Scientists have identified the temperature at which cooling magma breaks into the geometric columns that form Giant's Causeway in Northern Ireland and Devils Postpile in California.

At the Giant's Causeway, thousands of basaltic columns form a platform along the coast. The geologic phenomenon has inspired a number of mythologies through history.

The columned deposit was precipitated by an ancient volcanic fissure eruption. But until now, scientists weren't sure of the cooling patterns that allowed the magma to form some 40,000 columns.

To find out how the rocks cracked and formed the columns, scientists at the University of Liverpool built an apparatus to help them replicate the formation process. The contraption holds cooling lava in a press. As it contracts, cracks and forms columns, scientists can watch and measure the changes in temperature.

When rocks cooled to between 90 and 140 degrees Celsius below the threshold at which magma crystallizes into a rock, 980 degrees Celsius, they began to fracture. Thus, researchers believe the columns found at Giant's Causeway and Devils Postpile formed at temperatures ranging from 840 to 890 degrees Celsius.

"The temperature at which magma cools to form these columnar joints is a question that has fascinated the world of geology for a very long time," Yan Lavallée, a professor of volcanology at Liverpool, said in a news release. "We have been wanting to know whether the temperature of the lava that causes the fractures was hot, warm or cold."

The answer is that the columns were formed from hot rocks, but after the magma had solidified.

Researchers published their findings on Thursday in the journal Nature Communications.

"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," said Jackie Kendrick, a post-doctoral researcher at Liverpool. "Fluid flow controls heat transfer in volcanic systems, which can be harnessed for geothermal energy production. So the findings have tremendous applications for both volcanology and geothermal research."

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