Jökulsá á Fjöllum

Jökulsá Fjöllum, overlooking the Hafragilsfoss with the crater row that runs across the river

The Jökulsá Fjöllum (Eng. " glacial river in the mountains " is meant in the highlands ) is 206 km long, the second longest river of Iceland and rises at Brúarjökull, one of the valley glacier Vatnajökull ice sheet. It flows mostly through the uninhabited highlands of northeast Iceland and ends not far from Kópasker in the Öxarfjörður.

General characteristics

The Jökulsá Fjöllum features with 7380 km ² the largest catchment area of the rivers in Iceland. 1989, of which 1800 km ² still covered by glacial ice.

Their average amount of water at the waterfall Dettifoss 183 m³ / s. However, as the all glacial rivers, it is subject to large and rapid changes. On July 30, 2011 at 6 h in the morning she was, for example, near the Dettifoss at Grímsstaðir 583 m³ / sec, which in the case of both the increase in outdoor temperature ( up to 18 ° C at 29.7. ), As well as increased volcanic activity in the east of Vatnajökull stemmed under Bárðarbunga and Hamarinn.

Like all glacial rivers also carries the Jökulsá Fjöllum large amounts of debris into the mouth region, which, on average, 20 t / day amounts.

River course

Headwaters

The origins of the river between Dyngjujökull and Brúarjökull, two outlet glaciers of Vatnajökull. In the incision ( Isl kverk ) between these two glaciers, the mountain massif of Kverkfjöll rises. The spring water from the Jökulsá Fjöllum initially come from the glacier Dyngjujökull. Several tributaries also originate Kverkfjöll and the Brúarjökull, of which the Kreppa is the largest. After both rivers then flow 40 km more or less parallel to each other, this leads below the Herðubreið á in Jökulsá Fjöllum that flowed so far to the northeast.

Middle reaches

From there, the river widens and flows through the Ódáðahraun, a largely desert-like, marked by eroded lava and ash fields area. The current is now aligned more or less north and eventually follows the mountain range of the Hólsfjöll, after which it is named.

Underflow

In the last 50 km the river has become a current flows sequentially through three large waterfalls, the Selfoss, Dettifoss and Hafragilsfoss to finally enter through a body set up by himself deep three-part Jökulsárgljúfur canyon to the lowlands.

Mouth region in Kelduhverfi

From the height of the river flows Ásbyrgi another 20km in more arms to the north, then joins in Kelduhverfi in the Bay of Öxarfjörður in the Greenland Sea.

Geology: Volcanic eruptions and glacial cycles

The catchment area of this river is located on the northern arm of the active rift and volcanic zone of Iceland ( NVZ ) and is therefore particularly rich in geological phenomena. One can find Palagonitkegel and backing large lava fields, shield volcanoes, central volcanoes such as Askja, Bárðarbunga and Kverkfjöll, deep gorges and in the form of Vatnajökull one of the largest ice sheets in Europe. The landscape is characterized by significant traces of volcanic eruptions, sometimes under glaciers and glacier runs on an enormous scale.

Am Wasserfall Hafragilsfoss and Vesturdalur ( a valley in present-day Jökulsárgljúfur National Park ) also formed about 6,000 years ago as volcanic eruptions columns directly under the river, which are attributable to the volcanic system of Askja, the landscape in huge hydro- magmatic explosions. Later Jökulsá a bed has blazed through the Tephraschichten, lavas and dykes á Fjöllum again.

Jökulsárgljúfur National Park

Particularly sensitive sections of the river course were part of the Jökulsárgljúfur National Park, which is now part of the Vatnajökull National Park.