lava pillar

Lava pillars in Iceland may have formed without a boom

Land-based lava pillars in Iceland may have formed through an unusual reaction typically seen deep under the sea.

That finding is more likely than the one that suggests the rocky pillars dotting Iceland’s Skaelingar valley were projectiles tossed into the fields by warring trolls—a theory University at Buffalo geologist Tracy Gregg heard from a tour guide and local hiker.

The pillars, hollow and made from basalt, likely formed in a surprising reaction where lava met water without any explosion occurring.

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

lava pillar drips
Glassy drips on a pillar indicate that the lava cooled at a pace consistent with lava-water interaction: slow enough to form the drips, but fast enough to avoid forming crystals. (Credit: Tracy Gregg)

“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,” she says. “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.”

Deep-sea basalt pillars form when columns of super-heated 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.

In a new study published in the Journal of Volcanology and Geothermal Research, the scientists propose that the same phenomenon sculpted the land-based lava pillars in Iceland.

Kinder, gentler reaction

It happened in the 1780s, when lava from a nearby eruption entered the Skaelingar valley, which may have been covered by a pond or was super-swampy.

One reason no explosion occurred may have been because the lava was moving so slowly—centimeters per second—that it was able to react with the water in a “kinder, gentler” manner.

“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,” Gregg says. “There’s a lot more energy that will be released.”

The Iceland formations, some over 2 meters tall, display telltale features that hint at how they were created. For example:

  • They are hollow on the inside.
  • Their rocky exteriors bear vertical scars—scratches where pieces of floating crust may have rammed into the pillars and scraped the surface as lava levels in the valley declined.
  • The skin of the towers isn’t smooth, but gnarled with shiny drips of rock. The glassy texture suggests that the lava hardened quickly into rock, at a pace consistent with non-explosive water-lava interactions. Had the lava cooled more slowly in air, it would have formed crystals.

Each of these distinctive characteristics is also prevalent in deep-ocean pillars, says Gregg.

“I knew as soon as I saw them what they were. 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!’”

In the future, Gregg says, scientists 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.

Source: University at Buffalo

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