The Giant's Causeway in Ireland

Evening at the Giant's Causeway
Co. Antrim
Northern Ireland

Photo by Esler Crawford
Published by John Hinde, Ltd.

This postcard is unused.

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The Giant's Causeway is an area of about 40,000 interlocking basalt columns, the result of an ancient volcanic eruption.  It was declared a World Heritage Site by UNESCO in 1986.

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Incase anyone wants to know what basalt columns are...

During the cooling of a thick lava flow, contractional joints or fractures form. If a flow cools relatively rapidly, significant contraction forces build up. While a flow can shrink in the vertical dimension without fracturing, it can't easily accommodate shrinking in the horizontal direction unless cracks form; the extensive fracture network that develops results in the formation of columns. The topology of the lateral shapes of these columns can broadly be classed as a random cellular network. These structures are predominantly hexagonal in cross-section, but polygons with three to twelve or more sides can be observed.  The size of the columns depends loosely on the rate of cooling; very rapid cooling may result in very small (<1 cm diameter) columns, while slow cooling is more likely to produce large columns.