Esjufjöll

{{Infobox mountain

| name = Esjufjöll

| photo = Jökulsarlon.jpg

| photo_caption = Esjufjöll north of Jökulsárlón as nunataks of Vatnajökull glacier

| elevation_m = 1745

| elevation_ref = {{efn|The historic assigned height of Breiðamerkurjökull as a glacier is {{cvt|1760|m}}{{cite web|title=National Land Survey of Iceland-Mapviewer (Kortasja-Landmælingar Íslands) |url=https://kortasja.lmi.is/mapview/ |access-date=6 March 2024}} Lidar studies confirmed this with an icecap (not bare rock height) ±{{cvt|5|m}}. However the latest official source gives {{cvt|1745|m}} for Esjufjöll as the volcano so this height is used here as the mountain height.{{cite web|url =https://icelandicvolcanoes.is/?volcano=ESJ|title =Catalogue of Icelandic Volcanoes - Esjufjöll|access-date =6 March 2024| 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|last1 = Guðmundsson|first1 =Magnús T.}}|name=height}}

| prominence =

| location = Iceland, East Iceland

| range =

| coordinates = {{coord|64.27|N|16.65|W|type:mountain_region:IS|display=inline,title}}

| topo =

| type = Stratovolcano

| age = Holocene

| last_eruption = 1927?

| first_ascent =

| easiest_route =

| map_image ={{maplink|frame=yes|frame-align=center|frame-width=260|frame-height=220|frame-long=-16.65|frame-lat=64.27|zoom=8|raw={{Wikipedia:Map data/Öræfi volcanic belt}}

|text=Topographic features of Esjufjöll and to its south Öræfajökull. The Esjufjöll central volcano is outlined in red while the approximate outline of other central volcanoes are in brown. Nunataks have darker brown shading. Postulated or definite caldera features are in red shading. White/blue shading show glacier features relevant to jökulhlaup risk. More detail or zoom out to show other volcanoes in the Öræfi volcanic belt is available on clicking the image to enable mouse-over.

}}

The subglacial Esjufjöll ({{IPA|is|ˈɛːsjʏˌfjœtl̥|audio=Esjufjöll pronunciation.ogg}}) volcano is located in the south-east part of the Vatnajökull icecap. Esjufjöll is a strict nature reserve (IUCN category Ia).Stjórnunar- og verndaráætlun Vatnajökulsþjóðgarðs, 2. útgáfa, 2013. p. 12. [https://www.vatnajokulsthjodgardur.is/static/files/Stjornsysla/PDF-skjol-kort/stjornunar-og_verndar_2013.pdf] {{Webarchive|url=https://web.archive.org/web/20210417203239/https://www.vatnajokulsthjodgardur.is/static/files/Stjornsysla/PDF-skjol-kort/stjornunar-og_verndar_2013.pdf |date=2021-04-17 }}

Geography

The recognisable mountains associated with the volcano are nunataks within Vatnajökull. These are located about 20 km to the north of Öræfajökull volcano and about 20 km north-west of the Jökulsárlón glacial lake.Ísland Vegaatlas. Reykajvík (Ferðakort) 2006, p.7 The highest part of volcano is an ice-covered ridge called Snæhetta, whose assigned height is lower than previous figures, at {{cvt|1745|m}}{{efn|name=height}}. The mountain range to this ridge's south consists of four nunatak mountain massifs called Vesturbjörg, Skálabjörg, Esjubjörg and Austurbjörg, in a north-west to south-east alignment, with three valleys in between them.Ari Trausti Guðmundsson, Pétur Þorsteinsson: Íslensk fjöll. Gönguleiðir á 151 tind. Reykjavík 2004, p. 200.{{cite journal|last1 =Dabski|first1 =M.|last2 =Angiel|first2 =P.|year =2010|title =Geomorphic implications of the retreat of Breiðamerkurjökull in the southern part of the Skálabjörg ridge, Esjufjöll, Iceland|journal=Jökull|volume =60|pages =185–197|doi =10.33799/jokull2010.60.185|url=https://www.researchgate.net/publication/267422763|access-date=4 March 2024}}{{rp|p=185}} In the second half of the 20th century, a number of small nunataks appeared as the more southern ice cover decreased; and two of the largest are named Bræðrasker and Kárasker.{{cite journal|last1 =Guðmundsson|first1 =S.|last2 =Björnsson|first2 =H.|last3 =Pálsson|first3 =F.|year =2017|title =Changes of Breiðamerkurjökull glacier, SE-Iceland, from its late nineteenth century maximum to the present|journal =Geografiska Annaler: Series A, Physical Geography|volume =99|issue =4|pages =338–352|doi-access=free|doi =10.1080/04353676.2017.1355216|issn =1468-0459}}{{rp|p=340}}

The glaciers flowing around them are feeding the Breiðamerkurjökull, the most south-easterly part of the Vatnajökull icecap, immediately adjacent to Jökulsárlón, which it flows into. Breiðamerkurjökull, which had in 2010 an area of {{cvt|906|km2}}, covers the volcano. There are three main glacial catchments, with the western arm draining the north western slopes of the Öræfajökull volcano, being separated from the central arm by the Mávabyggðir (Fingurbjörg), {{cvt|1439|m}}, and Kárasker nunataks.{{rp|p=339}} To its west the central arm is associated with the Vesturbjörg and Skálabjörg nunataks and the eastern arm is associated with the Esjubjörg and Austurbjörg nunataks.{{rp|p=186}}{{rp|p=339}}

Volcanism

Esjufjöll is a volcanic system and is part of Iceland's Öræfi volcanic belt.{{cite journal|first1 =T.|last1 =Thordarson|first2 =G.|last2 =Larsen|title =Volcanism in Iceland in historical time. Volcano types, eruption types and eruption history|journal =Journal of Geodynamics|volume =43|issue=1|pages =118–152|year= 2007|doi =10.1016/j.jog.2006.09.005}} Also part of this zone are Öræfajökull and Snæfell (north-east of Vatnajökull).See eg.: Thor Thordarson, Armann Hoskuldsson: Classic geology in Europe 3. Iceland. Harpenden 2002, p. 14

The volcanic system consists of the Snæhetta central volcano with an assumed large caldera, but this has not yet been mapped well. Most of the volcano, including the {{cvt|40|km2}} caldera, is covered by the icecap. The latest data is suggestive of a volcano that may be {{cvt|20|km}} in diameter and its northern part is underlain by a dense intrusive body. Satellite imaging suggests a caldera that may be {{cvt|5|x|3|km|0}}.{{cite journal|last1 =Williams|first1 =R.S.|year =1987|title =Satellite remote sensing of Vatnajökull, Iceland|journal =Annals of Glaciology|volume =9|pages =127–135|doi =10.3189/S0260305500000501}} Vesturbjörg, Skálabjörg, Esjubjörg and Austurbjörg constitute the south-eastern flank of this caldera.{{cite gvp|vn=374020|title=Esjufjöll}} Most of the exposed rocks are mildly alkaline basalts, but to the east there are rhyolitic rocks.

In the beginning of September 1927, a glacial flood (jökulhlaup) came down the Jökulsá á Breiðamerkursandi (a short river from Breiðamerkurjökull to the sea). The glacier run was accompanied by a sulfur stench. On one occasion, ash fall on the Breiðamerkurjökull was thought to have possibly originated from Esjufjöll. Although Holocene eruptions from Esjufjöll have not been confirmed, earthquake swarms that could indicate magma movements were detected in October 2002, and again in October 2010.