Grimsvotn volcano (Grímsvötn) has multiple calderas, approximately 6 by 8 km space as well as a lake that is maintained by geothermal heat. The volcano can be found near the centre of Vatnajökull ice cap in the central region of Iceland.
Grimsvotn volcano is outstanding as it has the highest eruption frequency of all volcanoes erupting in Iceland.
The Grimsvotn core has had one eruption every decade. There were small eruptions in 1983 and 1998 and a subglacial eruption in 1996. Recent volcanoes erupted in 2004 and 2011.
Earthquake activity in Grimsvotn was noted in late October. On the 26th of October, there was raised water movement from Caldera Lake, which is a sign of a jökulhlaup, commonly known as glacier outburst flood.
Days later, an increased discharge was noted in river Skeiðará that was as a result of the high water level that was accumulating in Grimsvotn Caldera Lake from melted ice caused by high geothermal activity.
The overburden of the underlying magma chambers resulted in a release that triggered the eruption. Several tremors took place in the area before the main eruption which sent plumes into the air of almost 15 km in height.
This eruption was violent because of the interaction of hot magma with water and ice producing ash particles. This eruption started around 21st May and ended on 28 May 2011.
Intense geothermal activity in the Grimsvotn caldera still melts ice at the subglacial lake. A significant amount of ash plume was produced to a height of about 17km which illustrates the power of the eruption and the activity that took place following the initial eruption.