The year 2011 marked the first volcanic eruption in Grímsvötn for seven years and the 12th eruption since the 1900s. The seven year pause between eruptions in Grímsvötn caused crustal deformation do to magma movements in the volcanic system and seismic activity. The eruption was more powerful than expected but all the same a fairly standard phreatomagmatic eruption, releasing a substantial amount of tephra, ash, pumice and magma into the atmosphere. The ash cloud from the eruption on May 21st 2011, rose to about 15-17 km and the quantity of ash about 10 times greater than was yielded from the volcanic activity in Eyjafjallajökull in 2010. The glacial cap was melted by the flowing magma which scattered when it came in contact with water in the caldera, close to Svínahnúkur. Jökulhlaup is the Icelandic word used to describe a sudden flood following eruptions under glacial caps, when the melt water is released. In this case the eruption was not followed by such a flood because there was little melt water produced during the eruption. There was a massive widespread layer of ash clouds in the area, mainly reaching to the south and south west from Grímsvötn and Vatnajökull. The eruption was over in about a week.