UB geologist Tracy Gregg was hiking in Iceland’s Skaelingar Valley when she stumbled upon minarets of rock, dark and mysterious, rising from the grassy terrain. Having seen such structures on the ocean floor, she knew immediately what they were: pillars of lava, cooled into stone. But while they made sense deep underwater, where high pressure prevents the explosion that would normally occur when lava meets water, she was mystified by their presence on land.
When water and lava meet on land, there’s usually an explosion as water vaporizes into steam. But on the ocean floor, where high pressure prevents combustion, no such boom occurs. Instead, hollow rock pillars form as columns of heated water rise between lobes of lava (see below). Gregg thinks lava pillars in Iceland’s Skaelingar Valley formed the same way. The area may have been covered by a pond when a nearby volcano erupted in the 1700s. She proposes that the lava was moving so slowly, it was able to react with the water in a “gentler way.”