set: volcanoes // series: caldera // picture:
The hill is Keilir (Icelandic for cone-shaped). It is the tip of a basaltic volcanic eruption that took place ~14-20,000 years ago on the Reykjanes Peninsula, south west Iceland. This eruption took place under-water, resulting in pillow lava (see next image) which typically builds pillow mounds such as Keilir. This volcano is on a peninsula less than 20km from the sea (which can just be seen over the left shoulder of Keilir, so the eruption may have been submarine (because of fluctuating sea-levels during and towards the end of the last glaciation. It also possible that the eruption took place under a glacier, creating its own melt water lake. This style of eruption still occurs today in Iceland, where volcanoes erupt under ice-sheets. Most post-glacial lavas (those erupted over the past 13,000 years) are sub-aerial sheet flows, similar to those images in other drawers, either blocky, clinkery, aa flows or smoother pahoehoe lavas. The flow in the foreground of this picture is an aa flow about 2,000 years old, whereas the flow lapping around Keilir is a pahoehoe flow about 12,000 years old. The eruptive phases on the Reykjanes Peninsula last for approximately 300 years and occur around every 1000 years. The last eruptive event ended in the 13th Century. The infilling of valleys by recent eruptions make it impossible to accurately estimate the size of pillow mounds like Keilir, this 300m high hill could just be the tip! We are standing on another pillow mound where the basalt pillow lava has been altered to clay by hydrothermal activity (see black smokers in the previous drawer ).
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