Report on Grimsvotn (Iceland) — June 2011
Bulletin of the Global Volcanism Network, vol. 36, no. 6 (June 2011)
Managing Editor: Richard Wunderman.
Grimsvotn (Iceland) Eruption of 21-28 May 2011; ash plumes affect parts of Europe's air space
Please cite this report as:
Global Volcanism Program, 2011. Report on Grimsvotn (Iceland). In: Wunderman, R (ed.), Bulletin of the Global Volcanism Network, 36:6. Smithsonian Institution. https://doi.org/10.5479/si.GVP.BGVN201106-373010.
64.416°N, 17.316°W; summit elev. 1719 m
All times are local (unless otherwise noted)
Grímsvötn, a subglacial volcano, is located 140 km NE of Eyjafjallajökull volcano (figure 11), within the western region of Vatnajökull glacier, Europe's largest glacier. On 21 May 2011, Grímsvötn erupted and produced ash plumes that drifted toward western Norway, Denmark, and other parts of northern Europe and disrupted flights. This was Grímsvötn's first eruption since 2004, when it sent ash as far as Finland (BGVN 29:10). The eruption continued during 21-28 May 2011.
According to scientists from the Institute of Earth Sciences at the University of Iceland (IES) and the Icelandic Meteorological Office (IMO), a GPS-station on the rim of the Grímsvötn caldera recorded continuous inflation of several centimeters per year since the 2004 eruption, interpreted as inflow of magma to a shallow chamber. Other precursors over the previous few months included increased seismicity, bursts of tremor, and increased geothermal activity. The eruption was preceded by about an hour of tremor.
The eruption began during the late afternoon of 21 May 2011. According to IMO, the plume was monitored by two weather radars, one located at Keflavík International Airport more than 220 km from the volcano, and a mobile radar ~80 km from the volcano. B early evening on the 21st, the eruption plume rose to over 20 km in altitude. The plume altitude fell to 15 km during the night, although several times it reached 20 km. Ash from the lower part of the eruption plume drifted S and, at higher altitudes, drifted E. A few hours after the eruption began, ashfall covered an area S of the Vatnajökull ice cap, more than 50 km from the eruption site.
According to the Iceland Review, the State Road Authority closed the ring road in the area of the Skeidarársandur flood plain (located S of Grímsvötn) on 21 May. The road remained closed through 24 May due to the threat of eruption-triggered outwash along Iceland's SE coast. The ring road (Iceland Highway 1) follows the Iceland coastline, providing a connection for major towns.
During the morning of 22 May, the plume rose to an altitude of 10-15 km. The plume was brown-to-grayish, changing at times to black near the source. Most of the ash drifted S, but lower parts traveled SW affecting nearby farmers and their livestock (figure 12). Tephra fall was concentrated to the S and to a lesser extent N and E. Earthquake data as well as limited observations recorded during an initial overflight placed the vent location in the SW part Grímsvötn's caldera, the same site as the 2004 eruption (BGVN 29:10).
A set of photographs taken in the morning on 22 May by Ragnar Th. Sigurdsson shows the plume's N side with a well-defined E boundary and diffusion beginning high up on the W (figure 13). In an interview for Time: LightBox Sigurdsson explained: "When you have an eruption so big, you [get] a mushroom cloud like a nuclear bomb. The photos I shot are at the bottom of the mushroom—30 km wide and 15 km high. It was huge." Sigurdsson used wide-angle and telephoto lenses for this aerial photography and had to perch in the doorway of the plane to take these photos (Wallace, 2011).
On 22 May 2011, in the afternoon, lightning strikes ranged from 60-70 per hour (up to 300 during one hour) and were most frequent in portions of the ash plume dispersed S of the vent (figure 14). News sources noted that the Keflavík airport closed. Ash fell to the vent's SW, including the Reykjavík area and to the vent's N on the Tröllaskagi Peninsula.
During 22-23 May, the ash plume rose to an altitude of 5-10 km and drifted S at lower altitudes, and W at altitudes 8 km and higher. Ashfall was detected in several areas throughout Iceland, except in some areas to the NW. On 24 May the ash plume was estimated to be mostly below 5 km because meteorological clouds over the glacier were at 5-7 km altitude and the plume only briefly rose above the cloud deck. Satellite images showed the plume extending more than 800 km from the eruption site towards the S and SE.
Sigurdur Stefnisson, traveling by road on 23 May, took a picture of his car's air filter which had clogged with dark ash after only six hours of use (figure 15). He noted that "A stock of new air filters is a must during an eruption. You can always shake them out every few miles."
According to the IES and IMO, during the evening of 24 May, explosive activity occurred in Grímsvötn's main crater. (Eruptions along fissures outside of the main crater occurred during the last 200 years in ~7 out of the 20 recorded eruptions (Óladóttir and others, 2011).) Venting came from four tephra cones surrounded by meltwater. Regular bursts of ash plumes rose a few kilometers above the cones, producing only local fallout. Seismic tremor decreased.
Aviation issues. The London Volcanic Ash Advisory Centre (VAAC; also known as the Met Office) issued an ash plume advisory on 24 May, updated 26 May, that identified the location of heavy atmospheric ash and warned pilots to plan accordingly.
The graphic associated with that advisory appears as figure 16, presented here as a representative sample of the modeled ash plume at that time. According an Associated Press on 26 May, the European air traffic agency Eurocontrol, about 900 flights out of a total of 90,000 planned flights in Europe were cancelled between 23-25 May. The Associated Press also reported on 23 May that the extensive ash hazard forced U.S. President Barack Obama to shorten a visit to Ireland. The eruption forced cancellations of flights in Scotland, northern England, Germany and parts of Scandinavia. Iceland's main international airport at Keflavík closed for 36 hours.
|Figure 16. On 24 May 2011 the London Volcanic Ash Advisory Centre (VAAC) released this map of modeled ash concentrations for 0600 UTC. Concentrations are reported from 200 to over 4,000 micrograms per cubic meter (IFALPA, 2011).|
Since the costly disruptions in air traffic during the 2010 eruption at Eyjafjallajökull, aviation regulatory authorities took steps to assess current methods of volcanic ash detection, dispersion models, and air traffic management. According to the Executive Summary of Zehner (2010), the impact of the new guidelines for aviation introduced in Europe shifted from "zero tolerance to new ash threshold values [2 mg/m3 concentrations]"; this shift was the center of previous discussions in numerous scientific conferences and workshops worldwide. A sampling of those meetings was summarized in the BGVN 36:04 Eyjafjallajökull report.
During the 2011 Grímsvötn eruption, the London VAAC presented graphics with ash concentrations. (Prior to 21 April 2010, VAACs were not required to report this information (Zehner, 2010)). Within the London VAAC region, no-fly-zones were determined by atmospheric ash concentrations of 2 mg/m3 or greater. The International Volcanic Ash Task Force (IVATF), convened by the International Civil Aviation Organization (ICAO) in 2010, held a workshop in July 2011 to discuss the regulations regarding ash concentrations, but application of a single threshold value for all nine VAAC jurisdictions remained in review.
"The imposition of a limit implies that the dispersion model is capable of providing a contour showing ash concentrations and in particular that a level of 2 mg/m3 can be delineated. In order to be able to do this, accurate information on the volcanic source (e.g. the mass flux, vertical distribution of mass, the column height and the particle size distribution) is needed. Generally this kind of information is not readily available even at the most advanced and well-instrumented volcano observatories (Zehner, 2010)."
Later observations (25-30 May 2011). On 25 May IMO field investigators visited Grímsvötn and found ash plumes had ceased although steam bursts continued from the crater (figure 17). In addition, tremor was greatly reduced, and ground deformation was minor. Observers noted ash thicknesses varying from 10 to 130 cm in the vicinity of the eruption site (figure 18). Pilots reported widespread airborne ash 5-7 km W of the volcano and also some ash haze below 3 km altitude to the SW.
|Figure 17. White plumes drifted S from Grímsvötn's two small vents (center of photo). Tephra encircles the vents and three pools of water were visible within the fissure on 25 May 2011. Courtesy of IMO.|
|Figure 18. Photo taken 25 May 2011 just W and S of Grímsvötn's eruptive site, at a location where the ice was completely tephra covered. Note ash-covered ice on the steep slope below standing figures. Courtesy of Vilhjálmur Kjartansson, IMO.|
On 26 May minor steam explosions continued from the crater. According to news articles, air traffic disruption decreased in parts of Norway and Sweden. In the IES-IMO 26 May collective status report, IMO reported that long-term conductivity measurements of the Gígjukvísl river suggested that meltwater was draining freely from Grímsvötn. Monitoring had been continuous since a jökulhlaup (a catastrophic glacier-outburst flood) occurred 31 October 2010. Located 50 km upstream from the glacial edge, Grímsvötn's subglacial lake has overflowed periodically over the past 100 years.
On 28 May tremor rapidly decreased then disappeared, and on 30 May participants on the Iceland Glaciological Society's spring expedition confirmed that the eruption had ended. Satellite imagery and visual observations showed that only small amounts of ice melted during the eruption; no signs of flooding were detected.
References. International Federation of Air Line Pilots' Associations (IFALPA), 2011, Disruption from the eruption of the Grímsvötn volcano: IFALPA Safety Bulletin 12SAB03, 24 May 2011.
Lockwood, J.P., and Hazlett, R.W., 2010, Volcanoes : Global Perspectives: Hoboken, NJ, Wiley-Blackwell, ix, p.539.
Maria, A., Carey, S., Sigurdsson, H., Kincaid, C., and Helgadóttir, G., 2000, Source and dispersal of jökulhlaup sediments discharged to the sea following the 1996 Vatnajökull eruption, GSA Bulletin; v. 112; no. 10; p. 1507-1521.
Óladóttir, B.A., Larsen, G., and Sigmarsson, O., 2011, Holocene volcanic activity at Grímsvötn, Bárdarbunga and Kverkfjöll subglacial centres beneath Vatnajökull, Iceland, Bulletin of Volcanology, 73, 1-22. DOI: 10.1007/s00445-011-0461-4
Wallace, V., 2011, High Above the Glacier, TIME: LightBox, 26 May 2011. (URL: http://lightbox.time.com/2011/05/26/high-above-the-glacier/##6).
Zehner, C., Ed. 2010. Monitoring Volcanic Ash from Space. Proceedings of the ESA-EUMETSAT workshop on the 14 April to 23 May 2010 eruption at the Eyjafjoll volcano, South Iceland. Frascati, Italy, 26-27 May 2010. ESA-Publication STM-280. DOI: 10.5270/atmch-10-01
Geologic Background. Grímsvötn, Iceland's most frequently active volcano in historical time, lies largely beneath the vast Vatnajökull icecap. The caldera lake is covered by a 200-m-thick ice shelf, and only the southern rim of the 6 x 8 km caldera is exposed. The geothermal area in the caldera causes frequent jökulhlaups (glacier outburst floods) when melting raises the water level high enough to lift its ice dam. Long NE-SW-trending fissure systems extend from the central volcano. The most prominent of these is the noted Laki (Skaftar) fissure, which extends to the SW and produced the world's largest known historical lava flow during an eruption in 1783. The 15-cu-km basaltic Laki lavas were erupted over a 7-month period from a 27-km-long fissure system. Extensive crop damage and livestock losses caused a severe famine that resulted in the loss of one-fifth of the population of Iceland.
Information Contacts: Icelandic Meteorological Office (URL: http://en.vedur.is/); Institute of Earth Sciences (URL: http://earthice.hi.is/); International Federation of Air Line Pilot's Associations (IFALPA) (URL: http://www.ifalpa.org/); International Civil Aviation Organization (ICAO) (URL: http://www.icao.int/); London Volcanic Ash Advisory Centre (VAAC), Met Office, FitzRoy RoadExeter, Devon, EX1 3PB, UK; Agence France-Presse (AFP) (URL: http://www.afp.com/afpcom/en/); Associated Press (AP) (URL: http://www.ap.org/); Eurocontrol (URL: http://www.eurocontrol.in); Iceland Review (URL: http://icelandreview.com/); National Geographic News (URL: http://news.nationalgeographic.com/); Sigurdur Stefnisson (URL: http://www.flickr.com/photos/); Ragnar Th. Sigurdsson, Arctic-Images.com. (URL: http://www.arctic-images.com/); The Big Picture (URL: http://www.boston.com); The Local (URL: http://www.thelocal.se/33970/20110524).