GEOLOGY 101 Columnar Basalt

A distinctive volcanic structure found throughout the world has been given fanciful names: “Organ Pipes” in Namibia and Victoria, Australia; “Kilt Rock” and “Samson’s Ribs” in Scotland; “Giant’s Causeway” in Northern Ireland; “Thunderstruck Rocks” in Romania; “Devils Tower” in Wyoming and “Paul Bunyan’s Woodpile” in Utah, USA; the “Baigong Pipes” in China; and the “Cliff of Stone Plates” in Vietnam. High-resolution satellite images have even shown similar as-yet-unnamed structures on Mars.

- Jim Brace-Thompson

What is the distinctive structure all these have in common? They often are composed of basaltic lava flows that cooled to form “columnar basalt.” Columnar basalt exhibits massive, vertically standing columns. Although usually hexagonal (six-sided), such columns are polygonal (multi-sided) and may have anywhere from three to 12 sides. They are often so uniform in size and shape that they seem to have been artificially constructed, like giant columns of poured concrete. But these columns most definitely were not crafted by the hands of humans!

Rather, they are natural formations resulting from the cooling of thick outpourings of lava. Under certain conditions, lava contracts as it cools.