Mývatn
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Mývatn | |
---|---|
eutrophic | |
Primary outflows | Laxá |
Basin countries | Iceland |
Surface area | 37 km2 (14 sq mi) |
Average depth | 2.5 m (8 ft 2 in) |
Max. depth | 4.5 m (15 ft) |
Surface elevation | 288 m (945 ft) |
Official name | Myvatn-Laxá region |
Designated | 2 December 1977 |
Reference no. | 167[1] |
Mývatn (Icelandic pronunciation:
The name of the lake (Icelandic mý ("midge") and 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–Laxá Nature Conservation Area), which occupies 4,400 km2 (440,000 ha).
Since 2000, a
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.
Climate data for Reykjahlíð (1961–1990) | |||||||||||||
---|---|---|---|---|---|---|---|---|---|---|---|---|---|
Month | Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec | Year |
Record high °C (°F) | 9.4 (48.9) |
10.5 (50.9) |
10.9 (51.6) |
15.7 (60.3) |
23.3 (73.9) |
25.6 (78.1) |
24.0 (75.2) |
24.0 (75.2) |
19.0 (66.2) |
15.2 (59.4) |
11.0 (51.8) |
10.6 (51.1) |
25.6 (78.1) |
Mean daily maximum °C (°F) | −1.8 (28.8) |
−0.9 (30.4) |
−0.3 (31.5) |
3.0 (37.4) |
7.6 (45.7) |
12.3 (54.1) |
14.2 (57.6) |
12.9 (55.2) |
8.1 (46.6) |
3.6 (38.5) |
0.0 (32.0) |
−1.4 (29.5) |
4.8 (40.6) |
Daily mean °C (°F) | −4.8 (23.4) |
−4.1 (24.6) |
−3.5 (25.7) |
−0.3 (31.5) |
4.0 (39.2) |
8.3 (46.9) |
9.9 (49.8) |
9.0 (48.2) |
4.8 (40.6) |
1.2 (34.2) |
−2.7 (27.1) |
−4.5 (23.9) |
1.4 (34.5) |
Mean daily minimum °C (°F) | −8.4 (16.9) |
−7.6 (18.3) |
−7.2 (19.0) |
−3.9 (25.0) |
0.6 (33.1) |
4.5 (40.1) |
6.4 (43.5) |
5.6 (42.1) |
1.9 (35.4) |
−1.6 (29.1) |
−6.1 (21.0) |
−8.0 (17.6) |
−2.0 (28.4) |
Record low °C (°F) | −30.5 (−22.9) |
−26.6 (−15.9) |
−30.9 (−23.6) |
−25.7 (−14.3) |
−16.1 (3.0) |
−5.0 (23.0) |
−1.6 (29.1) |
−2.0 (28.4) |
−11.5 (11.3) |
−17.1 (1.2) |
−26.0 (−14.8) |
−27.5 (−17.5) |
−30.9 (−23.6) |
Average precipitation mm (inches) | 33.4 (1.31) |
26.2 (1.03) |
32.5 (1.28) |
25.4 (1.00) |
20.1 (0.79) |
32.3 (1.27) |
47.4 (1.87) |
45.6 (1.80) |
44.1 (1.74) |
46.2 (1.82) |
43.4 (1.71) |
38.0 (1.50) |
435.0 (17.13) |
Average precipitation days (≥ 1.0 mm) | 8.2 | 6.5 | 8.2 | 6.8 | 5.1 | 7.0 | 8.9 | 8.2 | 8.1 | 9.9 | 9.7 | 9.9 | 96.8 |
Mean monthly sunshine hours | 16.1 | 51.6 | 96.5 | 147.7 | 178.2 | 202.5 | 170.3 | 157.4 | 97.8 | 57.8 | 23.8 | 3.7 | 1,203.4 |
Source 1: Icelandic Met Office[2] | |||||||||||||
Source 2: Icelandic Met Office (monthly sunshine hours 1981-2010 for Haganes-9 km (5.6 mi) from Reykjahlíð) [3] |
Flora and fauna
Birds
The lake is fed by
Other common species include the
Other common waterbirds include the
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
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.[6][7]
Volcanism
Mývatn was created about 2300 years ago by a large
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 cones or pseudocraters. A group of such craters at Skútustaðir [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 [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 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 mountains (Bláfjall [ˈplauːˌfjatl̥], Sellandafjall [ˈsɛlˌlantaˌfjatl̥], Búrfell [ˈpurˌfɛtl̥], Gæsafjöll [ˈcaiːsaˌfjœtl̥]), those which did not formed hyaloclastite ridges (Vindbelgjarfjall [ˈvɪntˌpɛlcarˌfjatl̥], Námafjall [ˈnauːmaˌfjatl̥], Dalfjall [ˈtalˌfjatl̥], Hvannfell [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
Postglacial volcanism in the Mývatn district may be divided into three cycles. The Lúdent [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 [ˈcʰɛːtɪlˌtiɲca] was formed about 25 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)
.The third volcanic cycle began with the Mývatnseldar [ˈmiːˌvasːˌɛltar̥] eruptions in 1724–1729 which commenced with an explosion that formed the crater lake Víti [ˈviːtɪ]. Later lava flowed from Leirhnjúkur [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 1975–1984. 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, earthquakes 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 [ˈl̥iːðarˌfjatl̥], Jörundur [ˈjœːrʏntʏr̥], Hrafntinnuhryggur [ˈr̥apn̥ˌtʰɪnːʏˌr̥ɪkːʏr̥]).
Because of its volcanic origin, the lake was formerly mined for
See also
References
- ^ "Myvatn-Laxá region". Ramsar Sites Information Service. Retrieved 25 April 2018.
- ^ "Reykjahlíð 1961-1990 Averages". Icelandic Meteorological Office. Retrieved 29 May 2016.
- ^ "1961-90 Sunshine Averages for Haganes". Icelandic Meteorological Office. Retrieved 21 April 2021.
- ISBN 9781472919847.
- ^ BirdLife International (2015). Important Bird Areas factsheet: Mývatn-Laxá. Downloaded from http://www.birdlife.org on 13/02/2015.
- ^ "Unexpected good news from lake Mývatn: Large quantities of Marimo wash ashore". Icelandmag.
- ^ "Great news from Mývatn lake: Unique marimo colonies grow second year in a row". Icelandmag.
- ^ Centre, UNESCO World Heritage. "Mývatn and Laxá". UNESCO World Heritage Centre.
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. 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. 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.