Vatnajökull also known as the Vatna Glacier in English, is the largest and most voluminous ice cap in Iceland, and one of the largest in area in Europe. It is the second largest glacier in area after Austfonna on Svalbard in Norway but, nevertheless, larger by volume. It is located in the south-east of the island, covering more than 8 percent of the country.

The name Vatnajökull is derived from vatna, the genitive plural form of vatn which means "water" in Icelandic but is also used to refer to a lake, and jökull, the Icelandic for glacier.

With an area of 8,100 km², Vatnajökull is the largest ice cap in Europe by volume (3,100 km³) and the second-largest (after Austfonna on Nordaustlandet, Svalbard, Norway) in area (not counting the still larger Severny Island ice cap of Novaya Zemlya, Russia, which may be regarded as located in the extreme northeast of Europe). On 7 June 2008, it became a part of the Vatnajökull National Park.

The average thickness of the ice is 400 m (1,300 ft), with a maximum thickness of 1,000 m (3,300 ft). Iceland's highest peak, Hvannadalshnúkur (2,109.6 m (6,921 ft)), is located in the southern periphery of Vatnajökull, near Skaftafell National Park.

Under the ice cap, as under many of the glaciers of Iceland, there are several volcanoes. The volcanic lakes, Grímsvötn for example, were the sources of a large jökulhlaup (glacial lake outburst flood) in 1996. There was also a considerable but short-time eruption of the volcano under these lakes at the beginning of November 2004. In May 21, 2011 a volcanic eruption started in Grímsvötn in Vatnajökull National Park at around 7 p.m. The plume reached as high as 20 kilometres (12 mi). During the last ice age, numerous volcanic eruptions occurred under Vatnajökull, creating many subglacial eruptions.

New ice caves form each year due to the melting glacial ice-water. Those caves can be visited accompanied by a guide.

Source: https://en.wikipedia.org/wiki/Vatnaj%C3%B6kull