Jökulhlaup

A jökulhlaup (of the Icelandic “ race of glacier ”, to pronounce " yeukul-leuil-p") or glacial rout is a type of particularly powerful brutal rising and devastator.

The most frequent jökulhlaups are held in Iceland but they can occur as soon as certain conditions are réunies : a Volcano covered with a Icecap or a Ice cap (it is the case in Alaska, the United States, the Antarctic, the Andes, etc).

The jökulhlaup can be connected with the Lahar S although the latter are composed in majority of ashes and are generally formed at the time of torrential rains.

One should not confuse jökulhlaup and glacial Surge.

More and more often, the jökulhlaups are used to indicate any type of flood bringing into play a glacier : brutal draining of a lake of surface or a fjord blocked by a glacier (see Glacier Perito Moreno),…

Origin

When a subglacial volcano enters in eruption, the heat released by the magma dissolves enormous quantities of ices whose water can accumulate because blocked by rock faces or the edges of the icecap itself.

When the pressure becomes too important, the barrier which retained the subglacial lake breaks, releasing from enormous quantities of water.

An important erosion of the glacier occurs then, heated water notching the glacier and being able to carry enormous blocks of ices of several hundred tons.

Jökulhlaups famous

The jökulhlaup of the Grímsvötn in 1996

The volcanic eruption and preparation of the jökulhlaup

The September 29th 1996, a seism of magnitude 5 is recorded under the icecap of the Vatnajökull, in the South-east of the Iceland. It is the first of a series of small seisms which will proceed until the shortly and with the release after the Trémor.

An overflight in the plane on October 1st highlights a depression in Vatnajökull, signs that the ice is melting. Two other depressions will be formed thereafter, as well as a fault from five to six kilometers length on 500 meters broad and 100 to 200 meters of depth. In same time, a zone located at fifteen kilometers in the south of Grímsvötn and a diameter of ten kilometers is raised. All these signs indicate that enormous quantities of water found under the heat of the magma rejected by Grímsvötn and that this water moves in direction of the south under the icecap.

The October 2nd, the eruption bores the ice and of the plumes of steam mélés with volcanic ash and Lave pulverized is projected with 3 000 meters of altitude.

Until the November 5th, the situation remains stable, if it is not that the glacier is raised more and more. But nobody knew where would occur the jökulhlaup nor even if it would start. By precaution, the trunk road n°1 in the south of Vatnajökull is prohibited with circulation.

Of 1 455 meters of altitude and 1,5 km ³ of volume on September 29th, the lake reaches 1 now; 509,5 meters of altitude for 3 km ³ of volume.

The jokülhlaup

November 5th, 1996, at 8 hours 30 of the morning, the jökulhlaup is declared in the Sandur of the Skeiðarárjökull : the Skeiðarásandur. Very quickly, the discharge of river Skeiðará increases (multiplied per hundred in two hours) and of the blocks of ice coming from the glacier (weight higher than thousand tons and up to fifteen meters height) are carted at the beginning of the rising. The November 4th at the evening, of the movements of ice had been recorded on the level of the glacial depressions. Fifty kilometers separate Grímsvötn from the place of the jökulhlaup.

The trough of water was clearly visible, forming the same type of depression in the cap as above Grímsvötn. In the same way, with the water run-off, the depressions in the ice above Grímsvötn widened and the flood appeared between distant ice barriers of 200 meters.

The November 6th, the subglacial volcano Bárðarbunga between him also in eruption during twenty to thirty minutes. It is estimated that it is the decompression of the ices following the draining of the lake which with started the eruption.

The jökulhlaup finishes in the night from November 7th to 8th after 52 hours of rising; the flow of Skeiðará goes down again to 400 m ³ /s.

The remarks are with the measurement of the gigantism of the cap glaciaire :

the flood reached a peak of 45 000 m ³ /s (higher than the flow of the the Mississippi) over a width of fifty kilometers and a height of water from three to five meters at 11 p.m., hour of the maximum of the rising.
On the whole, trois km ³ of water flowed out of the glacier.
the muddy flood (hundred million volcanic tons of materials was carted) formed a fifteen kilometers length trail in the Atlantic Ocean.
the level of the subglacial lake is gone down again to 1 345 meters of altitude.
the valley of Skeiðará and part of the National park of Skaftafell were flooded, ten kilometers of the trunk road n°1 (Hringvegur) and of the bridges (Saeluhusakvisl, Gigya and Skeiðará) which compose it were destroyed and ten other kilometers damaged.
the layer of Sédiment S deposited raised the sandur of ten meters by places.
the entire amount of the damage (carried road and telephone cables) is of fifteen million American dollars.
Of the tremors of ice was noted during days because of the movements of the icecap and the falls of seracs in the depressions.

Previously, of the jökulhlaups had occurred starting from Vatnajökull, inter alia in 1934, 1938, 1954, 1960, 1965, 1972, 1976, 1982, 1983, 1986 and 1991.

See too

Volcanos of Iceland

External bonds

Photographs of the jökulhlaup of 1996 in Iceland
Photographs of the eruption and the jökulhlaup of 1996 in Iceland
Presentation of the eruption of 1996 in Iceland
'' Þröstur´s Jökulhlaup Site ''

Reference

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