We visited the Dettifoss Waterfall, which is situated on the Jökulsá á Fjöllum river, which flows from the Vatnajökull glacier and collects water from a large area in Northeast Iceland. The falls are 100 metres (330 ft) wide and have a drop of 45 metres (150 ft) down to the Jökulsárgljúfur canyon. This is the largest and most powerful waterfall in Europe in terms of volume discharge, having an average water flow of 193 m3/s.
Currently, at the end of august 2014, there is a possible eruption of Bárðarbunga volcano with many thousands of earthquakes some quite violent being recorded in the area and a short eruption has already taken place. If a larger eruption took place , it would be under a glacier between 150 and 600 meters thick. That means the ice would melt and Jökulsá á Fjöllum, and Dettifoss would flood. The river might increase 10 to 40-fold. After the start of an eruption the water would take about an hour to reach the border of the glacier. It would be at Herðubreiðarlindir in four and a half hours, at the bridge by Grímsstaðir in seven hours and down to Ásbyrgi, near the North coast in about nine hours.
Because nobody knows how big the flood might be, estimates of possible damage range widely. The three bridges over Jökulsá might all be washed away. In case of an extreme flood, in which the flow of water might increase 100-fold, there might be great damage to nature.
Jökulsá has not been flooded for about 300 years but there are recorded floods that caused great damage in the 15th, 17th, and 18th centuries. The areas in Kelduhverfi and Öxarfjörður were both flooded and people are said to have been saved by climbing to the roofs of their houses.
The eruption itself would send out tons of ashes, possibly having an effect on air traffic, although most anticipate that the effect would be smaller than in the Eyjafjallajökull eruption in 2010.