Longstanding Mystery About The Giant's Causeway Solved By Destructive Lab Experiments

We're still not quite sure why hexagons are the preferred shape, though. S-F/Shutterstock

The Giant’s Causeway in Northern Ireland’s County Antrim is ridiculously beautiful. Its strange, mostly hexagonal columns stand in stark contrast to nature’s general eschewing of clean, geometric shapes, and it’s all thanks to a quirk of volcanology.

Precisely how this UNESCO World Heritage Site formed, however, has eluded scientists – but, as spotted by The Guardian, a groundbreaking and frankly awesome experiment by the University of Liverpool has potentially solved this longstanding enigma. Reporting in Nature Communications, they explain how they destroyed some of these gorgeous colonnades in their very own laboratory to find out.

First, a quick geology lesson. The Giant’s Causeway represents a process known as columnar jointing, which can be found all over the world. The columns form in a variety of hot volcanic deposits, from lava flows to shallow crustal intrusions to even within ignimbrites, violent ash flow features. As the molten material is cooling down, you sometimes get columns forming just like those in Northern Ireland.

It's not entirely clear why hexagons are the preferred geometry, nor is it certain what cooling rates produce what size columns. Either way, we know that as the lava or magma cools, it contracts, which forms cracks. These cracks continue to grow at right angles to the surface of the flow.

We don't, however, know at what precise point during this cooling process these columns begin to form.

FYI, you get columnar jointing off-world too. Can you spot them here, on this image of Mars? ESO/NASA

There’s only so much you can learn by prodding at the real deal in the field, from the Devil’s Tower in Wyoming to those scattered around Iceland. Sometimes, you’ve just got to beat nature at its own game and cook some up yourself. Well, sort of.

To wit, the team stole a few basalt cores from Eyjafjallajökull, took them to a lab, and heated them up toward their melting point, watching as they morphed into lava once more. At the same time, a huge grip held them in place, while also applying hefty mechanical pressure on them.

Remember, the point at which that cracking commences represents the start of the formation of those beautiful columns. The team suspected this only happens when the rock is deformable but still rigid enough to crack, which is why this artificially applied pressure was used to reveal the precise temperature at which this takes place.

As it turns out, the cores fragmented at temperatures between 840°C and 890°C (1,544°F to 1,634°F). At standard atmospheric pressure and with a somewhat “normal” water content, basaltic rock generally starts melting at temperatures above 980°C (1,796°F), which means columnar jointing definitely commences while it’s solid.

So there you have it: a major mystery surrounding what the authors refer to as “one of the most awe-inspiring geological features” has arguably been crossed off, all thanks to some engineering ingenuity.

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