How Giant’s Causeway Formed Its Spectacular Array of Columns

Scientists recreated the process behind the formation’s near-perfect hexagonal columns

A new study reveals at which temperature the Giant Causeway were formed. Chmee2/Wikimedia Commons

The spectacular columns of Giant’s Causeway in Northern Ireland look like an architectural marvel, but the formation is entirely natural. It developed between 50 to 60 million years ago when a flood of lava oozed from fissures in the earth. The molten rock cooled and contracted, cracking into a series of some 40,000 columns, mostly in near-perfect hexagonal shapes.

But the exact temperature at which the cooling lava cracked has long been a mystery. Now, as Hannah Devlin reports for The Guardian, scientists have figured out the answer: the Giant’s Causeway (and other similar formations) formed at temperatures between 1,544 and 1,634 degrees Fahrenheit.

“[This] is a question that has fascinated the world of geology for a very long time,” Yan Lavallée, professor of volcanology at the University of Liverpool, says in a press release. So to come up with answers Lavallée and his colleagues recreated the formation process in a lab.

They collected cores of the dark volcanic rock, called basalt, from deep inside the Icelandic Eyjafjallajökull volcano—the same material that makes up the Giant's Causeway. They then heated the cores, which were about eight inches long, to more than 1,800 degrees Fahrenheit.

During heating, the rocks began to soften and turn into molten rock. The researchers then used a mechanical device to secure the rocks during cooling, measuring the temperature at which they fracture.

This gave researchers a solid estimate for the temperatures at which Giant’s Causeway started splitting into columns. The results suggest it takes place just below the temperature at which the lava turns to rock, which is roughly 1,800 degrees Fahrenheit. The researchers describe the process in a new study published in the journal Nature Communications.

When the Giant’s Causeway formed, the region was under intense volcanic activity. And the results of the roaring Earth have long inspired wonder and even mythos to explain the curious formations. As Devlin reports, one legend holds that Finn MacCool, an Irish giant, built the Giant’s Causeway as a way to cross into Scotland to confront a rival.

This study marks the first time scientists have reproduced the formation process and could help explain how other basaltic columns came to be. Similar sites exist in Iceland, the U.S. (for example, the rock formation at Devils Postpile National Monument) and and even Mars, reports David Nield for Science Alert. But they’re not always the same shape and size. Several variables, including cooling rates, can change how the columns appear.

The results of this latest study could also have implications for volcanology and geothermal research. As Jackie Kendrick, a post-doctoral researcher and author of the study, explains in the press release, the results could help researchers better understand heat transfer, a vital component of harnessing geothermal energy.

“Knowing the point at which cooling magma fractures is critical, as—beyond leading to the incision of this stunning geometrical feature—it initiates fluid circulation in the fracture network,” Kendrick says. “Fluid flow controls heat transfer in volcanic systems, which can be harnessed for geothermal energy production.”

As Devlin reports, Lavallée hopes to expand the study in the future by recreating these features with a larger pool of molten rock. But the latest study answered many lingering questions about the process.

“I have spent over a decade pondering how to address this question and construct the right experiment to find the answer to this question,” Lavallée says in the statement. “Now, with this study, we have found that the answer is hot, but after it solidified.”

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