And the tuff cone from Victoria Land, Antarctica, is placed next to known granitic plutonic complexes and seems to be a parasitic cone of a stratovolcano, whereas Keilir is located adjacent to presently active volcanic systems and looks as if it were placed on top of the shield volcano Þráinskjöldur, though the last one is younger than the subglacial formation. Additionally, the Antarctic cone is much older (around 640 000 years), whereas Keilir is up to 100 000 years old. The Antarctic cone did lie under a polar ice sheet and not a temperate glacier as was the case with Keilir. Smellie and other scientists newly discovered a similar monogenetic subglacial tuff cone within the ice of Antarctica and could determine the thickness of ice which covered the vent during eruption. Comparison to an Antarctic subglacial tuff cone Ice thickness and more exact time of eruption in the case of Keilir are not known, just that it took place during the Pleistocene ( Weichselian). In the top region of Keilir, there is a small cap of lava (area of lava cap 0,020 km2 ) which could mean that the volcanic mountain is a tuya (the lava being from subaerial eruptions at the end of the eruption series) or perhaps just represents a volcanic plug (the lava cooled and plugged up the vent). When such an eruption is continued over a longer time span, the water in the end does not reach the vent(s) any more and lava begins to flow. With time, the tephra built up a hill and small elongated mountain over the vent(s). Tephra set down in layers into the subglacial lake. The water very soon touched the magma within the vent and caused explosive activity. When stratigraphy is considered in detail, it tells about the different parts of this eruption: The eruption thawed the glacier ice and formed a subglacial lake in which the volcano continued to develop. Eruptions under the Weichselian glaciers on Reykjanes Peninsula Except the cone, also some small subglacially formed hills to the north are results of this eruption. Keilir was formed during a subglacial fissure eruption which concentrated in the end at one vent. 1.2 Comparison to an Antarctic subglacial tuff cone.1.1 Eruptions under the Weichselian glaciers on Reykjanes Peninsula.
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