Skaftá

The Skaftá () is a river in South Iceland. It is primarily glacial in origin and has had its course modified by volcanic activity; as a result of both, it often floods because of glacial melting.

Course The river's primary source is two subglacial "cauldrons" beneath Skaftájökull, part of the Vatnajökull glacier in the interior of Iceland. It also receives spring-fed water from Langisjór, a lake a short distance to the west from which a tributary called the Útfall runs into the Skaftá. Other tributaries include the North and South Ófaerá, the Grjótá, and the Hellisá.

West of Skaftárdalur, a farm named for the river valley, the Skaftá runs over a lava field in many channels, which recombine into three for the remainder of its course to the Atlantic: the Eldvatn or Ása-Eldvatn combines with the River Kúðafljót; the Ásakvísl or Árkvísla flows under a sand-covered lava field and has been affected by road construction; the third, easternmost branch, which flows near Kirkjubæjarklaustur, retains the name Skaftá but has extremely low water levels when temperatures are lowest. Its total length is approximately .

The river was bridged at Kirkjubæjarklaustur in 1903 and the Ása-Eldvatn was bridged soon after. Efforts to bank and bridge the Ásakvísl have led to undermining of the bridge works and to erosion of land formerly watered by it.

Jökulhlaups Beginning on June 8, 1783, the multi-year eruption of the volcanic system including Grímsvötn and Þórðarhyrna (sometimes referred to in Icelandic as the Skaftáreldur, Skaftá Fires) filled the river valley with lava, including a gorge thought to have been deep, diverting its flow into the multiple shallow channels that now characterize its course. As a result it is more susceptible to jökulhlaups (glacial outburst floods), which occur every one to two years. The 2015 flood was unusually damaging, the largest since records began.

Jökulhlaups may originate from either or both the western ice cauldron () or eastern ice cauldron () and it may initially be difficult to assign a source with confidence. The cauldrons are associated with the two subglacial lakes (), separated by a ridge at least high with no direct contact between them at the glacier bed bottom. Sampling of microfloria has suggested not only that the two Skaftá ice lakes are connected through an aquifer in the underlying permeable basalt, but that this connection extends to the more distant Grímsvötn cauldron which drains via a different watershed.

The long term trend appears to be for the western cauldron to produce floods more frequently and for the eastern cauldron to produce the largest floods. + Skaftá Jökulhlaups since 2000 (minor not shown, see Atladóttir 2013 for those between 1955 and 2000) Year Source Maximum Flow Comment 2025 Unknown 2023 Eastern 2021 Eastern 2021 Western modest flood that preceded the significant Eastern Cauldron flood by a few days 2018 Both Large flood, but little impact due to accurate warning technology apart from destroyed bridges. 2015 Eastern The October event was the largest flood on record with significant infrastructure impact. 2012 Western 2011 Western 2010 Eastern Large downstream area flooded Eldhraun to the sea. 2010 Western 2008 Eastern 2008 Western 2006 Western 2006 Eastern 2005 Western 2003 Eastern 2003 Western 2002 Eastern 2002 Western 2000 Eastern 2000 Western

Skaftá

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