Water and Lava Mixed in Iceland Without an Explosion: Rock Pillar Mystery Solved

In Iceland's Skaelingar valley, rocky pillars dot the region. In folklore, these pillars were projectiles that were tossed into the fields by warring trolls. Now, though, scientists have uncovered the real explanation behind these unusual lava formations.

The pillars are hollow and made from basalt, a material associated with volcanic activity. In fact, deep-sea basalt pillars form when columns of superheated water rise between pillows of lava on the ocean floor, cooling the molten rock into hollow, pipe-like minarets. The structures grow taller as lava levels rise, and remain standing even after volcanic eruptions end and lava levels fall again. But the pillars in Skaelingar valley are on land--so how exactly did they form?

"Usually when lava and water meet in aerial environments, the water instantly flashes to steam," said Tracy Gregg, one of the researchers, in a news release. "That's a volume increase of eight times--boom. Formations like the ones we see in Iceland are common in the ocean under two miles of water where there's so much pressure that there's no explosion. They've never been described on land before, and it's important because it tells us that water and lava can come together on land and not explode. This has implications for the way we view volcanic risk."

In fact, the researchers believe that the columns formed on land much as they did underwater. It's possible that no explosion occurred because the lava was moving so slowl-y-centimeters per second. This allowed the lava to react with the water in a gentler manner.

"If you're driving your car at five miles per hour and you hit a stop sign, it's a lot different than if you hit the same stop sign at 40 miles per hour," said Gregg in a news release. "There's a lot more energy that will be released."

The findings could allow scientists to better understand the geological processes that help form our planet. In the future, researchers could hunt for land-based lava pillars near oceans to learn about the height of ancient seas, or search for such formations on Mars and other planets to determine where water once existed.

The findings are published in the Journal of Volcanology and Geothermal Research.