Grimsvotn, under the centre of the Vatnajokull Ice Cap, is a large central volcano about 45 km from its western edge and 50 km from the northern one. The 35 km², ice filled caldera is usually the only conspicuous part of the volcano.
Eruptions are and have been frequent, but some of them do not endure long enough to melt all the way through the thick sheet of ice. Geothermal activity keeps some areas at the caldera’s edges ice free, depending on their capacity each time. The caldera is partly surrounded with precipitous, mostly hyaloclastite mountains, and depression in the landscape under the ice.
During the short period of time scientists have had to inspect and research the area, the flood waves rushing underneath the ice have taken two courses depending of the location of the volcanic or geothermal activity. A minute part has sought outlets to the west and caused floodings in River Skafta, but the greatest volume has found its way through toward east and then been diverted by solid mountains toward south. The caldera empties, when the water level has risen high enough to lift the ice sheet above. The last major floodings (glacier burst) were caused by the 1996 eruption to the west of the main volcano, when road and bridges across the alluvial plain Skeidararsandur were damaged.
The oldest source mentioning the Grimsvotn Area is a letter from Skalholt’s Schoolmaster Olafur Einarsson, but the area was lost for decades for the lack of communications across the ice cap. The annals mention eruptions in unconfirmed areas of the interior, which makes it difficult, if not impossible, to locate them. Two Swedes, Hakon Wadell and Erik Ygberg, found the area in 1919 and called the volcano “The Swedish Crater”. In 1934 in spring the volcano erupted and offered the first opportunity for modern man to witness and register its behaviour pattern. At that time the geologist of the expedition confirmed by reason the rediscovery of the ancient Grimsvotn. The Swedes, however, are remembered by the naming of a nearby mountain, “The Swedish Peaks”.
The renowned, late geophysicist and geologist, Sigurdur Thorarinsson, studied the documentation and old sources to reach the conclusion of 21 certain and almost certain eruptions of the volcano during historical times. The first was considered to have taken place in 1332. Glacier bursts almost always were the results of the eruptions, but they also happened in-between because of the constant geothermal activity. The Glaciological Society was founded in 1950, and since then expeditions have been sent for research purposes to the Grimsvotn Area. This area has been watch closely during the last few decades. In 1955 the GS built a hut in Jokulheimar at the western edge of the ice cap and two years later another one on the top of one of the two “Swedish Peaks”. Common travellers are welcome to use those huts upon prior notice.
Photo Credit: Vedur.is