View source for Mývatn

{{refimprove|date = March 2024}}
{{short description|Lake in Iceland}}
{{Infobox body of water
| name = Mývatn
| image =  Mývatn-pjt.jpg
| caption = Mývatn, near [[Höfði (park)|Höfði Nature Park]]
| image_bathymetry =
| caption_bathymetry = Map with surrounding lakes and ponds. The river Laxá in the upper left corner.
| location =
| coords = {{coord|65|36|N|17|00|W|region:IS_type:waterbody|display=inline,title}}
| pushpin_map = Iceland
| lake_type = [[Volcanogenic lake|Volcanogenic]], [[eutrophic]]
| inflow =
| outflow = [[Laxá]]
| catchment =
| basin_countries = Iceland
| length =
| width =
| area = {{convert|37|km2|abbr=on}}
| depth = {{convert|2.5|m|abbr=on}}
| max-depth = {{convert|4.5|m|abbr=on}}
| volume =
| residence_time =
| shore =
| elevation = {{convert|288|m|abbr=on}}
| islands =
| cities =
| embedded = {{Designation list
| embed = yes
| designation1 = Ramsar
| designation1_offname = Myvatn-Laxá region
| designation1_date = 2 December 1977
| designation1_number = 167<ref>{{Cite web|title=Myvatn-Laxá region |website=[[Ramsar Convention|Ramsar]] Sites Information Service|url=https://rsis.ramsar.org/ris/167|access-date=25 April 2018}}</ref>}}
}}
'''Mývatn''' ({{IPA|is|ˈmiːˌvahtn̥|audio=Mývatn pronunciation.ogg}}) is a shallow lake situated in an area of active volcanism in the north of [[Iceland]], near [[Krafla]] [[volcano]]. It has a high amount of [[Eutrophic|biological activity]]. The lake and the surrounding wetlands provides a habitat for a number of [[waterbird]]s, especially [[duck]]s.
The lake was created by a large [[basalt]]ic lava eruption 2300 years ago, and the surrounding landscape is dominated by volcanic landforms, including [[lava pillars]] and [[rootless vents]] ([[pseudocrater]]s). The effluent river [[Laxá]] {{IPA-is|ˈlaksˌauː|}} is known for its rich fishing for [[brown trout]] and [[Atlantic salmon]].
The name of the lake ([[Icelandic language|Icelandic]] {{lang|is|[[wikt:mý#Icelandic|mý]]}} ("[[midge]]") and {{lang|is|[[wikt:vatn#Icelandic|vatn]]}} ("lake"); "the lake of midges") comes from the large numbers of midges present in the summer.
The name Mývatn is sometimes used not only for the lake but the whole surrounding inhabited area.  The river Laxá, the lake Mývatn and the surrounding wetlands are protected as a nature reserve (the Mývatn&ndash;Laxá Nature Conservation Area), which occupies {{convert|440,000|ha|km2|order=flip|abbr=on}}.
Since 2000, a [[marathon (sport)|marathon]] around the lake has taken place in the summer.
==Geography==
The lake has an average depth of 2.5 metres and a maximum depth of 4.5 metres.
===Climate===
The Mývatn area features a [[tundra climate]] ([[Köppen climate classification]] ET), bordering on a [[subarctic climate]] ([[Köppen climate classification]] Dfc). Summers are typically cool with crisp nights while winters are very long and cold.
{{Weather box
|width = 78
|location = Reykjahlíð (1961&ndash;1990)
|metric first = Y
|single line = Y
|Jan record high C = 9.4
|Feb record high C = 10.5
|Mar record high C = 10.9
|Apr record high C = 15.7
|May record high C = 23.3
|Jun record high C = 25.6
|Jul record high C = 24.0
|Aug record high C = 24.0
|Sep record high C = 19.0
|Oct record high C = 15.2
|Nov record high C = 11.0
|Dec record high C = 10.6
|year record high C = 25.6
|Jan high C = -1.8
|Feb high C = -0.9
|Mar high C = -0.3
|Apr high C = 3.0
|May high C = 7.6
|Jun high C = 12.3
|Jul high C = 14.2
|Aug high C = 12.9
|Sep high C = 8.1
|Oct high C = 3.6
|Nov high C = 0.0
|Dec high C = -1.4
|year high C = 4.8
|Jan mean C = -4.8
|Feb mean C = -4.1
|Mar mean C = -3.5
|Apr mean C = -0.3
|May mean C = 4.0
|Jun mean C = 8.3
|Jul mean C = 9.9
|Aug mean C = 9.0
|Sep mean C = 4.8
|Oct mean C = 1.2
|Nov mean C = -2.7
|Dec mean C = -4.5
|year mean C = 1.4
|Jan low C = -8.4
|Feb low C = -7.6
|Mar low C = -7.2
|Apr low C = -3.9
|May low C = 0.6
|Jun low C = 4.5
|Jul low C = 6.4
|Aug low C = 5.6
|Sep low C = 1.9
|Oct low C = -1.6
|Nov low C = -6.1
|Dec low C = -8.0
|year low C = -2.0
|Jan record low C = -30.5
|Feb record low C = -26.6
|Mar record low C = -30.9
|Apr record low C = -25.7
|May record low C = -16.1
|Jun record low C = -5.0
|Jul record low C = -1.6
|Aug record low C = -2.0
|Sep record low C = -11.5
|Oct record low C = -17.1
|Nov record low C = -26.0
|Dec record low C = -27.5
|year record low C = -30.9
|precipitation colour = green
|Jan precipitation mm = 33.4
|Feb precipitation mm = 26.2
|Mar precipitation mm = 32.5
|Apr precipitation mm = 25.4
|May precipitation mm = 20.1
|Jun precipitation mm = 32.3
|Jul precipitation mm = 47.4
|Aug precipitation mm = 45.6
|Sep precipitation mm = 44.1
|Oct precipitation mm = 46.2
|Nov precipitation mm = 43.4
|Dec precipitation mm = 38.0
|year precipitation mm = 435.0
|unit precipitation days = 1.0 mm
|Jan precipitation days = 8.2
|Feb precipitation days = 6.5
|Mar precipitation days = 8.2
|Apr precipitation days = 6.8
|May precipitation days = 5.1
|Jun precipitation days = 7.0
|Jul precipitation days = 8.9
|Aug precipitation days = 8.2
|Sep precipitation days = 8.1
|Oct precipitation days = 9.9
|Nov precipitation days = 9.7
|Dec precipitation days = 9.9
|year precipitation days = 96.8
| Jan sun = 16.1
| Feb sun =51.6
| Mar sun =96.5
| Apr sun = 147.7
| May sun =178.2
| Jun sun = 202.5
| Jul sun = 170.3
| Aug sun =157.4
| Sep sun =97.8
| Oct sun = 57.8
| Nov sun =23.8
| Dec sun =3.7
|source 1 = [[Icelandic Meteorological Office|Icelandic Met Office]]<ref>{{Cite web |url=http://en.vedur.is/Medaltalstoflur-txt/Reykjahlid_468_med6190.txt|title=Reykjahlíð 1961-1990 Averages|publisher=[[Icelandic Meteorological Office]] |access-date=29 May 2016}}</ref>
| source 2 = [[Icelandic Meteorological Office|Icelandic Met Office]] (monthly sunshine hours 1981-2010 for Haganes-9 km (5.6 mi) from Reykjahlíð) <ref>{{Cite web |url=https://www.vedur.is/Medaltalstoflur-txt/Stod_465_Haganes.ManMedal.txt|title=1961-90 Sunshine Averages for Haganes|publisher=[[Icelandic Meteorological Office]] |access-date=21 April 2021}}</ref>}}
==Flora and fauna==
===Birds===
[[File:Myvatn shore.jpg|thumbnail|right|Shore of Mývatn.]]
The lake is fed by [[nutrient]]-rich springwater and has a high abundance of aquatic insects ([[Chironomidae]]) and [[Cladocera]] that form an attractive food supply for ducks. Fifteen species of ducks breed at the site, the largest such number in Europe.<ref>{{cite book |last1=Couzens |first1=Dominic |title=Top 100 Birding Sites of the World |date=2015 |publisher=Bloomsbury |isbn=9781472919847 |pages=47–49 |edition=2}}</ref> The duck species composition has a mixture of European and North American species, and also of [[boreal ecosystem|boreal]] and [[arctic]] species. Most of the ducks are migratory, arriving in late April to early May from north-western Europe. The commonest species at the lake is the [[tufted duck]] with 6,000 pairs present, whilst the second most abundant species is the [[greater scaup]] with 1,500 pairs.
Other common species include the [[Barrow's goldeneye]], 700 pairs of [[red-breasted merganser]], 1000 pairs of [[Eurasian wigeon]], around 300 pairs of [[gadwall]], 200 pairs of [[mallard]], around 350 pairs of [[common scoter]], 150 pairs of [[long-tailed duck]] and 75 pairs of [[Eurasian teal]]. The [[northern shoveler]] and  [[northern pintail]] also regularly breed at the lake, albeit in smaller numbers, whilst [[common pochard]] used to breed regularly, but they have not done so regularly since the 1950s. The outflowing Laxá river contains around 250 pairs of [[harlequin duck]] and there is a large colony of [[eider]] at the river mouth some 50&nbsp;km away from Mývatn.  The Barrow's goldeneye and the harlequin duck are both [[nearctic]] duck species.  The population of the Barrow's goldeneye (of about 2000 individuals) relies entirely on the habitat provided by the Mývatn&nbsp;Laxá water system and its surrounding lava fields. Most of the Barrow's goldeneyes overwinter there, using ice-free areas kept open by emerging spring water (both warm and cold) and in the strong river current. This species is a hole-nester, in North America using tree-holes, but at Mývatn the birds use cavities in the lava for nesting. The other duck species nest abundantly in the numerous islands of the lake and the surrounding marshlands.
Other common waterbirds include the [[Slavonian grebe]], [[red-necked phalarope]], [[great northern diver]], [[red-throated diver]] and [[whooper swan]].  The lake is included in an [[important bird area]].<ref>BirdLife International (2015). [http://www.birdlife.org/datazone/sitefactsheet.php?id=524 Important Bird Areas factsheet: Mývatn-Laxá]. Downloaded from http://www.birdlife.org on 13/02/2015.</ref>
Bird populations have been monitored annually since 1975 by the Mývatn Research Station. There is a long tradition of harvesting duck eggs for home use on the local farms. To ensure sustainability, the harvesting follows strict age-old rules of leaving at least four eggs in a nest for the duck to incubate.
The lava flows and moorlands surrounding the lake are home to [[rock ptarmigan]]s and occasionally [[gyr falcon]]s may be present.
{{wide image|Mývatn surrounds.jpg|1200px|The plateau surrounding Mývatn. In the distance are [[Gæsafjöll]] (882m, left), [[Krafla]] (818m, centre-left, behind the dark [[Vindbelgur]] (529m)), [[Hverfjall]] (caldera at centre), [[Búrfell]] (953m, centre-right), and [[Bláfjall]] (1222m, right).}}
===Plants===
Mývatn is one of the few places in the world where [[marimo]] grows naturally. Also known as Cladophora ball it is a species of filamentous green [[algae]]. Due to environmental factors their population has rapidly declined and the algae appeared to have become extinct in 2013. The ecosystem is now improving and small marimo balls are forming again.<ref>{{Cite web|url=https://icelandmag.is/article/unexpected-good-news-lake-myvatn-large-quantities-marimo-wash-ashore|title=Unexpected good news from lake Mývatn: Large quantities of Marimo wash ashore|website=Icelandmag}}</ref><ref>{{Cite web|url=https://icelandmag.is/article/great-news-myvatn-lake-unique-marimo-colonies-grow-second-year-a-row|title=Great news from Mývatn lake: Unique marimo colonies grow second year in a row|website=Icelandmag}}</ref>
== Volcanism ==
[[File:Mývatn, edged with pseudocraters.jpg|thumb|right|225px|Panorama of Mývatn from the town of [[Skútustaðir]], November 2007]]
[[File:FieldOfRocksInAkureyri.jpg|thumb|225px|right|The [[Hverfjall]] crater, immediately east of Mývatn]]
[[File:MyvatnIsland.jpg|thumb|225px|right|Lava island in Mývatn]]
Mývatn was created about 2300 years ago by a large [[fissure eruption]] of [[basalt]]ic lava. The lava flowed down the valley [[Laxárdalur]] to the lowland plain of [[Aðaldalur]] {{IPA-is|ˈaːðalˌtaːlʏr̥|}} where it entered the [[Arctic Ocean]] about 50&nbsp;km away from Mývatn. The [[fissure vent|crater row]] that formed along the eruptive fissure is called Þrengslaborgir {{IPA-is|ˈθreiŋstlaˌpɔrcɪr̥|}} (or Lúdentarborgir {{IPA-is|ˈluːˌtɛn̥tarˌpɔrcɪr̥|}}) and has often been used as a textbook example of this type of volcanic activity.  There was a large lake in the area at the time, a precursor of the present-day Mývatn. When the lava encountered the lake some of the water-logged lake [[sediment]] was trapped underneath it, generating steam explosions.
By repeated explosions in a number of locations, groups of craters built up and now dominate the landscape on the shore of Lake Mývatn and also form some of the islands in the lake.  This type of lava formation is known as [[rootless cone]]s or pseudocraters. A group of such craters at Skútustaðir {{IPA-is|ˈskuːtʏˌstaːðɪr̥|}} on the south shore of the lake is protected as a natural monument. Other rootless cone groups in this lava field are in the valley Laxárdalur and the plain Aðaldalur. The formation of rootless cones halted the advance of the lava in some places creating temporary lava lakes. The lava eventually drained from the lakes, leaving behind a forest of rock pillars.  The biggest of these formations is named [[Dimmuborgir]].  At another place, Höfði {{IPA-is|ˈhœvðɪ|}}, the pillars stand in the lake water.  The lava created by the Þrengslaborgir eruption is known as the Younger Laxá Lava.
The Mývatn district lies on the western border of the volcanic zone which cuts across north-eastern Iceland from north to south and is an extension of the [[Mid-Atlantic Ridge]]. All geological formations are quite recent, dating from the [[Last Glacial Period|Ice Age]] and postglacial times.
The [[bedrock]] of the moors west of Mývatn is made up of [[interglacial]] lava flows. Most of the mountains in the vicinity of the lake were formed by eruptions under the ice sheet in the glacial periods of the Ice Age. Eruptions that melted their way up through the ice formed [[table (landform)|table mountain]]s (Bláfjall {{IPA-is|ˈplauːˌfjatl̥|}}, Sellandafjall {{IPA-is|ˈsɛlˌlantaˌfjatl̥|}}, Búrfell {{IPA-is|ˈpurˌfɛtl̥|}}, Gæsafjöll {{IPA-is|ˈcaiːsaˌfjœtl̥|}}), those which did not formed [[hyaloclastite]] ridges (Vindbelgjarfjall {{IPA-is|ˈvɪntˌpɛlcarˌfjatl̥|}}, Námafjall {{IPA-is|ˈnauːmaˌfjatl̥|}}, Dalfjall {{IPA-is|ˈtalˌfjatl̥|}}, Hvannfell {{IPA-is|ˈkʰvanːˌfɛtl̥|}}).
At the close of the Ice Age, about 10,000 years ago, the Mývatn basin was covered by a glacier which pushed up huge [[end moraine]]s which can still be seen at the north end of the lake. After the glacier started melting, a [[glacial lake]] was dammed up in the Mývatn depression until the glacier retreated from the present course of Laxá river.
Postglacial volcanism in the Mývatn district may be divided into three cycles. The Lúdent {{IPA-is|ˈluːˌtɛn̥t|}} cycle commenced shortly after the close of the Ice Age. The explosion crater ([[tephra]] ring) Lúdent dates from this cycle. Its eruption was followed by a number of small fissure eruptions. About 3800 years ago the [[shield volcano]] [[Ketildyngja]] {{IPA-is|ˈcʰɛːtɪlˌtiɲca|}} was formed about 25&nbsp;km south-east of Mývatn, and from it a huge lava flow, the Older Laxá-lava, spread over the southern part of the district, plunged down the valley Laxárdalur and flowed almost to the sea. This lava dammed up the first Mývatn, which was about as large as the present lake.
The second volcanic cycle, the Hverfjall cycle, began 2500 years ago with a gigantic but brief eruption, which formed the explosion crater (tephra ring) [[Hverfjall]] (also named Hverfell). An eruption in [[Jarðbaðshólar]] {{IPA-is|ˈjarðˌpaðsˌhouːlar̥|}} followed, producing the lavafield between [[Reykjahlíð]] and [[Vogar]]. Approximately 200 years later a vast lava flow, the Younger Laxá Lava, was erupted (see above). The lava dammed up the present lake Mývatn and also the lakes [[Sandvatn]] {{IPA-is|ˈsantˌvahtn̥|}}, [[Grænavatn]] {{IPA-is|ˈkraiːnaˌvahtn̥|}} and [[Arnarvatn]] {{IPA-is|ˈa(r)tnarˌvahtn̥|}}.
The third volcanic cycle began with the Mývatnseldar {{IPA-is|ˈmiːˌvasːˌɛltar̥|}} eruptions in 1724–1729 which commenced with an explosion that formed the [[Volcanic crater lake|crater lake]] Víti {{IPA-is|ˈviːtɪ|}}. Later lava flowed from Leirhnjúkur {{IPA-is|ˈleirˌn̥juːkʏr̥|}} down to the north end of Mývatn, destroying two farms. The Mývatnseldar eruptions are quite similar in character to the recent volcanic activity near Krafla in 1975&ndash;1984. The source of both is a [[central volcano]] lying between Krafla and Gæsafjöll. Inside the volcano resides a [[magma chamber]] from which molten [[magma]] periodically bursts into a swarm of fissures that cut through the volcano from north to south.
The recent activity was characterized by periods of slow land rise, interspersed by shorter periods of rapid subsidence, underground magma bursts, rifting, [[earthquake]]s and eruptions (nine in all). This is an example of the process of [[continental drift]] in Iceland.  A central volcano and its associated fissure swarm is called a volcanic system.  The Krafla volcanic system is one of several such systems which together form the volcanic zone of Iceland.
A few [[rhyolite]] mountains border the Krafla central volcano (Hlíðarfjall {{IPA-is|ˈl̥iːðarˌfjatl̥|}}, Jörundur {{IPA-is|ˈjœːrʏntʏr̥|}}, Hrafntinnuhryggur {{IPA-is|ˈr̥apn̥ˌtʰɪnːʏˌr̥ɪkːʏr̥|}}).
Because of its volcanic origin, the lake was formerly mined for [[diatomite]], but this ceased in 2004.<ref>{{Cite web|url=https://whc.unesco.org/en/tentativelists/5586/|title=Mývatn and Laxá|first=UNESCO World Heritage|last=Centre|website=UNESCO World Heritage Centre}}</ref>
==See also==
*[[Cladophora]]
*[[Geography of Iceland]]
*[[List of lakes of Iceland]]
*[[Volcanism of Iceland]]
==References==
{{reflist}}
==Bibliography==
*Einarsson, Á., Stefánsdóttir, G., Jóhannesson, H., Ólafsson, J.S., Gíslason, G.M., Wakana, I., Gudbergsson, G. and Gardarsson, A. 2004. The ecology of Lake Mývatn and the River Laxá: variation in space and time. ''Aquatic Ecology'' 38: 317–348.
*Gardarsson, A. and Einarsson, Á. eds. 1991. ''Náttúra Mývatns. Hið íslenska Náttúrufræðifélag,'' Reykjavík. 372 pp. (in Icelandic)
*Gardarsson, A. and Einarsson, Á. 2000. Monitoring waterfowl at Mývatn, Iceland. Pp.&nbsp;3–20 in F.A. Comin, J.A. Herrera-Silveira and J.Ramirez-Ramirez (eds.): ''Limnology and Aquatic birds. Monitoring, Modelling and Management.'' Universidad Autonoma de Yucatán, Mérida, Yucatán, Mexico.
*Gíslason, G.M. 1994. River management in cold regions: a case study of the River Laxá, North Iceland. Pp.&nbsp;464–483 in: ''The Rivers Handbook. Hydrological and Ecological Principles.'' Vol. 2. Eds. P. Calow & G.E. Petts. Blackwell, Oxford. 483 pp.
*Jónasson, P.M. ed. 1979. Ecology of Eutrophic, Subarctic Lake Mývatn and the River Laxá. Oikos 32.
== Notes ==
{{notelist}}
==External links ==
{{Commons}}
{{wikivoyage|Mývatn}}
*[http://wayback.vefsafn.is/wayback/20041022000000/www.hi.is/HI/Stofn/Myvatn/geomap.htm Geological map]
*[https://notendur.hi.is/~arnie/myreflst.htm A complete bibliography on the natural history of Mývatn]
*[http://hraun.vedur.is/ja/englishweb/myvatn.html Current seismic activity at Mývatn]
*[http://www.picturechoice.org/iceland/myvatn.html Lake Myvatn images]
*[http://www.eldey.de/English/sights/north/north.html Facts and photos]
*[https://web.archive.org/web/20071216083149/http://www.seacology.org/projects/individualprojects/ICELAND_myvatn2000.htm Seacology Lake Myvatn Project] [[Seacology]]
*[http://www.icelandvirtualtour.com/myvatn-skutustadir-pseudocraters.html Mývatn panoramic virtual tour]
*[https://www.discover.is/tours/myvatn-must-sees/ Mývatn Private Day Tour]
{{Lakes of Iceland}}
{{Authority control}}
{{DEFAULTSORT:Myvatn}}
[[Category:1724 in Europe]]
[[Category:Birdwatching sites]]
[[Category:Important Bird Areas of Iceland]]
[[Category:Lakes of Iceland]]
[[Category:Lava dammed lakes]]
[[Category:North Iceland]]
[[Category:North Volcanic Zone of Iceland]]
[[Category:Ramsar sites in Iceland]]
[[Category:Rift lakes of Iceland]]