The steam-and-ash plume from Eyjafjallajokull in Iceland, March 22, 2010.
Overnight, the Eyjafjallajokull eruption in Iceland added to its oeuvre, producing what is being reported to be a 8-km plume. Images of the plume (above) suggest (to me) that it is very water-rich, so likely this is the expanding(?) fissure interacting with snow, ice or groundwater, producing steam explosions. These explosions have some minor ash component to them, mostly from the shattering of rapidly cooled lava, but are dominated by steam.
The eruption appears to be continuing into its third day unabated. Flights have resumed to and from Iceland as well. Minus the phreatomagmatic explosions of earlier today, the eruption has been relatively passive (in the grand scheme of volcanic eruptions) and the hazard of ash at high altitudes right now is low. However, many things can change quickly. The AP has posted a little bit more daylight footage from the eruption, showing the pulsing fire fountains along the fissure vent. There have also been some nice, sensational headline like "Eruption of Dormant Volcano Causes Panic in Iceland" (the evacuations actually seem to be calm) and "Iceland will maybe get blown up by huge volcano soon" (OK, so that was from Gawker), but on the whole, the coverage of the Icelandic eruption has been fairly calm and rational.
Here is the official press release from the Nordic Volcanological Center and Icelandic Meteorological Office:
An eruption began in South Iceland in late evening of 20 March 2010 at the
Eyjafjallajökull volcanic system (also known as Eyjafjöll volcano - Global
Volcanism Program Volcano number 1702-02=). The initial visual report of
the eruption was at 23:52 GMT, when a red cloud was observed at the
volcano, lightening up the sky above the eruptive site. The eruption was
preceded with intense seismicity and high rates of deformation in the
weeks before the eruption, in association with magma recharging of the
volcano. Immediately prior to the eruption the depth of seismicity had
become shallow, but was not significantly enhanced from what it had been
in the previous weeks. Deformation was occurring at rates of up to a
centimetre a day since March 4 at continuous GPS sites installed within 12
km from the eruptive site.
The eruption broke out with fire fountains and Hawaiian eruptive style on
about 500 m long NE-SW oriented eruptive fissure at N63º 38.1′, W19º
26.4′ on the northeast shoulder of the volcano at an elevation of
about 1000 m. It was observed from air from 4-7 A.M. on March 21. Lava
flows short distance from the eruptive site, and minor eruption plume at
elevation less than 1 km was deflected by wind to the west. Volcanic
explosive index (VEI) is 1 or less. Tephra fall is minor or insignificant.
The eruption occurs just outside the ice cap of Eyjafjallajökull, and no
ice melting is occurring at present.
Satellite data is being used to study the eruption and associated
intrusion. Several MODIS thermal images on 21 March show a temperature
anomaly where the eruption is occurring. ENVISAT ASAR images before and
during the eruption have been acquired, and a series of TerraSAR-X images
cover the area.
The eruption is located on about 2 km wide pass of ice-free land between
Eyjafjallajökull and the neighbouring Katla volcano with its overlying
Myrdalsjökull ice cap. Katla volcano is known for powerful subglacial
phreatomagmatic eruptions producing basaltic tephra layers with volumes
ranging from ~0.01 to more than 1 cubic kilometer.
Three previous eruptions of Eyjafjallajökull are known in the last 1100
years (historical time in Iceland). The most recent began in December 1821
and lasted intermittently for more than a year. The neighbouring volcano
Katla erupted then on 26 June 1823. Other eruptions include an eruption in
1612 or 1613, and about 920 A.D.
Episodes of unrest are known at Eyjafjallajökull, with documented sill
intrusions in 1994 and 1999.
For information see:
and the following references:
Sturkell, E., P. Einarsson, Freysteinn Sigmundsson, A. Hooper, B. G.
Ófeigsson, H. Geirsson and H. Ólafsson, Katla and Eyjafjallajökull
volcanoes, In: The Mýrdalsjökull Ice cap, Iceland - Glacial processes,
sediments and landforms on an active volcano. Developments in Quaternary
Sciences, vol., 13, eds. Anders Schomacker, Johannes Krüger and Kurt H.
Kjær, p. 5-21, 2009.
Hjaltadottir, S., K. S. Vogfjord and R. Slunga, 2009. Seismic signs of
magma pathways through the crust at Eyjafjallajokull volcanoe, South
Iceland, Icelandic Meteorological office report, VI 2009-013
Hooper, A., R. Pedersen, F. Sigmundsson, Constraints on magma intrusion at
Eyjafjallajökull and Katla volcanoes in Iceland, from time series SAR
interferometry, In: The VOLUME project - Volcanoes: Understanding
subsurface mass movement, eds. C. J. Bean, A. K. Braiden, I. Lokmer, F.
Martini, G. S. O'Brien, School of Geological Sciences, University College
Dublin, p. 13-24, 2009
Larsen, G., 1999. Gosið í Eyjafjallajökli 1821-1823 (The eruption of the
Eyjafjallajökull volcano in 1821-1823). Science Institute Research Report
RH-28-99. 13 p. Reykjavík.
Oskarsson, Birgir Vilhelm 2009. The Skerin ridge on Eyjafjallajökull,
South Iceland: Morphology and magma-ice interaction in an ice-confined
silicic fissure eruption. M.Sc. thesis, Faculty of Earth Sciences,
University of Iceland. 111 p.
Pedersen, R., Freysteinn Sigmundsson and Páll Einarsson, 2007: Controlling
factors on earthquake swarms associated with magmatic intrusions;
Constraints from Iceland, Journal of Volcanology and Geothermal
Pedersen, R., Sigmundsson, F., Temporal development of the 1999 intrusive
episode in the Eyjafjallajökull volcano, Iceland, derived from InSAR
images, Bull. Volc., 68, 377-393, 2006.
Pedersen, R., F. Sigmundsson, InSAR based sill model links spatially
offset areas of deformation and seismicity for the 1994 unrest episode at
Eyjafjallajökull volcano, Iceland, Geophys. Res. Lett., 31, L14610,
Sigmundsson, F., Geirsson, H., Hooper, A. J., Hjaltadottir, S., Vogfjord,
K. S., Sturkell, E. C., Pedersen, R., Pinel, V., Fabien, A., Einarsson, P.
Gudmundsson, M. T., Ofeigsson, B., Feigl, K., Magma ascent at coupled
volcanoes: Episodic magma injection at Katla and Eyjafjallajökull
ice-covered volcanoes in Iceland and the onset of a new unrest episode in
2009, Eos Trans. AGU, 90(52), Fall Meet. Suppl., Abstract V32B-03