Skjaldbreiður

{{Short description|Volcano in Iceland}}

{{Expand Icelandic|topic=geo|date=January 2022}}

{{Infobox mountain

| name = Skjaldbreiður

| photo = Skjaldbreidur_Herbst_2004.jpg

| photo_caption = Skjaldbreiður as seen from Þingvellir

| elevation_m = 1066

| elevation_ref ={{cite web|url =https://kortasja.lmi.is/mapview/|title=National Land Survey of Iceland (kortasja)–Map Viewer|access-date=2024-05-01}}

| prominence_m =

| map = Iceland

| map_caption =

| map_size = 200

| label_position = right

| translation = broad shield

| language = Icelandic

| location = Iceland

| coordinates = {{coord|64|24|36|N|20|45|44|W|type:mountain_region:IS_scale:100000|format=dms|display=inline,title}}

| range_coordinates =

| coordinates_ref =

| type = shield volcano

| age = 9,500 years

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|text=Selected geological features near the Skjaldbreiður shield volcano.(red outline). Light violet shading shows the current surface area of the Skjaldbreiður lava flows. Shading also shows: {{legend-inline|#dbb252}} calderas, {{legend-inline|#d9cf90}}central volcanoes and {{legend-inline|#fae8c0}}fissure swarms, {{legend-inline|#cecc90}}subglacial terrain above {{cvt|1100|m}}, and {{legend-inline|#f9f5db}}seismically active areas. Clicking on the image enlarges to full window and enables mouse-over with more detail.

}} }}

Skjaldbreiður ({{IPA|is|ˈscaltˌpreiːðʏr̥|audio=Skjaldbreiður pronunciation.ogg}}, "broad shield") is an Icelandic lava shield formed in a huge and quite protracted eruption series from about roughly 9,500 years ago.{{Cite web |title=Global Volcanism Program {{!}} Image GVP-05768 |url=https://volcano.si.edu/gallery/ShowImage.cfm?photo=GVP-05768 |access-date=2022-12-20 |website=volcano.si.edu |language=en}} The extensive lava fields which were produced by this eruption, flowed southwards, and formed the basin of Þingvallavatn, Iceland's largest lake, and Þingvellir, the "Parliament Plains" where the Icelandic national assembly, the Alþing was founded in 930.

The volcano summit is at {{cvt|1066|m}}, and its crater measures roughly {{cvt|300|metres}} in diameter. The Skjaldbreiður lava shield covers {{cvt|170|km2}} with a volume of about {{cvt|13|km3}}.{{Cite web| url = https://icelandicvolcanoes.is/?volcano=LAN| title =Oddnýjarhnjúkur-Langjökull Alternative name: Langjökull, Hveravellir (northern-) and Skjaldbreiður (southern part)| work = Catalogue of Icelandic Volcanoes| language = en| access-date = 2024-05-01|first1 =Guðrún|last1 =Larsen|first2 =Magnús T.|last2 =Guðmundsson|year =2019}}{{rp|loc=Detailed Description:2. Morphology and topography}} and is sometimes considered as a separate southern part of the Oddnýjarhnjúkur-Langjökull volcanic system which it is usually classified as being within.{{cite gvp|name=Oddnýjarhnjúkur-Langjökull|vn=371080|access-date=2024-05-01}} In this context its most recent eruption would be 3600 years ago, and the earliest eruption after the last ice age 10,200 years ago.{{Cite web| url = https://icelandicvolcanoes.is/?volcano=LAN| title =Oddnýjarhnjúkur-Langjökull Alternative name: Langjökull, Hveravellir (northern-) and Skjaldbreiður (southern part)| work = Catalogue of Icelandic Volcanoes| language = en| access-date = 2024-05-01|first1 =Guðrún|last1 =Larsen|first2 =Magnús T.|last2 =Guðmundsson|year =2019}}{{rp|loc=Detailed Description:4. Eruption history and pattern}} There are at least three lava units deposited between 6000 and 9000 years BP,{{cite journal|last1 =Hjartardóttir|first1 =Á.R.|last2 =Einarsson|first2 =P.|year =2015|title=The interaction of fissure swarms and monogenetic lava shields in the rift zones of Iceland|journal=Journal of Volcanology and Geothermal Research|volume =299|pages =91–102|doi =10.1016/j.jvolgeores.2015.04.001|bibcode =2015JVGR..299...91H}}{{rp|p=93}}

Straddling the Mid-Atlantic Ridge, the lava fields from Skjaldbreiður have been torn and twisted over the millennia, forming a multitude of fissures and rifts inside the Þingvellir National Park, the best known of which are Silfra, Almannagjá {{IPA|is|ˈalˌmanːaˌcauː|}}, Hrafnagjá {{IPA|is|ˈr̥apnaˌcauː|}} and Flosagjá {{IPA|is|ˈflɔːsaˌcauː|}}.