Jökull is Icelandic for glacier. Vatnajökull is the largest glacier in Iceland. Vatna is a form of the Icelandic word vatn, in which we recognise the English word water, but it also means lake. In the plural vatn becomes vötn in nominative and accusative, vötnum in dative, and vatna in genetive (of lakes). So Vatnajökull means Glacier of Lakes. Vatnajökull is located in the south-east of the island, covering more than 8% of the country. With an area of 8,100 km², it is the largest ice cap in Europe by volume (3,100 km³). The average thickness of the ice is 400 m, with a maximum thickness of 1,000 m. Under the Vatnajökull ice cap there are in fact several volcanoes, the Grimsvötn also known as Grímsfjall volcano is just one of them. Grímsvötn are situated in a caldera, where only the southern rim of the 6 x 8 km caldera is exposed.
NASA Earth Observatory image of 22 May 2011: http://earthobservatory.nasa.gov/IOTD/view.php?id=50684
Grímsvötn is a basaltic volcano which has the highest eruption frequency of all the volcanoes in Iceland - it erupted nine times between 1922 and 2004. It has a southwest-northeast-trending fissure system. The 2011 volcanic eruption in Grímsvötn is the largest in that volcano for 100 years and larger than the one in Eyjafjallajökull last year. I suppose we all remember how air travel was disrupted last year, when a cloud of ash from the Eyjafjallll volcano grounded more than 100,000 flights and left eight million passengers stranded. So far the new Grimsvötn eruption has been less drastic for aviation for several reasons. The ash particles from Grimsvötn are greater and heavier than those from Eyjafjallajökull and therefor fall faster to the ground. The European aviation reaction is different this time having learnt from last year’s event. The weather situation is different, especially winds and in particular the position of the jet stream.
Many people think that the Grimsvötn eruption has finally ended, but according to what Jón Frimann wrote yesterday on his Iceland Volcano and Earthquake blog it is not over yet.