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

Bardabunga urolig.

Jordrystelser begyndte I går under vulkanen Bárðarbunga, der ligger under den nordvestlige del af Vatnajökull – isbræen. Rystelserne fortsætter i øjeblikket og det tyder på starten af en såkaldt subglacial eruption i vulkanen, d.v.s. et udbrud under isen af Vatnajøkull. Der var udbrud i Bárðarbunga I året 1797, og et andet udbrud fandt sted I 1910, dog i den nærliggende vulkan Hamarinn, som tilhører samme vulkankomplekse system.

Bárdarbunga Vulkanen betragtes som en såkaldt skjoldvulkan, d.v.s. bred og flad i det men ca. 2000 meter og dens udbrudstype er både af eksplosiv og mere rolig karakter, alt afhængigt af smeltet tilførsel af magma og gasundvigelse i forbindelse med smeltning af isdækket, der ligger oven over vulkanen.

”Magmaen bevæger sig under jordskorpen og vores målinger viser, at der sker noget”, udtaler Gunnar Guðmundsson, Politiet har øget beredskabet og overvåger situationen tæt. Myndighederne bereder sig på et muligt udbrud og beredskabet er klar til at sikre kommunikation og information.

Leder af civilforsvaret i Island Víðir Reynisson siger, at der er stor sandsynlighed for et udbrud i Bárðarbunga, som ligger under gletsjeren Vatnajökull. Et vulkanudbrud under gletsjeren kan give lokale oversvømmelser og medføre askeskyer i op til 10–20 km højde, hvor de kan være en risiko for den nordatlantiske flytrafik.

Gunnar Guðmundsson: ”Vi har endnu ikke set nogle udbrud. Men hvis magmaen kommer op til overfladen under gletsjeren, vil den være eksplosiv, og så kan der opstå store askeskyer”.

I 2010 lammede vulkanen Eyjafjallajökull den europæiske flytrafik og forstyrrede de transatlantiske ruter i flere uger med en enorm askesky.

Kilde: Henning Andersen

vulkaneksperten.dk

Kilde: Nordic Volcanological Institute, Reykjavik, Island

GPS coordinates: 64°25’12” N, 17°19’48” W Max. elevation: 1725 m.a.s.l.
Grimsvötn volcano, situated near the center of the Vatnajökull ice cap in central Iceland, is one of Iceland’s most active volcanoes. It has a complex of calderas (Gudmundsson and Milsom, 1997), and a subglacial caldera lake sustained by geothermal heat. Small eruptions have occurred at the volcano in 1983 and 1998 (around 0.1 km3). In 1996, the Gjálp subglacial eruption occurred north of the volcano (Gudmundsson et al., 1997).

Kilde: “Norvulk” Nordic Volcanological Institute Reykjavik, Island

The Vatnajökull glacier is a temperate glacier covering about 8300 km2 in the SE part of Iceland. Volcanic fissure systems of the Mid-Atlantic Ridge plate boundary are partly covered by the western part of the ice sheet. Two major volcanic centers lie beneath the ice, the Bardarbunga volcanic centre and the Grimsvötn volcanic centre, both with large subglacial caldera depressions. The Bardarbunga centre is a part of a fissure system extending over 100 km to the south and some 50 km to the north of the glacier. The last eruption within the Bardarbunga centre occurred in 1910, but eruptions on the fissure system have occurred in 871 AD, 1477 AD and 1862 AD, all producing substantial amounts of lava. The Grimsvötn centre is the more active of the two with an eruption frequency during past centuries close to one eruption per decalast eruption occurred in 2011. As Bardarbunga, the Grimsvötn centre is a part of a a fissure system which includes the Laki fissure, which in 1783 produced about 12-14 km3 of basaltic lava. Within the ice filled Grimsvötn caldera intense geothermal activity continuously melts the ice to form a subglacial lake, which at intervals of 5 to 10 years is emptied along subglacial channels to create large floods (jökulhlaup) on the sandur plain, Skeidararsandur, on the Icelandic south coast.

Kilde: volcanolive.com John Seach

Iceland

64.63 N, 17.53 W
summit elevation 2000 m
stratovolcano(keglevulkan)

Bardarbunga volcano is located under NW part of the Vatnajökull icecap. Vatnajökull is the largest glacier in Europe. Veidivötn and

Trollagigar are related fissure systems, which extend about 100 km SW. It has been one of the most active volcanoes in Iceland the past few hundred years.

A fissure eruption at Thjorsarhraun produced the largest holocene lava flow on earth with a volume of 21 cu km. The 1477 eruption of Bardarbunga was large with a volcanic explosivity index of 5.

2014 Earthquake swarm
An earthquake swarm began under Bárdarbunga volcano, Iceland on 16th August 2014.

2010 Earthquake swarm
An earthquake swarm began at Bardarbunga volcano on 26th September 2010.

Henning Andersen

vulkaneksperten.dk

Tlf. 38 – 193411 og 20-764247

Hennings nye bog: “Vulkanen Hekla – Islands dronning udkommer i november 2014 på Mellemgaards Forlag.