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They consists of stone, of course, but have strange U cross section, as if they were the remaining of some ships without the head and tail section. Could anyone tell how have they formed? They almost perfectly in the center of the old, flat volcano (Strytur) near Hveravellir, Iceland. They are quite high uphill and I am surprised how lava could get into that place and then made into such a shape as it probably only flows down.

enter image description here

enter image description here

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  • $\begingroup$ Are there any photos of the cross-sections? $\endgroup$ – naught101 Sep 2 '14 at 5:09
  • $\begingroup$ Sometimes the magmatic action under ground combined with cooling and venting can change the landscape so that up is not in the same direction as when the flow occurred. Alternatively, there is also momentum in the flow, and it is possible for a little uphill travel. Really hard to tell from just this one picture. $\endgroup$ – farrenthorpe Sep 2 '14 at 5:32
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    $\begingroup$ Close-voters should clarify why this question is unclear. Seems reasonably clear to me, although it would be better with a bit more detail (e.g. a picture from another angle). $\endgroup$ – naught101 Sep 8 '14 at 5:56
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If U-shaped in cross-section, it is plausible that these are the partial remnants of lava tubes. See, for example, Morphology and mechanism of eruption of postglacial shield volcanoes in Iceland (Rossi, 1996). It is difficult to propose more detailed formation mechanisms in the absence of significantly more information about the structure.

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