The columns at The Devils Causeway in Ireland (and elsewhere basaltic flows are found) are a product of the lava's cooling. The cracks occur at right angles to the top and bottom of the flow and form columns that are inevitably six sided. The hexagonal cross-section reflects the fact the dominant stresses in the cooling rock are planar, parallel with the flow's surface.

The columns in the cliffs behind Bombo beach at Kiama on the New South Wales south coast occur in a rock unit with the charming name of the "Bumbo Latite"! Latite is a cousin-brother of basalt. A little further south, one of the columns has fallen out of a flow that protrudes into the sea. This forms "The Little Blowhole" - lots of fun to drop things into just as the swell rushes up the underside of the flow!!

stales