Braided River, Skeidararsandur, Iceland
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.
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.