Islandsk vulkanudbrud er startet i nat…

Fissure eruption in Holuhraun lava field

Fyrst birt: 29.08.2014 01:04, Síðast uppfært: 29.08.2014 02:14

A snapshot from a webcam overlooking the eruption. (mila.is)

A fissure eruption started around midnight in the Holuhraun lavafield, ca. 9 kilometers north of Dyngjujokull glacier. Lava streams out of a 100 meter long fissure, in the northern part of the lava field, about 15 kilometers south of the Askja caldera. IMO has issued a red alert for aviation

The eruption seems to have started near the northern end of the magma intrusion that has been propagating northward from the Bardarbunga caldera since August 16.

Small surface crevasses were seen in the Holuhraun lava field yesterday, leading to increased interest among scientists. The possibility of an eruption migrating southwards, towards the Dyngjujokull glacier cannot be excluded at this time.

Benedikt Ofeigsson, staff member at the Icelandic Met Office is at the scene. In an interview with RUV tonight, he described the eruption as small; lava is flowing to the southeast and some small tephra mantles are coming out of the fissure.

The IMO has issued a red alert (highest) for aviation. That means that airtraffic is restricted in a large area around the eruption.

The fissure lies on a northeast – southwest direction. A live webcam of the eruption can be found at www.mila.is

Road and area restrictions that have been enforced over the last days are still in effect in the area north of the Vatnajokull glacier.

bjornm@ruv.is

This story, by the Icelandic National Broadcasting Service (RUV), was updated on August 29. 2014, at 01.54 GMT.

Updates in English will be posted at: ruv.is/volcano. Follow us on Twitter @ruvfrettir

Navnet Hraun betyder lavamark.

Caldera betyder kraterindsynkning.

vulkaneksperten.dk

Tlf. 20 – 764247

Bardarbunga driller indtil videre…

Bárðarbunga – Dyngjujökull – aircraft observations on 23 August

Detailed observations from TF-SIF, the Coast Guard Dash 9 were performed in the afternoon of the 23rd of August. The observations revealed that no signs of an ongoing eruption could be detected and it is concluded that a subglacial eruption did not happen. Increased low frequency tremor observed on that day must therefore have a different explanation.

The SAR-radar images obtained by the aircraft in the afternoon of 23 August show that no changes have occurred, neither subsidence, or unusal discharge of rivers.

Experience from subglacial eruptions in the past suggests the following:

· Large scale melting of ice occurs if an eruption takes place beneath a glacier. Even very small eruptions (like the eruption at Fimmvorðuháls that preceded the Eyjafjallajökull eruption in 2010) if they had taken place under ice, would melt of the order of 100 cubic meters per second of ice and cause notable increase in discharge in glacial rivers.

· In most cases meltwater will flow away from the eruption site towards the edge of the glacier. If an eruption occurs in late summer the drainage system at the bottom of the glacier is well developed. This means that water will drain fast to the edge of the glacier. For example, if an eruption site is located under ice, 5-10 km from the edge of the glacier it is expected that meltwater will reach the edge in about an hour.

· The time it takes an eruption to melt its way to the surface is strongly dependent on the ice thickness. As an example, the moderate sized eruption of Grímsvötn in 2004, melted through 150 m of ice in about one hour while the more powerful Gjálp eruption in 1996 took 31 hours to melt through 600 m of ice.

· The above implies that the meltwater from an eruption beginning under e.g. 500 m of ice in Dyngjujökull would emerge from the glacier several hours before the eruption melts through the glacier sparking off an explosive eruption because of magma-water interaction.

MTG
Further material:

Hazard due to eruptions, including subglacial ones (Jökull 2008): https://notendur.hi.is//~mtg/pdf/2008Jokull58_MTGetal_volchaz.pdf On the volcano-ice interaction in the Gjálp eruption: https://notendur.hi.is//~mtg/pdf/1997Nature_MTG_FS_HB.pdf and https://notendur.hi.is//~mtg/pdf/2003BullVolc66_MTGetal_Gjalp.pdf And on eruptions in glaciers in general: https://notendur.hi.is//~mtg/pdf/2005SubglacVolcAct_MTG-DQS.pdf https://notendur.hi.is//~mtg/pdf/2003GeopMono140_MTG_magma-ice-water.pdf

Hvad der sker i Island…

Aviation colour code map This map is issued by the Icelandic Meteorological Office and it shows the current status of Icelandic volcanic systems. It is refreshed at 09:00 UTC daily and will timely reflect any signs of unrest. Colour codes, which are in accordance with recommended International Civil Aviation Organisation (ICAO) procedures,are intended to inform the aviation sector about a volcano’s status. Notifications are issued for both increasing and decreasing volcanic activity, and are accompanied by text with details (as known) about the nature of the unrest or eruption, especially in regard to ash-plume information and likely outcomes. GREY: Volcano appears quiet but is not monitored adequately. Absence of unrest unconfirmed. GREEN: Volcano is in typical background, non-eruptive state. YELLOW: Volcano is exhibiting signs of elevated unrest above known background level. ORANGE: Volcano shows heightened or escalating unrest with increased potential of eruption. RED: Eruption is imminent or in progress – significant emission of ash into atmosphere likely. RED: Eruption is imminent or in progress – significant emission of ash into atmosphere likely.

Hvad sker der under vulkanen…

Since the start of the earthquake swarm, precise continuous GPS stations located in the vicinity of the Bárðarbunga central volcano have shown movements which indicate that magma is propagating in the crust. During the period between 8 am on the 15th of August and 4 pm on the 18th of August a GPS station on Dyngjuháls moved 5,4 cm towards the northwest and a GPS station near Grímsvötn moved 1,8 cm towards the south.

The map shows locations of earthquakes detected by the SIL network of the Icelandic Meteorological Office. Movements on continuous GPS stations are shown as blue arrows, the continuous stations are run in cooperation between the Institute of Earth Sciences at the University of Iceland and by the Icelandic Meteorological Office. Fractures and eruptive fissures in the area are denoted by yellow and red lines respectively.

The orange arrows show a model on how the GPS stations could be moving if a dike was propagating (see thick red line on map), and magma was draining away from the Bárðarbunga magma chamber („Mogi center“). It has to be mentioned, however, that this model is only one of several models that can explain the movements seen on the GPS stations.

——-

Possible model of the dike intrusion:

Length of dike: 20 km

Height of dike: 2,1 km

Opening of dike: 1,6 m

Depth to the dike: 3 km

Volume of dike: 80-90 million cubic meters

Strike = 47,51, dip 90 (predefined)

Depth to Mogi source: 1 km

Volume change of Mogi source:

-10 til -30 million cubic meters

——-

References

GPS data – Institute of Earth Sciences, University of Iceland and the Icelandic Meteorological Office

Model calculations: Elías Rafn Heimisson, Freysteinn Sigmundsson

Earthquakes: Icelandic Meteorological Office (part of the earthquakes have not been reviewed).

Fractures near Tungnafellsjökull: Þórhildur Björnsdóttir and

Páll Einarsson (Jökull, 2013).

Fractures and eruptive fissures in the Northern Volcanic Zone: Ásta Rut Hjartardóttir

and Páll Einarsson (2012), Ásta Rut Hjartardóttir (2013).

Background: IS50 database of the National Land Survey of Iceland.

Bárðarbunga – New map with GPS and seismic data