Iceland's Basalt Pillars Formed By Slow Lava And Water
October 9, 2013

Iceland’s Bizarre Basalt Pillars Formed By Slow Mix Of Water And Lava

Brett Smith for - Your Universe Online

Icelandic folk legend has it that the rocky pillars in the country’s Skaelingar Valley were projectiles fired into the ground by armies of warring trolls.

However, a new study in Journal of Volcanology and Geothermal Research indicates that these hollow pillars of basalt were formed by a very slow lava flow oozing from Iceland's volcanoes and interacting with water. The researchers’ conclusion is unusual because the mixing of water and liquid rock usually results in an explosion.

“Usually, when lava and water meet in aerial environments, the water instantly flashes to steam,” said study author Tracy Gregg, a UB associate professor of geology. “That’s a volume increase of eight times — boom.”

“Formations like the ones we see in Iceland are common in the ocean beneath two miles of water, where there’s so much pressure that there’s no explosion,” she said. “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.”

The same types of pillars form deep  in the ocean when columns of super-heated water ascend between bunches of lava on the sea floor, cooling the molten rock into hollow, vertical pipes. As lava levels rise, they push the columns higher and higher and they will remain standing even after an eruption event ends.

In the study, Gregg and co-author Kenneth Christle propose that the same occurrence created the land-based rock columns in Iceland. The eruption event most likely took place in the 1780s, when a nearby eruption sent lava flowing into the Skaelingar Valley. Gregg said the valley was likely covered by a pond or swamp at the time.

She said the interaction between water and molten rock didn’t cause an explosion because the lava was moving so slowly — allowing it to react with the water in a “kinder, gentler” fashion.

“If you’re driving your car at 5 miles per hour and you hit a stop sign, it’s a lot different than if you hit that same stop sign at 40 miles an hour,” she said. “There’s a lot more energy that will be released.”

The study researchers’ careful examination of the pillars revealed exterior vertical scars — where pieces of floating crust may have contacted the pillars and scraped the surface. The scientists also found shiny drips of rock indicating that the lava hardened quickly and at a pace consistent with non-explosive water-lava interactions.

Gregg said she recognized the nature of the pillars when she first spotted them during a trip to Iceland in the 1990s.

“I knew as soon as I saw them what they were,” she said. “I had, at that time, been on submarine cruises and seen these things deep under the sea, so I was just hysterical, saying, ‘Look at these!’ So I ran around and started taking pictures until the light started running out.”

After receiving a research grant from the Geological Society of America, Gregg was able to return in an attempt to confirm her initial suspicions from 2010.