Jökulsá á Fjöllum

{{Infobox river

| name = Jökulsá á Fjöllum

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| image = Iceland near Dettifoss 1972.jpg

| image_size = 300

| image_caption = Jökulsá á Fjöllum downstream from Dettifoss

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| subdivision_name1 = Iceland

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| length_km = 206|length_ref= approx.

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| discharge1_avg = {{convert|183|m3/s|cuft/s|abbr=on}} approx.

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| source1 = Vatnajökull

| source1_location = Central Iceland

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Jökulsá á Fjöllum ({{IPA|is|ˈjœːkʏlsˌauː auː ˈfjœtlʏm|audio=Jökulsá á Fjöllum pronunciation.ogg}}; "glacial river in the mountains") is the second longest river in Iceland (206 km). Its source is the Vatnajökull glacier. It flows into the Greenland Sea. Jökulsá á Fjöllum streams over the waterfalls Selfoss, Dettifoss, Hafragilsfoss, and {{ill|Réttarfoss|de}}, the second of which is the most powerful waterfall in Europe.{{cite news | url=https://www.bbc.co.uk/news/science-environment-31356229 | title=Canyon carved by three short, savage floods | work=BBC News | date=February 2015 | access-date=10 February 2015}}

The source of the river is in the Vatnajökull National Park, one of three national parks in Iceland. The river is located in the northeast of Iceland and forms the eastern boundary of Ódáðahraun, an extensive lava field. Its drainage basin is the largest in Iceland at 7,380 square kilometers.

File:Selfoss July 2014.JPG, one of the main waterfalls in Jökulsá á Fjöllum river]]

Glacial flooding

Dettifoss drops into the Jökulsárgljúfur canyon, a feature which, along with the Ásbyrgi gorge, appears to have been formed by catastrophic glacial flooding caused by volcanic activity. The volcano in question was possibly Bárðarbunga, which has been identified as posing the risk of a similar event in the future.[http://icelandmag.com/article/dettifoss-waterfall-could-be-completely-reformed-glacial-flooding-bardarbunga-volcano Dettifoss waterfall could be completely reformed by glacial flooding from Bárðarbunga volcano]

The largest jökulhlaups (glacial floods) in Iceland are known to have occurred along Jökulsá á Fjöllum between 7100 and 2000 yr BP.{{cite journal |author=Petteri Alho |author2=Andrew J. Russell |author3=Jonathan L. Carrivick |author4=Jukka Käyhkö |year=2005 |title=Reconstruction of the largest Holocene jökulhlaup within Jökulsá á Fjöllum, NE Iceland |journal=Quaternary Science Reviews |volume=24 |issue=22 |pages=2319–2334 |doi=10.1016/j.quascirev.2004.11.021 |bibcode=2005QSRv...24.2319A }}

The source of these floods were likely eruptions of a major volcano under the Vatnajökull glacier, in the late Holocene. The peak discharge of this flood is estimated to have been {{convert|900000|m3/s|cuft/s}}. This can be compared to the flow of the Amazon River, which has an average discharge of {{convert|209000|m3/s|cuft/s}}.

The latest research concludes that the Jökulsárgljúfur canyon was formed by three flooding events. These key events occurred two, five and nine thousand years ago, separated by millennia of relative stability.

Jökulsá á Fjöllum

Glacial flooding

See also

References

Further reading