Normally found underwater, the rocky structures form on land too
Courtesy of T. Gregg
Hollow pillars of lava in an Icelandic valley like those found on the seafloor actually formed when molten rock oozed over soggy land, researchers propose in the Aug. 15 Journal of Volcanology and Geothermal Research.
The rocky structures stand about 2.5 meters tall in the picturesque Skaelingar valley. Though hikers are familiar with the destination’s pillars, they have been overlooked by scientists, says geologist Tracy Gregg of the University of Buffalo in New York. She and a colleague are the first to offer an explanation for the pillars’ origins.
In 1783, a volcanic fissure called Laki spewed lava into southern Iceland. The lava pushed up Skaelingar, creeping forward one blob at a time over water-logged ground. Usually these blobs, or lobes, merge, but patches of wet earth between the lobes cooled the hot rock, forming solid crusts, Gregg suggests.
The crusts blocked the lava flow, rerouting lobes around the wet spots. As the lobes inched around a spot’s perimeter, lava hardened into a crusty ring.
Inside the ring, heat from the lava caused underlying groundwater to rise, building the crust up as lava continued to
pump into the valley. When the lava eventually drained away, the hollow crusts stayed behind like the papier mâché shells of deflated balloons.
Gregg first recognized that the pillars’ similarity to underwater lava structures on a hiking trip in the mid-1990s and was inspired to investigate them.
T.K.P. Gregg and K.W. Christle. Non-explosive lava-water interaction in Skaelingar, Iceland and the formation of subaerial lava pillars. Journal of Volcanology and Geothermal Research. Vol. 264, August 15, 2013, p. 36. doi:10.1016/j.jvolgeores.2013.07.006.
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