the beginning, a 2–4 km long N–S trending depression was formed above the fissure, with time three ice cauldrons were built at each end and in the middle, but the eruption concentrated later on one of them where a 200–300 m wide crater came to light. After some time, an open ice canyon was built above the fissure. It had a length of about 3,5 km and was up to 500 m in width. The meltwater drained first through the ice canyon and then disappeared into subglacial channels and run from there to the subglacial caldera lake of Grímsvötn. The subglacial channels were easily recognized, because continuous melting caused by the hot water from the eruption site initiated the formation of depressions on the ice surface. And so the scientists followed the melting path down to Grímsvötn caldera. Though the eruption was mostly explosive, the ash was not expelled far from the vents, but fell back into the canyon. The quantity of eruption products stayed more or less the same the whole time which was explained by ice flow into the crater. During the two weeks of eruption, volcanic activity thawed no less than 3 km3 of ice, and this continued to a lesser extent for some time after the end of the eruption. The newly formed tindar disappeared again completely under the glacier ice about 1 year later. Eruption products The eruptive products consisted of basaltic andesite which surprised the scientists as these more evolved rocks are neither typical for Bárðarbunga nor for Grímsvötn, both more connected to basaltic volcanism. Some scientists thought that Gjálp could be an independent volcano. Jökulhlaup in 1996 In the beginning, scientists presumed that the eruption would be followed immediately by a big jökulhlaup (sort of a meltwater tsunami including large blocks of ice and a high quantity of sediment). But it took some time to fill the subglacial lake of Grímsvötn in such a manner that the ice wall holding it back would break. Not before some weeks had passed after the eruption was terminated, the expected jökulhlaup took place from 4 to 7 November 1996. The meltwater streamed mostly in subglacial channels and in the end under the outlet glacier Skeiðarárjökull. There, to everybody's surprise, the water masses streamed in such a quantity that the whole glacier was lifted up. In the end, the water sprang up from under the glacier edge