Grímsvötn
Grímsvötn and the Vatnajökull glacier, Iceland, July 1972
Elevation	1,725 m (5,659 ft)[1]
Listing	List of volcanoes in Iceland
Location
Grímsvötn Austur-Skaftafellssýsla / Vestur-Skaftafellssýsla,  Iceland
Coordinates	64°25′12″N 17°19′48″W / 64.42°N 17.33°W / 64.42; -17.33Coordinates: 64°25′12″N 17°19′48″W / 64.42°N 17.33°W / 64.42; -17.33
Geology
Type	Volcanic caldera
Last eruption	24 May 2011

The Grímsvötn sub-glacial lakes (Icelandic pronunciation: [ˈkrimsvœʰtn̥];^[2] vötn = "waters", singular: vatn) and the volcano of the same name are in South-East Iceland. They are in the highlands of Iceland at the northwestern side of the Vatnajökull ice-cap. The lakes are at 64°25′N 17°20′W / 64.417°N 17.333°W / 64.417; -17.333, at an elevation of 1,725 m (5,659 ft). Beneath the lakes is the magma chamber of the Grímsvötn volcano.

Grímsvötn is a basaltic volcano which has the highest eruption frequency of all the volcanoes in Iceland and has a southwest-northeast-trending fissure system. The massive climate-impacting Laki fissure eruption of 1783–1784 was a part of the same fissure system. Grímsvötn was erupting at the same time as Laki during 1783, but continued to erupt until 1785. Because most of the volcano lies underneath Vatnajökull, most of its eruptions have been subglacial and the interaction of magma and meltwater from the ice causes phreatomagmatic explosive activity.^{[citation needed]}

On 21 May 2011 at 19:25 UTC, an eruption began, with 12 km (7 mi) high plumes accompanied by multiple earthquakes,^[3][4][5][6] resulting in cancellation of 900 flights^[7] in Iceland,^[8][9] and in the United Kingdom, Greenland, Germany, Ireland and Norway on 22–25 May. Until 25 May the eruption scale had been larger than that of the 2010 eruption of Eyjafjallajökull. The eruption paused at 02:40 UTC on 25 May 2011, although there was some explosive activity from the tephra vents affecting only the area around the crater.^[10][11][12]

Jökulhlaup[link]

Eruptions in the caldera regularly cause glacial outbursts known as jökulhlaup.^[13] Eruptions melt enough ice to fill the Grímsvötn caldera with water, and the pressure may be enough to suddenly lift the icecap, allowing huge quantities of water to escape rapidly. Consequently, the Grímsvötn caldera is monitored very carefully.

When a large eruption occurred in 1996, geologists knew well in advance that a glacial burst was imminent. It did not occur until several weeks after the eruption finished, but monitoring^[14] ensured that the Icelandic ring road (Hringvegur) was closed when the burst occurred. A section of road across the Skeiðará sandur was washed away in the ensuing flood, but no one was hurt.

1998 and 2004 eruptions[link]

Satellite images of the November 2004 Grímsvötn Eruption

A week-long eruption occurred at Grímsvötn starting on 28 December 1998, but no glacial burst occurred. In November 2004, a week-long eruption occurred. Volcanic ash from the eruption fell as far away as mainland Europe and caused short-term disruption of airline traffic into Iceland, but again no glacial burst followed the eruption.

2011 eruption[link]

2010 pre-eruption glacial flood[link]

Harmonic tremors were recorded twice around Grímsvötn on 2 and 3 October 2010, possibly indicating an impending eruption.^[15] At the same time, sudden inflation was measured by GPS in the volcano, indicating magma movement under the mountain. On 1 November 2010 meltwater from the Vatnajökull glacier was flowing into the lake, suggesting that an eruption of the underlying volcano might be imminent.

Eruption[link]

Satellite image from 22 May 2011 of the volcanic plume above Iceland

View of Icelandic landscape beneath the ash-cloud during the 2011 eruption

Grímsvötn in August 2011. Ash covering the surrounding snow and ice

On 21 May 2011 at 19:25 UTC, an eruption began, with 12 km (7 mi) high plumes accompanied by multiple earthquakes.^[4][5][6] The ash cloud from the eruption rose to 20 km (12 mi), and is so far 10 times larger than the 2004 eruption, and the strongest in Grímsvötn in the last 100 years.^[16]

During 22 May the ash plume fell to around 10 km altitude, rising occasionally to 15 km.^[17] On 23 May, the eruption was releasing about 2000 tons of ash per second, totalling 120 million tons in the first 48 hours.^[18] The 2011 eruption of Grímsvötn thus qualified as at least 4 (VEI4) on the Volcanic Explosivity Index (VEI), releasing more ash in the first 24 hours than Eyjafjallajökull released during its entire 2010 eruption.^[19] On 24 May poor weather prevented visual observation of the eruption plume, but it had an estimated height of below 5 km, implying that the eruption is significantly weaker than on previous days.^[20] A IMO scientific flight over the eruption on the evening of 24 May site showed there was explosive activity from two vents which are surrounded by tephra debris, with the eruption plume reaching between 3 and 7.5 km in height.^[21]

On 25 May Iceland Met Office has confirmed that the eruption has paused at 02.40 local time on 25th.^[10] However there are still pulsating explosions producing ash and steam clouds, some reaching a few kilometres in height, rising up from the vents. There is still widespread ash in cloud layers up to 5 km from the eruption site.^[22]

On 26 May the Icelandic Meteorological Office and the University of Iceland reported that ashfall is only occurring adjacent to the eruption site. Visual observations indicate that little ice meltwater was produced during the eruption, so that an outburst flood (jökulhlaup) is not expected. Joint status reports will no longer be issued, unless something notable is observed.^[12]

Disruption to air travel[link]

Satellite image from 23 May 2011 of the ash-cloud to the south of Iceland

Disruption to air travel in Iceland^[8] commenced on 22 May, followed by Greenland, Scotland,^[23] Norway, Svalbard^[24] and a small part of Denmark on subsequent days. On 24 May the disruption spread to Northern Ireland and to airports in northern England.^[8] At this point, the actor-geologist Nick Schofield was drafted in to assess the situation, and correctly predicted that the highly variable situation was unlikely to be as disruptive as the previous year's Icelandic eruption ^[25]. On 25 May the disruption spread to Northern Germany - airports at Hamburg and Bremen were closed for a few hours.^[26] On 27 May Greenlandic airspace was closed due to a concentration of ash over Greenland and the North Atlantic.^[27]

The cancellation of 900 out of 90 000 European flights^[7] in the period 23–25 May was much less widespread than the 2010 disruption after the Eyjafjallajökull eruption.

United States President Barack Obama cut short his visit to Ireland on 23 May so he could guarantee his arrival for a scheduled state visit to Britain the following day. Obama had been due to spend 24 hours in Ireland, but he departed after only twelve hours owing to concerns about the approaching ash cloud.^[28]

Bacteria in the subglacial lakes[link]

In summer 2004, a community of bacteria was detected in water of the Grímsvötn lake under the glacier, the first time that bacteria have been found in a subglacial lake. The lakes never freeze because of the volcanic heat. The bacteria can also survive at low concentrations of oxygen. The site is a possible analogue for life on the planet Mars, because there are also traces of volcanism and glaciers on Mars and thus the findings could help identify how to look for life on Mars.^[29][30]

Future trends[link]

Studies indicate that volcanic activity in Iceland rises and falls so that e.g. the frequency and size of eruptions in and around the Vatnajökull ice cap varies with time. It is believed that four eruptions, that have taken place in the last fifteen years, are the beginning of an active period, during which an eruption in Grímsvötn in Vatnajökull may be expected every 2–7 years. Parallel volcanic activity in nearby Bárðarbunga is known to be associated with increased activity in Grímsvötn. Seismic activity has been increasing in the area in recent years, indicating the entry of magma.^[31]

See also[link]

• Volcanism in Iceland
• List of volcanoes in Iceland
• Geography of Iceland
• Glaciers of Iceland
• Glacial lake outburst flood
• Iceland plume
• Iceland hotspot
• Lakes of Iceland
• List of islands of Iceland
• Timetable of major worldwide volcanic eruptions
• Plate tectonics

References[link]

External links[link]

Wikimedia Commons has media related to: Grímsvötn

• Update on Grímsvötn Activity – from the Icelandic Met Office and University of Iceland (updated at least daily)
• Current seismology around Grímsvötn – Earthquakes in last 48 hours
• Webcam by Míla, Iceland (exact location unknown)
• Webcam at Jökulsárlón, south of the volcano, by Míla, Iceland
• Grímsvötn volcanic ash advisory from regional Volcanic Ash Advisory Centre, London (updated every 6 hours)
• Grímsvötn updates from NATS – UK air traffic control plus the Eastern part of the North Atlantic
• BBC news report of the 23 May 2011 eruption
• Report on the start of the Grímsvötn eruption from the Icelandic Met Office
• "Grímsvötn". Global Volcanism Program, Smithsonian Institution. http://www.volcano.si.edu/world/volcano.cfm?vnum=1703-01=. 
• Photo report of the November 2004 eruption
• Independent news report of the 2004 eruption

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