 Vatnajokull is named after sub-glacial lakes in a very volcanically active region in its centre. The sub glacial landscape is an undulating plateau (600-1000m) with valleys and gorges. The icecap rises between 1400 and 1800 m above sea level. The ablation elevation is a bit different, 1100 m in the south, 1200 m in the west and 1300 m in the north. A great number of glacier snouts of different sizes flows down onto the lower lying areas. No glacier in Iceland has been researched more thoroughly than Vatnajokull. The research started in 1934, when the lake region erupted and ever since the Iceland Glaciological Society was founded in 1950 it has been continued every year. The Iceland Glaciological Society owns huts in several places on the icecap. The latest eruptions of the lake region took place in 1996, in 1998 and again in 2003. The first confirmed trip across the icecap from the south and back was accomplished in 1875 by an Englishman and a few Icelanders. They were the first to see the Askja eruption the same year and report it to the people living on Lake Myvatn.
Volcanic fissure systems of the Mid-Atlantic Ridge plate boundary are partly covered by the western part of the Vatnajokull ice cap. Two major volcanic centers lie beneath the ice, the Bardarbunga volcanic centre and the Grimsvotn volcanic centre, both with large subglacial caldera depressions. The Bardarbunga centre is a part of a fissure system extending over 100 km to the south and some 50 km to the north of the glacier. The last eruption within the Bardarbunga centre occurred in 1910, but eruptions on the fissure system have occurred in 871 AD, 1477 AD and 1862 AD, all producing substantial amounts of lava.
Late in the evening of September 30, 1996, seismometers detected the beginning of an eruption under the glacier. One of the volcanoes had previously collapsed and formed a caldera named Grimsvotn, in which a subglacial lake had been accumulated. Late on the first of October, the day after the eruption started, the surface of the ice over the caldera had risen ten to fifteen meters. The next day, the eruption broke through the surface of the ice, emitting an ash cloud ten kilometers high. The volcano quieted on the thirteenth, but the ice continued to melt and overflow the Grimsvotn lake. More than three cubic kilometers of ice melted, but little was emitted through normal runoff points. Since an ice dam and the caldera itself held the melt back, the jokulhlaup would not occur until November, or at least one month later.
At 7:20am on the fifth of November, the meltwater burst vertically from two kilometers above the tongue of the glacier. By four that afternoon, the jokulhlaup was fully realized. A mixture of sediment, meltwater, and ice moved at ten kilometers per hour from the full twenty-kilometer width of the glacier's terminus across Skeidararsandur, forming standing waves three and four meters high. The total flow peaked at over fifty thousand cubic meters per second in the five outwash channels, making it briefly the second largest river of the world. The flood obliterated a 376-meter-long bridge, the majority of a second bridge nine hundred meters in length, twelve kilometers of roadway, twenty-three power-line towers, and causing fourteen million United States dollars in damage while adding seven square kilometers to the area of Iceland. Thankfully, there were no fatalities or injuries, and the flood did not reach any nearby settlements.
There is little doubt that the events occuring on the eastern part of Iceland in late 1996 had an impact felt around the world. The phenomenon of a sub-glacial volcanic eruption is not often encountered; therefore, numerous journalists and scientists from around the world met in Iceland during the eruption to study the events and ramifications of these occurances. The study of volcanoes, especially active ones, located under glaciers, or "glacivulcanology", if not already an area of study, should become one in the future, in order to unlock more of the secrets of our planet. Undoubtedly, anything learned from the Vatnajokull incident and others like it can be applied to other fields, including plate tectonics, the behavior of the land on other planets, and run-of-the-mill vulcanology. For myself and other exchange students in Iceland at this time, these events added another facet to our own appreciation for this little Atlantic island, one that captured the attention of the world for a few months.
The largest glacier in Iceland is Vatnajokull and it is the largest glacier mass in Europe. It covers an area of roughly 8100 km 2, and is about 1000m thick where it is thickest. Its average thickness is between 400 and 500m, and the total ice volume of Vatnajokull is probably in the vicinity of 3300 cubic km. The ELA lies at ca. 1100 m a.s.l. along its southern margins, at 1200 m along its western part, and at 1300 m in its northern part. About 60% of the glacier surface is above the ELA. The ice cap covers a highland plateau, generally reaching 600-800 m altitude, but dissected by numerous broad and narrow subglacial valleys. A number of large volcanoes are covered by the great ice cap, including Oraefajokull (Öræfajökull) (2111 m), Bardarbunga (Bárðarbunga) (2020 m) and Grimsvotn.
Seven volcanoes are situated underneath the Vatnajokull ice-cap and most of them are active volcanoes. Grimsvotn volcano is together with Hekla, Iceland's most active volcano since the Middle Ages. Grimsvotn last erupted in 1996, in 1998 and yet again in 2004. Kverkfjoll is a large glaciated central vulcano on the northern edge of Vatnajokull, with a powerful highteo-nature ared where there are mudholes. Steam bowholes and a luke-warm lake. Undereneath the glacier is an ice cavern system several km long. |
