland and South Iceland seismic zone,Template:SnfTemplate:Snf and is co-located to the plate boundary between the North American, Eurasian and Hreppar plates. This intersection is called the Hengill triple junction.Template:Snf
Hveragerdi to the south is a volcano in the volcanic system that became extinct 300,000 years ago, but still has significant seismic activity.Template:Snf It can be regarded as a predecessor volcano.Template:Snf 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 Template:Cvt locally.Template:Snf The earthquake distribution has been interpreted to have defined the heat source of the Hengill volcano.Template:Snf
Extending to the north-east from the central volcano is a fissure swarm with a number of tindars associated with an asymmetrical graben.Template:Snf 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.Template:Snf
Towards the south-east from the mountain towards the sea is a lava covered plateau whose height is about Template:Cvt with scattered higher tindars and tuyas.Template:Snf
During the Holocene volcanic eruptions in the zone have been predominantly effusive and basaltic with minor tephra production. Erupted lava volumes have ranged from Template:Cvt.Template:Snf
| Date | Event | Comment |
|---|---|---|
| 2008 CE | Earthquake | No loss of life but 50% property damage in Ölfus regionTemplate:Snf |
| 1789 CE | Subsurface dyke intrusion | Dyke injection later identifiedTemplate:Snf |
| 1000 CE | Adjacent volcanic system eruption | Fissure west of Hengill, in the Brennisteinsfjöll volcanic system.Template:Snf This eruption was at the time of a meeting of the Icelandic parliament at Thingvellir.<ref name=gvp/> |
| 150±75 CE | Eruption | Along a fissure length of Template:Cvt and about Template:Cvt lava eruptedTemplate:Snf. Included phreatomagmatic eruption from lake Thingvallavatn.Template:Snf<ref name=gvp/> |
| 80±75 BCE | Eruption | <ref name=gvp/> |
| 1730±50 BCE | Eruption | <ref name=gvp/> |
| ~3250 BCE | Eruption | <ref name=gvp/> |
| ~3750 BCE | Eruption | Along a fissure length of Template:Cvt and about Template:Cvt lava eruptedTemplate:Snf<ref name=gvp/> |
| ~5000 BCE | Eruption | <ref name=gvp/> |
| ~5550±500 BCE | Eruption | Not well datedTemplate:Snf<ref name=gvp/> |
| ~7100 BCE | Eruption | <ref name=gvp/> |
| ~7300 BCE | Eruption | <ref name=gvp/> |
| ~7550 BCE | Eruption | <ref name=gvp/> |
| ~8200 BCE | Eruption | Template:Snf<ref name=gvp/> |
| ~8250 BCE | Eruption | <ref name=gvp/> |
| ~8350 BCE | Eruption | <ref name=gvp/> |
RiskEdit
The official view of the volcanic hazard is that it is confined to a radius of Template:Cvt and is related to lava flows, plugging of geothermal boreholes by lava, volcano-tectonic faulting and volcanic gas pollution.Template:Snf <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 Template:Cvt 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 Template:Cvt north-west from an area of uplift between 1993 and 1999.Template:Snf
Geothermal resourcesEdit
There are three associated geothermal areas related to the high amount of fissuring in the Hengill volcanic system producing high water subsurface permeability.Template:Snf These areas include Iceland’s second largest geothermal field which now is an important source of energy for the south of the country.Template:Snf The three areas are:
- Nesjavellir 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 Template:Cvt 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.
CultureEdit
Some folk tales are connected to the region.<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> For example, in a folk tale collected and published by Jón Árnason in 1862, a young farmer is said to have killed the sleeping troll woman Jóra {{#invoke:IPA|main}} while she lay in wait for innocent wanderers or horsemen on the trail over Dyrafjöll {{#invoke:IPA|main}} north of Hengill.<ref name=":0">Template:Cite book</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 alsoEdit
NotesEdit
ReferencesEdit
SourcesEdit
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