Wikipedia
Grímsvötn (; vötn = "waters", singular: ) is a volcano in South-East Iceland. It is in the highlands of Iceland at the northwestern side of the Vatnajökull ice-cap. The caldera is at , at an elevation of . Beneath the caldera 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.
On 21 May 2011 at 19:25 UTC, an eruption began, with high plumes accompanied by multiple earthquakes, resulting in cancellation of 900 flights in Iceland, 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 stopped 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.